Genetics and Diabetes (Joslin Diabetes Center)

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).

Caucasians (whites) have a higher risk of type 1 diabetes than any other race. Whether this is due to differences in environment or genes is unclear. Even among whites, most people who are susceptible do not develop diabetes. Therefore, scientists are studying what environmental factors may be at work. Genes influencing the function of the immune system are the most closely linked to type 1 diabetes susceptibility, regardless of race. One of those genes is HLA-DR. Most Caucasians with diabetes carry alleles (gene variants) 3 and/or 4 of the HLA-DR gene. The HLA-DR7 allele plays a role in diabetes in blacks, while HLA-DR9 allele is important in diabetes among Japanese.