Abundant kif21b expression is associated with a shorter disease duration and accelerated progression to sustained neurological disability. Kif21b expression was correlated with the disease duration of A) Alzheimer patients and B) multiple sclerosis patients. In both diseases, shorter disease duration was associated with abundant kif21b expression. C) Kif21b expression in MS patients was dichotomised for the expression above the median and below the median and survival analysis was performed in MS patients. MS patients with kif21b expression above the median had a significantly shorter time to develop EDSS 6.0, the neurological score for sustained disability. D) The time to develop EDSS 6.0 was stratified according to kif21b MS risk SNP carriership. The rs12122721 [A] SNP is not associated with accelerated time to develop EDSS 6.0.