Should we expect a wave of type 1 diabetes following SARS-CoV-2 pandemic?

The relationship between SARS-CoV-2 infection and type 1 diabetes mellitus

Environmental factors, in particular viral infections, are thought to have an important role in the pathogenesis of type 1 diabetes mellitus (T1DM). The COVID-19 pandemic reinforced this hypothesis as many observational studies and meta-analyses reported a notable increase in the incidence of T1DM following infection with SARS-CoV-2 as well as an association between SARS-CoV-2 infection and the risk of new-onset T1DM. Experimental evidence suggests that human β-cells express SARS-CoV-2 receptors and that SARS-CoV-2 can infect and replicate in β-cells, resulting in structural or functional alterations of these cells. These alterations include reduced numbers of insulin-secreting granules, impaired pro-insulin (or insulin) secretion, and β-cell transdifferentiation or dedifferentiation. The inflammatory environment induced by local or systemic SARS-CoV-2 infection might result in a set of signals (such as pro-inflammatory cytokines) that lead to β-cell alteration or apoptosis or to a bystander activation of T cells and disruption of peripheral tolerance that triggers autoimmunity. Other mechanisms, such as viral persistence, molecular mimicry and activation of endogenous human retroviruses, are also likely to be involved in the pathogenesis of T1DM following SARS-CoV-2 infection. This Review addresses the issue of the involvement of SARS-CoV-2 infection in the development of T1DM using evidence from epidemiological, clinical and experimental studies.

PDE12 in type 1 diabetes

Type 1 diabetes (T1D) incidence is increased after COVID-19 infection in children under 18 years of age. Interferon-α-activated oligoadenylate synthetase and downstream RNAseL activation degrade pathogen RNA, but can also damage host RNA when RNAseL activity is poorly regulated. One such regulator is PDE12 which degrades 2'-5' oligoadenylate units, thereby decreasing RNAseL activity. We analyzed PDE12 expression in islets from non-diabetic donors, individuals with newly (median disease duration 35 days) and recently (5 years) diagnosed T1D, and individuals with type 2 diabetes (T2D). We also analyzed PDE12 single-nucleotide polymorphisms (SNPs) relative to T1D incidence. PDE12 expression was decreased in individuals with recently diagnosed T1D, in three of five individuals with newly diagnosed T1D, but not in individuals with T2D. Two rare PDE12 SNPs were found to have odds ratios of 1.80 and 1.74 for T1D development. We discuss whether decreased PDE12 expression after COVID-19 infection might be part of the up to 2.5-fold increase in T1D incidence.

BNT162b2 mRNA COVID-19 Vaccine Does Not Impact the Honeymoon Phase in Type 1 Diabetes: A Case Report

Type 1 diabetes (T1D), which is caused by the autoimmune destruction of insulin-secreting pancreatic beta cells, represents a high-risk category requiring COVID-19 vaccine prioritization. Although COVID-19 vaccination can lead to transient hyperglycemia (vaccination-induced hyperglycemia; ViHG), its influence on the course of the clinical remission phase of T1D (a.k.a. “honeymoon phase”) is currently unknown. Recently, there has been an increasing concern that COVID-19 vaccination may trigger autoimmune phenomena. We describe the case of a 24-year-old young Italian man with T1D who received two doses of the BNT162b2 mRNA (Pfizer-BioNTech) COVID-19 vaccine during a prolonged honeymoon phase. He experienced a transient impairment in glucose control (as evidenced by continuous glucose monitoring) that was not associated with substantial changes in stimulated C-peptide levels and islet autoantibody titers. Nonetheless, large prospective studies are needed to confirm the safety and the immunometabolic impact of the BNT162b2 vaccine in T1D patients during the honeymoon phase. Thus far, T1D patients who are going to receive COVID-19 vaccination should be warned about the possible occurrence of transient ViHG and should undergo strict postvaccination surveillance.