Marfan syndrome: An inherited disorder of connective tissue that is characterized by abnormalities of the eyes, skeleton, and cardiovascular system. Nearsightedness (myopia) is the most common eye feature in Marfan syndrome. Displacement of the lens from the center of the pupil occurs in more than half of patients. Patients with Marfan syndrome have an increased risk for retinal detachment, glaucoma, and early cataracts. The skeleton shows bone overgrowth and loose joints. The arms and legs are unusually long, as are the fingers and toes. Due to overgrowth of the ribs, the sternum may be pushed in (pectus excavatum) or out (pectus carinatum). Scoliosis is common. Cardiovascular manifestations in Marfan syndrome include enlargement of the aorta at the level of the aortic valve, aortic aneurysm, prolapse of the mitral and tricuspid valves, and enlargement of the pulmonary artery. The major causes of disease and death in the syndrome are related to the heart and blood vessels. Marfan syndrome is inherited in an autosomal dominant manner and is caused by mutation in the FBN1 gene that encodes fibrillin 1. About 75 percent of people with Marfan syndrome have an affected parent, and 25 percent have a new gene mutation. Pregnancy can be dangerous for women with Marfan syndrome because the aorta can widen. Prevention of complications is key and includes exercise, blood pressure control, monitoring of the eyes, heart, and lungs, and physical therapy. Given good medical management, the life expectancy in Marfan syndrome now approximates that for the general population.