In our study, the observed association between cell cycle control genes and quit status may be driven by association of SNPs at FBXL17 (gene-level, p = 0.021, rs1433050) and NFKB1 (rs10489113, gene-level P = 0.022). FBXL17 is one of 68 members of the human F-box protein superfamily, a large group of ubiquitin ligases [85]. Ubiquitin ligases function in the ubiquitin-proteasome complex, which regulates protein assembly, trafficking and degradation, a cellular activity itself regulated by nicotine [86]. FBXL17 was also identified in the NICSNP GWAS [59] as significantly associated with FNTD, via another SNP (rs10793832). None of the SNPs in the same high linkage-disequilibrium bin as rs10793832 (according to the Pelegen genome browser) were in high linkage disequilibrium with rs1433050, the FBXL17 SNP identified in this study. One SNP genotyped in this study (rs885624) was in the same LD block as rs10793832 but was not significantly associated with quit status in either this study alone or in the combined analysis (p = 0.39).
