It doesn't, that's why not everybody has that gene; if Alzheimers was something you developed as a teen, I'm sure that mutation would spread and soon everybody

It doesn't, that's why not everybody has that gene; if Alzheimers was something you developed as a teen, I'm sure that mutation would spread and soon everybody would have it. Maybe we could use that gene in the future on patients at the onset of regular Alzheimers.