Hypospadias, increased

Hypospadias is a malformation of the penis where the urethral opening is displaced from the tip of the glans, usually on the ventral side on the phallus. Most cases of hypospadias are milder where the urethral opening still appears on the glans proper or on the most distal part of the shaft. In more severe cases, the opening may be more proximally placed on the shaft or even as low as the scrotum or the perineum.

In addition to the misplacement of the urethral opening, hypospadias is associated with an absence of ventral prepuce, an excess of dorsal preputial tissue, and in some cases a downward curvature of the penis (chordee).  Patients with hypospadias may need surgical repairment depending on severity, with more proximal hypospadias patients in most need of surgeries to achieve optimal functional and cosmetic results (Baskin, 2000; Baskin & Ebbers, 2006; Mattiske & Pask, 2021). The incidence of hypospadias varies greatly between countries, from 1:100 to 1:500 of newborn boys (Skakkebaek et al., 2016), and the global prevalence seems to be increasing (Paulozzi, 1999; Springer et al., 2016; Yu et al., 2019).

The external genitalia arise from the biphasic genital tubercle during fetal development. Androgens (testosterone and dihydrotestosterone) drive formation of the male external genitalia. In humans, the urethra develops by fusion of two endoderm-derived urethral folds. Disruption of genital tubercle differentiation results in an incomplete urethra, i.e. hypospadias.  (Baskin, 2000; Baskin & Ebbers, 2006).

In humans, hypospadias is diagnosed clinically by physical examination of the infant and is at first recognized by the absence of ventral prepuce and concurrent excess dorsal prepuce (Baskin, 2000). Hypospadias may be classified according to the location of the urethral meatus: Glandular, subcoronal, midshaft, penoscrotal, scrotal, and perineal (Baskin & Ebbers, 2006).

In mice and rats, macroscopic assessment of hypospadias may be performed postnatally, and several OECD test guidelines require macroscopic examination of genital abnormalities in in vivo toxicity studies (TG 414, 416, 421/422, 443). The guidelines do not define hypospadias or how to identify them. Fetal and neonatal identification of hypospadias may require microscopic examination for proper evaluation of the pathology. This can be done by scanning electron microscopy (Uda et al., 2004), or by histological assessment in which the presence of the urethral opening in proximal, transverse sections (for example co-occuring with the os penis or corpus cavernosum), indicates hypospadias (Mahawong et al., 2014; Sinclair et al., 2017; Vilela et al., 2007). In a semiquantitative, histologic approach, the number of transverse sections of the penis with internalization of the urethra was related to the total length of the penis, achieving a percentage of urethral internalization. In this study, ≤89% of urethral internalization was defined as indicative of mild hypospadias (Stewart et al., 2018).

Taxonomic applicability: Numerous studies have shown an association in humans between in utero exposure to endocrine disrupting chemicals and hypospadias. In mice and rats, in utero exposure to several endocrine disrupting chemicals, in particular estrogens and antiandrogens, have been shown to cause hypospadias in male offspring at different frequencies (Mattiske & Pask, 2021).

Life stage applicability: Penis development is finished prenatally in humans, and hypospadias is diagnosed at birth (Baskin & Ebbers, 2006). In rodents, penis development is not fully completed until weeks after birth, but hypospadias may be identified in early postnatal life as well, and in some cases in late gestation (Sinclair et al., 2017).

Sex applicability: Hypospadias is primarily used in reference to malformation of the male external genitalia. 

In the OECD guidelines for developmental and reproductive toxicology, several test endpoints include examination of structural abnormalities with special attention to the organs of the reproductive system. These are: Test No. 414 ‘Prenatal Developmental Toxicity Study’ (OECD, 2018a); Test No. 416 ‘Two-Generation Reproduction Toxicity’ (OECD, 2001) and Tests No. 421/422 ‘Reproduction/Developmental Toxicity Screening Test’ (OECD, 2016a, 2016b). In Test No. 443 ‘Extended One-Generation Reproductive Toxicity Study’ (OECD, 2018b), hypospadias is specifically mentioned as a genital abnormality to note.

Baskin, L. S. (2000). Hypospadias and urethral development. The Journal of Urology, 163(3), 951–956.

