Types of birth defects:
The major categories of birth defects are chromosomal conditions
, abnormalities involving a known mutation in a particular gene
, structural birth defects unrelated to chromosomal abnormalities or a specific known gene, and birth defects due to certain maternal infections
or environmental exposures.
Fort Sanders Perinatal Center staffs genetic counselors
that will review your family history to help determine if your baby is at an increased risk for a birth defect.
Many mutations in specific genes have been identified. Cystic fibrosis
is one of the most commonly inherited single gene disorders. Tay-Sachs disease
is more common in individuals of Ashkenazi Jewish ancestry, French-Canadian ancestry or Cajun ancestry. Sickle cell disease
is the most common single gene disorder in African-Americans, and alpha-thalassemia
occurs most commonly in those of Asian ancestry.
The importance of chromosomes to a person's genetic makeup is so much so that individuals with missing or extra chromosomes usually have quite significant physical impairments. Down syndrome
is a condition in which an individual carries an extra copy of chromosome number 21. Individuals with Down syndrome have characteristic facial appearance, moderate mental retardation, short stature, and can have major internal abnormalities, such as heart defects or abnormalities of the formation of the trachea, esophagus or intestines.
An extra number 18 chromosome results in trisomy 18 (Edwards syndrome
), a much rarer disorder that results in miscarriage, stillbirth or death in early infancy more than 90% of the time. Individuals with trisomy 18 have multiple physical abnormalities, including abnormalities of the brain, heart and extremities, and have profound mentally retardation.
Trisomy 13 (Patau syndrome
) results when an individual has an extra copy of chromosome number 13. Individuals with trisomy 13 also have a very high rate of miscarriage, stillbirth and death in the newborn period. The few survivors have profound mentally retardation and have major structural malformations, including brain, spine, heart, intestinal and limb abnormalities.
An extra or missing sex chromosome causes problems, but these are not as profound as Down syndrome, trisomy 18 or trisomy 13.
- These are females with an extra X chromosome. Women who have an extra X chromosome have an average IQ of 85 to 90, as opposed to the general population, which has an IQ average of about 100. However, most individuals with an extra X chromosome do not have identifiable physical abnormalities and function normally in society.
- These are boys with an extra X chromosome. Boys with an extra X chromosome (Klinefelter syndrome
) are typically tall and slim and usually have problems with sperm production.
- These are males with an extra Y chromosome. Recent data suggests that individuals with an extra Y chromosome do not have any differences in the rate of physical or behavioral problems compared to individuals with the standard 46,XY male chromosome type.
45,X (Turner syndrome)
- This occurs when there is only a single X chromosome. Individuals with Turner syndrome can have medical and developmental problems, including short stature, failure to begin puberty, infertility, heart defects and certain learning disabilities.
There are many other types of chromosome abnormalities, including missing or extra fragments of chromosomes, or chromosomal rearrangements.
Maternal infections, including toxoplasmosis, syphilis and cytomegalovirus, can cause birth defects.
most commonly is transmitted by eating raw or undercooked meat, but also can be transmitted to pregnant women by contact with the fecal matter of cats. If you think you may have been exposed, please let your doctor know.
typically is transmitted through contact with saliva, urine, or other body fluids of an affected individual. Cytomegalovirus infection can cause abnormalities of the brain, intestines, or other organs of the baby.
Exposures to teratogens
also can cause birth defects. The most common teratogen exposure during pregnancy is alcohol. Certain drugs and medications also are teratogenic. We recommend that women planning on pregnancy review all of the medications they are taking, including over-the-counter medicines, vitamins and herbal supplements, with their health care provider either before they become pregnant or very early on in the pregnancy.