@Dessito, you have never heard that? I have heard that my whole life. Turns out, when I searched, its a bit more complicated than that. That’s probably not the best way of describing what happens. That might be kinda ‘old wives tale-ish’ Here is a better source of statistics from Joslin…
Genetics and Diabetes
"Type 1 Diabetes Odds
Just who is at risk for developing type 1 diabetes? Here’s a sampling of what Dr. Warram, a Lecturer in Epidemiology at Harvard School of Public Health, said is known:
If an immediate relative (parent, brother, sister, son or daughter) has type 1 diabetes, one’s risk of developing type 1 diabetes is 10 to 20 times the risk of the general population; your risk can go from 1 in 100 to roughly 1 in 10 or possibly higher, depending on which family member has the diabetes and when they developed it.
If one child in a family has type 1 diabetes, their siblings have about a 1 in 10 risk of developing it by age 50.
The risk for a child of a parent with type 1 diabetes is lower if it is the mother — rather than the father — who has diabetes. “If the father has it, the risk is about 1 in 10 (10 percent) that his child will develop type 1 diabetes — the same as the risk to a sibling of an affected child,” Dr. Warram says. On the other hand, if the mother has type 1 diabetes and is age 25 or younger when the child is born, the risk is reduced to 1 in 25 (4 percent) and if the mother is over age 25, the risk drops to 1 in 100 — virtually the same as the average American.
If one of the parents developed type 1 diabetes before age 11, their child’s risk of developing type 1 diabetes is somewhat higher than these figures and lower if the parent was diagnosed after their 11th birthday.
About 1 in 7 people with type 1 has a condition known as type 2 polyglandular autoimmune syndrome. In addition to type 1 diabetes, these people have thyroid disease, malfunctioning adrenal glands and sometimes other immune disorders. For those with this syndrome, the child’s risk of having the syndrome, including type 1 diabetes, is 1 in 2, according to the American Diabetes Association (ADA)."