IgG4 antibodies have unique properties, including being functionally monovalent as a result of hemi-antibody exchange, having very high affinities, and not fixing complement.20 IgG4 antibodies to CAMs like neurofascins may act by disrupting their interactions with other CAMs.21 Testing for IgG4 to NF155, not just IgG to NF155, may increase the specificity of a positive finding for treatment-resistant CIDP. The gene discussed is NFASC; the disease is chronic inflammatory demyelinating polyradiculoneuropathy.