Diabetes as we know it is typically organized into two neat categories: type 1 and type 2. In type 1 diabetes, antibodies from your own immune system destroy the cells which produce insulin. The disease starts suddenly and is usually diagnosed in children. Type 2 diabetes most often develops in adults as a result of insulin resistance (your cells don't use the insulin well), not insulin production.
In reality, diabetes is much more complicated, and it can manifest in at least one other form, often referred to as type 1.5. This type of diabetes, explains Ping H. Wang, MD, chair of the department of diabetes, endocrinology, and metabolism at City of Hope in Duarte, California, has features of both type 1 and type 2.
What-Is-Type-1.5-Diabetes-AdobeStock_284696761 , type 1.5 has an autoimmune component, which means antibodies from your immune system mistakenly destroy the pancreatic beta cells which produce insulin. Insulin is the hormone needed to get blood sugar out of the bloodstream and into the cells. Without it, glucose accumulates in the blood, leading to potentially life-threatening complications.
Unlike type 1, though, type 1.5 does not have to be treated with insulin right away, and is generally diagnosed in younger adults, not kids. This makes it more like type 2, as does the fact that it progresses much more gradually than type 1, says John B. Buse, MD, PhD, chief of endocrinology at the University of North Carolina School of Medicine in Chapel Hill.
While type 1 diabetes is primarily a problem of insulin production and type 2 one of insulin resistance, type 1.5 seems to include both of those issues. "It's a term used to describe patients who have some level of decreased insulin production due to decreased functioning of the beta cells of the pancreas," explains Deena Adimoolam, MD, a specialist in endocrinology and preventative medicine in New Jersey. "Patients with Type 1.5 diabetes are able to produce some insulin, but not enough insulin, and over time they may not produce any insulin at all."
To be clear, type 1.5 is not a medical term and some experts object to its use. The term can describe Maturity Onset Diabetes of the Young (MODY), a genetic condition which occupies another grey area between type 1 and type 2. But it's perhaps most commonly associated with latent autoimmune diabetes in adults (LADA) and is often used synonymously with that condition.
Causes of type 1.5 diabetes
No one knows exactly why antibodies which normally guard against foreign invaders decide instead to destroy the body's own insulin-producing cells. Genetics plays a role in all forms of diabetes. The first genome-wide association study of type 1.5 diabetes found that the genetic signature overlapped both type 1 and type 2 diabetes but had more in common with type 1 than with type 2.
Even when genes are involved, an environmental trigger usually sets the process in motion, regardless of what the disease is. "You have to have the right genetic predisposition, but something has to set your immune system off on a course to destroy the cells that make insulin," explains Dr. Buse. "It's unclear what those are."
Researchers have discovered links with weight gain, viral infections and stress but nothing is certain. It's also possible that type 2 diabetes morphs into type 1.5. "Some patients with type 2 diabetes who are not well-controlled for. Years may develop 'beta cell burnout' over time where their pancreas produces less insulin," says Deena Adimoolam, MD, a specialist in endocrinology and preventative medicine in New Jersey.
Symptoms of type 1.5 diabetes
There are usually no symptoms in the beginning of type 1.5. That's because the beta cells are destroyed so gradually, life seems to continue as normal. Adults diagnosed with autoimmune diabetes usually develop symptoms when they're down to about 10% of the normal number of beta cells, says Dr. Buse.
Once symptoms do appear, they are similar to those for other forms of diabetes. "They're all related to high levels of blood glucose—blurred vision, increased urination, increased thirst, increased yeast infections (mainly in women), weight loss, feeling hungry and feeling tired," says Dr. Adimoolam.
The first symptom of type 1.5 and type 1 can be diabetic ketoacidosis (DKA), when stratospherically high blood sugar levels lead to dangerously high levels of acid in your bloodstream.
Long-term complications of diabetes are also similar for all forms of diabetes and include heart disease. People with type 1.5 or adult autoimmune diabetes are more likely to develop microvascular complications (problems in the small blood vessels) such as neuropathy. Diabetes complications in general, says Dr. Buse, "generally develop over decades."
Type 1.5 diabetes diagnoses
Part of diagnosing so-called type 1.5 or any other form of diabetes is to check for abnormally high blood sugar levels. But this test alone won't tell you what type of diabetes you have. To help pinpoint type 1.5, doctors will also test for the presence of glutamic acid decarboxylase antibodies (GAD). These are the most common antibodies to destroy insulin-producing pancreatic cells in people with type 1.5
"Antibody tests are positive in about 70% of cases but there are antibody negative patients," says Dr. Buse.
When investigating LADA, doctors also look for traits of "atypical diabetes," says Dr. Buse. "If everything aligns—if someone has a strong family history of type 2 and they're overweight, they have high blood pressure and high triglycerides and a lot of features of metabolic syndrome—they likely have type 2." Being diagnosed in younger adulthood suggests type 1.5, as does weight loss, being under the age of 30 or so and having a family history of autoimmune disease.
Another tip-off is that people with LADA typically don't respond as well to oral diabetes medications, but they do respond well to insulin, says Dr. Buse.
The differences can be subtle and, as a result, LADA or type 1.5 is often mistaken for type 2 diabetes. As many as 3%-12% of all diabetes in adults may be LADA, according to one estimate. This means that many folks with so-called type 1.5 are funneled into the wrong kind of treatment.
Treatment and prevention options for type 1.5 diabetes
Like everything else about type 1.5, treatment has settled on a halfway mark between type 1 and type 2 diabetes. People with type 1.5 will eventually need insulin but usually not right away. This may seem strange given that diagnosis usually takes place when patients have only had one-tenth the number of original beta cells. But, says Dr. Buse, "the pace at which those remaining cells die is much slower [than type 1] so you can get away with diet modification at the beginning." A carbohydrate-restricted diet often works well, as it does in type 2, he adds.
Oral medications can also help in those early days, but most will need insulin eventually, says Dr. Adimoolam.
While there's no known way to prevent type 1 diabetes, you may be able to stave off 1.5 with lifestyle factors like maintaining a normal weight, sticking to healthy foods and exercising.
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