AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Background

The thalassemias are inherited disorders of hemoglobin (Hb) synthesis. Their clinical severity varies widely, ranging from asymptomatic forms to severe or even fatal entities. The name Mediterranean anemia, which Whipple introduced, is misleading because the condition can be found in any part of the world. As described below, different types of thalassemia are more endemic to certain geographic regions.

In 1925, Thomas Cooley, a Detroit pediatrician, described a severe type of anemia in children of Italian origin. He noted abundant nucleated red blood cells (RBCs) in the peripheral blood, which he initially thought was erythroblastic anemia, an entity that von Jaksh described earlier. Before long, Cooley realized that erythroblastemia is neither specific nor essential in this disorder and that the term erythroblastic anemia was nothing but a diagnostic catchall. Although Cooley was aware of the genetic nature of the disorder, he failed to investigate the apparently healthy parents of the affected children.

In Europe, Riette described Italian children with unexplained mild hypochromic and microcytic anemia in the same year Cooley reported the severe form of anemia later named after him. In addition, Wintrobe and coworkers in the United States reported a mild anemia in both parents of a child with Cooley anemia. This anemia was similar to the one that Riette described in Italy. Only then was Cooley's severe anemia recognized as the homozygous form of the mild hypochromic and microcytic anemia that Riette and Wintrobe described. This severe form was then labeled as thalassemia major and the mild form as thalassemia minor. The word thalassemia is a Greek term derived from thalassa, which means "the sea" (referring to the Mediterranean), and emia, which means "related to blood."

These initial patients are now recognized to have been afflicted with b thalassemia. In the following few years, different types of thalassemia that involved polypeptide chains other than b chains were recognized and described in detail.

In recent years, the molecular biology and genetics of the thalassemia syndromes have been described in detail, revealing the wide range of mutations encountered in each type of thalassemia (see Image 3). b thalassemia alone can arise from any of more than 150 mutations.

Pathophysiology

The thalassemias are inherited disorders of Hb synthesis that result from an alteration in the rate of globin chain production. A decrease in the rate of production of a certain globin chain or chains (α, β, γ, δ) impedes Hb synthesis and creates an imbalance with the other, normally produced globin chains.

Because 2 types of chains (α and non-α) pair with each other at a ratio close to 1:1 to form normal Hbs, an excess of the normally produced type is present and accumulates in the cell as an unstable product, leading to the destruction of the cell. This imbalance is the hallmark of all forms of thalassemia. For this reason, most thalassemias are not considered hemoglobinopathies because the globin chains are normal in structure and because the defect is limited to a decreased rate of production of these normal chains. However, thalassemic hemoglobinopathies exist, as discussed below (see Molecular pathology).

The type of thalassemia usually carries the name of the underproduced chain or chains. The reduction varies from a slight decrease to a complete absence of production. For example, when β chains are produced at a lower rate, the thalassemia is termed β+, whereas β-0 thalassemia indicates a complete absence of production of β chains from the involved allele.

The consequences of impaired production of globin chains ultimately result in the deposition of less Hb into each RBC, leading to hypochromasia. The Hb deficiency causes RBCs to be smaller, leading to the classic hypochromic and microcytic picture of thalassemia. This is true in almost all anemias caused by impairment in production of either of the 2 main components of Hb: heme or globin. However, this does not occur in the silent carrier state, since both Hb level and RBC indices remain normal.

In the most common type of β thalassemia trait, the level of Hb A₂ (δ2/α2) is usually elevated. This is due to the increased use of δ chains by the excessive free α chains, which results from a lack of adequate β chains with which to pair. The δ gene, unlike β and α genes, is known to have a physiologic limitation in its ability to produce adequate δ chains; by pairing with the α chains, δ chains produce Hb A₂ (approximately 2.5-3% of the total Hb).

Some, but not all, of the excessive α chains are used to form Hb A₂ with the δ chains, while the remaining α chains precipitate in the cells, reacting with cell membranes, intervening with normal cell division, and acting as foreign bodies, leading to destruction of RBCs. The degree of toxicity caused by the excessive chains varies according to the type of such chains (eg, the toxicity of α chains in β thalassemia is more prominent than the toxicity of β chains in α thalassemia).

In other types of β thalassemia traits, the mutation is not limited to the β gene but extends to the adjacent δ gene; thus, no elevation of the Hb A₂ level is expected; instead, γ chains are activated, resulting in an elevated Hb F level (another abnormal finding on Hb electrophoresis in b thalassemias). The thalassemia types associated with elevated levels of both Hbs A₂ and F are less common.

In the severe forms, such as β thalassemia major or Cooley anemia, the same pathophysiology applies with substantial exaggeration. The significant excess of free α chains caused by the deficiency of β chains causes destruction of the RBC precursors in the bone marrow (ie, ineffective erythropoiesis).

Globin chain production

To understand the genetic changes that result in thalassemia, one should be familiar with the physiologic process of globin chain production in the healthy individual. The globin chain as a unit is a major building block for Hb: together with heme, it produces the Hb molecule (heme plus globin equals Hb). Two different pairs of globin chains form a tetrameric structure with a heme moiety in the center. All normal Hbs are formed from 2 α-like chains and 2 non-α chains. Various types of Hb are formed, depending on the types of chains pairing together. Such Hbs exhibit different oxygen-binding characteristics, normally related to the oxygen delivery requirement at different developmental stages in human life.

In embryonic life, ζ chains (α-like chains) combine with γ chains to produce Hb Portland (ζ2/γ2) and with ε chains to produce Hb Gower-1 (ζ2/ε2).

Subsequently, when α chains are produced, they form Hb Gower-2, pairing with ε chains (α2/ε2). Fetal Hb is composed of α2/γ2 and the primary adult Hb (Hb A) of α2/β2. A third physiologic Hb, known as Hb A₂, is formed by α2/δ2 chains (see Image 1).

Genetic changes

All the genes that control the production of globin chains lie within 1 of 2 clusters located on 2 different chromosomes. Chromosome 11 is the site of 5 functional b-like globin genes arranged in a link cluster over 60 kilobases (kb). From left to right (5'-3'), they are ε/γ-G/γ-A/δ/β. γ-G and γ-A differ by only one amino acid (alanine vs glycine).

A critical control region of the d-globin gene (promoter) is known to be defective; it inhibits messenger RNA (mRNA) processing, resulting in only a small amount of Hb A₂ (α2/δ2) production, which thus accounts for less than 3% of total Hb in adult RBCs.

The α-like globin gene cluster is located on chromosome 16 and consists of 3 functional genes. From left to right (5'-3'), the genes are α/α2/α1.

Understanding the structure of the globin genes, how they are regulated to produce globin chains, and how the chains pair together to produce the various Hbs is critical for appreciating the different pathologic changes of this process that result in thalassemia.

Molecular biology

Each globin gene consists of a string of nucleotide bases divided into 3 coding sequences, termed exons, and 2 noncoding regions, known as introns or intervening sequences (IVS; see Image 2). Three other regions, known as regulatory regions, also exist in the 5' noncoding or flanking region of each globin gene.

The first is the promoter, which plays a major role in the transcription of the structural genes. The second region is the enhancer, which has an important role in promoting erythroid-specific gene expression, as well as in coordinating the changes in globin gene activity at different stages of development (embryonal, fetal, adult). Enhancers can influence gene expression, despite being located some distance away from the gene itself, and, unlike the promoter, they can stimulate transcription irrespective of their orientation relative to the transcription start site. Finally, master regulatory sequences, known as locus control regions (in the β-globin gene family) and HS40 (in the α gene complex), are responsible for activating the genes in erythroid cells.

Each of these regulatory sequences has a modular structure that consists of short nucleotide motifs that act as binding sites for transcriptional activator or suppressor molecules. Such molecules activate or suppress gene expression in different cell types at different stages of development. A certain gene is transcribed by an initiation complex formed of certain proteins and a number of transcription factors, which interact with binding sites on the promoters and other regulatory sequences of the relevant genes.

When a gene is transcribed, mRNA is synthesized from one of the gene's DNA strands by the action of RNA polymerase. The initial product is a large mRNA precursor. Both exons and introns are initially present on this mRNA precursor; the introns are ultimately subsequently eliminated, and the exons are spliced together in the nucleus. At this stage, the mRNA, which has also been modified at both 5' and 3' ends, moves to the cytoplasm to act as a template for the production of globin chains.

