Background: Congenital cataract is a sight-threatening disease that affects about 1 - 6 cases per 10000 live births and causes 10% - 30% of all blindness in children. About 25% of all cases are due to genetic defects. We identified autosomal dominant congenital coralliform cataracts-related genetic defect in a four-generation Chinese family.
Methods: Complete ophthalmological examinations were performed prior to lens extraction. Lens samples were then studied by electron microscopy. Genomic DNA from family members were examined using whole-genomic linkage analysis, with two-point logarithm of odds (LOD) scores calculated using the Linkage program package (version 5.1). Mutation analysis of candidate genes was performed by direct sequencing. Finally, a three-dimensional protein model was predicted using Swiss-Model (version 2.0).
Results: Eleven of the 23 examined individuals had congenital cataracts. Ultrastructure studies revealed crystal deposits in the lens, and granules extensively dispersed in transformed lens fiber cells. The maximum two-point LOD score, 3.5 at theta = 0.1, was obtained for the marker D2S325. Mutation analysis of the gamma-crystallin (CRYG) gene cluster identified a mutation (P23T) in exon 2 of gammaD-crystallin (CRYGD). Protein structure modeling demonstrated that the P23T mutation caused a subtle change on the surface of the gammaD protein.
Conclusions: The results suggest that the coralliform cataract phenotype is due to a mutated CRYGD gene, and that this sequence change is identical to one reported by Santhiya to be related to another distinct clinical condition, lamellar cataract. This study provides evidence that this same genetic defect may be associated with a different phenotype. This is the first report identifying the genetic defect associated with an autosomal dominant congenital coralliform cataract.