Unmethylated Insulin as an Adjunctive Marker of Beta Cell Death and Progression to Type 1 Diabetes in Participants at Risk for Diabetes.

Islet autoantibody (iAb)-positive individuals have a high risk of progression to type 1 diabetes (T1D), although the rate of progression is highly variable and factors involved in the rate of progression are largely unknown. The ratio of unmethylated/methylated insulin DNA levels (unmethylated ratio) has been shown to be higher in participants at high risk of T1D compared to healthy controls. We aimed to evaluate whether an unmethylated ratio may be a useful biomarker of beta cell death and rate of progression to T1D. In TrialNet participants who were followed in the Pathway to Prevention Study and progressed to diabetes ( = 57, median age of onset 15.3 years), we measured unmethylated ratio and autoantibodies by electrochemiluminescence (ECL) assays (ECL-IAA, ECL-GADA, and ECL-IA2) and radioimmunoassays (RIA) (mIAA, GADA, IA2A, and ZnT8A) longitudinally for 24 months prior to diagnosis. Linear models were used to test the association between unmethylated ratio and the age at T1D diagnosis and unmethylated ratio and iAb over time. Close to diabetes onset, the unmethylated ratio was associated with mIAA ( = 0.003), ECL-IAA ( = 0.002), and IA2A ( = 0.01) levels, but not with GADA, ECL-GADA, ECL-IA2, or ZnT8A levels. No significant associations were found at baseline (24 months prior to T1D diagnosis). Only mIAA levels were significantly associated with an unmethylated ratio over time, with a 0.24 change in the ratio for each 0.1 change in mIAA z-score ( = 0.02). Adjusting for a baseline unmethylated ratio, an increased rate of change in unmethylated ratio from baseline to diabetes onset was associated with a five-year decrease in age at T1D diagnosis ( = 0.04).