This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Psychiatry
A 25 year old male believes that his penis is decreasing in size everyday and one day it will disappear one day and he will die. Diagnosis is ? 
Select and explain. 
A. Obsession, B. Somatization, C. Hypochondriasis, D. Delusion disorder
D: Delusion disorder
Answer: D: Delusion disorder 
Explanation: Ans. D. Delusion disorderDescription given in the question is of Koro syndrome, a delusional disorder.Koro syndromeKoro is a culture-specific syndrome delusional disorder in which an individual has an overpowering belief that one's genitalia are retracting and will disappear, despite the lack of any true longstanding changes to the genitals.Koro is also known as shrinking penis. The syndrome is commonly known as genital retraction syndrome.