June 13, 2005
Question from Christchurch City, New Zealand:
My husband has had type 1 for 27 years. We have three children. In January 2004, our 13 month old son was diagnosed with type 1. Our middle child who has Down Syndrome, age five and a half, has just had the immune markers done. I would appreciate your comments as I just want to know if it possible these results could be positive and lead to type 1. Our daughter, age 10.5 years old, is too scared to have the blood tests done. Anti-GAD test: Negative; ICA: 5. I was told you need a value of 10 to be a true positive. Is this correct? The third test is still to be completed. The scientist who was doing all this testing e-mailed me and said that if the anit-IA2 is negative, she would feel more confident about not repeating the blood test in the short term. She mentioned that it is important to note that children may be negative when first tested for antibodies, but develop antibodies when they are older.
Antibody testing to pre-diagnose type 1 diabetes has several problems:
the antibody tests are only positive about 60 to 80% of the time;
if several tests are done in research laboratories, i.e. three antibody tests, the chances of false positive and false negatives decreases;
Down syndrome, by itself, includes a higher risk for developing autoimmune problems, including type 1 diabetes, celiac disease and autoimmune Hashimoto’s thyroiditis. Celiac and thyroiditis are more common in Down syndrome patients than diabetes, but if there are two first degree relatives, as in your case, a sibling and father, I would test for all three periodically;
I am not sure that I agree that a ten year old should have the final say about blood work that is so potentially important. I think this should be up to the parents and the physician;
the physician who has ordered the testing should be the best person to advice you about specific risks for your children so I would go back to consult with them.