NCIt definition : A rare autosomal recessive disorder characterized by abnormalities in the metabolism
of phenylalanine and tyrosine. It results in the accumulation in the blood of homogentisic
acid which is excreted in the urine. The presence of homogentisic acid in the urine
causes its color to turn black. The excessive amount of homogentisic acid in the blood
may cause damage to cartilage and heart valves, and may result in the formation of
kidney stones.;