Clues That It Might Be Monogenic

Monogenic diabetes is usually diagnosed because someone noticed the picture did not fit. These are the features that should prompt the question.

• Diabetes diagnosed young — typically before about 35.
• A strong family history running through several generations, with a parent and grandparent affected.
• Being lean, or of normal weight, at diagnosis.
• No islet autoantibodies, despite a Type 1 label.
• Still producing your own insulin years after diagnosis, shown by a measurable C-peptide.
• Mild, stable blood glucose rather than the swings of Type 1.
• No ketoacidosis, ever.
• Unusually low insulin requirements, or good control on very small doses.

The family-history pattern is the most useful single clue. Type 2 diabetes clusters in families too, but the monogenic pattern is more striking: roughly half the relatives in each generation affected, often diagnosed young and often lean.

In one Asian Indian clinic study, the features that identified people worth testing included a BMI in the 21 to 23 range, HbA1c between about 7.2% and 10%, and a measurable C-peptide sitting between typical Type 1 and Type 2 values.

None of these individually proves anything. Several together are a reasonable basis for asking your doctor whether antibody and C-peptide testing is worth doing.