DEAR DR. ROACH: My mom has Capgras syndrome and firmly believes that her husband (my dad) is dead. She won't go see any medical professionals (since they believe that she has Capgras and her husband isn't dead). Lewy body dementia is responsible for about 70% of Capgras syndrome cases. Capgras syndrome is rare. Most critically, the person must present a danger to themselves or others, which is particularly important in Capgras syndrome.