Can Alzheimer’s be hereditary?

Yes. That's how they do research on Alzheimer's. An line of rats have been engineered to express Alzheimer's symptoms. They are literally born with it. They are the control use to test Alzheimer's treatments.

To be technical, they may not have Alzheimer's. They were engineered to have the plaques that are associated with Alzheimer's. They do show Alzheimer's symptoms just like in humans. But whether those plaques cause Alzheimer's is an open question. No one knows what causes Alzheimer's.

ALZ is considered a Dementia but the cause is not like the Dementias you hear about that are caused by head injuries, smoking, drinking plaque, etc.

My boss, an RN, explained it this way.

Dementia - You know its a stove but you cannot remember how to work it

ALZ - you don't remember its a stove.

Great grandma, Grandma and both her sisters, maybe mom ... yes, can run in families.

Yes, runs in my Dads family. Mother and Aunt had it. My Aunt and her brother were diagnoised and a cousin. All my Grandmothers side.

Yes. I see your friend is very young to have Alzheimer’s.
Here is a link to PBS special on early onset Alzheimer’s in families. It might be helpful.

http://www.pbs.org/program/forgetting/