MODY: A Rare but Increasingly Common Form of Diabetes

It wasn't until a quarter century after being diagnosed with type 1 diabetes (T1D) that Lori Salsbury in Arkansas realized the condition she'd been living with since she was 15 years old might not be what she thought it was.

Though her mom and sister were both initially misdiagnosed with type 2 diabetes (T2D) and later correctly dubbed T1Ds, Lori didn't have a reason at first to be suspicious of her own T1D diagnosis. Not until 2015, when she began seeing more people with diabetes sharing their stories online and realized something was off for her.

Sure, there is a mantra in our community that "Your Diabetes May Vary." But for Salsbury, the particulars of her T1D just "didn't match" what she saw others in the D-Community sharing or what doctors and nurses described as the symptoms most newly diagnosed T1D experience.

At the time of her diagnosis, Salsbury was in her mid-20s and seemed quite healthy. She didn't get nauseous or sick, even a full day after missing an insulin dose. Her insulin dosing needs would change frequently, often sending her into super high glucose levels for weeks until adjusting her insulin or carb ratios; the same would happen on the low end of the scale.

One day, Salsbury heard about a rare, inherited form of diabetes called MODY (maturity onset diabetes of the young), that doesn't require as much insulin, at least initially. That piqued her interest.

She did some online research, and then consulted her endocrinologist and received antibody tests that came back negative. He also ran a C-peptide test that came back at T1D levels, but that was most likely due to her 20+ years of using insulin. A referral to a geneticist led to more bloodwork, and in January 2020 the findings came back showing a genetic mutation, which causes one of the several different known types of MODY.

MODY has the potential of changing how you manage your diabetes, depending on the particular form you're diagnosed with. Some changes could include stopping medications completely or changing from insulin to a different injectable or oral medication, while some MODY forms mandate changes in your diet.

In Salsbury's case, the MODY diagnosis brought her some clarity, and finally an explanation of why her diabetes experience seemed so different than others in the T1D community. But she continues insulin therapy.

"Since I was originally diagnosed T1D, I am still (labeled that) in my charts so that I won't lose coverage for my insulin pump and CGM that I require to live by," Salsbury said. "Most often, if asked I just tell people that I was diagnosed with type 1. It's easier than going through the whole 'What is MODY?' spiel."

What is MODY?

The easiest way to think about MODY is that it's a subset of diabetes caused by a mutation in one of at least 14 genes in a person's DNA. That mutation impacts the insulin-producing beta cells, which in turn impacts insulin production and glucose regulation.

Since just an estimated 1 to 2 percent of those with diabetes have a genetic mutation leading to MODY, there isn't much discussion about it within the patient community, and most medical professionals don't bring it up unless they are questioned. Yet some advocates and researchers believe the various types of MODY are more common than many think, and that view is becoming more accepted as genetic testing becomes more widely available.

The term MODY was first coined in the 1970s by pioneering researchers who identified what appeared to be a mild form of diabetes in children that didn't necessarily require insulin as was needed for those with the more common "juvenile diabetes" (before it was later renamed type 1). At that time, MODY was defined as "fasting hyperglycemia diagnosed under age 25 which could be treated without insulin for more than two years," and it is inherited, as they found.

While most research existing shows it's as rare as 1 to 2 percent of all diabetes cases, more current research now indicates that as many as 6.5 percent of children with antibody-negative diabetes may have a form of MODY.

MODY is passed down genetically from parent to child, making that the common thread for this form of diabetes compared to the other types that are autoimmune, partially genetic, or more lifestyle-based. The typical diagnosis comes before age 25, and it's rarely diagnosed in those older than 35 or 40. While children have roughly a 50 percent chance of developing MODY if one of their parents has it, that does not mean mutations can't occur at random and appear in those without a family history of gene mutation.

The gene mutations aren't the same for everyone, and they affect different organs in the body, meaning it's difficult to diagnose without genetic testing, and it can be more challenging to recognize glucose fluctuations commonly found in those who are newly diagnosed.

Significantly, 80 percent of MODY cases are misdiagnosed as T1D or T2D as the signs are pretty much the same — extreme thirst, increased urination, and weight loss. But some forms of MODY do not produce any symptoms. The number of misdiagnoses may be even higher at 95 percent in the United States, according to some researchers.

How many types of MODY exist?

Currently, there are 14 recognized types of MODY caused by mutations in different genes. Those gene mutations can include, per the latest research: GCK, HNF1A, HNF4A, HNF1B, INS, NEURO1, PDX1, PAX4, ABCC8, KCNJ11, KLF11, CEL, BLK, and APPL1. The different genes vary with respect to age of onset, response to treatment, and the presence of extra-pancreatic manifestations.

Three of the more common types of MODY are:

• MODY 1. Gene mutation in the hepatocyte nuclear factor 4 alpha (HNF4A). Although it's less common, it may account for 5 to 10 percent of MODY cases.
• MODY 2. Gene mutations in the glucokinase (GCK) enzyme account for 30 to 50 percent of the cases of MODY. Patients with a GCK mutation typically display "mild and nonprogressive hyperglycemia," which is generally not symptomatic, meaning they don't notice it.
• MODY 3. Gene mutation in the hepatocyte nuclear factor 1 alpha (HNF1A) accounts for 30 to 50 percent of MODY cases. This is a progressive beta cell dysfunction, and diagnosis is typically made between ages 21 and 26.

Finding out the probability of developing MODY is becoming more accessible in recent years, with new tools like a probability calculator and subtype app developed by the Exeter Centre of Excellence for Diabetes Research (EXCEED) in the United Kingdom.

