Fig. 4
Candidate CpG loci with differential atrial-ventricular methylation pattern. Identified CpG loci (16 loci) and associated genes with greatest DNA methylation value differences (Δβ-value) between atrial and ventricular samples based on the t test (q ≤ 1 × 10−6, σ/σmax > 0.4) comparing 450K array data of 44 atrial and 5 ventricular heart tissue samples (a). All CpG loci show a difference of at least Δβ ≥ 0.4 in their DNA methylation values (see column ‘Δβ(atrium-ventricle)’) between atrial and ventricular samples (b). Additional information regarding chromosomal position (CHR), CpG island regions (N_Shore, 0–2 kb upstream (5′); S_Shore, 0–2 kb downstream (3′) of island) and RefSeq Group gene position annotation (TSS200, 0–200 bases upstream of the transcriptional start site; body, intragenic localization of the CpG site) are given according to Illumina’s 450K array classifications and UCSC classifications [37]. Heart enhancer, overlap of CpG locus with predicted human heart enhancers identified by a study of Dickel et al. [35] are marked as ‘true’ (for details, see Additional file 15: Table S2). These 16 CpG loci were selected as candidate CpG loci to test further sample cohorts using bisulfite pyrosequencing