Phenylketonuria patients and normal people’s urine color, appearance is almost the same, there is not much difference. Phenylketonuria is a common hereditary metabolic disease, mainly due to abnormalities in the metabolism of the enzyme phenylalanine hydroxylase, which leads to an increase in the amount of phenyl lactic acid, phenyl acetic acid and phenyl pyruvic acid in the urine of the human body, and this is why it is called phenylketonuria. All three substances are clear in color in the urine, so the color and appearance of the urine of patients with phenylketonuria is the same as that of normal people. However, the urine of these patients is accompanied by a peculiar odor, which is clinically described as ratty. These patients have mental retardation and abnormal skin and hair development and should be screened early in pregnancy. If phenylketonuria is already present, early intervention and treatment is essential, and the earlier the better.