Genetics of Type II Diabetes

Type 2 diabetes definitely runs with both families and “super families; e.g., the humongous risk of developing type 2 diabetes among Pima native Americans).

1.  The brothers and sisters of a type 2 diabetic have an almost a 40% risk of developing type 2 diabetes or pre-diabetes.

2.  The children of a type 2 diabetic parent have a 33% chance of developing type 2 diabetes or pre-diabetes.

3.  The identical twin of a type 2 diabetic has a 70% to 80% chance of developing type 2 diabetes.

4.  The best data on genetic contribution in most diseases comes from MX-DZ twin studies (mono-zygotic vs di-zygotic), which provide the optimal means known of trying to separate out the effects of shared environment from shared genes (for example, the sibling risk of 40% in example #1, above, could result from either a shared gene, or from the fact that most members of a family have similar eating habits and activity levels (e.g., being overweight also tends to run in families), or from a combination of the two.   Here’s the only MX-DZ data I know about for type 2 diabetes:

In one study researchers looked at 56 pairs of twins in which at least one twin had type 2 diabetes.

* Number of twin pairs in which both twins had type 2 diabetes

This suggests that genes and environment contribute roughly equally to the familial risk of type 2 diabetes.

For the overwhelming majority of persons with typical type 2 diabetes, a single gene variant does not appear to be responsible.  Rather, the genetic component of their disease is likely the result of multiple genes acting together.  A number of genes have been identified that probably contribute (to a lesser or greater degree) to type 2 diabetes, but for most of them the responsible gene variant that contributes the risk (if any exists) has not yet found.