Based on van den Akker et al. [22] and Minogue et al. [23], the characteristics of AF-specific gene expression (Table 1) were relative high expression of COL1A1, COL5A1, COL12A1, and SFRP2, and relatively low expression of the COL2/COL1 ratio as compared to NP cells. The gene discussed is SFRP2; the disease is atrial fibrillation.