Genetic Counseling in Congenital Heart Defects

Published on 07/06/2015 by admin

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Last modified 07/06/2015

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33 Genetic Counseling in Congenital Heart Defects

II. THE PROCESS OF COUNSELING

III. ETIOLOGIC CATEGORIES IN CONGENITAL HEART DISEASES

A. Incidence

TABLE 33-1 ETIOLOGIC DISTRIBUTION OF CONGENITAL HEART DISEASE

Etiology Percentage
Multifactorial 85%
Chromosome abnormalities 8–10%
Single gene disorders 3–5%
Maternal disease (IDDM, PKU, SLE etc.) 1%
Maternal exposures (infections, teratogens etc.) 1%

B. Mode of inheritance

1. Multifactorial inheritance (Fig. 33-1).

a. Multifactorial inheritance is the result of interactions of many genes (genes on different chromosomes and involved in a certain function) and environmental factors.

b. The sum of the genetic and environmental contribution determines the person’s liability to develop a disorder.

c. This liability has a bell-shaped curve in the general population, where most of the population is in the mean and unaffected, and a small portion of the population past the threshold and expresses the clinical manifestations.

d. This mode of inheritance is the most common cause of genetic disorders and is responsible for the greatest number of patients who will need special care or hospitalization because of genetic diseases, including congenital heart disease.

e. Up to 10% of newborn children express a multifactorial disease at some time in their lives, such as atopic reactions, diabetes, cancer, spina bifida, anencephaly, pyloric stenosis, cleft lip, cleft palate, congenital hip dysplasia, club foot, and congenital heart disease, among others. Some of these diseases occur more frequently in female patients (scoliosis, congenital dislocation of the hips) and some are more common in male patients (pyloric stenosis).

f. Hallmarks for multifactorial inheritance.

g. Empirical risk for some congenital cardiac abnormalities is outlined in Table 33-2.

2. Chromosome abnormalities.

a. Chromosome abnormalities are detected in about 10% of newborns with congenital heart disease (Ferencz et al, 1989).

b. The incidence in fetuses with prenatally diagnosed congenital heart disease is most probably threefold higher (Berg et al, 1988).

c. Because specific congenital heart diseases are known to be associated with certain chromosome abnormalities, we can assume that the gene or genes associated with these abnormalities must have a major role in cardiac development (Table 33-3).

d. This is emphasized in contiguous-gene disorders where a specific gene known to have a major role in the development of the heart is deleted and results in specific cardiac abnormalities (Table 33-4).

3. Single-gene disorders.

a. Autosomal recessive inheritance and conditions.

b. Autosomal dominant inheritance and conditions.

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