The Diabetes You’ve Never Heard Of: Why MODY Is So Often Missed

What Is MODY Diabetes?

When I was 14, I was diagnosed with diabetes. I remember hearing the word insulin and feeling my heart drop. My doctor told me I had Type 1 diabetes, just like my dad, and sent me off with various prescriptions and a warning to not eat more than 90g/ carbs a day.

And for years that's what I did. I learned how to count carbs, take injections, and manage blood sugar highs and lows. It wasn’t until 2017 (over a decade later) that a lone researcher wandered in to my dad's hospital room and asked if we had heard of MODY. At that point we started learning that, for decades, we had been following the wrong path.

“MODY” stands for Maturity-Onset Diabetes of the Young (though that name is a bit of a misnomer today). MODY is a genetic form of diabetes- not autoimmune like Type 1 and not lifestyle-driven like Type 2. It’s caused by a mutation in a single gene that affects how your pancreas makes insulin. If one parent has the gene, there’s a 50 percent chance their child will inherit it.

In my family, that statistic played out perfectly. My dad has MODY. So do I and my sister. But my brother doesn’t.

For decades, doctors lumped anyone with early-onset diabetes into the Type 1 category. But MODY is its own condition- one that sits quietly between the two major types, often mistaken for both. Because of that, many people are treated with therapies that don’t actually match what their bodies need.

There are multiple subtypes of MODY (over 14 genes identified so far), the most common being:

• MODY2 (mutation in GCK, the glucokinase gene): often mild, stable hyperglycemia, sometimes manageable without treatment.

• MODY3 (mutation in HNF1A): more progressive, more likely to respond to sulfonylurea drugs initially.

• MODY1 (mutation in HNF4A), MODY5 (HNF1B), and others are less common but present in some patients.

  
  

Because the underlying problem is genetic and centered on beta cell dysfunction, treatment and prognosis are different from typical Type 1 / Type 2 approaches.

In the population of people with “diabetes,” MODY is relatively rare; it’s estimated to account for 1–5% of cases. But many cases go unrecognized since genetic testing remains expensive and inaccessible for many.

Clinical Features & Clues That It’s MODY

Because MODY sits somewhat between Type 1 and Type 2 in presentation, there are “clues” (not guarantees) that suggest MODY might be the correct diagnosis. These include:

• Early onset of diabetes (often before age 25, though not always)

• Strong family history of diabetes across generations (parent, grandparent)

• Not obese, and lacking features of insulin resistance. Many MODY patients are lean with healthy BMIs

• Negative autoantibodies (no evidence of autoimmune β-cell destruction)

• Low to moderate insulin requirement and persistence of residual insulin secretion (measured via C-peptide)

• Milder hyperglycemia in some subtypes (especially MODY2) that does not worsen rapidly

  
  

However - and this is key- none of these clues is definitive, so many patients are initially labeled as either Type 1 or Type 2.

Why MODY Is Often Misdiagnosed

In fact, 50–90% of MODY cases are estimated to be misdiagnosed as Type 1 or Type 2 diabetes. There are several contributing reasons:

1. Overlap of age / presentation with Type 1

Because MODY often appears in adolescence or young adulthood, it can mimic Type 1 diabetes in timing. A young person with hyperglycemia often triggers the reflex diagnosis of Type 1. Clinicians may assume that any child or teen with new-onset diabetes must have the autoimmune Type 1 form, unless proven otherwise.

2. Absence of typical Type 2 features

Likewise, because many MODY patients are not obese and do not show insulin resistance, they don’t “look like” Type 2. So the default assumption of Type 2 (especially in adults) may steer treatment incorrectly.

3. Lack of awareness among clinicians

MODY is rare, and many primary care providers or even general endocrinologists may not routinely consider it in the differential. The clinical guidelines often emphasize distinguishing only between Type 1 and Type 2, and MODY slips through the cracks.

4. Cost and accessibility of genetic testing

To definitively diagnose MODY, you need genetic testing, which is rarely covered by insurance and not often ordered unless the Dr is specifically trained in MODY.

5. Phenotypic variability / mild cases

Some MODY cases have very mild hyperglycemia and slow progression (especially MODY2), making the difference from Type 2 or prediabetes subtle. Patients might be treated conservatively and never fully labeled, or only recognized later. Furthermore, overlapping traits (e.g. mild insulin resistance or slightly elevated BMI) can blur the lines in real patients.

6. "Default to insulin” bias

Once a patient is diagnosed with “Type 1,” insulin therapy is often started quickly, and that treatment can mask the underlying disease process, making it harder to revisit the diagnosis of MODY later. Similarly, for “Type 2” patients, the treatment pathway often goes toward oral medications and then eventually insulin. Clinicians and patients may stick with those labels rather than revisit the diagnosis.

Because of all these factors, patients with MODY may spend years under a misdiagnosis.

Living With the Wrong Label

Being treated for the wrong type of diabetes can have real consequences. When I was first diagnosed, I was on insulin for years. It led to constant low blood sugars, frequent seizures and non stop side effects, because my body didn't really need it. Once I was re-evaluated and genetic testing confirmed MODY, my care plan changed dramatically. I transitioned off insulin and onto a medication that works better for my genetic subtype, allowing my body’s own insulin production to do most of the work.

Why a Correct Diagnosis Matters

The right diagnosis changes everything — from treatment choices to long-term health outcomes.

1. Treatment becomes more precise. Different subtypes of MODY respond differently. For example, some people with HNF1A or HNF4A MODY do extremely well on low-dose sulfonylureas instead of insulin. Others with GCK MODY often don’t need medication at all — their blood sugar may run slightly high, but it stays stable over time.

2. Family members can get tested. Because MODY is inherited, identifying one case opens the door for relatives to test and understand their own risks. In my family’s case, it provided clarity across generations — and helped prevent unnecessary insulin use for my sister.

3. It brings peace of mind. There’s something empowering about understanding the why behind your condition. When diabetes doesn’t fit the textbook, it’s easy to feel confused or frustrated. A clear diagnosis helps you make sense of it — and advocate for yourself more effectively.

When Should You Suspect MODY?

• You were diagnosed with diabetes before age 30, but your presentation doesn’t fully fit Type 1 or Type 2

• You have a strong family history of diabetes across several generations

• You’re lean or physically active, without signs of insulin resistance

• You’ve tested negative for autoimmune antibodies

• You still make some insulin and have good glucose control on minimal therapy

Bottom line: MODY may be the forgotten diabetes, but it doesn’t have to stay that way. The more we talk about it — in clinics, families, and communities — the fewer people will spend years living under the wrong diagnosis.