Factors
Contributing to Congenital Heart Disease
A congenital
heart defect (CHD) is a heart problem which is
present at birth, caused by improper development
of the heart during fetal development. In the
majority of the instances when a baby is born
with congenital heart disease, there is no known
reason for the heart to have formed improperly.
Scientists know that some types of congenital
heart defects can be related to an abnormality
of an infant's chromosomes (5 to 6 percent), single
gene defects (3 to 5 percent), or environmental
factors (2 percent). In 85 to 90 percent of cases,
there is no identifiable cause for the heart defect,
and they are generally considered to be caused
by multifactorial inheritance.
Multifactorial
inheritance means that "many factors" (multifactorial)
are involved in causing a birth defect. The factors
are usually both genetic and environmental, where
a combination of genes from both parents, in addition
to unknown environmental factors, produce the
trait or condition.
Most
mothers of babies born with congenital heart disease
will look critically at their own behaviors during
pregnancy to try to find a cause for their child's
illness. It is important to remember that most
cases of congenital heart disease have no known
cause. However, some types of congenital heart
defects are known to occur more often when the
mother comes in contact with certain substances
during the first few weeks of pregnancy, while
the baby's heart is developing. Some maternal
illnesses and medications taken for these illnesses
have been shown to affect the heart's development.
Other illnesses or medications seem to have no
impact on the baby's heart. Always consult your
physician or obstetrician for more information.
Women
who have seizure disorders and need to take anti-seizure
medications may have a higher risk for having
a child with congenital heart disease, as do women
who take lithium to treat depression. Mothers
who have phenylketonuria (PKU) who do not adhere
to the special diet necessary to manage the disease
during pregnancy have a higher risk of having
a child with congenital heart disease. Also, women
with insulin-dependent diabetes (particularly
if the diabetes is not well-controlled) or lupus
may have a higher risk of having a child with
heart defects. Counseling is important for women
with these chronic illnesses before becoming pregnant.
Rubella,
a virus that most people in the United States
either had as a child, or were immunized against
when they received the MMR vaccine, is known to
cause birth defects. A woman who has never had
rubella nor been vaccinated against the disease
should consult her physician before becoming pregnant.
A mother who contracts rubella during her pregnancy
has a very significant chance of having a baby
with birth defects, including congenital heart
disease.
Always
consult your physician before taking any medications
while you are pregnant.
In the
general population, about 1 percent of all children
are born with congenital heart disease. However,
the risk increases when either parent has congenital
heart disease (CHD), or when another sibling was
born with CHD.
Consider
the following statistics:
- If you have had one
child with congenital heart disease, the chance
that another child will be born with CHD ranges
from 1.5 to 5 percent, depending on the type
of CHD in the first child.
- If you have had two
children with CHD, then the risk increases to
5 to 10 percent, to have another child with
CHD.
- If the mother has CHD,
the risk for a child to be born with CHD ranges
from 2.5 to 18 percent, with an average risk
of 6.7 percent.
- If the father has CHD,
the risk for a child to be born with CHD ranges
from 1.5 to 3 percent.
- Congenital heart defects
involving obstructions to blood flow in the
left side of the heart have a higher rate of
reoccurrence than other heart defects.
- If another child is
born with CHD, it can be a different type of
defect than seen in the first child.
- Some heart defects
are considered to have autosomal-dominant inheritance;
meaning that a parent with the defect has a
50 percent chance, with each pregnancy, to have
a child with the same heart defect, and males
and females are equally affected. Similarly,
there is also a 50 percent chance that an offspring
will not be affected.
Consultation
with a genetic counselor or genetic specialist
is encouraged for women with congenital heart
disease before becoming pregnant. In families
with CHD either in the parents or offspring, fetal
echocardiography can be performed in the second
trimester, at about 18 to 22 weeks of pregnancy,
to determine the presence of major heart defects
in the fetus.
Problems
with chromosomes that result in genetic syndromes,
such as Down syndrome, often result in a higher
incidence of infant heart malformations. Five
to 8 percent of all babies with CHD have a chromosome
abnormality. Chromosomes are the structures in
your cells that contain your genes; genes code
for your traits such as eye color and blood type.
Usually there are 46 chromosomes in each cell
of the body. Having too many or too few chromosomes
results in health problems and birth defects.
Structural defects of the chromosomes, where a
piece of the chromosome is missing or present
in duplicate, also causes health problems.
There
are a number of chromosome abnormalities associated
with congenital heart defects. Some of these include
the following:
- Down syndrome
- trisomy 18 and trisomy
13
- Turner's syndrome
- Cri du chat syndrome
- Wolf-Hirshhorn syndrome
- DiGeorge syndrome (deletion
22q11)
Chromosome
analysis can be performed from a small blood sample
to rule out the presence of a chromosome abnormality
in a child with a congenital heart defect.
There
are an estimated 70,000 genes contained on the
46 chromosomes in each cell of the body. Genes
come in pairs, one which is inherited from the
mother, the other from the father. Genes not only
compose our individual traits, but also compose
health problems when gene alterations (mutations)
are present. When a gene is mutated, a number
of health problems may occur in a person, due
to the single underlying genetic mutation. Several
health problems with one genetic cause are often
referred to as a syndrome. Some of the genetic
syndromes associated with a higher incidence of
heart defects include, but are not limited to,
the following:
- Marfan syndrome
- Smith-Lemli-Opitz syndrome
- Ellis-van Creveld
- Holt-Oram syndrome
- Noonan syndrome
- Mucopolysaccharidoses
Other
genetic syndromes which are not due to a single
gene defect but are associated with CHD include
Goldenhar syndrome (hemifacial microsomia), William's
syndrome, and the VACTERL association (tracheal
and esophageal malformations associated with vertebral,
anorectal, cardiac, renal, radial, and limb abnormalities
make up the VACTERL syndrome).
When
a child is born with a congenital heart defect,
if there is a suspicion that the child has some
type of genetic syndrome, a physician who specializes
in genetics (called a clinical geneticist) may
be asked to evaluate your child.
If a
child has been diagnosed with a chromosomal or
other genetic abnormality, genetic counseling
is helpful to determine the risk of heart defects
occurring in future children.
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