Phenylalanine (Phe) free protein substitutes are typically presented in ready to drink liquid or powder format and are made up with water to a set volume. Despite recent advancements related to the taste, scent and texture of commercially available protein substitutes, a proportion of PKU patients choose to consume tablet-based protein substitutes. Protein substitutes in tablet format may help overcome taste, scent and texture concerns associated with powdered and liquid preparations. Indeed, previous research has shown that protein substitute tablets are an effective strategy to manage PKU in children, teenagers and adults. Nonetheless, the daily burden and discipline required often impedes compliance, especially alongside the restrictive low-protein diet. Achieving compliance with multivitamin supplements when given alongside protein substitutes therefore becomes especially challenging. This is particularly true for adolescent, adult and maternal populations.

PKU Microtablets have recently been developed. PKU Microtablets are a new phenylalanine-free tablet protein substitute combined with vitamins, minerals and trace elements. As patient acceptability is fundamental to the successful use of any protein substitute, investigation is needed to assess the compliance, tolerance and acceptability of PKU Microtablets as part of a low phenylalanine dietary regimen in PKU patients.

This series of case-studies aims to evaluate the gastrointestinal tolerance, acceptability, compliance, and safety of this protein substitute in both adults and children from 4 years. These case studies will last 29 days in total, including a 1-day baseline period followed by a 28-day intervention period. The case studies will be conducted across multiple specialist metabolic centres in the UK.

Inclusion Criteria:

• Male or female
• Over 4 years of age
• Patients diagnosed with any phenotype of PKU characterised by hyperphenylalaninaemia
• Have been compliant in taking at least one protein substitute, providing at least 20g protein equivalent, for at least 1 month prior to trial commencement
• Have a prescribed daily phenylalanine allowance for PKU
• Written or electronic informed consent from patient, and/or from parent/caregiver if applicable
• Participants who are anticipated to be able to take at least 20g protein equivalent of the case study product per day

Exclusion Criteria:

• Pregnant or lactating
• Requiring parenteral nutrition
• Major hepatic or renal dysfunction
• Participation in other studies within 1 month prior to entry of this study
• Allergy to any of the study product ingredients
• Investigator concern around willingness/ability of patient or parent/caregiver to comply with protocol requirement
• Treatment with Sapropterin dihydrochloride for less than 6 months