Identification Of The Mutation Of A Congenital Cataract Family

Objectives: Congenital cataract is one of the main causes of children visual impairment and blindness. Heredity, infection, metabolism, X-ray and other reasons, can be caused by gene mutation or chromosomal abnormalities, resulting in cataract. Through the screening and research of candidate genes of congenital cataract family, can help us better understand the pathogenesis of congenital cataract, which lay a foundation for the prevention and treatment of the diseases.Methods: This present study including a 3 generation Chinese family suffers from congenital cataract. Detailed clinical and ophthalmologic examinations were recorded to determine the phenotype of cataract, and all the family members’ blood samples were collected for DNA extraction. We PCR-amplified and sequenced the candidate disease-causing genes associated with congenital cataract from genomic and cloned DNA in affected members. Sequence were analyzed to determine the pathogenic gene in the family. Using DNA recombinant technique in vitro to construct the expression vector of wild type and mutation gene. Effects of amino acid changes on the structure and function of protein were predicted by confocal microscopy.Results: According to ocular examinations and analysis of pedigree chart, the clinical phenotype of patient from family was cortical cataract, and hereditary pattern showed autosomal dominant inheritance. Direct DNA sequencing analysis revealed a novel single deletion of c.655 del T in exon4 of the MIP(Major Intrinsic Protein)gene, causing a frameshift mutation after the codon for amino acid 219 and generating a new stop codon into the abnormal reading frame. This mutation co-segregated with all affected individuals and was not observed in unaffected or in 100 ethnically matched Controls. Confocal immunocytochemical analysis showed that wild-type MIP was localized in the cytoplasm and plasma membrane, while the MIP mutant protein was localized abundantly in the nucleus of HLE cells. MIP unable to transfer to the cell membrane so that this change affected the water permeability of lens fiber cells, Which lead to congenital cataract.Conclusions: Our study revealed a novel single deletion of c.655 del T mutation of the MIP gene in a Chinese congenital cataract family. Based on the study of this mutation, we better understood the pathogenesis of congenital cataract in this family, and further supported the pathogenicity of MIP mutated gene to congenital cataract.