Type 1 Diabetes Causes
No one knows the exact cause of type 1 diabetes. In the vast majority of patients who have type 1 diabetes, the disease is a result of a problem in the immune system. Normally the immune system helps fight off pathogens, such as viruses and bacteria. Instead of making antibodies to fight off pathogens, the immune system makes autoantibodies. Autoantibodies are directed toward a person’s own tissue.
In the case of type 1 diabetes, the autoantibodies are directed toward the islet or beta cells of the pancreas. These are the cells that produce insulin in response to high blood glucose levels in the bloodstream. When the islet cells are attacked by autoantibodies, they are destroyed and no longer produce insulin. It is believed that there is a combination of heredity and environment that ultimately cause the autoantibodies to be made, resulting in type 1 diabetes.
The Role of Insulin in Type 1 Diabetes
As the antibodies attack enough islet cells, these cells are destroyed and the patient makes very little or no insulin. Insulin is a protein-based hormone that is secreted by the pancreas, which is an endocrine and exocrine gland located slightly behind and underneath the stomach.
In a normal person, the pancreas secretes insulin into the blood when the blood sugar level rises. The insulin circulates throughout the body, allowing glucose to enter the cells for use as cellular fuel. Insulin is responsible for lowering the amount of glucose in the blood. When the blood glucose level drops to a significant degree, the insulin is secreted less and less from the pancreas.
The Role of Glucose in Type 1 Diabetes
Glucose is a type of sugar that is the primary source of cellular energy in muscle cells and in other tissues of the body. The glucose comes from two different places. The first is through the food you eat and the second is through the breakdown of glycogen in the liver cells.
Glucose is absorbed by the small intestines into the bloodstream where it goes into the cells after being facilitated by insulin. Extra glucose is stored in the liver as glycogen. When the glucose levels are decreased, either because you haven’t eaten for a long period of time or because you have been exercising and using up glucose, the liver takes its glycogen stores and turns it into more glucose to keep the glucose within a normal range.
In patients who develop type 1 diabetes, the insulin isn’t available to allow the glucose to enter the cells. The cells are starved of energy and the blood glucose levels in the bloodstream goes up, causing many different diabetic complications if the condition is left unchecked.
Type 2 diabetes mellitus has a different etiology than type 1 diabetes. In type 2 diabetes, the islet cells are still putting out insulin but the cells of the body are resistant to the insulin and the blood glucose levels go up. In some type 2 diabetes cases, the body doesn’t produce enough insulin, similar to type 1 diabetes.
While it isn’t completely clear exactly what the triggers are for coming down with type 1 diabetes, scientists believe that genetics plays a role in getting the disease. The disease does seem to run in families but not in any predictable way. There is something in the environment that sets the immune system off so that it makes the autoantibodies found in type 1 diabetic patients.
Genetics and Type 1 Diabetes
There are some people who just can’t ever get type 1 diabetes because they don’t have the genes that lead to the disease. Researchers have determined that type 1 diabetes only develops in patients who have a particular HLA complex on their cells. The term, HLA, stands for human leukocyte antigen. Antigens are molecules that trigger some type of immune reaction in the body. All of the HLA complexes linked to type 1 diabetes are located on the 6th chromosome.
In fact, there are different HLA complexes for the different types of autoimmune diseases, including ankylosing spondylitis, rheumatoid arthritis, and juvenile rheumatoid arthritis. Just as is seen in type 1 diabetes, there is an environmental trigger, such as a viral infection, that causes the autoantibodies to develop.
Triggers for Type 1 Diabetes
This is what happens when a person with the right HLA type develops a viral infection. The virus initially invades the tissues of the body and the immune system responds by making antibodies designed to fight off the infection. It is the B cells of the immune system that are responsible for making the antibodies to fight off the virus.
If the virus happens to have some of the same antigens as the beta cells of the pancreas, the antibodies can become autoantibodies that fight off the beta cells of the pancreas as well as the virus. The beta cells become destroyed just like the virus particles are and you can no longer make insulin. This ultimately leads to type 1 diabetes—a process that is not reversible.
Researchers have determined that not all viruses have the ability to trigger autoantibodies against the beta cells of the pancreas. The virus needs to have similar antigens to the beta cells in order for this to turn into type 1 diabetes.
Common viruses that can underlie the causation of type 1 diabetes include the following:
- Rotavirus (an intestinal virus)
- Mumps
- German measles
- Coxsackie B virus, in particular the B4 strain
Some research has been done linking the drinking of cow’s milk as a small child who then develops type 1 diabetes. This is controversial research and not all scientists agree with this. Some researchers have discovered that certain protein’s in cow’s milk are very similar to a protein that affects the immune system called glycodelin.
The infant’s immune system attacks the foreign antigen in cow’s milk but also attacks glycodelin, which leads to an overproduction of immune cells. If there are too many autoantibodies produced by the immune system, the autoantibodies attack the individual’s beta cells and this starts the process of getting type 1 diabetes.
Researchers have so far made good progress in trying to understand the cause of type 1 diabetes and they are trying to determine why only certain viruses trigger the production of autoantibodies that ultimately lead to type 1 diabetes. With further research, more about the causation of type 1 diabetes will be able to be understood.
References:
- Type 1 diabetes causes. http://www.endocrineweb.com/conditions/type-1-diabetes/type-1-diabetes-causes. Accessed 5/17/16.
- Causes of type 1 diabetes. http://www.mayoclinic.org/diseases-conditions/type-1-diabetes/basics/causes/con-20019573. Accessed 5/17/16.