Which part of the brain causes narcolepsy?

Hypothalamus. The part of the brain known as the hypothalamus is responsible for narcolepsy. Lack of a neurotransmitter called hypocretin (orexin) in this part of the brain results in the illness.
Hypothalamus. Narcolepsy is a chronic condition leading to excessive daytime sleepiness, among other symptoms. In most patients it is caused by the destruction (thought to be autoimmune) of cell in the hypothalamus which produce a chemical (hypocretin or orexin) needed to stay wake. The loss of these cells and the chemical results in the condition.