Etiology of Hypospadias: A Comparative Review of Genetic Factors and Developmental Processes Between Human and Animal Models

X-chromosome association study reveals genetic susceptibility loci of hypospadias in southern Chinese population

PURPOSE

X-chromosome variants contribute significantly to hypospadias risk but have not been fully elucidated in the Chinese population. Here we aim to assess how X-chromosome variants contribute to hypospadias susceptibility in the Chinese population.

METHODS

We recruited 1,073 boys with hypospadias and 5,150 controls in a southern Chinese population. Single-variant and gene/pathway-based association analyses were conducted for the distal and proximal hypospadias. Haplotype analysis was performed on top susceptibility genes. Additionally, we performed a multi-ancestral comparison between the East Asian and European populations.

RESULTS

We performed an X-chromosome-wide association study on 987 patients and 4,761 controls that met quality control standards. We confirmed DGKK variants as multi-ancestral susceptibility loci for distal hypospadias (lead SNP: rs5961181, P = 1.82 × 10- 7), but not for the proximal subtype. Distinct association signals were identified for distal hypospadias (DGKK-CCNB3-AKAP4, PNPLA4, AR-OPHN1, TAF7L, IL1RAPL1) and proximal hypospadias (SMIM10L2A, PRR32 and Xq28 gene cluster). Pathway analysis revealed that distal hypospadias is associated with male gamete generation, epithelial cell polarity, and lipid/sterol metabolism, while proximal hypospadias is linked to amino acid metabolism and gastrulation. Except for DGKK, all candidate genes showed population-favored associations compared to European studies. Haplotype analysis of DGKK, PNPLA4, OPHN1 and IL1RAPL1 showed increased risk for specific risk haplotypes (OR ranged from 4.35 to 6.25).

CONCLUSION

Our findings highlight the importance of X chromosome variants in hypospadias etiology and reveal subtype- and population-specific genetic architecture. Our results improve the understanding of genetic susceptibility for hypospadias risk and provide insights into risk prediction and personalized prevention strategies in hypospadias management.

Differences in Formation of Prepuce and Urethral Groove During Penile Development Between Guinea Pigs and Mice Are Controlled by Differential Expression of Shh, Fgf10 and Fgfr2

The penile tubular urethra forms by canalization of the urethral plate without forming an obvious urethral groove in mice, while the urethral epithelium forms a fully open urethral groove before urethra closure through the distal-opening-proximal-closing process in humans and guinea pigs. Our knowledge of the mechanism of penile development is mainly based on studies in mice. To reveal how the fully opened urethral groove forms in humans and guinea pigs, we compared the expression patterns and levels of key developmental genes using in situ hybridization and quantitative PCR during glans and preputial development between guinea pigs and mice. Our results revealed that, compared with mouse preputial development, which started before sexual differentiation, preputial development in guinea pigs was delayed and initiated at the same time that sexual differentiation began. Fgf10 was mainly expressed in the urethral epithelium in developing genital tubercle (GT) of guinea pigs. The relative expression of Shh, Fgf8, Fgf10, Fgfr2, and Hoxd13 was reduced more than 4-fold in the GT of guinea pigs compared to that of mice. Hedgehog and Fgf inhibitors induced urethral groove formation and restrained preputial development in cultured mouse GT, while Shh and Fgf10 proteins induced preputial development in cultured guinea pig GT. Our discovery suggests that the differential expression of Shh and Fgf10/Fgfr2 may be the main reason a fully opened urethral groove forms in guinea pigs, and it may be similar in humans as well.

Identification of Small Regions of Overlap from Copy Number Variable Regions in Patients with Hypospadias

Hypospadias is a common form of congenital atypical sex development that is often associated with other congenital comorbidities. Many genes have been associated with the condition, most commonly single sequence variations. Further investigations of recurrent and overlapping copy number variations (CNVs) have resulted in the identification of genes and chromosome regions associated with various conditions, including differences of sex development (DSD). In this retrospective study, we investigated the DECIPHER database, as well as an internal institutional database, to identify small recurrent CNVs among individuals with isolated and syndromic hypospadias. We further investigated these overlapping recurrent CNVs to identify 75 smallest regions of overlap (SROs) on 18 chromosomes. Some of the genes within these SROs may be considered potential candidate genes for the etiology of hypospadias and, occasionally, additional comorbid phenotypes. This study also investigates for the first time additional common phenotypes among individuals with hypospadias and overlapping CNVs. This study provides data that may aid genetic counseling and management of individuals with hypospadias, as well as improve understanding of its underlying genetic etiology and human genital development overall.