Fair Vote Canada Election Results

 
Here's what the result would have been with a nation-wide proportional system from Fair Vote Canada.

Conservatives - 38% of the popular vote: 117 seats (not 143)
Liberals - 26% of the popular vote: 81 seats (not 76)
NDP - 18% of the popular vote: 57 seats (not 37)
Bloc - 10% of the popular vote: 28 seats (not 50)
Greens - 7% of the popular vote: 23 seats (not 0)

I don't favor such a system. I like the Mixed Member Proportional MMP) system based on provinces.

The British Columbia referendum on the Single Transferable Vote (STV) system for provincial elections is set for May 12, 2009. 58% of voters supported the new voting system in the last referendum (2005). This was just short of the required 60%. It is very likely that the new proportional system will be adopted this time around, making British Columbia the first of many provinces to enter the 21st century.

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Nigeria Has Competition

 
I just got this email message and I thought I'd share it with the rest of you. All my money is tied up in deals with Nigerians and investments in Viagra so I can't take advantage of this fabulous offer.

I expect to be flush with cash by next week because I just won the European lottery but I'll be spending most of it to enlarge one of my vital organs.

Hello Pal,

I hope my email fine you well. I am in need of your assistance. My name is Sgt. Jarvis Reeves. I am an American soldier serving in the 1st Armored Division in Iraq, we have just been posted out of Iraq and to return in a short while. My colleague and I need your help to transfer out the sum of Twenty Five Mllion U.S Dollars ($25 MUSD). If you are interested I will furnish you with more details

As awair your response.
Email:sgt.jr@hotmail.com

Yours,
Sgt. Jarvis Reeves

God Bless America!!

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Move to Canada

 

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[Hat Tip: The Unexamined Life]

Bacteria Phylogeny: Facing Up to the Problems

There are millions of species of bacteria. Sorting out their evolutionary history has been a major challenge for decades. Unlike the much bigger, multicellular, eukaryotes, there are few morphological markers to assist scientists in classifying bacteria. The fossil record is mostly silent.

Molecular evolution came to the rescue thirty years ago when cloning and sequencing became common. Soon there were elaborate and detailed phylogenetic trees based on comparing sequences of conserved genes from many species.

The gene of choice was the one for the small subunit ribosomal RNA (SSU rRNA). This gene was well conserved in bacteria and it was easy to get sequences simply by PCR. (The ends of the SSU rRNA gene are conserved and this means that you can develop universe primers for PCR.)

Over the years, the SSU rRNA gene has become what is called the "gold standard" in bacterial phylogeny and taxonomy. Many species have been assigned to taxa based entirely on the sequence of their SSU rRNA gene. Unfortunately, the "gold standard" has become somewhat tarnished lately.

Our fellow blogger, Jonathan Eisen of The Tree of Life, has recently published a paper that looks at the problems with bacterial phylogeny (Wu and Eisen, 2008). He posted a brief summary of the paper and commented on why he likes the journal Genome Biology [Happy Open Access Day: Back to Genome Biology for Me].

There is much to like about this paper. The authors face up to the problems with the current bacterial phylogeny, which is based almost entirely on a single gene (SSU rRNA). They point out that this is risky given what we know about molecular phylogenies. Furthermore, in the case of the SSU ribosomal RNA gene we know for a fact that this has led to problems and inconsistencies. In addition to the practical difficulties there are good theoretical reasons for being suspicious of phylogenies constructed from nucleotide sequences.

What to do? One possible solution is to abandon SSU rRNA as a "gold standard" and replace it with a highly conserved protein coding gene. Unfortunately, this doesn't get around the problem of relying on a single gene. The way around this is to use an artificial concatenated sequence made up of several different conserved genes laid out end-to-end in one large string of amino acids.

So why isn't this done? Because, as Wu and Eisen point out, it ain't that easy. The main difficulty in any phylogenetic study is getting a proper alignment. This is a problem that many workers simply ignore when they use automated alignment software like CLUSTALW. These workers assume that the alignments are valid.

