SUN-534 Recognition of MODY Misdiagnosed as Gestational and Type 2 Diabetes Mellitus

Abstract Disclosure: M. Murugesh: None. S. Nair: None. B. Simon: None. Glucokinase (GCK) maturity-onset diabetes of the young (MODY) is often misdiagnosed as Type 1 or Type 2 diabetes mellitus (T2DM). The first detection of hyperglycemia can also occur during pregnancy. It often presents with mild fasting hyperglycemia, is not associated with typical vascular complications and can often be managed with diet alone. Accurate diagnosis can be elusive since it requires a high clinical suspicion, thorough patient and family history, and ultimately, genetic testing. This is not only crucial for treatment decisions but also for tailoring management for pregnant patients based on fetal genotype. Despite its clinical relevance, MODY remains underdiagnosed, partly due to underutilization of genetic testing. We present a case of an Asian American female, initially diagnosed with prediabetes at age 30 by hemoglobin A1c (HbA1c) of 6.0%. Family history was significant for presumed T2DM in her father and paternal grandfather. During her first pregnancy at age 34, she was started on insulin and had an uncomplicated delivery (baby weight 7 pounds (lbs.) 14 ounces (oz)). HbA1c increased to 7% one year later, leading to a T2DM diagnosis. Due to metformin intolerance, she resumed insulin. During her second pregnancy at age 35, she continued insulin and had another uncomplicated delivery. When she established care at our institution at age 37, she remained on 15 units of intermediate-acting insulin nightly, reporting hypoglycemia at least once monthly. On physical exam, she was well-appearing with normal vitals, weight 137 lbs., and body mass index (BMI) 22.8. Labs showed HbA1c 6.2%, C-peptide 1.8, glucose 108 mg/dL and negative T1DM associated antibodies. Given her labs, young age at diagnosis, low BMI and family history, genetic testing for MODY was performed and returned positive for GCK MODY. Insulin was stopped, and her HbA1c remained controlled at 6.2% 5 months later. She was referred to medical genetics, with plans to test her children. This patient was treated for gestational DM, subsequently for T2DM, and remained on insulin for 2 years before her MODY diagnosis. Her history, lack of T2DM features, normal C-peptide, negative T1DM antibodies and the non-progressive nature of hyperglycemia prompted the MODY evaluation. The correct diagnosis led to discontinuation of insulin, reduction of hypoglycemia risk, and reassurance of the low risk of diabetic complications over time. Further, treatment during pregnancy may not have been warranted if fetal testing was also positive for the GCK variant. Presentation: Sunday, July 13, 2025