We recently reported that spinocerebellar ataxia type 2 (SCA2) caused familial parkinsonism in 2 brothers with predominant symptoms of resting tremor, rigidity, and bradykinesia that responded to levodopa.
To investigate SCA2 as the possible cause of familial parkinsonism in our series and subsequently to analyze the correlation between the clinical manifestation and CAG repeat size in the ataxin-2 gene product.
One hundred thirty patients from 41 families with familial parkinsonism were examined for SCA2. Another 8 patients with the classic ataxic phenotype of SCA2 from 6 families were the control group.
The length of expanded CAG repeat was analyzed by means of polymerase chain reaction. The clinical data and genetic findings in the parkinsonian phenotype were then compared with those in the ataxic phenotype.
We found expanded CAG repeats in the ataxin-2 gene product in 7 patients from 4 families with parkin-sonism, which was about 10% of our familial parkinsonism series. The parkinsonian phenotype was characterized by resting tremor, rigidity, and bradykinesia. Only mild dysarthria, ataxic gait, and instability were noted, particularly in the late stage. Patients with the parkinsonian phenotype had an older mean ± SD age of symptom onset (45.8 ± 13.9 years) and shorter mean ± SD abnormal CAG length (36.2 ± 1.1 repeats) than did those with the ataxic phenotype (26.9 ± 11.0 years and 43.1 ± 3.2 repeats). Parkinsonian SCA2 responded well to levodopa.
We conclude that SCA2 is a minor cause of familial parkinsonism, particularly in Taiwan. The parkinsonian phenotype is associated predominantly with a shorter abnormal range of CAG repeat lengths and older onset age. Because of the clinical resemblance among familial parkinsonisms, we suggest that SCA2 should be excluded in cases of familial parkinsonism.