This transcript has been edited for clarity.
I'm going to briefly discuss the other types of diabetes. I personally see many patients with monogenic diabetes, but that's because I tend to be referred those patients. Many of you may see other types. There is cystic fibrosis–related diabetes, transplant-related diabetes, and there are medication causes for diabetes. I think that these are all patients who need good treatment for their diabetes but are also being treated for another disorder, such as cancer, a heart transplant, or cystic fibrosis.
There are many centers that focus on the treatment of these individual patients, and I would urge you to learn about how these patients should best be treated. Some of them, like checkpoint inhibitor–induced diabetes, is often just treated like type 1 diabetes, but get to know what other factors exist for your patient, and then treat them based on what they need.
Monogenic diabetes is something near and dear to my heart because it's unusual and because I can diagnose it. If you have a patient who was diagnosed with type 1 diabetes before they were 6 months old, they probably don't have type 1 diabetes. They likely have a specific gene mutation that leads to a Kir6.2 subunit defect. Although that's complicated, it's simple that if a person has had the diagnosis of type 1 since they were a baby, maybe you need to send them for gene testing because that's an individual who can get off insulin and be treated with sulfonylurea agents.
Let's return to the concept of diagnosing type 1 diabetes in adulthood. I talked about the older adults, those older than 35 years of age, where it's often hard to tell if they have type 1 or type 2 or an in-between state. If someone is diagnosed at younger than 35 years of age, and their islet autoantibodies are negative, you're going to wonder whether that person has monogenic diabetes.
There is a maturity-onset diabetes of the young (MODY) calculator; you can plug in the features the patient has to see whether they're more likely to have MODY or not. I mostly get a family history, and my MODY patients have a very strong family history of early-onset diabetes because it's a dominant gene. If a person has a family history of many cases of diabetes diagnosed at a younger age, you may want to consider MODY.
If you consider that the person might have MODY, test a C-peptide level. If it's > 0.6, that could well be MODY because patients with MODY are still making insulin. If somebody's C-peptide level is low, < 0.6, that's someone who probably does have type 1 diabetes. You can't tell for sure, but it's most likely. If the C-peptide level is elevated, and you think someone has type 2, then you're going to characterize them as either type 2 or some sort of indeterminate type.
There's a company called Invitae, which will do MODY gene testing and other endocrine types of gene testing for $150 per test, so I can get my patients MODY gene tested at this site, and all they'd have to pay out of pocket is $150. If someone can't afford that, they have patient assistance programs. When I can't get insurance to cover the test, I will use Invitae as my site for the testing.
Alternatively, you can have patients look at the Monogenic Diabetes Registry at the University of Chicago, which is where they track the most patients anywhere with monogenic diabetes, and they're incredibly helpful. There are many resources both for clinicians and patients.
If you have a patient who seems unusual to you, you can look up the RADIANT study, which is the Rare and Atypical Diabetes Network. I send many people into RADIANT, and they'll do all the testing and everything else that's needed to try to see what's really happening with your patient. Sometimes, they come up with an answer. Sometimes, they say, "We still don't know," but at least it's good to know you've tried everything you can, mostly because patients like to know the prognosis for their diabetes. It also helps me know how to treat an individual patient.
In conclusion, I may have confused you more than I've helped you, but hopefully, I've given you permission to wonder what's happening with an individual patient and to really follow up in terms of testing, if necessary, in terms of measuring islet autoantibodies, measuring C-peptide levels, and potentially sending blood off to see whether they have monogenic diabetes. Whatever it is, you're going to treat the patient based on what seems best for the patient rather than based on a label.
I have patients I've diagnosed with adult-onset type 1, who, for the first year or 2, may not need much insulin or maybe just basal insulin. I think to some degree, it's helpful to get them through that part. Then, they begin to notice that their after-eating glucose levels are higher, and they become more willing to give mealtime insulin than I think they might have if I just said in the beginning, "Here, you're on multiple daily insulin injections. Let's see what happens."
In this series, hopefully I've given you permission to wonder what a patient has; to do the tests we have available, such as C-peptide levels and insulin autoantibodies; and to really think about what a patient might have and then how you're going to treat them. Know that treatment will change over time. It's okay to tell a patient you can't tell for sure, but let's just watch what happens.
By using what we know, the newer medications for the management of diabetes, and all the other medications we have to reduce risk for cardiovascular disease and other complications of diabetes, we can help our patients live long and healthy lives. Thank you.
Anne L. Peters, MD, is a professor of medicine at the University of Southern California (USC) Keck School of Medicine and director of the USC clinical diabetes programs. She has published more than 200 articles, reviews, and abstracts, and three books, on diabetes, and has been an investigator for more than 40 research studies. She has spoken internationally at over 400 programs and serves on many committees of several professional organizations.
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Cite this: Diagnosing Diabetes: Monogenic Diabetes and Other Rare Forms - Medscape - Oct 13, 2023.
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