Genetics and congenital heart disease: perspectives and prospects

Genetic counseling for congenital heart disease: new approaches for a new decade

Congenital heart disease (CHD), which occurs in about 0.7% of all live-born children, is the leading cause of death from birth defects. Understandably, parents of patients, and increasingly patients themselves, are interested in the risk that further offspring will be affected. Advances in genetics now permit accurate estimation for many forms of CHD, especially the identification of patients and families with recurrence risks of up to 50%. The increased availability of genetic information, combined with the use of noninvasive imaging to look for subtle defects and targeted genetic testing, have demonstrated that the relevant question to ask about an individual's apparently isolated CHD is whether it is syndromic or familial. Syndromes that involve clinically important noncardiac findings may best be managed by, or in consultation with, a clinical geneticist. Other familial syndromes remain entirely within the purview of the cardiologist. The practicing cardiologist needs to continue to stay abreast of genetic discoveries in the field of CHD in order to provide proper management, including genetic counseling, to patients and their families.

The genetic basis of paediatric heart disease

This review focuses on recent advances in understanding the pathogenesis of paediatric heart disease and on the known single gene defects responsible for these diseases. Many paediatric cardiovascular diseases are heritable, have clinical manifestations in adult ages, are frequent in occurrence, and can have significant social and economic impact. Specific gene defects have been identified for hypertrophic and dilated cardiomyopathies, mitochondrial cardiomyopathies, Marfan's syndrome, Williams syndrome, familial supravalvar aortic stenosis, CATCH-22 syndrome and atrioventricular canal. Limited phenotypic response of the developing heart accounts for similar cardiovascular defects from differing gene defects. Although environmental factors affect expression of many of these genes, it is clear that single gene defects can be identified which cause paediatric cardiovascular disease. Interactions among cardiologists, cardiovascular surgeons, geneticists and basic scientists are vitally important in understanding the genetic basis of paediatric heart disease, its diagnosis and its therapy.

A second-generation study of 427 probands with congenital heart defects and their 837 children

OBJECTIVES

This study attempted to answer the question, Do mothers with congenital cardiovascular defects have more affected children than fathers with cardiac anomalies?

BACKGROUND

In the 1950s to 1960s, concern was expressed about the safety of pregnancy in women with cardiac anomalies and the possibility of inheritance.

METHODS

In a prospective study over 25 years, 236 women with cardiac defects were followed through pregnancy, and their 418 offspring were examined during their 1st 3 years. A high incidence of congenital cardiac malformations was noted. Then, a retrospective study of 191 men from the same clinic group and their total family (419 children) was performed to compare the incidence of affected children between the maternal study and this subsequent paternal study.

RESULTS

Of 837 live children of these 427 probands, 14.1% (118) had a congenital heart defect (13.4% in the maternal study, 14.8% in the paternal study). There was no correlation with the surgical status of the proband. Concordance was somewhat greater among the children of affected mothers compared with those of affected fathers. Included in these studies were 31 high risk probands, 10 with genetic syndromes and 21 who had an affected sibling. Respectively, 53% and 41% of their children had cardiac anomalies, with a concordance > 50%; three fourths of these children had moderate to severe anomalies.

CONCLUSIONS

The incidence of congenital heart defects in the children was not statistically different between the maternal and paternal studies. With removal of the high risk probands from the total study group, the risk of one affected parent having a child with a cardiac anomaly was 10.7%. Of the entire 837 children, only 7.5% had moderate or severe defects.

