Genetic risk factors

If an immediate relative (parent, sibling, or child) has type 1 diabetes, one's risk of developing the disease is 10 to 20 times that of the general population. Your risk can rise from 1 in 100 to roughly 1 in 10 or possibly higher, depending on which family member has diabetes and when he or she developed it:

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• If one child in a family has type 1 diabetes, 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 who has diabetes than if it is the father. If the mother is 25 or younger when the child is born, the child's risk is 1 in 25, compared with about 1 in 17 when the father has diabetes. When the mother is over age 25, the risk drops to 1 in 100 -- virtually the same as for the average American. The risks are somewhat higher when a parent developed diabetes before age 11.
• About 1 in 7 people with type 1 diabetes has a condition known as type 2 polyglandular autoimmune syndrome. These people have thyroid disease, malfunctioning adrenal glands, and sometimes other immune disorders. When a parent has this syndrome, the child's risk of developing it--including type 1 diabetes--is 1 in 2, according to the American Diabetes Association.

Caucasians 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, so scientists are studying what environmental factors may be at work. Genes influencing the function of the immune system are the most closely linked to susceptibility, regardless of race. One of those genes is HLA-DR. Most Caucasians with diabetes carry gene variants (alleles) 3 or 4 (or both) of the HLA-DR gene, known as HLA-DR3 or HLA-DR4. The HLA-DR7 allele plays a role in diabetes in blacks, while HLA-DR9 allele is significant in diabetes among Japanese.