PML and progressive multifocal leukoencephalopathy: However, differently from HC, in whom predominant usage of the IGHJ4 gene is observed46, in our PML patients, two IGHJ were almost equally represented, with IGHJ6 being the most abundant, followed by IGHJ4. Finally, despite the preferential usage, rearrangement and joining of certain V and J genes, a no dominant or common features of IGH sequences were observed at PML onset.