This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Delusional Disorder, Subject name: Psychiatry
The deliusion which involves replacement of a familiar person by someone else is - 
Select and explain. 
A. Capgras syndrome, B. Cotard syndrome, C. Othello syndrome, D. None
A: Capgras syndrome
Answer: A: Capgras syndrome 
Explanation: Ans. is 'a' i.e., Capgras syndrome The delusional misidentification syndromeso DSM is characterized by misidentification delusions of other or self. Four main syndromes are differentiated : -Capgras syndrome (Delusion of double) : - Patient falsely sees a familiar person as a complete stranger who is imposting on him as a familiar person.Fregoli syndrome (illusion de fregoli) : - The patient falsely identifies stranger as familiar person.Syndrome of subjective double : - The patients own self is perceived as being replaced by a double.Syndrome of intermetamorphosis ; - A false belief that a person can transform into another person.o These syndrome most commonly appear in schizophrenia. Other causes axe Alzheimer syndrome, head injuries, and delusional disorders.