Why does congenital
cardiovascular disease happen?
Three to five percent (3-5%) of
all babies born have some type of identified birth defect. Of those
babies born with a birth defect, 10-25% have something different
about how their heart or it’s vasculature is structured or
functions. In other words, approximately 1 out of 100 babies born
have a congenital heart defect (CHD).
In the majority of cases, it is
not possible to identify a specific factor that caused the problem.
However, among the known causes of congenital heart defects are:
combination of both genetic and environmental factors
The cause of a particular heart
defect may differ from individual to individual. For example, two
individuals may appear to have the same heart defect. However, for
one, a change in genetic information may be the suspected culprit,
whereas the other’s heart defect may have been associated with an
environmental factor. In a third individual a combination of both
genetic and environmental factors may better explain the process.
Genetic factors may be
sporadic (identified for the first time in the affected
individual) or inherited (passed from parent(s) to child).
In other words, just because a problem is “genetic” doesn’t mean
that it was inherited. While a change in the genetic information
may be implicated in cardiac disease, that change may have occurred
soon after conception affecting all or most cells of the body and
therefore affecting the health of that person. Sometimes, however,
changes in genetic information are passed from parent to child.
There are some families in which
more than one member has a heart defect. When we see multiple
affected members in a single family, we suspect that there may be
genetic factors involved in the cause of the heart defects.
Genetic factors may include
congenital heart defects associated with single gene
mutations (alterations in the
DNA). Examples of conditions commonly seen in cardiology clinic
single gene alterations are
Alagille Syndrome and
Marfan Syndrome. Other genetic conditions are caused by
contiguous gene deletions or additions, where more than one
gene may be involved.
Velocardiofacial Syndrome (also known as DiGeorge, VCFS, or
22q11 Deletion syndrome) is an example of a genetic condition caused
by a contiguous gene deletion. Another group of heart defects are
mitochondrial defects. This is a relatively newly described
classification of genetic disease that involves genetic defects in
the mitochondria, the energy powerhouses found in most of our cells.
Sometimes, mitochondrial disease can be seen in conjunction with
Environmental factors may
interfere with heart development.
Teratogens are substances found in the environment that can
cause birth defects. Certain teratogens have been associated with
an increased risk of congenital heart defects. Some of the
teratogens that have been associated with an increased risk of
congenital heart defects are:
• Chemicals or
o Alcohol during pregnancy
o Retinoic Acid
• Maternal diseases
o Rubella Virus (German measles)
o Maternal Diabetes Mellitus
o Maternal Lupus
In some instances, both genetic
and environmental factors may interact to interrupt the development
of the heart. A condition that is caused by effects caused by the
genes and environment is known as a multifactorial condition.
A person with a multifactorial condition may have specific changes
in their genetic information predisposing them to the occurrence of
a heart defect. When those genes interact with certain
environmental agents, genetic disease can occur, causing (for
example) congenital heart disease.
For more answers to this question,
please visit the American Heart Association
Congenital Cardiovascular Defects page.
Last Update 6-22-04