TYPE 1 DIABETES

In type 1 diabetes (formerly referred to as juvenile onset diabetes or insulin-dependent diabetes mellitus), a person’s immune system attacks its own beta cells and destroys them. This is known as autoimmune injury. To control the ele­vated glucose levels, a person with this kind of diabetes has to be treated with insulin injections. Most people with this kind of diabetes are thin.

Type 1 diabetes occurs when the immune system that normally protects the body against infections goes wrong and attacks the beta cells that make insulin. There are genetic factors and environmental factors that cause the immune system to do this.

Type 1 Diabetes and Genetics

Scientists have identified a number of genes that increase an individual’s risk for developing type 1 diabetes. The genes that are particularly important include the following:

• Several genes located in a region of the human genome called human leukocyte antigen (HLA). Two of the genes (called DR and DQ) code for proteins that help the immune system recognize foreign proteins such as those that make up viruses and bacteria. There are many forms of these two genes, and the ones that increase the individual’s susceptibility to type 1 diabetes are called DR3.DQ2 and DR4.DQ8.

• The insulin gene. It has been shown that insulin teaches the immune system not to react against the beta cells—this teaching process is referred to as inducing tolerance. People with type 1 diabetes are more likely to have a form of the insulin gene that is less effective in maintaining tolerance.

These genetic factors explain why the risk of type 1 diabetes is increased if you have a family member with the disease. If you have a family member with type 1 diabetes, your risk is 5 to 6 percent, compared to the risk in the general population, which is 0.4 percent. In identical twins this risk increases to 30 to 40 percent. Table 2-1 summarizes the risk if a family member has type 1 diabetes:

Type 1 Diabetes and the Environment

The environment plays a big role in the development of type 1 diabetes—in fact it’s twice as important as the genes. The evidence for this comes from several different observations:

•           First, for the past forty years, the incidence of type 1 diabetes has been increasing, and it is occurring in younger children. This time period is too short for this to be a change in the genetic makeup of the population.

•           Second, type 1 diabetes is more common in the northern latitudes ( Scandinavia) and becomes less frequent as you go toward the equator. This is not because people at the equator are genetically protected—when they migrate to northern latitudes, they too become susceptible to type 1 diabetes. For example, it was recently shown that Pakistani children born and raised in England have a higher risk for developing type 1 diabetes compared to children who have lived in Pakistan all their lives.

What is it in the environment that increases the risk of getting type 1 diabetes? We do not know. However, there have been a number of hypotheses: one hypothesis relates type 1 diabetes to infections with viruses such as rubella and Coxsackie B4; another hypothesis relates type 1 diabetes to the consumption of cow’s milk. So far, neither of these has been confirmed as being the culprit.

One reason it is hard to figure out which environmental factor is important is that the factor may be important for initiating the autoimmune process, but not for main­taining it. Since the immune attack starts many years before a person develops dia­betes, it is diffi cult to figure out what environmental factor was present right at the beginning when the autoimmune process first started. There has been a suggestion that in the developed countries, a lack of childhood infections means that the immune system does not develop properly, and this leads to autoimmunity and the development of conditions such as asthma and diabetes. This theory is known as the hygiene hypothesis.

Other Autoimmune Diseases in People with Type 1 Diabetes

The genetic and environmental factors that increase the risk for type 1 diabetes also increase the risk for other autoimmune diseases. Up to 20 percent of people with type 1 diabetes also have autoimmune thyroid disease, especially underactive thy­roid disease (Hashimoto’s thyroiditis). Once in while, we also see thyroid over activity

 (Graves’ disease) accompanying type 1 diabetes. Another disease that occurs more frequently in people with type 1 diabetes is celiac disease. In this dis­ease, a person is very sensitive to gluten in wheat. About 5 percent of children diag­nosed with type 1 diabetes have gluten sensitivity. Addison’s disease, a rare condi­tion in which there is autoimmune failure of the adrenal glands, also occurs with slightly increased frequency in people with type 1 diabetes

HOW IS TYPE 1 DIABETES TREATED?

Type 1 diabetes is treated using insulin injections. Oral medicines that are used to treat type 2 diabetes do not work in people with type 1 diabetes because they depend on having the pancreas still making significant amounts of insulin. Early in the dis­ease, a person with type 1 diabetes still has the ability to make and release insulin, and so you will require only a small amount of insulin to keep glucose under con­trol. This early period is referred to at the as the honeymoon phase and can last from a few months to several years. Eventually, however, most of the beta cells are lost, and you will be totally dependent on insulin injections for your insulin needs.

Type 1 diabetes can occur at any age and in any ethnicity, but is more common in children and young adults of Caucasian ancestry. Most cases occur in families where there is no history of type 1 diabetes, but when you have a family member with type 1 diabetes, your risk of getting the disease is higher.