PSMC5 and neurodevelopmental disorder: In this study, we identified three heterozygous PSMC5 missense variants: P320R, R325W, and Q160A, and one nonsense variant: Q69, from cases with neurodevelopmental disorders, and discovered that insufficiency of PSMC5 (and also other subunits of the 19S RP) and the PSMC5 P320R mutation impair proteasome function and activate apoptosis.