In Phenome-wide MR Analysis, XBP1 was shown to play a role in the risk of endocarditis, and considering that the correlation between AF and infective endocarditis has been pointed out, (Ferrera et al., 2016) we hypothesized that this may be one of the mechanisms by which XBP1 causes the development of AF. The gene discussed is XBP1; the disease is endocarditis.