A 17-year-old lean girl is found to have fasting glucose of 118 mg/dL that has been stable across three years. Her father and paternal grandmother were diagnosed with diabetes before age 25 and remain on no medication. Anti-GAD antibodies are negative, C-peptide is present, and she has never had ketoacidosis. Which is the most likely diagnosis?

• A Type 1 diabetes mellitus, slowly progressive form
• B Type 2 diabetes mellitus with strong genetic loading
• C Latent autoimmune diabetes of adults
• D Maturity-onset diabetes of the young due to a glucokinase mutation ✓

Explanation

Early onset, autosomal dominant transmission across generations, absence of autoantibodies, ketosis resistance, and stable mild fasting hyperglycaemia are classic for GCK-MODY (formerly MODY 2). Glucokinase mutations reset the glucose sensing threshold, so microvascular complications are rare and pharmacotherapy is usually unnecessary, even in pregnancy except when the fetus inherits the mutation. Slowly progressive type 1 diabetes would show declining C-peptide and eventual insulin requirement.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.