High prevalence of spinocerebellar ataxia type 1 in an ethnic Tamil community in India

Objective: To study the prevalence, clinical and molecular genetic characteristics of cerebellar ataxia in an ethnic Tamil community in India.
Methods: An epidemiological study of cerebellar ataxia was done in two villages in the Indian state of Tamilnadu where its prevalence was observed to be high. All the people were screened and the clinical characteristics of those with ataxia were recorded. Genetic analysis was done in those with ataxia and in two asymptomatic control groups - group I belonging to the affected community and group II belonging to the unaffected community. The clinical and genetic results are correlated. Measures to help the community are suggested.
Results: The total population of the two villages was 378. Among them 345 belonged to Vanniyakula Kshatriyar community and 33 to another. Cerebellar ataxia was found in 25 individuals belonging only to the former community (7.2%). The mean age of onset was 39.8 years and the salient features were ataxic gait (100%), dysarthria (100%), pyramidal signs (72%), slow saccades (48%) and bleeding diathesis (12%). Genetic studies were done in 17 of the study group. All showed pathological expansion of CAG repeats above 40, in chromosome 6p, diagnostic of SCA1. 7 of the 18 in the control group (I) and none in control group (II) had CAG repeats above 40.
Conclusion: The prevalence of SCA1 is high (7.2%) in this ethnic Tamil community with a large asymptomatic group waiting to manifest. The symptomatic individuals need social support and rehabilitation. Appropriate counseling, prenatal evaluation and therapy will prevent the spread of disease to the next generation.