So sorry about your situation but (1) you may not necessarily be at risk and (2) we are learning more and more that we can work to overcome what may be in family history. Maybe this can be true for your mother also.
In my family it is vascular disease, stroke, and dementia. This makes me so determined to do everything I can to keep myself as well as possible. Eating carefully, good weight, good variety of exercise, keeping the old brain active, and daily meditation. Hope you are potently motivated to fight what may be possible for you.