Among 10 potential causal variants tested, 4 SNPs, including one synonymous SNP (rs8053), are within the PSMA4 region. PSMA4, which encodes proteasome subunit alpha type-4, was reported as a strong candidate mediator of lung cancer cell growth [30]. Liu et al. [30] reported PSMA4 mRNA levels were increased in lung tumors compared with normal lung tissues. However, no change in PSMA4 mRNA expression was detected in another study of paired normal lung and lung adenocarcinoma tissue [21]. Our eQTL analysis showed none of the variants tested within and flanking CHRNA5 and PSMA4 is associated with PSMA4 total mRNA levels (Table S2). In addition, we did not observe any correlation between CHRNA5 and PSMA4 mRNA expression in the brain samples tested. It is possible that the association between the 4 SNPs in PSMA4 (rs11858230, rs8025429, rs4887062 and rs8053) and the changes in CHRNA5 transcript levels results from the LD between these SNPs with rs880395.
