Increased glycemic variability has been proposed as an independent predictor of hypoglycemia in diabetic patients. Likewise, episodes of dysglycemia have been found to be predictive of diabetes in antibodypositive nondiabetic individuals. We hypothesise that an in-depth observational study comparing state-of-the-art measures of functional beta cell mass and glycemic variability will specify the relationship between both variables over a broad range of residual function and will identify treatment goals for functional beta cell mass to be reached in future beta cell therapy trials in order to avoid frequent hypoglycemia in patients and dysglycemia in risk groups. The available expertise and infrastructure (see background and (inter)national context) place the promoters of the present project in a unique position to carry out the planned experiments and support their feasibility.

The established clinical network and the developed dynamic function tests and biological markers provide us with the unique opportunity to identify sufficiently large groups of high-risk first-degree relatives (> 50% risk of diabetes) of a proband with type 1 diabetes and of recent-onset type 1 diabetic patients with the overall aim to investigate the correlation between functional beta cell mass and glycemic variability in relation to metabolic outcome in order to determine thresholds of residual function below which:

1. glucose tolerance starts to decline sharply in relatives
2. the risk of deteriorating metabolic control and (severe) hypoglycemic events strongly increases in patients

To this effect we will:

1. measure and follow over a two-year period

   1. the functional beta cell mass of participants as determined by AUC C-peptide release - the preferred outcome measure in type 1 diabetes trials during hyperglycemic clamp test
   2. the participants' within- and between-day glycemic variability as determined by seven point selfmonitoring of blood glucose (SMBG) and continuous glucose monitoring (CGM) during 5 days preceding each clamp procedure

2. perform oral glucose tolerance tests (OGTTs; only in relatives), determine HbA1c levels centrally (relatives and patients) and record insulin requirements and hypoglycemic episodes (in patients) Our previous experiments have documented that the selected patients and relatives (see workplan) display large inter-individual differences in functional beta cell mass (ranging anywhere between control values and < 10% of controls) allowing to study glycemic variability as a function of residual cell function over a large range of values. They also illustrate that the recruitment capacity of the clinical network and the acceptance rate and compliance of the patients and relatives for the clamp procedure is high and sufficient to carry out the planned experiments.

Inclusion Criteria:

Type 1 diabetic patients:

1. aged 12-39 years at diagnosis
2. treated with insulin for less than 4 weeks
3. optimally treated with intensified insulin treatment: minimal three preprandial injections of ultra-rapidly acting analogs and one evening injection of long-acting insulin (Lantus®, Sanofi Aventis)
4. positive for autoantibodies against insulin (IAA-sampled within the first week of insulin treatment), 65kDa glutamate decarboxylase (GADA), IA-2 protein (IA-2A) and/or zinc transporter 8 (ZnT8A)

First-degree relatives:

1. aged 12-39 years at inclusion
2. sibling or offspring of a type 1 diabetic patient diagnosed before age 35 or between age 35 and 50 with in addition a body mass index < 28 kg/m2 and an initial insulin dose > 0.25 U.kg -1.d-1
3. > 50% risk of diabetes within 5 years as indicated by positivity for at least 2 diabetes antibodies including IA-2A and/or ZnT8A in absence of protective HLA-DQ genotypes (6)

Exclusion Criteria:

• pregnancy or lactation in women
• use of illicit drugs or overconsumption of alcohol or history of drug or alcohol abuse
• being legally incapacitated, having significant emotional problems at the time of the study, or having a history of psychiatric disorders
• having received antidepressant medications during the last 6 months
• treatment with immune modulating or diabetogenic medication (such as corticosteroids)
• history of any illness that, in the opinion of the investigator, might confound the results of the study or pose additional risks to the subjects
• patients not treated with Lantus as insulin therapy.