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

BackgroundHereditary spinocerebellar ataxia(SCA) is a group of neurodegenerativedisease caused by genetic reasons, which shares high clinical and geneticheterogeneity. The common age at onset occurs at youth and adult. Itprimarily shows cerebellar ataxia, also accompanied by dysarthria,intention tremor, ophthalmoparalysis, pyramidal and (or) extrapyramidalsigns. It mainly involves the cerebellum, the brainstem and the spinal cord.Most of the patients are of an autosomal dominant inheritance trait,whereas sporadic cases are common relatively. There's also autosomalrecessive inheritance or X-linked inheritance. There're at least 28genotypes of SCAs which display autosomal dominant inheritance.Amoung them, 15 genes responsible for the disease have been cloned.,including SCA1,SCA2,MJD1,PLEKHG4,SPTBN2,CACNA1A,SCA7,SCA8,SCA10,PPP2R2B,KCNC3,PRKCG,TBP,FGF14 and DRPLA.Based on our previous research, a large Chinese family suffered from SCAwas found in Hunan province. By mutation and linkage analysis, weexcluded the known genetypes. It was proved to be a novel SCA subtype.We got a maximum two-point LOD score of 2.79 at D16S415. Thedisease-causing gene for this family was finally assigned to a 15cM interval between D16S3136 and D16S3057, that is equal to 16q12.1-q13.ObjectiveTo clone the disease-causing gene for this novel SCA subtype.MethodsWith the"positional-cloning strategy" and by bioinformatics inquiry, 9candidate genes were chosen. Mutation detection was performed bysequencing the exons and intron-exon junctions of these genes directly.ResultsBy the bioinformatics method, 9 candidate genes were chosen:HERP UD1,MT3,AMFR,FTS,CAPNS2,TM4SF11,GNAO1,PLEKHG4,THAP11. And by direct sequencing, we found no disease-causing mutation.As for the six genes of MT3,AMFR,FTS,CAPNS2,GNAO1,THAP11,13 sequence variations were detected in all, which are as follows: MT3(99-76C＞T and IVS2+185G＞A),AMFR (IVS3-38G＞A,IVS4+14T＞C,IVS12+62A＞G,~*335G＞A and 742G＞A),FTS (71-21_-25agggc),CAPNS2(720A＞G),GNAO1(IVS4+22T＞C,IVS4+178T＞C,IVS5+117C＞T,513C＞T),THAP11(321A＞G). Among them, there're 2 sequence variationsof MT3 (IVS2+185G＞A) and FTS(71-21_-25agggc), which have not beenreported before. As for the THAP11 gene, it includes 25 CAG repeats, justwithin the normal range (20-41 repeats).Conclusion The 9 candidate genes of HERPUD1,MT3,AMFR,FTS,CAPNS2,TM4SF11,GNAO1,PLEKHG4 and THAP11 were ruled out as thedisease-causing gene for this novel SCA subtype; We found 13 sequencevariations in all, which are as follows: MT3 (99-76C＞T and IVS2+185G＞A),AMFR (IVS3-38G＞A,IVS4+14T＞C,IVS12+62A＞G,~*335G＞Aand 742G＞A),FTS (71-21_-25agggc),CAPNS2 (720A＞G),GNAO1(IVS4+22T＞C,IVS4+178T＞C,IVS5+117C＞T,513C＞T),THAP11(321A＞G).Among them, there are 2 sequence variations of MT3 (IVS 2+185G＞A)and FTS(71-21_-25agggc), which have not been reported before. As for theTHAP11 gene, it contains 25 CAG repeats, just within the normal range(20-41 repeats).