CNTN1 and idiopathic membranous glomerulonephritis: In contrast to PLA2R, which is undetectable in the serum of either controls or anti-PLA2R MGN patients [7], we detected CNTN1 protein in the serum of healthy controls, as well as seronegative CIDP and other forms of nephrotic syndrome, but levels were significantly lower in CNTN1 antibody-positive patients (Fig 2).