Congenital Heart Defects

A congenital heart defect, also referred to as congenital heart disease or CHD, is a heart problem that is present at birth and is caused by an error in the development of the heart during fetal development.

In most cases when a baby is born with a congenital heart defect, there is no known reason for the heart to have formed incorrectly. Scientists know that some types of congenital heart defects can be related to an abnormality of an infant's chromosomes, single gene defects or environmental factors. Most cases are considered “multifactorial inheritance” because there is no identifiable cause for the heart defect.

Multifactorial inheritance means that "many factors" (multifactorial) are involved in causing a birth defect. The factors are usually both genetic and environmental, which means a combination of genes from both parents, in addition to unknown environmental factors, produce the trait or condition.

Many mothers of babies born with a congenital heart defect may blame themselves for their child's illness. It is important to remember that the cause of most congenital heart defects are not known. 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. Because of this, it is very important for women to speak with their doctor or obstetrician about the medications they take as soon as they find out they may be pregnant or when they are thinking about becoming pregnant.

Women who have seizure disorders and need to take antiseizure medications may have a higher risk for having a child with a congenital heart defect, 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 a congenital heart defect. 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 very important for women with these chronic illnesses before becoming pregnant, so that they understand the risks involved.

Rubella, a virus that most people in the United States 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 health care provider before becoming pregnant. A mother who contracts rubella during her pregnancy has a very significant chance of having a baby with birth defects.

In the general population, about 1 percent of all children are born with a congenital heart defect. However, the risk goes up when either parent has a CHD or when another sibling was born with a CHD.

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.

Families with a history of congenital heart defects can meet with a genetic counselor or genetic specialist before becoming pregnant to talk about the risks of passing on the defect. 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.

Approximately 30 percent of children with abnormal chromosomes that result in genetic syndromes, like Down syndrome, are born with a congenital heart defect. Chromosomes are the structures in the body’s cells that contain genes. Genes code traits like 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 duplicated, 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 21)
• Trisomy 18 and trisomy 13
• Turner's syndrome
• Cri du chat syndrome
• Wolf-Hirshhorn syndrome
• DiGeorge syndrome (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 that is inherited from the mother, the other from the father. Genes not only compose our individual traits, but also may be responsible for 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:

• Marfan syndrome
• Smith-Lemli-Opitz syndrome
• Ellis-van Creveld
• Holt-Oram syndrome
• Noonan syndrome.

Other genetic syndromes that 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).

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 doctor who specializes in genetics (called a clinical geneticist) may be asked to evaluate the child.

If a child has been diagnosed with a chromosomal or other genetic abnormality, genetic counseling is helpful to determine the risk for heart defects occurring in future children.