Adult Phenylketonuria

Adult PKU is not a childhood condition that can be safely outgrown. The immediate clinical question is whether current blood phenylalanine is within the Canadian target of 120–360 µmol/L, even when the person feels well. An adult with a level of 450 µmol/L may have no obvious acute symptom, yet remains above target; the 2025 European upper limit of 600 µmol/L should not be imported into Canadian practice. Management links three tasks: reduce phenylalanine exposure, replace ordinary dietary protein with phenylalanine-free medical nutrition, and detect the cognitive, psychiatric, skeletal, nutritional, and reproductive consequences of poor control. A high result should not automatically be labelled PAH deficiency, because BH4 synthesis or recycling defects require a different treatment approach. That distinction directs the diagnostic workup before long-term therapy is chosen.