Intrathecal IgG synthesis, determined by CSF-specific OCBs, the positive MRZR as well as the number of CSF B cells and plasma cells in MS patients are strongly associated with HLA-DRB1*15:01, while HLA-DRB1*04 is more frequently present in patients without CSF-specific OCBs [4,6]. The gene discussed is HLA-DRB1; the disease is myeloid sarcoma.