If phenylketonuria is not corrected through diet, it can lead to:

• A. Major neurophysiological and neuropsychological consequences
• B. Only minor physical symptoms
• C. No cognitive impact
• D. Immediate recovery with age

Answer: (A)

Untreated phenylketonuria leads to significant brain-related problems because high levels of phenylalanine disrupt brain development and function. When the diet isn’t restricted, the excess phenylalanine interferes with myelination, neurotransmitter synthesis (notably dopamine and serotonin), and the maturation of neural circuits. This damage manifests as major neurophysiological and neuropsychological consequences, including intellectual disability, learning and attention deficits, impaired memory and executive function, and motor coordination problems. The focus is on enduring cognitive and neurological impact, not just transient physical symptoms. By contrast, this kind of brain impact is not reversed simply with age, and the notion of only minor symptoms or immediate recovery with age doesn’t fit how PKU affects the developing brain. Early dietary management can prevent or greatly reduce these outcomes.