The routine prenatal diagnosis includes a standard cytogenetic study and a careful evaluation of the fetus by one or more ultrasonographic scans. Usually there is a full concordance between cytogenetic and ultrasonographic fetal sex determination, but occasionally a discordant result may be observed (1/2500 pregnancies). In these cases, besides a possible mistake and an exchange between amniotic fluid samples, a disorder of sex determination should be considered. Sex reversal can be divided into 46, XY female sex reversal syndrome and 46, XX male sex reversal syndrome. The XX male syndrome (OMIM 278850) is a rare condition affecting 1 in 20000 newborn males. Molecular analysis of sex-reversed patients led to the discovery of the SRY gene (sex-determining region on Y), a gene playing a crucial role in the male differentiation of the bipotential gonad (Sinclair et al., 1990).

The XX male syndrome was first described by de la Chapelle et al.(1964). Recently a revised nomenclature proposed to rename it as 46, XX testicular disorder of sex development or 46, XX testicular DSD (Hughes et al., 2006). The 46, XX testicular DSD is characterized by the presence of a 46, XX karyotype, male external genitalia that range from normal to ambiguous (micropenis, penoscrotal hypospadias with or without chordee, cryptorchidism), two testicles, and azoospermia. Mullerian structures are absent.