It affects the body's production of fibrillin, which is a protein that is an important part of connective tissue.
Fibrillin is the primary component of the microfibrils that allow tissues to stretch repeatedly without weakening.
Because the child's fibrillin is abnormal, his or her connective tissues are looser than usual, which weakens or damages the support structures of the entire body.
The rate of mutation of the fibrillin gene, however, appears to be related to the age of the child's father; older fathers are more likely to have new mutations appear in chromosome 15.
Marfan syndrome is caused by a single gene for fibrillin on chromosome 15, which is inherited in most cases from an affected parent.