Identification Of Candidate NSMR Gene Variants In Qinba Area Using Whole-exome Sequencing

Backgroud:The high incidence of Mental Retardation(MR) in Qinba area caused serious influence to local development and patients themselves. MR has various etiological factors,and genetic factors are 2/3 of MR cases. There are little studies on Non-Specific Mental Retardation(NSMR) because it has no specific clinical features. So research on the genetic basis of NSMR is of great importance for the diagnosis and treatment of the disease.Methods:(l)We chose a NSMR family in Zha Shui(ZS2024) as samples. Seven members of this family, including 4 NSMR,2 edge and 1 control were taken to whole-exome sequencing(WES).(2)Single-nucleotide variants were called after blast with hg19.We firstly selected nonsynonymous mutation which are located in exome or splice site, not record in dbSNP and 137dbSNP and related to mental disorders. Next, mutations with high expression in brain area and consistent with disease phenotype and Mendelian laws,are taken to function prediction.(3) Genotypes were detected in 300 sporadic NSMR samples and 987 cases of random samples,to detect whether it is an SNP.(4) Combined with transfection and cytoskeleton staining, we transfected SHY5Y and PC 12 cells with mutant expression vector to carry on the preliminary investigation of the mutation protein.Results:7 mutant genes that may be associated with NSMR are choosed from 74657 mutations by the preliminary screening. MTMR9(G341T) gene was found to be the candidate gene of NSMR. the amino acid has a high conservation among different species. The mutation leads to changes in alpha helix and beta folding in protein secondary structure. Reults of function prediction indicated tha the mutation was harmful and might affect the function of the protein.The mutation didn’t be found in 300 sporadic NSMR samples and 987 cases of random samples. The results of cytoskeleton staining showed fluorescence intensity of microtubule protein in mutant cells is weak than that of wild types. And microtubule bundles become sparse and slightly depolymerization compared with wild cells.Conclusion:The mutation G341T in MTMR9 gene, which is specific in ZS2024 family, might be associated to MR.The possible mechanism is that the mutation could affect on the formation of cytoskeleton,which could lead to MR.