CHRNB1 and Alzheimer disease: Of note, although the DHR residing in the transcription start site (TSS) of CHRNB1, of which all probes show hyperhydroxymethylation in the AD cases, did not correlate with CHRNB1 mRNA expression (ρ = − 0.09, pFDR > 0.05), a linear regression analysis of regressed MTG expression data of CHRNB1 showed a significant elevation of CHRNB1 mRNA levels in AD cases (estimate = 0.13, p = 1.37E−04) (Additional file 2: Figure S4).