Evaluation of the Express Plus Range

This is a prospective acceptability study of the express plus range in 40 participants aged at least three years of age for the dietary management of IEM (PKU, MSUD, HCU, TYR and GA ). The study will involve a Transition Period where patients will build-up to at least one sachet of express plus per day. During the Transition Period, daily intake of express plus and the patient's other PS will be recorded, including the time taken to consume. The Transition Period will last a maximum of 6 weeks, after which the patient will enter a 28-day Evaluation Period. During the Evaluation Period, patients will continue to record intakes, as well as GI tolerance and a final evaluation of the product's palatability and usability. Some patients, likely adults, will not require a transition from their original protein substitute to at least one sachet of express plus. These patients can enter the Evaluation Period directly. The end of the 4-week Evaluation Period is defined as the participant's End of Study. Following this, participants will be followed up as per standard of care. Some of this standard of care data may be relayed to the sponsor for a maximum of 26 weeks. This will last for a maximum of 26 weeks and will involve the collection of routine phe and tyrosine levels, as well as amount of PS prescribed and taken. Information will also be collected from patients regarding the reasons for the success or indeed failure of transition to PKU express plus. This data will come from routine clinical contact and will be recorded by the HCP, rather than by the patient.