It’s called FFI–fatal familial insomnia. And it’s basically the inability to sleep that’s inherited. Once the symptoms start, the estimated life expectancy is 18 months. The symptoms involve worsening insomnia to the point that the person cannot sleep at all, which results in hallucinations, delirium, and confused states similar to dementia.

The good news is that it’s a very rare autosomal dominant inherited prion disease of the brain, which you can be tested for. Only 40 families worldwide have actually tested positive for the gene.

The bad news is that there’s no known cure. According to Wikipedia, “It has been proven that sleeping pills and barbiturates are unhelpful; on the contrary, in 74% of cases they have been shown to worsen the clinical manifestations and hasten the course of the disease.”

But it raises the question about why we need to sleep in the first place. Even animals need sleep, though many of them have the ability to keep half their brains in awake and alert to ward off predators. The predominant theory of sleep is that the brain demands it.

But does the brain sleep? National Geographic takes a comprehensive look at sleep in its November issue, which comes to one conclusion: While there is a bank of knowledge about sleep, the mystery remains. And it challenges the old belief that the only necessities in life are food and water.