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Spinocerebellar ataxia type 21
Spinocerebellar ataxia type 21 (SCA21) is a very rare subtype of type I autosomal dominant cerebellar ataxia (ADCA type I; see this term). It is characterized by slowly progressive cerebellar ataxia, mild cognitive impairment, postural and/or resting tremor, bradykinesia, and rigidity.
ORPHA:98773Classification level: Disorder
Prevalence is unknown. Fewer than 20 cases in a 4-generation French family have been reported to date.
Mean age of onset is 17.4 years and is relatively early compared to most type I ADCAs. Individuals in successive generations tend to have earlier ages of onset. Parkinsonism was not responsive to L-dopa and magnetic resonance imaging (MRI) revealed cerebellar and brainstem atrophy.
SCA21 maps to chromosome 7p21.3-p15.1 but the gene and gene mutation have not been identified.
There is insufficient clinical data to draw conclusions concerning prognosis.
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