Epidemiology of congenital heart disease in Louisiana: an association between race and sex and the prevalence of specific cardiac malformations

We hypothesized that susceptibility to the genetic and environmental factors that disrupt cardiac development is associated with race and sex. To evaluate this hypothesis, we asked whether the prevalence of specific cardiac malformations differs by race and sex. We attempted to include all infants born alive in the State of Louisiana from January 1, 1988, through December 31, 1989, and diagnosed by echocardiography, catheterization and/or autopsy within a year of birth as having one of ten specific cardiac malformations. The prevalence of atrioventricular canal defects (AVCD) per 1,000 live births was significantly higher for black females (.744) compared to black males (.198) and for white females (.414) compared to white males (.116). Complete transposition of the great arteries (TGA) was significantly higher for white males (.559) compared to white females (.122); in contrast, TGA was not significantly different for black males (.198) and black females (.169). Obstructive left heart syndrome (OLHS)--aortic stenosis and/or coarctation of the aorta--was significantly higher for white males (.652) compared to white females (.317); in contrast, OLHS was not significantly different for black males (.264) and black females (.169). Single ventricle (SV) was significantly higher for whites (.202) compared to blacks (.067). We did not find that race and sex were associated with differences in the prevalence of tetralogy of Fallot and hypoplastic left heart syndrome. The numbers of infants with anomalous pulmonary venous return, tricuspid atresia, double outlet right ventricle, or truncus arteriosus were too small to measure an association with race and sex. These results demonstrate that the prevalence of a subset of cardiac malformations differs by race and sex.(ABSTRACT TRUNCATED AT 250 WORDS)

Spectrum of heart malformations in mice with situs solitus, situs inversus, and associated visceral heterotaxy

BACKGROUND

We present a study of the heart malformations found in a collection of mouse fetuses of the iv/iv strain between days 16.5 and 18.5 of gestation.

METHODS AND RESULTS

One hundred hearts were serially sectioned and studied by segmental analysis with a light microscope. Forty additional hearts were analyzed with a scanning microscope. Forty percent of the hearts were found to be malformed. The most frequently occurring heart malformations were persistence of the sinus venosus (9%), common atrium (17%), common atrioventricular canal (24%), double-outlet right ventricle (12%), Fallot's tetralogy (8%), and transposition of the great arteries (5%). These malformations do not usually occur in isolation but rather appear in the formation of complex cardiopathies. The most severe and frequent is the combination of persistence of sinus venosus, common atrium, common atrioventricular canal, and double-outlet right ventricle; this is the "bulboventricular heart." The morphology of each lesion, as well as the degree of association, is similar to that found in human hearts with complex cardiopathies. Some of these cardiopathies appear to be directly related to formation of the cardiac loop. The iv/iv mouse appears to constitute an excellent model with which to study the etiology and pathogenesis of complex heart defects in humans. These hearts show a high phenotypic variability in the presentation of heart lesions. From a genetic viewpoint, there is a basic defect--the bulboventricular heart--which can be considered congenital. The other malformations can be considered formes frustes of the defect type.

CONCLUSIONS

The iv gene is a developmental gene that affects basic developmental mechanisms. In this regard, heart lesions may not be the primary result of the abnormal gene activity but rather are secondary to defective interactions during cardiac development.

Fascinating rhythm: a primer on chaos theory and its application to cardiology

Nonlinear dynamics is an exciting new way of looking at peculiarities that in the past have been ignored or explained away. We have attempted to give a general introduction to the basics of the mathematics, applications to cardiology, and a brief review of the new tools needed to use the concepts of nonlinear mathematics. The careful mathematical approach to problems in cardiac electrical dynamics and blood flow is opening a window on behaviors and mechanisms previously inaccessible.

Angular homeostasis: VI. Threshold processes with bivariate liabilities

The general structure of the threshold model of multifactorial determination is discussed. It is supposed that in place of a single liability (in Falconer's sense) there are two separate liabilities; and whether or not the pathological trait is present depends on a non-additive interaction between the liabilities, so that the region has curved boundaries. The genetics of ontogeny of a process involving spatial orientation (e.g., cardiac ontogeny) is used as a substantive illustration. Genetic analysis of the trait (as contrasted with the liabilities) yields results that on the one hand may seem quite counterintuitive, yet on the other hand they correspond to the kind of bizarre patterns encountered in quasi-empirical genetic counseling for cleft palate or neural tube defect. The impact of refinement of phenotype made possible by non-invasive methods is sketched. This model can be generalized to any number of liabilities, independent or not.