Following quality control and imputation, data was available on 4,009,606 markers genome-wide, in 504 individuals. We performed association testing between 370 cases and 134 controls, adjusting for population structure using two ancestry-informative dimensions generated using multidimensional scaling. We found no evidence for residual population structure after using these covariates, as shown in the QQ plot in Fig 1 (GWAS λ median = 1.026). In this study, the most significant markers demonstrated p-values of 10−7 (Table 2). Association testing identified suggestive association between heroin dependence and several markers located within genes that may be of relevance to heroin dependence; the 25 most associated independent markers are listed in Table 2. Among these were several markers located on chromosome 17p13.1; indeed the three most associated genotyped SNPS were all located either in or near the gene CCDC42 (coiled coil domain containing 42) on chromosome 17 (see Table A in S2 File for details on the 100 most associated genotyped SNPs). Many of the top markers are located within or close to the genes CCDC42, BRSK2 (BR serine/threonine kinase 2), ZNF546 (zinc finger protein 546), CHIT1 (chitinase 1) and PPP1R12B (protein phosphatase 1, regulatory subunit 12B) and NEK1 (NIMA-related kinase 1).