Carrier molecules (transfer RNA [tRNA]) transport amino acids to the mRNA template. Each amino acid has a specific tRNA, which also contains 3 bases (anticodon), complimentary to the mRNA codons for that amino acid. The position of each amino acid in the globin chain is thus established by its corresponding triplet code (codon) in the globin gene. The cytidine, uridine, and guanosine (CUG) codon, for example, encodes the amino acid leucine, while the adenosine, adenosine, and adenosine (AAA) codon encodes lysine. When a tRNA molecule carries the initial amino acid to the template, directed by codon-anticodon base pairing, globin chain synthesis begins.

Once the first tRNA is in place, a complex is formed between several protein initiation factors and the subunit of the ribosome that is to hold the growing peptide chains together on the mRNA as it is translated. A second tRNA moves in alongside, and a new amino acid is bound to the first with a peptide bond, resulting in a peptide chain 2 amino acids long. This process continues from left to right until a specific codon for termination is reached. At this point, the completed peptide chain drops off the ribosome-mRNA complex and the ribosomal subunits are recycled. The globin chain is now ready to join a heme molecule and 3 other globin chains to form an Hb molecule.

The developmental switches from embryonic to fetal and then to adult Hb production are synchronized throughout the different organs of hematopoiesis (yolk sack, liver, bone marrow), which function at various stages of development. Even though the mechanism of such switches is not clearly understood, the globin gene promoter is known to contain information that specifies developmental stages of transcription.

Molecular pathology

To date, more than 1000 inherited mutations that affect either the structure or synthesis of the α- and β-globin chains are known. Mutations that result in β or α thalassemia are similar in principle but different in their patterns. Presently, more than 200 molecular defects known to downregulate the expression of β globin have been characterized. Such defects result in various types of β thalassemia.

Major deletions in β thalassemia are unusual (in contrast to α thalassemia), and most of the encountered mutations are single base changes, small deletions, or insertions of 1-2 bases at a critical site along the gene (see Image 3). These mutations occur in both exons and introns. For example, in a nonsense mutation, a single base change in the exon generates a stop codon in the coding region of the mRNA, resulting in premature termination of globin chain synthesis. This termination leads to the production of short, nonviable β chains.

Conversely, in the frame shift mutation, one or more bases on the exon are lost or inserted, resulting in a change in the reading frame of the genetic code or the production of a new stop codon.

RNA-splicing mutations are fairly common and represent a large portion of all mutations that result in β thalassemia. These mutations corrupt the splicing process. The importance of precise splicing in the quantitative production of stable functional mRNA cannot be overemphasized.

Slippage by even one nucleotide changes the reading frame of the mRNA. Both ends of the RNA introns (at the junction with the exons) have specific consensus sequences; these motifs include GT in the 5' (left end or donor site) consensus sequence and AG in the 3' (right end or acceptor site) consensus sequence. Such sequences are obligatory for correct splicing, and a single substitution at the invariant GT or AG sequence prevents splicing altogether and results in β-0 or α-0 thalassemia. Mutations in the other members of the consensus sequences, although still highly conserved, result in variable degrees of ineffective β-globin production, causing milder types of β thalassemia.

Mutations in exon sequences may activate a cryptic splice site. For example, in exon 1 of the β-globin gene, a consensus sequence that resembles a sequence in IVS-1 has been identified as the site for several distinct mutations, resulting in a gene that carries the features of both thalassemia and hemoglobinopathy simultaneously (quantitatively and qualitatively abnormal Hb production). This type of mutation represents a clear link between the thalassemias and the hemoglobinopathies, and, accordingly, these are labeled thalassemic hemoglobinopathies.

Thus, mutations at codon 19 (A to G), 26 (G to A), and 27 (G to T)—all in exon 1—result in reduced production of mRNA (thalassemia) because of inefficient splicing and an amino acid substitution encoded by the mRNA that is spliced and translated (albeit inefficiently) into protein. The resulting abnormal Hbs are Malay, E, and Knossos, respectively.

The flanking regions of the β-globin gene are also sites for various mutations. A single base substitution that involves the promoter element, for example, can downregulate β-globin gene transcription, resulting in a mild form of β thalassemia. Conversely, a mutation that affects the 3' end of the β-globin mRNA can interfere with its processing, resulting in a severe form of β thalassemia.

Clearly, many different β thalassemia mutations exist, and compound heterozygosity is frequently encountered. The resulting laboratory findings may lead to confusion. An example is the patient who manifests symptoms of β thalassemia major without an elevated Hb A₂ level. The explanation for such a situation is often co-inheritance of β and δ thalassemia. δ/β thalassemia further is divided into δ/β+ or δ/β-0.

In the first type, a misalignment in the δ/β genes during meiosis results in the production of fused δ/β genes, a process responsible for the production of an Hb variant termed Hb Lepore.

The fused δ/β gene is under the control of a δ-globin gene promoter region (the β gene promoter is deleted in the process). Because the δ gene promoter carries mutations that lead to ineffective transcription, the fused δ/β chains are produced in limited amounts, resulting in thalassemia. This is in addition to the hemoglobinopathy.

Conversely, in d/β-0 thalassemia, a large deletion occurs in the β-globin gene cluster, removing both the δ and the β genes, which can also extend to involve all globin genes on chromosome 11, thus producing ε, γ, δ, and β-0 thalassemia.

Cellular pathophysiology

The basic defect in all types of thalassemia is imbalanced globin chain synthesis (see Molecular biology). However, the consequences of accumulation of the excessive globin chains in the various types of thalassemia are different. In β thalassemia, excessive α chains, unable to form Hb tetramers, precipitate in the RBC precursors and, in one way or another, produce most of the manifestations encountered in all of the β thalassemia syndromes; this is not the situation in α thalassemia.

The excessive chains in α thalassemia are γ chains earlier in life and β chains later in life. Because such chains are relatively soluble, they are able to form homotetramers that, although relatively unstable, nevertheless remain viable and able to produce soluble Hb molecules such as Hb Bart (4 γ chains) and Hb H (4 β chains). These basic differences in the 2 main types of thalassemia are responsible for the major differences in their clinical manifestations and severity.

α chains that accumulate in the RBC precursors are insoluble, precipitate in the cell, interact with the membrane (causing significant damage), and interfere with cell division. This leads to excessive intramedullary destruction of the RBC precursors. In addition, the surviving cells that arrive in the peripheral blood with intracellular inclusion bodies (excess chains) are subject to hemolysis; this means that both hemolysis and ineffective erythropoiesis cause anemia in the person with β thalassemia.

The ability of some RBCs to maintain the production of γ chains, which are capable of pairing with some of the excessive α chains to produce Hb F, is advantageous. Binding some of the excess a chains undoubtedly reduces the symptoms of the disease and provides additional Hb with oxygen-carrying ability.

Furthermore, increased production of Hb F, in response to severe anemia, adds another mechanism to protect the RBCs in persons with β thalassemia. The elevated Hb F level increases oxygen affinity, leading to hypoxia, which, together with the profound anemia, stimulates the production of erythropoietin. As a result, severe expansion of the ineffective erythroid mass leads to severe bone expansion and deformities. Both iron absorption and metabolic rate increase, adding more symptoms to the clinical and laboratory manifestations of the disease. The large numbers of abnormal RBCs processed by the spleen, together with its hematopoietic response to the anemia if untreated, results in massive splenomegaly, leading to manifestations of hypersplenism.

If the chronic anemia in these patients is corrected with regular blood transfusions, the severe expansion of the ineffective marrow is reversed. Adding a second source of iron would theoretically result in more harm to the patient. However, this is not the case because iron absorption is regulated by 2 major factors: ineffective erythropoiesis (IE) and iron status in the patient.

IE results in increased absorption of iron because of downregulation of the HAMP gene, which produces a liver hormone called hepcidin, a major regulator of iron absorption from the guts and iron recycling by macrophages. In addition to the increased absorption of iron due to the severe hepcidin deficiency, macrophages are also iron depleted, such as is observed in patients with thalassemia intermedia. By administering blood transfusions, the IE is reversed, and the hepcidin level is increased; thus, iron absorption is decreased and macrophages retain iron.

Iron status is another important factor that influences iron absorption. In patients with iron overload (eg, hemochromatosis), the iron absorption decreases because of an increased hepcidin level. However, this is not the case in patients with severe β thalassemia because a putative plasma factor overrides such mechanisms and prevents the production of hepcidin. Thus, iron absorption continues despite the iron overload status.

