Neurophysiological features in spinocerebellar ataxia type 2: Prospects for novel biomarkers.

Electrophysiological biomarkers are useful to assess the degeneration and progression of the nervous system in pre-ataxic and ataxic stages of the Spinocerebellar Ataxia Type 2 (SCA2). These biomarkers are essentially defined by their clinical significance, discriminating patients and/or preclinical subjects from healthy controls in cross-sectional studies, their significant changes over time in longitudinal studies, and their correlation with the cytosine-guanine-adenine (CAG) repeat expansion and/or clinical ataxia scores, time of evolution and time to ataxia onset. We classified electrophysiological biomarkers into three main types: (1) preclinical, (2) disease progression and (3) genetic damage. We review the data that identify sural nerve potential amplitude, maximum saccadic velocity, sleep efficiency, rapid eye movement (REM) sleep percentage, K-complex density, REM sleep without atonia percentage, corticomuscular coherence, central motor conduction time, visual P300 latency, and antisaccadic error correction latency as reliable preclinical, progression and/or genetic damage biomarkers of SCA2. These electrophysiological biomarkers will facilitate the conduction of clinical trials that test the efficacy of emerging treatments in SCA2.