Causes of Type 1 Diabetes


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Autoimmune Disease

The main cause of type 1 diabetes is an autoimmune destruction of the β cells within the pancreas. Our bodies have their own system for destroying bacteria and viruses, known as the immune system. This contains all the cells that combat infections, some of which produce molecules called antibodies, which bind to and destroy bacteria. In some circumstances, our immune system can produce molecules called auto-antibodies that instead of binding to bacteria, bind to our own cells. This leads to the destruction of the cells within our body and is called autoimmune disease.

In the case of type 1 diabetes, your own immune system produces auto-antibodies that bind to and destroy the β cells of the pancreas. This prevents the pancreas from producing or releasing any insulin into your blood stream. Therefore when you eat, your body is not able to store any of the glucose that you absorb, leading to your blood sugar levels becoming dangerously high.

Other parts of the immune system involved in this process are cells called lymphocytes. There are 2 main types, the B lymphocytes are responsible for producing the auto-antibodies mentioned above, whereas the second type, the T lymphocytes produce molecules called cytokines. When the auto-antibodies bind to the β cells within the islets of langerhans, they attract other immune cells to the site such as the B and T lymphocytes. The T lymphocytes then produce these cytokines, which help activate the destruction of the β cells.

Once the process of β cell destruction has started, it cannot be stopped. Unfortunately, destruction of the β cells leads to more auto-antibodies being produced, specifically against the insulin they contain. This is the first part of the disease and is known as insulitis, which means inflammation or swelling of the insulin producing cells. It can take a number of years before you experience any symptoms of type 1 diabetes, by which time over 90% of your β cells will be destroyed. They do not regenerate.

It is not yet known what leads to production of these auto-antibodies, however some experts believe that it is a mix between a genetic predisposition, i.e.within your genes and environmental factors.

Genetic Factors for Type 1 Diabetes

All the cells of our body contain the same DNA. This allows us to produce cells that are genetically identical to each other, and is what makes us unique. This DNA contains all the information to produce and identical copy of ourselves and is made up from a mix of our parents DNA. Some conditions can be passed down from our parents to us within the DNA of our genes.

With regards to type 1 diabetes, scientists have found approximately 20 genes that are implicated in the abnormal immune attack on the β cells of the pancreas. They believe that these abnormal genes, which produce molecules known as major histo-compatibility molecules 1 and 2 (MHCI and MHCII) are responsible for the β cell destruction.

These MHC molecules are normally responsible for allowing our own immune cells to recognise foreign invaders such as bacteria and viruses. When we have problems in these molecules, our own immune cells begin to believe that the β cells in the pancreas are foreign, so start to destroy them. This causes the problems that are associated with type 1 diabetes mellitus.

Even though these MHC molecules are made from genes that have been passed down from our parents, there is only a 1 in 10 chance that you will develop type 1 diabetes mellitus if either of your parents have it (it is more likely if your father has it). Even twins, who have identical genes and therefore identical MHC molecules have only a 1 in 3 chance of developing diabetes mellitus if their twin develops it. This goes to show that there are other factors, such as our environment that are implicated in the development of this condition.

Viruses

Some scientists have suggested that some viruses can cause the development of type 1 diabetes mellitus in people who have a slightly weaker immune system. In normal circumstances, if you become infected by a virus they use your own cells to replicate. This causes your cells to produce many proteins which it normally wouldn’t. In some cases, researchers believe that viruses can cause your cells to produce proteins that resemble parts of the pancreatic β cells. When this happens, your own immune system produces antibodies that recognise and destroy the protein which resembles the β cells. These antibodies also bind to the β cells, leading to the autoimmune destruction of the β cells that is characteristic of type 1 diabetes.

Some of the viruses that are thought to invoke this detrimental response are viruses that infect our digestive system. Some studies have suggested that some viruses that cause respiratory infections in children under one year old can protect against type 1 diabetes mellitus. This still needs further research to help validate the results.


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