XO/XY mosaicism in delayed puberty.

Two adolescent boys with 45,X/46,XY (XO/XY mosaicism), presented in adolescence with pubertal delay and short stature. Both patients had a history of hypospadias repair, but otherwise normal male genitalia. Scrotal testes were present bilaterally, and no Müllerian structures were identified by pelvic ultrasound. The XO/XY mosaicism suggests that this chromosomal abnormality might be more common in phenotypic males than previously recognized. Because of the increased incidence of testicular neoplasia in patients with XO/XY mosaicism, it is important to document this chromosomal abnormality. We recommend cytogenetic analyses for boys with pubertal delay and hypospadias. If XO/XY mosaicism is documented, the patient must be closely followed for possible development of testicular failure and/or gonadoblastoma.