Two young sisters with spinocerebellar ataxia type 2 showing different clinical progression of disease.

Spinocerebellar ataxia type 2 is a neurodegenerative disease caused by a CAG repeat expansion in the ataxin-2 gene. Gain-of-toxic effects caused by expanded polyglutamine tracts are important for the disease pathogenesis and there is an inverse relationship between the number of CAG repeats and the age of onset and clinical severity. Previously, we reported an extended Turkish family with spinocerebellar ataxia type 2 with several affected members in three generations. Two sisters in this generation showed an earlier age of onset (5 and 7 years, respectively) than their father (30 years). In this paper, we present a further interesting finding regarding the disease onset and manifestation in the two sisters. Interestingly, the age of onset was delayed and the clinical severity of the disease was milder in the child who had more CAG repeats (84 vs. 70). This finding suggests that there are other factors contributing to the age of onset and clinical severity in spinocerebellar ataxia type 2 other than the increased CAG repeat.