Hypoplastic right heart syndrome (HRHS) is not linked to genetic mutations or heredity, but insufficient folic acid intake or certain medications/substances increase the risk. HRHS occurs due to improper development of the pulmonary valve and artery, resulting in an undersized right ventricle and undersized tricuspid valve and atrium. It is not curable, but surgeries or a heart transplant are options. Lack of appropriate levels of folic acid has been linked to HRHS, and some drugs and substances have been identified as potentially causing it. There has not been a consistent identification of a set of genes affecting pulmonary valve and fetal right heart development.
Generally, the causative factors of hypoplastic right heart syndrome (HRHS) are not identifiable. Medical science cannot tie the condition to genetic mutations or heredity, although there is a very marginal risk of having more than one child with HRHS. Insufficient folic acid intake or certain medications or substances are linked to an increased risk of fetal heart defects, including hypoplastic right heart syndrome. Some genetic multisystem disorders may also have a higher incidence of HRHS.
In fetal development, hypoplastic right heart syndrome occurs due to improper development of the pulmonary valve and artery. When these are underdeveloped, they don’t allow for proper blood circulation through the right side of the heart. This circulation is necessary for the structures of the heart to mature.
The result is an undersized right ventricle and undersized tricuspid valve and atrium. While still in the uterus, the fetus receives oxygen from the mother and this defect is often survived. Serious problems occur after birth because the heart is unable to support blood circulation to the lungs and the body quickly becomes deprived of oxygen.
HRHS is currently not curable, although a series of surgeries or a heart transplant are options. Survival into adulthood is now expected for many children born with the condition, but actual heart defects are not repairable. More research on surgical repair is needed, but understanding what causes hypoplastic right heart syndrome would also be helpful.
Currently, there has not been a consistent identification of a set of genes affecting pulmonary valve and fetal right heart development. Some conditions with a genetic basis occasionally, but not always, produce HRHS. These include Ivemark syndrome, which has related spleen disorders, dextrocardia, and a variety of right-sided defects. Down syndrome is associated with heart defects and can cause hypoplastic right heart syndrome in some, but not all, individuals.
A number of drugs and substances have been identified as potentially causing hypoplastic right heart syndrome and other heart defects. Several of the selected serotonin reuptake inhibitors and serotonin norepinephrine reuptake inhibitors have been reliably linked to an increase in heart defects in children. Mood stabilizers such as valproic acid, carbamazepine and lithium have similar risks. Cocaine and amphetamines also appear to cause heart defects and other birth defects.
Lack of appropriate levels of folic acid has been linked to a variety of birth defects for some time. It now appears that insufficient levels may make conditions such as hypoplastic right heart syndrome or other heart defects more likely to occur. Ideally, folic acid use should begin before conception to reduce this risk.
Parents of children with HRHS are often concerned that there is no explanation for these serious and dangerous defects. A mother can do “everything right” and still have a baby with hypoplastic right heart syndrome. While increased survival rates encourage families, they may become disheartened that researchers can’t reliably identify a clear cause.
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