Glycomacropeptide: long-term use and impact on blood phenylalanine, growth and nutritional status in children with PKU

Orphanet J Rare Dis. 2019 Feb 15;14(1):44. doi: 10.1186/s13023-019-1011-y.


In phenylketonuria, casein glycomacropeptide (CGMP) requires modification with the addition of some essential and semi essential amino acids to ensure suitability as a protein substitute. The optimal amount and ratio of additional amino acids is undefined.

Aim: A longitudinal, parallel, controlled study over 12 months evaluating a CGMP (CGMP-AA2) formulation compared with phenylalanine-free L-amino acid supplements (L-AA) on blood Phe, Tyr, Phe:Tyr ratio, biochemical nutritional status and growth in children with PKU. The CGMP-AA2 contained 36 mg Phe per 20 g protein equivalent.

Methods: Children with PKU, with a median age of 9.2 y (5-16y) were divided into 2 groups: 29 were given CGMP-AA2, 19 remained on Phe-free L-AA. The CGMP-AA2 formula gradually replaced L-AA, providing blood Phe concentrations were maintained within target range. Median blood Phe, Tyr, Phe:Tyr ratio and anthropometry, were compared within and between the two groups at baseline, 26 and 52 weeks. Nutritional biochemistry was studied at baseline and 26 weeks only.

Results: At the end of 52 weeks only 48% of subjects were able to completely use CGMP-AA2 as their single source of protein substitute. At 52 weeks CGMP-AA2 provided a median of 75% (30-100) of the total protein substitute with the remainder being given as L-AA. Within the CGMP-AA2 group, blood Phe increased significantly between baseline and 52 weeks: [baseline to 26 weeks; baseline Phe 270 μmol/L (170-430); 26 weeks, Phe 300 μmol/L (125-485) p = 0.06; baseline to 52 weeks: baseline, Phe 270 μmol/L (170-430), 52 weeks Phe 300 μmol/L (200-490), p < 0.001)]. However, there were no differences between the CGMP-AA2 and L-AA group for Phe, Tyr, Phe:Tyr ratio or anthropometry at any of the three measured time points. Within the CGMP-AA2 group only weight (p = 0.0001) and BMI z scores (p = 0.0001) increased significantly between baseline to 52 weeks. Whole blood and plasma selenium were significantly higher (whole blood selenium [p = 0.0002]; plasma selenium [p = 0.0007]) at 26 weeks in the CGMP-AA2 group compared L-AA. No differences were observed within the L-AA group for any of the nutritional markers.

Conclusions: CGMP-AA increases blood Phe concentrations and so it can only be used partly to contribute to protein substitute in some children with PKU. CGMP-AA should be carefully introduced in children with PKU and close monitoring of blood Phe control is essential.

Keywords: Glycomacropeptide; Large neutral amino acids; Phenylalanine; Phenylketonuria; Protein substitute.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Adolescent
  • Caseins / therapeutic use*
  • Child
  • Child, Preschool
  • Female
  • Humans
  • Longitudinal Studies
  • Male
  • Nutritional Status
  • Peptide Fragments / therapeutic use*
  • Phenylalanine / blood*
  • Phenylketonurias / blood*
  • Phenylketonurias / drug therapy*


  • Caseins
  • Peptide Fragments
  • caseinomacropeptide
  • Phenylalanine