The challenges of identifying and studying type 1 diabetes in adults – published online 20/09/2023

Nicholas J. Thomas, Angus G. Jones

Type 1 diabetes occurs at any age, but diagnosis in adults is difficult as type 2 diabetes predominates. In this issue, Thomas and Jones (https://doi.org/10.1007/s00125-023-06004-4) review the challenges of robustly identifying type 1 diabetes in older adults and outline how these can be addressed. The authors also discuss the potential implications of misclassification for our understanding of type 1 diabetes presenting in adults. The phenotype of type 1 diabetes is commonly reported to be different at older onset ages, overlapping with that of type 2 diabetes. Studies suggest that misclassification of clinically diagnosed type 1 diabetes is increasingly common with older age. The authors state that the inadvertent study of participants with and without autoimmune aetiology diabetes may explain many of the reported changes in the characteristics of those with type 1/autoimmune diabetes with older age. However, when robust disease definitions are used, the phenotype of older-onset type 1 diabetes appears broadly similar to that of type 1 diabetes occurring earlier in life, without differences in presentation, genotype or progression across adult-onset ages. The authors conclude that, in the clinic, biomarker investigation is essential for the diagnosis of adult-onset type 1 diabetes, while, in research, use of high-specificity approaches to define type 1 diabetes in adults is critical to understanding the phenotype of adult-onset autoimmune aetiology diabetes. The figures from this review are available as a downloadable slideset

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