These studies showed that the majority (45 to 63%) of patients were affected with PCH2/4 with mutations in one TSEN gene, mostly the A307S mutation in TSEN54. In our cohort of 40 PCH patients referred to our reference center, CASK-related PCH was the second most frequent cause (13/40, 32%) behind PCH2/4 (18/40, 45%, manuscript under preparation). The gene discussed is TSEN54; the disease is pontocerebellar hypoplasia.