(To preface this, I've 0 knowledge of medicine)
If diseases such as Huntington's are hereditary and you can't develop/catch them later in life, how did the original person in the family bloodline get it? Because if their parents didn't have it and, therefore they weren't born with it, surely that means that they must've developed or acquired later it in life meaning that you either could've developed way back when or can still develop it now?