what causes most birth defects
About 3 percent to 4 percent of babies are born with some type of birth defect. Most birth defects are caused by genetic or environmental factors or a combination of the two (multifactorial birth defects). In most cases, however, the cause is unknown. Genetic or inherited causes include:
Some birth defects are caused by a mutation (change) in a single gene. In 1991, Stephen Warren, PhD, a March of Dimes grantee at Emory University in Atlanta, Georgia, identified the gene that causes fragile X syndrome, the most common inherited cause of intellectual disabilities.