Pontocerebellar hypoplasias (PCH) comprise a group of genetically heterogeneous disorders profoundly impacting on child neurodevelopment. Genotype-phenotype associations are still limited, with negative consequences on prognosis and counselling. Here, we provide a comprehensive and systematic phenotypic assessment of 56 PCH patients with different genetic etiology. We identified three major PCH genes and investigated their association with individual phenotypic features as well as with phenotypic clusters based on the simultaneous presence of multiple features. Phenotypic variability associated with the commonest genetic causes of PCH is wider than previously thought, with marked overlap between CASK and TSEN54-associated disorders. (By Dr. Sara Nuovo, https://jmg.bmj.com/content/early/2021/03/05/jmedgenet-2020-107497 )