February 27, 2001
Genetics and Heredity
Question from Windsor, Ontario, Canada:
I have 14 year old friends who are identical twins. One twin has had type 1 diabetes for many years, but the other does not have diabetes. If diabetes is a genetic disorder, and identical twins have identical genetic information, why does one twin have diabetes and not the other?
In the older studies, it had been shown that there was concordance for diabetes in only about 30% of cases of identical twins. This was the basis of arguments for the relative importance of environmental triggers over genetic predisposition. However, the follow up period was limited to less than 10 years from the onset of diabetes in the affected twin. When follow-up was extended to forty years, the concordance for clinical diabetes had more than doubled, and, in addition, an even higher percentage of cases had evidence of islet cell autoimmunity. in the form of antibodies.