The Distribution Characteristics And Screening For Novel Mutations Of Autosomal Dominant Cerebellar Ataxia In China

Autosomal dominant cerebellar ataxia(ADCA)is one of the most common hereditary diseases of the nervous system,mainly affecting the cerebellum,brainstem and spinal cord.Currently,there are more than 40 disease-causing genes associated with ADCA.Spinocerebellar ataxia(SCA)is the most common type of ADCA.The genotypes and phenotypes of ADCA are extremely heterogeneous,and the distribution characteristics of different races and regions are also different.As we known,there is no large-scale study on the distribution characteristics of ADCA subtypes in China.Genetic analysis is the gold standard for the diagnosis of ADCA.Targeted sequencing is one of the next-generation sequencing methods,which can sequence multiple genes at the same time,with less time and high efficiency.In present study,a large number of ADCA patients data and biological samples have been collected in recent ten years.The objective of this study is to describe the distribution characteristics of ADCA subtypes in China by summarizing the clinical data and genetic testing for common dynamic mutations.For ADCA patients with unknown molecular diagnosis,targeted sequencing technology is then performed to identify the pathogenic genes.ACMG guidelines are used to interpret the sequence variants.Section 1 The distribution characteristics of autosomal dominant cerebellar ataxia subtypes in China PurposeTo analyze the distribution characteristics of autosomal dominant cerebellar ataxia(ADCA)subtypes in China,and to summarize the clinical features of common SCAs.MethodsCollect the clinical data and biological samples of ADCA patients.Polymerase chain reaction(PCR),agarose gel electrophoresis combined with Sanger sequencing were performed on dynamic mutation including SCA1,2,3,6,7,12,17 and DRPLA.Besides,SCA8 and SCA10 were detected using repeat primers PCR and capillary electrophoresis technology.In addition,the clinical features of common SCAs were summarized.ResultsA total of 1121 cases from 868 ADCA families were recruited between 2008 and2018.SCA3 is the most common ADCA subtype(75.9%),and the remaining common subtypes are SCA2(7.5%),SCA1(6.1%),SCA6(1%),SCA7(1.2%),SCA12(1%)and SCA17(0.7%).The age at onset of SCA subtypes was different from each other and negatively correlated with the number of CAG repeats.Clinical phenotypes of SCAs were significantly diverse and heterogeneous.In addition,we found that the age at onset of homozygous SCA3 patients was significantly earlier than that of heterozygous SCA3 patients.ConclusionsThe genetic distribution of ADCA in China is dominated by the dynamic mutation type and SCA3 is the most common subtype.Clinical phenotypes of different SCAs are heterogeneous.Section 2 Novel mutations identified in autosomal dominant cerebellar ataxia by targeted next-generation sequencing PuroposeTo identify rare subtypes and pathogenic variants of ADCA patients,and to evaluate the application value of targeted next-generation sequencing technology in ADCA molecular diagnosis.MethodsWe recuited a total of 65 probands of cerebellar ataxia,including 55 cases with ADCA,10 cases with sporadic ataxia.Common dynamic mutation of ADCA were excluded including SCA1,2,3,6,7,8,10,12,17 and DRPLA in Section 1.The genetic variants were screened by targeted sequencing and confirmed by Sanger sequencing.Bioinformatics analysis and family cosegregation analysis were performed.The interpretation of sequence variants was according to the ACMG guidelines.ResultsWe found the pathogenic gene mutations in 10 patients through targeted nextgneration sequencing and the diagnostic rate was 15.4%(10/65).In patients with ADCA,4 pathogenic or likely pathogenic variants were found,including 1 reported variants(OPA1 p.S509R)and 3 novel variants(PRKCG p.V583 M,AFG3L2 p.K687 E,IFRD1p.T414M).In patients with sporadic ataxia,a total of 4 pathogenic or likely pathogenic variants were found.Among them,2 were reported variants(CACNA1A p.R1346 Q,NEU1 p.S182G)and 2 were novel variants(CACNA1A p.R1667 G,NEU1 p.P267S).ConclusionsIn this study,SCA28 were reported for the first time in Chinese population,and the genotype mutation spectrum and phenotype spectrum of ADCA were expanded.Targeted sequencing is an effective method to identify the pathogenic variants of ADCA.