In order to test this hypothesis, we have chosen to examine the potential contribution of the susceptibility SNPs in IL2RA, IL7R, CLEC16A, RPL5, CD40, CD58 and the Chr12 loci to MS severity, using a well-defined cohort of 1006 patients with relapsing-remitting and secondary progressive MS from Australia. Here, IL7R is linked to myeloid sarcoma.