Diabetes Has Five Distinct Types, Not Two: Study

Most diabetes cases are split into two groups: type one and type two. A new study including nearly 15,000 diabetic patients suggests this decades-old distinction only tells part of the story. A new report divides diabetes mellitus into five separate conditions.

The advancement that could improve patient care. Because each group has different causes and complication risks, the authors of the study, published Thursday in the Lancet Diabetes and Endocrinology, believe the results are a "first step" towards precision medicine in diabetes.

Diabetes is a chronic metabolic disorder characterized by high blood sugar. Over time, it can lead to heart attack, limb amputation and blindness.

Almost 10 percent of the U.S. population—30.3 million people—has a form of diabetes, according to the Centers for Disease Control and Prevention. Type 2 diabetes accounts for between 90 and 95 percent of these cases, and roughly 5 percent are type 1. Less common forms of the disorder include gestational diabetes and neonatal diabetes.

Some diabetic patients use insulin to control their disorder. In this picture, a medical assistant administers a insulin to a patient in New Dehli, November 8, 2011. Sajjad Hussain/AFP/Getty Images

A complex picture

In type 1 diabetes, the body's own immune system attacks beta cells, which produce insulin. This malfunction leaves the body without enough insulin to regulate blood sugar levels effectively.

Type 2 diabetes occurs when either the body does not produce enough of the hormone, or its insulin fails to work properly. Usually linked to obesity and a lack of exercise, type 2 diabetes may also have underlying genetic factors.

Researchers analyzed data including long-term blood glucose control for 14,775 diabetic patients. They identified five genetically distinct diabetes subgroups. Three were classified as "severe", while two were "mild."

In the report, the authors identified these groups as clusters. The first cluster includes severe autoimmune diabetes, which is similar to traditional type 1. Patients with this form of diabetes are usually young and generally healthy but they struggle to make insulin as the result of an errant immune system.

Cluster 2 patients have what the authors call severe insulin-deficient diabetes. Similar to cluster 1 patients, this group includes young people of a healthy weight whose bodies do not produce insulin properly. The distinguishing feature in this cluster is that the problem is not triggered by a problem in the immune system. In addition, these patients have a higher risk of diabetic eye disease.

In cluster 3—severe insulin-resistant diabetes—patients are often overweight and their bodies have stopped responding properly to insulin. These patients are at a greater risk of kidney and liver disease.

Clusters 4 and 5 include mild diabetes. The former group includes patients who are very overweight but whose metabolism functions more normally. The latter group of patients develop a milder form of diabetes at an older age than the other groups.

More effective treatment prospects

3_2_Blood Glucose Moniter
Diabetic patients usually measure their glucose level with a drop of blood. Intel Free Press/Flickr

The authors hope their work will eventually help medical professionals tailor treatment more effectively to patients in the different clusters, writing that it represents "a first step towards precision medicine in diabetes."

"More accurately diagnosing diabetes could give us valuable insights into how it will develop over time," said lead author, Leif Groop, who studies diabetes and endocrinology at Lund University Diabetes Centre in Sweden, in a statement, "allowing us to predict and treat complications before they develop."

Victoria Salem, who researches investigative medicine at Imperial College London, told the BBC that specialists have long recognized that type 1 and type 2 were not particularly accurate classifications. The new study, she said, could help lead scientists towards a diabetes cure by changing the way they approach future study.

"What we need to start doing is thinking less about treating the end problem, which is high blood sugar, and more about what's causing you to have your diabetes," Salem said, according to the BBC. "Once we really understand that then we can start targeting the disease better with new drugs."

The study did have limitations. Most notably, the population on which the findings are based does not necessarily represent the population of people diagnosed with the disease in real life. In the U.S., diabetes disproportionately affects Native Americans, Asian Indians and other ethnic minority groups. This paper was based in Scandinavian countries with relatively homogenous populations.

Expanding the classification system to include the entire at-risk population could lead to additional clusters, Salem told the BBC. "It may well be that worldwide there are 500 subgroups."