title: Glycomacropeptide in children with phenylketonuria: does its phenylalanine content affect blood phenylalanine control?
abstract: In phenylketonuria (PKU), there are no data available for children with respect to evaluating casein glycomacropeptide (CGMP) as an alternative to phenylalanine-free protein substitutes [Phe-free L-amino acid (AA)]. CGMP contains a residual amount of phenylalanine, which may alter blood phenylalanine control.
  
  
  
  In a prospective 6-month pilot study, we investigated the effect on blood phenylalanine control of CGMP-amino acid (CGMP-AA) protein substitute in 22 PKU subjects (13 boys, nine girls), median age (range) 11 years (6-16 years). Twelve received CGMP-AA and nine received Phe-free L-AA, (1 CGMP-AA withdrawal). Subjects partially or wholly replaced Phe-free L-AA with CGMP-AA. If blood phenylalanine exceeded the target range, the CGMP-AA dose was reduced and replaced with Phe-free L-amino acids. The control group remained on Phe-free L-AAs. Phenylalanine, tyrosine and Phe : Tyr ratio concentrations were compared with the results for the previous year.
  
  
  
  In the CGMP-AA group, there was a significant increase in blood phenylalanine concentrations (pre-study, 275 μmol L-1; CGMP-AA, 317 μmol L-1; P = 0.02), a decrease in tyrosine concentrations (pre-study, 50 μmol L-1; CGMP-AA, 40 μmol L-1; P = 0.03) and an increase in Phe : Tyr ratios (pre-study, Phe : Tyr 4.9:1; CGMP-AA, Phe : Tyr 8:1; P = 0.02). In the control group there was a non-significant fall in phenylalanine concentrations (pre-study 325μmol/L: study 280μmol/L [p = 0.9], and no significant changes for tyrosine or phe/tyr ratios [p = 0.9]. Children taking the CGMP-AA found it more acceptable to L-AA.
  
  
  
  Blood phenylalanine control declined with CGMP-AA but, by titrating the dose of CGMP-AA, blood phenylalanine control remained within target range. The additional intake of phenylalanine may have contributed to the change in blood phenylalanine concentration. CGMP-AA use requires careful monitoring in children.
authors.affiliation: Birmingham Children's Hospital, Dietetic Department, Birmingham, UK.
authors.forename: A
authors.initials: A
authors.lastname: Daly
authors.affiliation: Birmingham Children's Hospital, Dietetic Department, Birmingham, UK.
authors.forename: S
authors.initials: S
authors.lastname: Evans
authors.affiliation: Birmingham Children's Hospital, Dietetic Department, Birmingham, UK.
authors.forename: S
authors.initials: S
authors.lastname: Chahal
authors.affiliation: IMD (Inherited metabolic department) Birmingham Children's Hospital, Birmingham, UK.
authors.forename: S
authors.initials: S
authors.lastname: Santra
authors.affiliation: Birmingham Children's Hospital, Dietetic Department, Birmingham, UK.
authors.forename: A
authors.initials: A
authors.lastname: MacDonald
mesh_terms: D000293:Adolescent; D000596:Amino Acids / Q000008:administration & dosage / Q000097:blood; D000886:Anthropometry; D002364:Caseins / Q000097:blood*; D002648:Child; D004032:Diet; D005260:Female; D006801:Humans; D008297:Male; D018977:Micronutrients / Q000008:administration & dosage / Q000097:blood; D015596:Nutrition Assessment; D010446:Peptide Fragments / Q000097:blood*; D010649:Phenylalanine / Q000097:blood*; D010661:Phenylketonurias / Q000097:blood*; D010865:Pilot Projects; D011446:Prospective Studies; D014443:Tyrosine / Q000097:blood
chemical_list: D000596:Amino Acids; D002364:Caseins; D018977:Micronutrients; D010446:Peptide Fragments; C065989:caseinomacropeptide; D014443:Tyrosine; D010649:Phenylalanine
keywords: amino acid; glycomacropeptide; phenylalanine; phenylketonuria; protein substitute