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October 3, 2001

Genetics and Heredity

Question from Brooklyn, New York, USA:

I am dating a 21 year old girl whose father developed type 1 diabetes at age 12 and passed away because of it. We are both of Jewish Ashkenazi descent. My grandfather also has diabetes, but he is in his 90's and just came down with it recently. My sister also had some form of diabetes when she was pregnant with her third child, but I think it only lasted during her pregnancy (I would guess that my sister and grandfather had type 2). I read on your website that there is about a 6% chance of a father passing diabetes type 1 to his daughter. I read that there's 4% chance if the mother has it, but here it would be the maternal grandfather and maternal great uncle. I noticed that you write that there is about a 5% chance for a parent with diabetes passing it to their child, and you also write that there is about a 5% chance of couples with no family history of diabetes, having a child with diabetes. To someone with no medical knowledge that seems to say that there is no higher risk than to someone who has it in their family. Please explain to me (and I think it should be posted for the public) where I went wrong with this assumption. How much does the percentage decrease the chance of the girl I'm dating still getting it, since she is already 21 and is totally healthy? What is the chance of, if our relationship develops, of passing it to our kids?

Answer:

Most of the answers to your question are in The Risk of Developing Type 1 Diabetes, which has recently been revised. The figures can only be approximate however because the biases introduced by the various different forms of type�1 diabetes as well as the complexity of the many inherited and so far unknown environmental factors cannot yet be calculated.

At age 21, your girl friend is well past the peak incidences of developing type�1A (autoimmune) diabetes, and I would judge her chances of developing this form of diabetes as less than 1%. The probability of any children getting type 1A would be that for the population as a whole that is ‘about’ 0.4% in the first 20 years of life. I don’t know where you found the 5% figure for this which must either be a typo or a misunderstanding.

DOB