The effect of hepcidin on iron recycling is carried through another hormone called ferroportin, which exports iron from enterocytes and macrophages to the plasma and exports iron from the placenta to the fetus. Ferroportin is upregulated by iron stores and downregulated by hepcidin. This relationship may also explain why patients with β thalassemia who have similar iron loads have different ferritin levels based on whether or not they receive regular blood transfusions.
 
For example, patients with β thalassemia intermedia who are not receiving blood transfusions have lower ferritin levels than those with β thalassemia major who are receiving regular transfusion regimens, despite a similar iron overload. In the latter group, hepcidin allows recycling of the iron from the macrophages, releasing high amounts of ferritin. In patients with β thalassemia intermedia, in whom the macrophages are depleted despite iron overload, lower amounts of ferritin are released, resulting in a lower ferritin level.

Most nonheme iron in healthy individuals is bound tightly to its carrier protein, transferrin. In iron overload conditions, such as severe thalassemia, the transferrin becomes saturated, and free iron is found in the plasma. This iron is harmful since it provides the material for the production of hydroxyl radicals and additionally accumulates in various organs, such as the heart, endocrine glands, and liver, resulting in significant damage to these organs.

By understanding the etiology of the symptoms in thalassemia, one can appreciate that certain modifiers may result in the development of milder types of thalassemia. Factors that may reduce the degree of globin chain imbalance are expected to modify the severity of the symptoms; co-inheritance of α thalassemia, the presence of higher Hb F level, or the presence of a milder thalassemia mutation all typically ameliorate the symptoms of thalassemia.

Malaria hypothesis

In 1949, Haldane suggested a selective advantage for survival in individuals with the thalassemia trait in regions where malaria is endemic. He argued that lethal RBC disorders such as thalassemia, sickle cell disease, and G-6-PD deficiency are present almost exclusively in tropical and subtropical regions of the world. The incidence of these genetic mutations in a certain population thus reflects the balance between the premature death of homozygotes and the increased fitness of heterozygotes.

For instance, in b thalassemia, the frequency of the gene is greater than 1% in the Mediterranean Basin, India, Southeast Asia, North Africa, and Indonesia; it is very uncommon in other parts of the world. α thalassemia may be the most common single gene disorder in the world (5-10% in the Mediterranean, 20-30% in West Africa, approximately 68% in the South Pacific); however, the gene prevalence in Northern Europe and Japan is less than 1%.

The mechanism of protection against malaria is not clear. Hb F in cells has been demonstrated to retard the growth of the malaria parasite, and, by virtue of its high level in infants with β thalassemia trait, the fatal cerebral malaria known to kill infants in these areas may be prevented. The RBCs of patients with Hb H disease have also shown a suppressive effect on the growth of the parasites. This effect is not observed in α thalassemia trait.

Classification of thalassemia

A large number of thalassemic syndromes are currently known; each involves decreased production of one globin chain or more, which form the different Hbs normally found in RBCs. The most important types in clinical practice are those that affect either α or β chain synthesis.

α thalassemia

Several forms of α thalassemia are known in clinical practice. The most common forms are as follows:

• Silent carrier α thalassemia
• • This is a fairly common type of subclinical thalassemia, usually found by chance among various ethnic populations, particularly African American, while the child is being evaluated for some other condition. As pointed out above (see Genetic changes), 2 α genes are located on each chromosome 16, giving α thalassemia the unique feature of gene duplication (see Image 2). This duplication is in contrast to only one β-globin gene on chromosome 11.
  • In the silent carrier state, one of the α genes is usually absent, leaving only 3 of 4 genes (aa/ao). Patients are hematologically healthy, except for occasional low RBC indices.
  • In this form, the diagnosis cannot be confirmed based on Hb electrophoresis results, which are usually normal in all α thalassemia traits. More sophisticated tests are necessary to confirm the diagnosis. One may look for hematologic abnormalities in family members (eg, parents) to support the diagnosis. A CBC count in one parent that demonstrates hypochromia and microcytosis in the absence of any explanation is frequently adequate evidence for the presence of thalassemia.
• α thalassemia trait: This trait is characterized by mild anemia and low RBC indices. This condition is typically caused by the deletion of 2 α (a) genes on one chromosome 16 (aa/oo) or one from each chromosome (ao/ao). This condition is encountered mainly in Southeast Asia, the Indian subcontinent, and some parts of the Middle East. The ao/ao form is much more common in black populations because the doubly deleted (oo) form of chromosome 16 is rare in this ethnic group.
• Hb H disease: This condition, which results from the deletion or inactivation of 3 α globin genes (oo/ao), represents α thalassemia intermedia, with mildly to moderately severe anemia, splenomegaly, icterus, and abnormal RBC indices. When peripheral blood films stained with supravital stain or reticulocyte preparations are examined, unique inclusions in the RBCs are usually observed. These inclusions represent b chain tetramers (Hb H), which are unstable and precipitate in the RBC, giving it the appearance of a golf ball. These inclusions are termed Heinz bodies (see Image 4).
• α thalassemia major: This condition is the result of complete deletion of the a gene cluster on both copies of chromosome 16 (oo/oo), leading to the severe form of homozygous a thalassemia, which is usually incompatible with life and results in hydrops fetalis unless intrauterine blood transfusion is given.

β thalassemia

Similar to α thalassemia, several clinical forms of β thalassemia are recognized; some of the more common forms are as follows:

• Silent carrier β thalassemia: Similar to patients who silently carry α thalassemia, these patients have no symptoms, except for possible low RBC indices. The mutation that causes the thalassemia is very mild and represents a β+ thalassemia.
• β thalassemia trait: Patients have mild anemia, abnormal RBC indices, and abnormal Hb electrophoresis results with elevated levels of Hb A₂, Hb F, or both. Peripheral blood film examination usually reveals marked hypochromia and microcytosis (without the anisocytosis usually encountered in iron deficiency anemia), target cells, and faint basophilic stippling (see Image 6). The production of β chains from the abnormal allele varies from complete absence to variable degrees of deficiency.
• Thalassemia intermedia: This condition is usually due to a compound heterozygous state, resulting in anemia of intermediate severity, which typically does not require regular blood transfusions.
• β thalassemia associated with β chain structural variants: The most significant condition in this group of thalassemic syndromes is the Hb E/β thalassemia, which may vary in its clinical severity from as mild as thalassemia intermedia to as severe as β thalassemia major.
• Thalassemia major (Cooley anemia): This condition is characterized by transfusion-dependent anemia, massive splenomegaly, bone deformities, growth retardation, and peculiar facies in untreated individuals, 80% of whom die within the first 5 years of life from complications of anemia. Examination of a peripheral blood preparation in such patients reveals severe hypochromia and microcytosis, marked anisocytosis, fragmented RBCs, hypochromic macrocytes, polychromasia, nucleated RBCs, and, on occasion, immature leukocytes (see Image 5).

Frequency

United States

Because of immigration to the United States from all parts of the world and the intermarriages that have taken place over the years, all types of thalassemia occur in any given part of the country. However, until recently, the number of patients with severe forms of both b and a thalassemia has been very limited. For this reason, finding more than 2-5 patients with the very severe forms in any pediatric hematology center is unusual (except for in the few referral centers in the United States).

However, this situation is changing rapidly in certain parts of the country. In the last 10 years, Asian immigration has been steadily increasing. According to the Federal Census Bureau, in 1990, 6.9 million Asians were in the United States, twice that reported in the 1980 Census count. The prevalence of various thalassemia syndromes in this population is very high. b and a thalassemia, as well as Hb E/b thalassemia, are currently on the rise in the state of California as a result of the large concentration of Asian immigrants in that part of the country.

The interaction between Hb E (a b chain variant) and b thalassemia (both very common among Southeast Asians) has created the Hb E/b thalassemia entity, which is now believed to be the most common thalassemia disorder in many regions of the world, including coastal North America, thus replacing b thalassemia major in frequency. For this reason, the cord-blood screening program for detection of hemoglobinopathy in California has recently been modified to include the detection of Hb H disease. In California alone, 10-14 new cases of b thalassemia major and Hb E/b thalassemia and 40 cases of neonatal Hb H disease are detected annually.

International

Worldwide, 15 million people have clinically apparent thalassemic disorders. Reportedly, disorders worldwide, and people who carry thalassemia in India alone number approximately 30 million. These facts confirm that thalassemias are among the most common genetic disorders in humans; they are encountered among all ethnic groups and in almost every country around the world.

