What are common symptoms of phenylketonuria (PKU)?

Children with untreated PKU appear healthy at birth. But by 3 to 6 months of age, they begin to lose interest in their surroundings. By age 1, children are developmentally delayed and their skin has less pigmentation than that of someone without the condition. If people with PKU do not restrict the phenylalanine in their diet, they develop severe intellectual and developmental disabilities.

Other symptoms include:

  • Behavioral or social problems
  • Seizures, shaking, or jerking movements in the arms and legs
  • Stunted or slow growth
  • Skin rashes, like eczema
  • Small head size, called microcephaly
  • A musty odor in urine, breath, or skin that is a result of the extra phenylalanine in the body
  • Fair skin and blue eyes, due to the body’s failure to transform phenylalanine into melanin, the pigment responsible for a person’s coloring1


  1. MedlinePlus. (2023). Phenylketonuria. Retrieved December 21, 2023, from https://medlineplus.gov/genetics/condition/phenylketonuria/
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