Heroin addiction is a chronic, relapsing brain disease that is characterized by drug dependence, tolerance and compulsive seeking and use despite harmful consequences. This complex disorder is a worldwide major public health problem. The relatively high heritability (40-60%) of this disorder (Tsuang et al., 1996) indicates that genetic variants may play a role in vulnerability to its development. Chronic drug use alters gene expression, which activates or attenuates biochemical pathways and produces neuroadaptive changes in signal transduction functions. Identifying these variants is important for the understanding of the possible causes of this disease and to improve its diagnosis and treatment, as well as for primary prevention purposes.
