A 22-year-old man has features of arm span greater than height, subluxed lenses, flattened corneas, and dilation of the aortic ring. Which of the following is the most likely diagnosis?

The severe form of Marfan syndrome is caused by a mutation in a single allele of the fibrillin gene (FBN1). The gene product is a major component of elastin-associated microfibrils. Long, thin extremities; ectopia lentis; and aortic aneurysms are the classical triad. Milder forms of the disease probably also occur but are hard to classify. Mutations in the FBN2 gene can also cause Marfan syndrome, but without aneurysms.