Down's syndrome with X0/XY mosaicism.

A 5-month-old Chinese infant with combined Down's syndrome and X0/XY mosaicism is presented. The phenotypical features of mongolism are classical and unmodified. The somatic effects of X0/XY mosaicism is that of incomplete masculinization with short phallus, hypospadias, bifid scrotum, urogenital sinus, and bilateral extra-abdominal infantile testicles. These features together with the absence of internal female organs and signs of Turner's syndrome in this patient are different from the previous reported cases of mixed gonadal dysgenesis.