What are Genetic Birth Defects?

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  • Written By: wiseGEEK Writer
  • Edited By: O. Wallace
  • Last Modified Date: 11 October 2019
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Understanding genetic birth defects first means understanding the term genetic. There can be differences in the way this word is used. Sometimes genetic means due to inheritance of one more genes that result in expression of one or more symptoms or changes to average body function. Another way this term is used is to express errors in the way chromosomes or genes work that don’t have an inheritance bias; such errors could occur from environment, disease, age, or unknown factors, resulting in a form of genetic birth defects that aren’t inherited.

Inherited birth defects exist in many forms, and may be passed to children in a number of ways. Parents may each need to carry a gene for a defect for it to be expressed genetically. In these cases, defects only happen if the child inherits a recessive gene from each parent, which doesn’t always happen. In other instances, anytime a single gene is inherited, the birth defect will occur, which is called autosomal dominant. Defect doesn’t always mean malformation of body, and some people don’t show evidence of genetic birth defects when they are born. Instead, the defects manifest later.


There are many examples of genetic birth defects that can be very serious. These include Tay-Sachs disease, which causes gradual deterioration and has an exceptionally high fatality rate. It can be said this is gene related because people do or don’t carry this gene, and when two parents are carriers they have a one in four risk of having a child with this disease. It is a recessive illness, but people who don’t get the illness may become carriers of the gene, and should undergo genetic testing prior to having children. Other illnesses that are inherited include sickle cell anemia, cystic fibrosis, muscular dystrophy, and Marfan syndrome; many more examples exist.

Errors in genes can cause the other type of genetic birth defects. Either through environment or through some accident of nature, one or more genes can fail to work as they should. This is the case with heart defects, though there are a few rare heart defect conditions like heterotaxy that are inherited. The majority occur for unknown reasons, but these reasons clearly involve genes failing to order the work of building the body properly.

It should also be noted that this second type of defect might be hereditary. Just because an inheritance pattern hasn’t been established, doesn’t mean it’s not there. It just means medical researchers have not uncovered it.

Another defect that is fairly common and may be hereditary or inherited some of the time is cleft palate. Sometimes doctors are not necessarily sure what creates the problem. Other conditions could result from environmental factors changing the way genes are expressed.

For instance Down syndrome may be inherited and is more common in families with Down’s kids. Risk of having a baby with the condition increases with age, too, as a woman’s eggs or ova get older. Down syndrome goes up significantly for women over the age of 35, regardless of whether people have a family history.

Lack of certain things like supplements of folic acid before and during pregnancy may create neural tube defects of the spine, and there’s growing evidence that genes that build the heart may falter, heart resulting in defects. Illnesses, most illegal drugs, and alcohol can also cause faulty gene expression resulting in a variety of defects that are not inherited.

Many people who have a child with a birth defect do not expect it and have no family history of defects. In one sense this makes hereditary or genetic birth defects a little easier to catch early, given access to genetic counseling. Knowing family history is a good way of knowing whether work with a genetic counselor would be advisable prior to trying to conceive. Yet, even with a clear family history, the failure of genes to sometimes work properly means that risk is always present, though most defects are fortunately rare.


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