They aren't, and this is another example of facing up to the problem. Many scientists agonize over what program to use when constructing their trees—should they use maximum likelihood, parsimony, etc. etc.? In most cases these decisions are a complete waste of time because their alignments aren't good enough to make a difference.

Here's how Wu and Eisen explain it ...

It has been shown that alignment quality can have greater impact on the final tree than does the tree-building method employed [20]. Therefore, preparing high quality sequence alignments is a most critical part of any molecular phylogenetic analysis. This preparation typically involves careful but tedious manual editing and trimming of the generated alignments, and thus remains the biggest challenge to automation. When scaling up this process, the trimming step is often simply ignored. Automated trimming based on the number of gaps in each column or each column's conservation score can be used to select conserved blocks, but still is not satisfactory when a high quality tree is required.

Keep in mind that what is being proposed is a large tree based on concatenated sequences from many genes. You don't want to do multiple sequence alignments for every gene by hand, and yet up until now, that was the only way to get accurate results.

Wu and Eisen have written a program called AMPHORA that hopefully solves this problem. They begin by manually creating "seed alignments" that are manually curated. Then they use AMPHORA to align all the other sequences to the seed alignments. In this way they hope to overcome the limitations of automated multisequence alignment without having to align everything by hand.

None of this would be possible, of course, unless there were large numbers of species where every one of the target genes have been cloned and sequenced. In the 20th century this would have been impossible but now there are hundreds of completely sequenced bacterial genomes. This means that each one of them has a sequenced copy of the genes required for this kind of analysis.

All that's left is to identify the completely sequenced genomes and pick the set of genes. There are 578 genomes in the database but many of these are close relatives that will not be useful in constructing a large tree of all bacterial sequences. The final set contains 310 genomes with representatives of all the major groups.

The authors selected 31 genes for their initial proof of principle paper (dnaG, frr, infC, nusA, pgk, pyrG, rplA, rplB, rplC, rplD, rplE, rplF, rplK, rplL, rplM, rplN, rplP, rplS, rplT, rpmA, rpoB, rpsB, rpsC, rpsE, rpsI, rpsJ, rpsK, rpsM, rpsS, smpB, tsf). Those of you who recognize these genes will see that 21 of them are small ribosomal proteins. This was not the best choice, in my opinion, but the authors of the paper note that they are continuing the study by incorporating better genes such as HSP70 (dnaL) and EF-Tu (tufA). You can't just choose any conserved gene because it has to be present in most species and there are surprisingly few genes that meet that criterion.

After all that, what's the bottom line? The grand phylogeny is shown at the top of this posting. It resolves many groups that are unresolvable using the SSU rRNA tree. In some cases this tree reveals species that have been incorrectly assigned to higher taxa. These species will have to be reclassified if this result holds up.

The most important finding is that the method works and it yields trees with excellent resolution of the major bacterial taxa.

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Wu, Martin, Eisen, Jonathan (2008). A simple, fast, and accurate method of phylogenomic inference Genome Biology, 9:R151 [Genome Biology] [doi:10.1186/gb-2008-9-10-r151]

Gene Genie #38

 
The 38th edition of Gene Genie has been posted at ScienceRoll [Gene Genie: Back in Action!].

Gene Genie is the blog carnival of clinical genetics and personalized medicine. Enjoy the numerous posts and articles focusing on these interesting fields of medicine. We dedicate this carnival edition to genetic testing, SNP watch and DNA.

The beautiful logo was created by Ricardo at My Biotech Life.

The purpose of this carnival is to highlight the genetics of one particular species, Homo sapiens.

Here are all the previous editions .....

