Defining the Decline in Endogenous Insulin Secretion in Type 1 Diabetes Diagnosed After 30 Years of Age.

Defining the Decline in Endogenous Insulin Secretion in Type 1 Diabetes Diagnosed After 30 Years of Age.

The study aims is to find out if people with type 1 diabetes diagnosed in later life (after age 30) have the same rapid loss of insulin secretion (measured using C-peptide) that occurs in younger adults with type 1 diabetes. The investigators will recruit 135 participants aged over 30 years with a clinical diagnosis of type 1 diabetes and diabetes duration ≤100 days. The investigators will also recruit a comparison group of 61 participants aged 18-30 with a clinical diagnosis of type 1 diabetes and diabetes duration ≤100 days. C-peptide will be measured during mixed meal tolerance tests (MMTT) performed at baseline, 6 months and a year.

This study also aims to test a new more practical way of monitoring insulin secretion at home using a finger prick 'blood spot' rather than time consuming tests in a hospital. Finger-prick C-peptide samples will be collected after the MMTT and by the participants at home throughout the year.

The study aims to evaluate progression of type 1 diabetes. Primary analysis will be conducted on those with >=1 diabetes autoantibody positive (GAD, IA2 ZNT8). Sensitivity analysis will be performed by repeating all analysis defining T1D as a) double antibody positivity and b) single antibody positivity combined with a high genetic risk score for T1D (T1DGRS>5th centile of a control population).

Further aims will be to evaluate the utility of dried blood spot testing to detect change in C-peptide and the utility of home test results as a marker of hypoglycaemia and glucose variability.

Inclusion Criteria:

• Adults with a clinical diagnosis of Type 1 diabetes within the previous 100 days.
• Aged >30 at the time of Type 1 diabetes diagnosis OR (additional early onset Type 1 diabetes cohort) aged ≥18 and ≤30 at the time of Type 1 diabetes diagnosis.
• Insulin treated at the time of recruitment
• Able and willing to provide informed consent.

Exclusion criteria

• Pregnancy
• Known monogenic diabetes
• Known secondary diabetes (diabetes considered likely due to medication, cystic fibrosis, pancreatitis, pancreatic cancer, pancreatic surgery, hemochromatosis or Cushing's syndrome).