Unraveling De Novo Copy Number Variants in Congenital Heart Defects: The Bottom of the Iceberg Is Under Attack.

During the 1980s, it was commonly accepted that congenital heart defects (CHDs) were secondary to multifactorial components. Nora and Nora presented a graph of a Gaussian curve with a vertical bar. Individuals of a general population were under the curve with individuals on the left side of the Gaussian curve carrying the least amount of CHD genetic predisposing factors and individuals on the right side carrying the greatest amount of genetic predisposing factors. The vertical bar symbolized the environment. Among the population, only those who were on the right of the environmental bar had a CHD. The bright side of this presentation was that you could easily explain any case of CHD whether sporadic or familial. The negative side of the concept was that it was depressing for those who envisaged deciphering CHD predisposing factors because the large number of environmental and genetic factors suggested by the graph meant that each of them had a small effect.