Mutant gene linked to most severe type of TB

People who carry a mutant gene can develop potentially fatal meningitis if they get infected with the drug resistant Beijing strain of tuberculosis, a study in Vietnam has found.

Tuberculous meningitis is the most severe form of the disease in which the infection spreads to membranes enveloping the brain and the spinal cord. One in three people who develop TB meningitis dies, even if he or she gets hospital treatment.

The study published in the open-access journal PLoS Pathogens (plospathogens.org), found people most likely to develop TB meningitis were those who carried a variant of the TLR2 gene and who get infected with the Beijing TB strain, prevalent in Asia and the former Soviet states.

Previous studies have linked TLR2 to the immune system and it seems to be important for recognising and initiating a defensive response to the TB bacteria.

The researchers took bacteria samples from 187 patients who suffered tuberculous meningitis and 236 other patients who suffered the more common pulmonary tuberculosis.

Most of the patients then had their genes analysed to see if they carried the TLR2 variant.

"Together, these results suggest that the association of the (variant gene) with tuberculous meningitis is strongest among those infected with the Beijing lineage," the scientists wrote.

The "Beijing" family of TB strains is prevalent in Asia and former Soviet states. It has become more drug resistant in recent years and has been responsible for outbreaks of multi-drug resistant tuberculosis in the United States.

More than one-third of the world's population is infected with TB and the infection rate is one every second. However, only one in 10 infected persons will develop symptoms and that usually happens when their immune systems are weak.

Left untreated, TB kills half its victims. The disease kills over 2 million people each year.

One of the researchers, Maxine Caws at the Hospital for Tropical Diseases in Vietnam, said the latest finding was a reason to develop more sophisticated and targeted treatments and vaccines.

"This is particularly important in this era of emerging 'untreatable' bacteria infections due to antibiotic resistance," Caws wrote.

Bones show humans in Europe 1.2 mln years ago

Early humans may have roamed Europe as much as 1.2 million years ago, far earlier than previously thought, scientists said on Wednesday, based on fossils they found in northern Spain.

Researchers excavated a jaw bone, teeth and simple tools in a cave near the city of Burgos dated around 400,000 years older than the previously oldest-known remains found at a nearby site 14 years ago, a paper published in the journal Nature said.

The remains are accurately dated and lay to rest doubts about when early humans first lived in Europe, said Andreu Olle, who has worked at the Atapuerca site since 1990.

"These are the oldest human remains in Europe. With this fossil, we can say it (Europe) was populated earlier than was thought," he told Reuters.

The bones are similar to fossils thought to be 800,000 years old found at the same site in 1994, suggesting a continuous human presence in Western Europe.

Up to now archaeologists had found evidence of human activity in Spain, France and Italy around 1 million years ago but no human remains, only animal bones and stone tools.

Scientists generally agree that modern humans spread out of Africa starting about 50,000 years ago, quickly establishing Stone Age cultures throughout Europe, Asia and Australia.

However the fossil, thought to be from the 'Homo antecessor' species, would have shared common ancestors with modern man and may have mixed with the more recent newcomers from Africa.

Flakes of flint embedded in animal bones, suggesting the use of a crude knife, were amongst the finds discovered at the site last June.

The find adds weight to the theory that early humans spread from Africa via the Middle East, not across the Straits of Gibraltar separating Africa from Europe, because the jaw was a similar shape to one unearthed in the central Asian country of Georgia thought to be 1.7 million years old.

Growth hormone no benefit to athletes

People who take human growth hormone in the hope of boosting athletic performance are not only breaking the law and risking their health, but likely are not even achieving their objective, U.S. researchers reported on Monday.

While some reports show that some illegal steroids may help athletes bulk up and train harder, human growth hormone is not one of them, the report in the Annals of Internal Medicine suggests.

"What we saw is that while there was a change in body composition, we didn't find evidence that growth hormone improves athletic performance," Dr. Hau Liu of Stanford University in California, who led the study, said in a telephone interview.

Liu's team looked at 27 studies covering 303 people aged 13 to 45. They found that, overall, those who took growth hormone did develop more lean body mass, but this did not translate to either more strength or exercise capacity.

People who took growth hormone had swelling of their tissues and more fatigue compared to people not taking the drug, they added.

Use of growth hormone is banned by the International Olympic Committee, Major League Baseball and the National Football League. U.S. law prohibits its use for sports enhancement.

When the hormone is given to people with growth hormone deficits caused by pituitary tumors or other conditions, it can improve strength. But it does not enhance strength in normal, healthy people.

For example, people given hormone generated more lactate, a byproduct of exercise that can cause pain and muscle fatigue. In one study meant to see if human growth hormone might boost strength or endurance, two cyclists given the hormone stopped a workout because of fatigue.

"The key takeaway is that we don't have any good scientific evidence that growth hormone improves athletic performance," Dr. Andrew Hoffman, a professor of endocrinology, gerontology and metabolism who worked on the study, said.

Hoffman noted that other hormones have been shown to benefit athletes -- notably testosterone.

"Athletes probably take much more hormone than the investigators felt that they could ethically try to give to healthy people; in addition, some athletes combine growth hormone with other anabolic hormones like testosterone," Hoffman added in an e-mail.

Hoffman said people get side-effects from high doses of hormones. "You you get fluid accumulating in the legs, you get pain in the joints," he said in a telephone interview.

"From what we hear the athletes are taking very, very large doses," he added.

Other hormones do, however bulk up athletes -- although not without risk, Hoffman said. "The findings with growth hormone absolutely do not extend to other hormones like testosterone which work through entirely different mechanisms," he said.

Hospital tests for 'superbug' effective

Testing every hospital patient to find and treat carriers of a drug-resistant bacteria can curtail outbreaks of dangerous infections, according to a study released on Monday, but some researchers questioned whether universal screening is the solution to the problem.

The authors of the four-year study conducted in three suburban Chicago hospitals concluded that universal patient screening for methicillin-resistant Staphylococcus aureus, or MRSA, reduced infection rates by 70 percent.

But another researcher who wrote an editorial accompanying the study, which was published in the Annals of Internal Medicine, said credit for fewer illnesses could be due to better hand-washing and cleaning practices by hospital staff.

The study compared MRSA infection rates when no screening protocol was in place, to when only intensive care unit patients were tested, and to when nearly all patients were screened over a 21-month period.

Without the screening there were nearly nine new infections per 10,000 days of patient care. After universal testing was put in place, infections declined to about four per 10,000 patient-days, a 70 percent drop.

