A novel deletion variant of γD-crystallin responsible forcongenital nuclear cataract

[摘要] Purpose: To investigate a novel deletion variant of γD-crystallin (CRYGD) identified in a Chinese family with nuclearcongenital cataract.Methods: A Chinese family with five affected members diagnosed withnuclear cataract and four unaffected members were recruited for themutational screening of 15 known candidate genes for autosomal dominantcongenital cataract. Two-point linkage analysis with single nucleotidepolymorphism markers and microsatellite markers flanking these genestogether with direct sequencing was applied to identify thedisease-causing mutation. Recombinant NH2-terminal FLAG-taggedwildtype or mutant γD-crystallin was expressed in COS-7 cells. Theexpression pattern, protein solubility and intracellular distributionwere analyzed by western blotting and confocal doubleimmunofluorescence.Results: Linkage analysis located the candidate region in the γC-crystallin and γD-crystallin gene cluster. Direct sequencingidentified a c.494delG in CRYGD, which cosegregated with the diseasein all affected members. Neither the unaffected family members nor the103 unrelated controls carried this deletion mutation, which causes aframeshift and an early termination of polypeptide to become G165fs. Asignificantly reduced solubility was observed for this mutant. Unlikewildtype γD-crystallin, which existed in both the nucleus andcytoplasm, G165fs was colocalized with lamin A/C on the nuclearenvelope.Conclusions: We have identified a novel mutation, c.494delG, inCRYGD, which was associated with nuclear cataract. This is the firstdeletion mutation of CRYGD found to cause autosomal dominantcongenital cataract. The mutant protein with loss of solubility andlocalization to the nuclear envelope is hypothesized to impair nucleartransfiguration and degradation in lens fiber cell differentiation,leading to opacity formation during lens development.

[学科分类] 生物化学/生物物理