Certain types of thalassemia are more common in specific parts of the world. b thalassemia is much more common in Mediterranean countries such as Greece, Italy, and Spain. Many Mediterranean islands, including Cyprus, Sardinia, and Malta, have a significantly high incidence of severe b thalassemia, constituting a major public health problem. For instance, in Cyprus, 1 in 7 individuals carries the gene, which translates into 1 in 49 marriages between carriers and 1 in 158 newborns expected to have b thalassemia major. As a result, preventive measures established and enforced by public health authorities have been very effective in decreasing the incidence among their populations. b thalassemia is also common in North Africa, the Middle East, India, and Eastern Europe. Conversely, a thalassemia is more common in Southeast Asia, India, the Middle East, and Africa.

Mortality/Morbidity

• a thalassemia major is a mortal disease, and virtually all affected fetuses are born with hydrops fetalis as a result of severe anemia. Several reports exist of newborns with a thalassemia major who survived after receiving intrauterine blood transfusions. Such patients require extensive medical care thereafter, including regular blood transfusions and chelation therapy, similar to patients with b thalassemia major. Morbidity and mortality remain high among such patients. In the rare reports of newborns with a thalassemia major born without hydrops fetalis who survived without intrauterine transfusion, high level of Hb Portland, which is a normally functioning embryonic Hb, is thought to be the cause for the unusual clinical course.
• Patients with Hb H disease also require close monitoring. They may require frequent or only occasional blood transfusions, depending on the severity of the condition. Some patients may require splenectomy. Morbidity is usually related to the anemia, complications of blood transfusions, massive splenomegaly in some patients, or the complications of splenectomy in others.
• In patients with various types of b thalassemia, mortality and morbidity vary according to the severity of the disease and the quality of care provided. Severe cases of b thalassemia major are fatal if not treated. Heart failure due to severe anemia or iron overload is a common cause of death in affected persons. Liver disease, fulminating infection, or other complications precipitated by the disease or by its treatment are some of the causes of morbidity and mortality in the severe forms of thalassemia.
• Morbidity and mortality are not limited to untreated persons; those receiving well-designed treatment regimens also may be susceptible to the various complications of the disease. Organ damage due to iron overload, chronic serious infections precipitated by blood transfusions, or complications of chelation therapy, such as cataracts, deafness, or infections with unusual microorganisms (eg, Yersinia enterocolitica), are all considered potential complications.

Race

Although thalassemia occurs in all races and ethnic groups, certain types of thalassemia are more common in some ethnic groups than in others (see Frequency). b thalassemia is common in southern Europe, the Middle East, India, and Africa. a thalassemia is more common in Southeast Asia; nevertheless, it is also seen in other parts of the world. Furthermore, specific mutations of the same type of thalassemia are more common among certain ethnic groups than others; this facilitates the screening and diagnostic processes, since certain probes for the more common mutations in a particular region are usually readily available.

The a thalassemia trait in Africa is usually not of the cis deletion on chromosome 16, unlike the condition in Southeast Asia, which is associated with complete absence of the a gene on one chromosome. When both parents have the cis deletion, the fetus may develop hydrops fetalis. For this reason, hydrops fetalis is not a risk in the African population, while it remains a risk for Southeast Asian population.

Sex

Both sexes are equally affected with thalassemia.

Age

Despite thalassemia's inherited nature, age at onset of symptoms varies significantly. In a thalassemia, clinical abnormalities in patients with severe cases and hematologic findings in carriers are evident at birth. Unexplained hypochromia and microcytosis in a neonate are highly suggestive of the diagnosis (see Image 7). However, in the severe forms of b thalassemia, symptoms may not be evident until the second half of the first year of life; until that time, the production of g-globin chains and their incorporation into fetal Hb can mask the condition.

Milder forms of thalassemia are frequently discovered by chance and at various ages. Many patients with an apparent homozygous b thalassemia condition (ie, hypochromasia, microcytosis, electrophoresis negative for Hb A, evidence that both parents are affected) may show no significant symptoms or anemia for several years. Almost all such patients' conditions are categorized as b thalassemia intermedia during the course of their disease. This situation usually results when the patient has a milder form of the mutation, is a compound heterozygote for b+ and b-0 thalassemia, or has other compound heterozygosity.

CLINICAL

Section 3 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

History

The history in patients with thalassemia varies significantly, depending on the severity of the condition and the age at the time of diagnosis.

• In most patients with thalassemia traits, no unusual signs or symptoms are encountered.
• Some patients, especially those with somewhat more severe forms of the disease, manifest some pallor and slight icteric discoloration of the sclerae with splenomegaly, leading to slight enlargement of the abdomen. An affected child's parents or caregivers may report these symptoms. However, some rare types of b thalassemia trait are caused by a unique mutation, resulting in truncated or elongated b chains, which combine abnormally with a chains, producing insoluble dimers or tetramers. The outcome of such insoluble products is a severe hemolytic process that needs to be managed like thalassemia intermedia or, in some cases, thalassemia major.
• The diagnosis is usually suspected in children with an unexplained hypochromic and microcytic picture, especially those who belong to one of the ethnic groups at risk. For this reason, physicians should always inquire about the patient's ethnic background, family history of hematologic disorders, and dietary history.
• Thalassemia should be considered in any child with hypochromic microcytic anemia that does not respond to iron supplementation.
• In more severe forms, such as b thalassemia major, the symptoms vary from extremely debilitating in patients who are not receiving transfusions to mild and almost asymptomatic in those receiving regular transfusion regimens and closely monitored chelation therapy.
• Children with b thalassemia major usually demonstrate none of the initial symptoms until the later part of the first year of life (when b chains are needed to pair with a chains to form Hb A, after g chains production is turned off). However, in occasional children younger than 3-5 years, the condition may not be recognized because of the delay in cessation of Hb F production.
• Patients with Hb E/b thalassemia may present with severe symptoms and a clinical course identical to that of patients with b thalassemia major. Alternatively, patients with Hb E/b thalassemia may run a mild course similar to that of patients with thalassemia intermedia or minor. This difference in severity has been described among siblings from the same parents. Some of the variation in severity can be explained based on the different genotypes, such as the type of b thalassemia gene present (ie, b+ or b-0), the co-inheritance of an a thalassemia gene, the high level of Hb F, or the presence of a modifying gene.
• Patients with heterozygous or homozygous Hb E are usually slightly anemic, with hypochromasia and microcytosis, and are usually asymptomatic.
• If further studies are not performed, benign homozygous Hb E is usually misdiagnosed as Hb E/b thalassemia, a condition that is frequently severe.
• In a thalassemia, the hematologic abnormalities are clearly evident in newborns with mild or moderate forms of the disease. Lethal clinical consequences and physical deformities encountered at the time of birth are the rule in severe homozygous a thalassemia.
• In b thalassemia, symptoms of anemia start when the g chain production is switched off and the b chains fail to form in adequate numbers.
• Manifestations of anemia include extreme pallor and enlarged abdomen due to hepatosplenomegaly.
• • Patients' typical reports may lead a physician who is not familiar with the condition to a first impression of acute leukemia.
  • This impression is supported by the large spleen, which leads to thrombocytopenia, and by the high WBC count and immature WBCs seen on the peripheral blood film due to the extreme activity of the marrow.
  • To support the impression of acute leukemia further, the elevated level of reticulocytes expected in all hemolytic anemias does not occur, despite the severe hemolysis; this anomaly is due to the massive splenomegaly and the ineffective erythropoiesis that prevents the release of the cells from the bone marrow. Evidence of hemolysis is usually present, with elevated indirect bilirubin level, high lactate dehydrogenase (LDH) level, and low level of haptoglobin.
• Bony changes may be severe, resulting in a characteristic radiologic picture (see Imaging Studies, Image 9). These changes are caused by massive expansion of the bone due to the ineffective erythroid production.
• The ineffective erythropoiesis also creates a state of hypermetabolism associated with fever and failure to thrive.
• Occasionally, gout due to hyperuricemia may be encountered.
• Iron overload is one of the major causes of morbidity in all patients with severe forms of thalassemia, regardless of whether they are regularly transfused.
• • In transfused patients, heavy iron turnover from transfused blood is usually the cause; in nontransfused patients, this complication is usually deferred until puberty (if the patient survives to that age).
  • Increased iron absorption is the cause in nontransfused patients, but the reason behind this phenomenon is not clear. Many believe that, despite the iron overload state in these patients and the increased iron deposits in the bone marrow, the requirement for iron to supply the overwhelming production of ineffective erythrocytes is tremendous, causing significant increases in GI absorption of iron.
  • Bleeding tendency, increased susceptibility to infection, and organ dysfunction are all associated with iron overload.
• Poor growth in patients with thalassemia is due to multiple factors and affects patients with well-controlled disease as well as those with uncontrolled disease.
• Patients may develop symptoms that suggest diabetes, thyroid disorder, or other endocrinopathy; these are rarely the presenting reports.

