More specific defects in testosterone biosynthesis [17β-hydroxysteroid dehydrogenase deficiency (17β-HSD) type 3 (HSD17B3)], in the conversion of testosterone to dihydrotestosterone [5α-reductase deficiency type 2 (SRD5A2)], or in androgen action [androgen insensitivity syndrome (AIS), androgen receptor] can sometimes be suspected on clinical or biochemical grounds, but genetic testing is becoming increasingly important given the overlap in clinical features among various causes [8, 9]. Here, HSD17B3 is linked to androgen insensitivity syndrome.