All participants will be identified from existing research cohorts managed by the NIHR Exeter Research Facility (Exeter CRF) and/or the Oxford Biobank (OBB) and recruitment will be facilitated within the Exeter CRF and/or Oxford Centre for Diabetes, Endocrinology and Medicine (OCDEM). Individuals will be identified with the variant of interest or as gender, age and BMI matched controls. All potential participants will be 'blinded' by a Data Manager so that the study team does not know which participants have the variant and which are controls. They will be invited into the study by letter, and provided with the study information sheet and study team contact details. A member of the study team will contact them within 2-3 weeks to determine whether they are interested in participating, to offer them greater explanation of what the study entails, and to check their eligibility. If they agree to take part, verbal consent for a fasted visit will be sought and an appointment will be made and confirmed in writing/by email.