The β-cell killing that characterizes type 1 diabetes (T1D) is thought to begin years before patients present clinically with metabolic decompensation; however, this primary pathologic process of the disease has not been measured.

The kinetics of disease progression is limited because there are no methods that directly measure β-cell death, but a method has been recently developed for assessing β-cell death in vivo by measuring the relative amount of β-cell-derived unmethylated insulin (INS) DNA in the circulation.

A team of scientists led by those at Yale University (New Haven, CT, USA) performed an observational study of 50 participants from two cohorts at risk for developing T1D from the TrialNet Pathway to Prevention study and of four subjects who received islet autotransplants. DNA was purified from serum samples using QIAamp DNA Blood Kits (Qiagen; Venlo, The Netherlands).

Analysis of β-cell death was carried out by measuring the levels of unmethylated INS DNA by droplet digital polymerase chain reaction (ddPCR). The DNA content of the droplets was analyzed with a QX100 Droplet Reader (Bio-Rad; Hercules, CA, USA). Plasma C-peptide levels were measured using the Tosoh AIA 1800 assay (Tokyo, Japan).

In at-risk subjects, those who progressed to T1D had average levels of unmethylated INS DNA that were elevated modestly compared with those of healthy control subjects. In at-risk individuals that progressed to T1D, the observed increases in unmethylated INS DNA were associated with decreases in insulin secretion, indicating that the changes in unmethylated INS DNA are indicative of β-cell killing. Subjects at high risk for T1D had levels of unmethylated INS DNA that were higher than those of healthy controls and higher than the levels of unmethylated INS DNA in the at-risk progressor and at-risk non-progressor groups followed for four years. Evaluation of insulin secretory kinetics also distinguished high-risk subjects who progressed to overt disease from those who did not.

The authors concluded that that a blood test that measures unmethylated INS DNA serves as a marker of active β-cell killing as the result of T1D-associated autoimmunity. Together, the data support the concept that β-cell killing occurs sporadically during the years prior to diagnosis of T1D and is more intense in the peridiagnosis period. The study was published on February 2, 2015, in the Journal of Clinical Investigation.

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