Klinefelter syndrome
Klinefelter syndrome is a 47,XXY sex chromosome disorder and the most common cause of primary male hypogonadism, occurring in about 1 in 600 live births. Adult men present with tall stature, small firm testes, gynecomastia, and infertility from azoospermia; the diagnosis is confirmed by karyotype showing 47,XXY, and treatment is lifelong testosterone replacement, which does not restore fertility.
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What this article covers
- Overview
A sex chromosome disorder causing primary male hypogonadism: Klinefelter syndrome is caused by an extra X chromosome, producing a 47,XXY karyotype, and it is the most common cause of primary hypogonadism in men.
- Epidemiology
Occurs in about 1 in 600 live births: this makes Klinefelter syndrome the most common cause of primary hypogonadism in men.
- Risk factors
An extra X chromosome from meiotic nondisjunction: aneuploidy most commonly arises from nondisjunction during meiosis, producing the 47,XXY karyotype; there is no established modifiable risk factor.
- Pathophysiology
An extra X chromosome disrupts normal testicular development: the 47,XXY karyotype results in progressive testicular fibrosis and hyalinization, producing small, firm testes and impaired spermatogenesis.
- Clinical features
Adult men present with tall stature, small firm testes, and infertility: the classic adult phenotype includes tall stature with eunuchoid proportions, small firm testes less than 4 mL in volume, and infertility due to azoospermia.
- Differential diagnosis
Anabolic androgenic steroid use: a muscular appearance with acne, gynecomastia, and small, soft (not firm) testes; laboratory testing shows low testosterone with low or inappropriately normal LH and…
- Diagnosis
Klinefelter syndrome is confirmed by karyotype analysis revealing a 47,XXY karyotype, the diagnostic basis that establishes the disease once the clinical and biochemical pattern of primary hypogonadism is identified.
- Management
First, confirm the diagnosis with karyotype before starting hormone replacement, since androgen treatment is lifelong and the karyotype result also guides counseling about fertility and associated risks.
- Complications
Infertility from azoospermia: the most consistent complication of Klinefelter syndrome, present in essentially all affected men and not reversed by testosterone replacement.
- Prognosis
Normal life expectancy with appropriate hormone management: testosterone replacement corrects the androgen deficiency and its downstream effects on muscle mass, sexual function, and secondary sexual characteristics.
- Prevention
No primary prevention exists: Klinefelter syndrome results from sporadic meiotic nondisjunction producing an extra X chromosome, with no established modifiable risk factor or preventive intervention.
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