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Lisa Letourneau Part 3, Genetic Testing for Monogenic Diabetes




In part 3 of this Exclusive Interview, Lisa Letourneau talks with Diabetes in Control Publisher Steve Freed about testing for monogenic diabetes and the impact of monogenic diabetes on blood sugar levels, which may vary depending on the type of monogenic diabetes diagnosed and other patient-specific factors.

Lisa Letourneau MPH, RD, LDN, is a dietitian and diabetes & genetics clinical research manager at the University of Chicago.

Transcript of this video segment:

Freed: Do you see anything unique about their blood sugars? You know, because it is a unique disease, you would think that their blood sugars are elevated all the time or they’re fluctuating all the time, especially if they’re being mistreated as far as in the type of medicines they’re given.

Letourneau: Yeah. So, there is one type of monogenic diabetes that has a very distinct phenotype. And so, I mentioned before in the kind of clinical features to look for if someone has incredibly stable fasting blood sugars, so always somewhere between a 100 and 140 milligrams per deciliter. Their postprandial blood sugars are usually under 200. Their A1C never really goes above 7.5% to 8%. That’s pretty characteristic of GCK-MODY. So, the problem is that some people with type 2 diabetes can kind of overlap into that category. And so, it can be a little difficult to sort those out. If the person with GCK-MODY is also a little bit overweight, it’s hard to kind of differentiate them sometimes. But that’s one example of the type of monogenic diabetes that has very consistent blood sugars. Other types, not so much. So, there’s HNF1alpha MODY, that’s also called MODY 3. People with that type of MODY can have pretty aggressive blood sugars where most of them don’t present NDK because they tend to still have a little bit of their own insulin production still, but they can have A1Cs up into the 10% and higher range. So, it really just depends on the type.

Freed: So, a person is diagnosed with an elevated A1C, are there ways to eliminate the monogenic,  to know that it’s type 1 or type 2? The only way from what you’re saying is through genetic testing. So, is it recommended that we do genetic testing for people that are diagnosed with elevated A1Cs?

Letourneau: So, not for everyone because it wouldn’t be cost effective. Monogenic diabetes in general is pretty rare. It only affects about 2% of all people with diabetes. So, for the neonatal forms that are under age one that’s a pretty easy category to just test all of those people. For people who are diagnosed later and might have MODY it becomes a little more challenging to decide who to test and who not to test. What we usually tell providers is they’re the expert of their own patients. And so, if they feel like their patient just isn’t quite fitting with their usual type 1 and type 2 pictures, that might be reason enough to discuss that case further with a center that has expertise in this area. So, we’re certainly happy to do that. We talk to health care providers very frequently via email or phone. There’s other institutions in the world that do this type of research as well, but we’re always happy to help review cases. I would say if at least a few of those clinical features that I mentioned before are true then it might be worth giving them another look, so negative antibodies, normal BMI, and a strong linear family history.  

Freed: Now, you’re at the University of Chicago and they have a monogenic diabetes registry. What is the purpose of that and does the university pick up some of the cost of the genetic testing if you participate?

Letourneau: Oh, that’s a very good question. (Laughs) So, the purpose, the registry was formally started in 2008 and so it’s our 10-year anniversary this year, so the purpose is really to follow patients that have these rare forms of diabetes over time, so that we can learn more about what are the best clinical features to look for, what’s the best treatment for them. So, it’s a longitudinal study that tries to address all of those things. We are able to provide a limited amount of research-based genetic testing for people free of charge. So, we do try to reserve that funding for people who are uninsured or whose insurance companies won’t cover the cost of their genetic testing. So, we have the funds to do that through combinations of research grants and grateful patients –we have a foundation where people can donate. So, we are able to do limited amount of testing. And our registry has over 3,000 people in it at the moment; about 900 of them have known monogenic form of diabetes. And some of those people we’ve tested in our lab, I would say maybe a third to half, and then the rest of them were able to get genetic testing done elsewhere.

Freed: What percentage of people come to you after being misdiagnosed with type 1 or type 2 and then you do the genetic testing and you find out that it’s monogenic diabetes and you change their treatment, and then they walk out the door very happy?

Letourneau: Yeah. So, unfortunately it’s a pretty high number of patients who have that situation. Something I think that’s really interesting is that about 50% of our referrals to the registry come from health care providers and then the rest come from patients themselves. So, we do get a lot of patients who are kind of their own advocates. They recognize that their condition isn’t quite like type 1 or type 2. They feel like they’re a little bit different. And so, they can also contact us directly and kind of be their own advocate. So, we have had many situations where people were misdiagnosed as something else. We’re able to help them get genetic testing and they end up having one of these forms that can be treated with a different medication, so that happens, not infrequently.

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