1. Scienceroll
2. Sciencesque
3. Genetics and Health
4. Sandwalk
5. Neurophilosophy
6. Scienceroll
7. Gene Sherpa
8. Eye on DNA
9. DNA Direct Talk
10. Genomicron
11. Med Journal Watch
12. My Biotech Life
13. The Genetic Genealogist
14. MicrobiologyBytes
15. Cancer Genetics
16. Neurophilosophy
17. The Gene Sherpa
18. Eye on DNA
19. Scienceroll
20. Bitesize Bio
21. BabyLab
22. Sandwalk
23. Scienceroll
24. biomarker-driven mental health 2.0
25. The Gene Sherpa
26. Sciencebase
27. DNA Direct Talk
28. Greg Laden’s Blog
29. My Biotech Life
30. Gene Expression
31. Adaptive Complexity
32. Highlight Health
33. Neurophilosophy
34. ScienceRoll
35. Microbiology Bytes
36. Human Genetic Disordrs
37. The Genetic Genealogist
38. ScienceRoll

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Have Fun on Voting Day

 
Here's a video to keep you happy as you hold your nose and go to the polls (in Canada). There's a metaphor in it somewhere but I can't for the life of me figure it out. Maybe it has something to do with where my vote is going?

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[Hat Tip: psa at Canadian Cynic. Jennifer Smith at Runesmith's Canadian Content had the same idea I had about linking the video to voting day.]

PZ Myers in Toronto

 
Email me if you would like to meet PZ before his talk on Friday afternoon.

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Strategic Voting

 
Damn.

The Canadian election is tomorrow and I had almost made up my mind to vote for the Liberal candidate in my riding. He's a man I can respect and he will be a much better member of parliament than the Conservative candidate.

Up until last week I was considering a vote for the New Democratic Party because their policies are close to my personal position. Also, I wanted to send a message to Stéphane Dion, who I don't think is up to the job as leader of the Liberal party. I realized that my vote might result in the election of the Conservative candidate in my riding since the race between the Conservative challenger and Liberal incumbent is very close. That risk was worth it, in my opinion, because Stéphane Dion needed to lose in order to resign from the leadership.

The latest poll results indicate that the Conservatives might win a majority and I don't want that to happen. So I decided to vote Liberal, hoping that the events of the election campaign would be enough for Stéphane Dion. When he loses tomorrow he will resign.

At least that's what I thought until I read this morning's newspapers [The Canadian Press].

"I will never quit. I will stay for my country," the Liberal leader said Sunday during a last swing through southeastern Ontario before flying off on a frenetic coast-to-coast tour seeking the NDP and Green votes he desperately needs.

"But I'm working hard now. We're working all of us for a victory, for a progressive government. This is what is at stake."

When pressed on how he would respond if Liberal rivals push to oust him, a chippy Dion raised his voice.

"I'm the leader! I am the leader. And I'm working to win. I'm not a quitter."

...

Dion's strident tone may raise eyebrows in Liberal circles where private reaction to his campaign performance has typically ranged from tepid praise to hand wringing. Dion, a political scientist and former professor of public administration, has a reputation for tenacity and a mile-wide stubborn streak.

He is set to face a Liberal party leadership review next spring.

That's it for me. I'm voting NDP and I'm going to tell my Liberal candidate exactly why I'm doing it. If the only way to save the Liberal party is for Dion to quit ASAP and if the only way that will happen is if he's kicked out, then it looks like the Liberals are going to have to lose a lot of seats before they get the message.

I'll suffer the short term pain for the long term gain.

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Monday's Molecule #92

 
Today's molecule is a cartoon drawing of an image that depicts something very important. Your task is to explain what the image shows. Then you have to explain why this is important when it comes to describing the function of something called a "balancer."

It's a short step from there to this weeks Nobel Laureates. They used balancers in their work.

You need to describe what you see in the cartoon as accurately as possible and name the species. Then identify the Nobel Laureates, taking care to name only those ones who might have used balancers in their prize winnning work.

The first one to correctly identify the molecule and name the Nobel Laureate(s), wins a free lunch at the Faculty Club. Previous winners are ineligible for one month from the time they first collected the prize. There are three ineligible candidates for this week's reward. You know who you are.

