Presently, only three GWAS has been conducted investigating responses to stimulant drugs. One study investigated the therapeutic response to methylphenidate (Mick et al. 2008). Children diagnosed with ADHD (n = 187), received varying doses of methylphenidate over a 5-week period, and were phenotyped with the ADHD-RS IV scale and then genotyped at about 300,000 SNPs. No associations reached genome-wide significance, and the strongest associations were not in genes examined in any previous candidate gene studies. Two studies have examined genetic variation underlying stimulant abuse. Uhl et al. (2008) used a case–control nested study to investigate genetic variants underlying methamphetamine dependence, with the goal of identifying genes with an unexpected accumulation of low p-values, and Yu et al. (2008) took a family-based association test (FBAT) approach and scanned evenly spaced markers for association with cocaine dependence and cocaine-induced paranoia. As previously mentioned, the association between MANEA SNP (rs1133503) and cocaine-induced paranoia was the most significant result in this study, but after correction for multiple testing this result was not statistically significant.
