Congenital heart defects
Congenital heart defects, which can occur as a single defect in the presence of
normal chromosomes, are relatively
common (1%). Such defects have both a hereditary and an environmental component
(multifactorial inheritance). In other words, both genes and environmental factors
are involved. Little is known at the present time about the hereditary and environmental
factors that cause these defects. If an infant is born with a heart defect, there
is a 5-10% recurrence rate in each subsequent pregnancy. The risk of recurrence
does not relate only to that particular defect, but to all heart defects. This risk
increases to 25% if there are already two children in the family with the same condition.
The risk of recurrence is higher the greater the number of cases in the family and
the worse the defect in the previous children.
There are reports of cases of both autosomal recessive (a 25% recurrence risk)
dominant (a 50% recurrence risk) inheritance. However, these are unusual
and should only be considered when there are several affected family members.
The defect is diagnosed using
fetal echocardiography and ultrasound testing directed at the fetus's heart.
This test is performed by a pediatric cardiologist, usually in the 24th week of
In about 10% of cases of heart defects detected during pregnancy, a very small deletion
(a piece of the chromosome that is missing) is found in chromosome 22q (see: Velo-cardio-facial
syndrome or DiGeorge syndrome), demonstrated using a fluorescent cytogenetic test
(FISH - Fluorescent In Situ Hybridization). It is therefore advisable to perform
this test in cases of heart defects in pregnancy in addition to regular chromosome
testing. If such a deletion is detected, there is also a risk for further defects
and mental retardation, and also a 20% risk that
the deletion is present in one of the parents, with a possibility of recurrence
in each subsequent pregnancy. If the parents or any of their relatives have a history
of similar heart defects in addition to mental retardation or other defects (in
the intestinal system or other systems), this may indicate a genetic syndrome. Some
of these may be identified by chromosome testing, FISH or molecular tests. Such tests are becoming increasingly
available as more and more of the causative genes are being discovered - for example,
a specific gene responsible for determining the location of the heart, a mutation
of which causes a disorder in the location of the heart with reference to the abdominal
organs, has been found. In all cases of possible genetic syndromes, all available
information must be given to the geneticist for clinical and laboratory evaluation.