Klinefelter Syndrome

Klinefelter syndrome is a sex-chromosome condition that usually produces a 47,XXY karyotype. The extra X chromosome gradually impairs testicular function, so the clinical pattern is one of primary testicular failure: testosterone falls while LH and FSH rise in an unsuccessful attempt to stimulate the testes. For the REx-PN, connect that pattern to the patient in front of you. A child may have few physical findings but language or learning needs; an adolescent may show delayed puberty, and an adult may present with infertility, small firm testes, gynecomastia, or complications of chronic testosterone deficiency. Karyotype confirms the chromosome pattern, while morning testosterone and gonadotropins determine whether biochemical hypogonadism is present. Testosterone replacement requires symptom-based prescribing, contraindication screening, and ongoing blood-count and prostate surveillance.