In EAs, we identified one GWS signal, mapped near the CACNA2D1 locus. This gene encodes a protein that is part of a calcium channel (27)—we previously identified calcium signaling genes as important for risk for opioid (2) and cocaine (1) dependence. Variation at this locus, the protein product of which interacts indirectly with the μ-opioid receptor (28), has previously been associated with opioid sensitivity in a small human sample (29).
