CHRNA4 and Norrie disease: There were three objectives of this study: (1) to determine which individual SNPs or haplotypes in nAChR subunit genes are associated with ND in a Chinese Han smoker sample, a less commonly investigated population; (2) to detect significant interactive effects among these genes in exerting influence on the etiology of ND; and (3) to link risk variants for ND and differential DNA methylation loci by cis-mQTLs analysis to explore the underlying mechanisms involved in ND.