Girls with unexplained short stature are routinely screened for the presence of Ullrich-Turner syndrome by clinical examination, laboratory tests, and karyotyping. In this study, we performed chromosomal analysis in boys to explore the role of 45,X/46,XY mosaicism for short stature in males. Short-term effects of growth hormone treatment in male 45,X/46,XY individuals were compared retrospectively to those in female patients. We report six boys with a normal-appearing male phenotype and 45,X/46,XY mosaicism, four of whom were diagnosed postnatally because of short stature. Two boys were diagnosed prenatally by amniocentesis. Five boys were short and were treated with growth hormone (0.04-0.05 mg/kg per day) in analogy to girls with Ullrich-Turner syndrome and gonadal dysgenesis. With the exception of one patient in whom treatment was initiated only at the age of 14.6 years, the male patients with 45,X/46,XY mosaicism responded to short-term growth hormone treatment similarly to females with an increasing height SDS.
Conclusion: 45,X/46,XY mosaicism remains undetected in some short boys because this group is not routinely karyotyped. We recommend chromosomal analysis of boys with otherwise unexplained short stature who are short for their families. Growth hormone treatment should be offered to short boys with 45,X/46,XY mosaicism and a predicted adult height below the mid-parental range within clinical trials.