SUN-561 - Diagnostic Value of Continuous Glucose Monitoring (CGM) in Late-Onset MODY Type I (HNF4A Mutation)

Background: Mature-onset diabetes of the young (MODY) is a monogenic form of diabetes with autosomal dominant inheritance that is frequently unrecognized, particularly in adults without a strong family history. MODY is typically associated with diabetes onset before age 30; later-onset cases are frequently misdiagnosed as type 1 or type 2 diabetes, resulting in suboptimal management.

Clinical

Case: 59 year old male with presumed non-insulin dependent type II diabetes (T2DM) presented for evaluation of persistent fasting hyperglycemia. Despite adherence to metformin therapy, dietary modifications, and regular exercise, fasting glucose levels remained elevated. Hemoglobin A1c levels however consistently ranged from normal to prediabetic levels after lifestyle interventions, creating an inconsistency between laboratory values and capillary glucose readings. Family history was notable for only grandmother and distant relatives with diabetes, without early-onset disease. CGM revealed frequent sustained hyperglycemia, with glucose levels greater than 200mg/dl in the fasting and postprandial periods. Given the atypical clinical course and glycemic discordance, genetic testing was performed which confirmed a HNF4A mutation, establishing a diagnosis of MODY type I.

Conclusion: Clinicians should maintain a high index of suspicion for monogenic diabetes in patients with atypical glycemic patterns, regardless of age or family history. Early recognition of MODY has important therapeutic and prognostic implications. This case highlights the utility of CGM in identifying hidden patterns hyperglycemia to aid in diagnosis.

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