MMN In a national study on MMN we identified 97 patients. Eighty-eight patients participated in our study. Multivariate analysis showed that axon loss and longer disease duration without IVIg were independent determinants of more severe weakness and disability. IMMUNE PATHOGENESIS Prevalence and specificity of antibodies against single gangliosides and ganglioside complexes in serum were investigated. Anti-ganglioside IgM antibodies in MMN had a surprisingly limited specificity (against GM1, and occasionally against GD1b and GM2). Therefore, we investigated whether anti-ganglioside antibodies also showed limited clonality. Using light chain analysis of anti-GM1 IgM antibodies, we demonstrated that serum anti-GM1 IgM antibodies in the majority of patients with MMN have the same Ig light chain, suggesting that these antibodies are monoclonal. Patients with anti-GM1 IgM antibodies had more disability, more axon loss and more severe weakness compared to patients without anti-GM1 IgM antibodies.These findings support the assumption that antiganglioside IgM antibodies play a role in MMN pathogenesis. It is not clear whether MMN is a ‘classic’ autoimmune disease (AID). Since different AID often co-occur within patients and their families, we studied the prevalence of AID among MMN patients and their families. In a case-control study encompassing 81 MMN patients and 417 first-degree relatives, and 438 controls and 2,377 first-degree relatives we found that AID are more common in MMN patients (11%) compared to controls (5%). We also studied variation in the activity of the classical and lectin pathway of the complement system in MMN patients and controls. We found no difference in activity of both pathways and complement activity was not associated with outcome of MMN. GENETICS The human leukocyte antigen (HLA) locus is highly heterogeneous, and several HLA alleles have been found associated with AID. A case-control study showed that HLA-DRB1*15 is associated with MMN. Although this finding may support the hypothesis ...