Marfan syndrome, type I (MFS1; MIM 154700) is an autosomal dominantly inherited disorder potentially affecting numerous organ sites. These include: the bones, eyes, lungs, skin, CNS and cardiovascular system. The most serious consequence of Marfan syndrome is due to the progressive dilatation of the aortic root and the consequent potential for dissection. MFS1 is caused by mutations in the FBN1 gene. This gene codes for fibrillin 1, a component of microfibrils. Microfibrils are found in both elastic and non-elastic tissues. Over 1000 different FBN1 mutations have been identified in Marfan syndrome, type I. Most mutations are single nucleotide substitutions or small insertions and deletions. Large FBN1 gene deletions are estimated to represent 2% of the mutations.