Of the polyQ diseases, biofluid NfL has been studied in patients with Huntington's disease (Johnson et al., 2018, 2021; Byrne et al., 2017) and multiple spinocerebellar ataxias (SCAs), including SCA1 (Wilke et al., 2018, 2022a; Coarelli et al., 2021; Peng et al., 2022), SCA2 (Peng et al., 2022; Coarelli et al., 2021), SCA3 (Wilke et al., 2018, 2020b; Peng et al., 2022; Garcia-Moreno et al., 2022; Coarelli et al., 2021; Prudencio et al., 2020; Li et al., 2019), SCA6 (Peng et al., 2022; Wilke et al., 2018) and SCA7 (Peng et al., 2022; Coarelli et al., 2021). The gene discussed is ATXN3; the disease is juvenile Huntington disease.