Physical

• Patients with thalassemia minor rarely demonstrate any physical abnormalities. Because the anemia is never severe and, in most instances, the Hb level is not less than 9-10 g/dL, pallor and splenomegaly are rarely observed.
• In patients with severe forms of thalassemia, the findings upon physical examination vary widely, depending on how well the disease is controlled.
• • Children who are not receiving transfusions have a physical appearance so characteristic that an expert examiner can often make a spot diagnosis.
  • In Cooley's original 4 patients, the stigmata of severe untreated b thalassemia major included the following:
    • Severe anemia, with an Hb level of 3-7g/dL
    • Massive hepatosplenomegaly
    • Severe growth retardation
    • Bony deformities
  • These stigmata are typically not observed; instead, patients look healthy. Any complication they develop is usually due to adverse effects of the treatment (transfusion or chelation).
  • Bony abnormalities, such as frontal bossing, prominent facial bones, and dental malocclusion, are usually striking.
  • Severe pallor, slight to moderately severe jaundice, and marked hepatosplenomegaly are almost always present.
• Complications of severe anemia are manifested as intolerance to exercise, heart murmur, or even signs of heart failure.
• Growth retardation is a common finding, even in patients whose disease is well controlled by chelation therapy.
• Patients with signs of iron overload may also demonstrate signs of endocrinopathy caused by iron deposits. Diabetes and thyroid or adrenal disorders have been described in these patients.
• In patients with severe anemia who are not receiving transfusion therapy, neuropathy or paralysis may result from compression of the spine or peripheral nerves by large extramedullary hematopoietic masses.

Causes

Thalassemias are inherited disorders caused by various gene mutations. The clinical expression and severity are subject to numerous factors that may either mask the condition or exaggerate the symptoms, leading to a more severe disease.

DIFFERENTIALS

Section 4 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Other Problems to be Considered

The differential diagnoses of thalassemic states in general depend on the age of the child at the time of presentation, the type of thalassemia and its severity, and, in severe cases, whether it is treated and well controlled. Furthermore, the form of thalassemia then has to be identified once the thalassemic condition is suspected because of the numerous thalassemic conditions.

Congenital dyserythropoietic anemia is a condition that may mimic severe forms of thalassemia in children. A bone marrow examination, Hb electrophoresis, and other tests reveal the diagnosis. Diamond-Blackfan anemia may also resemble severe forms of thalassemia in young infants.

The a thalassemia trait is similar to the b thalassemia trait. Both traits should be differentiated from iron deficiency anemia, which is the most common cause of hypochromasia and microcytosis in children and should be excluded before considering thalassemia. A child with presumed iron deficiency anemia that has not responded to adequate iron treatment is a good candidate for thalassemia workup.

In b thalassemia, elevated levels of Hb A₂, F, or both are usually helpful in confirming the diagnosis. However, in a thalassemia, the Hb electrophoresis results are usually normal; in this case, and in cases in which iron study results are also nondiagnostic, nonspecific tests may help to differentiate iron deficiency anemia or anemia of chronic inflammation from thalassemia. Free erythrocyte protoporphyrin (FEP) levels are usually elevated in patients with iron deficiency or anemia of chronic inflammation but not with thalassemia. The soluble transferrin receptors (sTfR) levels are high in patients with iron deficiency but not in those with anemia of chronic infection or thalassemia.

The process of differentiating thalassemia trait from iron deficiency anemia must include the patient's medical, developmental, nutritional, and family history and a review of the child's CBC, with emphasis on the RBC indices. Proper interpretation of the CBC may save the physician time and may save the patient from unnecessary further testing (see Lab Studies). The anemia in patients with thalassemia trait is usually mild; the Hb level is rarely, if ever, less than 9 g/dL, unless the cause of the anemia is multifactorial. The RBC count is almost always higher in patients with thalassemia than in those with iron deficiency anemia; in fact, it is frequently higher than the reported reference range for the age.

In thalassemia, the RBC indices, including the mean corpuscular volume (MCV) and mean corpuscular Hb (MCH), are both significantly low for an Hb level that is either normal or only slightly low. In addition, the RBC distribution width (RDW) is usually normal, reflecting the homogenous population of the RBCs in thalassemia (see Image 6), whereas iron deficiency anemia is known to be associated with anisocytosis (see Image 8). A faint basophilic stippling may be seen in the RBCs of patients with thalassemia but not typically in those of patients with iron deficiency.

Many formulae have been introduced to help in differentiating thalassemia trait from iron deficiency. The most practical and easiest to remember is the Mentzer index, which divides the patient's MCV by the RBC count (MCV/RBC). A result of less than 13 usually suggests thalassemia trait, while a result greater than 13 is indicative of iron deficiency.

Confirmation by Hb electrophoresis in b thalassemia is essential before the patient and the family are counseled. The Mentzer index loses its value if the patient has a combination of thalassemia and iron deficiency. In such patients, Hb electrophoresis results may also be inaccurate and misleading, since iron deficiency suppresses production of all Hbs, including Hb A₂. For this reason, the Hb A₂ level does not rise and is typically normal in these patients, masking the diagnosis of b thalassemia. In such cases, Hb electrophoresis should be repeated after the iron deficiency has been treated to obtain an accurate Hb A₂ fraction.

When b and a thalassemia coexist, the elevated levels of Hb A₂ and Hb F usually present in b thalassemia may also be lost. Furthermore, a thalassemia ameliorates the severity of b thalassemia since the decrease in a chains results in less inclusions and, hence, less hemolysis.

However, the confirmation of b thalassemia is easier than that of the a trait. The Hb electrophoresis result is usually normal, and DNA testing or globin chain synthesis enumeration are the only studies that confirm the diagnosis. A moderately severe form of a thalassemia, which some consider equivalent to b thalassemia intermedia, is termed Hb H disease. The disease is characterized by moderately severe anemia, splenomegaly, some jaundice, and, possibly, some bone changes due to marrow expansion. In this form, Hb electrophoresis is diagnostic in revealing the abnormal Hb, which is unstable and may be detected on the supra vital stain as inclusions in the RBCs (Heinz bodies).

The severity of Hb H disease depends on the inherited mutation. Seventy-five percent of Hb H mutations are caused by deletions on chromosome 16, which are usually associated with the milder forms of Hb H. Nondeletional forms are usually associated with severe Hb H and require transfusion. The diagnosis of Hb H may be difficult to establish, since it is unstable and may go undetected. The b tetramers of Hb H are replaced by g tetramers in the form of Hb Bart. Patients with Hb H disease usually have more than 20% Hb Bart at birth, a finding that has helped to identify 90% of the neonates with Hb H disease in the newborns screening program in California.

Hb Constant Spring (CS) is the most common nondeletional a thalassemia mutation associated with Hb H disease. The cells that contain Hb CS are usually overhydrated, which causes the loss of the traditional microcytosis seen in patients with thalassemia. Hb H/CS disease is more severe than Hb H disease, sometimes requiring splenectomy to improve the anemia, a procedure associated with a high rate of portal vein thrombosis.

Many clinical entities associated with splenomegaly and anemia, such as storage diseases, and other forms of chronic hemolytic anemias are to be considered in the differential diagnosis. The homozygous a thalassemia is not compatible with life (unless intrauterine blood transfusion is administered), and a baby with hydrops fetalis is usually delivered.

Other causes of immune and nonimmune hydrops fetalis are also to be differentiated from the hydrops fetalis of a thalassemia major, a condition that was rarely seen in the past since the mutation that predisposes to this condition is limited to the Southeast Asian population, not the African population.

Rare forms of a thalassemia are also described. Hb CS results from a specific mutation in the a thalassemia gene, leading to the production of elongated a chains. The clinical manifestations in the homozygous state are similar to those encountered in patients with Hb H disease; however, they differ in the electrophoretic pattern. g tetramers that consist of Hb Bart replace the b tetramers of Hb H.

