The main breakthrough in this neuropathy was the discovery by Latov and colleagues of IgM immunoreactivity to myelin-associated glycoprotein (MAG), a 100 kDa glycoprotein of the central and peripheral nerve myelin.17 Sera from approximately 50% of these patients react with MAG or with acidic glycolipids that share antigenic determinants with MAG10,16, , –19 and reside in the carbohydrate component of the MAG molecule, as we have demonstrated by loss of reactivity after deglycosylation of purified MAG18 (Figure 2A). This evidence concerns the gene CD40LG and neuropathy.