Home » Science & Nature » Molecular Biology/Medicine » MAD COW DISEASE - Page 2

MAD COW DISEASE - Page 2

© Juan C. Mendible

The two other human diseases, which are usually inherited and in general appear in midlife, are Gerstmann-Sträussler-Scheinker Syndrome, which also curses with ataxia, dementia and damage to the cerebellum, and insomnio fatal, which starts with difficulty sleeping and is followed by dementia.

The initial advances in spongiform diseases started in 1972 when Stanley Prussiner from the University of California at San Francisco realized that scrapie, CJ disease and Kuru had all been shown to be transmissible by injecting extracts of brains of animals that had died of these diseases into the brains of healthy animals. It was thought that a slow-acting virus caused the infections, yet no one had managed to isolate it.

Prussiner was also impressed by a report by the late Tikvah Alper and her colleagues at the Hammersmith Hospital in London, who took extracts of scrapie-infected brains, destroyed all of the nucleic acids, DNA and RNA, and noticed that the extracts still retained ability to transmit the disease, suggesting that the scrapie agent might lack nucleic acid. This finding meant it was not a virus or any other known type of infectious agent, all of which contain genetic material So, what was the cause of the disease?

The answer came about 40 years later when Prussiner proposed that the agent was a protein. You can imagine the resistance Prussiner and his colleagues met, since this was against the belief that all pathogenic inheritable entities required some sort of genetic material, either DNA or RNA, in order to establish an infection in a host.

Prussiner was proved to be right when he managed to isolate a protein from the brains of mice that had died of the disease, injected it into the brains of healthy ones and--viola!!! The injected animals got the disease and died, which strongly suggested that this protein was the pathogenic agent. He called it prion (pronounced "pree-ons"), which stands for "proteinaceous infectious particles."

Later on, his and other laboratories cloned the gene of the protein, now called PrP (for prion protein), which allowed them to study the structure of its 250 amino acids chain.

With the gene isolated, several groups demonstrated that most animals make the Prp protein without getting sick. This told them that Prp was produced in two forms: a disease causing mutant and the normal one. Soon, they found that the difference between them was a single amino acid change. The mutant one has the amino acid proline instead of leucine at position 34 on the chain.

The copyright of the article MAD COW DISEASE - Page 2 in Molecular Biology/Medicine is owned by . Permission to republish MAD COW DISEASE - Page 2 in print or online must be granted by the author in writing.