This review provides a comprehensive overview of RAI1’s role, integrating both clinical and basic research on Smith–Magenis syndrome (SMS) and Potocki–Lupski syndrome (PTLS) while also summarising research progress on its involvement in spinocerebellar ataxia (SCA), autism spectrum disorder (ASD), schizophrenia, bipolar disorder and major depression. Here, RAI1 is linked to autism spectrum disorder.