The Study Of Disease-Causing Genes Of Autosomal Dominant Congenital Cataract

Objective: To map and identify autosomal dominant congenital cataract disease-causing gene(s) .Methods: 1. Collect the ADCC families and establish the clinical and the sample database. 2. Exclude the known gene(s) and/or mutation(s): Choosing 2-3 microsatellite markers tightly encompass the known gene(s) to the linkage analysis on the families. According to the LOD value (lod Score value, which indicates the possibility of disease gene linked to the specific locus). and haplotype analysis to synthesize new microsatellite markers to minimum the interval, and at last do the DNA sequencing analysis to find out the exact mutation in the specific gene(s). 3. If there is no known mutation in the family after performed linkage analysis and mutation screening, we further perform linkage analysis for a novel locus: (1)Using more than 400 STR markers(ABI PRISM Linkage Mapping Sets V2.5-MD)to carry out the whole genome gene scan.(2) Using specific software to calculate the LOD value. which based on the allele (haploid) typing result together with two-point and multi-point method to definite the positive loci by the largest LOD value. (3) Using the fluorescence-labeled STR to perform further genotyping analysis, to find a real linkage locus and narrow down the MGI ( Minimum Genetic Interval ). 4. Within the MGI using the candidate gene approach to screen the disease-causing gene and mutation .Results: 1. Collected clinical and genetic information of ADCC families. 2. Excluded known genes for several ADCC families. 3. Finished the whole genome scan of more than 400 STR markers and mitochondrial genome sequence analysis of a family, and found 3 positive loci. 4. Successfully found the mutations for two ADCC families: (1) the recurrent mutation 262C>T(P88S) in a big nuclear cataract family is in the exon 2 of GJA8. (2) A novel mutation 139G>T(D47Y) is in GJA8 gene, too . It have not reported in the world before.Conclusion :Although 262C>T(P88S) is a known mutation, the result offers evidence for studying the fuction of Cx50 , the interaction of the genes and the regulation to the growth and development. At the same time, it offers rational proofs to the study of the ADCC etiopathogenesis which caused by Cx50. The other mutation 139G>T(D47Y) is novel. We consider it happened in the first ectodomain of the gap junction. It can form half GJ with cytomembrane, but it can't conjugate intact GJ with vicinity cells. Thus the gap junctions of flanking cells reduce. The new mutation located in the first signal domain and participated in regulating the electrical resistance in order to benefit permeation of the small ion material. It has reported that the mouse model without Cx50 developed crystalline hypoevolutism, eyeball hypoevolutism and nuclear cataract. It hints that Cx50 is not only required for the transparency of crystalline but also needed for the development of the oculus normalis. This study has finished the initial research of virulence genes of ADCC families, and offers evidence for the research of genetic mechanism of congenital cataract.