Severe venous thromboembolism in a young man with Klinefelter's syndrome and heterozygosis for both G20210A prothrombin and factor V Leiden mutations.

Klinefelter's syndrome is the most common cause of primary testicular failure, resulting in impairment of both spermatogenesis and testosterone production. It is a chromosomal disorder characterized by small, firm testes, azoospermia, gynecomastia, varying degrees of eunuchoidism and testosterone deficiency with elevated gonadotropin plasma levels. In Klinefelter's syndrome there is an increase of certain systemic diseases including venous thromboembolism.