Type 1 diabetes is an autoimmune disease, in which the immune system destroys the body’s capacity to produce insulin. Insulin is a hormone that helps cells use glucose (blood sugar) for energy.

Researchers have found many factors that appear to be linked to type 1 diabetes, but there does not seem to be any single cause. Some of the factors include viruses, certain diets, chemicals and other environmental factors. Genetics is also believed to play a role, which is indicated by the disease occurring multiple times in a family.

A family history of type 1 diabetes is a major indicator that a person may also develop the disorder. The risk of a child developing type 1 diabetes in association with a parent with the disease is the following:

• 1 in 17 when the father has diabetes
  
  
• 1 in 25 when the mother has diabetes and gave birth to the child before age 25
  
  
• 1 in 100 when the mother has diabetes and gave birth to the child after age 25
  
  
• 1 in 4 to 1 in 10 when both parents have diabetes

For each of these figures, the risk of diabetes doubles if the parent developed the disease before age 11.

The high rate of occurrence of diabetes within families helped encourage research into genetic links to the disease. Scientists are trying to determine which genes are involved in individuals with type 1 diabetes and how genetic mutations interfere with the production of insulin. To date, they have not found a single gene responsible for type 1 diabetes. However, there are about 19 sections of the human genome that appear to be related to a susceptibility to type 1 diabetes.

One section of the genome contains several genes involved in building human leukocyte antigens (HLA). The proteins formed by these genes help the immune system recognize the body’s own cells. When HLA genes malfunction, an autoimmune disorder may occur.

There are many types (alleles) of HLA genes. According to the American Diabetes Association, 95 percent of people with type 1 diabetes have HLA-DR3, HLA-DR4 or both alleles. The HLA genes involved in diabetes also vary by ethnicity and race. HLA-DR3 and HLA-DR4 are most common in white diabetic patients, but HLA-DR7 is common in patients of African descent and HLA-DR9 is common in patients of Japanese descent.

The inherited HLA-DR gene makes individuals more susceptible to type 1 diabetes, but it is not the only factor. Other genes, including other HLA genes (HLA-DQ) and IDDM2 (the insulin gene), are also likely to be involved. Researchers are continuing to study additional gene clusters and chromosomes to determine their role in type 1 diabetes.

The genetic factor is a complicated issue in the development of type 1 diabetes. Most people with the disease do not have a parent or sibling with it. Also, identical twins have identical genes, but there is only a 50 percent chance of both twins developing the disease. This means that factors in addition to genetics play a role in the development of the disease.

A form of type 1 diabetes that can develop in adults is known as latent autoimmune diabetes of adulthood (LADA). It is not known how the genetic risk factors for LADA may differ from those of standard type 1 diabetes.