Phenylketonuria (PKU) is a common disorder of amino acid metabolism, mainly due to the lack of or reduced activity of phenylalanine hydroxylase or enzymes related to the synthesis of coenzyme tetrahydrobiopterin, which prevents the body tissues from converting phenylalanine into tyrosine, resulting in the accumulation of phenylalanine and its metabolites in the body, causing a series of functional abnormalities and the excretion of a large amount of metabolites such as phenylpyruvate in the urine of affected children. A large amount of metabolites such as phenylpyruvic acid is excreted in the urine of the affected children. Phenylketonuria can be broadly divided into typical PKU and BH4 deficient PKU according to different enzyme defects. (1) Typical PKU: Hepatocytes lack phenylalanine hydroxylase and cannot convert phenylalanine into tyrosine, therefore, the concentration of phenylalanine in blood, cerebrospinal fluid, various tissues and urine is extremely high, and a large amount of bypass metabolites such as phenyl pyruvate and phenylacetic acid are produced. High concentrations of phenylalanine and its bypass metabolites lead to brain cell damage, and the majority of children with phenylketonuria have typical PKU. (2) Tetrahydrobiopterin deficiency PKU: It is caused by a deficiency of tetrahydrobiopterin, a coenzyme of phenylalanine hydroxylase, which is involved in the phenylalanine metabolic pathway. 2, the manifestation of phenylketonuria: (1) children can be normal at birth, and gradually develop symptoms. (2) neurological system: the main developmental lag in intelligence, dull expression, may be accompanied by convulsions, such as untreated, most of the development of serious intellectual disability. bH4 deficiency neurological symptoms appear early and heavy, common hypotonia, drowsiness or convulsions, intelligence lag is obvious. (3) Appearance: The hair color is normal at birth, but a few months after birth, due to insufficient melanin synthesis, the hair, skin and iris color becomes lighter, and there may be eczema-like rash on the face. (4) urine and sweat have “musty odor” or “rat urine” smell, often with vomiting. 3, the key to the treatment of phenylketonuria is to reduce the intake of phenylalanine. Once diagnosed, it should be treated immediately; the younger the age of starting treatment, the better the effect. (1) Low-phenylalanine diet: infants can be given special low-phenylalanine milk powder; young children can choose low-phenylalanine flour and other supplemental foods, and protein foods can be added under the guidance of doctors. The daily phenylalanine intake varies by age, and it is appropriate to maintain the blood phenylalanine concentration at 0.12-0.6 mmol/L (2-1 mg/d); dietary control should be continued at least until after puberty. (2) In addition to dietary control, children with BH4 deficiency should be given BH1, 5hydroxytryptophan and levodopa.