We also highlight the relationship between Tfh cells and galactose-deficient IgA1 (Gd-IgA1) production, compare Tfh-mediated immune responses in HSP with those in IgA nephropathy (IgAN) and systemic lupus erythematosus (SLE), and discuss emerging therapeutic strategies targeting the Tfh-B-cell axis. The gene discussed is IGHA1; the disease is hereditary spastic paraplegia.