**4.2 Clinical features**

The characteristic phenotype of 17-HSD3 deficiency is a 46,XY individual with testes and male wolffian-duct derived urogenital structure (e.g. epydidymus, vas deferens and seminals vesicles), but with undervirilization of the external genitalia. Patients show a phenotypic variability ranging from undervirilization of the external genitalia with or without clitoromegaly and/or labial fusion, to complete female external genitalia and a blind-ending vagina; testes may be situated in the abdomen or in the inguinal channels or in the labia majora (Grumbach et al., 1998). Gynecomastia, likely as consequence of high 4-A levels and its conversion to estrogens in peripheral tissues, is not usually present (Andersson et al, 1996; Balducci et al., 1985; Mendonca et al., 2000). Two late-onset variants of uncertain pathophysiology, one of which is characterized by gynecomastia in boys (Rogers et al., 1985; Castro-Magana et al., 1993) and the other by polycystic disease in woman have been described (Pang et al., 1987).
