FBN1 and Marfan syndrome: The clinical manifestations are due to mutation in the fibrillin-1 (FBN-1) gene located on chromosome 15Q21.[2] It is inherited in approximately 75% of cases and occurs due to spontaneous mutation in the remaining 25%.[3] More than 150 different mutations of the FBN-1gene have been isolated, and it may be that each family has a unique genetic mutation for the syndrome.[4] This could explain the considerable variability in the clinical presentations of Marfan syndrome.