"The program we began in August of 2005 had a major patient safety impact for all our patients and demonstrated that a comprehensive effort to reduce MRSA infection can be accomplished," Dr. Lance Peterson of Evanston Northwestern Healthcare in Illinois, who worked on the study, said in a statement.

Among the authors of the study were several researchers with financial ties to Becton Dickinson & Co, a manufacturer of a test for MRSA.

Dr. Ebbing Lautenbach of the University of Pennsylvania, commenting on the study in an editorial in the journal, said it was premature to recommend universal MRSA screening.

Lautenbach said pressure on hospital staff to perform the screening consequently focused attention on following proper hygiene practices.

He also cautioned that extensive use of an antibiotic ointment to treat MRSA carriers may promote additional drug resistance. Only a few antibiotics are effective against MRSA, which is resistant to common infection-fighting medications.

As many as 1.5 percent of Americans carry MRSA, and they may spread it to others while not developing an infection themselves. Most dangerous infections occur in hospitals, where weakened patients are susceptible, and it was blamed for 19,000 U.S. deaths in 2005.

A Geneva, Switzerland, hospital study published in the Journal of the American Medical Association last week concluded universal patient screening did not curtail in-hospital MRSA infections, and found screening was costly because of the need to isolate and treat patients.

But critics of that study said the screening test used was too slow, taking nearly a day to produce results, a gap that might have allowed the contagious bug to spread.

Newer tests can identify carriers in two hours.

Monday's study credited universal screening with preventing 85 MRSA infections, Lautenbach wrote. But he suggested less costly approaches to universal screening, such as testing only at-risk patients and strict adherence to proper hygiene.

A few U.S. states have called for universal patient screening for MRSA, and some hospitals have adopted it. Hospitals face an added financial risk in October when the Medicare and Medicaid health insurance programs plan to halt reimbursements for treating hospital-acquired infections and other "preventable" conditions.

Pain lasts long after traumatic injury

A surprising number of people -- more than 60 percent -- still suffer significant pain a year after a traumatic injury in a car crash or other cause, showing the need for better pain treatment, researchers said.

In a study published on Monday in the journal Archives of Surgery, researchers tracked 3,047 patients ages 18 to 84 from 14 U.S. states who survived an acute traumatic injury.

A year after the injury, 63 percent reported that they still experienced pain related to the injury, with most having pain in more than one region of the body.

On average, the patients assessed their pain at 5.5 on a 10-point scale -- a level at which they would be expected to have moderate to severe interference with daily activities.

"I was surprised that the pain was as common and as severe as they reported it to be," said Dr. Frederick Rivara of the University of Washington in Seattle, who led the study.

"The implications are that we need to do a much better job of identifying pain in these patients, treating it adequately and treating it early," Rivara added in a telephone interview.

The people in the study sustained head injuries, broken limbs, chest or abdominal trauma and other injuries in motor vehicle crashes, falls and other circumstances.

Pain was most commonly seen in joints and limbs (44 percent of patients), the back (26 percent), the head (12 percent) and neck (7 percent).

Rivara noted that people who experience chronic pain are at higher risk for depression and for being unable to work or function normally.

"The focus up until now in a lot of our care is on whether you live or die, which is obviously important. But we can't just stop there. And I think we need to look at what are the things we can do to improve people's lives after serious illness or injury," Rivara added.

The American Pain Foundation, a Baltimore-based advocacy group, said the financial cost exacted by chronic pain in the United States -- including health-care expenses, lost income and lost productivity -- is estimated at $100 billion a year.

The group said back pain is the leading cause of disability in Americans under 45 years old.

"There are hundreds of thousands, if not millions, of people who have had traumatic injury when the focus has been the injury and the destruction of tissue and not the pain. Pain has been a secondary consideration (during treatment)," said Will Rowe, American Pain Foundation chief executive officer.

"In many instances, the injury heals and the pain persists. That's the story that needs to be told," Rowe said.

Folate helps keep men's sperm normal

Vitamins known as folates that prevent birth defects when consumed by women also help to keep men's sperm normal, researchers reported on Wednesday.

Men who took folic acid supplements and who ate folate-rich foods such as leafy greens had fewer abnormal sperm, the team at the University of California, Berkeley said.

Specifically, the men had fewer abnormal sperm in which a chromosome had been lost or gained, known as aneuploidy, they reported in the journal Human Reproduction.

"We found a statistically significant association between high folate intake and lower sperm aneuploidy," said Brenda Eskenazi, who helped lead the study.

"There was increasing benefit with increasing intake, and men in the upper 25th percentile who had the highest intake of folate between 722-1150 micrograms, had 20 percent to 30 percent lower frequencies of several types of aneuploidy compared with men with a lower intake," Eskenazi added in a statement.

She said larger studies were needed to confirm the findings.

Sperm aneuploidy can cause failure to conceive, causes up to a third of miscarriages and causes children to be born with Down's syndrome and other rare chromosomal syndromes.

Chemotherapy for cancer and exposure to pesticides also can damage sperm in this way but diet had not been investigated, the researchers said.

Folic acid can prevent nerve damage in growing babies and is so important that it is added to flour, rice and other staples in many countries.

But few studies had looked its effects on fathers.

Eskenazi's team said estimates suggest that between 1 percent and 4 percent of sperm in a healthy man have some type of aneuploidy but this varies from man to man.

Her team analyzed sperm samples from 89 healthy, non-smoking men of all ages and also questioned them about their daily total intake of zinc, folate, vitamin C, vitamin E and beta-carotene in both food and supplements.

Eskenazi said her team and others had previously shown that vitamin intake may help make men more fertile by improving the quality of the sperm. "This study is the first to suggest that paternal diet may play a role after conception in the development of healthy offspring," she said.

The current U.S. recommended daily intake of folate for men aged over 19 is 400 micrograms. Men seeking to become fathers may need more, Eskenazi said.

Men who ate the most zinc and beta-carotene also had fewer instances of some sperm abnormalities, but not aneuploidy, the researchers found.

Fresher blood poses fewer surgery risks

People who got old, stale blood during surgery were 30 percent more likely to die than people who got fresh blood, U.S. researchers reported on Wednesday.

Two weeks seemed be the cutoff, with older blood causing more complications, the researchers reported in the New England Journal of Medicine.

"We report that the relative risk of postoperative death is increased by 30 percent in patients given blood that has been stored for more than two weeks," the researchers wrote.

This can cause a dilemma, as many blood banks and hospitals cannot keep enough blood on hand that is so fresh.

The U.S. Food and Drug Administration allows blood to be held for as long as six weeks, and blood banks typically give out the oldest blood first.

