Childhood membranous nephropathy and dietary antigens

Heterozygous Loss-of-Function SEC61A1 Mutations Cause Autosomal-Dominant Tubulo-Interstitial and Glomerulocystic Kidney Disease with Anemia

Autosomal-dominant tubulo-interstitial kidney disease (ADTKD) encompasses a group of disorders characterized by renal tubular and interstitial abnormalities, leading to slow progressive loss of kidney function requiring dialysis and kidney transplantation. Mutations in UMOD, MUC1, and REN are responsible for many, but not all, cases of ADTKD. We report on two families with ADTKD and congenital anemia accompanied by either intrauterine growth retardation or neutropenia. Ultrasound and kidney biopsy revealed small dysplastic kidneys with cysts and tubular atrophy with secondary glomerular sclerosis, respectively. Exclusion of known ADTKD genes coupled with linkage analysis, whole-exome sequencing, and targeted re-sequencing identified heterozygous missense variants in SEC61A1-c.553A>G (p.Thr185Ala) and c.200T>G (p.Val67Gly)-both affecting functionally important and conserved residues in SEC61. Both transiently expressed SEC6A1A variants are delocalized to the Golgi, a finding confirmed in a renal biopsy from an affected individual. Suppression or CRISPR-mediated deletions of sec61al2 in zebrafish embryos induced convolution defects of the pronephric tubules but not the pronephric ducts, consistent with the tubular atrophy observed in the affected individuals. Human mRNA encoding either of the two pathogenic alleles failed to rescue this phenotype as opposed to a complete rescue by human wild-type mRNA. Taken together, these findings provide a mechanism by which mutations in SEC61A1 lead to an autosomal-dominant syndromic form of progressive chronic kidney disease. We highlight protein translocation defects across the endoplasmic reticulum membrane, the principal role of the SEC61 complex, as a contributory pathogenic mechanism for ADTKD.

Antibodies to m-type phospholipase A2 receptor in children with idiopathic membranous nephropathy

Idiopathic membranous nephropathy (IMN), the commonest cause of adult nephrotic syndrome (NS), accounts for only a minority of paediatric NS. Antibodies to m-type phospholipase A2 receptor (PLA2R) are seen in two-thirds of adult IMN cases. PLA2R staining in glomerular deposits is observed in 74% and 45% of adult and paediatric IMN cases, respectively. However, there are no reports of anti-PLA2R in paediatric IMN. We evaluated anti-PLA2R levels and PLA2R in gloemrular deposits in paediatric IMN seen at our center. Five cases were enrolled, all the cases stained for PLA2R in glomeruli and three (60%) had antibodies to PLA2R antigen. There was a parellel reduction in proteinuria and anti-PLA2R titer. The present report suggests that PLA2R has a contributory role in the pathogenesis of paediatric IMN.

Phospholipase A2 receptor staining in pediatric idiopathic membranous glomerulopathy

BACKGROUND

Membranous glomerulopathy, though typically a disease of adults, does occur in children. Antiphospholipase A2 receptor (PLA2R) autoantibodies have recently been implicated as a causative agent in most cases of adult primary (idiopathic) membranous glomerulopathy. PLA2R staining of renal biopsies in two recent large case series of adults with primary membranous glomerulopathy showed a sensitivity of approximately 75 % for detecting primary membranous glomerulopathy. To our knowledge, this is the largest study of its kind to assess PLA2R staining in a pediatric population.

METHODS

Forty-one consecutive cases of pediatric membranous glomerulopathy were identified from our database, and clinical follow-up was performed to confirm primary membranous glomerulopathy. Twenty-two patients met inclusion criteria and are the subject of this report.

RESULTS

Granular, capillary loop immunofluorescence staining for immunoglobulin G (IgG) was present in 100 % of patients, and C3 staining was present in 77 %. PLA2R staining was identified in ten patients, providing a sensitivity of 45 % [confidence interval (CI) 25-67 %]. Bovine serum albumin staining was performed in all PLA2R-negative cases and showed no positivity. Morphologic findings associated with negative PLA2R staining included segmental membranous lesions, mesangial and subendothelial deposits, C1q and "full-house" staining, and lower-stage lesions by electron microscopy. At 38 months' average follow-up, all patients were still considered as having primary membranous glomerulopathy, with none developing a clinically detectable secondary etiology.

CONCLUSIONS

PLA2R staining sensitivity is much lower in the pediatric than the adult primary membranous glomerulopathy population. This finding suggests a more diverse and currently incompletely described set of etiologies for this disease in this group.