What doctor do I see to get Alzheimer's genetic testing?

My mother is currently in a nursing home with early-onset Alzheimer's disease at age 64. My grandmother (her mother) died in September 2009 of AD, after having it for about 8 years. I understand there is some kind of genetic test that I can get to see if I have the "gene" to end up with it as well. I am 39 years old and very concerned and want to know so I can better plan for my future. What kind of a doctor should I go to to get tested?