Evaluation of PKU Sphere in Maternal PKU

Inclusion Criteria: * Diagnosis of phenylketonuria (PKU) or hyperphenylalaninemia (hyperphe) which requires dietary management during pre-conception and/or pregnancy. * Aged 16 years and above. * Following dietary management advice pre-conceptually and/or during pregnancy, aiming for phenylalanine levels of 120-250µmol/L. * Prior positive PKU sphere taste test completed as part of routine care. * Chosen to take part or full requirement of protein substitute as PKU sphere pre-conceptually and/or during pregnancy. * Willingly given, written, informed consent from patient. * Participant is, in the opinion of the investigator, able to participate and can comply with the study protocol. Exclusion Criteria: * Conception of pregnancy without commencement of phe-restricted diet and blood phenylalanine not maintained within target range by 10 weeks' gestation. * Patients with known soya, milk or fish allergies / intolerance. * Intake of pegvaliase or large neutral amino acids within 30 days prior to screening visit. * Patients who are currently participating in, plan to participate in, or have participated in an interventional investigational drug, food or medical device trial within 30 days prior to screening visit.