1 Departments of Genetics, Pediatrics, Preventive Medicine, and Biometrics, University of Colorado, School of Medicine, Denver, CO 80262
To the Editor.
Newman1 has restated the multifactorial inheritance hypothesis of the etiology of congenital heart diseases to emphasize the element of chance (which is, of course, inherent in the hypothesis) and proposes what he considers to be a new hypothesis. There is, of course, a very large element of chance in multifactorial inheritance for an individual with a genetic predisposition to ventricular septal defect or other congenital heart defect also to have a genetic predisposition to an environmental teratogen and finally to have these two predispositions triggered during the very short vulnerable period of cardiogenesis (approximately 1 month or less in duration for most lesions).