Thalassemia may also interact with other globin structural variants, whether they involve b, a, or other chains. In the b variants, Bs, Bc, and Be are some of the globin chain's most common mutations. For instance, the interaction of Bs with b thalassemia produces a condition associated with sickle cell disease. Conversely, when Bs (sickle trait gene) interacts with an a thalassemia gene, less Hb S is present in the RBCs than when only Bs is present. Such interactions modify the severity of each separate condition.

The incidence of Hb E/b thalassemia has increased considerably in the United States in recent years due to the immigration of individuals from Southeast Asia, where the incidence of both Hg E and b thalassemia is high (see Frequency). Clinically, the severe forms of Hb E/b thalassemia are similar to the transfusion-dependent b thalassemia major. For this reason, the diagnosis Hb E/b thalassemia should be considered in patients of Southeast Asian descent.

Other rare thalassemia variants include Hb Lepore and hereditary persistence of fetal Hb (HPFH).

WORKUP

Section 5 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Lab Studies

• The CBC count and peripheral blood film examination results are usually sufficient to suspect the diagnosis. Hb evaluation confirms the diagnosis in b thalassemia, Hb H disease, and Hb E/b thalassemia.
• • In the severe forms of thalassemia, the Hb level ranges from 2-8 g/dL.
  • MCV and MCH are significantly low, but, unlike thalassemia trait, thalassemia major is associated with a markedly elevated RDW, reflecting the extreme anisocytosis.
  • The WBC count is usually elevated in b thalassemia major; this is due, in part, to miscounting the many nucleated RBCs as leukocytes. Leukocytosis is usually present, even after excluding the nucleated RBCs. A shift to the left is also encountered, reflecting the hemolytic process.
  • Platelet count is usually normal, unless the spleen is markedly enlarged.
  • Peripheral blood film examination reveals marked hypochromasia and microcytosis, hypochromic macrocytes that represent the polychromatophilic cells, nucleated RBCs, basophilic stippling, and occasional immature leukocytes (see Image 5). Contrast this with the abnormalities associated with Hb H, an a thalassemia (see Image 4).
  • Hb electrophoresis usually reveals an elevated Hb F fraction, which is distributed heterogeneously in the RBCs of patients with b thalassemia, Hb H in patients with Hb H disease, and Hb Bart in newborns with a thalassemia trait. In b-0 thalassemia, no Hb A is usually present; only Hb A₂ and Hb F are found.
• Iron studies are as follows:
• • Serum iron level is elevated, with saturation reaching as high as 80%.
  • The serum ferritin level, which is frequently used to monitor the status of iron overload, is also elevated. However, an assessment using serum ferritin levels may underestimate the iron concentration in the liver of a transfusion-independent patient with thalassemia. 
• Complete RBC phenotype, hepatitis screen, folic acid level, and human leukocyte antigen (HLA) typing are recommended before initiation of blood transfusion therapy.
  

Imaging Studies

• Skeletal survey and other imaging studies reveal classic changes of the bones that are usually encountered in patients who are not regularly transfused.
• • The striking expansion of the erythroid marrow widens the marrow spaces, thinning the cortex and causing osteoporosis. These changes, which result from the expanding marrow spaces, usually disappear when marrow activity is halted by regular transfusions. Osteoporosis and osteopenia may cause fractures, even in patients whose conditions are well-controlled.
  • In addition to the classic "hair on end" appearance of the skull, which results from widening of the diploic spaces and observed on plain radiographs (see Image 9), the maxilla may overgrow, which results in maxillary overbite, prominence of the upper incisors, and separation of the orbit. These changes contribute to the classic "chipmunk facies observed in patients with thalassemia major.
  • Other bony structures, such as ribs, long bones, and flat bones, may also be sites of major deformities. Plain radiographs of the long bones may reveal a lacy trabecular pattern. Changes in the pelvis, skull, and spine become more evident during the second decade of life, when the marrow in the peripheral bones becomes inactive while more activity occurs in the central bones.
  • Compression fractures and paravertebral expansion of extramedullary masses, which could behave clinically like tumors, more frequently occur during the second decade of life.
  • MRI and CT scanning are usually used in diagnosing such complications.
• Chest radiography is used to evaluate cardiac size and shape.
• MRI and CT scanning can be used as noninvasive means to evaluate the amount of iron in the liver in patients receiving chelation therapy.
• A newer noninvasive procedure involves measuring the cardiac T2 with cardiac magnetic resonance (CMR). This procedure has shown decreased values in cardiac T2 due to iron deposit in the heart. Unlike liver MRI, which usually correlates very well with the iron concentration in the liver measured using percutaneous liver biopsy samples and the serum ferritin level, CMR does not correlate well with the ferritin level, the liver iron level, or echocardiography findings. This suggests that cardiac iron overload cannot be estimated with these surrogate measurements. This is also true in measuring the response to chelation therapy in patients with iron overload. The liver is clear of iron loading much earlier than the heart, which also suggests that deciding when to stop or reduce treatment based on liver iron levels is misleading.

Other Tests

• ECG and echocardiography are performed to monitor cardiac function.
• HLA typing is performed for patients for whom bone marrow transplantation is considered.
• Eye examinations, hearing tests, renal function tests, and frequent blood counts are required to monitor the effects of deferoxamine (DFO) therapy and the administration of other chelating agents (see Treatment, Medication).

Procedures

• Bone marrow aspiration is needed in certain patients at the time of the initial diagnosis to exclude other conditions that may manifest as thalassemia major.
• Liver biopsy is used to assess iron deposition and the degree of hemochromatosis. However, using liver iron content as a surrogate for evaluation of cardiac iron is misleading. Many recent studies have shown very poor correlation between the two; hence, cardiac evaluation for the presence of iron overload needs to be addressed separately.
• Measurement of urinary excretion of iron after a challenge test of DFO is used to evaluate the need to initiate chelation therapy and reflects the amount of iron overload.

Histologic Findings

All severe forms of thalassemia exhibit hyperactive marrow with erythroid hyperplasia and increased iron stores in marrow, liver, and other organs. In the untreated person with severe disease, extramedullary hematopoiesis in unusual anatomic sites is one of the known complications.

Erythroid hyperplasia is observed in bone marrow specimens. Increased iron deposition is usually present in marrow (see Image 10), liver, heart, and other tissues.

Staging

Some use a relevant staging system based on the cumulative numbers of blood transfusions given to the patient to grade cardiac-related symptoms and determine when to start chelation therapy in patients with b thalassemia major or intermedia. In this system, patients are divided into 3 groups.

• The first group contains those who have received fewer than 100 units of packed RBCs (PRBCs) and are considered to have stage I disease. These patients are usually asymptomatic; their echocardiograms reveal only slight left ventricular wall thickening, and both the radionuclide cineangiogram and the 24-hour ECG findings are normal.
• Patients in the second group (stage II patients) have received 100-400 units of blood and may report slight fatigue. Their echocardiograms may demonstrate left ventricular wall thickening and dilatation but normal ejection fraction. The radionuclide cineangiogram findings are normal at rest but show no increase or fall in ejection fraction during exercise. Atrial and ventricular beats are usually noticed on the 24-hour ECG.
• Finally, in stage III patients, symptoms range from palpitation to congestive heart failure, decreased ejection fraction on echocardiogram, and normal cineangiogram results or decreased ejection fraction at rest, which falls during exercise. The 24-hour ECG reveals atrial and ventricular premature beats, often in pairs or in runs.

A second classification, introduced by Lucarelli, is used for patients with severe disease who are candidates for hematopoietic stem cell transplantation (HSCT). This classification is used to assess risk factors that predict outcome and prognosis and addresses 3 elements: (1) degree of hepatomegaly, (2) presence of portal fibrosis in liver biopsy sample, and (3) effectiveness of chelation therapy prior to transplantation.

If one of these elements is unfavorable prior to HSCT, the chance of event-free survival is significantly poorer than in patients who have neither hepatomegaly nor fibrosis and whose condition responds well to chelation (class 1 patients). The event-free survival rate after allogeneic HSCT for class 1 patients is 90%, compared to 56% for those with hepatomegaly and fibrosis and whose condition responds poorly to chelation (class 3).

