Nyssen-Van Bogaert Syndrome

Certain of the royal family of the Glu'gu'ik are susceptible to a version of this mental illness, presumably due to some inbreeding in the past history of the royal house. Symptoms include irritability, extreme impatience, radical and sudden mood swings, violent behaviors, possible hallucinations, megalomania, and possibly the onset of dementia.

There is also a human version.