Phenylketonuria (PKU)

Symptoms

Symptoms of phenylketonuria (PKU) usually develop within a few months after birth, once phenylalanine has built up in a baby's system from consuming the protein in formula or breast milk. Before birth, the mother's body filters out the excess phenylalanine for the unborn baby.

Early symptoms of PKU, which occur in more than 50% of babies with this condition, include:³

• A musty odour to the skin, hair, and urine.
• Vomiting and diarrhea, leading to weight loss.
• Irritability.
• Skin problems, such as dry skin, or itchy skin rashes (eczema).
• Sensitivity to light (photosensitivity).

If a baby has a severe enzyme deficiency or if PKU is not detected and treated soon enough, phenylalanine builds up in the brain tissue and affects mental skills and the central nervous system. Symptoms can become severe by about 8 weeks of age and may include:

• Unusual behaviour, such as screaming episodes, repetitive rocking, head banging, and arm biting (common in older children).
• Loss of skills and abilities related to severe mental retardation.
• Growth and developmental delays.
• Seizures.

PKU also affects the synthesis of melanin, which provides pigment (colour) to the skin, eyes, and hair. About 90% of children with PKU have blond hair, fair skin, and blue eyes.³

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Author:	Amy Fackler, MA Carrie Henley	Last Updated: May 26, 2006
Medical Review:	Michael J. Sexton, MD - Pediatrics Thomas Emmett Francoeur, MDCM, CSPQ, FRCPC - Pediatrics
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