OBJECTIVETo identify the genetic defect for the autosomal dominant coralliform cataract affecting a four-generation Chinese family.

METHODSGenomic DNA from the family members was typed for whole genomic linkage analysis. Two-point LOD scores were calculated using the LINKAGE program package (version 5.1). Mutation analysis of candidate genes was performed by direct sequencing.

RESULTSThirteen of the 38 individuals had congenital cataracts. The maximum two point LOD score, 3.5 at theta=0.1 was obtained for the marker D2S325. Mutation analysis of the gamma-crystallin gene cluster identified a C --> A mutation in exon 2 of gamma-D crystallin gene (CRYGD) associated with cataracts in this family. This mutation resulted in a substitution of threonine for proline at amino acid 23 (P23T) of the protein.

CONCLUSIONThe results suggest that the coralliform cataract phenotype is due to a mutated gamma-D gene, and the sequence change is identical with that recently reported to be related with lamellar cataract, a distinct clinical entity, thus providing evidence that the same genetic defect may be associated with different opacity location. The pathogenesis needs further investigation.