HLA-DRB1 and secondary progressive multiple sclerosis: After excluding all SPMS patients, there were still no differences in the frequencies of either allele between northern and southern patients (HLA-DRB1 04:05, 37.6 vs. 43.7 %, p = 0.2403; HLA-DRB1 15:01, 30.9 vs. 27.5 %, p = 0.4816) (Additional file 2: Table S5).