Blue diaper syndrome is a rare, autosomal recessive metabolic disorder characterized in infants by bluish urine-stained diapers. It is also known as Drummond's syndrome, and hypercalcemia. It is caused by a defect in tryptophan absorption. Bacterial degradation of unabsorbed tryptophan in the intestine leads to excessive indole production and thus to indicanuria which, on oxidation to indigo blue, causes a peculiar bluish discoloration of the diaper (indoluria). Symptoms typically include digestive disturbances, fever and visual problems. Some may also develop disease due to the incomplete breakdown of tryptophan.