Huntington’s Disease is not known to skip generations. If your mother does not have it, you will not either. There are a number of genetic conditions along the DNA strand that Huntington’s is on, such as Parkinson’s, Multiple Sclerosis etc. Your grandfather may have had something like that. Genetic testing for HD was finalized in about 1985 so, if he hadn’t had the DNA test, it would have only been if your grandfather had an autopsy that HD would have been identified. There are Huntington Disease Family groups around the world. You might try contacting one of them if you are still concerned.