Phenylketonuria is a common autosomal recessive genetic disorder and is the most common congenital disorder of amino acid metabolism. Clinically, its main features are intellectual disability, light skin and hair pigmentation, and a mouse-like urine odor. The disease is primarily due to a deficiency of phenylalanine hydroxylase, which inhibits the conversion of phenylalanine to tyrosine, leading to increased concentrations of phenylalanine in the blood, cerebrospinal fluid, and various tissues. Due to the obstruction of the main metabolic pathway, the secondary metabolic pathway is enhanced. Under the action of transaminase, phenylalanine undergoes deamination to produce a large amount of phenylpyruvic acid, which, through oxidation, generates side metabolic products such as phenylacetic acid, phenyllactic acid, and para-hydroxyphenylpyruvic acid, which are then excreted in high amounts in the urine. The high concentrations of phenylalanine and its metabolic byproducts accumulate in the brain tissue, causing damage to brain cells.