Fig. 4

Scatterplots for CpG methylation and CHRNA5 mRNA expression in BrainCloud and MuTHER. CHRNA5 expression is moderately correlated with CpG methylation measured in the BrainCloud prefrontal cortex data by probes cg22563815 (a) and cg17108064 (b). Similar results were obtained for the same probes in the MuTHER adipose tissue (c and d). However, the correlation between expression and CpG methylation is explained by rs7164030 genotype, apparent by the stratification of the genotype groups in the scatterplots (A/A = red circles, A/G = blue squares, G/G = black diamonds). Furthermore, linear regression performed within each genotype group finds no significant relationship between methylation and expression, arguing against direct modulation of expression by methylation