One solution may be to use the freshest blood first. Another is to use techniques to reduce the need for a transfusion in the first place, said Dr. Colleen Gorman Koch of the Cleveland Clinic Foundation, who led the study.

Her team studied 6,002 patients who received heart surgery at the Cleveland Clinic Foundation. Koch and her colleagues compared the outcome with the storage time of the blood transfused in each operation.

The rate of death while in the hospital was 1.7 percent among fresh blood recipients versus 2.8 for older blood. Rates for kidney failure, infection, respirator use and multiorgan failure were also higher if older blood was used.

However, a system that uses blood no older than two weeks would make it harder to keep blood banks properly stocked, and much more blood would be discarded. There are times when the blood supply falls to critically low levels, even with the current six-week limit.

SUPPLY VERSUS DEMAND

"It is just not feasible to shorten storage time significantly without restricting the blood supply," Dr. John Adamson of the University of California at San Diego wrote in a commentary.

Adamson also said there are important unanswered questions about whether the results would apply to other medical procedures where transfusions are common. For example, the process of sending blood through a heart-lung machine may be causing damage to blood cells, reducing the shelf-life of each pint.

Older blood may be acceptable for other uses.

Koch said patients should be asking their surgeons if the hospital has a blood management program in place.

"For cardiac surgery there are a lot of things you can do in the operating room to minimize the risk of receiving a blood transfusion at all," Koch said. One method scavenges and recycles blood that would normally be lost in an operation.

And if surgery is being done on a nonemergency basis, doctors should first be treating any underlying anemia a patient might have, Koch said. "So they're getting themselves in tip-top shape prior to surgery to decrease their need for blood."

In October, researchers reported that donated blood quickly loses nitric oxide in red blood cells -- which is key to transferring oxygen in the blood to tissues.

But if nitric oxide is restored, banked blood appears to regain its power, the team at Duke University in North Carolina found.

Currently, about 5 million Americans receive blood transfusions each year, according to the National Institutes of Health.

Better to walk away than punish

Harvard study

Punishing a lazy team member can be counterproductive and it may be better to simply walk away, researchers said on Wednesday.

The researchers at Harvard University found that people who go to the trouble of punishing colleagues, co-workers or others in one-on-one situations do not profit from their revenge.

Such behavior does not pay off for a group, either, they reported in the journal Nature.

"Put simply, winners don't punish," said David Rand, who worked on the study. "Punishment can lead to a downward spiral of retaliation with destructive outcomes for everybody involved."

Rand works in Harvard's Program for Evolutionary Dynamics and Department of Systems Biology, which combines the study of evolution with economics.

His team studied people playing the so-called prisoner's dilemma computer-based game, in which 104 Boston-area students could choose to cooperate, defect or punish.

"Cooperation meant paying one unit for the other person to receive two units," the researchers wrote. So if both players cooperated, each got two units. Defectors could take off with three units, unless the other player defected too, in which case both ended up with only one.

"That makes defection tempting for most people and cooperation generally breaks down at some point in a prisoner's dilemma game," Manfred Milinski and Bettina Rockenbach of the Max-Planck-Institute for Evolutionary Biology in Ploen, Germany wrote in a commentary.

The Harvard game added two dimensions -- punishment and familiarity. The five top-ranked players never used costly punishment, while players who won the least amount had punished the most often.

An equivalent situation might be in the workplace, Rand said.

"Say you have a project that you have to complete with someone else and you feel like someone else is not contributing as much as they should; they are not pulling their weight," Rand said in a telephone interview.

"The thing that is best for you is to stop contributing, to walk away, as opposed to expending a lot of effort insulting them, threatening them or taking aggressive action."

Punishing someone else in a situation where both parties are equal creates an "opportunity cost," Rand said. "The time that you are spending being punitive toward the other person could be spending doing things that are more productive."

But it also does not pay to let the freeloader ride along. "It's not quite turn the other cheek," Rand said. "We are saying you should only do as much as the other person is doing."

He said the findings only apply in one-on-one situations -- not to societies or cultures as a whole, or situations in which one person is more powerful than the other.

Why do birds sing? It's all in the brain

Birds start singing in the spring because of a biological response to longer days, researchers said on Wednesday.

When birds are exposed to light for longer periods, certain brain cells trigger a series of hormonal reactions telling them to find a mating partner, which they do by singing, a team of Japanese and British researchers reported in the journal Nature.

"While we knew what area of the brain was affected by seasonal change, until now we did not know the exact mechanism involved," said Peter Sharp, a researcher at the Roslin Institute near Edinburgh, who worked on the study.

The researchers, led by Takashi Yoshimura of the Nagoya University in Japan, scanned 38,000 genes present in brain samples taken from Japanese quails to see which of the birds' genes were affected by varying degrees of light.

Genes in cells on the surface of the brain switched on when the birds received more light and began releasing a thyroid-stimulating hormone.

The genes activated 14 hours after dawn on the first day of sufficient length, the researchers said.

"Such knowledge would have been impossible in the past, but advances in technology enabled us to scan thousands of genes so that we could work out which ones are affected by seasonal change," Sharp said in a telephone interview.

This hormone, previously associated with growth and metabolism, helped to stimulate the pituitary gland to secrete other hormones. In turn this caused the birds' testes to grow, which eventually resulted in crowing to attract a mate.

The findings could also one day lead to better treatments for infertility because humans have the same cells in the same part of the brain, Sharp added.

"It is sitting there and standing there with the same characteristics as in birds," he said. "The big question is whether these cells are involved in the reproductive system."

Popcorn ingredient causes lung disease

A chemical used to give butter flavor to popcorn can damage the lungs and airways of mice, U.S. government experts reported on Thursday.

Tests on mice show that diacetyl, a component of artificial butter flavoring, can cause a condition known as lymphocytic bronchiolitis, said the team at the National Institute of Environmental Health Sciences, part of the National Institutes of Health.
A popcorn seller stocks up in Barnes, southwest London July 5, 2007. A chemical used to give butter flavor to popcorn can damage the lungs and airways of mice, U.S. government experts reported on Thursday. (REUTERS/James Boardman)

The condition can lead to obliterative bronchiolitis -- or "popcorn lung" -- a rare and debilitating disease seen in workers at microwave popcorn packaging plants and at least one consumer.

At least two microwave popcorn makers -- ConAgra Foods Inc and Weaver Popcorn Co Inc -- have said recently they would stop using diacetyl.

Laboratory mice made to inhale diacetyl vapors for three months developed lymphocytic bronchiolitis, the NIEHS team said.

