The stable CNTN1 levels in serum are seemingly in contrast to the trend toward higher cross-sectional levels in CSF of SPMS and PPMS patients compared to RRMS that has been reported earlier.22 However, the lower cross-sectional sCNTN1 levels in our RRMS cohort compared to our HC cohort are in accordance with several previous studies. This evidence concerns the gene CNTN1 and secondary progressive multiple sclerosis.