[Atypical presentation of Klinefelter syndrome].

Klinefelter syndrome (KS) is the most common sex chromosomal abnormality and is associated with hypergonadotropic hypogonadism as an endocrine disorder. The phenotype is characterized by tall stature, abdominal adiposity and small testicles, and often appears after puberty.We report two cases of SK. The first patient is a 2-year-old boy with short stature who received growth hormone therapy. Because of non-progressive puberty, an evaluation of the reproductive axis was performed, showing increased basal gonadotropins. The karyotype (48 XXYY) confirmed the presence of KS. The second patient is an 8 year-old boy in whom peripheral precocious puberty was suspected. Laboratory tests showed high chorionic gonadotropin levels, and a chest CT scan revealed a mediastinal mass. The karyotype in peripheral blood disclosed a 48 XXYY formula (KS).Short stature does not exclude SK. In patients with a mediastinal mass and neurobehavioral deficits, KS should be suspected.