Type 5 diabetes mellitus – where did that come from?

27th May 2025, A/Prof Chee L Khoo

Classification of diabetes mellitus

We know about type 1 to type 3 diabetes mellitus. I didn’t know that there was a type 4 and now they tell us there is a type 5. For someone who has a special interest in things diabetes, this is definitely news to me. Actually, on further research, it’s actually not that new. Type 4 is the label they are now giving to gestational diabetes mellitus. So, what is type 5 and who is the “they”? In the headlines that you may have come across of this newly discovered diabetes, it is supposed to be diabetes related to the famished and malnourished people of Africa and India. We better go back to our classification from the beginning and explore this “new” type 5 diabetes in detail.

While diabetes mellitus has been described in ancient Egypt, India, China and Europe, it really didn’t come into the radar till the late 1800’s.  Joseph von Mering and Oskar Minkowski are commonly credited with the formal discovery in 1889 of the role of the pancreas in causing the condition (1). In 1893, Édouard Laguesse suggested that the islet cells of the pancreas, described as “little heaps of cells” by Paul Langerhans in 1869, might play a regulatory role in digestion (2). These cells were named islets of Langerhans after the original discoverer.

Of course, we all know the recipients of the 1923 Nobel prize for “the discovery of insulin and their exploration of its clinical and physiological characteristics” – Banting, Best, MacLeod and Collip (2). There wasn’t really any classification of the types of diabetes mellitus for a long time even though they knew there were two distinct types of diabetes. There were people with diabetes who were lean, had severe symptoms, poor outcomes, and pancreatic lesions at autopsy (diabetes maigre), and those that were overweight, presented later in life with a milder form of the disease and had a better prognosis if put on a low-calorie diet (3).

In 1950, R. D. Lawrence observed that some diabetics were deficient in insulin and that some were not. Philip Hugh-Jones, while working in Jamaica in 1955, clarified Lawrence’s classification and coined the terms “type 1” and “type 2” diabetes (4). Of course, we now know that type 1 diabetes (T1D) is an autoimmune condition and any diabetes that is not T1D was called type 2 diabetes (T2D).

We explored Ahlqvist E et al‘s attempt at further classifying diabetes mellitus here in 2018 (wow, it’s 7 years ago since GPVoice profile the subject). They weren’t the first to notice that not all T2D were the same. Some are more insulin resistant than others and some are more insulin secretion deficient than others. We further discussed the skinny T2D here in 2021 when we looked at what to look out for when managing these patients.

Just a reminder of Ahlqvist’s classification:

  1. Severe autoimmune diabetes (SAID) – Characterised by early onset disease, relatively low BMI, poor metabolic control, insulin deficiency and GADA positive
  2. Severe insulin deficient diabetes (SIDD) – Characterised by early onset disease, relatively low BMI, poor metabolic control, insulin deficiency and GADA negative
  3. Severe insulin resistance diabetes (SIRD) – Characterised by significant insulin resistance and high BMI
  4. Mild obesity-related diabetes (MOD) – Characterised by obesity but no insulin resistance
  5. Mild age-related diabetes (MARD) – Characterised by older patients but modest metabolic derangements

At the recent International Diabetes Federation (IDF) World Diabetes Congress 2025 in Bangkok, Thailand, IDF President Professor Peter Schwarz announced the launch of a working group to develop formal diagnostic criteria and therapeutic guidelines for a type of diabetes linked to malnutrition that was formally classified as “type 5 diabetes” (6).

Type 5 diabetes is estimated to affect between 20 to 25 million people worldwide, primarily in regions such as Asia and Africa. This recognition marks a pivotal moment in the understanding of diabetes and how the condition affects lean and malnourished teens and young adults in low- and middle-income countries (LMICs) (6). Really?

Of course, type 5 is Ahlqvist’s severe insulin deficient diabetes (SIDD) which is characterised by early onset disease, relatively low BMI, poor metabolic control, insulin deficiency and GADA negative.

We are already seeing many of these patients in Southwest Sydney. These are patients from the Indian subcontinent, Indochina and Africa. They don’t look like your usual T2D with obesity and insulin resistance. They are not easy to distinguish from T1D and often, we need antibody screen to exclude T1D. They are not just skinny (sarcopenic) but also younger than your usual T2D. The natural course of disease tends to be more aggressive and often reach insulin therapy.

By the way, these are the same group of patients that will suffer from metabolic-dysfunction associated fatty liver disease (MAFLD), even though they are “skinny”, a topic we also explore many times here at GPVoice. They, too need our special attention as we, in Southwest Sydney, have our fair share of these patients.

The IDF working group have 2 years to come up with the criteria for type 5 diabetes mellitus. We don’t have to wait that long to start treating this group of patients differently. Type 5 diabetes is already here.

So, type 5 diabetes is not new. You are already seeing them in your practice. Their phenotype, the natural course of the disease, the likely complications and their management can be very different depending which sub-type of “T2D” they belong to. People with T5 diabetes need less carbohydrates and more protein in their diet. They need more resistance exercise and avoid excessive aerobic exercise which burns away too much calories. We need to ensure that they are not calorie deficit in their diet. The usual “diabetic diet” does not apply to these people. We need to treat them as sarcopenic. We explore sarcopenia in its many facets here over the last 3-4 years. We also need to be cautious when using GLP1-RA as they may lose more weight and muscles.

References:

  1. Karamanou M (2016). “Milestones in the history of diabetes mellitus: The main contributors”. World Journal of Diabetes. 7 (1): 1–7
  2. https://en.wikipedia.org/wiki/History_of_diabetes Accessed on 27th April 2025
  3.  Rachmiel, Rachmiel (1979). “The Endocrine Pancreas, past and present”. In Klachko, David M.; Anderson, Ralph R.; Burns, Thomas W.; Werner, Harold V. (eds.). The Endocrine Pancreas and Juvenile Diabetes. Springer Science & Business Media. pp. 2–3.
  4. Hugh-Jones, P. (1955-10-29). “Diabetes in Jamaica”. The Lancet. 266 (6896): 891–897.
  5. Ahlqvist E et al. Novel subgroups of adult onset diabetes and their association with outcomes: a data driven analysis of 6 variables. Lancet Diabetes Endocrinol 2018; 6; 361-69
  6. https://idf.org/news/new-type-5-diabetes-working-group/ Accessed 27th April 2025