Marfan disease is a result of defects in the connective protein fibrillin. This disorder results in individuals that can be very tall and thin, have pectus excavatum (depression under the sternum in chest), and develop cataracts and/or dislocated retinas. Defects in the aorta (mitral valve prolapse, aortic dilation, and aortic aneurysm) can be life threatening - especially for pregnant women. In the United States, it is estimated that 1 in 10,000 are at risk for developing Marfan disease. However, the risk may be much higher because many cases remain undiagnosed due to variable expression.
Most Marfan disease is inherited in an autosomal dominant pattern as the result of a defective fibrillin gene located on chromosome 15. However, a large proportion of cases appear spontaneous and variable expression can obscure the inheritance patterns. Therefore, direct testing for the mutations is often the only way to confirm the disease in many patients. Detection of mutations by sequencing of the fibrillin gene ranges from 35% to 85% depending on family history.