Marfan syndrome is a genetic disorder that affects the body’s connective tissue. Connective tissue holds all the body’s cells, organs and tissue together. It also plays an important role in helping the body grow and develop properly.Connective tissue is made up of proteins.The protein that plays a role in Marfan syndrome is called fibrillin-1. Marfan syndrome is caused by a defect (or mutation) in the gene that tells the body how to make fibrillin-1.This mutation results in an increase in a protein called transforming growth factor beta, or TGF-β.he protein that plays a role in Marfan syndrome is called fibrillin-1. Marfan syndrome is caused by a defect (or mutation) in the gene that tells the body how to make fibrillin-1.