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Xanthine oxidase is the enzyme required to produce uric acid by the breakdown of purine nucleotides. The uric acid itself, as well as the reactive oxygen species released during the enzymatic reaction, can have detrimental effects on the body. Gout is a common condition that occurs due to elevated uric acid production via this mechanism. As a result, many drugs have been formed to combat gout, by inhibiting xanthine oxidase enzyme activity. Moreover, regulations of this enzyme have proven to be effective for anti-cancer purposes.[1]

The deficiency of xanthine oxidase leads to a condition called hereditary xanthinuria type 1, attributed to a mutation in the XDH gene that leads to decreased amounts of xanthine oxidase production. Although rare, this condition can have detrimental effects on the individual, whereby a decreased metabolism of xanthine leads to elevated systemic levels of xanthine. The xanthine precipitates in the renal tubules and forms the rare xanthine kidney stones. If left untreated, this obstructs the renal parenchyma and can result in life-threatening renal failure. Patients also complain of recurrent episodes of muscle aches and joint pain. Patients with hereditary xanthuria type 1 are advised to limit their intake of proteins such as those found in meat products; this prevents the buildup of excess xanthine from protein breakdown and prevents the disease from worsening into a more severe state. Patients with type 2 of the condition have a normal expression of the XDH gene, but the final protein product fails to incorporate a sulfur molecule into its core, which ultimately limits the functionality of the protein. The symptoms of type 1 and type 2 hereditary xanthinuria are the same.  Studies have also indicated that patients with higher levels of XDH gene expression have a direct link to the survival rates of certain cancers. For example, patients with lung adenocarcinoma and a higher expression of the XDH gene had lower survival rates. Although this area is not particularly well studied, further research in this field is warranted.[8]