TREATMENT

Section 6 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Medical Care

Patients with thalassemia traits do not require medical or follow-up care after the initial diagnosis is made. Iron therapy should not be used unless a definite deficiency is confirmed and should be discontinued as soon as the potential Hb level for that individual is reached. Counseling is indicated in all persons with genetic disorders, especially when the family is at risk of a severe form of disease that may be prevented.

Patients with severe thalassemia require medical treatment, and a blood transfusion regimen was the first measure effective in prolonging life. In the process of experimenting with blood transfusion, it was found to provide patients with many benefits, including reversal of the complications of anemia, elimination of ineffective erythropoiesis and its complications, allowance of normal or near-normal growth and development, and extension of patients' life spans. Blood transfusion should be initiated at an early age when the child is symptomatic and after an initial period of observation to assess whether the child can maintain an acceptable level of Hb without transfusion.

After many years of monitoring transfused patients, the inadequacy of transfusion alone as a therapy became clear. Accumulation of transfused iron and its consequences also needed to be addressed. Chelation therapy was considered after extensive research and many clinical trials. Today, regular blood transfusion combined with well-monitored chelation therapy has become the standard therapy and has drastically changed the outlook for this population of patients.

• Blood transfusions
• • Several blood transfusion regimens have been introduced. Of these, one seems practical, less demanding, and more cost-effective than any of the others. This regimen attempts to maintain a pretransfusion Hb level of 9-9.5 g/dL at all times.
  • Like all patients who require long-term regular blood transfusions, patients with thalassemia require a pretransfusion workup. This workup should include RBC phenotype, hepatitis B vaccination (if needed), and hepatitis workup. Iron and folate levels should also be measured.
  • Transfused blood should always be leukocyte poor; 10-15 mL/kg PRBCs at the rate of 5 mL/kg/h every 3-5 weeks is usually adequate to maintain the pretransfusion Hb level needed.
  • Consider administration of acetaminophen and diphenhydramine hydrochloride before each transfusion to minimize febrile or allergic reactions.
  • Patients with documented transfusion reactions may benefit from having RBCs washed with saline or from receiving deglycerolized RBCs.
• Complications of blood transfusion: The major complications of blood transfusions are those related to transmission of infectious agents or the development of iron overload.
• • Infectious agents
  • • As recently as a few years ago, 25% of transfused patients were exposed to hepatitis B virus. At present, both immunization and strict screening of potential donors have significantly decreased the incidence. Hepatitis C virus (HCV) is the most common cause of hepatitis in adolescents older than 15 years with thalassemia (risk of exposure was 6%). Because both liver failure and hepatocellular carcinoma have been attributed to HCV in patients with thalassemia, aggressive treatment with interferon alpha is warranted in patients who contract HCV.
    • The incidence of transfusion-transmitted HCV is expected to drop significantly because of stricter blood screening now mandated. Data from the Registry of the Thalassemia Clinical Research Network (TCRN) demonstrated how successful the screening for HCV was in reducing the incidence of HCV infection in such patients. The incidence was shown to be only 5% in children younger than 15 years compared to 75% in adults older than 25 years; unfortunately, this is not true in developing countries.
    • Infection with rare organisms that are not considered pathogenic in healthy hosts may cause febrile illness and symptoms of enteritis in patients with iron overload, especially those receiving chelation therapy with DFO. The pathogen Y enterocolitica uses the abundant iron scavenger molecules, known as siderophores, which the microorganism needs but cannot synthesize. Fever without any apparent cause, especially when associated with diarrhea, should be treated with gentamicin and trimethoprim-sulfamethoxazole, even when culture results are negative.
  • Iron overload
  • • Even though blood transfusion is supposed to decrease the excessive iron absorption in the GI tracts of patients with thalassemia, patients nevertheless receive large amounts of iron with each blood transfusion. Why patients with excessive iron absorb large amounts of iron from the GI tract is not clear.
  • • Many believe that the highly active marrow in these patients is iron deficient and needs large amounts of iron to produce the massive numbers of RBCs usual in this disease. The iron absorbed from the gut by the enterocyte, which coordinates iron uptake and transport into the body with its release from the reticuloendothelial system, is bound to transferrin in the plasma. The erythron claims most of the iron, while other tissues and cells that express transferrin receptors pick most of the rest. Both iron and transferrin enter the cells by endocytosis, forming the labile iron pool that provides iron to the cells and the iron-containing enzymes.
    • As iron accumulates and exceeds body needs, production of apoferritin is accelerated to provide means for storing iron in nontoxic forms as ferritin or hemosiderin. Measuring the ferritin level in the first few years after the diagnosis of thalassemia is usually helpful in detecting iron overload status because ferritin correlates well with total body iron burden at this time. Later on, the correlation becomes poor, since ferritin is produced by hepatocellular damage and it acts as an acute-phase reactant. The ferritin level rises in individuals with hepatitis, infections, and heart failure. When ferritin molecules accumulate further, the protein moiety disintegrates, leaving small iron-concentrated hemosiderin particles; this alone is not harmful, but it may cause release from lysosomes of hydrolytic enzymes that are toxic to the cells.
    • In patients with iron overload, a unique situation develops as a result of the very high saturation of the carrier protein transferrin, approximately 90% or more (reference range for children and adults, 23-34%). A new iron pool, which is not present in healthy individuals, is formed (the nontransferrin-bound or the free serum iron pool), which is probably an expansion of the labile pool.
  • Tissue toxicity in iron overload
  • • Peroxidation of cell membrane components by iron in the free pool is probably the major cause of organ damage from excessive iron. This effect was noted to worsen when ascorbic acid was added and was corrected partially by either vitamin E or deferoxamine. Patients with thalassemia with iron overload are typically deficient in vitamin E.
    • The route of iron access to the body and its relation to the development of hemosiderosis have been controversial issues for some time. Many believe that absorption of iron from the bowel is the major factor in the etiology of this condition. The parenchymal tissue damage in the livers of patients with hereditary hemochromatosis and those with thalassemia intermedia who are not receiving transfusions and the lower incidence of liver cirrhosis in heavily transfused patients with aplastic anemia support their claims.
    • This interpretation should not create the wrong impression that transfusional iron is not involved in the etiology of iron overload; on the contrary, every effort should be made to minimize all iron intake from any source in patients at risk whenever possible.
• Chelation therapy
• • Until recently, patients with thalassemia major who received only transfusion therapy could not survive beyond adolescence, largely because of cardiac complications caused by iron toxicity. The introduction of chelating agents capable of removing excessive iron from the body has dramatically increased life expectancy.
  • When administered in conjunction with blood transfusion regimens, chelation can delay the onset of cardiac disease and, in some patients, even prevent its occurrence.
  • Several chelating agents have been tested, and, although many failed, one particular agent was proven effective and safe. DFO is a complex hydroxylamine with high affinity for iron; it targets the labile pool, the nontransferrin-bound iron (free pool), and the ferritin generated from reticuloendothelial iron.
  • Route of administration is critical in achieving the goal of therapy, which is reaching a negative iron balance (ie, excreting more iron than acquired from both intestinal absorption and transfusion). In the adult, reaching this goal involves removing 35 mg of iron per day.
  • Because the agent is not absorbed in the gut, it must be administered parenterally, whether intramuscularly, intravenously, or subcutaneously. Because of its short half-life, subcutaneous infusion must be prolonged if it is to achieve the stated goal.
  • A total dose of 30-40 mg/kg/d is infused over 8-12 hours during the child's sleep for 5 d/wk by a mechanical pump.
  • If doses larger than those tolerated by the subcutaneous route are needed, the intravenous route may be safely used, especially when a vascular access device is in place.
  • Doses as high as 6-10 g were administered intravenously in selected patients and proved effective in reversing serious iron overload complications.
  • The optimal time to initiate chelation therapy is dictated by the amount of accumulated iron and its accessibility for chelation. This usually occurs after 1-2 years of transfusions. Severe toxicity may develop if chelation is started prematurely. A DFO challenge test is usually helpful in deciding whether a patient is a candidate for chelation.
  • DFO toxicity concerns are as follows:
  • • Local reaction at the site of injection is reported in many patients and can occasionally be severe.
    • High-frequency hearing loss has been reported in 30-40% of patients. Other neurosensory complications of chelation therapy include color and night blindness and visual field loss. These complications are frequently reversible and more commonly occur when not enough iron is available for chelation, when aggressive chelation therapy is administered, or when the chelation agent is administered in continuous intravenous infusions in a dose greater than 50 mg/kg/d. For this reason, eye and hearing examinations are to be scheduled every 6-12 months in patients receiving chelation therapy.
    • Pulmonary infiltrates as a complication have been reported in only a few patients.
    • For several reasons and despite all the advantages of DFO, chelation with this agent has been inadequate. In countries where it is needed the most, the high cost of the drug and the supplies needed for its administration make it unavailable for most patients. DFO has been prescribed for only 25,000 of 72,000 patients with thalassemia major receiving blood transfusion worldwide. In the Western world, on the other hand, despite the wide availability of the agent, some patients do not comply because of the unpleasant and cumbersome nature of the regimen. Others who cannot tolerate the drug have to modify the dose or the route or stop use all together.
    • A recent report showed that 105 of 328 patients in North America had to modify their regimen, and 20 patients had to stop taking the agent. For such reasons, the search for more practical chelators (especially the targeted chelators that can more effectively remove iron from specific organs [eg, heart, liver]) has continued to be a major task for the last few decades.
  • Oral chelating agents have been in use in other countries for some time, and newer ones are showing efficacy and some specificity for removing iron more efficiently from certain organs than DFO.
  • Deferasirox (Exjade) is a new oral chelating agent administered once daily. It was shown to be comparable with the parenteral agent DFO in maintaining or reducing liver iron concentration when administered in the appropriate dosage.
  • Deferasirox toxicity concerns include the following:
  • • Skin rash
    • Hepatic dysfunction
    • Postmarketing surveillance reports of acute renal failure
    • Cytopenia (eg, agranulocytosis, neutropenia, thrombocytopenia)
    • Auditory disturbances
    • Ocular disturbances
    • Hypersensitivity reactions
  • The previously known oral chelating agent deferiprone (Ferriprox, DFP), which failed when administered alone, is now showing superiority in reducing cardiac iron concentration. DFP is co-administered with DFO or is administered sequentially with DFO. The additive and synergistic effects contribute to significant removal of iron from different organs at risk for siderosis, such as the liver and heart. DFP is currently designated as an orphan drug in the United States.
  • Initially, DFP provided some promising results. However, after a few years of observation and monitoring, the agent was found to be less effective than DFO in preventing organ damage. In addition, some adverse effects such as neutropenia or even agranulocytosis were reported in as many as 8% of patients.
  • More recently, DFP was demonstrated to have efficacy comparable to that of DFO, with minimal adverse effects and better compliance, leading some investigators to reconsider the use of DFP. The drug is now in use in more than 50 countries. Significant improvement based on cardiac MRI findings, indicating a reduction in cardiac iron overload and improved cardiac function, was reported in some studies as a result of DFP therapy. This observation suggests a cardioprotective role of DFP. This observation was recently confirmed by more than one study.
  • Finally, combinations of 2 iron chelators (parenteral DFO plus the oral chelator) have been demonstrated to produce additive and synergistic effects. Such an approach would enable a flexible schedule and improve compliance and overall quality of life.
  • Patients receiving chelation therapy have been demonstrated to have some degree of vitamin C deficiency. This deficiency has been attributed, in part, to increased catabolism. Administration of vitamin C increases the urinary excretion of iron and raises both serum iron and ferritin levels; this is probably related to the fact that vitamin C slows down the conversion of ferritin to hemosiderin, leading to the availability of more chelatable iron. Conversely, vitamin C enhances iron-mediated peroxidation of membrane lipids, leading to significant toxicity, mostly cardiac dysfunction in patients who are receiving large doses of vitamin C supplementation in addition to chelation therapy. For this reason, only small doses should be administered to enhance chelation (3 mg/kg/d at the start of infusion of the chelator). Large doses should be avoided.
• Vitamin E deficiency: Vitamin E deficiency has been reported in patients with severe thalassemia. Some of the hemolysis in this population was attributed to peroxidation of the RBC membrane lipids by an iron-mediated free radical effect. As an antioxidant, vitamin E is expected to decrease cell toxicity.
• Folic acid deficiency: This deficiency is a common complication in patients with thalassemia, mainly because of the extreme demand associated with the severe expansion of the marrow. Other causes, such as poor absorption and intake, can also contribute to folate deficiency. For this reason, folic acid (1 mg/d) has been recommended as a supplement for this patient population.
• Hematopoietic stem cell transplantation
• • HSCT is recommended only for selected patients; it is the only known curative treatment for thalassemia. Poor outcome after HSCT correlates with the presence of hepatomegaly and portal fibrosis and with ineffective chelation prior to transplant. The event-free survival rate for patients who have all 3 features is 59%, compared to 90% for those who lack all 3.
  • Even though blood transfusion is not required after a successful transplant, certain individuals need continued chelation therapy to remove excessive iron. The optimal time to start such treatment is a year after the successful HSCT.
  • Parents and caregivers of patients with severe thalassemia are frequently confronted with a choice between standard therapy and HSCT. The 15-year cardiac disease-free survival rate for patients receiving standard therapy exceeds 90% and is similar for those without risk factors who have undergone HSCT.
  • Long-term outcome for transplant patients, including fertility, is not known. The cost of long-term standard therapy is known to be higher than the cost of transplant. The possibility of developing cancer after HSCT should also be considered. In many centers, the donor has to be a matched sibling with or without a thalassemia trait.
• Investigational agents known to increase Hb F level: This therapeutic strategy is investigational at this time. Several agents administered to raise the Hb F level have been investigated in patients with severe thalassemia. Unfortunately, the initial results of these studies are not promising.
• Gene therapy: This therapy is an attractive therapeutic modality, the efficacy of which remains to be demonstrated.

