A novel γD-crystallin mutation causes mild changes in protein properties but leads to congenital coralliform cataract

Purpose: To identify the genetic lesions for congenital coralliform cataract. Methods: Two Chinese families with autosomal dominant coralliform cataract, 12 affected and 14 unaffected individuals, were recruited. Fifteen known genes associated with autosomal dominant congenital cataract were screened by two-point linkage analysis with gene based single nucleotide polymorphisms and microsatellite markers. Sequence variations were identified. Recombinant FLAG-tagged wild type or mutant gamma D-crystallin was expressed in human lens epithelial cells and COS-7 cells. Protein solubility and intracellular distribution were analyzed by western blotting and immunofluorescence, respectively. Results: A novel heterozygous change, c.43C>A (R15S) of gamma D-crystallin (CRYGD) co-segregated with coralliform cataract in one family and a known substitution, c.70C>A (P24T), in the other family. Unaffected family members and 103 unrelated control subjects did not carry these mutations. Similar to the wild type protein, R15S gamma D-crystallin was detergent soluble and was located in the cytoplasm. ProtScale and ScanProsite analyses revealed raised local hydrophobicity and the creation of a hypothetical casein kinase II phosphorylation site. Conclusions: A novel R15S mutation caused congenital coralliform cataract in a Chinese family. R15S possessed similar properties to the wild type gamma D-crystallin, but its predicted increase of hydrophobicity and putative phosphorylation site could lead to protein aggregation, subsequently causing opacification in lens.