WASHINGTON — Having one type of diabetes is bad enough, but two? Doctors are seeing a new phenomenon called "double diabetes," which makes it harder to diagnose and treat patients, especially children.

The mix can strike at any age, and comes in various forms: Children who depend on insulin injections because of Type 1 diabetes gain weight and then get the Type 2 form in which their bodies become insulin resistant, for example.

Or someone with classic Type 2 symptoms isn't responding to therapy, and tests reveal he also is developing the insulin-dependent form of the disease. Or a patient may not fall clearly into either category.

The labels are important: Different forms of the disease require different treatments.

Yet "there are many people in which it's very blurred as to what kind of diabetes they have," said Dr. Francine Kaufman, a University of Southern California pediatric endocrinologist and past president of the American Diabetes Association.

There are no good statistics on this complex disease-mixing.

But the Children's Hospital of Pittsburgh counts about 25 percent of child patients with Type 1 diabetes who also are overweight and have other Type 2 features, said Dr. Dorothy Becker, a pediatric endocrinologist and leading double-diabetes researcher.

And an ongoing study to determine the best treatment for child Type 2 diabetics is uncovering many participants who harbor antibodies that signal they have or are developing the Type 1 form, too, Kaufman said.

Those findings echo a handful of recent research reports raising concern about the phenomenon, which some call atypical diabetes or "diabetes 1 ½" or even Type 3 diabetes.

Diabetes occurs when the body can't turn blood sugar, or glucose, into energy, either because it doesn't produce enough insulin or doesn't use it correctly.

With the Type 1 form, the patient's own immune system attacks the insulin-producing islet cells in the pancreas. Once thought to strike only in childhood, it also can develop in adults. Insulin, given by shots or a pump, is required to survive.

With the Type 2 form, the body loses its ability to use insulin properly, even though the pancreas pumps out extra and drugs often are given to rev up that production even more.

Type 2 once was thought to hit only the middle-aged but now is striking even overweight children.

Then specialists began spotting double diabetics.

The theory: Overweight people need more insulin to process glucose regardless of whether they're insulin-resistant yet.

So, perhaps obesity overworks the pancreas until it wears out, Becker suggests.

Or perhaps obesity accelerates the autoimmune destruction, meaning that someone genetically predisposed to Type 1 diabetes might not have gotten it had he or she stayed thin.