Based in part on a report of an MS cohort with overrepresentation of specific BAFF-related polymorphism that could lead to B-cell dysregulation (19), we next examined levels of the protein, B cell activation factor (BAFF), also termed B lymphocyte stimulator, that affects the survival of cells of the B lineage. The gene discussed is TNFSF13B; the disease is myeloid sarcoma.