Phospholipase A2 receptor (PLA2R1) sequence variants in idiopathic membranous nephropathy

Abstract

The M-type receptor for phospholipase A2 (PLA2R1) is the major target antigen in idiopathic membranous nephropathy (iMN). Our recent genome-wide association study showed that genetic variants in an HLA-DQA1 and phospholipase A2 receptor (PLA2R1) allele associate most significantly with biopsy-proven iMN, suggesting that rare genetic variants within the coding region of the PLA2R1 gene may contribute to antibody formation. Here, we sequenced PLA2R1 in a cohort of 95 white patients with biopsy-proven iMN and assessed all 30 exons of PLA2R1, including canonical (GT-AG) splice sites, by Sanger sequencing. Sixty patients had anti-PLA2R1 in serum or detectable PLA2R1 antigen in kidney tissue. We identified 18 sequence variants, comprising 2 not previously described, 7 reported as rare variants (<1%) in the Single Nucleotide Polymorphism Database or the 1000 Genomes project, and 9 known to be common polymorphisms. Although we confirmed significant associations among 6 of the identified common variants and iMN, only 9 patients had the private or rare variants, and only 4 of these patients were among the 60 who were PLA2R positive. In conclusion, rare variants in the coding sequence of PLA2R1, including splice sites, are unlikely to explain the pathogenesis of iMN.

Figure 1.

Structure of PLA2R1. The amino acid sequence of PLA2R1 starts with a 20–amino acid signal peptide, followed by a large extracellular segment, a transmembrane domain, and a short intracellular domain containing an endocytosis motif. The extracellular segment contains a cystine-rich domain at the N-terminal, followed toward the membrane surface by a fibronectin type II domain and eight C-type lectin-like domains/carbohydrate recognition. CD, intracellular domain; COOH, intracellular C terminal end; CRD, cystine-rich domain (thin vertical lines, S-S bounds); FNII, fibronectin type II domain; CTLD, C-type lectin-like domain; NH2, extracellular N terminal end; TMD, transmembrane domain. In red, common variants significantly associated with iMN. Rare and new coding variants were found in only nine patients.