Different birth defects have different causes. A specific condition might be caused by one or more of the following problems:
- Genetic problems. One or more genes might have a change or mutation that results in them not working properly, such as in McCune Albright syndrome. Similarly, a gene or part of the gene might be missing.
- Chromosomal problems. In some cases, a chromosome or part of a chromosome might be missing, such as in Turner syndrome, when a female is missing an X chromosome. Other birth defects result from having an extra chromosome, such as in Klinefelter syndrome and Down syndrome.
- Exposure to medications, chemicals, or other agents during pregnancy. The infants whose mothers took thalidomide are examples of an exposure leading to birth defects. Other examples include exposure to rubella (also called German measles) and toxic chemicals, such as hydrocarbons.