Diabetes is often the result of obesity and poor diet choices, but for some older adults the disease might simply be a consequence of aging. New research has discovered that diabetes--or insulin resistance--in aged, lean mice has a different cellular cause than the diabetes that results from weight gain (type 2). And the findings point toward a possible cure for what the co-leading scientists, Ronald Evans and Ye Zheng, are now calling a new kind of diabetes (type 4). "A lot of diabetes in the elderly goes undiagnosed because they don't have the classical risk factors for type 2 diabetes, such as obesity," says Evans, director of Salk's Gene Expression Laboratory and senior author of the new paper, which was published November 18, 2015 in Nature. "We hope our discovery not only leads to therapeutics, but to an increased recognition of type 4 diabetes as a distinct disease."

In healthy people, the pancreas produces the hormone insulin, which signals to cells to take sugar out of the blood after a meal. In people with diabetes, however, the cycle is broken: either insulin is not produced in response to a meal or the muscle and liver cells don't respond to the insulin (also known as insulin resistance). In either case, sugar stays in the bloodstream for longer times, leading to a host of health issues ranging from loss of limbs to death.

Traditionally, diabetes has been grouped into the rarer type 1 disease, which most often appears in childhood when the pancreas stops producing insulin; and type 2, which is characterized by the body's failure to respond to insulin and most often attributed to being overweight. Both forms of the disease lead to high blood sugar levels. A third type of diabetes results in symptoms mimicking Alzheimer's. But Evans--after a thin, older family friend developed diabetes--wondered why some people developed the disease later in life without weight gain.