Canadian scientists crack hidden DNA code

Last Updated: Wednesday, May 5, 2010 | 1:11 PM ET

Canadian researchers have unraveled a genetic “code within a code” that helps explain how the instructions for building complex organisms, like humans, can be found in a small number of genes.

University of Toronto scientists Brendan Frey and Benjamin Blencowe said they have found a hidden code in DNA that helps explain how a small number of genes can contain instructions for a larger number of proteins and structures.

When researchers fully sequenced the human genome in 2004, they were surprised at how few genes humans actually have.

“Human DNA has 22,000 genes. That might seem like a lot, but not when you consider that a poplar tree has 45,000,” said Frey, in a statement.

Frey said his team, including Blencowe and Yoseph Barash, found a second level of information that the cells of living organisms use to create a larger set of instructions.

“We discovered a hidden code within DNA that living cells use to turn 20,000 genes into hundreds of thousands of genetic messages, by rearranging their parts,” he said.

Barash and Frey, who is also a professor of computer science and engineering, created a computer program that analyzes DNA to find “code words” in the genome.

The code words together are called the “splicing code,” containing the biological information needed to splice together different parts of the genetic code in different orders to generate a greater number of messages.

“For example, three neurexin genes can generate over 3,000 genetic messages that help control the wiring of the brain,” said Frey.

Neurexin is a protein that glues together the connections between nerve cells in the brain.

Frey said their work is the result of a close collaboration between computer scientists and experimental biologists.

“Understanding a complex biological system is like understanding a complex electronic circuit. Our team ‘reverse-engineered’ the splicing code using large-scale experimental data generated by the group,” he said.

The research was the cover story in this week’s issue of the journal Nature.

DNAWellnessinfo.com Resource: http://www.cbc.ca/technology/story/2010/05/05/tech-dna-splicing-code.html#ixzz0n9Wn5yO0

DNA Swap Between Eggs May Curb Inherited Disorders, Study Finds

April 14, 2010, 4:59 PM EDT  BusinessWeek

By Kristen Hallam

April 14 (Bloomberg) — Scientists discovered a way to transfer DNA from one fertilized human egg to another in a pioneering effort to avert the spread of a host of genetic disorders such as learning disabilities and diabetes.

The researchers at Newcastle University in northern England extracted the genetic material contributed by the egg and sperm and implanted it into a donor egg, according to the study published today by the journal Nature. It’s the first time DNA has been transferred between two fertilized human eggs.

The approach discards almost all the defective DNA inherited from the mother that disrupts the tiny energy generators inside cells, and may prevent related disorders such as blindness and liver failure, the researchers said. They are planning further experiments to see whether the technique could help people who carry mutated genes to have healthy babies — an end result that may still be a decade away.

“We have no way of curing these diseases at the moment, but this technique could allow us to prevent the diseases occurring in the first place,” said Doug Turnbull, the lead researcher and a professor at the university’s medical school, in a statement. “It is important that we do all we can to help these families and give them the chance to have healthy children, something most of us take for granted.”

Parents contribute a total of 23,000 genes to a child. In a fertilized egg, this genetic material is housed in two pronuclei, one from the egg and one from the sperm. The egg also contains mitochondria, tiny structures found in every cell that produce the chemical fuel needed for life. Mutations in the mitochondrial DNA, which are passed on from the mother, can disrupt the functioning of these energy generators.

‘Changing the Batteries’

The Newcastle scientists were able to extract both pronuclei and implant the material that makes each child unique into a donor egg with healthy mitochondria. They created 80 fertilized eggs using the technique and grew them in a laboratory for six to eight days. That showed for the first time that eggs produced in this way could reach the stage at which they each had divided into about 100 cells.

“It’s like changing the batteries,” Turnbull said today at a news conference in London. “These are diseases where there is battery failure. Because mitochondria are everywhere, these diseases can affect all parts of the body. None of my patients is exactly the same.”

About 1 out of every 200 children is born each year with mutations in mitochondrial DNA that cause no symptoms or only mild conditions. One in every 6,500 children is born with a more serious mitochondrial disease, ranging from muscular weakness to fatal heart failure. Some disorders lead to death in early infancy.

The research was funded by the Muscular Dystrophy Campaign, the U.K. Medical Research Council and the London-based Wellcome Trust, the world’s second-biggest medical research charity.

–Editors: Phil Serafino, Angela Cullen

To contact the reporter on this story: Kristen Hallam in London at khallam@bloomberg.net

To contact the editor responsible for this story: Phil Serafino at pserafino@bloomberg.net

DNAWellnessinfo.com Resource:  http://www.businessweek.com/news/2010-04-14/dna-swap-between-eggs-may-curb-inherited-disorders-study-finds.html

Key protein aids in DNA repair

April 11, 2010- physorg.com

Scientists have shown in multiple contexts that DNA damage over our lifetimes is a key mechanism behind the development of cancer and other age-related diseases. Not everyone gets these diseases, because the body has multiple mechanisms for repairing the damage caused to DNA by aging, the environment and other human behaviors – but the mechanisms behind certain kinds of DNA repair have not been well-understood.

In a paper published today in the journal Nature, researchers at the University of North Carolina at Chapel Hill’s Lineberger Comprehensive Cancer Center have shown that a particular protein – called Ku – is particularly adept at healing damaged strands of DNA.

According to Dale Ramsden, PhD, associate professor in the department of biochemistry and biophysics and a member of the curriculum in genetics and molecular biology, Ku is a very exciting protein because it employs a unique mechanism to repair a particularly drastic form of DNA damage.

“Damage to DNA in the form of a broken chromosome, or double strand break, can be very difficult to repair – it is not a clean break and areas along the strand may be damaged at the level of the fundamental building blocks of DNA – called nucleotides,” he notes.

