also been tested, including the dopaminergic, glutamatergic, GABAergic, and serotonergic [8–10] systems. The candidate gene approach relies on a prior hypothesis of functionally plausible genes, yet has yielded few robust or replicated findings, being limited by a number of flaws including a neglect of the false positive rate inherent in genetic studies. One can posit that other biological systems, hitherto untested, may be relevant and indeed provide information related to mechanisms underlying heroin addiction; the genome-wide approach which is agnostic to prior hypotheses offers the opportunity of finding such novel genetic variants.
