Marfan syndrome is a disorder of connective tissue, the tissue that strengthens the body's structures. Disorders of connective tissue affect the skeletal system, cardiovascular system, eyes, and skin.

Marfan syndrome is caused by defects in a gene called fibrillin-1. Fibrillin-1 plays an important role as the building block for elastic tissue in the body.

A problem with this gene leads to changes in elastic tissues, particularly in the aorta, eye, and skin. The gene defect also causes too much growth of the long bones of the body. This causes the tall height and long arms and legs seen in people with this syndrome. How this overgrowth happens is not well understood.

In most cases, Marfan syndrome is inherited, which means it is passed down through families. However, up to 30% of cases have no family history. Such cases are called "sporadic." In sporadic cases, the syndrome is believed to result from a spontaneous new gene defect.