Antibodies against the CNTN1/CASPR1 complex occur in a subset of patients with CIDP who share common clinical features. The finding of this biomarker may help to explain the symptoms of these patients and the heterogeneous response to therapy in CIDP.

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is a heterogeneous disease in which diverse autoantibodies have been described but systematic screening has never been performed. Detection of CIDP-specific antibodies may be clinically useful. We developed a screening protocol to uncover novel reactivities in CIDP. Sixty-five CIDP patients and 28 controls were included in our study. Three patients (4.6%) had antibodies against neurofascin 155, four (6.2%) against contactin-1 and one (1.5%) against the contactin-1/contactin-associated protein-1 complex. Eleven (18.6%) patients showed anti-ganglioside antibodies, and one (1.6%) antibodies against peripheral myelin protein 2. No antibodies against myelin protein zero, contactin-2/contactin-associated protein-2 complex, neuronal cell adhesion molecule, gliomedin or the voltage-gated sodium channel were detected. In IgG experiments, three patients (5.3%) showed a weak reactivity against motor neurons; 14 (24.6%) reacted against DRG neurons, four of them strongly (7.0%), and seven (12.3%) reacted against Schwann cells, three of them strongly (5.3%). In IgM experiments, six patients (10.7%) reacted against DRG neurons, while three (5.4%) reacted against Schwann cells. However, results were not statistically significant when compared to controls. Immunoprecipitation experiments identified CD9 and L1CAM as potential antigens, but reactivity could not be confirmed with cell-based assays. In summary, we describe a diverse autoantibody repertoire in CIDP patients, reinforcing the hypothesis of CIDP's pathophysiological heterogeneity.Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is a disabling disease with a pathogenesis that remains largely unknown 1 . CIDP response to immune therapies and scarce experimental evidence on passive transfer animal models suggest that humoral factors play a role in its pathogenesis 2 . CIDP diagnosis is based on clinical and electrophysiological criteria 3 that allow the inclusion of a broad spectrum of patients within CIDP, including typical and atypical variants. This heterogeneity has hindered the description of disease-specific biomarkers, despite intensive research efforts 4 .The response of CIDP patients to intravenous immunoglobulin (IVIg) and plasma exchange (PlEx) suggests that humoral factors are involved in its pathogenesis. The search of autoantibodies has been the most important laboratory research topic in CIDP. Initial focus was placed on myelin antigens. Classical studies, using diverse techniques, detected higher frequencies of antibodies against myelin protein zero (MPZ), peripheral myelin protein 2 (PMP2) or peripheral myelin protein 22 (PMP22) [5][6][7][8][9][10] . However, meaningful clinical-immunological correlations with those antigens were not established. CIDP patients harboring antibodies against LM1-containing