C. Family, adoption and twin data that each support substantial polygenic heritability for addictions Current models for the genetic architecture for substance dependence in the population are based on information from: 1) family, adoption and twin data that each support substantial heritability for addictions, 2) twin data (in which concordance in genetically-identical monozygotic and genetically-half-identical dizygotic twins are compared) that document that most of this heritable influence is not substance-specific, 3) linkage based (and genome wide association) studies that fail to provide evidence for genes of major effect (eg for any single gene whose variants produce substantial differences in addiction vulnerability) for substance dependence.
