Phenylketonuria is an autosomal invisible genetic disorder of amino acid metabolism due to an enzyme defect in the phenylalanine metabolic pathway. The vast majority of phenylketonuria is due to the lack of phenylalanine hydroxylase, which cannot convert phenylalanine to tyrosine. As a result, phenylalanine is present in extremely high concentrations in blood, cerebrospinal fluid, various tissues, and urine, and large amounts of bypass metabolites such as phenyl pyruvate, phenylacetic acid, and phenyl lactate are produced and excreted in the urine. The high concentration of phenylalanine and its bypass metabolites leads to brain damage. Generally, children are born normal, and symptoms appear at 3 to 6 months of age, and become obvious at 1 year of age. The main manifestations are: 1, neurological system: the main focus of intellectual development is backward, with varying degrees of intellectual decline. Epilepsy may also appear, which may decrease or stop with age. It may be accompanied by dull expression, abnormal behavior, hyperactivity, muscle spasms, increased muscle tone, etc. 2. Change in appearance: The hair color is normal at birth, but a few months after birth, due to insufficient melanin synthesis, the hair color becomes lighter and eczema may appear. 3. Abnormal urine and sweat: There is a smell of rat urine because phenylacetic acid is excreted in urine and sweat. Early diagnosis and treatment can avoid irreversible neurological damage through newborn screening and screening of phenyl pyruvate and its metabolites in urine, and only early treatment can prevent intellectual developmental disorders. The key to treatment is to reduce the intake of phenylalanine, and 5-hydroxytryptophan and levodopa should be given in addition to dietary control.