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Background: Oxalate nephropathy is a potentially underestimated cause of kidney failure characterized by massive deposition of calcium oxalate crystals in the renal parenchyma. The prevalence and modes of presentation of this entity are ill-defined. Methods: Here we report on the largest consecutive series of cases of adult oxalate nephropathy diagnosed on native kidney biopsies from January 2010 to December 2018 in the UCLouvain Kidney Disease Network. Results: We screened 2265 native kidney biopsies and identified 22 cases (1%) of oxalate nephropathy. Patients had a mean age at diagnosis of 61 years (±20) and presented either with acute on chronic kidney disease (CKD) (62%) or with acute kidney injury (AKI) (38%). Mean serum creatinine at biopsy was 8.0 ± 4.5 mg/dl. Kidney biopsies showed abundant calcium oxalate crystal deposits, associated with acute interstitial nephritis and tubular necrosis, and variable degrees of interstitial fibrosis and tubular atrophy. Chronic pancreatitis and gastric bypass were the most common causes of oxalate nephropathy (48%). During a mean follow-up of 29 months, half of the patients (52%) progressed to kidney failure, all within the month following diagnosis. Higher serum creatinine level at presentation and interstitial fibrosis and tubular atrophy score were associated with progression to kidney failure. Conclusion: Oxalate nephropathy is the cause of kidney disease in 1% of consecutive native kidney biopsies and typically presents as acute on CKD or AKI. The prognosis of the disease is poor, with a high rate of kidney failure within the first month after the diagnosis.

Fibrinogen A alpha chain amyloidosis is an autosomal dominant disease associated with mutations in the fibrinogen A alpha chain (FGA) gene, and it is the most common cause of hereditary renal amyloidosis in the UK. Patients typically present with kidney impairment and progress to end-stage renal disease over a median time of 4.6 years. Methods: Six patients presented with proteinuria, hypertension, and/or lower limb edema and underwent detailed clinical and laboratory investigations. Results: A novel FGA gene mutation was identified in each case: 2 frameshift mutations F521Sfs*27 and G519Efs*30 and 4 single base substitutions G555F, E526K, E524K, R554H. In 5 subjects, extensive amyloid deposits were found solely within the glomeruli, which stained specifically with antibodies to fibrinogen A alpha chain, and in one of these cases, we found coexistent fibrinogen A alpha chain amyloidosis and anti-glomerular basement membrane antibody disease. One patient was diagnosed with light-chain amyloidosis after a bone marrow examination revealed a small clonal plasma cell population, and laser microdissection of the amyloid deposits followed by liquid chromatography and tandem mass spectrometry identified kappa light chain as the fibril protein. Discussion: We report 6 novel mutations in the FGA gene: 5 were associated with renal fibrinogen A alpha chain amyloidosis and 1 was found to be incidental to light-chain amyloid deposits discovered in a patient with a plasma cell dyscrasia. Clinical awareness and suspicion of hereditary amyloidosis corroborated by genetic analysis and adequate typing using combined immunohistochemistry and laser microdissection and mass spectrometry is valuable to avoid misdiagnosis, especially when a family history of amyloidosis is absent.