Alzheimer's, for instance (8)
I believe the answer is:
dementia
'alzheimer's for instance' is the definition.
(I know that Alzheimer\\u0027s disease is a type of presenile dementia)
This is the entire clue.
(Other definitions for dementia that I've seen before include "Detain me, having distressing condition of old age" , "It's caused by brain diseases" , "Disorder of the mind" , "Detain me in distressed state of old age" , "Severe or persistent mental disorder, often to do with age" .)