Monday, February 12, 2007

Section 11-C(4) Primary congenital glaucoma (PCG)

Many cases of primary congenital glaucoma (PCG) appear to be sporadic; however, as many as 10-40% cases are familial with autosomal recessive inheritance. Many large PCG pedigrees with clear autosomal recessive inheritance have been reported. In addition, twin studies have provided strong evidence that PCG has a genetic basis. Twins with identical DNA (identical, monozygotic twins) tend to both have PCG at a much higher rate than twins with only 50% identical DNA (fraternal, dizygotic twins). This difference in concordance indicates that genes have important roles in the development of PCG.

Research studies of several large families have shown that mutations in the gene cytochrome P450 1B1 (CYP1B1) cause many cases of PCG. Most patients with PCG (87% of familial cases and 27% of sporadic cases) have glaucoma due to variations in the CYP1B1 gene.

The CYP1B1 gene encodes a protein that metabolizes or breaks down certain molecules or drugs. The mechanism by which defects in the CYP1B1 gene causes PCG is unknown. However, it has been theorized that mutations in this gene may alter its ability to break down factors that are vital to the normal development of drainage angle. A defective CYP1B1 gene might, therefore, result in an abnormal concentration of these developmental factors and lead to the abnormal formation of the drainage angle and PCG.

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