Yet, only the FOS binding site, a repressor of JCPyV infection, occurred more frequently in block “d” of CSF sequences isolated from patients with PML and HCV-related liver disease and patients with PML and Sarcoidosis compared to sequences isolated from the urine of healthy individuals (unadjusted p < 0.01, Figure 2D). Here, FOS is linked to progressive multifocal leukoencephalopathy.