[Congenital heart disease, heterotaxia and laterality].

Congenital heart disease occurs in about 0,8% of all newborns. Many cardiac malformations occur among relatives and have a polymorphic presentation. The origin of most congenital heart disease is thought to be multifactorial, implying both anomalous expression of genes and the influence of epigenetic factors. However, in a small number of cases, the origin of congenital heart disease has been directly related to chromosomal anomalies or to defects in a single gene. Curiously, defects in a single gene can explain a polymorphic presentation if the anomalous gene controls a basic embryonic process that affects different organs in time and space. Some of these genes appear to control the establishment of laterality. The establishment of the left-right asymmetry starts at the Hensen node. Here, the initial embryonic symmetry is broken by cascades of gene activation that confer specific properties on the left and right sides of the embryo. Although there are variations between species, some basic patterns of gene expression (Nodal, Pitx2) appear to be maintained along the phylogenetic scale. Anomalous expression of these genes induces the heterotaxia syndrome, which usually courses with congenital heart disease. The development of heart malformations is illustrated with the mouse mutant iv/iv, which is a model for the heterotaxia syndrome and the associated congenital heart disease.