Four included studies investigated the association between the risk alleles [T] of HAAO rs3816183 and susceptibility to hypospadias, indicating a significantly increased risk of hypospadias (ORs = 1.23, 95% Cl: 1.16–1.31, p < 0.00001) (shown in Figure2(a)). The gene discussed is HAAO; the disease is hypospadias.