system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does Alzheimer's kill?

A family friend's mother just passed away last night from it. Here's the thing, I don't understand how it actually kills? (i.e heart attack, low immune, stroke?) 
I always thought it was like HIV/AIDS where it isn't the disease that kills, but the sicknesses that the patient catches because of a bad immune system. HELP!
gpt
Paraphrased from Wikipedia:

The cause and progression of Alzheimer's disease is not well understood but it's associated with abnormal build-up of 'plaques' in the brain.

As well as the emotional and thought deterioration, in moderate to advanced Alzheimer's, speech and other motor skills are effected, making patients less coordinated and unable to perform most activities of daily living.

During the final stage of AD, symptoms include extreme apathy and exhaustion. 

People with AD will ultimately not be able to perform even the simplest tasks without assistance (because of the motor deterioration)

Because of this, muscle mass and mobility deteriorate to the point where they are bedridden and they lose the ability to feed themselves.

The cause of death is usually infection of pressure ulcers or pneumonia (made much more likely by being bed-bound and malnourished)