Diagnostic pitfalls in a young adult with new diabetes

Abstract

A 20-year-old South Asian male presented with polyuria, polydipsia, HbA1c 81 mmol/mol, BMI 28.8 and family history of both type 1 and type 2 diabetes mellitus. As autoantibody testing was negative and c-peptide level demonstrated significant endogenous insulin secretion, type 1 diabetes was excluded. Given his age and family history, the differential diagnosis included maturity-onset diabetes of the young (MODY), a rare form of diabetes caused by a single-gene variant. A high probability of MODY was calculated and he was subsequently referred for genetic testing. Although a useful tool, the pre-test probability calculator for MODY is only validated in White Europeans. A heterogenous variant of unknown clinical significance of the NEUROD1 gene was detected, leading to gliclazide use with poor response. The patient responded well to metformin. Type 2 diabetes was considered the most likely diagnosis. This case highlights the diagnostic challenges in young patients of Asian ethnicity and the importance of interpreting genetic results of unknown significance within the clinical context. Ethnicity-specific BMI thresholds should be used when classifying patients as overweight or obese.