Detection of PLA2R Autoantibodies before the Diagnosis of Membranous Nephropathy

Abstract

Background: Circulating serum autoantibodies against the M-type phospholipase A2 receptor (PLA2R-AB) are a key biomarker in the diagnosis and monitoring of primary membranous nephropathy (MN). However, little is known about the appearance and trajectory of PLA2R-AB before the clinical diagnosis of MN.

Methods: Using the Department of Defense Serum Repository, we analyzed PLA2R-AB in multiple, 1054 longitudinal serum samples collected before diagnosis of MN from 134 individuals with primary MN, 35 individuals with secondary MN, and 134 healthy volunteers. We evaluated the presence and timing of non-nephrotic range proteinuria (NNRP) and serum albumin measurements in relation to PLA2R-AB status.

Results: Analysis of PLA2R-AB in longitudinal serum samples revealed seropositivity in 44% (59 out of 134) of primary MN cases, 3% (one out of 35) of secondary MN cases, and in 0% of healthy controls. Among patients with MN, PLA2R-AB were detectable at a median of 274 days before renal biopsy diagnosis (interquartile range, 71-821 days). Approximately one third of the participants became seropositive within 3 months of MN diagnosis. Of the 21 individuals with documented prediagnostic NNRP, 43% (nine out of 21) were seropositive before NNRP was first documented and 28.5% (six out of 21) were seropositive at the same time as NNRP; 66% (39 out of 59) of those seropositive for PLA2R-AB had hypoalbuminemia present at the time antibody was initially detected. Twelve participants (20%) were seropositive before hypoalbuminemia became apparent, and eight participants (14%) were seropositive after hypoalbuminemia became apparent.

Conclusions: Circulating PLA2R-AB are detectable months to years before documented NNRP and biopsy-proven diagnosis in patients with MN.

Keywords: glomerular disease; glomerulopathy; membranous nephropathy; nephrotic syndrome; proteinuria.

Graphical abstract

Figure 1.

PLA2R-AB is elevated months to years before MN diagnosis. Longitudinal profile of patients with seropositive PLA2R-AB before clinical diagnosis of MN. Autoantibody analysis identified 59 patients with MN with prediagnostic seropositive PLA2R-AB, in which (A) 33 patients developed seropositivity <1 year before MN diagnosis and (B) 26 patients demonstrated seropositivity >1 year before MN diagnosis. The PLA2R-AB levels in LU derived from serial samples of the seropositive cases are plotted on the y axis using a log10 scale. The cut-off value for determining PLA2R-AB seropositivity is shown by the dotted line. Time zero represents biopsy-proven diagnosis of MN.

Figure 2.

PLA2R-AB can significantly elevate over weeks to months prior to MN diagnosis. Rapid appearance of prediagnostic PLA2R-AB. Autoantibody analysis identified five patients with PLA2R-AB–positive MN that demonstrated a rapid rise from seronegative to significantly elevated in <1 year. The PLA2R-AB levels in LU derived from serial samples of the seropositive cases are plotted on the y axis using a log10 scale. The cut-off value for determining PLA2R-AB seropositivity is shown by the dotted line. Time zero represents biopsy-proven diagnosis of MN.

Figure 3.

In the majority of MN cases, PLA2R-AB is elevated before or at the time of prediagnostic NNRP, a surrogate for the earliest evidence of clinical disease. A flow diagram of the temporal relationship between prediagnostic NNRP and PLA2R-AB. As described in the Methods, examination of the EMR from the 59 patients with MN who were positive for PLA2R-AB found evidence of prediagnostic NNRP in 21 patients. Further analysis was used to segregate the case according to whether NNRP occurred before, at the same time, or after detectable PLA2R seropositivity.

Figure 4.

PLA2R-AB is elevated months to years before NNRP as a surrogate marker for earliest clinical evidence of MN. Examples of MN cases showing seropositive PLA2R-AB before abnormal prediagnostic NNRP. The PLA2R-AB levels are plotted on the y axis and the horizontal dotted line is the cut-off value for determining seropositivity. The first clinical evidence of abnormal prediagnostic NNRP is indicated by time zero.

Figure 5.

PLA2R-AB most often occurs at or before the first documented prediagnostic hypoalbuminemia. A flow diagram of the temporal relationship between prediagnostic serum albumin and PLA2R-AB. As described in the Methods, the serial serum samples from the 59 PLA2R-AB–positive cases were also analyzed for serum albumin levels to determine whether albumin levels were normal or abnormally low before, at the same time, or after detectable PLA2R seropositivity.

Figure 6.

PLA2R-AB is elevated months to years before prediagnostic hypoalbuminemia in some cases. Five cases showing evidence of seropositive PLA2R-AB before prediagnostic hypoalbuminemia. The horizontal dotted line is the cut-off for determining PLA2R-AB seropositivity. The first clinical evidence of prediagnostic hypoalbuminemia is indicated by time zero.

Figure 7.

Prediagnostic hypoalbuminemia occurs before PLA2R-AB elevation in a minority of cases. Representative MN cases showing prediagnostic hypoalbuminemia before seropositive PLA2R-AB. The left y axis represents the scale of the PLA2R-AB levels and the values are plotted in blue. The blue, horizontal dotted line is the cut-off for determining PLA2R-AB seropositivity. The right y axis denotes the serum albumin levels, and the cut-off value for determining hypoalbuminemia is shown by the black dotted line. (A) In patient 1, prediagnostic hypoalbuminemia occurs before elevated PLA2R-AB. (B) In patient 2, hypoalbuminemia occurs before elevated PLA2R-AB. (C) In patient 3, hypoalbuminemia occurs before elevated PLA2R-AB. (D) In patient 4, hypoalbuminemia occurs before elevated PLA2R-AB.

Figure 8.

PLA2R-AB is elevated years to decades before MN diagnosis in a minority of cases. Five unusual cases with detectable seropositive PLA2R-AB over 10 years before diagnosis of MN. The longitudinal PLA2R-AB profile is shown for the unusual MN cases. The cut-off value for determining PLA2R-AB seropositivity is shown by the dotted line and time zero represents biopsy-proven diagnosis of MN. Cases 1–5 are shown by the orange, magenta, green, blue, and red lines, respectively.