Identification of MUC5AC-associated core genes. Shown is a volcano plot comparing the normalized expression of gene probe sets in the 10-12th order brushed airway epithelial cells of nonsmoker-high MUC5AC expressors vs low MUC5AC expressors; y-axis - negative log of p value; x-axis - log2-transformed fold-change; red dots - probe sets with significant p value; blue dots - probe sets with non-significant p value. Differentially expressed genes were determined by unequal variance Student’s t-test followed by Benjamini-Hochberg correction (p < 0.05). There were 528 genes identified genome-wide that were significantly correlated with MUC5AC high expressors. Of these, 73 genes were identified as MUC5AC-associated core genes based on literature mining (Table1, Additional file 1: Table S1, S2).