Phenylketonuria is an autosomal recessive genetic disease and the most common congenital amino acid metabolic disorder, characterized clinically by intellectual disability, light skin and hair pigmentation, and a musty urine odor. Phenylketonuria is due to a deficiency in phenylalanine hydroxylase, resulting in the inability to convert phenylalanine to tyrosine. This increases the concentration of phenylalanine in the blood, cerebrospinal fluid, and various tissue fluids. Due to the blockage of the main metabolic pathway, the secondary metabolic pathway is enhanced. Under the action of transaminases, phenylalanine is deaminated to produce a large amount of phenylpyruvic acid. Through oxidation, this leads to the production of phenylacetic acid, phenyllactic acid, and para-hydroxyphenylpyruvic acid, among other metabolic byproducts, thus causing a series of clinical symptoms. It is a hereditary metabolic disease and is not contagious.