17β-Hydroxysteroid dehydrogenase 3 (17β-HSD3) deficiency is a rare 46XY disorder of sex development (DSD) of androgen biosynthesis. We aimed to describe the complexities in diagnosis, gender assignment, and the timing of irreversible surgical interventions in 17β-HSD3 deficiency. We described three genetically confirmed cases of 46XY DSD due to 17β-HSD3 deficiency. All of them had female-appearing external genitalia, and the third case had well-developed breasts with clitoromegaly. The biochemical evaluation showed hCG-stimulated T/A ratios of 0.4 and 0.35 in Cases 1 and 2, respectively, and an unstimulated T/A ratio of 0.25 in Case 3. Molecular analysis revealed three different HSD17B3 variants: c.72C>A(p.Cys24Ter), c.764C>T(p.Ser255Leu), and c.607-1G>A(3'splice site) in the respective cases. Despite the female-appearing external genitalia in Case 1, the parents decided to rear the child as male, whereas Cases 2 and 3 retained a female gender identity. The first two cases were advised to have regular follow-up for gender dysphoria, while Case 3 was managed with injectable leuprolide depot and anti-androgens. 17β-HSD3 deficiency remains a challenging 46 XY DSD due to its clinical heterogeneity and diverse molecular spectrum. This report adds to current molecular knowledge by reporting two novel variants in the HSD17B3 gene.

The 17-beta-hydroxysteroid dehydrogenase type 3 (17-β-HSD3) enzyme converts androstenedione to testosterone and is encoded by the HSD17B3 gene. Homozygous or compound heterozygous HSD17B3 mutations block the synthesis of testosterone in the fetal testis, resulting in a Disorder of Sex Development (DSD). We describe a child raised as a female in whom the discovery of testes in the inguinal canals led to a genetic study by whole exome sequencing (WES) and to the identification of a compound heterozygous mutation of the HSD17B3 gene (c.608C>T, p.Ala203Val, and c.645A>T, p.Glu215Asp). Furthermore, we review all HSD17B3 mutations published so far in cases of 17-β-HSD3 deficiency. A total of 70 different HSD17B3 mutations have so far been reported in 239 patients from 187 families. A total of 118 families had homozygous mutations, 63 had compound heterozygous mutations and six had undetermined genotypes. Mutations occurred in all 11 exons and were missense (55%), splice-site (29%), small deletions and insertions (7%), nonsense (5%), and multiple exon deletions and duplications (2%). Several mutations were recurrent and missense mutations at codon 80 and the splice-site mutation c.277+4A>T each represented 17% of all mutated alleles. These findings may be useful to those involved in the clinical management and genetic diagnosis of this disorder.