Phenylketonuria is a common disorder of amino acid generation, mainly due to the lack or reduced activity of phenylalanine hydroxylase or related enzymes for synthesizing coenzyme tetrahydrobiopterin, which prevents tissues in the body from converting phenylalanine to tyrosine, resulting in the accumulation of phenylalanine and its metabolites in the body, causing a series of functional abnormalities and the excretion of large amounts of metabolites such as phenylketonate in the urine of affected children. The clinical features are mental retardation, seizures and hypopigmentation. The disease is autosomal recessive and its incidence varies with race. The clinical manifestations are as follows: 1. Growth retardation: In addition to somatic growth retardation, untreated individuals begin to have significant mental retardation and language development disorders at the same age of 4-9 months. Later the degree of mental retardation varies, about 60% belong to heavy hypo (IQ<50), the rest are medium and light, only 1%-4% of untreated children with typical phenylketonuria 1Q≥80. 2, neuropsychiatric manifestations: there are cerebellar malformations and recurrent convulsions due to cerebral atrophy, but it decreases with age. Increased muscle tone and hyperactive tendon reflexes. There are often mental behavior abnormalities, such as excitement, hyperactivity, aggressive behavior, etc. 3, skin and hair performance: skin is often dry, prone to eczema and skin scratching syndrome. Due to the inhibition of tyrosinase, melanin synthesis is reduced, so the affected children’s hair color is light and brown. 4.Other: Due to the lack of phenylalanine hydroxylase, phenylalanine produces phenyl lactic acid and phenylacetic acid from another pathway, which is excreted from sweat and urine and has a musty odor (or rat odor).