Baskin, L. S., & Ebbers, M. B. (2006). Hypospadias: Anatomy, etiology, and technique. In Journal of Pediatric Surgery (Vol. 41, Issue 3, pp. 463–472). https://doi.org/10.1016/j.jpedsurg.2005.11.059

Mahawong, P., Sinclair, A., Li, Y., Schlomer, B., Rodriguez, E., Ferretti, M. M., Liu, B., Baskin, L. S., & Cunha, G. R. (2014). Prenatal diethylstilbestrol induces malformation of the external genitalia of male and female mice and persistent second-generation developmental abnormalities of the external genitalia in two mouse strains. Differentiation, 88(2–3), 51–69. https://doi.org/10.1016/j.diff.2014.09.005

Mattiske, D. M., & Pask, A. J. (2021). Endocrine disrupting chemicals in the pathogenesis of hypospadias; developmental and toxicological perspectives. In Current Research in Toxicology (Vol. 2, pp. 179–191). Elsevier B.V. https://doi.org/10.1016/j.crtox.2021.03.004

OECD. (2001). Test No. 416: Two-Generation Reproduction Toxicity. In OECD Guidelines for the Testing of Chemicals, Section 4. OECD Publishing. https://doi.org/10.1787/9789264070868-en

OECD. (2016a). Test No. 421: Reproduction/Developmental Toxicity Screening Test. In OECD Guidelines for the Testing of Chemicals, Section 4. OECD Publishing. https://doi.org/10.1787/9789264264380-en

OECD. (2016b). Test No. 422: Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test. In OECD Guidelines for the Testing of Chemicals, Section 4. OECD Publising. https://doi.org/10.1787/9789264264403-en

OECD. (2018a). Test No. 414: Prenatal Developmental Toxicity Study. In OECD Guidelines for the Testing of Chemicals, Section 4. OECD Publishing. https://doi.org/10.1787/9789264070820-en

OECD. (2018b). Test No. 443: Extended One-Generation Reproductive Toxicity Study. In OECD Guidelines for the Testing of Chemicals, Section 4. OECD Publishing. https://doi.org/10.1787/9789264185371-en

Paulozzi, L. J. (1999). International Trends in Rates of Hypospadias and Cryptorchidism. Environmental Health Perspectives, 107(4), 297–302. https://doi.org/10.1289/ehp.99107297

Sinclair, A. W., Cao, M., Pask, A., Baskin, L., & Cunha, G. R. (2017). Flutamide-induced hypospadias in rats: A critical assessment. Differentiation, 94, 37–57. https://doi.org/10.1016/j.diff.2016.12.001

Skakkebaek, N. E., Rajpert-De Meyts, E., Buck Louis, G. M., Toppari, J., Andersson, A.-M., Eisenberg, M. L., Jensen, T. K., Jørgensen, N., Swan, S. H., Sapra, K. J., Ziebe, S., Priskorn, L., & Juul, A. (2016). Male Reproductive Disorders and Fertility Trends: Influences of Environment and Genetic Susceptibility. Physiological Reviews, 96(1), 55–97. https://doi.org/10.1152/physrev.00017.2015.-It

Springer, A., van den Heijkant, M., & Baumann, S. (2016). Worldwide prevalence of hypospadias. Journal of Pediatric Urology, 12(3), 152.e1-152.e7. https://doi.org/10.1016/j.jpurol.2015.12.002

Stewart, M. K., Mattiske, D. M., & Pask, A. J. (2018). In utero exposure to both high- and low-dose diethylstilbestrol disrupts mouse genital tubercle development. Biology of Reproduction, 99(6), 1184–1193. https://doi.org/10.1093/biolre/ioy142

Uda, A., Kojima, Y., Hayashi, Y., Mizuno, K., Asai, N., & Kohri, K. (2004). Morphological features of external genitalia in hypospadiac rat model: 3-dimensional analysis. The Journal of Urology, 171(3), 1362–1366. https://doi.org/10.1097/01.JU.0000100140.42618.54

Vilela, M. L. B., Willingham, E., Buckley, J., Liu, B. C., Agras, K., Shiroyanagi, Y., & Baskin, L. S. (2007). Endocrine Disruptors and Hypospadias: Role of Genistein and the Fungicide Vinclozolin. Urology, 70(3), 618–621. https://doi.org/10.1016/j.urology.2007.05.004

Yu, X., Nassar, N., Mastroiacovo, P., Canfield, M., Groisman, B., Bermejo-Sánchez, E., Ritvanen, A., Kiuru-Kuhlefelt, S., Benavides, A., Sipek, A., Pierini, A., Bianchi, F., Källén, K., Gatt, M., Morgan, M., Tucker, D., Canessa, M. A., Gajardo, R., Mutchinick, O. M., … Agopian, A. J. (2019). Hypospadias Prevalence and Trends in International Birth Defect Surveillance Systems, 1980–2010. European Urology, 76(4), 482–490. https://doi.org/10.1016/j.eururo.2019.06.027