Getting a correct MODY diabetes diagnosis

Dr. Miriam Udler at Massachusetts General Hospital is one of the more well-known names in MODY clinical research. She believes more cases are being diagnosed in recent years as genetic testing has become more available, particularly after COVID-19 led to a telehealth explosion and more at-home testing kits for bloodwork and diagnostic tests normally done in a lab.

"It used to be rare and expensive, and that was a barrier to testing and diagnosing MODY correctly," she told DiabetesMine. "But now, more providers have access to this and can order the tests to their clinics or patients at home, and insurance is increasingly covering MODY genetic testing."

While MODY is still less common and infrequently discussed in clinics, Udler says it comes down to that particular doctor or patient recognizing something might be "different" about their diabetes.

"That matters a lot, and a correct diagnosis can change management," Udler said. "In most common MODY forms, it could mean coming off medication."

For Salsbury, the particular BLK gene mutation she has causes MODY 11, an insulin secretion defect that makes her beta cells less responsive to glucose and leads to less insulin being sent out by the body when it's needed. Being overweight is one common feature of this particular gene mutation, according to research.

Once MODY is recognized and diagnosed, it can also be difficult to regulate glucose levels in the same ways that T1D and T2Ds often do, because the symptoms and glucose levels can vary significantly.

As MODY 11 usually presents like T1D and is treated in much the same way, Salsbury has been using insulin since she was diagnosed at age 15 in 1991 and wears an Omnipod tubeless insulin pump and Dexcom CGM, combined into a homemade do-it-yourself (DIY) closed loop system. For her, life with MODY isn't much different from being T1D.

But she knows everyone is not as fortunate on that front and can have many challenges in getting a correct diagnosis and finding a management routine that works for their particular form of MODY.

In New York, Laurie Jones shares her story of being diagnosed at 30 with gestational diabetes late in her first pregnancy through the test often given to pregnant women. She changed her diet and followed it to the letter on exact carb and calorie allowances, and took varying doses of long and short-acting insulins. Though she describes it as "intense," all signs of diabetes went away after her first pregnancy.

But within a few years during her second pregnancy, gestational diabetes returned. She began insulin injections right away as well as a strict diet, but Jones found it more difficult than before to regulate high and low blood sugars.

A number of years later, her A1C results were creeping higher and that led to a T2D diagnosis. She took Metformin on the advice of her doctor, but it didn't work to keep her blood sugars in check.

"Most adult medicine endos do not push for MODY testing even when the medicine is not working," she explained. "Being overweight is usually assumed the reason, therefore even star doctors don't push for MODY testing unless weight is lost."

Her son's diagnosis changed everything. When he was 6 years old, he was diagnosed with eosinophilic esophagitis, and that mandated a diet free of the top allergens. He was about 12 when she took him to an endocrinologist, as he was not growing and low on the weight scale and didn't show any signs of puberty. That endo noticed his blood sugars were elevated and assumed he was in the "honeymoon period" prior to becoming a fully diagnosed T1D.

Months progressed, and the doctor suggested it was MODY. Genetic testing led to a MODY 2 diagnosis.

"We had no idea what that was, and before [the doctor] explained it to us, she noted that most endocrinologists and almost all doctors outside of major medical teaching and research hospitals have not heard of it," the D-Mom said.

After her son's diagnosis, Jones got her own genetic testing and learned she also had MODY 2.

Most controlled by diet, MODY 2 is one of the more common but less intensive forms of MODY that usually doesn't require insulin or other glucose-lowering meds.

That led her to stopping Metformin, and she's been eating healthier and managing her weight for better glucose levels.

"MODY 2 is not just about how you produce or use insulin, but mainly when you produce the insulin," she said. "We were both told that our pancreas is like a house cooling or heating system that is off-kilter. Basically, our sugar levels have to get much higher than what is considered normal before the pancreas produces insulin. There are also insulin efficiency issues."

Without her son's diagnosis, Jones doesn't think she would've ever had the needed genetic testing and would have remained with a T2D diagnosis taking the wrong medications.

That's likely the story for so many people in our D-Community, she believes.

"With a 50 percent chance of being passed on, chances are MODY is not as rare as it is now believed," Salsbury said. "If more people knew of it and were tested, we may come to find out that it is the most common or second only to T2D in commonality."

Possibility of other health concerns

Importantly, a correct MODY diagnosis can highlight other health issues that might potentially arise. For example, a MODY 11 mutation to the BLK gene can increase the chances of developing systemic lupus erethematosus (SLE).

"While being correctly diagnosed as MODY may not change your treatment, it can give you other information," Salsbury said. "Many forms of MODY also come along with other health issues that the mutation may have caused. Knowing you have MODY can alert your doctors to watch you or check you for other related health conditions."

Researchers note the same, including Dr. Toni Pollin, a genetic researcher and counselor who in 2016 co-founded the Monogenic Diabetes Research and Advocacy Project (MDRAP) at the University of Maryland School of Medicine. The MDRAP effort promotes the correct diagnosis of MODY and also helps raise money for that effort. She co-founded MDRAP with a patient advocate who'd been diagnosed with a form of MODY.

"While improving MODY diagnosis will certainly improve the clinical care for patients, it will also have broader implications," researchers wrote in this 2015-published Undiagnosed MODY: Time for Action manuscript. "Screening and genetic testing for MODY among patients with diabetes will provide a model for identifying and diagnosing highly penetrant forms of other otherwise common complex diseases [through] the power of genetics and genomics for improving patient care and public health."

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Originally published at DiabetesMine