Context: Differentiation of testicular tissue in 46,XX individuals is seen either in XX males, the majority of them with SRY gene, or in individuals, usually SRY(-), with ovotesticular disorder of sex development (OT-DSD). Although they are sporadic cases, there are some reports on familial recurrence, including coexistence of XX maleness and OT-DSD in the same family.

Objective: We report on a case of SRY(-) 46,XX monozygotic twins with genital ambiguity.

Methods: Hormonal evaluation included testosterone (T), FSH, and LH measurements. SRY gene was investigated by PCR and two-steps PCR in peripheral leukocytes and gonadal tissues, respectively. Direct DNA sequencing of the DAX-1 coding sequence was performed. Real-time PCR for SOX9 region on chromosome 17 was obtained.

Results: Both twins had a 46,XX karyotype. Twin A had a 1-cm phallus with chordee, penoscrotal hypospadias, and palpable gonads. Serum levels of FSH (2.34 mUI/mL), LH (8.8 mUI/mL) and testosterone (1.6 ng/mL) were normal, and biopsies revealed bilateral testes. Twin B had a 0.5-cm phallus, perineal hypospadias, no palpable gonad on the right and a left inguinal hernia. Hormonal evaluation revealed high FSH (8.2 mUI/mL) and LH (15 mUI/mL) and low testosterone (0.12 ng/mL). Upon herniotomy, a right testis (crossed ectopia) and a small left ovotestis were found. SRY gene was absent in both peripheral leukocytes and gonadal tissue samples. Neither DAX-1 mutations nor SOX9 duplication was identified.

Conclusions: This case evidences that both XX maleness and XX OT-DSD are different manifestations of the same disorder of gonadal development.