Clinical Scenario:
A 3-year-old boy with classic phenylketonuria (PKU), diagnosed by newborn screening, has remained on a phenylalanine-restricted diet since 10 days of age, with consistently well-controlled plasma phenylalanine levels. His parents ask whether the diet can be stopped. What is the most appropriate advice?
A. Stop the diet at 2 years
B. Continue dietary control lifelong
C. Stop when IQ is normal
D. Restart only if symptoms develop
E. Relax the diet after starting school
Correct answer & Explanation:
Answer: B. Continue dietary control lifelong
Discussion
Dietary treatment of PKU should be continued lifelong to maintain plasma phenylalanine within the recommended range. The previous practice of discontinuing dietary restriction during childhood has been abandoned because elevated phenylalanine after treatment withdrawal can be associated with executive dysfunction, attention problems, mood disturbances, and other neurocognitive difficulties, even when overt intellectual disability does not recur.
Strict metabolic control is particularly important during pregnancy in women with PKU. Maternal hyperphenylalaninemia can cause maternal PKU syndrome, including fetal microcephaly, congenital heart disease, and impaired neurodevelopment, even when the fetus does not have PKU.
Key exam point:
PKU is not a condition in which dietary treatment can safely be stopped after early childhood. Lifelong phenylalanine control is recommended.
