HAAO and hypospadias: In 2019, all of 17 SNPs were replicated and performed in a Japanese case-control study (including 169 patients and 1148 controls), and only rs6499755 of iroquois homeobox 6 (IRX6) and rs3816183 of 3-hydroxyanthranilate-3,4-dioxygenase (HAAO) are found significantly associated with susceptibility to hypospadias [8].