I have type 1 diabetes (diagnosed at age 38), I am not overweight, and both my older sister (diagnosed at age 27) and my younger brother (diagnosed at age seven) have it as well. My maternal grandmother had type 1, two of my maternal uncles type 1, three first cousins (mother’s side) have type 1, and the rest of my mother’s brothers and sisters (five) have type 2.

My doctor has told me that type 1 is not inherited and that you only get type 1 from a viral infection. Can you give me a clear answer to why so many of my close relatives have the same diagnosis?

Our current understanding of the development of type 1 diabetes is that it is dependent on an inherited predisposition as well as an environmental trigger. The inherited predisposition can control the way the immune system works, so you can see that this might be similar in other members of your family. The environmental trigger is rather vague. It could be a viral infection. This might explain why several members of a family may develop type 1 diabetes within a short time. Other triggers may be toxins or other infections agents. The trigger is less well worked out.

I would have to say that the family history you describe is quite dramatic. It might be possible that you have a gene for another type of diabetes that is uncommon. It might also be possible that some have type 2 diabetes and not type 1 diabetes.

JTL