Marfan syndrome is a systemic disorder of connective tissue with a high degree of clinical variability. Cardinal manifestations involve the ocular, skeletal, and cardiovascular systems. FBN1 mutations associate with a broad phenotypic continuum, ranging from isolated features of Marfan syndrome to neonatal presentation of severe and rapidly progressive disease in multiple organ systems. Myopia is the most common ocular feature; displacement of the lens from the center of the pupil, seen in approximately 60% of affected individuals, is a hallmark feature. People with Marfan syndrome are at increased risk for retinal detachment, glaucoma, and early cataract formation. The skeletal system involvement is characterized by bone overgrowth and joint laxity. The extremities are disproportionately long for the size of the trunk (dolichostenomelia). Overgrowth of the ribs can push the sternum in (pectus excavatum) or out (pectus carinatum). Scoliosis is common and can be mild or severe and progressive. The major sources of morbidity and early mortality in the Marfan syndrome relate to the cardiovascular system. Cardiovascular manifestations include dilatation of the aorta at the level of the sinuses of Valsalva, a predisposition for aortic tear and rupture, mitral valve prolapse with or without regurgitation, tricuspid valve prolapse, and enlargement of the proximal pulmonary artery. With proper management, the life expectancy of someone with Marfan syndrome approximates that of the general population.
Marfan syndrome is a clinical diagnosis based on family history and the observation of characteristic findings in multiple organ systems. Ectopia lentis and aortic aneurysm are given special significance in the diagnosis of Marfan syndrome because of their relative specificity or frequency and clinical significance, respectively. Molecular genetic testing of FBN1 is available in clinical laboratories. It remains unclear whether the lack of full sensitivity of this test relates to an atypical location or character of FBN1 mutations in some individuals (e.g., large deletions or promoter mutations) or to locus heterogeneity.
Marfan syndrome is inherited in an autosomal dominant manner. Approximately 75% of individuals with Marfan syndrome have an affected parent; approximately 25% of probands with Marfan syndrome have a de novo mutation. The risk to the sibs of the proband depends on the status of the parents. If a parent is affected, the risk is 50%. If an affected child is born to clinically unaffected parents, it is likely that the child has a de novo mutation, and the risk to sibs is far less than 50% but above the population risk because of reported (but rare) cases of somatic and germline mosaicism. The children of an individual with Marfan syndrome are at 50% risk of inheriting the mutant allele and the disorder. Prenatal testing for pregnancies at increased risk is possible if the disease-causing mutation in the family is known.