ABO and progressive multifocal leukoencephalopathy: Despite these limitations, our study is in line with a published literature (Khoury et al., 2013), and meta‐analysis of the ABO distribution of the German PML patients included in this study and a US PML population depict a consistent trend with blood group O in PML in 60 of 124 individuals (48.4% (95% CI 39.8%–57.1%)).