Narcolepsy is a sleep disorder that occurs when a small set of cells located deep in the brain die off. Narcoleptic patients have excessive sleepiness and other symptoms. The area of the brain affected is the hypothalamus, which controls basic drives like appetite and sleep. Elevated body weight is a common finding in patients with narcolepsy, and some studies have suggested that problems with glucose (blood sugar) metabolism could be involved. However, it's not clear if it's the narcolepsy itself that could alter glucose metabolism or the obesity associated with the narcolepsy that is responsible.
In the Journal Sleep, Beitinger et al did a study comparing the glucose metabolism of narcoleptics to healthy control patients that had the same body mass index, age, and gender. Their results showed no difference in glucose metabolism in the narcoleptic patients versus the matched controls. This means that the higher rates of glucose metabolism problems seen in narcoleptics are due to elevated weight, not from the narcolepsy itself.