Spinocerebellar Ataxias

The most common spinocerebellar ataxias (SCAs) in populations of developed countries are SCA3, SCA2, SCA1, SCA7, and SCA6 - all of which are caused by CAG repeat expansions resulting in extended polyglutamine tracts in the mutant protein. Pathological classifications of ataxias historically have been separated into three patterns of neurodegeneration: cerebellar cortical degeneration; olivo-ponto-cerebellar degeneration or atrophy (OPCA); and spinocerebellar degeneration. Neuroimaging studies can be helpful although many of the forms of SCA have similar findings. Magnetic resonance imaging (MRI) is valuable for distinguishing simple cerebellar atrophy from cases with brainstem involvement. There are a couple of encouraging points worth noting regarding treatments for the SCAs. First, there is evidence, at least for SCA1, that pathology and neurological deficits can be reversed even after disease is underway. The second key point is that for the SCAs - regardless of the mechanism by which disease develops - pathogenesis requires the presence of the mutant protein.