CUL4B and Intellectual disability: Cabezas syndrome (MIM 300354), a recently characterized X-linked form of syndromic intellectual disability, arises from mutations in the CUL4B gene.520 Located on chromosome Xq24, the CUL4B gene comprises 22 exons and encodes cullin4B, a component of the cullin-RING Ub ligase family, which plays a vital role in the regulation of cellular protein degradation.521 Seizures or epilepsy were observed in 43% of male individuals with hemizygous variants in the CUL4B gene linked to Cabezas syndrome.522 The mechanisms underlying CUL4B-related epilepsy are likely multifactorial.