Phenylketonuria is detected around one year after birth and is characterized by mental retardation, difficulty speaking, salivation, muscle weakness, inability to walk and even violent tendencies, and a tendency to tap and hit objects. Phenylketonuria is caused by a genetic defect in the fetus that leads to an endocrine disorder in the metabolism of amino acids in the body and affects the brain, intelligence, mental development, bone development, and muscle growth of the patient. Patients with phenylketonuria not only suffer from mental retardation, but also have a series of mental symptoms such as unresponsiveness. At about one year of age, the patient is prone to the smell of rat urine, and also has symptoms of lighter pigmentation of the body skin and hair due to abnormal amino acid metabolism leading to abnormal pigmentation in the body.