Saccade velocity is reduced in presymptomatic spinocerebellar ataxia type 2

OBJECTIVE A characteristic feature of spinocerebellar ataxia type 2 (SCA2) is saccadic slowing at early disease stages. We sought to determine whether this sign is detectable before clinical manifestation and quantifies the disease progression throughout life in linear fashion. METHODS In a specialized ataxia clinic, 54 presymptomatic carriers of SCA2 polyglutamine expansions and 56 relatives without mutation were documented with regard to their maximal saccade velocity (MSV). RESULTS Among the control individuals, a significant effect of aging on MSV was observed. After elimination of this age influence through a matched-pair approach, a presymptomatic decrease of MSV could be shown. The MSV reduction was stronger in carriers of large expansions. In the years before calculated disease manifestation, the MSV impairment advanced insidiously. CONCLUSION Saccade velocity is a sensitive SCA2 endophenotype that reflects early pontine degeneration and may be a useful diagnostic parameter before the onset of ataxia. SIGNIFICANCE Future neuroprotective therapies of polyglutamine neurodegeneration may be assessed by MSV from earliest to prefinal disease stages.

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