33 Genetic Counseling in Congenital Heart Defects
I. INTRODUCTION
B. Counseling for congenital heart diseases
a. Obtain a family history and pregnancy history.
b. Discuss the fetal ultrasound findings.
d. Discuss the options available.
2. Throughout this process, the family should be made to feel secure that they will be supported by the health care professionals involved in their care, regardless of any decision they make.
II. THE PROCESS OF COUNSELING
A. Obtaining a family history
1. A three-generation family history should be obtained that contains critical medical data and biological relationships.
2. The risk is much greater if it is the mother rather than the father who has the heart defect.
3. Information regarding family members with congenital abnormalities, recurrent miscarriages, stillbirths, mental retardation, inherited conditions, and consanguinity should be recorded.
4. The family pedigree is a tool for:
a. Making a medical diagnosis.
b. Deciding on testing strategies.
c. Establishing the pattern of inheritance.
d. Identifying at-risk family members.
f. Determining reproductive options.
g. Distinguishing genetic from other risk factors.
h. Making decisions on medical management and surveillance.
i. Developing patient rapport.
j. Educating the patient and exploring the patient’s understanding.
C. Discussing the cardiac abnormalities
1. The cardiac abnormalities should be discussed in the context of the other abnormalities detected in the fetus or newborn. For example, the cardiac abnormality may be minor, and yet the overall prognosis can be grim because of major brain abnormalities.
2. In cases with isolated cardiac abnormality or when the extracardiac abnormalities are minimal, the information regarding the prognosis and the surgical procedures should be provided mainly by the cardiologist.
3. When multiple abnormalities are detected or a specific condition is detected, the counseling should be given by a multidisciplinary group that includes everyone involved in the child’s care.
D. Providing support
1. The diagnosis of a fetal or newborn cardiac abnormality can be a time of crisis for the family.
2. The crisis can be exacerbated by not being able to secure an accurate diagnosis or by the unpredictability of the findings and prognosis.
3. This crisis can lead to a feeling of loss of control for the family.
4. Providers of genetic counseling should bear this in mind, and the session should be tailored to support the personal interests, beliefs, and coping mechanisms of the family.
III. ETIOLOGIC CATEGORIES IN CONGENITAL HEART DISEASES
A. Incidence
1. The majority of isolated cardiac abnormalities are multifactorial (85%).
2. Chromosome abnormalities are associated with 8% to 10%.
3. Single-gene disorders are found in 3% to 5% (Table 33-1).
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.
. Thus, the lower the incidence of a condition in the population, the greater the relative increased risk for siblings (e.g., cleft lip). Environmental factors as well as genetic factors are involved.g. Empirical risk for some congenital cardiac abnormalities is outlined in Table 33-2.
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).
a. Autosomal recessive inheritance and conditions.
b. Autosomal dominant inheritance and conditions.
