Analysis of β-cell death in type 1 diabetes by droplet digital PCR

Type 1 diabetes (T1D) and other forms of diabetes are due to the killing of β-cells. However, the loss of β-cells has only been assessed by functional studies with a liquid meal or glucose that can be affected by environmental factors. As an indirect measure of β-cell death, we developed an assay using a novel droplet digital PCR that detects INS DNA derived from β-cells. The release of INS DNA with epigenetic modifications (unmethylated CpG) identifies the β-cellular source of the DNA. The assay can detect unmethylated DNA between a range of approximately 600 copies/μL and 0.7 copies/μL, with a regression coefficient for the log transformed copy number of 0.99. The assay was specific for unmethylated INS DNA in mixtures with methylated INS DNA. We analyzed the levels of unmethylated INS DNA in patients with recent onset T1D and normoglycemia subjects at high risk for disease and found increased levels of unmethylated INS DNA compared with nondiabetic control subjects (P < .0001). More than one-third of T1D patients and one-half of at-risk subjects had levels that were more than 2 SD than the mean of nondiabetic control subjects. We conclude that droplet digital PCR is a useful method to detect β-cell death and is more specific and feasible than other methods, such as nested real-time PCR. This new method may be a valuable tool for analyzing pathogenic mechanisms and the effects of treatments in all forms of diabetes.