"This is one of the first studies to evaluate the respiratory toxicity of diacetyl at levels relevant to human health," Daniel Morgan at NIEHS, whose team led the study, said in a statement.

Writing in the journal Toxicological Sciences, the researchers said findings suggest that workplace exposure to diacetyl contributes to the development of obliterative bronchiolitis.

The hard-to-treat condition causes vague symptoms such as cough and shortness of breath, and steadily worsens, according to the U.S. Centers for Disease Control and Prevention.

Congress has been working on a bill to order quick action by the Occupational Safety and Health Administration to limit exposure to diacetyl. The House of Representatives passed a bill last year but the Senate has not acted.

The Food and Drug Administration said last September it was investigating a report of a man who came down with the life-threatening disease after eating several bags of butter-flavored microwave popcorn each day.

DEET works by masking body odor from bugs

The bug repellent DEET works by making mosquitoes and their brethren unable to smell the sweet aroma of human sweat that alerts them that a meal of blood is nearby, scientists said on Thursday.

This knowledge may help guide the creation of new repellents based on the same principle but without possible health worries, they said.

The chemical was first produced by government scientists in 1946 after the jungle warfare of World War II hammered home the need to prevent mosquito and other insect bites. It has been available to the public since 1957.

It is the world's most widely-used topical agent against mosquitoes and other blood-eating insects. It repels mosquitoes which spread malaria, a leading killer in parts of the developing world, as well as ticks which spread Lyme disease. But it does not kill them.

Until now scientists had not grasped exactly how it works.

Mosquitoes are crazy for two human scents: sweaty body odor and the carbon dioxide in breath. They use different receptors in their olfactory system -- the sensing system for smell -- to detect these odors to locate their prey.

"Humans are very smelly, so there's a large number of compounds that attract mosquitoes," Leslie Vosshall, head of Rockefeller University's Laboratory of Neurogenetics and Behavior, said in a telephone interview.

In experiments on mosquitoes and fruit flies, her team determined that DEET serves sort of a chemical cloak, masking certain human odors.

"You become invisible to them," Vosshall said.

The scientists tracked the electrical activity of cells in the mosquito olfactory system while exposing them to DEET. They found that it blocked bugs from smelling body odor but not the carbon dioxide in breath.

Without the scent of body odor, the bugs cannot figure out that a succulent person is nearby, the scientists said.

"Lots of things out in nature will release carbon dioxide -- swamps, for example -- and that's not a good thing to go after if you're a mosquito," said Vosshall, whose findings were published in the journal Science.

The U.S. Environmental Protection Agency said about a third of the U.S. population is expected to use DEET annually. The agency said about 140 products containing DEET are registered with the EPA by about 39 different companies.

A safety review concluded in 1998 that insect repellents containing DEET are not a health threat, but DEET should not be used on children under two months old, the EPA said.

"There are problems with DEET," Vosshall said. "It's oily, it melts plastic, you can't use it on babies, you have to reapply it on every piece of exposed skin frequently. It does actually penetrate your skin and enter your blood stream."

She said there have been rare cases in which people had seizures after putting on too large a dose.

Streamlined meteorite hit Peru fast and hard

A meteorite that struck Peru in September, digging out a deep hole and startling nearby residents, traveled faster and hit harder than would have been expected, researchers reported on Tuesday.

The object, which left a 49-foot-wide (15 meter) crater, was made of rock and, in theory, should have disintegrated in the atmosphere long before reaching the Earth's surface, said Peter Schultz, a professor of geological sciences at Brown University in Rhode Island.

And it may have. But the pieces stayed together and were speeding at 15,000 mph (24,000 kph) when they hit, Schultz told the Lunar and Planetary Science Conference in League City, Texas.

Usually only meteorites made of metal make it to the surface intact enough to scoop out a crater.

"They come into the atmosphere, they slow down, and they plop," Schultz said in a telephone interview.

"It would make a hole in the ground, like a pit, but not a crater. But this meteorite kept on going at a speed about 40 to 50 times faster than it should have been going."

It landed in an arroyo, or dry stream, and the pit quickly filled with water from underneath the surface.

Schultz said his team's observations suggest that scientists may need to change theories about the different ways objects can hit planets. "We have to go back to the drawing board and think again," he said.

Dozens of people who visited the crater, near Lake Titicaca and the border with Bolivia, reported vomiting and headaches afterward. Some questioned whether the noise and hole were actually caused by a meteorite.

"That is one of the reasons we went down. We wanted to distinguish fact from fiction," Schultz said. "These reports of all these people being sick were grossly exaggerated. They didn't get sick. They were surprised."

FASTBALL FROM SPACE

A team from Johnson Space Center in Houston analyzed two chunks of dark gray rock from the meteorite and told the meeting they look nothing like meteorites from known sources such as Mars.

Schultz, whose team inspected the crater 800 miles (1,300 km) south of Lima, said its unusually loud and messy impact happened because it was spinning and going so quickly.

"This just isn't what we expected," Schultz said. "It was to the point that many thought this was fake. It was completely inconsistent with our understanding how stony meteorites act."

At such high velocity, fragments may not escape past the "shock-wave" barrier accompanying the meteorite, he said.

"It became very streamlined and so it penetrated the Earth's atmosphere more efficiently," Schultz said. He compared it to a flock of geese drafting behind one another in V-shaped flight.

He said this could challenge conventional wisdom that all small, stony meteorites disintegrate before striking Earth.

"You just wonder how many other lakes and ponds were created by a stony meteorite, but we just don't know about them because when these things hit the surface they just completely pulverize and then they weather," said Schultz.

The findings may also help explain what caused various craters on Mars, he said.

Factors behind head and neck cancer revealed

There are two distinct culprits behind head and neck cancer -- the long-recognized heavy tobacco and alcohol use as well as a common sexually transmitted virus, researchers said on Tuesday.

The risk factors are so dramatically different in head and neck cancer in people infected with the human papillomavirus, or HPV, that it should be considered a separate disease from cases in which patients are not infected, researchers at Johns Hopkins University in Baltimore said.

Head and neck cancer includes tumors in the mouth, tongue, nose, sinuses, throat and lymph nodes in the neck.

"These are completely different cancers and we need to view them as such. They just happen to occur in the same place. The risk factors didn't appear to overlap at all, and there didn't appear to be any interaction between them," Dr. Maura Gillison, a professor of oncology and epidemiology, said in a telephone interview.

More than 35,000 people are diagnosed with head and neck cancer annually in the United States alone. If found early, such cancer may respond well to treatment with surgery, radiation therapy and chemotherapy.

