Objective      To do genetic diagnosis of an autosomal dominant spinocerebellar ataxia family and discuss its clinical characteristics.     Methods      Familial investigation and pedigree analysis were performed. The duplicate number of tri-nucleotides in pathogenic CAG  was detected by polymerase chain reaction (PCR) and direct DNA sequencing in the family members.     Results      Autosomal dominant heredity was found in this family. Clinical symptoms such as gait

dysphagia and slurred speech occurred in three spinocerebellar ataxia patients of the family at the age of over 30 years. Genetic diagnosis of spinocerebellar ataxia showed that the CAG duplicate number of SCA2 and SCA3 was normal in all the family members of spinocerebellar ataxia patients

and abnormal allelic gene SCA1 was detected in 3 spinocerebellar ataxia patients. The CAG was amplified 43

48

and 51 times

respectively

and amplified 53 and 50 times for another 2 members of the family who were diagnosed as presymptomatic SCA1.     Conclusion      Type 1 spinocerebellar ataxia can be diagnosed in the family members of spinocerebellar ataxia patients according to their autosomal dominant heredity caused by dynamic mutations. Genetic diagnosis can be established in 2 presymptomatic SCA1 patients of the family.