Previous studies have shown that OPN levels are increased in secondary progressive MS (SPMS; Comabella et al., 2005; Romme Christensen et al., 2013; Shimizu et al., 2013), PPMS and RRMS (Vogt et al., 2003; Romme Christensen et al., 2013). Here, SPP1 is linked to secondary progressive multiple sclerosis.