SPON1 and atrial fibrillation: Here, MR analysis suggested that five proteins might have a causal role in AF, including higher levels of dual specificity protein phosphatase 13 isoform A (DUSP13), peptidyl−prolyl cis−trans isomerase FKBP7 (FKBP7) and spondin − 1 (SPON1), and lower levels of interleukin 6 receptor (IL-6R) and tumour necrosis factor ligand superfamily member 12 (TNFSF12) (Figure 5A).