Impact Of A Phe-Restricted Diet On Gut Health In Children With PKU

This is a single-centre, cross-sectional observational study conducted at Birmingham Children's Hospital. The study investigates the association between phenylketonuria (PKU) treatment, degree of dietary restriction, gastrointestinal health, and the composition and functional potential of the gut microbiota.

Children and adolescents aged 3-17 years with early-treated PKU are recruited into one of three cohorts according to their existing clinical management: treatment with a phenylalanine-restricted diet alone (anticipated n=30), treatment with sapropterin alongside an individualised phenylalanine-restricted diet (anticipated n=30), or treatment with sepiapterin alongside an individualised phenylalanine-restricted diet (anticipated n=14). Participants receiving sapropterin or sepiapterin have been receiving treatment for at least three months and have achieved at least a 100% increase in natural protein tolerance compared with their pre-treatment prescription. Treatment allocation, medication dosage, and dietary management are determined as part of routine clinical care and are not assigned or modified by the study.

One healthy household control is recruited for each participant with PKU. Household controls are aged 3 years or older and do not have PKU or another inherited metabolic disorder. Recruiting controls from the same household aims to reduce the influence of shared environmental factors, including living conditions and food availability, when comparing gut microbiota profiles. The anticipated total enrolment is 148 participants, comprising 74 participants with PKU and 74 household controls.

Each participant provides a single faecal sample. Samples are stored at -80°C and analysed using shotgun metagenomic sequencing to characterise microbial taxonomic composition, within-sample diversity, between-sample community differences, and microbial functional potential. Taxonomic profiles are assessed at multiple levels, including phylum, genus, and species. Functional annotation is used to characterise microbial genes, enzymes, and metabolic pathways.

Dietary intake is assessed using a 24-hour dietary recall, including natural protein intake, protein substitute intake, dietary fibre intake, and consumption of special low-protein foods. Gastrointestinal symptoms are assessed using the age-appropriate self-report or parent-proxy version of the PedsQL Gastrointestinal Symptoms Module, and stool form is assessed using the Bristol Stool Form Scale. Relevant demographic and clinical information, including age, sex, anthropometric measurements, PKU treatment, and metabolic control, is also collected.

The findings from this study may support the development of nutritional strategies and protein substitutes that more effectively promote gastrointestinal and metabolic health in individuals with PKU.

Inclusion criteria

Participants with PKU:

• Aged 3-17 years.
• Confirmed diagnosis of phenylketonuria following newborn screening.
• Receiving ongoing clinical management for PKU.
• For the diet-only cohort: managed with standard phenylalanine-restricted dietary treatment and not receiving sapropterin or sepiapterin.
• For the sapropterin cohort: receiving sapropterin for at least three consecutive months and having achieved at least a 100% increase in natural protein tolerance compared with the pre-treatment prescription.
• For the sepiapterin cohort: receiving sepiapterin for at least three consecutive months and having achieved at least a 100% increase in natural protein tolerance compared with the pre-treatment prescription.

Healthy household controls:

• Aged 3 years or older.
• Living in the same household as a participating child or adolescent with PKU.
• No known diagnosis of PKU or another inherited metabolic disorder.

Exclusion criteria

• Congenital malformations.
• Chronic gastrointestinal disease.
• Endocrine, liver, or kidney disease.
• Other chronic medical conditions likely to affect gut microbiota composition.
• Following a therapeutic diet for a medical condition other than PKU within the six months before stool sample collection.