The Diabetes Prevention Trial—Type 1 Diabetes (DPT-1) consisted of two randomized clinical trials to determine whether insulin could prevent or delay the onset of overt diabetes in relatives of patients with diabetes. One study investigated the effects of parenteral insulin in relatives with a projected five-year risk of diabetes higher than 50 percent, while the other looked at the effects of oral insulin in relatives with a projected five-year risk of 26 to 50 percent.

First and second-degree relatives were screened for islet-cell antibody (ICA) titer ≥ 10 and then staged to assess risk of diabetes. Those with a high risk were eligible for the parenteral insulin trial, and those with a low risk were eligible for the oral insulin trial. In the parenteral insulin trial, subjects in the intervention group received parenteral insulin subcutaneous injections twice daily, plus annual intravenous infusions; the control group received no treatment. In the oral insulin trial, subjects were assigned to receive capsules of either oral insulin or matched placebo. For both trials, participants were seen every 6 months, and at those visits an oral glucose tolerance (OGT) test was performed to assess glycemic status, the primary study end point. Other assessments included intravenous glucose tolerance tests and mixed-meal tolerance tests performed at baseline, as well as at various points during the study. Results showed that neither parenteral nor oral insulin succeeded in delaying or preventing the development of diabetes in high-risk relatives of current diabetes patients. Long-term follow-up to detect any effects on the course of diabetes was initiated.

The DPT-1 study aimed to determine if insulin could prevent or delay the onset of overt diabetes in high-risk relatives of patients with diabetes.

The primary outcome measure was an OGT test, used to assess glycemic status. Secondary outcome measures included intravenous glucose tolerance and mixed-meal tolerance tests.

Participants were enrolled who were relatives of current diabetes patients at high- to intermediate-risk of developing diabetes. Risk was defined for different populations based on relationship to the diabetes patient using insulin autoantibody (IAA) status, first-phase insulin response (FPIR) to intravenous glucose, oral glucose tolerance (OGT), and presence or absence of HLA-DQA10102/DQB10602 (a protective haplotype that excluded subjects from participation). Relatives with a 5 year risk of ≥50% (defined as “high-risk”) were eligible for the parenteral insulin trial, while relatives with a 5 year risk of 26-50% (defined as “intermediate risk”) were eligible for the oral insulin trials. More details on inclusion and exclusion criteria for both trials are documented in the study protocol.

The study concluded that neither parenteral nor oral insulin succeeded in delaying or preventing the development of diabetes in high-risk relatives of current diabetes patients. Long-term follow-up to detect any effects on the course of diabetes was initiated.