The genes responsible for neurocristopathies have been identified in the cases of several clinical abnormalities, as follows: tfap2a (Branchio‐oculo‐facial syndrome), zic2a1 (holoprosencephaly), pax3, sox10, and snail2 (Waardenburg syndrome and Hirschsprung's disease), and sox9 (Pierre Robin sequence).74, 75, 80, 81, 83, 105. This evidence concerns the gene SOX9 and holoprosencephaly.