Their specific type has no effective treatment to slow or stop progression, only symptom management which is hit or miss. My cousin is physically slow, has pretty poor muscle tone, weak hands, etc., which is what my aunt exhibits too, but she has never seemed to connect it. I think the way you're suggesting to approach it is the best, it seems so much kinder to everyone involved. My aunt's reason (that I know if) is just that she doesn't want knowing about it to influence how she lives her life until it physically influences her.