The slow and clumsy motor cyclist

摘要

Brain MRI showed cerebellar and pontine atrophy, consistent with his cerebellar dysarthria and ataxia. He agreed to genetic analysis after appropriate counselling, and tested positive for the SCA type 2 gene (SCA2), with 40 trinuce-otide repeats (normal range 13-34). SCAs, which have a prevalence of 1-4/100 000, are a clinically heterogeneous group of disorders characterized by progressive cerebellar dysfunction and other neurological signs, including oculomotor and pyramidal disorders, dysarthria, dysmetria, kinetic tremor and gait ataxia. They may also manifest" pigmentary retinopathy, pyramidal signs, cortical symptoms such as seizures and cognitive impairment, peripheral neuropathy and extrapyramidal movement disorders comprising parkinsonism, dyskinesias, dystonia or chorea.1 Due to the wide phenotypic heterogeneity of the SCAs, identification of the specific subtype is confirmed by genetic testing.2 Clinical features which predict genetic confirmation of SCA include positive family history, hypertonia, chorea, dystonia, fasciculations of muscle or tongue and gaze-evoked nystagmus.