Contactin 1, a Potential New Antigen Target in Membranous Nephropathy: A Case Report.

Several novel antigens have recently been characterized in membranous nephropathy (MN), but those involved in the rare cases of MN associated with inflammatory neuropathies (IN) remain elusive. Although several antibody specificities were identified in the serum, there is no evidence so far for their deposition in glomeruli. We report the case of a 73 y/o woman who was referred because of subacute onset of proximal asymmetric lower limb weakness together with ataxic gait. She was diagnosed with IN. Blood tests showed an eGFR of 73 ml/min/1.73m2, hypoalbuminemia (2.89 g/dl) and proteinuria (3.6 g/24h). Autoantibodies (ANA, ENA, DNA, LAC, anti-cardiolipin, ANCA) were undetectable. Serum Ig and complement levels were normal. A kidney biopsy with electron microscopy examination showed a classical picture of MN. Anti-PLA2R antibody was negative in the serum and PLA2R and THSD7A antigens were not detected in kidney tissue. Anti-contactin1 (CNTN1) antibody was found by ELISA at 1:100 serum dilution and shown to be mostly of IgG4 subclass by Western blot. CNTN1 antigen was co-localized with IgG4 within immune deposits by confocal microscopy. This observation suggests a pathophysiological link between IN and MN. CNTN1 should be considered as a potential candidate antigen involved in MN and tested in PLA2R negative forms associated with IN.