The primary goal is to correlate beta cell mass to beta cell function from measurements during and shortly after the honeymoon phase of type 1 diabetes, to improve understanding of the change in metabolic control after the honeymoon phase.

The exact role of beta cell mass during the development and course of diabetes is still poorly understood. Further research on beta cell mass is essential to obtain more insights that might aid in the development of diabetes treatment. This study aims at a specific phase of T1D that is called the 'honeymoon phase' or period of partial remission. Once insulin treatment has started, the honeymoon phase will arise in most patients. In this period, T1D patients become temporarily less insulin-dependent. Unfortunately, the honeymoon phase is only temporary, in which a decline in blood glucose regulation will be seen afterwards, leading to an increasing demand for insulin. To increase understanding of this change in metabolic control after the honeymoon phase, repeated measurements of the beta cell mass and function are performed during and shortly after the honeymoon phase. The comparison of both measurements might lead to an increased understanding whether changes in insulin demand after the honeymoon phase is mainly dependent on a decline in the beta cell mass, or because of a decrease in functional beta cells. The outcome of this study can provide new insights, which can contribute to the development of novel treatment options.

Inclusion Criteria:

• Age ≥ 16 years
• Diagnosed with T1D
• Presence of anti-GAD
• Subject is in honeymoon phase
• 17 ≤ BMI ≥ 30 kg/m^2 at moment of visit
• Ability to sign informed consent

Exclusion Criteria:

• Previous treatment (within 6 months) with synthetic Exendin (Exenatide, Byetta®) or Dipeptidyl-Peptidase IV inhibitors
• Liver disease
• Renal disease
• Pregnancy or the wish to become pregnant within 6 months after the study
• Breastfeeding
• BMI <17 kg/m2 or BMI >30 kg/m2
• Age <16 years
• When the end of the honeymoon phase is not observed within 11 to 13 months after the inclusion of the subject
• Inability to sign informed consent