The Terrifying Biology of Prion Diseases: Robert Sapolsky on Creutzfeldt-Jakob Disease

Creutzfeldt-Jakob disease belongs to one of the strangest and most frightening categories of illness in medicine: prion diseases. These disorders are rare, fatal, and biologically unlike almost anything else that infects the human brain.

Robert Sapolsky describes them as nightmare diseases—not only because of their devastating symptoms, but because of the bizarre mechanism behind them. They are part of a family known as spongiform encephalopathies, a term that refers to the sponge-like appearance of the brain after the disease has progressed.

In many neurological diseases, damage is selective. One region suffers while another remains relatively intact. Certain neurons die while neighboring glial cells survive. But in Creutzfeldt-Jakob disease and related prion disorders, the destruction is far less specific. The brain can appear as though a bomb has gone off inside it. Neurons, glial cells, and even blood vessel structures are damaged. Under the microscope, the tissue becomes riddled with holes. In extreme cases, there is cavitation—empty spaces where brain tissue has collapsed.

The result is catastrophic neurological decline. Once symptoms begin, the disease usually progresses rapidly, often leading to death within months. There is currently no cure and no effective treatment capable of stopping the process.

Prion diseases include Creutzfeldt-Jakob disease, fatal familial insomnia, scrapie in sheep and goats, bovine spongiform encephalopathy—better known as mad cow disease—and kuru, a disease once found among the Fore people of the New Guinea highlands.

Kuru played a crucial role in revealing the mystery of prion disease. It was studied by Carleton Gajdusek, who showed that the condition was transmissible. The route of transmission was deeply unusual: ritual endocannibalism, in which relatives consumed the remains of deceased family members as an act of respect. The infectious material was especially dangerous when raw brain tissue was handled during preparation.

What shocked scientists was the incubation period. Unlike ordinary viral infections, which produce symptoms within days or weeks, kuru could remain silent for years or even decades. Some cases appeared more than 50 years after exposure. This led to the concept of “slow” infectious diseases.

But the story became even stranger with the work of Stanley Prusiner, who studied scrapie and eventually identified the infectious agent. Scientists expected to find a virus containing DNA or RNA. Instead, Prusiner found something almost unthinkable: the infectious agent appeared to be made only of protein.

No DNA. No RNA. Just protein.

This was a radical challenge to biology’s central dogma. Viruses replicate by using genetic material. Prions do something different. They are misfolded proteins that force normal versions of the same protein to adopt the abnormal shape.

Sapolsky compares this to Ice-nine from Kurt Vonnegut’s Cat’s Cradle: one abnormal molecule touches a normal one and converts it; then two convert more; then the process accelerates exponentially. In prion disease, one misfolded protein can eventually seed a growing aggregate of abnormal proteins inside the brain.

The strange part is that the normal and abnormal prion proteins may have the same amino acid sequence. The difference is not necessarily in the genetic code, but in the protein’s shape. The same protein can fold into a harmless form—or into a deadly infectious conformation.

That insight changed biology.

It also helps explain why prion diseases are so hard to control. Prions are extraordinarily resistant to ordinary sterilization methods. Heat, radiation, and standard disinfectants may not reliably destroy them. This has led to rare cases of iatrogenic transmission—disease accidentally spread through medical procedures, contaminated surgical instruments, transplanted tissues, or, historically, cadaver-derived growth hormone preparations.

Most cases of Creutzfeldt-Jakob disease, however, are not inherited from parents. Inherited forms do exist, but they are extremely rare. A mutation in the prion protein gene can make the abnormal folding more likely, and in those rare families the disease can be passed to offspring. But for the overwhelming majority of cases, Creutzfeldt-Jakob disease is sporadic or acquired through rare exposure.

Mad cow disease raised global alarm because it showed that prion diseases could cross species barriers. When bovine spongiform encephalopathy emerged in cattle, it eventually led to variant Creutzfeldt-Jakob disease in humans exposed through contaminated beef products. The feared global catastrophe did not occur, but the episode revealed how dangerous prion contamination in the food supply could be.

Other cultural dietary practices involving consumption of sheep or goat brain tissue have also been linked to clusters of prion disease, because cooking does not necessarily eliminate infectivity.

Despite how horrifying these diseases are, they remain extremely rare. That rarity is one reason they are difficult to study and why progress toward treatment has been slow. By the time symptoms appear, the disease is usually already advanced. The abnormal protein cascade has spread widely, and the brain has suffered irreversible damage.

Still, prion diseases have taught medicine something profound: infection does not always require genes. A protein’s shape alone can carry biological information, spread through tissue, and transform the structure of other proteins.

Creutzfeldt-Jakob disease remains one of the most devastating diagnoses in neurology. But scientifically, it also stands as one of the most astonishing discoveries in medical history—a disease that forced biology to rethink what an infectious agent can be.

Reference: 

Creutzfeldt-Jakob and other prion diseases by Robert Sapolsky 
https://www.youtube.com/watch?v=tZeVafsBrKQ 

© 2000-2030 Sieglinde W. Alexander. All writings by Sieglinde W. Alexander have a five-year copyright. Library of Congress Card Number: LCN 00-192742 ISBN: 0-9703195-0-9