THEME:

Nobel Laureates
Send your guess to Sandwalk (sandwalk (at) bioinfo.med.utoronto.ca) and I'll pick the first email message that correctly identifies the molecule and names the Nobel Laureate(s). Note that I'm not going to repeat Nobel Laureate(s) so you might want to check the list of previous Sandwalk postings by clicking on the link in the theme box.

Correct responses will be posted tomorrow. I reserve the right to select multiple winners if several people get it right.

Comments will be blocked for 24 hours. Comments are now open.

UPDATE: This weeks winner is Bill Chaney from Nebraska. He recognized that the "molecule" depicted a chromosomal inversion in a Drosophila chromosome. Such inversions are a characteristic of balancer chromosomes. Balancers are used in maintaining fly stocks, especially ones carrying homozygous lethal mutations.

The Nobel Laureates must be Christiane Nüsslein-Volhard and Eric Wieschaus

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Are Science and Religion Compatible?

 
I've been somewhat remiss in posting for a few days as I've been catching up on some reading and discussing science and religion with my friends.

The question that interests me is whether basic religious tenets are compatible with science, where "science" is defined as a way of knowing—a way that combines evidence and rational thinking to come up with "truths" about the universe we inhabit.

It seems obvious to me that there are some forms of deism that do not conflict with science. Is that it?¹ Are there any other versions of religion that maintain an appropriate distance from science?

I'd like to hear from people who are religious but not deists. Can they give me some example of their religious claims that do not in any way conflict with science? I'm thinking specifically of those religions that promote belief in a personal God.

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1. Buddhism may count if it's the form of Buddhism that doesn't believe in supernatural beings. I don't call that a religion.

Activist Scientists

 
We seem to have forgotten that scientists can be social activists. In my time it was common for scientist to take an active role in social causes. It was the time of "Science for the People" and similar organizations. Very little remains of that kind of activism, David Suzuki is just about the only one of those scientists who is still trying to change the world. Some of them have become administrators and advisers to Presidents.

Given the antagonism that greets modern scientists who step out of line (i.e., Richard Dawkins) I can understand why social activism is out of favor.

I was reminded that in the early part of the last century, there were scientists who took up social causes. I happened to stumble on the website of my colleague, Donald Forsdyke of Queen's University [Haldane's Rule]. Here's one of the photographs from that site.

JBS Haldane addressing a 'United Front' meeting in January 1937. Photograph from the Sun newspaper reproduced in Ronald Clark's 1968 biography of Haldane, published by Hodder & Stoughton.

It's hard to picture any of today's most prominent scientist in such a scene. Perhaps the "United Front" movement¹ is too liberal for the average scienist?

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1. It was a socialist movement with strong ties to Marxism as a philosophy and communism as an economic and political strategy

Why Do We Call them IDiots? (Part CCCLXVII)

 
Rebecca of Skepchick writes about a YouTube fight involving a creationist.

You know what’s hilarious? Seeing a jerk get schooled. You know what’s even funnier? When the jerk happens to be a creationist who has spent a lot of time and effort filling YouTube with the same old oft-debunked creationist garbage we see all the time, and who then illegally attempts to silence his rational critics.

I’ve been following the fight between creationist VenomFangX and pure awesomeness Thunderf00t for quite some time. For an overview, watch some of Thunderf00t’s excellent series, “Why Do People Laugh at Creationists?” VFX shows up a LOT. This upset him quite a bit.

Basically, VFX filed DMCA takedown notices on Thunderf00t’s videos, despite the fact that VFX knew those notices were false and malicious. This is illegal, and Thunderf00t obtained clear proof of the action. He could have sued the living pants off VFX and had him banned permanently from YouTube, but instead, he did this:

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Epigenetics, Again

 
The National Institutes of Health (NIH) have launched a $190 million research effort to learn about epigenetics. According to Nature News ...
It’s not that epigenetics is totally useless. I just don’t see why it’s worth 190 million dollars.

