Dear Science,

If humans ate a diet consisting of other humans, could a mad-cow-like disease develop?

Hungry

Yes. In fact, it happened. Charlton Heston wasn't involved. The Fore tribes from Papua New Guinea, as a part of the grieving process, ate their dead relations. A bizarre disease spread in the population, taking as long as 50 years to appear. The illness starts with tremors, stumbling, and an inability to stand up straight. With time the afflicted lose the ability to walk, their muscles moving on their own accord. Eventually, one passes away under the thick cloud of dementia.

Kuru (the name means "shivering" in the tribal language) is in a family of diseases—including the genetic fatal familial insomnia and Gerstmann-Straussler-Scheinker syndrome, as well as Creutzfeldt-Jakob disease (CJD)—caused by misfolded proteins, called prions.

All proteins start as a long chain of amino acids, eventually folding into complex three-dimensional structures capable of doing work. When most proteins fold the wrong way, they are promptly torn apart by the cell, and a new copy is made. Rarely, a misfolded protein evades being destroyed and can make copies of itself by converting properly folded proteins into this new, wrong shape. How, exactly? Figure that out—and not by citing a Kurt Vonnegut novel—and you'll probably earn a Nobel Prize.

Each of these diseases is caused by improperly folded protein accumulating like tar in the brain, killing off ever-increasing numbers of neurons. Eating prions—the nervous systems of creatures with the disease are filled with them—can teach your proteins how to misfold, spreading the disease. Cooking doesn't help—the prions stick around even when other proteins are denatured. On the positive side, the misfolded prion proteins are almost exclusively found in nervous-system tissue. Blood transfusions, for example, seem to be safer.

Sounds crazy, right? The notion of self-replicating proteins—exactly the same amino acid sequence as normal proteins, capable of converting these normal proteins to their shape and replicating themselves completely independent of RNA or DNA—is a startling wrinkle to the central dogma of biology where DNA is transcribed into RNA, which in turn is translated into a single kind of protein. It took a series of clever experiments before prions became widely accepted as yet another cause of misery and disease in the world: blasting away the DNA and RNA from plaques from a sick animal to show that the disease can still be spread with only the remaining protein; digesting the protein from the plaque to show how destroying the prion prevents the spread; isolating the specific protein behind these diseases and engineering mice to misfold the protein to show that adding prions causes the disease.

So, yes there is mad human disease. Don't eat any Soylent Green meals, please.

Cannibalistically Yours, Science

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