SOSTDC1 and atrial fibrillation: Analysis of the NP-specific marker genes (SNAP25, KRT8, KRT18, KRT19, CDH2 and SOSTDC1; Figure 3a) demonstrated significantly higher expression in NP cells when compared with either AF (all genes P < 0.0001) or AC cells (all genes P < 0.0001), which confirmed the microarray findings.