In contrast, a greater CORT response has been observed in G118 allele-carriers following a naloxone challenge, which may suggest an elevated tonic inhibition of CRF by β-endorphin (Chong et al., 2006; Hernandez-Avila et al., 2007; Hernandez-Avila et al., 2003). Interestingly, one of these studies found population-specific effects in which G118 allele-carriers of European descent displayed elevations in CORT responses to naloxone, while G118 allele-carriers of East Asian descent did not (Hernandez-Avila et al., 2007). These population-specific differences could suggest that the A118G SNP is in high linkage disequilibrium (LD) with other SNPs that may mediate the observed alterations.
