Genetics of Diabetes
You've probably wondered how you developed diabetes. You may worry that your children will develop it too.
Unlike some traits, diabetes does not seem to be inherited in a simple pattern. Yet clearly, some people are born more likely to develop diabetes than others.
What Leads to Diabetes?
Type 1 and type 2 diabetes have different causes. Yet two factors are important in both. You inherit a predisposition to the disease then something in your environment triggers it.
Genes alone are not enough. One proof of this is identical twins. Identical twins have identical genes. Yet when one twin has type 1 diabetes, the other gets the disease at most only half the time.
When one twin has type 2 diabetes, the other's risk is at most 3 in 4.
Type 1 Diabetes
In most cases of type 1 diabetes, people need to inherit risk factors from both parents. We think these factors must be more common in whites because whites have the highest rate of type 1 diabetes.
Because most people who are at risk do not get diabetes, researchers want to find out what the environmental triggers are.
One trigger might be related to cold weather. Type 1 diabetes develops more often in winter than summer and is more common in places with cold climates.
Another trigger might be viruses. Perhaps a virus that has only mild effects on most people triggers type 1 diabetes in others.
Early diet may also play a role. Type 1 diabetes is less common in people who were breastfed and in those who first ate solid foods at later ages.
In many people, the development of type 1 diabetes seems to take many years. In experiments that followed relatives of people with type 1 diabetes, researchers found that most of those who later got diabetes had certain autoantibodies in their blood for years before.
(Antibodies are proteins that destroy bacteria or viruses. Autoantibodies are antibodies 'gone bad,' which attack the body's own tissues.)
Type 2 Diabetes
Type 2 diabetes has a stronger link to family history and lineage than type 1, although it too depends on environmental factors.
Studies of twins have shown that genetics play a very strong role in the development of type 2 diabetes.
Lifestyle also influences the development of type 2 diabetes. Obesity tends to run in families, and families tend to have similar eating and exercise habits.
If you have a family history of type 2 diabetes, it may be difficult to figure out whether your diabetes is due to lifestyle factors or genetic susceptibility. Most likely it is due to both. However, don’t lose heart. Studies show that it is possible to delay or prevent type 2 diabetes by exercising and losing weight.
Have you recently been diagnosed with type 2 diabetes? Join our free Living With Type 2 Diabetes program and the information and support you need to live well with diabetes.
Type 1 Diabetes: Your Child's Risk
In general, if you are a man with type 1 diabetes, the odds of your child developing diabetes are 1 in 17.
If you are a woman with type 1 diabetes and your child was born before you were 25, your child's risk is 1 in 25; if your child was born after you turned 25, your child's risk is 1 in 100.
Your child's risk is doubled if you developed diabetes before age 11. If both you and your partner have type 1 diabetes, the risk is between 1 in 10 and 1 in 4.
There is an exception to these numbers. About 1 in every 7 people with type 1 diabetes has a condition called type 2 polyglandular autoimmune syndrome. In addition to having diabetes, these people also have thyroid disease and a poorly working adrenal gland. Some also have other immune system disorders. If you have this syndrome, your child's risk of getting the syndrome — including type 1 diabetes — is 1 in 2.
Researchers are learning how to predict a person's odds of getting diabetes. For example, most whites with type 1 diabetes have genes called HLA-DR3 or HLA-DR4. If you and your child are white and share these genes, your child's risk is higher. (Suspect genes in other ethnic groups are less well studied. The HLA-DR7 gene may put African Americans at risk, and the HLA-DR9 gene may put Japanese at risk.)
Other tests can also make your child's risk clearer. A special test that tells how the body responds to glucose can tell which school-aged children are most at risk.
Another more expensive test can be done for children who have siblings with type 1 diabetes. This test measures antibodies to insulin, to islet cells in the pancreas, or to an enzyme called glutamic acid decarboxylase. High levels can indicate that a child has a higher risk of developing type 1 diabetes.
Type 2 Diabetes: Your Child's Risk
Type 2 diabetes runs in families. In part, this tendency is due to children learning bad habits — eating a poor diet, not exercising — from their parents. But there is also a genetic basis.
In general, if you have type 2 diabetes, the risk of your child getting diabetes is 1 in 7 if you were diagnosed before age 50 and 1 in 13 if you were diagnosed after age 50.
Some scientists believe that a child's risk is greater when the parent with type 2 diabetes is the mother. If both you and your partner have type 2 diabetes, your child's risk is about 1 in 2.
People with certain rare types of type 2 diabetes have different risks. If you have the rare form called maturity-onset diabetes of the young (MODY), your child has almost a 1-in-2 chance of getting it, too.
More Information on Genetics
If you would like to learn more about the genetics of all forms of diabetes, the National Institutes of Health has recently published The Genetic Landscape of Diabetes. This free online book provides an overview of the current knowledge about the genetics of type 1 and type 2 diabetes, as well other less common forms of diabetes. The book is written for health professionals and for people with diabetes interested in learning more about the disease.