Global Use of Casein Glycomacropeptide Protein Substitutes for Phenylketonuria (PKU): Health Professional Perspectives

Background/Objectives: Casein glycomacropeptide (cGMP) has been modified to enable its suitability as a low phenylalanine (Phe) protein substitute (PS) in phenylketonuria (PKU). No data is available about its global usage. Methods: A 60-item multiple choice and short answer/extended response questionnaire examining the use of modified cGMP in PKU was distributed globally to dietitians and physicians via web-based professional inherited metabolic disorder groups. Results: Respondents (n = 208) from 45 countries across 6 continents completed the questionnaire. Of these, 83.7% (n = 174) were dietitians/nutritionists, 14.9% (n = 31) medical doctors/physicians and 1.4% (n = 3) other health professionals, caring for both paediatric and adult patients (59.1%), paediatrics only (25.0%) or adults only (15.9%). cGMP PS were reported as not available in their centre/hospital by 19.7% (n = 41), mostly in Africa, South America, and southern and western Asia. The main reasons included lack of regulatory approval (65.8%), not promoted by manufacturers (41.5%), and cost (29.3%). An estimated 25% of represented patients globally were using cGMP PS; 78.4% (n = 163) following refusal/poor adherence with Phe-free amino acids and 54.8% (n = 114) for adult patients recommencing dietary treatment. There were concerns about the residual Phe in cGMP negatively impacting blood Phe levels in children <12y (66.3%), adolescents (48.0%), adults (34.6%), and the first trimester of pregnancy (53.1%). Sixty nine percent (n = 145) adjusted dietary Phe prescription according to the cGMP Phe content, particularly in regions with a higher percentage of severe PKU variants. Commonly perceived clinical advantages with cGMP were improved taste/palatability (93.2%, n = 194) and fewer gastrointestinal symptoms (55.8%, n = 116). Perceived clinical disadvantages were residual Phe (72.1%, n = 150), lack of data in children < 3 years (48.1%, n = 100), and the high energy content of some brands (45.2%, n = 94). There were concerns that cGMP PS were too high in sugar (34.1%, n = 71) and dissatisfaction or uncertainty about the adequacy of its Phe (66.3%) and amino acid (34.1%) content. Conclusions: There is global inconsistency in access to cGMP PS suitable for PKU, and in the interpretation of evidence-based research. Some professionals have significant concerns about its nutritional composition particularly residual Phe, limiting its estimated use to approximately 25% of PKU patients globally.