Not completely sure why I am writing. My father had huntingtons, which he inherited from his mother, who in turn inherited it from her mother. My father was tested in the 90's with a blood test. I was already married and decided to have predictive testing to determine whether or not to have children. My testing went through a well respected university with a huntington's center and Ohio State University was the chosen lab. My results were a repeat of 26 from my father and 17 from my mother. Three children later, I am exhibiting many signs of the disease. I have called back the university more than once and have been told that being raised by a difficult huntington's parent could result in changes in brain chemistry, which could explain my symptoms. They stand by their lab of choice, but suggest I could retest again for peace of mind! I have spoken to another equally prestigious university and was told that they have had at least one documented case of a false negative result, so it is possible. I also have a daughter who is showing signs of juvenile huntingtons. I just read on the site that the previously held belief that juvenile hd rarely comes from an affected mother was proven wrong in a recent study.
I was tested because i never wanted to be a parent with huntingtons. Now, I can retest, but for what? I already have three children because I trusted science, which apparently is based on the best guesses of experts on a given day. I don't believe anything I read about the disease anymore because I have read so many conflicting "facts". I don't think doctors are any closer to understanding the disease than they were when huntington first named it.

Since you had the test and it came back negative i would think the odds of testing positive on a second test would be very low odds. You are right. Human or scientific errors are possible and do happen.
If it was me, I would want to find out if symptoms I and my daughter are displaying are due to a treatable condition that i would be neglecting in searching for an answer for.
I guess, i would repeat the HD test as the first step and then continue my search in finding out what was affecting my health. I bet I would always doubt any other diagnosis a doctor came up with and always have in the back of my mind that I needed to truely rule out HD first as the cause so that I could be reassured for good that my health issues were not caused by HD. I would want my child who was having medical problems also to have the opportunity to be able to obtain accurate information concerning their health and wellbeing.
But, i am not you and i am sure all these things have already crossed your mind. I am sure it is disheartening to know you did everything you could in advance to help your children and yet the question still remains.
Sorry about your journey but we are here if you need us.
Lizzieann

I wonder if it's a similar disease?

I'm sorry for your situation, but i think you really Have to re-test, for your child's sake, because you are suspecting jhd. There are other things that can have some similarities to jhd like ADD, autism, etc. This is where the problem is. There are some ADD meds that are good for ADD, but very bad for jhd. So if you don't have a proper diagnosis for your child, they could be given meds that could make them worse instead of better.
About false negatives. I have seen Marsha post about this before, but i don't remember how it works. If a cag count is very high, if they don't count it proper? or test it proper? a very high count can come out looking like a normal count. I'm not sure how that works, but Marsha has posted before of that happening in some cases of jhd. Hope this is helpful, and sorry for the reason you are here