Inflammation of the blood vessels (vasculitis). It causes ulcers and sores in the mouth, genitalia, and skin. Patients can also have stiffness and swelling in the joints (arthritis), eye involvement (uveitis), and form blood clots, especially in the legs. The inflamed blood vessels are thought to be caused by an overactive immune system, but what triggers this abnormal response is not known. The disease is more common in young adults from the Middle East, Japan, and Asia.