Figure 2.

Maternal and fetal risk factors in congenital heart block (CHB). Environmental and genetic factors that have been implicated in the development of CHB to date are depicted. Whereas maternal major histocompatibility complex (MHC) genes influence the generation of autoantibodies, fetal genes influence the susceptibility of the fetal heart to the pathogenic effects of maternal antibodies. Both the age of the mother and the winter season at the time of pregnancy have recently been linked to CHB. It is possible that an increased risk for CHB with increased maternal age corresponds to the appearance of pathogenic autoantibodies. Further studies are needed to elucidate how other factors linked to age, as well as possible events linked to the winter season, may influence the risk for CHB. Low levels of vitamin D and increased rates of infection have been suggested as potential risk factors that account for the risk association with the winter season. AV, atrioventricular; TGFβ, transforming growth factor-beta.