Congenital cardiac malformations can occur with mendelian inheritance directly as a result of a genetic abnormality, be strongly associated with an underlying genetic disorder (e.g., trisomy), be related directly to the effect of an environmental toxin (e.g., alcohol), or result from an interaction between multifactorial genetic and environmental influences too complex to allow a single definition of cause (e.g., CHARGE syndrome; see Syndromes in Congenital Heart Disease later). The last group is shrinking as genetic research identifies new genetic abnormalities underlying many conditions.