Klinefelter syndrome in an adolescent with severe obesity, insulin resistance, and hyperlipidemia, successfully treated with testosterone replacement therapy.

Klinefelter syndrome (KS) is a sex chromosome disorder characterized by the presence of one or more extra X chromosomes. The classical KS karyotype is 47, XXY, and the incidence of KS is approximately 1 in 660 births (1). KS in adults is characterized by tall stature, gynecomastia, late-onset puberty, azoospermia, erectile dysfunction, reduced libido, and neurodevelopmental disorders (1). Stereotypically, patients with KS are tall and slender with narrow shoulders, long extremities, and sparse body hair. In recent studies, 44% and 42.6% patients with KS aged >18 yr had metabolic syndrome (2) and obesity (3), respectively. Some adult patients with KS have insulin (IRI) resistance and type 2 diabetes mellitus (2,3,4,5). In patients with KS, the risks of obesity, metabolic syndrome, and type 2 diabetes mellitus increase from adolescence to adulthood. Diabetes-related mortality and comorbidities are serious problems in adulthood in patients with this syndrome (6, 7). In prepubertal patients, the common features of KS are cryptorchidism and neurodevelopmental disorders, whereas those in pubertal patients are small penises, small testes, cryptorchidism, gynecomastia, and neurodevelopmental disorders. In pediatric patients, obesity is seldom observed as a clinical symptom of KS (8). Here, we have reported a case of a pubertal patient with KS who developed severe obesity and hypergonadotropic hypogonadism. Testosterone replacement therapy led to an improvement obesity and hyperlipidemia. We suggest that testosterone therapy not only improves sexual development but also has anti-obesity and metabolic effects in adolescent patients with KS.