Type 1 Diabetes - Types Of Diabetes: Diabetes

Content provided by the Faculty of the Harvard Medical School

Type 1 diabetes

This type of diabetes, also known as insulin-dependent diabetes mellitus (IDDM), is an autoimmune disease. That means the body's immune system turns inexplicably against its own cells, destroying them as if they were foreign invaders.

The destruction of the insulin-producing beta cells begins when the T-lymphocytes of the immune system fail to recognize the beta cells as friendly and turn against them. Other immune system cells, the B-lymphocytes, are recruited and the destruction proceeds. One by-product of this destruction is the formation of autoantibodies, which are directed against specific components of the pancreatic beta cells. Autoantibodies that are frequently found in people with type 1 diabetes variously target the islet cells, insulin, and other beta cell proteins such as glutamic acid decarboxylase (GAD) and tyrosine phosphatase. The presence of these antibodies signals the ongoing destruction of the beta cells; they usually appear years before you notice any symptoms or are diagnosed with diabetes.

Eventually, total destruction of the beta cells leaves the body unable to produce insulin and metabolize nutrients properly. As a result, blood sugar levels rise and cells starve, even though they are bathed by glucose-rich blood. A person with type 1 diabetes must take insulin daily to survive.

Type 1 diabetes is sometimes referred to as juvenile diabetes because it usually develops in children and adolescents, most often around puberty. It's the most common serious chronic disorder in children and adolescents. Type 1 can also develop in adulthood, although this is uncommon.

Type 1 diabetes is an inherited disease, so people with a family history of it are at greatest risk. For instance, if you have an identical twin with type 1, you have a 50% chance of getting it as well. If you have a sibling with the disorder, your risk of developing it is 5%–10%; that's 10 times the rate of someone without a diabetic sibling. White people of northern European heritage are more prone to type 1 than members of other racial and ethnic groups.

What causes type 1 diabetes?

Scientists don't know what triggers the autoimmune response, but they've uncovered several factors that appear to be involved.

Genes. People with type 1 diabetes and their nondiabetic family members are more likely to develop other autoimmune diseases such as thyroiditis, Addison's disease (adrenal failure), and lupus. The primary gene associated with type 1 is found on chromosome 6 and involves human leukocyte antigens (HLAs). HLAs are proteins on cell surfaces that enable the body to distinguish its own cells from foreign intruders; in effect, they instruct the immune system not to attack the body's own cells. In type 1 diabetes, an unknown abnormality associated with the HLAs may lead the immune system to mistakenly identify the beta cells as alien. As a result, the immune system attacks and obliterates these cells.

Everyone inherits HLA genes. Among people with type 1 diabetes, 95% have HLA-DR3, HLA-DR4, and a specific HLA-DQ-Beta. However, nearly half of all Americans without diabetes also carry HLA-DR3 and HLA-DR4 genes, so having them doesn't necessarily mean you'll have the condition. Studies have shown that the siblings of a person with type 1 who share two of the same HLA variants have a 15% chance of getting the disease, but when only one HLA variant is identical, the risk drops to 5%. Although testing for HLA type can indicate a higher risk for developing diabetes, it's not conclusive and isn't used in clinical practice.

Additional genes linked to diabetes susceptibility are located on chromosome 11, near genes coding for insulin and insulin-like growth factor. Genetics doesn't tell the entire story, though. Other factors probably trigger the disease in people who are genetically vulnerable to developing type 1 diabetes.

The viral connection. Some scientists believe that certain viruses, such as the coxsackievirus or those that cause mumps and German measles, may activate type 1 diabetes. According to this theory, the viruses may resemble some component of the beta cell, leading the immune system, in resisting the viral invaders, to destroy beta cells as well. Others postulate that a viral infection may somehow alter the islet cells, leaving them vulnerable to autoimmune attack. Yet another opinion is that a slow-acting virus causes the disease.

Foods. Some studies have shown an association between drinking cow's milk and eating wheat products early in life and the development of type 1 diabetes, because some children with type 1 diabetes have antibodies to a protein in cow's milk or to gluten, a protein component of grains. But this needs further study. It's still not clear whether children who have a higher risk of developing type 1 diabetes (because they have a diabetic sibling, for example) should avoid cow's milk.

Last updated:	January 23, 2007