Antiphospholipid syndrome in a 21-year-old with Klinefelter syndrome.

We describe a patient with Klinefelter syndrome presenting with recurrent arterial thromboses secondary to the antiphospholipid syndrome. Previous case reports noted association of Klinefelter syndrome with systemic lupus erythematosus including some cases with antiphospholipid syndrome. Clinicians should consider autoimmune processes, including the antiphospholipid syndrome, when patients with Klinefelter syndrome present with recurrent thrombosis or additional features of a systemic autoimmune disorder.