Clinical and genetic study of spinocerebellar ataxia type 7 in East Asian population

Background Spinocerebellar ataxia type 7 (SCA7) is known as an autosomal dominant cerebellar ataxia; patients with genetically confirmed diagnoses of SCA7 have increased rapidly in recent years.However, SCA7 is a rare subtype of SCA, and most data available about SCA7 are those of white people.The aim of the present study was to systematically review the prevalence and clinical and genetic aspects of SCA7 patients in East Asian population.Methods A search for publications on SCA7 was performed by using the "PubMed" database with the published language limited in English.Publications mainly focusing on the prevalence of SCA7 in patients with SCA and the clinical and genetic features of SCA7 patients were fully reviewed and analyzed.Results The prevalence of SCA7 in SCA patients ranged from 0 to 7.7%, which was similar to those reported previously.The clinical manifestations were typically present at the 30's of its victims (median, 29 years; interquartile range (IQR),19.5-36.5 years), and the symptoms appeared 15 years ((15.17±4.22) years) earlier on average in the offspring than in the parents.Gait ataxia and visual impairment were both found in all patients of whom the clinical features were described.Mutant SCA7 alleles contained 40-100 CAG repeats, with a median of 47 repeats (IQR, 44.5-50.0); and the offspring had 13 more repeats on average compared with their parents (12.62±19.03).A strong negative correlation was found between CAG repeat size and the onset age of patients (r=-0.739, P=0.000).In addition, no significant difference was found in CAG repeat sizes between patients with visual impairment as the initial symptom and those with gait disturbance as their initial symptom (P=0.476).Conclusions The prevalence of SCA7 in SCA patients, the age at onset and CAG repeats of SCA7 patients in East Asia are consistent with those of white people.However, larger population study is needed to assess the correlation between the CAG repeat size and initial symptoms of SCA7 patients in East Asia.