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Definition
By Mayo Clinic staffPhenylketonuria (fen-ul-ke-to-NU-re-uh) is a birth defect in which a mutation occurs in a gene containing instructions for making the enzyme needed to break down the amino acid phenylalanine.
Amino acids are the building blocks for protein, and too much phenylalanine can cause a variety of health problems. People with phenylketonuria — babies, children and adults — need to follow a diet that limits phenylalanine, which is found mostly in high-protein foods.
Babies in the United States and many other countries are screened for phenylketonuria soon after birth. Although phenylketonuria is rare, recognizing phenylketonuria right away can help prevent serious health problems.
Symptoms
