Targets by Subtype

This is the point where monogenic diabetes departs most sharply from ordinary diabetes advice, and getting it wrong causes real harm in both directions.

In GCK-MODY, a mildly raised HbA1c is the expected result of the condition, not a failure of control. Fasting glucose typically sits around 100 to 145 mg/dL, with HbA1c usually below about 7.6%, and untreated people in one registry reported HbA1c between 5.8% and 6.4%.

Chasing that number down with medication does not work — treatment is described as almost always unnecessary and ineffective outside pregnancy — and attempting it risks lows for no benefit. In a UK study, GCK-MODY patients who stopped all treatment had exactly the same HbA1c a year later.

So in GCK-MODY the target is essentially your own baseline, and the honest instruction is to stop treating the number.

In HNF1A and HNF4A-MODY, targets do matter, because these subtypes progress and carry the complication risks of ordinary diabetes. In the UK study, successful treatment change brought HbA1c from about 7.5% down to around 6.4% at two years — a real and worthwhile improvement.

In HNF1B, kidney function needs its own targets alongside glucose.

The single most useful question to ask your doctor: given my specific gene, what is my target, and is it a target at all?