This is a prospective, observational research study in 5 children with Maple Syrup Urine Disease (MSUD). Subjects who are currently taking a valine and isoleucine supplement for MSUD will be recruited for a 56 day trial, of a new ready-to-use valine supplement and a new ready-to-use isoleucine supplement, to evaluate the tolerability and acceptability of the study products compared with their usual products.

This is a prospective, observational 2-part research study in 5 children with Maple Syrup Urine Disease (MSUD). Subjects who are currently taking a valine and isoleucine supplement for MSUD will be recruited for a 56 day trial, of a new ready-to-use valine supplement (Part 1) and a ready-to-use isoleucine supplement (Part 2), to evaluate the tolerability and acceptability of the study products compared with their usual products.

When an appropriate subject has been identified, they and their parents/ caregivers will be sent a study information sheet via the post. They will be invited to request further information about the study if they wish by contacting the Dietitian. The Dietitian will explain the study in more detail either by telephone or via a face-to-face consultation in a convenient location/preferred venue for the participant and their parent/caregiver. Recruitment of each patient will be by written informed consent, which will be completed by the parents/primary caregivers and taken by the Dietitian. Children will also complete an assent/ consent form. Reimbursement will be offered for any travel expenses incurred for any visits to the hospital that are over and above normal/routine visits.

Subjects will replace their usual daily dose of powdered valine supplement with the equivalent amount of the liquid valine supplement for 28 days (Part 1). They will then return to their usual valine supplement and replace their usual powdered isoleucine supplement with the new liquid isoleucine supplement for a further 28 days (Part 2). The outcome of this assessment will be used in a submission to regulatory authorities to enable the study products to be reimbursable on prescription in the United Kingdom (UK). Subjects will be asked to take the new valine supplement for 28 days (Part 1), then the new isoleucine supplement for 28 days (Part 2). During this time, caregivers will be asked to complete a daily acceptability and tolerance questionnaire recording information on:

• Usage and adherence
• Ease of use and any issues with administration
• Any gastro-intestinal side effects The questions should take a maximum of 10 minutes to complete each day. Additional questions will also be completed at the beginning and end of the study that will consider opinion on both usual valine and isoleucine, and study valine and isoleucine, with respect to taste, appearance, smell, presentation and packaging; ease of administration; how the valine is taken; and any other problems or symptoms.

Weight, height and 3 day dietary intake will also be recorded at the beginning and end of Part 1 and Part 2 of the study. A 3-day food diary will record food/drink intake at the beginning of the study whilst taking their usual supplements (Day -3, -2, -1), for 3 days at the end of Part 1 of the study whilst taking the new valine supplement (Days 26, 27, 28), and for 3 days at the end of Part 2 of the study whilst taking the new isoleucine supplement (Days 54, 55, 56).

Meta healthcare will supply the valine oral solution (50mg/ml) and isoleucine oral solution (25mg/ml) for participants free of charge.

During the 56 day trial, weekly routine blood samples will be posted and analysed for valine, leucine and isoleucine as is usual clinical practice. At recruitment, the previous 4 blood results for valine, leucine and isoleucine will be recorded for comparison.

Inclusion Criteria:

• Male and female MSUD patients ≥1 year and <16 years of age.
• Patients diagnosed with MSUD.
• Taking both valine and isoleucine supplements for MSUD and willing to take the new supplements for 56 days.
• Absence of comorbidities.
• Adherence with dietary management and valine and isoleucine supplements.
• Able to understand and comply with the requirements of the investigation and sign the Informed Consent Form/Assent form

Exclusion Criteria:

• Age <1 year old and >16 years old.
• Patients with comorbidities.
• Any moderate to severe acute illness which in the opinion of the Investigator would interfere with the study procedures or study outcome.
• History of poor co-operation, non-adherence with dietary management, or poor adherence to investigation procedures.
• Participation in any other studies involving investigational or marketed products concomitantly or within two weeks prior to entry into the study.

No identifiable individual patient data will disclosed outside of the clinical care team.