Symptoms in young children with phenylketonuria include sweat and urine that smells like rat urine, fair skin, hair that changes from black to yellow, increased muscle tone, and intellectual development that lags behind that of children of the same age. Phenylketonuria is a more common amino acid metabolic disease, due to abnormalities in the metabolism of phenylalanine, resulting in the accumulation of phenylalanine and its keto acids in the body. The main symptoms are: 1. Sweat and urine emit the odor of rat urine: due to the deficiency of phenylalanine hydroxylase, phenylalanine produces more phenyl lactic acid and phenyl acetic acid from another pathway and excrete them from sweat and urine causing them to emit the odor of rat urine. 2. Fair skin, hair from black to yellow: due to the inhibition of tyrosinase, so that the melanin synthesis is reduced, the affected children will have fair skin, hair from black to yellow symptoms. 3. Increased muscle tone: due to cerebellar malformations, young children will have repeated episodes of convulsions, increased muscle tone and hyperreflexia. 4. Intellectual development lags behind children of the same age: growth retardation, mainly in intellectual development delay, IQ lower than normal children of the same age. If you feel unwell, please go to the regular hospital, once the diagnosis is clear, you should give active treatment as soon as possible, the younger the age of treatment, the better the result.