What Causes Type 1 Diabetes?
Type 1 diabetes used to be referred to as “Juvenile Onset Diabetes”, however, as children now are developing Type 2 diabetes at younger ages, this descriptive title is no longer accurate.
Type 1 diabetes is a complex diseases which is said to be “multifactorial” and “polygenic.” Meaning that there are several different genes which predispose (and some which protect) a person to Type 1 diabetes-but there is no one gene which acts like a switch to give a person this disease-and it is likely that unknown factors in the environment somehow contribute to the development of this disease.
In fact, when genetically identically twins are looked at for a diagnose of Type 1 diabetes, if one twin as the disease there is a less than 50% chance that the other twin will have Type 1 diabetes as well.
Why do Type 1 diabetes patients need insulin?
Patients with Type 1 diabetes have abnormally low levels of the hormone insulin which, when present in sufficient quantities, lowers the level of glucose in the blood by facilitating its entry into the body’s cells. This is a good thing as high levels of sugar in the blood damage blood vessels, and as human cells need a steady supply of glucose to function normally.
Normally insulin is secreted by the beta cells in the human pancreas, however, in Type 1 diabetes it appears that a person’s immune system destroys these insulin secreting beta cells in a process called an “autoimmune response.” Therefore, Type 1 diabetics need insulin injections in order to prevent excessive levels of glucose in the blood called “hyperglycemia”.
Why Do Type 1 Diabetics mount an immune response against their own cells?
Scientists have postulated for decades that an infectious agent(s), such as a virus, infects the beta cells in the pancreas and causes the human immune system to recognize them as foreign and initiate some sort of a harmful autoimmune response.
It may also be possible that several different infectious agents are capable of starting a biological cascade which leads to the development of Type 1 diabetes. So far there is no “smoking gun” or one single required factor, genetic or environmental, which is necessary for disease progression.
As the destruction of beta cells is autoimmune in nature, it is not possible that a viral agent destroys the beta cells. However, an interesting theory called the “fertile field theory” postulates that chronic viral infection of the beta cells (or other cells in the pancreas) alerts the human immune system that the beta cells are abnormal and they are slowly targeted for destruction. Specifically, chronic viral infection may cause a molecule called MHC-1, or Major Histocompatibility complex Type 1, to be displayed on the beta cell’s surface in a much higher concentration that it normally would, and a molecule called interferon may also be required for beta cell destruction.
Interestingly, industrialized countries may have higher rates of Type 1 diabetes due to excessively cleanliness, and a resulting immature immune system which is “under challenged” and inexperienced-to put it in literary terms. Basic research involving branches of the immune system which help to diminish the harmful autoimmune destruction of beta cells may result in clinically useful therapies.
What about beta cell transplants?
When first introduced as a therapy for Type 1 diabetes, it was hoped that transplants of beta cells would basically cure this devastating disease which leads to a high incidence of blindness, heart attacks and strokes in the people who are unfortunate enough to develop it.
Currently, most beta cell transplants (given to Type 1 diabetes patients from donors) are attacked by the same immune response which destroyed the patient’s own beta cells, and fail to function after six months to four years. Nonetheless, new immunosuppressive and immune modulating therapy may mean that beta cell transplants could in the future provide a practical cure.