# Double diabetes—when type 1 diabetes meets type 2 diabetes: definition, pathogenesis and recognition

## TL;DR

Double diabetes combines features of type 1 and type 2 diabetes, leading to higher complication risks and requiring better identification and treatment strategies.

## Contribution

This paper reviews the evolving definition of double diabetes and proposes methods for its clinical identification and potential therapies.

## Key findings

- Double diabetes is associated with increased risk of complications regardless of blood sugar control.
- Insulin resistance markers can help identify individuals with double diabetes in clinical practice.
- The global rise in obesity and T1D suggests an increasing prevalence of double diabetes.

## Abstract

Currently, the differentiation between type 1 diabetes (T1D) and type 2 diabetes (T2D) is not straightforward, and the features of both types of diabetes coexist in one subject. This situation triggered the need to discriminate so-called double diabetes (DD), hybrid diabetes or type 1.5 diabetes, which is generally described as the presence of the insulin resistance characteristic of metabolic syndrome in individuals diagnosed with T1D. DD not only raises the question of proper classification of diabetes but is also associated with a significantly greater risk of developing micro- and macroangiopathic complications, which was independent of glycaemic control. When considering the global obesity pandemic and increasing incidence of T1D, the prevalence of DD may also presumably increase. Therefore, it is of the highest priority to discover the mechanisms underlying the development of DD and to identify appropriate methods to prevent or treat DD. In this article, we describe how the definition of double diabetes has changed over the years and how it is currently defined. We discuss the accuracy of including metabolic syndrome in the DD definition. We also present possible hypotheses connecting insulin resistance with T1D and propose possible methods to identify individuals with double diabetes based on indirect insulin resistance markers, which are easily assessed in everyday clinical practice. Moreover, we discuss adjuvant therapy which may be considered in double diabetic patients.

The online version contains supplementary material available at 10.1186/s12933-024-02145-x.