Abstract Objective 17β-Hydroxysteroid dehydrogenase 3 deficiency (17β-HSDD) and 5α-reductase type 2 deficiency (5α-RD) are rare 46,XY differences of sex development (DSD). This study aims to enlarge the limited knowledge on long-term gonadal function and gonadal pathology in these conditions. Design Retrospective multicentre cohort study. Methods Data on phenotype, laboratory results, and hormone treatment were collected from patients aged ≥16 years at time of data collection with genetically confirmed 17β-HSDD and 5α-RD from 10 centres via the I-DSD Registry. If gonadectomy or gonadal biopsy had been performed, pathology reports and/or gonadal tissue or images were collected. Results All 16 patients with 17β-HSDD were raised female; 1 (6%) changed to male gender at age 14. Three females were treated with gonadotrophin-releasing hormone agonists (GnRHa) to prevent virilisation. Thirteen underwent gonadectomy at median age 8 (range 0-17). None had germ cell (pre)malignancies. Of 14 patients with 5α-RD, 10 (71%) were raised female. Five changed gender at age 7-23, of whom 4 to male gender. One was treated with GnRHa. Six underwent gonadectomy at median age 10 (range 0-31). None had germ cell (pre)malignancies. With gonads in situ, puberty spontaneously progressed. Three were treated with dihydrotestosterone. Conclusions A significant percentage of individuals with 17β-HSDD and 5α-RD changed gender, and some were treated with GnRHa to prevent virilisation before making a definitive decision about gonadectomy. When left in situ, spontaneous puberty occurs and germ cell (pre)malignancies seem uncommon at least until early adulthood. Together, these data support delaying a decision about gonadectomy until late adolescence in these conditions.

Gonadal function and pathology in 17beta-HSD 3 and 5alpha-reductase deficiency