What Causes Hypoplastic Right Heart Syndrome?

Tricia Christensen
Tricia Christensen

Generally, causal factors of hypoplastic right heart syndrome (HRHS) are not identifiable. Medical science cannot tie the condition to genetic mutations or inheritance, though a very marginal risk of having more than one child with HRHS exists. Getting insufficient folic acid or taking some medications or substances are linked to a greater risk of fetal heart defects, including hypoplastic right heart syndrome. A few multi-system genetic disorders also may have a higher HRHS incidence.

In hypoplastic right heart syndrome, the right side of the heart, including the ventricle, tricuspid valve and atrium do not develop properly.
In hypoplastic right heart syndrome, the right side of the heart, including the ventricle, tricuspid valve and atrium do not develop properly.

In fetal development, hypoplastic right heart syndrome occurs as a result of improper development of the pulmonary valve and artery. When these are underdeveloped, they don't allow proper circulation of blood through the right side of the heart. This circulation is needed to mature the heart's structures.

Cocaine use during pregnancy may lead to hypoplastic right heart syndrome.
Cocaine use during pregnancy may lead to hypoplastic right heart syndrome.

The result is an undersized right ventricle, and a tricuspid valve and atrium that are too small. While still in utero the fetus gets oxygen from the mother, and this defect is often survivable. Severe problems occur after birth because the heart isn't able to support blood circulation to the lungs, and the body becomes oxygen-deprived quickly.

Some of those with Down syndrome will develop hypoplastic heart syndrome.
Some of those with Down syndrome will develop hypoplastic heart syndrome.

HRHS is not presently curable, though a staged series of surgeries or a heart transplant are options. Survival well into adulthood is now expected for many babies born with this condition, but the actual defects to the heart aren't reparable. More research on surgical repair is warranted, but understanding what causes hypoplastic right heart syndrome would be helpful, too.

Although HRHS is not presently curable, a series of surgeries or a heart transplant are options.
Although HRHS is not presently curable, a series of surgeries or a heart transplant are options.

Presently, there has been no consistent identification of a set of genes that affects the pulmonary valve and fetal right heart development. A few conditions with a genetic basis occasionally, but don't always, produce HRHS. These include Ivemark's syndrome, which has related spleen disorders, dextrocardia, and a variety of right-sided defects. Down syndrome is associated with heart defects, and may cause hypoplastic right heart syndrome in some, but not all, individuals.

A heart transplant may be an option for someone with hypoplastic right heart syndrome.
A heart transplant may be an option for someone with hypoplastic right heart syndrome.

A number of medications and substances have been identified as potentially causing hypoplastic right heart syndrome and other heart defects. Many of the selected serotonin reuptake inhibitors and serotonin norepinephrine reuptake inhibitors have been reliably linked to increased heart defects in children. Mood stabilizers like valproic acid, carbamazepine, and lithium have similar risks. Cocaine and amphetamines also appear to cause heart defects and other birth defects.

Insufficient folic acid may be linked to a greater risk of heart defects.
Insufficient folic acid may be linked to a greater risk of heart defects.

Lack of appropriate folic acid levels has been linked to a variety of birth defects for some time. It now appears that insufficient levels may make it more likely that conditions like hypoplastic right heart syndrome or other heart defects will occur. Ideally, folic acid use should begin prior to conception to reduce this risk.

Parents with kids with HRHS are often troubled because there is no explanation for these serious and dangerous defects. A mother may do "everything right" and still have a baby with hypoplastic right heart syndrome. While climbing survival rates encourage families, they may remain discouraged that researchers cannot reliably identify a clear cause.

Lack of appropriate folic acid levels during pregnancy may increase the risk of hypoplastic right heart syndrome.
Lack of appropriate folic acid levels during pregnancy may increase the risk of hypoplastic right heart syndrome.
Tricia Christensen
Tricia Christensen

Tricia has a Literature degree from Sonoma State University and has been a frequent wiseGEEK contributor for many years. She is especially passionate about reading and writing, although her other interests include medicine, art, film, history, politics, ethics, and religion. Tricia lives in Northern California and is currently working on her first novel.

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