Hyperinsulinism

This observational 'recruit by genotype' study aims to provide insights into the cellular and molecular pathways underlying beta cell disorders and their physiological consequences. Eligible individuals are those with and without a pathogenic genetic variant, acting as case and control, respectively. Using a "recruit by genotype" approach, the researchers will perform detailed and specific analysis according to the individual's genetic variant. The study's main aims are to : 1) identify and describe biomarkers and cellular features in blood samples that occur because of the rare causal genetic variant; 2) study the altered physiology or cellular function that are due to the rare causal genetic variant. Participants will attend a study visit that will entail: * Consent * Data collection * Height and weight measures * Blood samples * MRI (optional), dependent on genotype and sub-study objectives. There is no treatment and the participants' normal clinical care will be unaffected and will continue uninterrupted. A small subset of participants may be invited for further sub-studies in the future. Researchers may recruit sex-matched healthy controls (without the variant of interest