Alzheimer's disease: 70 genes?!

This doesn't sound like one coherent disease:

Alzheimer's disease | A tangled tale | Economist.com

...The Cure Alzheimer’s Fund, a charity, also had an important finding. It announced that its mapping of the disease’s genetic basis has found 70 genes that may be involved, far more than expected...

70 genes?! This sounds like schizophrenia -- lots and lots of mutations.

I've long felt that "Alzheimer's" wasn't a disease, but was the normal destination of the aging brain. Not so bad when it hits at age 105, but genuinely horrible when it hits at 55. A "70 gene" story fits with the theme that

1. It's really quite tricky to build a functioning human brain out of the flotsam of primate evolution. The current model has a lot of hacks and glitches.
2. Any one of hundreds of faults will derail the train early. To get to 105 without full dementia takes a perfect performance.
3. We ain't going to cure this anytime soon.