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Diabetes - type 1 - Causes

Description

An in-depth report on the causes, diagnosis, and treatment of type 1 diabetes.

Alternative Names

Type 1 diabetes; Insulin-dependent diabetes; Juvenile diabetes

Causes:

Autoimmune Response

Type 1 diabetes is usually a progressive autoimmune disease, in which the beta cells that produce insulin are slowly destroyed by the body's own immune system. It is unknown what first starts this cascade of immune events, but evidence suggests that both a genetic predisposition and environmental factors, such as a viral infection, are involved.

Islets of Langerhans contain beta cells and are located within the pancreas. Beta cells produce insulin which is needed to metabolize glucose within the body.

Certain factors are thought to be important in this process:

White blood cells called T lymphocytes produce immune factors called cytokines that attack and gradually destroy the beta cells of the pancreas. Important cytokines are interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma.
Specific proteins are also critical in the process. They include glutamic acid decarboxylase (GAD), insulin, and islet cell antigens. These proteins serve as autoantigens. That is, they trigger the self-attack of the autoantibodies on the body's own beta cells.

Progression from the first stage, known as insulitis, to full-blown diabetes can take 7 years or longer. Unfortunately, by the time a person is aware that something is wrong and goes to the doctor with symptoms of type 1 diabetes, about 80 - 90% of the beta cells have been destroyed.

More than half of patients with insulitis do not develop diabetes. Researchers are greatly interested in discovering any factors that prevent the disease.

Genetic Abnormalities

Researchers have found at least 18 genetic locations, labeled IDDM1 - IDDM18, that are related to type 1 diabetes. The IDDM1 region contains the HLA genes that encode proteins called major histocompatibility complex. The genes in this region affect the immune response. New advances in genetic research are identifying other genetic components of type 1 diabetes. Other chromosomes and genes continue to be identified.

The odds of inheriting the disease, however, are only 10% if a first-degree relative has diabetes, and even in identical twins, one twin has only a 33% chance of having type 1 diabetes if the other has it. Children are more likely to inherit the disease from a father with type 1 diabetes than from a mother with the disorder.

Genetic factors cannot fully explain the development of diabetes. Over the past 30 years, a major increase in the incidence of type 1 diabetes has been reported in certain European countries, and the incidence has nearly tripled in the northeastern U.S. If genetic factors were the only cause of type 1 diabetes, such an increase in cases would take at least 400 years.

Viruses

Some researchers believe one or more viral infections may trigger the disease in genetically susceptible individuals. Researchers suggest the following scenario:

An infection introduces a viral protein that resembles a beta-cell protein.
T cells and antibodies are tricked by this resemblance into attacking the beta protein as well as the virus.

Among the viruses under scrutiny are enteric viruses, which attack the intestinal tract. Coxsackieviruses are a family of enteric viruses of particular interest. Epidemics of Coxsackie virus, as well as mumps and congenital rubella, have been associated with incidence of type 1 diabetes.

Resources

www.diabetes.org -- American Diabetes Association
www.niddk.nih.gov -- National Institute of Diabetes and Digestive and Kidney Diseases
www.jdrf.org -- Juvenile Diabetes Research Foundation
www.nei.nih.gov -- National Eye Institute
www.eatright.org -- American Dietetic Association
www.kidney.org -- National Kidney Foundation
www.diabetestrialnet.org -- Type 1 Diabetes International Clinical Trial Net
www.medicalert.org -- Bracelets or neck chain emblems with personal medical information
www.childrenwithdiabetes.com -- Children with diabetes online community

References

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American Diabetes Association. Standards of medical care in diabetes -- 2008. Diabetes Care. 2008 Jan;31 Suppl 1:S12-54.

American Diabetes Association (ADA). Standards of medical care in diabetes. VI. Prevention and management of diabetes complications. Diabetes Care. 2007 Jan;30(Suppl 1):S15-24.

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Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study Research Group, Jacobson AM, Musen G, Ryan CM, Silvers N, Cleary P, et al. Long-term effect of diabetes and its treatment on cognitive function. N Engl J Med. 2007 May 3;356(18):1842-52.

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Hakonarson H, Grant SFA, Bradfield JP, Marchand L, Kim CE, Glessner JT, et al. A genome-wide association study identifies KIAA0350 as a type 1 diabetes gene. Nature. 2007 Aug 2;448(7153):591-4. Epub 2007 Jul 15.

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SEARCH for Diabetes in Youth Study Group , Liese AD, D'Agostino RB, Hamman RF, Kilgo PD, Lawrence JM, et al. The burden of diabetes mellitus among US youth: prevalence estimates from the SEARCH for Diabetes in Youth Study. Pediatrics. 2006 Oct;118(4):1510-8.

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Voltarelli JC, Couri CE, Stracieri AB, Oliveira MC, Moraes DA, Pieroni F, et al. Autologous nonmyeloablative hematopoietic stem cell transplantation in newly diagnosed type 1 diabetes mellitus. JAMA. 2007 Apr 11;297(14):1568-76.

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Reviewed last on: 4/17/2008
Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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