The pronounced heterogeneity of mental disorders has so far largely overshadowed the identification of monogenic entities, despite the detection of rare de novo variants particularly in individuals with schizophrenia [26, 27] as well as the association of adult-onset schizophrenia to SETD1A in the context of a severe and syndromic neurodevelopmental disorder. This evidence concerns the gene SETD1A and neurodevelopmental disorder.