Klinefelter's syndrome is associated with karyotype 47, XXY.

Features

• often taller than average
• lack of secondary sexual characteristics
• small, firm testes
• infertile
• gynaecomastia - increased incidence of breast cancer
• elevated gonadotrophin levels but low testosterone

Diagnosis is by karyotype (chromosomal analysis).

Klinefelter's syndrome is the strongest known risk factor for male breast cancer. It carries a 50-fold increase in the risk of breast cancer compared to men with a normal genotype.