HAO1 also known as GOX1 is one of three related genes that have 2-hydroxyacid oxidase activity yet differ in encoded protein amino acid sequence, tissue expression and substrate preference. HAO1 plays a significant role in organic acid metabolism through 2-hydroxyacid oxidase activity, which requires a flavin cofactor to catalyze the oxidation of 2-hydroxyacids to 2-ketoacids while simultaneously reducing oxygen to hydrogen peroxide. Notably, HAO1 preferentially oxidizes glycolate, producing glyoxylate, which is vital for the peroxisomal synthesis of glycine. Additionally, HAO1 can convert glyoxylate to oxalate, linking HAO1 to the pathophysiology of hyperoxaluria type 1, a condition characterized by the accumulation of oxalate due to defects in the peroxisomal enzyme AGXT. This accumulation can lead to the formation of calcium oxalate precipitates in the kidneys, posing serious health risks. HAO1′s ability to interact with various substrates, including 2-hydroxy fatty acids and L-α-hydroxy acids, further underscores HAO1′s importance in metabolic pathways.