Excerpt from Dystrophy, Crystalline

Synonyms, Key Words, and Related Terms: crystalline dystrophy, Schnyder's crystalline corneal dystrophy, SCCD, hereditary crystalline stromal dystrophy of Schnyder, corneal crystalline dystrophy of Schnyder, crystalline stromal dystrophy, central stromal crystalline corneal dystrophy, Schnyder crystalline dystrophy sine crystals

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Background: Schnyder crystalline corneal dystrophy (SCCD) is a rare autosomal dominant stromal dystrophy that is characterized by bilateral corneal opacification, resulting from an abnormal accumulation of cholesterol and lipid. Van Went and Wibaut first described it in the Dutch literature in 1924, and it was delineated further by Schnyder in the Swiss literature in 1929. While the incidence in the general population is unknown, the world's largest pedigree (>200 patients with SCCD) has a Swede-Finn heritage and has been traced to the southwest coast of Finland on the Bay of Bothnia. However, the dystrophy has been reported in other ethnicities and in all racial groups.

Pathophysiology: The pathogenesis remains unknown, but it is postulated to result from a localized defect of lipid metabolism. It has been demonstrated in affected versus normal corneas that the cholesterol content increases 10-fold and the phospholipid content increases 5-fold. Immunohistochemical analysis has revealed the preferential deposition of apolipoprotein components of high-density lipoprotein (HDL), ie, apoA I, apoA II, and apoC, but not of low-density lipoprotein (LDL), ie, apoB. This finding suggests an abnormal metabolism of HDL in the SCCD cornea. SCCD has been mapped to 2.3 Mbp on band 1p36.

Frequency:

In the US: The dystrophy has been reported in the United States, although the incidence in the general population is unknown.

Internationally: While the incidence is unknown, the dystrophy has been reported in eastern and western Europe, Taiwan, and Turkey.

Mortality/Morbidity: Morbidity derives from progressive corneal clouding, leading to glare and decreased vision in daylight.

Race: SCCD can occur in Caucasians, Asians, and African Americans.

Sex: Although rare sporadic cases have been reported, SCCD is primarily an autosomal dominant disease, affecting both sexes with equal probability.

Age: The disease may appear as early as the first decade of life and slowly progresses with age.