The genetic factor is REALLY complex in diabetes. Some 50 gene combinations are said to be involved in its development! That is really amazing!
While no person directly related to me has type 1 (besides a possible wasting disease in a great aunt at age 14 in the 1920s) no one has a trace of it.
However a great deal of my family has died from inflammation leading to cancer in the lower intestines and have suffered kidney diseases. My brother (age 21) already has kidney stones. A great grandparent died from kidney issues. And most of my family suffers from food intolerances (not as sever as mine.)
I truly believe it is passed down through the genes, the question is how those gene combinations are expressed in the individual in a given environment? For my family these genes were obviously very useful to my ancestors, even if they expressed themselves later in life (60+) to cause bowl and kidney diseases. So even with the painful deaths my ancestors when these genes finally started expressing themselves in a negative way, my great grandparent was old enough to have procreated three generations personally and lived to see grandchildren. My guess is that there is an environmental stimuli that has either changed(hygiene), disappeared (parasites), or been added (pesticides) that is causing a greater number of these genes to be expressed in youths in a non-beneficial way, like diabetes. Versus these autoimmune directing genes fighting infection/ parasites/ diseases and only negatively expressing themselves in our bodies later in life as the body ages.
But that is just my theory I put together.