Localization The Disease-associated Gene Of Autosomal Dominant Congenital Posterior Polar Cataract

Purpose:Congenital cataracts is the leading cause of visual disability in children worldwide.Among all the causes, genetic mutation is the most common one. To date, more than 24 cataract-related genes have been characterized. Our study is to localization the disease-associated gene of this congenital posterior polar cataracts.Methods:We studied a large, four-generation family containing members affected with bilateral congenital posterior polar cataracts.27 individuals participated in the study:9 affected individuals and 24 unaffected individuals. Affected status was determined by history records and ophthalmologic examination, which including slit-lamp examination under dilated pupils, visual acuity testing and fudus examination. Genomic DNA samples were extracted from peripheral blood of the pedigree members. All the exons and flanking intronic sequences of candidate gene were amplified by polymerase chain reaction (PCR) and screened for mutation by direct bidirectional DNA sequencing. The mutation was verified by restriction fragment length polymorphism (RFLP) analysis. Computational algorithms,including SIFT,PolyPhen and Align-GVGD,are used to predict whether a specific amino acid substitution of a protein sequence is deleterious or neutral to the function of the protein. Additionally, we used Kyte-Doolittle hydropathy plots for hydropathy analysis. Results:All affected family pedigree showed a special phenotype characterized posterior polar opacification by slit-lamp photography. The family inherited model was identified as autosomal dominant, according to the genealogy. Sequencing of the candidate genes detected a heterozygous c.5Câ†'T change in the coding region of theβB2-crystallin gene (CRYBB2), resulting in the substitution of a highly conserved alanine to valine (p. A2V). All nine family members affected with cataracts were positive for this change, but it was not observed in any of the unaffected members of the family and in all of the 100 unrelated individuals. The transition resulted in the loss of a Haeâ…¢restriction site in the affected members of the pedigree, which was present in the unaffected family members and in the 100 unrelated normal controls. All results of SIFT,PolyPhen and Align-GVGD indicated the A2V substitution was likely deleterious and possibly contributed to the disease. The Kyte-Doolittle algorithm for hydrophobicity analysis showed the local hydrophobicity at and near the altered amino acid was increased.Conclusions:This study has identified a novel CRYBB2 gene mutation, a Câ†'T heterozygous change at nucleotide position 5 in the exon 2 of CRYBB2,which co-segregated with the presence of the posterior subcapsular congenital cataract in this family and was not observed in 100 unrelated controls. This mutation is probably the causative lesion for the observed phenotype in this family. The study confirmed that the congenital cataract were phenotypically and genetially heterogeneous and the relative relationship between the genetype and the phenotype,futher supporting the notion thatβB2-crystallin play an important role in human lens development and cataract formation.