What Are the Causes and Genetic Components of Type 1 Diabetes?

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By : dLife Editors

Reviewed by: Dr. Qin Yang, M.D., Ph.D. 4/18.

The exact causes of type 1 diabetes are not yet known. But genetics, family history, and environmental factors appear to play a role in the development of this serious health condition. In this section, we’ll examine each of the potential causes.

Genetic Causes of Type 1 Diabetes

Type 1 diabetes is a polygenic disease; this means it is a disease that involves many genes. These gene groups are located on structures called chromosomes within the cell.

These genes make proteins that help maintain our immune system, fighting off unwanted cells or infectious agents. Discrepancies in the functioning of these genes lead to a discrepancy in the synthesis of the proteins.

In the case of type 1 diabetes, the β-cells of the pancreas are regarded as external harmful agents by the body’s immune system, and the body seeks to destroy them.

Around 20-40 different chromosomal gene groups have been linked to type 1 diabetes. The largest contributing gene for type 1 diabetes is called IDDM1; it is located in the Major Histocompatibility Complex (MHC) II region on chromosome six.

This gene accounts for at least 40 percent of the familial hereditary cause of type 1 diabetes.

Family History’s Role in Type 1 Diabetes

Approximately one in every 250 children in the United States is born into a family already affected by type 1 diabetes.

Children born into an affected family have a five percent increased risk of developing type 1 diabetes by age 20. In comparison, children with no such family history have only a 0.3 percent chance of developing this condition.

A child with a family history of type 1 diabetes can be classified further based on which family member has the disease. The chances of a child developing type 1 diabetes are as follows:

  • Five percent chance if the father has type 1 diabetes
  • Three percent chance if the mother has type 1 diabetes
  • Eight percent chance if the sibling has type 1 diabetes
  • 50 percent chance if the identical twin has type 1 diabetes

Children with affected immediate family members and affected first-degree relatives have a 20 percent risk of developing the condition.

The percentages listed above are dependent on the number and type of discrepant genes inherited from either parent. These factors ultimately decide whether the condition will be dominant or recessive in a child.

In the dominant condition, the child is more likely to get type 1 diabetes due to a higher combination of defective genes received.

Environmental Causes of Type 1 Diabetes

Despite the relevance of genetics that is seen with type 1 diabetes, there are still cases that develop in children with unaffected families.

Although the genetic risk can be considered substantial, the influence and association of environmental factors cannot be ignored. These factors can be potential triggers, casual, or protective.

Take the case of identical twins, for example. When one twin develops type 1 diabetes, the other twin has a 50 percent chance of developing the condition and a 50 percent chance of not developing it.

This statistic strongly suggests that in addition to genetic susceptibility, other factors like environmental exposure may also play a role in the onset of this condition.

As mentioned previously, this condition varies in occurrence in the same country due to differences in children’s infection history. Environmental factors are likely the cause.

Seasonal variations have been observed with more cases occurring in the autumn or winter months.  For this reason, vitamin D is thought to have a protective role in decreasing one’s susceptibility to type 1 diabetes (as more vitamin D is available in the summertime).

Other factors that may act as triggers and increase one’s susceptibility to this health condition include the following:

  • A disturbance of microorganisms (microbiota) in the gut
  • Enterovirus infections
  • Certain bacterial infections

While some environmental factors act as triggers, others seem to safeguard the body from type 1 diabetes. For example, dietary agents like gluten seem to have a protective role.

The timing of when these factors are introduced into the body play a significant role in the development or non-development of this life-changing condition. Ongoing research aims to gather more concrete evidence to support the relationship between type 1 diabetes and environmental causes.

Environmental influences may occur as early as in utero and may continue into the first few months or years of life, affecting the onset of antibody development against the β-cells of the pancreas.

Physiological events like immune system development and normal turnover of β-cells also contribute to the pathogenesis of the condition.

Inherent dysregulation in the immune system, probably due to genetic susceptibility, leads to the self-destruction of β-cells and production of autoantibodies in the blood.

However, not all individuals who develop this autoimmune dysregulation or produce these autoantibodies progress to the symptomatic stage of type 1 diabetes, developing symptoms of glucose intolerance.

This variation could be attributable to the influence of environmental factors.  Thus, the diverse nature of type 1 diabetes is an important aspect to consider. Because this blood sugar disease presents in some and not in others, researchers surmise that both genetics and the environment contribute to its onset.

Qin Yang, M.D., Ph.D., is an Assistant Professor of Medicine, Physiology, and Biophysics at the Center for Diabetes Research in the Department of Medicine, Division of Endocrinology, at the UC Irvine School of Medicine.  He specializes in Endocrinology & Metabolism and Internal Medicine.


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