Not only are the patient populations different in HPV-positive and HPV-negative head and neck cancer, but the tumors look different under a microscope, Gillison said. People with the viral-linked cancer also tend to respond better to treatment than those not HPV-infected, she added.

HPV is a common sexually transmitted virus. It is well known for causing cervical cancer and genital warts.

Since 2000, researchers have also known that HPV infection was linked to some cases of head and neck cancer, particularly in the upper throat and back of the tongue.

The new study, published in the Journal of the National Cancer Institute, focused on 240 people diagnosed with head and neck cancer between 2000 and 2006.

Nearly 40 percent of them had an HPV infection. Those patients did not have the well-known risk factors for head and neck cancer -- tobacco smoking, alcohol use and poor oral hygiene, the researchers found.

The people with viral-linked cancer cases had a completely different set of risk factors, including certain sexual behaviors and marijuana use, the researchers found.

Sexual behaviors linked to these patients included increasing numbers of lifetime sex partners including oral sex, and the presence of a sexually transmitted disease, they said.

Gillison said it is possible other behaviors linked with marijuana use could be responsible, but said chemicals in marijuana called cannabinoids could affect the immune system's ability to clear a viral infection.

Limit patient screening for infection, study says

Screening all incoming hospital patients for a dangerous drug-resistant staph infection and isolating those infected did not curtail its spread, and proved costly, Swiss researchers said on Tuesday.

Some hospitals and a few U.S. states have called for the controversial approach of testing every incoming patient for methicillin-resistant Staphylococcus aureus, known as MRSA, which was blamed for an estimated 19,000 U.S. deaths in 2005.

But a 1-1/2-year study at the University of Geneva Hospitals and Medical School, where MRSA has occasionally been a problem, found screening did not reduce the number of patients who caught the infection during their hospital stays.

Roughly 85 percent of MRSA cases, which is treatable only with a few antibiotics, occur in hospitals, where infection can kill weakened patients.

Hospitals undertake several approaches to combat outbreaks such as strict hand-washing by staff, frequent equipment changes, and extensive cleaning of operating rooms. MRSA outbreaks struck roughly one-quarter of U.S. hospitals in 2003.

As many as 1.5 percent of Americans carry the highly contagious infection and may spread it to others without developing a serious infection themselves.

In the study published in the Journal of the American Medical Association, 515 of the 21,754 surgical patients tested positive for MRSA. Of those, 337 might not have been caught because they had not been previously identified as MRSA carriers.

Infected patients received five days of treatment and special precautions such as isolated hospital rooms that strained hospital resources and raised costs considerably.

During the initial nine-month period when the screening was done in selected hospital wards, 93 patients contracted MRSA infections while in the hospital. That compared to 76 infected in the wards where standard prevention efforts were in place.

"Overall, our real-life trial did not show an added benefit for widespread rapid screening on admission compared with standard MRSA control alone in preventing (hospital) MRSA infections in a large surgical department," study leader Dr. Stephan Harbarth wrote.

The report recommended targeting the screening to patients undergoing elective surgery with a high risk of MRSA infection.

Two U.S. researchers agreed in an accompanying commentary that a multifaceted approach, and not universal patient screening, was likely to be more effective in combating MRSA and other types of hospital germs that infect a total of 1.7 million Americans and kill 100,000 each year.

Study sheds light on paralysing nerve condition

British researchers have discovered a genetic mutation that causes a paralysing illness called ALS in some people, a finding they said on Thursday may lead to treatments for the degenerative nerve condition.

Their study showed how this genetic variation produced proteins that were toxic and killed motor neuron cells in people with amyotrophic lateral sclerosis or ALS, also commonly known as motor neuron disease or Lou Gehrig's disease.

"We discovered that the mutation was appearing only in people who were affected," said Chris Shaw, a researcher at the Institute of Psychiatry in London who led the study published in the journal Science. "This suggested it is disease-causing."

The finding is important, he said, because the disease kills quickly -- usually between two and five years after symptoms start -- and has no effective treatments. Physicist Stephen Hawking is a rare example of a person who has survived for years with the condition.

ALS leaves people unable to walk, talk or feed themselves but does not usually affect their intellect and other senses. Doctors diagnose about 120,000 new cases each year, according to the International Alliance of ALS.

Shaw and colleagues isolated a mutation in a gene called TARDBP in people with a rare, inherited form of ALS. They found that people with this variation produced a mutant and toxic protein called TDP-43.

Previous research had suggested the protein might have existed as sort of cellular junk generated as a harmless by-product of the disease. But by injecting these mutated proteins into the spines of chicks in eggs, Shaw's team showed they actually killed motor neurons.

While only about 1 percent of people have this form of ALS, the findings have wider implications because most people with the disease have these proteins accumulating in the wrong place within the cell, Shaw said.

"It also means we develop new and better disease models, which will bring us close to developing more effective therapies," he said.

In 1993 a group of U.S. researches identified a gene called SOD1 that caused a form of ALS affecting about 5 percent of people with the disease -- the only people with the condition who do not accumulate TDP-43 proteins, Shaw said.

That finding triggered a flood of new research into the disease, and the discovery of a second gene could draw even more people into the field, said Brian Dickie, director of Research Development at Britain's Motor Neuron Disease Association.

"The discovery of a new cause of the disease is of international importance, allowing researchers around the world to rapidly generate more pieces of the complex puzzle that is motor neuron disease," he said.

Four in Forbes Asia list

Four Malaysians made it to the Forbes Asia list of the region’s most generous and interesting philanthropists.

Tan Sri Syed Mokhtar Albukhary, Hishamudin Ubaidulla, Datuk Zaid Ibrahim and Datuk Amar Leonard Linggi Tun Jugah were featured in the inaugural Forbes Asia Heroes of Philanthropy list in its March 10 issue.

Syed Mokhtar, 56, is founder and sole donor of a Muslim charity, Albukhary Foundation that assists the needy.

Established in 1996, the foundation funds remedial classes in English, science and math for 20,000 underachieving students each year and runs a college scholarship programme for 300 students from more than 40 countries.

Syed Mokhtar controls Malaysia Mining Corp and holds big stakes in Johor Port and other businesses.

Hishamudin, 52, oversees Yayasan Ubaidi, a foundation funded entirely with profits from commercial buildings and the sale of land bought by his father years ago.

The foundation helps families who cannot make ends meet, pays medical expenses, helps single mothers pay for tertiary education, assists hospitals that cannot afford equipment.

