Transposition of the great vessels in an infant exposed to massive doses of oral contraceptives

Cardiac Development and Factors Influencing the Development of Congenital Heart Defects (CHDs): Part I

The traditional description of cardiac development involves progression from a cardiac crescent to a linear heart tube, which in the phase of transformation into a mature heart forms a cardiac loop and is divided with the septa into individual cavities. Cardiac morphogenesis involves numerous types of cells originating outside the initial cardiac crescent, including neural crest cells, cells of the second heart field origin, and epicardial progenitor cells. The development of the fetal heart and circulatory system is subject to regulatation by both genetic and environmental processes. The etiology for cases with congenital heart defects (CHDs) is largely unknown, but several genetic anomalies, some maternal illnesses, and prenatal exposures to specific therapeutic and non-therapeutic drugs are generally accepted as risk factors. New techniques for studying heart development have revealed many aspects of cardiac morphogenesis that are important in the development of CHDs, in particular transposition of the great arteries.

Some Isolated Cardiac Malformations Can Be Related to Laterality Defects

Human beings are characterized by a left–right asymmetric arrangement of their internal organs, and the heart is the first organ to break symmetry in the developing embryo. Aberrations in normal left–right axis determination during embryogenesis lead to a wide spectrum of abnormal internal laterality phenotypes, including situs inversus and heterotaxy. In more than 90% of instances, the latter condition is accompanied by complex and severe cardiovascular malformations. Atrioventricular canal defect and transposition of the great arteries—which are particularly frequent in the setting of heterotaxy—are commonly found in situs solitus with or without genetic syndromes. Here, we review current data on morphogenesis of the heart in human beings and animal models, familial recurrence, and upstream genetic pathways of left–right determination in order to highlight how some isolated congenital heart diseases, very common in heterotaxy, even in the setting of situs solitus, may actually be considered in the pathogenetic field of laterality defects.

Transposition of great arteries: new insights into the pathogenesis

Transposition of great arteries (TGA) is one of the most common and severe congenital heart diseases (CHD). It is also one of the most mysterious CHD because it has no precedent in phylogenetic and ontogenetic development, it does not represent an alternative physiological model of blood circulation and its etiology and morphogenesis are still largely unknown. However, recent epidemiologic, experimental, and genetic data suggest new insights into the pathogenesis. TGA is very rarely associated with the most frequent genetic syndromes, such as Turner, Noonan, Williams or Marfan syndromes, and in Down syndrome, it is virtually absent. The only genetic syndrome with a strong relation with TGA is Heterotaxy. In lateralization defects TGA is frequently associated with asplenia syndrome. Moreover, TGA is rather frequent in cases of isolated dextrocardia with situs solitus, showing link with defect of visceral situs. Nowadays, the most reliable method to induce TGA consists in treating pregnant mice with retinoic acid or with retinoic acid inhibitors. Following such treatment not only cases of TGA with d-ventricular loop have been registered, but also some cases of congenitally corrected transposition of great arteries (CCTGA). In another experiment, the embryos of mice treated with retinoic acid in day 6.5 presented Heterotaxy, suggesting a relationship among these morphologically different CHD. In humans, some families, beside TGA cases, present first-degree relatives with CCTGA. This data suggest that monogenic inheritance with a variable phenotypic expression could explain the familial aggregation of TGA and CCTGA. In some of these families we previously found multiple mutations in laterality genes including Nodal and ZIC3, confirming a pathogenetic relation between TGA and Heterotaxy. These overall data suggest to include TGA in the pathogenetic group of laterality defects instead of conotruncal abnormalities due to ectomesenchymal tissue migration.

A multiple retinoic acid antagonist induces conotruncal anomalies, including transposition of the great arteries, in mice

BACKGROUND

The morphogenetic mechanisms that are responsible for the transposition of the great arteries are still largely unknown, mainly because this malformation is very difficult to experimentally reproduce. The aim of the present study was to test the effect of BMS-189453, a retinoic acid antagonist, on murine heart morphogenesis.

METHODS

We administered this drug at 5 mg/kg body weight (twice, at a 12-h interval) to pregnant mice on 6.25/6.75 days postcoitum (dpc) (Group A), 6.75/7.25 dpc (Group B), 7.25/7.75 dpc (Group C), 7.75/8.25 dpc (Group D), or 8.25/8.75 dpc (Group E). At birth, the anatomical features of fetuses were evaluated by stereomicroscopic examination.

RESULTS

In Group A (18 fetuses), cardiovascular anatomy was normal in 10 (56%) cases, and 8 (44%) fetuses presented with transposition of the great arteries. In Group B, no fetuses were obtained. In Group C (78 fetuses), cardiovascular anatomy was normal in 19 (24%) cases, while 59 (76%) mice presented with various types of cardiac defects, including 48 transpositions of the great arteries (61%). In Group D (80 fetuses), cardiac defects were seen in 22 (27%) mice: 14 of these (17%) were transpositions of the great arteries. In Group E (72 fetuses), cardiovascular anatomy was normal in all cases. Of 248 fetuses analyzed, 87% presented with thymic aplasia or hypoplasia, and 20% presented with meroanencephalia and/or rachischisis.

CONCLUSIONS

Transposition of the great arteries can be consistently reproduced in mice by administration of a retinoic acid competitive antagonist on 7.5 dpc.