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Knowledge of the occurrence and etiology of congenital defects is essential to improvements in diagnosis, management, and genetic counseling. Congenital heart disease refers to structural abnormalities of the heart or intrathoracic great vessels that impact the function of the cardiovascular system. This chapter summarizes current knowledge regarding epidemiology and etiology of congenital heart disease. Information regarding the etiology of inherited cardiomyopathies and arrhythmias is presented in Chapters 9 and 10, respectively.

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Epidemiologic studies seek to measure disease frequency and to establish associations between disease states and a multitude of other variables such as heart defects and maternal diabetes. These observational studies establish statistical associations (but not cause and effect) that are useful for (1) developing diagnostic screening studies; (2) defining heritability and recurrence risk; (3) evaluating the contribution of candidate genes identified in high-risk families or experimental models to disease in the general population; (4) characterizing environmental risk factors; (5) developing testable hypotheses regarding etiology and pathogenesis; and (6) planning for effective delivery of health care services.

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All epidemiologic studies begin with measures of disease frequency. The two most common measures are prevalence and incidence.

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  1. • Prevalence is the proportion of the population at risk affected by disease at a given point in time. Prevalence excludes those who have already died from the disease, those in whom the disease has been cured or has spontaneously resolved, and those with undetected disease. Prevalence answers the question, “how many people have this disease in this place, at this time?”

    • Incidence is expressed as a rate and is defined as the number of new cases among those at risk within a population over a certain period of time. Incidence answers the question, “how often does this disease occur?” For congenital heart disease, the total population at risk includes all embryos. However, even with advances in fetal echocardiography, the true incidence of congenital heart disease is difficult to measure. Many cardiovascular defects are associated with spontaneous abortion and stillbirth so that many of those embryos are never known to have heart disease. The prevalence of congenital heart disease is estimated to be about 15% in fetuses that have been spontaneously aborted and about 8% in stillborn infants. Based on these data, it is apparent that the true incidence of congenital heart disease is much greater than that reported in studies of the frequency of congenital heart disease at birth. Although incidence at birth is most frequently reported and is probably the most useful concept for the clinician, this figure must be interpreted with caution because the entire population with congenital heart disease is not considered. Consequently, the importance of chromosomal and genetic factors which are associated with spontaneous abortion or stillbirth will be underestimated.

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Counting congenital heart disease cases after birth depends on the accurate detection of persons with various cardiac defects, and the accuracy of detection depends on the method used. No one method ...

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