A 2010 study found an increased frequency of the HLA-DRB1*15 gene variant in MMN patients compared to controls, suggesting a genetic component to susceptibility — though no correlation has been found between this variant and age of onset, severity, or course of disease. A separate study tested several other candidate immune-related genes (PTPN22, BANK1, Blk, FCGR2B, CD1A/E, TAG-1) and found no association with MMN susceptibility, narrowing — but not yet answering — the genetic question. Because MMN is so rare, a large genome-wide association study (GWAS) has not been feasible to date; this remains an open area for future multi-center genetic research.