In patients with inborn errors of metabolism (IEM) and in those requiring a ketogenic diet for the treatment of medical conditions, relevant biochemical analytes are routinely and regularly measured in venous or capillary blood samples. Repeated venipuncture for blood collection is invasive, burdensome, and resource-intensive. As an alternative, capillary blood sampling can provide some relief for the measurement of a limited number of metabolites. Nevertheless, the frequent finger pricks required to obtain capillary blood samples can still be uncomfortable for patients. Therefore, patients could benefit if non-invasive breath measurements were to replace the currently invasive biochemical monitoring methods in the future.

In this study, the usability of metabolite measurements across matrices (venous blood, capillary blood, breath captured by a handheld sensor and breath in a collection bag) in IEM patients, individuals prescribed special health-related diets, and healthy volunteers will be investigated. The usability of a handheld breath sensor for remote monitoring of patients will also be tested. Lastly, exploratory investigations will be performed to identify new disease biomarkers in breath.

Inclusion Criteria:

• Patients aged 4-20 years old with refractory epilepsy on a ketogenic diet, or
• Patients aged 4 years old and above with a confirmed diagnosis of urea cycle disorders, organic acidurias, amino acidopathies and fatty acid oxidation defects, or
• healthy adults and
• informed consent

Exclusion Criteria:

• Physical findings at screening that would compromise safety of the participant or quality of study data. Examples include presentation of fever, pulmonary complications, presence of disease comorbidities that might interfere with study result and inability to comply with study procedures.

Patients who are routinely cared for at the study site will be invited to participate. Healthy volunteers will be recruited through communication with healthy family members accompanying patients to hospital visits and the general population through flyers.