Exome sequencing and chromosomal microarray testing of NDD patients identified de novo heterozygous loss-of-function mutations in CUL3 on chromosome 2 [26,27], homozygous or compound heterozygous loss-of-function mutations in CUL7 on chromosome 6, and hemizygous loss-of-function mutations in CUL4B on X chromosome [28,29] in NDD patients. The gene discussed is CUL4B; the disease is Neurodevelopmental delay.