Phenylketonuria is an autosomal recessive genetic disorder, a congenital amino acid metabolism disorder caused by mutations in the phenylalanine hydroxylase gene. This mutation leads to decreased enzyme activity, causing phenylalanine and its metabolic products to accumulate in the body, thereby causing the disease. If diagnosed and treated early, a child's intelligence can remain normal, and abnormalities in the electroencephalogram can be restored. If uncontrolled, typical symptoms will appear as the child grows, including delayed growth and development, primarily manifested as delayed intellectual development, as well as seizures, light brown hair, and other symptoms.