| science/technology news |
[Jan. 30th, 2004|08:47 am] |
Medical X-rays cause thousands of cancers
Medical X-rays are to blame for many thousands of fatal cancers every year, according to the most comprehensive analysis to date. Medical experts stress that X-rays and CT scans can be very beneficial, but believe the new work shows that they should be used as sparingly as possible.
They are of enormous benefit for such things as early cancer detection, but medical experts need to be aware of the quantifiable risks of X-rays." says Amy Berrington, of Oxford University, UK, and one of the research team. "If you need an X-ray for medical reasons then I should not worry about it."
But Peter Herzog, of Ludwig-Maximilians University in Munich, Germany, points out that many X-rays may be unnecessary. In some countries, up to a third of chest X-rays may not be required, he says. "In everyday practice, those ordering radiological procedures should think carefully about the benefits and risks to their patients for each examination."
The Oxford team first estimated the radiation dose received by patients for each X-ray. They then collated the numbers of X-rays performed each year in 15 developed nations.
This data was then fed into a computer model for estimating the risks posed by ionising radiation. This "Excess Relative Risk Model" is derived from data gleaned from Japanese atomic bomb survivors.
The authors found substantial world-wide variations in the numbers of cancers attributable to X-rays. The UK had the lowest, with 0.6 per cent of all cancers attributable to medical X-rays. About 0.9 per cent of all cancers in the US are caused by X-rays.
But in Japan, the corresponding figure was 3.2 per cent. Overall, Berrington and Darby estimate that X-ray-based medical imaging causes an extra 18,500 cases of cancer each year across the 15 countries studied.
Herzog cautions that the increased risk of cancer could have been over-estimated by the study, because of its reliance on the data from Japanese atomic bomb survivors. It is the most accurate data available, but the survivors were exposed to many types of radiation, not just X-rays alone.
Internet engineers planning assault on spam
The regulations should make it possible to verify whether the address an email appears to have been sent from is genuine. This is to prevent spammers using faked addresses, which pretend to come from domains such as hotmail.com. This trick can help the messages dodge spam filters and makes email users more likely to open them.
One of the key problems is that the current standard governing the sending and receiving of email, the Simple Mail Transfer Protocol (SMTP), includes no safeguards to prevent people forging email address.
Unfortunately it's an arms race that will go on until the SMTP protocol is rewritten," Linford says. He thinks this may become a necessity once spam has accounts for 90 per cent of all email. At the current rate of growth this would happen by February 2005.
New form of matter created in lab
A long-sought new form of matter has been created for the first time. The matter, called a fermionic condensate, consists of atoms that are ordinarily forbidden to exist in the same quantum state but have been tricked into it by linking into pairs.
It occupies the middle ground between loosely linked particles that form superconductors and tightly bound ones in Bose-Einstein condensates, another exotic form of matter produced fleetingly since 1995. The creation of the new condensate is considered the crucial first step toward producing superconductors that work at room temperatures.
The ability to create new forms of matter by simply tuning a magnetic field presents a powerful new tool to study basic physics, she says. Burnett says the research could lead to "forging other types of matter from the ground up", including condensates formed from linking three or more particles.
But the ultimate goal is to create room-temperature superconductors, which would revolutionise the supply of electric power. Currently, the highest temperature at which superconductors work is a chilly -135°C.
Maternal diet linked to offspring's longevity
Minor manipulations of a mother's diet can hugely affect the lifespan of her children, suggests a new study of mice.
"At the two extremes we looked at, the dietary changes increased the difference in lifespan by more than 50 per cent," says Susan Ozanne, who performed the research with Nicholas Hales at Cambridge University, UK.
"In humans, this could equate to the difference between reaching 50 and living to be 75 years old," she says. The research joins existing evidence that maternal diets in humans can have a life-long impact.
The researchers fed a variety of different diets to a group of 144 mice pups, as well as their mothers. The pups that lived longest were well fed in the womb and had mothers whose diets were relatively low in protein during lactation. Their lifespans were further enhanced if they were not given a "junk food" type diet, rich in sugar and fat.
The pups that had the shortest lives received a low-protein diet while in the womb, but were subsequently fed well by their mothers who ate a protein-rich diet whilst breast feeding. Their lifespans were further shortened if they ate junk food after weaning. Overall the research indicates that being well fed in the womb and during infancy helps mice resist the ill-effects of a junk food diet later.
"It is known that if you starve animals of calories while they are still in the womb then they can suffer from diabetes. The damage that's done in utero appears to be permanent," he says. "But the truth is, everything that we know about the effects of calorie restriction diets can be put on the head of a pin."
Test-tube sperm get new genes
Growing sperm in a test tube may offer a powerful new way to genetically modify animals and potentially correct human genetic diseases before conception.
The technology offers two advantages. Firstly, it creates GM animals in one generation rather than two, unlike most conventional techniques.
Secondly, because the genes are spliced into laboratory-born sperm, it may allow scientists to do sophisticated genetic manipulations in a wide range of animals. So far these have only been possible in mice.
"The big deal here is that this opens up vast possibilities to tailor this technique for different applications," says Shawn Burgess of the US National Institutes of Health in Bethesda, Maryland. But experts say the technology will need to be improved further before it shows real promise.
Burgess, with colleagues in Japan, developed the technique to introduce new genes into zebrafish, a favourite animal model for geneticists. Current techniques - such as introducing DNA into eggs, sperm or embryos shortly before fertilisation or implantation - results in a high percentage of "mosaic" fish possessing a mixture of GM and normal cells.
To create animals with the new genes in every cell, researchers then need to mate the mosaic fish and screen the offspring for those whose parents possessed a GM sperm or egg.
The new technique relies on culture techniques developed by the Japanese team to grow male germ cells and turn them into sperm in the test tube. Burgess then created retroviruses to infect the sperm cells and insert a new gene into their DNA.
The sperm was then used to fertilise eggs and make new animals. Only six of 1410 eggs exposed to the altered sperm eventually developed into transgenic animals, but every cell in their body contained the new gene.
"It's a technique that's worth keeping an eye on," says zebrafish geneticist Perry Hackett of the Minnesota-based biotech company Discovery Genomics.
But he points out that Burgess's success rate was so low researchers could actually end up screening fewer animals with conventional techniques. "And for those, you don't need special sperm cultures or viruses. So I don't think this is ready for prime time yet."
If the new procedure could be adapted to human sperm, Burgess says it might be used for a gentler type of gene therapy by allowing hereditary defects to be repaired before fertilisation.
The whole notion of germline gene therapy in humans remains highly controversial, but Burgess thinks this method offers some advantages. "It's an approach where you don't have to treat or kill embryos in order to correct a defect," he says.
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