Hishamudin, who helps run the family travel agency, is also chairman of Deir Yassin Remembered Malaysia, a movement committed to ending the war between Israel and Palestine.

Former MP for Kota Baru, Zaid, 57, who owns the country’s largest law firm, Zaid Ibrahim & Co, set up the Kelantan Foundation for the Disabled in 1998.

The foundation serves 2,400 people suffering from Down Syndrome, cerebral palsy and other disabilities.

Linggi, 67, a prominent Iban businessman has varied dealings, including real estate, plantation, shipping, hotel and other companies.

Tun Jugah Foundation gets virtually all of its contributions from him. It focuses on preserving the culture of the Ibans in Sarawak. In 2003, it began compiling the first Iban dictionary.

This year Forbes put together a list of 48 philanthropists.

Being overweight can damage your career

Being overweight or obese is not only bad for your health but can also be bad for your career, according to a U.S. study.

As obesity rates in the United States rise, researchers at Detroit's Wayne State University looked at over 25 years of research on weight-based bias in the workplace to see whether being overweight hindered the chance of getting a job or moving up the work ladder.

After examining the results of 25 separate studies, they concluded that obesity does have a denigrating effect in the workplace, with the weight-based bias stronger for sales positions than for managerial positions.

"There are a whole set of stereotypes that go along with being overweight, and a lot of them transfer into the workplace in terms of people's judgment about others' abilities and appearance in relation to job performance," researcher Cort Rudolph said in a statement.

The researchers found the results of all the studies examined were consistent in finding that people who are overweight are viewed more negatively in the workplace than those who are of average weight.

The bias was felt most when overweight people applied for a job and went through the initial selection process with body weight found to be less of a factor at the performance evaluation stage, and with stereotypes having a minimum influence when it comes to promotions.

Rudolph said this was not surprising based on what was known about weight-based stereotypes.

"Some of the basic stereotypes associated with being overweight include laziness, sloppiness, untidiness and lack of self-discipline and control," he said.

"Overweight people are also regularly labeled as having increased health problems, which is an issue often considered cumbersome by organizations."

But Rudolph, who will present the study's findings at a conference of the Society for Industrial and Organizational Psychology in San Francisco in April, said there was good news for overweight employees.

"The bias effect tends to decrease as people's tenure with an organization increases," he said.

Rudolph said this was an issue that could become more a problem as Americans became heavier.

"Considering this growth, stigmas associated with body weight can become more and more of an issue," he said.

Gene studies confirm "out of Africa" theories

Two big genetic studies confirm theories that modern humans evolved in Africa and then migrated through Europe and Asia to reach the Pacific and Americas.

The two studies also show that Africans have the most diverse DNA, and the fewest potentially harmful genetic mutations.

One of the studies shows European-Americans have more small mutations, while the others show Native Americans, Polynesians and others who populated Australia and Oceania have more big genetic changes.

The studies, published in the journal Nature on Wednesday, paint a picture of a population of humans migrating off the African continent, and then shrinking at some point because of unknown adversity.

Later populations grew and spread from this smaller genetic pool of founder ancestors -- a phenomenon known as a bottleneck.

Populations that remained in Africa kept their genetic diversity -- something seen in many other studies.

"The one thing that I think we cannot say from this study is that any one person's genome is any healthier or evolutionarily fit than another person's genome," said Carlos Bustamante of Cornell University in New York, who worked on one study.

"You have to think of this at the population level," Bustamante said in a telephone interview.

Bustamante's team has been looking at the DNA sequences of 15 African-Americans and 20 European-Americans, examining tiny one-letter changes in the DNA code called single-nucleotide polymorphisms or SNPs (pronounced "snips").

FIT OR EXTINCT

They tested these changes to qualify them as benign, or potentially affecting genes, amino acids and eventually proteins in a way that could damage health or make people less "fit" -- in evolutionary terms, less likely to survive and reproduce.

"Like every other study ... the African-American panel as a whole showed more variation than the European-American panel," Bustamante said.

Then his team did a computer simulation of a bottleneck, and found it predicted this pattern.

Bustamante said it is possible some of the SNPs are beneficial, and he said his team and others should compare the genetic changes they found to known genetic changes linked with diseases.

"I wish we had done that (already)," he admitted.

In the other study, Noah Rosenberg and colleagues at the University of Michigan and the National Institute on Aging analyzed DNA from 485 people around the world.

They looked for three types of genetic variation, including SNPs and larger changes that involve duplications, deletions and repetitions of large segments of DNA.

The patterns they found produced what they call the highest-resolution map yet of human genetic variation.

They also reinforce the idea that humans originated in Africa, then spread into the Middle East, followed by Europe and Asia, the Pacific Islands and finally to the Americas.

"Diversity has been eroded through the migration process," Rosenberg said in a statement.

People of African descent are the most genetically diverse, followed by people from the Middle East, and then Asians and Europeans. Native Americans resemble one another the most on a DNA level.

The study also found it is sometimes possible to trace a person's ancestry to a small group within a geographic region.

Memory loss declining among U.S. seniors

Older Americans are having less trouble with their memories, and it may be because they spent more time in school, U.S. researchers said on Wednesday.

They found the rate of cognitive impairment -- which includes a range of ills from significant memory loss to Alzheimer's disease -- fell 3.5 percentage points among people 70 and over between 1993 and 2002.

"We found a clear relationship. The more education people had, the better they performed on cognitive tests," said Dr. Ken Langa of the University of Michigan, whose study appears in the journal Alzheimer's & Dementia.

Langa said the research reinforces other studies that suggest people who do mentally challenging tasks early on build up a reserve of brain power that helps them withstand later injuries to the brain, such as a mini-stroke.

"Your brain is wired up differently. You can sustain more insults over your lifetime," Langa said in a telephone interview.

To test this, Langa and colleagues looked to see if there was a relationship between education and mental agility in older Americans.

They used data on 11,000 people from the Health and Retirement Study, a national survey of U.S. adults. The researchers compared data gathered in 1993 with data from 2002.

They found that in in 2002, 8.7 percent of those aged 70 or older had cognitive impairment, down from 12.2 percent in 1993. "We think education is part of the story here," Langa said.

In 1993, people who were 70 or older on average had 11 years of education. By 2002, those 70 and older had 12 years of education. "That is a relatively significant increase in the level of education," he said.

They also found that older adults with more education who did develop cognitive problems were more likely to die within two years.

Langa said the thinking is that people who have more education have developed different brain circuits that have allowed them to continue functioning at a high level.

"Once you put it off as long as you can, you are more likely to have a quicker decline and death," he said.

