Contactin-1 (CNTN1) is a member of the contactin family, proteins that are important for the function and maintenance of myelinated neurons.15,16 CNTN1 is specifically expressed in paranodal axonal domains and involved in myelin formation in the CNS due to its role in axo–glia interaction, the loss of which forms an important cause of neuronal dysfunction and subsequent axonal loss in MS.17, –19 Although primarily expressed in the CNS, CNTN1 is present in the peripheral nervous system (PNS) as well.20,21. This evidence concerns the gene CNTN1 and myeloid sarcoma.