Supplementary Material for: Involvement of the Auditory Pathway in Spinocerebellar Ataxia Type 7

<b><i>Background:</i></b> Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant disorder caused by a mutation in the <i>ATXN7</i> gene. The involvement of the brainstem auditory pathway in pathogenesis of this disease has not been systematically assessed. <b><i>Aim:</i></b> To determine involvement of the brainstem auditory pathway in SCA7 patients and its relationship to clinical features of the disease. <b><i>Methods:</i></b> In this case-control study, brainstem auditory-evoked potentials (BAEPs) were assessed in 12 SCA7 patients with clinical and molecular diagnosis, compared to 2 control groups of 16 SCA2 patients and 16 healthy controls. <b><i>Results:</i></b> SCA7 patients exhibited significant prolongation of I-wave and III-wave latencies, whereas SCA2 patients showed increased latencies for III and V waves and I–III interpeak interval. SCA7 patients with larger I-wave latencies exhibited larger CAG repeats, earlier onset age, and higher SARA scores, but in SCA2 cases, these were not observed. <b><i>Conclusions:</i></b> BAEP tests revealed functional involvement of the auditory pathway in SCA7 (mainly at) peripheral portions, which gave new insights into the disease physiopathology different from SCA2 and may unravel distinct pathoanatomical effects of polyQ expansions in the central nervous system. <b><i>Significance:</i></b> These findings offer important insights into the distinctive disease mechanisms in SCA7 and SCA2, which could be useful for differential diagnosis and designing specific precision medicine approaches for both conditions.