CUL4B encodes a protein subunit that forms the Cullin-RING ubiqutin ligase complex and participates in ubiquitin-dependent protein degradation. This fundamental cellular process has been implicated in cell cycle, immune response, and development. The CUL4B gene is located at Xq24 and contains 22 exons. Missense/nonsense mutations, small and gross deletions, and splicing mutations have been reported in CUL4B. The main clinical features of patients with mutations in CUL4B include mental retardation, aggressive outbursts, tremor, central obesity, and hypogonadism (Tarpey PS et al. Am J Hum Genet. 2007;80:345-352).