Kevin Struhl
Harvard Medical School

Epigenetics, described as "inheritance, but not as we know it"1, is now a blisteringly hot field. It is concerned with changes in gene expression that are typically inherited, but not caused by changes in gene sequence. In theory, epigenetic studies can help explain how the millions of cells in the human body can carry identical DNA but form completely different cell types, and perhaps why certain cells are susceptible to disease.

The NIH's epigenomics initiative is a plan for such studies on a grand scale including, for example, surveys in different human cell types of all the chemical tags, or epigenetic marks, that might control genes.

It seems strange to be spending so much research money on something that scientists can't even define properly [Epigenetics in New Scientist, Epigenetics Revisited, Epigenetics]. Perhaps some of this money will go toward coming up with a reasonable definition of what they're studying.

As far as I know we already have a good model for how totipotent cells can differentiate into many different cell types. We also understand how they can revert to pleuripotent cells. We even know that differentiated cells can be transformed back into stem cells by adding certain transcription factors.

Now we add in the fact that some DNA binding proteins can covalently modify DNA and this affects gene expression. What's the big deal?

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Humanism Is "Liberal"

 
I'm not a humanist and now I know why. Not only is it immoral and atheist but it's also (gasp!) LIBERAL! Now I know why the Christians are so frightened.

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[Hat Tip: Friendly Atheists]

P.S. I don't make fun of spelling errors because people in glass houses ....

P.P.S. As strange as it may seem to our neighbors to the south, in Canada we not only have a Liberal Party but people actually vote for it!

Nobel Laureate: Stanley Prusiner

 

The Nobel Prize in Physiology or Medicine 1997.

"for his discovery of Prions - a new biological principle of infection"

Stanley B. Prusiner (1942 - ) received the Nobel Prize in Physiology or Medicine for demonstrating that the prion protein was responsible for Creutzfeldt-Jakob disease (CJD) in humans and for scrapie in sheep. The significance of this work was that Prusiner rigorously eliminated any trace of RNA and DNA from the preparation of infectious disease particles. He showed for the first time that a protein cold be an infectious agent.

This was a major advance in our understanding of basic biological processes. It led to the discovery that a single protein could adopt two very different folds and one of them could induce folding changes in its neighbors in a catalytic manner. The discovery helps us understand protein folding and chaperones.

THEME:
Nobel LaureatesThe press release from the Nobel Prize website does a good job of describing Pusiner's contribution.

6 October 1997

The Nobel Assembly at the Karolinska Institute has today decided to award the Nobel Prize in Physiology or Medicine for 1997 to

Stanley B. Prusiner

for his discovery of "Prions - a new biological principle of infection".

Summary

The 1997 Nobel Prize in Physiology or Medicine is awarded to the American Stanley Prusiner for his pioneering discovery of an entirely new genre of disease-causing agents and the elucidation of the underlying priciples of their mode of action. Stanley Prusiner has added prions to the list of well known infectious agents including bacteria, viruses, fungi and parasites. Prions exist normally as innocuous cellular proteins, however, prions possess an innate capacity to convert their structures into highly stabile conformations that ultimately result in the formation of harmful particles, the causative agents of several deadly brain diseases of the dementia type in humans and animals. Prion diseases may be inherited, laterally transmitted, or occur spontaneously. Regions within diseased brains have a characteristic porous and spongy appearance, evidence of extensive nerve cell death, and affected individuals exhibit neurological symptoms including impaired muscle control, loss of mental acuity, memory loss and insomnia. Stanley Prusiner's discovery provides important insights that may furnish the basis to understand the biological mechanisms underlying other types of dementia-related diseases, for example Alzheimer's disease, and establishes a foundation for drug development and new types of medical treatment strategies.

