LY9 and progressive multifocal leukoencephalopathy: Based on the results of the association analysis in the drug-exposed PML cases, a panel of four rare variants in genes (C8B, FCN2, STXBP2, and LY9) with strong immune-linked biology was identified as being potentially useful to identify patients at high risk of PML (see Supplementary Table 9 for analysis of the four individual variants vs. the 4-variant panel test in three different groups of PML cases: All, any Drug-exposed, and Natalizumab-exposed).