the variability in mRNA expression [23]. Differential allelic expression of CHRNA5 was also detected in normal lung tissue and in lung adenocarcinoma; two single nucleotide polymorphisms (rs55853698 and rs55781567) in the 5′UTR of CHRNA5 were associated with significant imbalance in allelic expression ratio [24]. However, another study with 6 samples derived from human frontal cortex, amygdala or nucleus accumbens showed only one of the 6 samples revealed significant CHRNA5 allelic expression imbalance in amygdala and nucleus accumbens, but not in frontal cortex [25]. The subject which showed allelic expression imbalance was heterozygous for 2 SNPs in ∼13.5 kb region upstream of the gene, but was homozygous for the variant (rs3841324) in the promoter region adjacent to CHRNA5 transcription start site [25].