The prize winning research was initiated 25 years ago

In 1972 Stanley Prusiner began his work after one of his patients died of dementia resulting from Creutzfeldt-Jakob disease (CJD). It had previously been shown that CJD, kuru, and scrapie, a similar disease affecting sheep, could be transmitted through extracts of diseased brains. There were many theories regarding the nature of the infectious agent, including one that postulated that the infectious agent lacked nucleic acid, a sensational hypothesis since at the time all known infectious agents contained the hereditary material DNA or RNA. Prusiner took up the challenge to precisely identify the infectious agent and ten years later in 1982 he and his colleagues successfully produced a preparation derived from diseased hamster brains that contained a single infectious agent. All experimental evidence indicated that the infectious agent was comprised of a single protein, and Prusiner named this protein a prion, an acronym derived from "proteinaceous infectious particle." It should be noted that the scientific community greeted this discovery with great skepticism, however, an unwavering Prusiner continued the arduous task to define the precise nature of this novel infectious agent.

The infectious prion particle forms within the body

Where was the gene encoding the prion, the piece of DNA that determined the sequence of the amino acids comprising the prion protein? Perhaps the gene was closely associated with the protein itself as in a small virus? The answers to these questions came in 1984 when Prusiner and colleagues isolated a gene probe and subsequently showed that the prion gene was found in all animals tested, including man. This startling finding raised even more questions. Could prions really be the causative agent of several dementia-type brain diseases when the gene was endogenous to all mammals? Prusiner must have made a mistake! The solution to this problem became evident with the sensational discovery that the prion protein, designated PrP, could fold into two distinct conformations, one that resulted in disease (scrapie PrP = PrPSc) and the other normal (PrP = PrPc). It was subsequently shown that the disease-causing prion protein had infectious properties and could initiate a chain reaction so that normal PrPc protein is converted into the more stabile PrPSc form. The PrPSc prion protein is extremely stabile and is resistant to proteolysis, organic solvents and high temperatures (even greater than 100o C). With time, non-symptomatic incubation periods vary from months to years, the disease-causing PrPSc can accumulate to levels that result in brain tissue damage. In analogy to a well known literary work, the normal PrPc can be compared to the friendly Dr. Jekyll and the disease causing PrPSc to the dangerous Mr. Hyde, the same entity but in two different manifestations.

Mutations in the prion gene cause hereditary brain diseases

The long incubation time for prion based disease hampered the initial efforts to purify the prion protein. In order to assess purification schemes Prusiner was forced to use scores of mice and in each experiment wait patiently for approximately 200 days for the appearance of disease symptoms. The purification efforts accelerated when it was demonstrated that scrapie could be transferred to hamsters, animals that exhibited markedly shortened incubation times. Together with other scientists, Prusiner cloned the prion gene and demonstrated that the normal prion protein was an ordinary component of white blood cells (lymphocytes) and was found in many other tissues as well. Normal prion proteins are particularly abundant on the surface of nerve cells in the brain. Prusiner found that the hereditary forms of prion diseases, CJD and GSS (see the last section), were due to mutations in the prion gene. Proof that these mutations caused disease was obtained when the mutant genes were introduced into the germline of mice. These transgenic mice came down with a scrapie-like disease. In 1992 prion researchers obtained conclusive evidence for the role of the prion protein in the pathogenesis of brain disease when they managed to abolish the gene encoding the prion protein in mice, creating so called prion knock-out mice. These prion knock-out mice were found to be completely resistant to infection when exposed to disease-causing prion protein preparations. Importantly, when the prion gene was reintroduced into these knock-out mice, they once again became susceptible to infection. Strangely enough, mice lacking the prion gene are apparently healthy, suggesting that the normal prion protein is not an essential protein in mice, its role in the nervous system remains a mystery.
Structural variant disease-causing prions accumulate in different regions of the brain

Specific mutations within the prion gene give rise to structurally variant disease-causing prion proteins. These structural prion variants accumulate in different regions of the brain. Dependent upon the region of the brain that becomes infected, different symptoms, typical for the particular type of disease are evident. When the cerebellum is infected the ability to coordinate body movements declines. Memory and mental acuity are affected if the cerebral cortex is infected. Thalamus specific prions disturb sleep leading to insomnia, and prions infecting the brain stem primarily affect body movement.

