Phenylketonuria (PKU) is an amino acid metabolic disorder primarily caused by a deficiency in phenylalanine hydroxylase. This deficiency prevents phenylalanine from being converted to tyrosine, leading to a significant accumulation of phenylalanine, which is then excreted in large quantities in the urine. It is a common genetic metabolic disorder. If not treated, it can lead to developmental delays in children, particularly in intellectual development, with markedly lower IQ than peers, especially noticeable in language development disorders. Additionally, it can also present with neurological and psychiatric symptoms such as agitation, hyperactivity, increased muscle tone, and hyperreflexia. There is also depigmentation of the skin and hair, and the urine may have a mousy odor.