hiperoxaluria

Hyperoxaluria is a condition defined by excessive oxalate in the urine, which can lead to kidney stones, nephrocalcinosis, and progressive kidney disease. It is classified as primary (genetic) or secondary (acquired).

Primary hyperoxaluria comprises rare inherited disorders caused by defects in hepatic enzymes that normally metabolize glyoxylate to either glycine or oxalate. The main forms are type 1 (PH1) due to AGXT gene mutations, type 2 (PH2) due to GRHPR mutations, and type 3 (PH3) due to HOGA1 mutations. PH1 is the most common and can present in infancy or later with recurrent stone formation or kidney failure. PH2 and PH3 generally have a broader or milder course but can also lead to nephrolithiasis and impaired kidney function. In advanced disease, oxalate may deposit in other tissues (systemic oxalosis).

Secondary hyperoxaluria results from increased intestinal absorption or dietary intake of oxalate. Conditions causing enteric hyperoxaluria include fat malabsorption syndromes (such as inflammatory bowel disease or after bariatric surgery), small bowel resections, and chronic diarrhea. High dietary oxalate intake or excessive vitamin C can also contribute. In secondary forms, kidney stones and nephrocalcinosis occur due to enhanced oxalate absorption rather than hepatic overproduction.

Diagnosis typically involves measuring urinary oxalate excretion, often with a 24-hour urine collection, and may be supplemented by plasma oxalate measurement in advanced disease. Genetic testing is used to confirm PH1–PH3, and imaging detects stones or nephrocalcinosis.

Treatment focuses on reducing oxalate burden and preserving kidney function. General measures include high fluid intake, calcium supplementation with meals to bind dietary oxalate, and citrate to inhibit crystal formation. Vitamin B6 may reduce oxalate production in PH1. In PH1, disease-modifying options include liver transplant in severe cases and, more recently, RNA-based therapies. Management of secondary hyperoxaluria targets the underlying malabsorption and dietary oxalate reduction.