Phenylketonuria is a common autosomal recessive genetic disorder, the most frequent primary clinical manifestation among congenital amino acid metabolic disorders. It is characterized by intellectual disability, pale skin and hair pigmentation, and a mouse urine-like odor. The main cause is that phenylalanine is an essential amino acid for the human body. The phenylalanine ingested is partly used for protein synthesis and partly converted to tyrosine by the action of phenylalanine hydroxylase, which is necessary for the synthesis of substances like adrenaline, melanin, and thyroxine. The disease is mainly due to a deficiency of phenylalanine hydroxylase, which inhibits the conversion of phenylalanine to tyrosine, resulting in increased concentrations of phenylalanine in the blood, cerebrospinal fluid, and various tissues. At the same time, due to the predominance of the main pathway, the enhancement of the secondary metabolic pathway leads to the deamination of phenylalanine by transaminase, producing a large amount of phenylpyruvic acid, which through oxidation produces a large amount of phenylacetic acid, phenyllactic acid, and p-hydroxyphenylpyruvic acid. These metabolic by-products are excreted in large quantities in the urine, and the high concentrations of phenylalanine and its by-products accumulate extensively in brain tissue, thereby causing damage to brain cells.