The premanifest stage of HD is characterized by an increased prevalence of IL-17–producing T helper 17.1 (Th17.1) cells in the CSF of HTT gene expansion carriers compared with the healthy controls, indicating a positive correlation between CSF Th17.1 frequency and HD symptomatology and disease progression (von Essen et al., 2020). The gene discussed is IL17A; the disease is Huntington disease.