ARID3B and Down syndrome: The SRO is a gene-rich region that includes several genes including: CYP11A1, SEMA7A, CPLX3, ARID3B, STRA6, SIN3A and CSK. CYP11A1 encodes the cholesterol side-chain cleavage enzyme and it has been suggested that haploinsufficiency of CYP11A1 may contribute to the genital abnormalities in patients with 15q24 deletion syndrome [7].