Mutations in EXOSC3, EXOSC8, and EXOSC9 cause several forms of autosomal-recessive neurodegenerative disease, pontocerebellar hypoplasia (PCH), namely, PCH type 1b (PCH1b), PCH1c, and PCH1d, respectively [83,84,85]. The gene discussed is EXOSC9; the disease is pontocerebellar hypoplasia.