By now most people have heard of mad-cow disease and of the devastation it has brought to the cattle industry, especially in Europe. Scientists publishing in the online version of Nature Biotechnology report that they have created a genetically modified cow immune to the disease.

Mad-cow disease is a prion disease, which is both a fascinating and terrible class of neurological diseases. Prions are infectious proteins – a startling and controversial notion when first proposed, that a protein itself could be infectious. They are one of several brain proteins that can be made to fold in an alternate configuration. Proteins get their biochemical properties not only from their sequence of amino acids but also from the three-dimensional configuration into which they fold up. When prion proteins fold one way they function normally (they are mostly structural proteins, some of which may be involved in long term memory). When they fold a different way, however, they compromise the structure of the brain cells causing them to degenerate.

Even more curious is the fact that when one abnormally folded protein comes into contact with a normally folded protein, it can induce it to fold abnormally. This sets off a chain reaction, and is the reason prions are infectious.

Prions are responsible for a number of diseases, including Creutzfeldt-Jakob disease (CJD), kuru, and bovine spongiform encephalopathy (BSE) – mad-cow disease. CJD is essentially the human form of the disease, and is perhaps the most devastating neurological disease known. I have cared for a number of patients with this disease, which is characterized by progressive neurological deficits. Every part of the brain starts to shut down one by one, and they progress so rapidly that they are literally worse every day.

What Jürgen A Richt and his co-authors have done is to knock out the gene for the prion protein in a number of cows. They have then shown that these cows are resistant to BSE and that they develop normally. They appear to be normal cows in every way. This has two potential benefits. The first and most obvious is that this may lead to a breed of genetically modified cows for the cattle industry that are immune to mad-cow disease. The second is that it can teach us further about the function of prions, and this will help in further research.

It is not clear if what we learn, however, will apply to the human forms of the disease. For instance, cows may develop perfectly normally without the protein, but then again no one will notice if a cow loses a few IQ points or has difficulty with long-term memory. Humans are likely to notice such effects, however. Still, this is an exciting breakthrough for a terrible disease.