It’s a disease with mutlifactorial causes. There are many diseases out there that don’t have just ONE cause.

A good and pretty common example being cardiovascular conditions which have genetic, lifestyle and traumatic factors among others contributing to their manifestation.

If you want to work on a better definition of a disease like Alzheimer’s, join these guys who are working on the definitions of this disease:

https://academiccommons.columbia.edu/doi/10.7916/xwcq-7092/download

Or try and go into research of its treatment. But bashing OP for their quite knowledgeable approach isn’t polite. And shines bad light on you.