Mutation Analysis Of The Candidate Genes Of A Novel Subtype Of Spinocerebellar Ataxia

BackgroundHereditary spinocerebellar ataxias(SCAs)are a group of genetic disorders,which share high clinical and genetic heterogeneity.They usually occurs in adults and youth,characterized by a wide range of clinical manifestations,including ataxia,intentional tremor,external ophthalmoplegia,nystagmus,pyramidal and extrapyramidal signs.The cerebellum,the brainstem and the spinal cord were predominantly involved.Most cases are inherited as an autosomal dominant trait and few are sporadic.There are at least 28 genotypes of SCAs which display autosomal dominant inheritance.Amoung them,18 genes responsible for the disease have been identified,including SCA1,SCA2,MJD1,PLEKHG4,SPTBN2,CACNA1A,SCA7,ATXN8OS,ATXN10,TTBK2,PPP2R2B,KCNC3,PRKCG,ITPR1,CNTN4,TBP,FGF14 and DRPLA. Based on our previous research,a large Chinese family suffered from SCA was found in Hunan province.By mutation and linkage analysis,we excluded those known genotypes.It was proved to be a novel SCA subtype.We got a maximum two-point LOD score of 2.79 at D16S415. The disease-causing gene for this family was finally assigned to a 15cM interval between D16S3136 and D16S3057,which was equal to chromosome 16q12.1-q13.And this novel genotype was nomenclatured as SCA31.ObjectiveTo identify the disease-causing gene for this novel SCA subtype.MethodsWith "positional-cloning strategy" and bioinformatics inquiry,11 candidate genes were chosen.Mutation detection was performed by sequencing the exons and intron-exon junctions of these genes directly.ResultsBy the bioinformatics method,11 candidate genes were chosen: TOX3,SALL1,NDRG4,CBLN1,BBS2,FTO,IRX5,IRX6,SLC6A2,NUDT21 and POLR2C gene.After direct sequencing,we found no disease-causing mutations yet.There is no sequence variation in TOX3,CBLN1 and IRX5 gene.As for the other 8 genes,sequence variations were detected in all,which are as follows:SALL1 gene 3823G＞A (rs4614723);NDRG4 gene IVS3+196G＞A(rs2427787),IVS8+77A＞G(rs40185),IVS14+74A＞C(rs42944);BBS2 gene 209G＞A(rs478 4677);FTO gene IVS4+37A＞G(rs62033438),~*1380delG(rs708277), ~*2108G＞A(rs5816925);IRX6 gene IVS1+78A＞T(rs31078),IVS1+93T＞C(rs31079);SLC6A2 IVS7-66T＞C(rs2279805),IVS8-13A＞C (rs57905851),IVS13+66C＞T(rs2242447);NUDT21 gene ~*1199G＞A (rs8059717),IVS5+105G＞A(rs8056687);POLR2C gene IVS5+8G＞A(rs601194),all of which have been reported before.As for TOX3 gene and SALL1 gene,the CAG repeats are normal(7 and 10 repeats respectively).ConclusionThe 11 candidate genes of TOX3,SALL1,NDRG4,CBLN1,BBS2,FTO,IRX5,IRX6,SLC6A2,NUDT21 and POLR2C were ruled out as the disease-causing gene for this novel SCA genotype;We found 16 sequence variations in all,which are as follows:SALL1 gene 3823G＞A (rs4614723);NDRG4 gene IVS3+196G＞A(rs2427787),IVS8+77A＞G(rs40185),IVS14+74A＞C(rs42944);BBS2 gene 209G＞A(rs478 4677);FTO gene IVS4+37A＞G(rs62033438),~*1380delG(rs708277), ~*2108G＞A(rs5816925);IRX6 gene IVS1+78A＞T(rs31078),IVS1+93T ＞C(rs31079);SLC6A2 IVS7-66T＞C(rs2279805),IVS8-13A＞C (rs57905851),IVS13+66C＞T(rs2242447);NUDT21 gene ~*1199G＞A (rs8059717),IVS5+105G＞A(rs8056687);POLR2C gene IVS5+8G＞A(rs601194),all of which have ever been reported before in the dbSNP of NCBI.