FDR's affliction (5)
I believe the answer is:
polio
'fdr's affliction' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for polio that I've seen before include "Viral disease causing paralysis" , "Acute viral disease" , "Paralysing disease" , "Viral disease which can cause paralysis ( 5)" , "rarely seen complaint" .)