The genetics of diabetes
("What are the odds of my getting diabetes?")*

 

Type 1 Diabetes:

  • If your mother has Type 1 diabetes, you have a 3% risk of developing Type 1 diabetes.
  • If your father has Type 1 diabetes, you have a 6% risk of developing Type 1 diabetes.
  • If both your parents have Type 1 diabetes, you have a 30% risk of developing Type 1 diabetes.
  • If your brother or sister has Type 1 diabetes, you have a 5% risk of developing Type 1 diabetes.
  • If your non-identical twin has Type 1 diabetes, you have a 20% risk of developing Type 1 diabetes.
  • If your identical twin has Type 1 diabetes, you have a 35% risk of developing Type 1 diabetes.**
  • If there is no family history of diabetes, you have a 0.2% risk of developing Type 1 diabetes (by the age of 20).

 

 Type 2 Diabetes:

  • If your mother or father has Type 2 diabetes, you have a 15% risk of developing Type 2 diabetes.
  • If both your parents have Type 2 diabetes, you have a 75% risk of developing Type 2 diabetes.
  • If your brother or sister has Type 2 diabetes, you have a 10% risk of developing Type 2 diabetes.
  • If your non-identical twin has Type 2 diabetes, you have a 10% risk of developing Type 2 diabetes.
  • If your identical twin has Type 2 diabetes, you have a 90% risk of developing Type 2 diabetes.

 

*These figures are approximations. Quite different estimates of risk show up on different studies from different parts of the world. The estimates listed above are most applicable to North America. Also (and importantly), remember that at least for type 2 diabetes these risks can be substantially reduced by appropriate intervention with diet, exercise, weight control, and sometimes, with medication.

**Can you think of a better illustration of the fact that type 1 diabetes is clearly a mixture of both genetic susceptibility and environmental trigger? If it was all genetic then, if your identical twin had type 1 diabetes, you would have a 100% risk of developing type 1 diabetes. So what is the non-genetic, environmental factor that  triggers type 1 diabetes in susceptible individuals? Is it a virus? Something in the diet (such as nitrosamines in smoked meat)? Early exposure to cow's milk? We don't know, of course, and there is ongoing research to figure it out, including the exciting TRIGR study which is looking at the latter possibility.

Also of interest is that although we speak of family history as being so important, at most only 15% of people with type 1 diabetes have a first degree relative (brother, sister, father, mother, son or daughter) with type 1 diabetes.