My mother had it. There is no family history that we know of. At the time we were told it may be genetic, but it also may appear spontaneously. It affects peop

My mother had it. There is no family history that we know of. At the time we were told it may be genetic, but it also may appear spontaneously. It affects people differently. For some it strikes the feet and legs first, for some the arms and neck. Some people like Stephen Hawking live with it for years, some only survive a year or two after diagnosis. It's rare, so diagnosis is often preceeded by wrong guesses at more common explanations for the symptoms. There is no test for it; it's basically diagnosed by ruling out everything else.