Consistent across ‘all first demyelinating event’ and those with a first demyelinating event only at baseline interview, older age at baseline, higher past sun exposure, and an HLA-B SNP were associated with lower risk of progression to clinically definite multiple sclerosis, while SNPs within the vitamin D-binding protein gene and TNFRSF1A, and the presence of infratentorial lesions on baseline MRI, were associated with increased risk. Here, HLA-B is linked to multiple sclerosis.