A novel deletion variant of gammaD-crystallin responsible for congenital nuclear cataract.
OBJECTIVE
To investigate a novel deletion variant of gammaD-crystallin (CRYGD) identified in a Chinese family with nuclear congenital cataract.


METHODS
A Chinese family with five affected members diagnosed with nuclear cataract and four unaffected members were recruited for the mutational screening of 15 known candidate genes for autosomal dominant congenital cataract. Two-point linkage analysis with single nucleotide polymorphism markers and microsatellite markers flanking these genes together with direct sequencing was applied to identify the disease-causing mutation. Recombinant NH(2)-terminal FLAG-tagged wildtype or mutant gammaD-crystallin was expressed in COS-7 cells. The expression pattern, protein solubility and intracellular distribution were analyzed by western blotting and confocal double immunofluorescence.


RESULTS
Linkage analysis located the candidate region in the gammaC-crystallin and gammaD-crystallin gene cluster. Direct sequencing identified a c.494delG in CRYGD, which cosegregated with the disease in all affected members. Neither the unaffected family members nor the 103 unrelated controls carried this deletion mutation, which causes a frameshift and an early termination of polypeptide to become G165fs. A significantly reduced solubility was observed for this mutant. Unlike wildtype gammaD-crystallin, which existed in both the nucleus and cytoplasm, G165fs was colocalized with lamin A/C on the nuclear envelope.


CONCLUSIONS
We have identified a novel mutation, c.494delG, in CRYGD, which was associated with nuclear cataract. This is the first deletion mutation of CRYGD found to cause autosomal dominant congenital cataract. The mutant protein with loss of solubility and localization to the nuclear envelope is hypothesized to impair nuclear transfiguration and degradation in lens fiber cell differentiation, leading to opacity formation during lens development.
Zhang
Li-Yun
LY
Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China.
Yam
Gary Hin-Fai
GH
Fan
Dorothy Shu-Ping
DS
Tam
Pancy Oi-Sin
PO
Lam
Dennis Shun-Chiu
DS
Pang
Chi-Pui
CP
D044466:Asian People / Q000235:genetics; D002386:Cataract / Q000151:congenital* / Q000235:genetics*; D002874:Chromosome Mapping; D003459:Crystallins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005260:Female; D016368:Frameshift Mutation; D017353:Gene Deletion; D005799:Genes, Dominant; D014644:Genetic Variation; D006801:Humans; D007907:Lens Nucleus, Crystalline / Q000378:metabolism; D008297:Male; D005810:Multigene Family; D012995:Solubility; D014018:Tissue Distribution; D038222:gamma-Crystallins
C504903:CRYGD protein, human; D003459:Crystallins; D038222:gamma-Crystallins