Serine—pyruvate aminotransferase is an enzyme that in humans is encoded by the AGXT gene. This gene is expressed only in the liver and the encoded protein is localized mostly in the peroxisomes, where it is involved in glyoxylate detoxification. Mutations in this gene, some of which alter subcellular targetting, have been associated with type I primary hyperoxaluria. Defects in AGXT are the cause of hyperoxaluria primary type 1 (HP1), also known as primary hyperoxaluria type I (PH1) and oxalosis I. HP1 is a rare autosomal recessive inborn error of glyoxylate metabolism characterized by increased excretion of oxalate and glycolate, and the progressive accumulation of insoluble calcium oxalate in the kidney and urinary tract.