Langa said the results may also reflect better cardiovascular health, which can reduce strokes or other injuries that affect brain function. He said rising rates of obesity and diabetes could offset those gains.

"Cardiovascular risks have a close link to brain health," he said.

Langa said people should exercise their bodies to protect their cardiovascular health, and exercise their brains with puzzles and books.

Stem cells help rats recover function after stroke

Transplanting brain cells produced from human embryonic stem cells helped fix stroke damage in the brains of rats, according to scientists who hope to test the same thing in people whithin about five years.

Researchers have been looking for ways to repair the brain damage from a stroke, which can cause permanent disability. In a study published on Tuesday, researchers at Stanford University School of Medicine in California reported that treatment involving human embryonic stem cells may be a solution.

Embryonic stem cells are the master cells that give rise to every cell and tissue in the body.

The Stanford team reported they restored lost limb function in rats that had stroke-related brain damage. They induced human embryonic stem cells to develop into neural stem cells that, once transplanted in the rats, developed into neurons and two other important types of brain cells.

The researchers hope to use this approach within about five years in studies involving people who have had strokes.

"We have a lot of evidence that we'll be able to use this kind of stem cell regenerative therapy in patients, including stroke patients," Stanford's Dr. Gary Steinberg, who helped lead the study, said in a telephone interview.

Writing in the Public Library of Science journal PLoS ONE, Steinberg's team described how they caused strokes in 10 rats and then transplanted neural stem cells into their brains.

The cells made their way to the damaged brain region and incorporated themselves into surrounding brain tissue.

The cells never grew uncontrollably into tumors in lab dishes or inside the rats, the scientists said. The transplanted cells helped repair the stroke damage and enabled the rats to recover lost function in front legs weakened as a result of the stroke, they added.

"It was not quite back to normal but, at least in the rat, it looks like it's going to be close to normal -- very impressive," Steinberg said.

"Now remember, this is a rat, not a human. We still have to make that step. But if we could achieve that kind of recovery in humans, we would have a great therapy," Steinberg added.

In a stroke, the blood supply to any part of the brain is blocked. This can occur when a blood vessel bringing blood to the brain is blocked by a blood clot, or when a blood vessel bursts, causing blood to leak into the brain.

If blood flow is halted for more than a few seconds, the brain is deprived of blood and oxygen, brain cells die and permanent damage can result.

Some people oppose the use of human embryonic stem cells on ethical grounds because creating the reservoirs of these cells for use in research involves the destruction of human embryos.

Music matters for stroke patients, study finds

A little Beethoven is good for the brain, according to a Finnish study published on Wednesday showing that music helps people recover more quickly from strokes.

And patients who listened to a few hours of music each day soon after a stroke also improved their verbal memory and were in a better mood compared to patients who did not listen to music or used audio books, the researchers said.

Music therapy has long been used in a range of treatments but the study published in the journal Brain is the first to show the effect in people, they added.

"These findings demonstrate for the first time that music listening during the early post-stroke stage can enhance cognitive recovery and prevent negative mood," the researchers wrote.

Strokes, which occur when blood flow to the brain is blocked, can kill brain tissue and are one of the worldwide leading causes of death and permanent disability. Treatments include blood thinning drugs and attempts to lower cholesterol.

The study involved 60 people who recently had a stroke of the middle cerebral artery in the left or right side of the brain. This is the most common stroke and can affect motor control, speech and a range of other cognitive functions.

One group listened to their favourite music every day or used audio books while another did not listen to any music. All volunteers received standard rehabilitation treatment.

Three months after stroke music listeners showed a 60 percent better improvement in verbal memory compared to an 18 percent benefit for those using audio books and 29 percent for people who did not listen to either.

The ability to focus attention also improved by 17 percent in music listeners, said Teppo Sarkamo, a psychologist at the Cognitive Brain Research Unit at the University of Helsinki, who led the study.

"We can't say what is happening in the brain but based on previous research and theory it may be music listening could actually activate the brain areas that are recovering," he said in a telephone interview.

Music might also in some way activate more general mechanisms that repair and renew the brain's neural networks after stroke, Sarkamo said.

Larger studies are needed to better understand exactly what is going on but these findings show that music may offer a cheap, easy additional treatment for stroke patients, he said.

"This could be considered a pilot study," Sarkamo said. "It is a promising start.

Cardiac arrest: avoid nights, weekend

People who have a cardiac arrest in the hospital at night or on the weekend are far less likely to survive than those who suffer one during the day, U.S. researchers said on Tuesday.

Studies suggest this may be at least partly because of inadequate staffing at off-peak hours.

The researchers found only 14.7 percent of people whose hearts stop pumping during the night survive, compared with nearly 20 percent of people during the day.

Those who had a cardiac arrest at around 3 p.m. had the survival rate, Dr. Mary Ann Peberdy of Virginia Commonwealth University in Richmond and colleagues reported in the Journal of the American Medical Association.

The only part of the hospital with difference in survival day or night was the emergency department. "That survival difference by time of day was there regardless of where we looked, except in the emergency department," Peberdy said.

She said emergency departments are the one place in hospitals constantly staffed by senior-level physicians.

Cardiac arrest occurs when the heart stops circulating blood. Without cardiopulmonary resuscitation or CPR and often a shock from a defibrillator, patients can die within minutes.

"Doing the right thing and doing it quickly is very important," Peberdy said.

She said studies at individual hospitals suggested staffing played a role in whether a patient survived a cardiac arrest.

Other studies have shown that doctors make more mistakes at night, hospitals have fewer nurses per patient working at night and that fewer experienced supervisors work the night shift.

TIME TRUMPS OTHER FACTORS

Peberdy wanted to see how this affected survival of cardiac arrest. Her team scoured the National Registry of Cardiopulmonary Resuscitation, which included survival data for more than 86,000 adults who had heart attacks in more than 500 U.S. hospitals between January 2000 and February 2007.

They split up the data by time of day, with the day/evening defined as 7 a.m.-10:59 p.m., night as 11 p.m.-6.59 a.m. and weekends starting at 11 p.m. Friday and running through 6.59 a.m. Monday.

"We factored in how sick people were, what their initial rhythms were. None of that overshadowed the time of day," Peberdy said in a telephone interview.

"Weekend nights were pretty much the same as week nights. Weekend days were kind of in between week days and nights," she said.

She said the difference by time of day held regardless of whether a patient was in a bed with a heart monitor or even in the intensive care unit.

"I think the study confirms what some of us have suspected for a while: That how we staff the hospital determines how well patients do," said Dr. Graham Nichol who helps oversee the NRCPR registry for the American Heart Association.

