Sleep disturbance in spinocerebellar ataxias: is the SCA3 mutation a cause of restless legs syndrome?

OBJECTIVE

To identify and to characterize sleep disturbances in patients with hereditary ataxias.

BACKGROUND

We observed restless legs syndrome (RLS) and impaired sleep as a frequent yet unrecognized symptom in spinocerebellar ataxia type 3 (SCA3).

METHODS

A total of 89 patients with genetically defined subtypes of autosomal dominant cerebellar ataxias were investigated for sleep history and neurologic findings according to a standardized protocol. Nerve conduction studies were performed. Sleep was studied by overnight polysomnography in seven patients.

RESULTS

RLS was present in 45% of SCA3 patients but is rare in other types of autosomal dominant cerebellar ataxias. RLS was a frequent but not the only cause of sleep impairment in SCA3. Impaired sleep in SCA3 is associated with older age, long-standing disease, and brainstem involvement. RLS tended to be more frequent in patients with clinical signs of polyneuropathy, but RLS was not restricted to patients with peripheral neuropathy. RLS was not observed in healthy members of SCA3 families.

CONCLUSIONS

RLS is a frequent and treatable cause of disabling sleep disturbance in SCA3. This study provides evidence for the expanded CAG repeat in the SCA3 gene as a molecular factor causing RLS.