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Ieuan A Hughes and Carlo L Acerini

Descent of the testis from an intra-abdominal site in foetal life to an extracorporeal location after birth is a mandatory developmental process to ensure that the mature testis promotes normal spermatogenesis. The two phases of transabdominal and inguinoscrotal descent occur approximately during the first and last thirds of gestation respectively. Key anatomical events to release the testis from its urogenital ridge location and to guide the free gonad into the scrotum are the degeneration of the cranio-suspensory ligament and a thickening of the gubernaculum. Androgens play a role in both these processes, particularly with respect to enabling the testis to traverse the inguinal canal in the final phase of descent. Experiments in animals suggest that androgens mediate this effect via the release of calcitonin gene-related peptide by the genitofemoral nerve, but direct evidence for such a mechanism is lacking in humans. The transabdominal phase of descent is under the control of insulin-like 3 (INSL3), a product of the Leydig cells. Definitive evidence of its role in rodent testis descent is illustrated by the phenotype of bilateral cryptorchidism in Insl3−/− null mice. Circulating levels of INSL3 are higher in boys at puberty, are undetectable in girls and are lower in boys with undescended testes. A minority also have a mutation either in the INSL3 gene or affecting its receptor gene, relaxin/insulin-like family peptide receptor 2 (LGRF8). Other factors that may play a role in testis descent include the anti-Mullerian hormone and members of the HOX gene family. Evidence that the prevalence of undescended testis may be increasing provides a phenotypic readout for the effects of postulated chemicals in the environment interfering in some way with the action of factors that control testis descent. Epidemiological studies point to profound geographical variations in prevalence in countries such as Denmark and Finland. Associations have been found with levels of chemicals labelled as endocrine disruptors being higher in breast milk samples from mothers with cryptorchid boys when compared with controls. The adverse effects of these compounds (e.g. bisphenol A) can be replicated in the offspring of dams exposed during pregnancy. A sensitive marker of an anti-androgen effect of a compound is a reduction in the anogenital distance, an anthropometric measurement that is significantly greater in males compared with females. The observation of an association between the anogenital distance in infant boys and the level of pesticides in the urine of their mothers in late gestation indicates that this has the potential to be a useful surrogate marker of the effects of environmental chemicals on testis descent in human population studies. The rightful place for the testis at birth is in the scrotum in order to provide the temperature differential essential for normal spermatogenesis. Appropriate screening programmes and early surgical intervention are the prerequisites to ensure optimal fertility in adulthood and a considerably lessened risk of testis cancer.

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Angela K Lucas-Herald, Jillian Bryce, Andreas Kyriakou, Marie Lindhardt Ljubicic, Wiebke Arlt, Laura Audí, Antonio Balsamo, Federico Baronio, Silvano Bertelloni, Markus Bettendorf, Antonia Brooke, Hedi L Claahsen-van der Grinten, Justin Davies, Gloria Hermann, Liat de Vries, Ieuan A Hughes, Rieko Tadokoro-Cuccaro, Feyza Darendeliler, Sukran Poyrazoglu, Mona Ellaithi, Olcay Evliyaoglu, Simona Fica, Lavinia Stejereanu, Aneta Gawlik, Evgenia Globa, Nataliya Zelinska, Tulay Guran, Ayla Güven, Sabine Hannema, Olaf Hiort, P-m Holterhus, Violeta Iotova, Vilhelm Mladenov, Vandana Jain, Rajni Sharma, Farida Jennane, Colin Johnston, Gil Guerra-Junior, Daniel Konrad, Odile Gaisl, Nils P Krone, Ruth Krone, Katherine Lachlan, Dejun Li, Corina Lichiardopol, Lidka Lisá, Renata Levoni Markosyan, Inas Mazen, Klaus Mohnike, Marek Niedziela, Anna Nordenstrom, Rodolfo A Rey, Mars Skae, Lloyd JW Tack, Jeremy W Tomlinson, Naomi Weintrob, Martine Cools, and S Faisal Ahmed

Objectives: To determine trends in clinical practice for individuals with DSD requiring gonadectomy.

Design: Retrospective cohort study.

Methods: Information regarding age at gonadectomy according to diagnosis; reported sex; time of presentation to specialist center; and location of center from cases reported to the International DSD Registry and who were over 16 years old in January 2019.

Results: Data regarding gonadectomy were available in 668 (88%) individuals from 44 centers. Of these, 248 (37%) (median age (range) 24 (17, 75) years) were male and 420 (63%) (median age (range) 26 (16, 86) years) were female. Gonadectomy was reported from 36 centers in 351/668 cases (53%). Females were more likely to undergo gonadectomy (n=311, p<0.0001). The indication for gonadectomy was reported in 268 (76%). The most common indication was mitigation of tumour risk in 172 (64%). Variations in the practice of gonadectomy were observed; of the 351 cases from 36 centers, 17 (5%) at 9 centers had undergone gonadectomy before their first presentation to the specialist center. Median age at gonadectomy of cases from high income countries and low/middle income countries (LMIC) was 13.0 yrs (0.1, 68) years and 16.5 yrs (1, 28), respectively (p<0.0001) with the likelihood of long-term retention of gonads being higher in LMIC countries.

Conclusions: The likelihood of gonadectomy depends on the underlying diagnosis, sex of rearing and the geographical setting. Clinical benchmarks, which can be studied across all forms of DSD will allow a better understanding of the variation in the practice of gonadectomy.