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Klinefelter Syndrome

Klinefelter syndrome (KS) is a condition caused by at least one extra X chromosome in males (aneuploidy; e.g., 47,XXY). The prevalence is estimated to be 1 in 500 males, including individuals with variations in classic KS (e.g., 48,XXYY, 48,XXXY, and 49,XXXXY). KS is characterized by a tall, slender body habitus, with long legs and a shorter torso. Many of the notable features of KS are directly or indirectly related to testosterone deficiency. Postpubertal males typically are infertile and have small testes, decreased facial and pubic hair, swollen breasts (i.e., gynecomastia), and a small penis, with more severe phenotypes associated with KS karyotype variants. Only 1 in 10 children are diagnosed in childhood, because the most prominent symptoms do not become apparent until after puberty. ...

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