Klinefelter syndrome

Klinefelter syndrome is a genetic condition, usually with an extra X chromosome (47,XXY), that is one of the more common genetic causes of non-obstructive azoospermia and low testosterone in men. Features can include small, firm testes and, in some men, reduced body hair or gynaecomastia, though presentation varies and some men are diagnosed only during fertility evaluation. Diagnosis is confirmed by karyotype testing. Many men with Klinefelter syndrome have no sperm in the ejaculate, but a proportion have small pockets of sperm production that can sometimes be found using microdissection TESE for use with ICSI; testosterone therapy is managed separately and, if fertility is desired, decisions about its timing are made carefully with a specialist because testosterone therapy itself can suppress sperm production. Genetic counselling is recommended for men and couples affected.

Also known as: 47 XXY, Klinefelter's syndrome

Last reviewed: 9 September 2026. Written by the Antega Editorial Team. General information only — always follow the advice of your own clinic, doctor or pharmacist.