All the other signals reported by only one GWAS or meta-GWAS can be found in Table 3 and Figure 1, among which a missense variant rs6265 in BDNF was significantly associated with smoking initiation and an intergenic variant rs3025343 close to DBH was implicated in smoking cessation.16 It is worth noting that GWASs without GWS variant identification still render valuable information in determining susceptibility loci for ND. The first ND GWAS, performed by Bierut et al.,92 nominated NRXN1 in the development of ND, which was validated by a subsequent candidate gene association study.93 By using a network-based genome-wide association approach, Vink et al.87 discovered susceptibility genes encoding groups of proteins, such as glutamate receptors, proteins involved in tyrosine kinase receptor signaling, transporters, and cell-adhesion molecules, many of which were confirmed in later candidate gene association studies.89, 110 Please refer to Supplementary Table 1 for a list of GWASs without GWS results.
