46,XY Karyotype in a Female Phenotype Fetus: A Challenging Diagnosis

Background: The growing use of prenatal investigations allows an early detection of several inborn disorders, including disorders of sexual development. The management of these conditions is an arising problem. Case: 46,XY karyotype and female phenotype were detected in a fetus; 5α-reductase and androgen receptor gene analysis on chorionic villi revealed no relevant mutation. The newborn was assigned to female sex. The diagnosis of 17β-hydroxysteroid dehydrogenase-3 β-OL deficiency was reached at four months of age, by means of a low testosterone/Δ 4-androstenedione ratio after HCG test and HSD17B3 gene analysis. Summary and Conclusion: A 46,XY fetus with female external genitalia suggests different conditions, some very rare. Specific genetic investigations should be performed prenatally when possible. A complete evaluation is mandatory after delivery to reach a correct diagnosis.