Sometimes, an abnormal gene can cause or contribute to the occurrence of a birth defect. Birth defects are abnormal conditions of:
- Body structure (like achondroplasia, a form of dwarfism)
- Function (like fragile X syndrome, a common form of mental retardation)
- Body chemistry (like Tay-Sachs disease, in which a missing enzyme causes mental retardation and death mainly in people of Eastern European Jewish or French Canadian heritage)
Several thousand different birth defects have been identified. They occur in one of every 28 births, affecting millions of families.
Birth defects also may result from environmental factors, such as drug or alcohol abuse, certain infections, or exposure to certain medications or other chemicals. Often, birth defects seem to reflect a combination of both heredity and environment.
Genetic counseling helps people to identify and understand what particular traits they may pass on to their children and also to determine particular risks that may influence pregnancy outcome.