Surgical Care

Splenectomy is the principal surgical procedure used for many patients with thalassemia. The spleen is known to contain a large amount of the labile nontoxic iron (ie, storage function) derived from sequestration of the released iron. The spleen also increases RBC destruction and iron distribution (ie, scavenger function). These facts should always be considered before the decision is made to proceed with splenectomy. In addition, with recent reports of venous thromboembolic events (VTEs) after splenectomy, one should carefully consider the benefits and the risks before splenectomy is advocated. The spleen acts as a store for nontoxic iron, thereby protecting the rest of the body from this iron. Early removal of the spleen may be harmful (liver cirrhosis has occurred in such individuals).

Conversely, splenectomy is justified when the spleen becomes hyperactive, leading to excessive destruction of RBCs and thus increasing the need for frequent blood transfusions, resulting in more iron accumulation. Furthermore, if the labile iron pool in the spleen becomes the target for the action of the DFO (ie, removing the nonharmful pool and leaving the toxic one), splenectomy is further justified. The goal in this confusing dilemma should always be to achieve a negative iron balance, which, in many patients, has been possible by continuous administration of subcutaneous DFO.

• Several criteria are used to aid in the decision for splenectomy; a practical one suggests that splenectomy may be beneficial in patients who require more than 200-250 mL/kg of PRBC per year to maintain an Hb level of 10 g/dL.
• The risks associated with splenectomy are minimal, and many of the procedures are now performed by laparoscopy. Postsplenectomy risk of infections with encapsulated organisms and malaria in endemic areas is always a concern. The problem is minimal at the present time, since presplenectomy immunizations and postsurgical prophylactic antibiotics have significantly decreased the rates of such complications. Traditionally, the procedure is delayed whenever possible until the child is aged 4-5 years or older. Aggressive treatment with antibiotics should always be administered for any febrile illness while awaiting the results of cultures. Low-dose daily aspirin is also beneficial when the platelet count rises to more than 600,000/µL postsplenectomy.
• Another surgical procedure in patients with severe thalassemia on transfusion therapy is the placement of a central line for the ease and convenience of administering blood transfusions, chelation therapy, or both.

Consultations

• Pediatric surgeon
• Pediatric endocrinologist
• Pediatric ophthalmologist
• Pediatric otolaryngologist
• Pediatric gastroenterologist
• Pediatric HSCT specialist

Diet

• A normal diet is recommended, with emphasis on the following supplements: folic acid, small doses of ascorbic acid (vitamin C), and alpha-tocopherol (vitamin E).
• Iron should not be given, and foods rich in iron should be avoided. Drinking coffee or tea has been shown to help decrease absorption of iron in the gut.

Activity

• Patients with well-controlled disease are usually fully active.
• Patients with anemia, heart failure, or massive hepatosplenomegaly are usually restricted according to their tolerances.