Hydroxykynureninuria: A case of Abnormal Tryptophan Metabolism Probably Due to a Deficiency of Kynureninase

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Abstract
A patient is described who excreted large amounts of kynurenine, 3-hydroxykynurenine and xanthurenic acid in the urine. It is postulated that the increased excretion of these substances arises due to the absence in the tissues of the enzyme kynureninase which in turn, leads to a metabolic block in the pathway of tryptophan to nicotinic acid. In these conditions tryptophan can no longer be regarded as a source of nicotinic acid, and it is believed that the patient suffered from a deficiency of this vitamin when she was on an all milk diet. The hereditary nature of the condition is discussed.