Hello there quillan,
Well first of all I would like to say that I am so sorry that your twin brother has been diagnosed with Huntington's chorea. I am sure that roley has given you pretty good answer to your question and that you are satisfied with it. I would just like to add that you need to test yourself as well. Huntington's disease is very serious condition and in most of the cases it is fatal.
Unfortunately this is autoimmune disorder and that means that your brother’s body is attacking healthy cells and tissue, in this case nerves. This can result in various different complications as you can see by yourself. This condition is hereditary and even if you don’t have symptoms you may have the condition. I hope that you don’t. Good luck.