Definition: Genetic disorders resulting from the combined action of alleles of more than one gene (e.g., heart disease, diabetes, and some cancers). Although such disorders are inherited, they depend on the simultaneous presence of several alleles; thus the hereditary patterns are usually more complex than those of single- gene disorders. (In contrast, a single-gene disorder is a hereditary disorder caused by a mutant allele of a single gene.)
Source: Genetic and Rare Diseases (GARD) Information Center