Diagnostic Classification of Maturity-Onset Diabetes of the Young (MODY)

Introduction to MODY Diagnosis

The American Diabetes Association recommends considering MODY in patients with diabetes diagnosed at a young age, modest hyperglycemia, and negative autoimmune markers 1, 2
Patients with MODY typically have a family history of diabetes, with an autosomal dominant inheritance pattern 1, 2

Age <35 years at diagnosis is a characteristic feature of MODY, with most patients presenting before age 25 years 5, 6
Modest HbA1c elevation (<7.5% or <58 mmol/mol) at diagnosis is typical of MODY 1, 2
Normal C-peptide level indicates preserved insulin secretion with minimal insulin resistance, consistent with MODY 1, 2
Mildly elevated BMI (26 kg/m²) is more consistent with MODY than type 2 diabetes, which typically presents with significant obesity 1, 2

Normal C-peptide with hyperglycemia indicates preserved beta-cell function, without the severe insulin resistance of type 2 diabetes 3, 1
C-peptide values >600 pmol/L suggest type 2 diabetes, while values 200-600 pmol/L are consistent with MODY 1, 3
BMI is a crucial differentiating factor, with MODY patients typically having normal or only mildly elevated BMI 1

Obtaining a detailed family history is essential, looking for one parent with diabetes and an autosomal dominant inheritance pattern 1, 2
Checking for specific MODY features, such as renal cysts, partial lipodystrophy, or maternally inherited deafness, can aid in diagnosis 1, 2
Calculating MODY probability using the monogenic diabetes prediction model can help determine the need for genetic testing 1
Genetic testing for common MODY mutations (HNF1A, GCK, HNF4A, HNF1B) is recommended if clinical features support MODY 1

MODY patients often respond to oral agents, such as sulfonylureas, rather than requiring insulin 1, 2
Genetic diagnosis can change management, allowing for targeted therapy and family screening 1
Close monitoring of glycemic control is essential, with rechecking of autoimmune markers if control worsens unexpectedly 1, 2
Screening family members is indicated if MODY is confirmed genetically, with cascade screening of first-degree relatives recommended 1