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For most people, insomnia won't kill you. But in one very rare, very specific case, not only is it deadly, it's lurking in your genes.

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[ intro ].

We’ve all been there -- tossing and turning all night for absolutely no reason. But for the vast majority of people, insomnia can’t actually kill you.

In one very rare, very specific case, however, not only is insomnia deadly -- it’s lurking in your genes from the time you’re born. Familial fatal insomnia, or FFI, is an incredibly rare condition where patients experience lack of sleep and other psychiatric symptoms, and eventually die. And though we know what causes it, there’s a lot about that cause we don’t fully understand.

Familial fatal insomnia usually affects adults as early as their 30s, though there have been a very small number of cases in teenagers. And yes -- it is fatal. Unfortunately, there’s no cure, and patients usually die within a year or two of showing symptoms.

It usually starts when people report having a hard time falling or staying asleep. When they do sleep, they have a harder time achieving deep, restful sleep. And their brain activity actually changes.

The typical sleep cycles most people experience are altered for these patients. Sometimes their perceptions while awake during the day can become dream-like, either hallucinating, seeing double, or reacting to things in the dream. As the disease progresses, patients develop problems with balancing and walking, and experience actual dreams throughout the day.

But FFI is so rare that these symptoms can be really misleading. If a patient comes in complaining of hallucinations, for example, doctors might be more likely to think of something like schizophrenia. Because FFI is incredibly rare.

Only a few dozen cases have been described in the medical literature, though it might be slightly more common than that. So where does this disease come from? Well, autopsies of patients with this disease show something in common -- deterioration of tissue in the thalamus.

This region is often called a relay center, connecting different parts of the brain to each other. But it plays a specific role in regulating your sleep cycles. It’s involved in monitoring sensory information like vision, and seems to serve as a gate that chooses when to let that information pass to other parts of your brain.

Meaning it may help you become less aware of your surroundings as you drift off. So why do some people get this thalamus deterioration? That brings us to the "familial" part of the name -- it's genetic, and we know just which gene is to blame.

FFI is a prion disease -- specifically, an inherited one. These are a handful of rare diseases that cause neural degeneration, all associated with a specific protein called the prion protein. That protein is coded for by a gene called PRNP.

Variants of this gene can make the protein mutate, which causes all kinds of problems for your brain tissue. Quite a few variants in this gene have been documented, but only one results in the specific deterioration in the thalamus associated with FFI. And in patients with FFI, you can find this mutated protein in the deteriorated parts of the thalamus.

Another prion disorder, Creutzfeldt-Jakob disease, also follows a similar pattern -- but targets different brain regions that affect memory, coordination, and vision. We're not exactly sure how this misshapen protein causes neural degradation, but some researchers think it involves the body’s natural process of programmed cell death. Damaged brain regions like the thalamus look like they died from apoptosis -- but the protein can be detected outside of where the damage is.

Which gets to the big mystery about this disease: we don't really know why we have this protein in the first place. We really only tend to notice it when it goes wrong -- deteriorating neural tissue and ultimately leading to death. If it’s not doing anything terribly important when everything’s ok, but does horrible things when it mutates, you’d think evolution would get rid of it.

But it's found in other mammals and birds as well as humans, suggesting there could be a good reason to keep it around. We just don’t know what that is. Some studies in mice have found that when they have less of the regular, unmutated prion protein, they have less long-term potentiation in the hippocampus -- though those results haven’t been consistent.

Long-term potentiation is the idea that when a neuron fires repeatedly, it forges stronger synaptic connections, which is theorized to be an important part of how memory works. Furthermore, when mice have more of this protein than usual, they have even more synaptic transmission. So, possibly stronger memories.

Messing with the amounts of a protein to see what changes is scientists’ favorite method for figuring out what that protein does normally. These experiments tell us the prion protein could be critical for keeping your memory functioning, but not all studies actually agree. Another idea is that the common prion protein is just doing the opposite of what the misshapen one does -- instead of killing our neural tissue, it’s protecting it.

In those same kinds of more-or-less-protein experiments, mice bred to not have the prion protein would suffer larger lesions when researchers induced a stroke compared to normal mice. And having more of that protein seemed to protect against neural damage. So it's possible that having a better understanding of this protei n might unlock some ideas about why brains deteriorate as they age.

While research is ongoing about what makes this protein work, it could help us understand how memory works and how to prevent some of the neural changes associated with aging. Which could help us treat more common diseases like Alzheimer’s and MS, but also help those few people who develop fatal insomnia. Thanks for watching this episode of SciShow Psych, which was brought to you with the help of our community of amazing patrons.

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