Comment by bsder

> People with mutations in those genes got a particular type of inherited alzheimers early, this says nothing about the cause of general Alzheimers.

This is completely analogous to claiming that people with mutations in BRCA (which causes a lot of early breast cancers) says nothing about general "cancer".

That's simply flat-out wrong. Genetic mutations like BRCA affect certain subsystems and many of those subsystems are common and relevant to many different cancers outside of breast cancer or breast cancers that appear later. Lots and lots of cancer research proceeded by studying the common systems that BRCA affects. Sure, those subsystems aren't involved in every cancer, but they're involved in a solid chunk of them.

And, even better, when you find one that isn't affected by one of those subsystems that BRCA touches, that's an interesting result, too. Now you can look at what the differences are, figure out what the new subsystems are and categorize your cancer more specifically which makes successful treatment more likely.

There is absolutely no reason to believe that Alzheimer's is any different on that front.