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How can early dietary treatment prevent intellectual disability in phenylketonuria?

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BRCA2 tumor suppressor gene on chromosome 13 — human genetic disease Photomicrograph of the *BRCA2* tumor suppressor gene on chromosome 13 of the human genome. Inactivation of this growth-regulating gene is associated with a higher risk of developing breast cancer.

In phenylketonuria (PKU), individuals lack the enzyme phenylalanine hydroxylase, which is necessary to metabolize the amino acid phenylalanine. Without this enzyme, phenylalanine accumulates to toxic levels, interfering with central nervous system processes, including neurotransmitter synthesis and myelin formation, which can lead to intellectual disability and other neurological impairments.12

Early dietary treatment is essential to prevent this damage. By maintaining a strict diet low in phenylalanine—avoiding high-protein foods like meat and dairy—the body is prevented from accumulating the toxic levels of the amino acid that cause brain injury. Instead, patients consume special phenylalanine-free amino acid formulas or foods fortified with glycomacropeptide (GMP) to ensure proper nutrition.12

When implemented early, this dietary interdiction attenuates or prevents brain injury, allowing for normal neurological development. Because the risk of damage remains, individuals must adhere to these dietary regimens to maintain healthy metabolic function.21