subjects, identified only nominally significant SNP associations.(Agrawal et al., 2014; Liu et al., 2013; Nielsen et al., 2010; Uhl et al., 2008) In this study, we assembled a cohort of 10,587 subjects (3,742 AAs and 6,845 EAs) to conduct the largest GWAS of drug abuse, other than nicotine or alcohol, to date. Drug abuse cases were street-recruited people who inject drugs (PWID) and who reported abusing opioids, cocaine, marijuana, stimulants, and/or other drugs 10 or more times in the past 30 days – a phenotype highly predictive of clinical abuse/dependence (see Methods). Resembling approaches taken elsewhere (Cross-Disorder Group of the Psychiatric Genomics, 2013; Ruderfer et al., 2013; Steinberg et al., 2014; Wetherill et al., 2014; Yu et al., 2014), combining cases who abuse drugs across one or more categories for GWAS analyses focuses discovery on identifying variants that contribute the genetic susceptibility shared across drugs.
