Learning from similar analogous TR-FRET approaches to assess polyQ-expanded huntingtin in PBMC in HD [32] we developed two sensitive TR-FRET-based immunoassays to measure soluble total full-length ataxin-3 and specifically polyQ-expanded ataxin-3 in PBMC of SCA3 subjects. The gene discussed is ATXN3; the disease is Spinocerebellar ataxia type 3.