Truth Will Out explores the origins of CJD with a panel of specialists in this series of articles, originally published in July 2001

IS VCJD caused by BSE?
The only way to prove that variant CJD is caused by BSE is to inject infected material from a cow into a human and sit back and wait to see whether, in ten, twenty or even forty years time, that person develops vCJD. Curiously, there is a conspicuous shortage of volunteers for this crucial experiment. But without it, there is still no direct proof that vCJD is caused by BSE.

What causes BSE? Metals, organophosphates, tiny viruses called virions have all at one time been implicated. But the front runner is rogue prions.

Prions are elaborately folded proteins found in all species of animals - each species has their own sort. Researchers speculate that the job of normal prions might be that of an anti-oxidant in the brain. What an abnormal prion does is try and recruit all the normal prions it meets to the dark side, making them flip in shape to become like it. There is then a cascade effect with abnormal prions collecting in the brain and causing the symptoms that are now so familiar. Prion diseases include kuru, CJD and scrapie.

Stanley Prusiner, a Californian professor, won a Nobel Prize in 1997 for his prion hypothesis. At first his work was greeted with scepticism. After all, an infectious agent that contained no information in the form of DNA or RNA was hard to credit.

Personally I have no doubt that prions are the mechanism of these diseases. First, mice genetically engineered to have too much normal prion, develop a non-infectious type of brain disease. And if you subject infected tissue from a cow to extreme temperatures and pressures, of the sort that would crucify any self respecting virus or bacteria, it will still cause infection in a recipient animal. So that's it then. Prions and nothing else. Sorry, I don't buy it.

Levels of metals in the brain for instance are known to be important. There is a high incidence of CJD amongst South American manganese miners for instance. And your genetic make up may be the deciding factor in determining how early your symptoms will appear.

But here's the bit that foxes me. If you have a mouse, genetically engineered to have no prions, they don't catch any disease when injected with infected tissue. Fine. That's what you would expect. But take tissue from these non diseased animals and guess what, they can cause infection in normal mice, even though they have no prions. OK Professor Prusiner, get out of that one.

The latest theory, released after the programme was recorded, by the European Molecular Biology Laboratory in Germany is that there IS some other infectious agent. And it's a parasitic gene called an Alu. It interferes with the way proteins are produced, and eating meat from an infected animal may be enough to tip the balance and start a runaway acceleration of proteins - causing the symptoms of vCJD.

It's an interesting theory - and it could be right. Personally I believe that we are a long way from understanding the causes of BSE and until we know that, vCJD will remain an enigmatic mystery.

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