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

BackgroundHereditary spinocerebellar ataxias(SCAs)are a group of neurodegenerative disease,which shares high clinical and genetic heterogeneity.Patients with spinocerebellar ataxia experience a degeneration of the spinal cord,the cerebellum and the brainstem.The common age at onset occurs at youth and adult.Patients with spinocerebellar ataxias(SCAs)experience cerebellar ataxia,also accompanied by dysarthria,intention tremor,ophthalmoparalysis, pyramidal and(or)extrapyramidal signs.The symptoms of the condition vary with the specific type,and with the individual patient.Most of the patients are of an autosomal dominant inheritance trait,whereas sporadic cases are common relatively.There're at least 28 genotypes of SCAs which display autosomal dominant inheritance.Among them,18 genes responsible for the disease have been identified,including SCA1,SCA2, MJD1,PLEKHG4,SPTBN2,CACNA1A,SCA7,SCA8,SCA10,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 the 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 is equal to chromosome 16q12.1-q13.ObjectiveTo identify the disease-causing gene for this novel SCA subtype.MethodsWith the"positional-cloning strategy" and by bioinformatics inquiry,10 candidate genes were chosen.Mutation analysis was performed by sequencing the exons and intron-exon junctions of these genes directly.ResultsBy the bioinformatics method,10 candidate genes were chosenas follows:NUP93,IRX3,ZNF423,RSPRY1,ARL2BP,MMP2,CYLD,CES1, MT1B,MT2A.After direct sequencing,we found no disease-causing mutation yet.As for the seven genes of IRX3,ZNF423,RSPRY1,MMP2, CYLD,CES1,MT1B,20 sequence variations were detected in all,which are as follows:IRX3(-235C＞A,-31C＞G and IVS1-46T＞C),ZNF423(IVS8-23G＞A);MMP2(IVS2+185G＞A,750C＞T,1149T＞C,IVS8+85G＞C,IVS9+92G＞A,IVS9-66 T＞C,IVS11-4G＞A,IVS11-69C＞T);CYLD(IVS16+26A＞G, ~*4561G＞A);RSPRY1(IVS10+36 T＞C);CES1(IVS9-5T＞G);MT1B(IVS1-109G＞C,IVS1-112T＞A,IVS1-12 G＞T,IVS2+156G＞A).They have all been reported before.ConclusionThe 10 candidate genes:NUP93,IRX3,ZNF423,RSPRY1,ARL2BP, MMP2,CYLD,CES1,MT1B,MT2A,were ruled out as the disease-causing gene for this novel SCA subtype;We found 20 sequence variations in all, which are as follows:IRX3(-235C＞A,-31C＞G and IVS1-46T＞C),ZNF423 (IVS8-23 G＞A),MMP2(IVS2+185G＞A,750C＞T,1149T＞C,IVS8+85G＞C, IVS9+92 G＞A,IVS9-66T＞G,IVS11-4G＞A,IVS11-69C＞T),CYLD(IVS16 +26A＞G,~*4561G＞A),RSPRY1(IVS10+36 T＞C),CES1(IVS9-5T＞G),MT1B (IVS1-109G＞C,IVS1-112T＞A,IVS1-12 G＞T,IVS2+156G＞A).All these SNPs above have ever been reported before in dbSNP of NCBI.