Single nucleotide polymorphisms of HAAO and IRX 6 genes as risk factors for hypospadias.

PURPOSE: We evaluated the association of hypospadias with 17 susceptibility loci previously identified by a European genome-wide association study (GWAS) in Japanese patients. We also examined the expression of candidate genes in male mouse embryos to discuss the possible underlying mechanisms of this disease.

MATERIALS AND METHODS: We enrolled 169 Japanese patients (mean age at surgery: 3.7 years) who underwent repair of hypospadias. Genotyping of 17 SNPs was performed by using a multiplex-polymerase chain reaction (PCR) invader assay. We also performed in situ hybridization to determine whether candidate genes were expressed in the male genital tubercle during embryonic development of the external genitalia in mice.

RESULTS: SNP rs3816183 of HAAO was significantly associated with susceptibility to hypospadias in general (p=0.0019) and both anterior/middle hypospadias (p=0.0283) and posterior hypospadias (p=0.0226), while SNP rs6499755 of IRX6 showed an association with susceptibility to anterior/middle hypospadias (p=0.0472). In mouse embryos, there was no significant upregulation of Haao expression in the developing male external genitalia. Irx3 and Irx5, which are linked to Irx6 within the IrxB cluster, were expressed in the mesenchyme remote from the urethral plate epithelium during the critical embryonic period for masculinization. Irx6 was expressed in the ectodermal epithelium, showing prominent dorsal ectodermal expression without expression in ventral ectoderm adjacent to the urethral plate during the same period.

CONCLUSIONS: Genetic variations of HAAO and IRX6 influence susceptibility to hypospadias in Japanese population, although further study will be needed to clarify the mechanism by which contributes to the pathogenesis of hypospadias.