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(0:11) Alzheimer's Disease is horrible. It's a type of dementia that most people know from its most prominent symptoms -- loss of memory and reasoning -- but it can also very slowly degenerate some of the basic muscular functions that you need to stay alive, like swallowing and breathing.

(0:24) Now it should make sense that Alzheimer's isn't contagious, at least in the sense that you can't catch it from being around someone who has it, but it turns out that it is transmissible, just not directly.

(0:33) According to a study published this week in "Nature", you can essentially catch Alzheimer's, but only if the sick person's brain matter actually comes in contact with your brain matter.

(0:41) So how do you get someone else's brains in your brains? Well its not easy. Between 1958 and 1985, more than 1800 people in the UK, who suffered from various conditions that gave them a small stature, were given human growth hormone, or HGH, to help them grow.

(0:55) Human growth hormone is produced in the pituitary gland, which is in your brain. Until 1985, we didn't know how to synthesize it, so the only place to get human growth hormone, was from inside the pituitary glands of dead people. So doctors took the HGH out of dead people and put it into living people until some of those patients started dying from an extremely rare and fatal condition called Creutzfeldt-Jakob Disease.

(1:17) If Alzheimer's is horrible, which yeah it is, then Creutzfeldt-Jakob is whatever comes after horrible. The diseases aren't connected, though they do have a lot of the same symptoms -- loss of memory, impaired judgement, loss of muscle coordination, and dementia. But while people with Alzheimer's can live for decades, Creutzfeldt-Jakob will usually kill you in about a year. It's a prion disease, which we've talked about before.

(1:37) Prions are the mutated forms of normal proteins that exist in the brain. They have the same chemical makeup, but they've folded into a different and much more dangerous shape. Prion diseases, like Alzheimer's disease, manifest in the brain; basically eating holes in the brain tissue until it kinda looks like a sponge.

(1:52) But scientists didn't know that the pituitary gland could contain any dangerous tissue, so it seems that one of the cadavers harvested for human growth hormone was infected with Creutzfeldt-Jakob Disease and now, potentially a lot of the people who took the hormone are too.

(2:04) Now prion diseases have a real long incubation time. They can be dormant for up to 50 years so some of the people who were infected in the 60s, 70s, and 80s are only now developing symptoms and then very quickly dying.

(2:16) So far, out of the roughly 30,000 people who received hormone treatments before 1985, a few hundred -- up to about 6% depending on the country -- have developed Creutzfeldt-Jakob. That percentage is way too high to be natural. Every year there are usually only about 300 new cases of Creutzfeldt-Jakob in the United States and that's among a population of more than 300 million.

(2:34) John Collinge, author of the new report, conducted autopsies of 8 of these patients. All of them died between the ages of 36 and 51. What he and his team found was that 6 of the 8 patients not only had Creutzfeldt-Jakob Disease, but also showed signs of the premature onset of Alzheimer's. Specifically they showed signs of build-up of amyloid-beta, which is a sticky protein that forms clumps in the brain. Those clumps bond with a receptor found near your brain's synapses, the connections between your nerve cells, starting a chain reaction that eventually destroys the synapse. And you need synapses to do pretty much anything at all. Alzheimer's disease is what you get when so many clumps of amyloid-beta form in your brain that you experience widespread synaptic death.

(3:11) What's strange here is that these patients seemed to be manifesting both diseases and even though Creutzfeldt-Jakob and Alzheimer's share a lot of symptoms, they're not related to each other at all. And just like with the prions that caused Creutzfeldt-Jakob, scientists didn't think that the dangerous proteins that lead to Alzheimer's could be carried in HGH or found in the pituitary gland.

(3:29) What this means is that a lot of people who were injected with human growth hormone before 1985 will probably also develop Alzheimer's and we should probably stop putting anything that's been in or near one brain into another brain until we understand better how to detect and block the amyloid-beta protein.

(3:45) Creutzfeldt-Jakob has started showing up in people who've undergone other procedures too: like received cornea transplants, brain implants of inadequately-sterilized electrodes, and grafts of dura mater, which is like the soft tissue that covers your brain. And since in this new study, Creutzfeldt-Jakob and Alzheimer's seem to have been transmitted in the same way, through HGH, it's possible that Alzheimer's can transfer through all those other procedures too.

(4:04) We're all big fans of brains here at SciShow so we wanna make sure that we're keeping them healthy.

(4:09) Thanks for watching this episode of SciShow News and thanks especially to all of our patrons at Patreon who make this show possible. If you wanna help us keep making videos like this, you can go to Patreon.com/SciShow and don't forget to go to YouTube.com/SciShow and subscribe!

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