MGI:98973Homozygotes for a null allele are small and die prematurely while heterozygous females show a lactation defect. Most homozygotes for another null allele die within the first month of renal failure associated with uric acid depletion, renal tubular damage, inflammation, fibrosis and oxidative stress. Homozygosity for mutations that lock the enzyme into the xanthine oxidase (XO) form leads to increased number of peritoneal macrophages and increased ROS production after their stimulation. This in turn stimulates xenografted tumor growth.