Ajinomoto Cambrooke has developed a PKU protein substitute that is a proprietary blend of purified Glycomacropeptide (GMP) and essential amino acids, under the brand name Glytactin®. One serving of such Glytactin® products contains 20mg or less of Phenylalanine (Phe). The aim of the proposed study is to use this purified GMP-AA-based protein substitute, with less Phe per gram of protein equivalent than other commercially available products, in children with PKU at 100% of their protein substitute intake and evaluate its efficacy and the change in blood Phe in comparison to Phe-free L-AA-based protein substitutes.

Study Design This is a 2-stage, 15-week randomized crossover trial. The randomized crossover design was chosen as it reduces the influence of differences among individuals; and it offers statistical efficiency (requires fewer subjects than non-crossover designs).

In summary, 2 groups of 9 participants each will be assigned to either (1) sequence 1: take GMP-AA-based PS for the first 4 weeks and then take only L-AA-based Protein Substitute for 4 weeks, or (2) take only L-AA-based Protein Substitute for the first 4 weeks and then take GMP-AA-based PS for 4 weeks. At the end of the first 4 weeks, a 2-week washout period will follow with both groups only consuming L-AA-based PS. Randomization will be generated by a block randomization system and the random order will be kept within a sealed envelope.

Primary research objective The principal research objective of this study is to evaluate the effect on Phe levels of a low-Phe diet combined with a purified GMP-AA-based protein substitute (containing 1 mg Phe/g Protein Equivalent), in the treatment of paediatric patients with PKU.

Secondary research objectives The secondary objectives of the study aim to investigate whether there are any differences between the GMP-AA-based protein substitute and L-AA-based protein Substitute in the frequency and quantity of protein substitute intake, if any GI (gastrointestinal) symptoms occur with ingestion of the GMP-AA-based protein substitute, effect on satiety (hunger) and mood and any differences in anthropometric data.

Inclusion Criteria:

• Patients with PKU, aged 5 to 16 years of age, currently compliant with protein restricted diet and L-AA- and/or GMP-AA-based protein substitute willing to switch to a GMP-AA-based only product for 4 weeks.

  • 2 out of 4 last blood Phe levels within target range (i.e. 50%): Target range 120-360µmol/l <12 years Target range 120-600µmol/l >12 years

Exclusion Criteria:

• • Milk protein allergy

  • Pregnancy
  • Severe medical diagnosis not related to PKU
  • Treatment with Sapropterin hydrochloride (KUVAN)