Applying VEGAS2 [25] to the results of our genome-wide association results identified two genes CCDC42 and SPDYE4 meeting the significance threshold of α = 2.85x10-6 (Table 3), as suggested by Liu et al [26]. This threshold is likely to be overly conservative, meaning that the data provides good evidence for an association between these genes and heroin dependence; it should be noted that the two genes are located close to each other and may represent a single association signal. The VEGAS2 output represents non-significant regions from GWAS attaining significance in gene-based analysis; this is consistent with multiple relatively independent causal loci within the same gene. This is supported by multiple relatively independent signals in CCDC42 after clumping.
