Sections
Genetics of Addiction: Introduction | Importance of Genes for Drug Dependence Risk | Genomewide Linkage and Association Studies | Candidate Gene Studies | Gene-by-Environment Interaction | Genes That Influence Risk, and the Nature of Their
Effects | Key Points | References | Suggested Reading
Excerpt
Like other important psychiatric traits, substance
dependence (SD) is genetically influenced, and this genetic influence
is complex. This means that the genetic influence plays out in something
other than a Mendelian mode (i.e., dominant, recessive, or X-linked),
and, practically speaking, this means there are many genes involved—none
of which ever fully determines that a person will be affected. Moreover,
as with other complex traits, SD risk is influenced by both genetic
and environmental factors. But in the case of SD risk there is a
special twist: there is a necessary component
of gene-by-environment interaction. A person cannot become substance
dependent without exposure to the substance, regardless of genetic
constitution. This places a trait like cocaine dependence (you cannot
be cocaine dependent if you do not have access to cocaine) in contrast
to a trait like schizophrenia, in which, as far as we know, special
environmental exposure is not required for the condition to develop.