My boyfriends mom got early onset alzheimer's at 50. what's the chances he will get it? can it do anything preventative?

Depends on genetics: Several genes are related to early onset alzheimer's, such as ps-1, ps-2, app, but not clear that he has increased risk. Would behoove most people to consider that the incidence is lower when a person is social, physically active, and keeps learning. Some studies have suggested mediterranean diet, red wine, coffee, fatty fish, anti-oxidants as a way to decrease risk. Suggest he contact her doc.

Genetic?: Your boyfriend has a right to genetic screening for the common autosomal dominant causes of early-onset alzheimer's. If mom had one of these, he has a 50% chance of having it also.