Excerpt from Androgen Insensitivity Syndrome

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Background

Androgen insensitivity syndrome (AIS), formerly known as testicular feminization, is an X-linked recessive condition resulting in a failure of normal masculinization of the external genitalia in chromosomally male individuals. This failure of virilization can be either complete androgen insensitivity syndrome (CAIS) or partial androgen insensitivity syndrome (PAIS), depending on the amount of residual receptor function.

Both individuals with PAIS and individuals with CAIS have 46,XY karyotypes. Individuals with CAIS have female external genitalia with normal labia, clitoris, and vaginal introitus. The phenotype of individuals with PAIS may range from mildly virilized female external genitalia (clitorimegaly without other external anomalies) to mildly undervirilized male external genitalia (hypospadias and/or diminished penile size).

In either case, affected individuals have normal testes with normal production of testosterone and normal conversion to dihydrotestosterone (DHT), which differentiates this condition from 5-alpha reductase deficiency. Because the testes produce normal amounts of müllerian-inhibiting factor (MIF), also known as müllerian-inhibiting substance (MIS) or anti-müllerian hormone/factor (AMH/AMF), affected individuals do not have fallopian tubes, a uterus, or a proximal (upper) vagina.

Pathophysiology

The basic etiology of AIS is a loss-of-function mutation in the androgen receptor (AR) gene. This AR gene has been localized to the long arm of the X chromosome (ie, Xq11-13). Over 200 such mutations have been described, including complete and partial gene deletions, point mutations, and small insertions/deletions. These mutations can cause a variety of functional defects, ranging from a complete loss of receptors on the cell surface because of incomplete protein synthesis to alterations in substrate binding affinity. Altered substrate binding affinity causes a signal transmission loss, despite normal cell surface receptor numbers. While the genotypes causing CAIS are consistent in phenotypic presentation, the genotype/phenotype relationships for the mutations causing PAIS remain unclear.

Loss of AR function means that, despite normal levels of androgen synthesis, the typical postreceptor events that mediate the effects of hormones on tissues do not occur. This results in the phenotype of prenatal undervirilization of external genitalia, absence of pubic and axillary hair, lack of acne, and absence of voice changes at puberty.

Frequency

United States

Data currently are not available on the specific incidence of CAIS and/or PAIS.

International

The best available data suggest an AIS incidence of approximately 1 case per 20,400 liveborn males. This statistic is based on analysis of a Danish patient registry that included only hospitalized cases, so the true incidence of AIS may be higher. CAIS appears more common than PAIS, although exact figures are unavailable.

Mortality/Morbidity

AIS, either complete or partial, has little medical morbidity or mortality. Over time, untreated patients have a theoretical risk of malignant degeneration and development of gonadoblastoma of the testes. No documentation currently exists on the morbidity or mortality of these tumors specifically in individuals with AIS. The tumor is considered cured without need for further therapy if it is removed while still limited to the interior of the testes capsule. The tumor is considered curable in most patients even when undetected at this early state.

In contrast to medical morbidity, psychological morbidity is common. Phenotypic females who are discovered to be genetic males may have psychosocial problems. These females require sensitive psychological support. Their psychosocial problems range from identity issues to problems dealing with the gender perceptions of the outside world and the style and sensitivity (or lack thereof) they encounter within the medical system.

Most affected individuals report psychological trauma at diagnosis. Their reactions to the diagnosis frequently are compounded by their interactions with the medical care system, in which they often are treated as oddities and forced to undergo multiple examinations and interviews with students and residents for teaching purposes. Even in nonteaching situations, women with AIS report difficulties identifying offices where physicians and staff are familiar with their condition. Many of these patients have been told that they really are not women but actually are men because of the presence of a Y chromosome and testes. These difficulties and doubts often cause shame and self-doubt as well as anger and frustration with a medical system they had expected to take care of them.

Race

No racial differences in incidence or presentation of AIS have been described.

Sex

All patients with AIS are chromosomally and gonadally male. However, separating the concepts of sex and gender is crucial with these patients. The term sex usually is based on physical attributes, while the concept of gender is based on an individual's self-concept and self-identification as well as the role an individual assumes in society.

Most patients with CAIS have a female gender. This may be due, in part, to the patient's role assignment and upbringing before the diagnosis or to the patient's choice of female "sex/gender" at diagnosis. The significance of the androgen effect's absence increasingly is recognized for its influence on the maturing brain (and other systems) in terms of developing adult gender identity.

PAIS is a more complicated problem for gender identity. Just as the genitalia may be highly varied in the degree of virilization, gender identity may be either female or male. At present, no reliable predictors of eventual gender identity have been identified, including genotype or degree of genital virilization at birth.

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