The strength of this study lies in the homogeneous and novel population sample, and one that is not confounded by addiction to other drugs of abuse. We have identified suggestive association with a number of functionally plausible genes that might play a role in heroin dependence. Although the genes did not reach genome-wide significance, their putative role in addiction has been implicated through a range of post hoc analyses, such as our analysis of polygenic risk scores which revealed suggestive evidence that smoking-related behaviours may be modestly predictive of heroin addiction. Specifically, we find suggestive association with age at first cigarette, and ‘ever smoked’, which may indicate an overlapping susceptibility to novelty-seeking behavior; this may be confirmed in the future using higher-powered GWAS. Other genetic studies using Han Chinese subjects have tested similar sample sizes, of about 300 individuals [74]. Collecting large scale samples is difficult for substance use disorders such as heroin addiction; nonetheless, in order to achieve robust results, whether at the SNP level, gene or pathway level, a substantially larger sample size, in the range of tens