Other dementias may have a similar background

Prusiner's pioneering work has opened new avenues for understanding the pathogenesis of more common dementia-type illnesses. For example, there are indications that Alzheimer's disease is caused when certain, non-prion, proteins undergo a conformational change that leads to the formation of harmful deposits or plaques in the brain. Prusiner's work has also established a theoretical basis for the treatment of prion diseases. It may be possible to develop pharmacological agents that prevent the conversion of harmless normal prion proteins to the disease-causing prion conformation.

Intrinsic defense mechanisms do not exist against prions

Prions are much smaller than viruses. The immune response does not react to prions since they are present as natural proteins from birth. They are not poisonous, but rather become deleterious only by converting into a structure that enables disease causing prion proteins to interact with one another forming thread-like structures and aggregates that ultimately destroy nerve cells. The mechanistic basis underlying prion protein aggregation and their cummulative destructive mechanism is still not well understood. In contrast to other infectious agents, prion particles are proteins and lack nucleic acid. The ability to transmit a prion infection from one species to another varies considerably and is dependent upon what is known as a species barrier. This barrier reflects how structurally related the prions of different species are.

Prion diseases in animals and man

Without exception, all known prion diseases lead to the death of those affected. There are, however, great variations in pre-symptomatic incubation times and how aggressively the disease progresses.

Scrapie, a prion disease of sheep, was first documented in Iceland during the 18th century. Scrapie was transferred to Scotland in the 1940s. Similar prion diseases are known to affect other animals, e.g., mink, cats, deer and moose.

Bovine Spongiform Encephalopathy (BSE) - Mad cow disease is a prion disease that has recently received a great deal of publicity. In England BSE was transmitted to cows through feedstuff supplemented with offals from scrapie-infected sheep. The BSE epidemic first became evident in 1985. Due to the long incubation time the epidemic did not peak until 1992. In this year alone roughly 37,000 animals were affected.

Kuru among the Fore-people in New Guinea was studied by Carleton Gajdusek (recipient of the 1976 Nobel Prize in Physiology or Medicine). Kuru was shown to be transmitted in connection with certain cannibalistic rituals and was thought to be due to an unidentified "slow virus". The infectious agent has now been identified as a prion. Duration of illness from first symptoms to death: 3 to 12 months.

Gertsmann-Sträussler-Scheinker (GSS) disease is a hereditary dementia resulting from a mutation in the gene encoding the human prion protein. Approximately 50 families with GSS mutations have been identified. Duration of illness from evidence of first symptoms to death: 2 to 6 years.

Fatal Familial Insomnia (FFI) is due to another mutation in the gene encoding the human prion protein. Nine families have been found that carry the FFI mutation. Duration of illness from evidence of first symptoms to death: roughly one year.

Creutzfeldt-Jakob Disease (CJD) affects about one in a million people. In 85-90% of the cases it has been shown that CJD occurs spontaneously. Ten to fifteen per cent of the CJD cases are caused by mutations in the prion protein gene. In rare instances CJD is the consequence of infection. Previously infections were transmitted through growth hormone preparations prepared from the pituitary gland of infected individuals, or brain membrane transplants. About 100 families are known carriers of CJD mutations. Duration of illness from evidence of first symptoms to death: roughly one year.

A new variant of CJD that may have arisen through BSE-transmission. Since 1995 about 20 patients have been identified that exhibit CJD-like symptoms. Psychological symptoms with depression have dominated, but involuntary muscle contractions and difficulties to walk are also common.

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[Photo Credits top: David Powers University of California, San Francisco, bottom: Prionii si bolile prionice]