Klinefelter's syndrome.

THE LANCET • Vol 356 • July 22, 2000 333 Klinefelter’s syndrome Klinefelter’s syndrome is the most common cause of testicular failure that results in impairments in both spermatogenesis and—to a lesser extent—testosterone production. This syndrome is the most common sexchromosome disorder affecting 1 in 500 men across all ethnic groups, but the diagnosis is often delayed because of substantial variation in clinical presentation. Those affected possess an additional or “supernumerary” X chromosome that results in a 47XXY genotype. Those affected have severely impaired spermatogenesis (usually