The contribution of common genetic variants has been examined in Chiari malformation type II (CMII), where several studies failed to demonstrate consistent associations with developmental genes such as CRABP1, CRABP2, ALDH1A2, RALDH2, CYP26, HOX, NOG, SHH and TBX6 (reviewed in [62], [63], [64]). The gene discussed is CYP26A1; the disease is Chiari malformation type II.