Blue diaper syndrome is a rare metabolic disorder characterized by problems in the absorption of the aminoacid tryptophan and blue urine stains on diapers. Symptoms typically include digestive problems, fever, irritability, failure to thrive, and visual problems. The abnormally high levels of calcium in the blood (hypercalcemia) may result in accumulation of calcium in the kidneys (nephrocalcinosis) leading to impaired kidney function and possible kidney failure. The bluish urine-stained diapers occur when intestinal bacteria break down excessive amounts of tryptophan, a nutrient of the diet, leading to increase of indican and related compounds in the urine (indicanuria). Although the exact nature of the biochemical defect remains uncertain, it is believed to be related to a defect in the intestinal absorption and transport of tryptophan. The defect in tryptophan absorption may be associated with genetic changes in the LAT2 and TAT1 genes. Inheritance is autosomal recessive or X-linked recessive.