Peberdy said the study suggests hospitals need to focus on improving their resuscitation systems in off-hours

Scientists prove Napoleon not poisoned by British

Italian scientists say they have proved Napoleon was not poisoned, scotching the legend the French emperor was murdered by his British jailors.

File photo of an oil on canvas portrait "Napoleon at Fontainbleau" from the workshop of Paul Delaroche. Italian scientists say they have proved Napoleon was not poisoned, scotching the legend the French emperor was murdered by his British jailors. (REUTERS/Handout)

Napoleon's post-mortem said he died of stomach cancer aged 51, but the theory he was assassinated to prevent any return to power has gained credence in recent decades as some studies indicated his body contained a high level of the poison arsenic.

"It was not arsenic poisoning that killed Napoleon at Saint Helena," said researchers at the National Institute of Nuclear Physics and the University of Pavia who tested the theory the British killed him while he was in exile on the South Atlantic island in 1821.

The Italian research -- which studied hair samples from various moments in his life which are kept in museums in Italy and France -- showed Napoleon's body did have a high level of arsenic, but that he was already heavily contaminated as a boy.

The scientists used a nuclear reactor to irradiate the hairs to get an accurate measure of the levels of arsenic.

Looking at hairs from several of Napoleon's contemporaries, including his wife and son, they found arsenic levels were generally much higher than is common today.

"The result? There was no poisoning in our opinion because Napoleon's hairs contain the same amount of arsenic as his contemporaries," the researchers said in a statement published on the university's website.

The study found the samples taken from people living in the early 1800s contained 100 times as much arsenic than the current average. Glues and dyes commonly used at the time are blamed for high environmental levels of the toxic element.

"The environment in which people lived in the early 1800s evidently caused the intake of quantities of arsenic that today we would consider dangerous," the scientists said.

One theory was that Napoleon was poisoned accidentally by arsenic vapour from dyes in his wallpaper at Saint Helena, but the study showed there was no massive increase in arsenic levels in his latter years.

"It is clear that one cannot talk about a case of poisoning, but of a constant absorption of arsenic," the researchers said.

Napoleon had been exiled once before -- on the Italian island of Elba after his failed invasion of Russia. But he returned to France and was finally defeated at Waterloo in 1815 after which he was sent to the much more remote Saint Helena.

Airport noise instantly boosts blood pressure

Living near an airport isn't just irritating, it is also unhealthy, researchers said on Wednesday, in a study that showed loud noise instantly boosts a sleeping person's blood pressure.

The louder the noise, the higher a person's blood pressure went, a finding that suggests people who live near airports may have a greater risk of health problems, said Lars Jarup, who led the European Commission-funded study.

"Living near airports where you have exposure to night time aircraft noise is a major issue," Jarup, an environmental health researcher at the University of Glasgow, told Reuters.

"The reason we did airports is because there was no study that has looked at particular problems of aircraft noise."

High blood pressure can lead to stroke, heart failure, heart attack and kidney failure. It affects more than a billion adults worldwide.

The research team showed that people living for at least five years near a busy airport and under a flight path have a greater risk of developing chronic high blood pressure, also known as hypertension, than those who live in quieter areas.

That study of nearly 5,000 people found that an increase in night time airplane noise of 10 decibels increased the risk of high blood pressure by 14 percent in both men and women.

"We know that noise from air traffic can be a source of irritation, but our research shows that it can also be damaging for people's health, which is particularly significant in light of plans to expand international airports," Jarup said.

In the four-year study, published in the European Heart Journal, the researchers remotely measured the blood pressure of 140 volunteers every 15 minutes while they slept in their homes near London's Heathrow airport -- one of the busiest in the world -- and three other major European airports.

They used digital recorders to determine what noises had the biggest impact on blood pressure, ranging from road traffic to a partner's snoring to an airplane taking off or landing.

The Decibel level, not a sound's origin, was the key factor, but airplanes had the most significant impact, Jarup said.

"Most of the time you will find road traffic noise is not too bad during the night," he said. "If you live near an airport where there are night flights, that is quite another story."

Migrating people had 20,000-year campout

People who migrated from Asia to the New World camped out for 20,000 years on land now submerged under the Bering Strait between Alaska and Siberia, according to a genetic analysis published on Tuesday.

A team at the University of Florida combined studies of DNA, archeological evidence, climate data and geological data to come up with their new theory, which describes a much longer migration than most other researchers have proposed.

"We sort of went out onto a limb, incorporating all this nongenetic data," molecular anthropologist Connie Mulligan said in a telephone interview.

Mulligan's team proposes that the people who left Central Asia to eventually populate the Americas passed quickly through Siberia, and then got stuck in Beringia -- a former land mass that now lies under the frigid Bering Sea.

There they stayed for 20,000 years, until glaciers melted about 15,000 years ago, opening a route to the Americas.

"The reason there is no archeological evidence for that occupation is that the area is under water," Mulligan said.

The researchers used sequences of mitochondrial DNA taken from Asians and Native Americans for their analysis. This type of DNA is passed along virtually unchanged from mother to child.

The small mutations that occur can be used as a genetic clock to track the descent and the sizes of ancient populations.

"After a long period of little change in population size in greater Beringia, Amerinds (American Indians or native Americans) rapidly expanded into the Americas less than 15,000 years ago either through an interior ice-free corridor or along the coast," they wrote in their report.

"This rapid colonization of the New World was achieved by a founder group with an effective population size of 1,000 to 5,400 individuals."

WAITING AND MUTATING

The University of Florida's Michael Miyamoto said the DNA suggests a 20,000-year "waiting period" during which generations passed and genetic changes accumulated.

"By looking at the kinds and frequencies of these mutations in modern populations, we can get an idea of when the mutations arose and how many people were around to carry them," he said.

Other theories have suggested one single expansion of people from the Old World to the New around 15,000 years ago.

"If you think about it, these people didn't know they were going to a new world. They were moving out of Asia and finally reached a landmass that was exposed because of lower sea levels during the last glacial maximum, but two major glaciers blocked their progress into the New World," Mulligan said in a statement.

"So they basically stayed put for about 20,000 years. It wasn't paradise, but they survived. When the North American ice sheets started to melt and a passage into the New World opened, we think they left Beringia to go to a better place."

Anthropologist and genetics expert Henry Harpending of the University of Utah, who did not work on the study, said it made sense.

"The idea that people were stuck in Beringia for a long time is obvious in retrospect, but it has never been promulgated," he said. "It's very plausible that a bunch of them were stuck there for thousands of years."