Expert Consensus on the Long-Term Effectiveness of Medical Nutrition Therapy and Its Impact on the Outcomes of Adults with Phenylketonuria

Many adults with phenylketonuria (PKU) rely on medical nutrition therapy (MNT; low phenylalanine (Phe) diet with protein substitutes/medical foods) to maintain blood Phe concentrations within recommended ranges and prevent PKU-associated comorbidities. Despite disease detection through newborn screening and introduction of MNT as early as birth, adherence to MNT often deteriorates from childhood onwards, complicating the assessment of its effectiveness in the long term. Via a modified Delphi process, consensus (≥70% agreement) was sought on 19 statements among an international, multidisciplinary 13-member expert panel. After three iterative voting rounds, the panel achieved consensus on 17 statements related to the limitations of the long-term effectiveness of MNT (7), the burden of long-term reliance on MNT (4), and its potential long-term detrimental health effects (6). According to the expert panel, the effectiveness of MNT is limited in the long term, is associated with a high treatment burden, and demonstrates that adults with PKU are often unable to achieve metabolic control through dietary management alone, creating an unmet need in the adult PKU population.