Global Clinical Practice in Transitioning Protein Substitutes for Children with Phenylketonuria

<b>Background:</b> Protein substitutes are essential in the dietary management of phenylketonuria (PKU). Transition from first-stage phenylalanine (Phe)-free infant formula to second- and third-stage protein substitutes is carefully managed to meet a child's evolving nutritional needs, feeding abilities, and developmental progression. However, clinical protocols, product access, and reimbursement vary globally. This study assessed international transition practices. <b>Methods:</b> A cross-sectional online survey explored health professionals' practices on transition timing, influencing factors, product forms, casein-glycomacropeptide (cGMP) use, and perceived barriers and facilitators. <b>Results:</b> A total of 106 professionals from 32 countries participated: Europe (67%), Asia (12%), North America (10%), South America (8%), and Oceania (3%). Dietitians led transitions in 83% of centers. First-stage Phe-free infant formula was typically discontinued at 1-2 years (66%). Second-stage substitutes were introduced at 6-12 months in Europe (61%) and Oceania (100%), but after age one in Asia (69%), North America (72%), and South America (100%). Influencing factors included weaning alignment (46%) and nutritional needs (42%). Semi-solids were preferred in Europe (56%) and Oceania (67%), while powdered drinks dominated in Asia (62%), North America (82%), and South America (100%). Third-stage protein substitutes were introduced at 3-5 years (45%), with later transitions more common in South America (88%) and North America (63%). Ready-to-drink forms were frequent in Oceania (100%), Asia (92%), and Europe (85%). cGMP was prescribed by 61%, mainly guided by preference, Phe tolerance, and adherence; 26% reported no access. Key facilitators for transition included motivation (79%) and sensory properties (69%); barriers included aversion (70%) and poor taste/texture (69%). School involvement was reported by 32%. <b>Conclusions:</b> Protein substitute transition practices in PKU vary globally. International guidance and equitable product access are needed.