Screening For The Causative Gene In An Autosomal Recessive Cerebellar Ataxia Pedigree Using Exome Sequencing

Background:Autosomal recessive cerebellar ataxia, with the cerebellar ataxia as its main clinical manifestation is a rare monogenic genetic disease, which comprises a large group of clinically and genetically heterogeneous neurodegenerative disorders with more than20different forms currently recognized. Whole-exome sequencing is a powerful and cost-effective new research technology for dissecting the genetic basis of diseases, with highly sensitive to common and rare variants, which makes it very popular in the field of genetic research.Objective:We performed whole-exome sequencing combined with homozygous mapping on two typical patients of an ARCA pedigree, attempting to identify the genetic origin of their disorder.Methods and Results:Exon-enriched DNA was sequenced by the high-throughput sequencing technology. As a result, single nucleotide variants detected in the two patient samples were respectively10917and10354, with722SNVs were shared by both two samples; Meanwhile, Indels detected were respectively575and560, with72Indels shared by both two. After filtration of several known public databases and identification of homozygous regions, we got8new non-synonymous single nucleotide variants:SSRP1gene (Intron8, IVS8-10c>t)、TTYH2gene c.710g>a (p.R237H)、TNKS1BP1gene c.4015g>a (p. V1339M)、UBE2O gene c.1609g>a (p.D537N)、RCOR2gene c.634g>a (p.V212M)、MZT2B gene c.341c>t (p.A114V)、CCDC74A gene c.506t>c (p.M169T)、OR5J2gene c.831c>g (p. F277L). Then, we conducte more detailed biological analysis on these8genes, We use traditional sanger sequencing validates the exome sequencing results, and found that the mutations in gene SSRP1and OR5J2co-segregate with the phenotype of this ARCA pedigree. Whether these two genes were causative gene or not has to be further verified. Through detailed gene functional analysis, we suppose the SSRP1gene with DNA replication, transcription and repair function as the the candidate causative gene, it also mapped to high confidence homozygous regions.Conclusion:In this study, we locked the causative genes of an ARCA pedigree in SSRP1gene and OR5J2gene; we finally established the technique platform of cloning of ARCA causative gene with the technology of whole-exome sequencing combined with homozygous mapping.