Broken chromosomes can be compared to a break in a strand of yarn made up of several different threads or plies. Unless scissors are used to cut the yarn, the strand frays and may break or be damaged at several different places up and down the length of the yarn. These rough ends get “dirty” – making them harder to repair.

Provided by University of North Carolina

DNAWellnessinfo.com Resource:  http://www.physorg.com/news190207556.html

New study of autism reveals a ‘DNA tag’ (methylation) amenable to treatment

scienceblog.com  4/8/10

A new discovery raises hope that autism may be more easily diagnosed and that its effects may be more reversible than previously thought. In a new study appearing online in The FASEB Journal (http://www.fasebj.org), scientists have identified a way to detect the disorder using blood and have discovered that drugs which affect the methylation state (“DNA tagging”) of genes could reverse autism’s effects. This type of drug is already being used in some cancer treatments.

“As the mother of a now 22-year-old son with an autism spectrum disorder, I hope that our studies as well as those of others, will lead to therapies that are designed to address specific deficiencies that are caused by autism, thus improving the lives of affected individuals,” said Valerie W. Hu, Ph.D., one of the researchers involved in the work from the Department of Biochemistry and Molecular Biology at The George Washington University Medical Center in Washington, D.C. “Since autism is very diverse in the array of symptoms present in any given individual, it is first necessary to be able to identify specific deficits in each individual in order to design and then prescribe the best treatment. As an example of this personalized approach to medicine, we identified RORA as one of the genes that was altered specifically in the sub group of autistic individuals who exhibited severe language deficits.”

To make their discovery, Hu and colleagues identified chemical changes in DNA taken from cells of identical twins and sibling pairs, in which only one of the twins or siblings was diagnosed with autism. The researchers then compared genes that showed changes in DNA tagging (methylation) with a list of genes that showed different levels of expression from these same individuals. Then the scientists studied the amount of protein product produced by two genes that appear on both lists in autistic and control regions of the cerebellum and frontal cortex of the brain. They found that both proteins, as predicted by the observed increase in DNA tagging, were reduced in the autistic brain. This suggests that blocking the chemical tagging of these genes may reverse symptoms of the disorder and demonstrates the feasibility of using more easily accessible cells from blood (or other non-brain tissues) for diagnostic screening.

“For far too long, autism research has been side-tracked by the cranky notion that it’s caused by the MMR vaccine,” said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. “Studies like this, which define genetic and epigenetic changes in discrete subgroups of the autism spectrum, offer real hope that effective treatments and accurate diagnosis are closer at hand.”

Receive monthly highlights from The FASEB Journal by e-mail. Sign up at http://www.faseb.org/fjupdate.aspx. The FASEB Journal (http://www.fasebj.org) is published by the Federation of the American Societies for Experimental Biology (FASEB). The journal has been recognized by the Special Libraries Association as one of the top 100 most influential biomedical journals of the past century and is the most cited biology journal worldwide according to the Institute for Scientific Information.

FASEB comprises 23 societies with more than 90,000 members, making it the largest coalition of biomedical research associations in the United States. FASEB enhances the ability of scientists and engineers to improve — through their research — the health, well-being and productivity of all people. FASEB’s mission is to advance health and welfare by promoting progress and education in biological and biomedical sciences through service to our member societies and collaborative advocacy.

Details: AnhThu Nguyen, Tibor A. Rauch, Gerd P. Pfeifer, and Valerie W. Hu. Global methylation profiling of lymphoblastoid cell lines reveals epigenetic contributions to autism spectrum disorders and a novel autism candidate gene, RORA, whose protein product is reduced in autistic brain. FASEB J. doi:10.1096/fj.10-154484 ; http://www.fasebj.org/cgi/content/abstract/fj.10-154484v1

DNAWellnessinfo.com Resource:  http://www.scienceblog.com/cms/new-study-autism-reveals-dna-tag-methylation-amenable-treatment.html

Chronix Study Supports Use of Circulating DNA in Monitoring Disease Status

By a GenomeWeb staff reporter – 4/6/10

NEW YORK (GenomeWeb News) – Chronix Biomedical today announced that a study published in the current online edition of the Journal of Molecular Diagnostics supports the use of the firm’s technology in monitoring the clinical status of chronic disease.

The San Jose, Calif.-based firm said that the study is the first to show that its approach, which identifies disease-specific genetic fingerprints based on circulating DNA released into the bloodstream by damaged and dying cells, can be used for such monitoring purposes.

In the study, researchers used Chronix’s techniques to identify genomic fingerprints in the bloodstream of 28 multiple sclerosis patients known to have relapsing or stable disease. They compared these patients with 50 healthy volunteers.

According to Chronix, the researchers were able to distinguish the MS patients from the healthy volunteers. They also were able to use the circulating DNA fingerprints to differentiate periods of active disease attacks from the stable periods of disease remission characterizing relapsing-remitting MS, which affects about 85 percent of MS patients, the firm said.

“These positive data further validate the premise underlying the Chronix approach, showing that the many genetic anomalies associated with active and stable relapsing-remitting MS can be detected by analyzing DNA fragments circulating in the blood serum,” Mario Clerici, chair of immunology in the Department of Biomedical Sciences and Technologies at the University of Milano in Italy, and a co-author of the study, said in a statement. “The prognostic value achieved in this study supports the ability of this new approach to help manage relapsing-remitting multiple sclerosis, potentially offering clinicians a new tool to easily assess which MS treatment options are most effective for their patients, as well as providing critical information that will facilitate development of the next generation of MS therapeutics.”

The firm noted that Clerici is a member of the Chronix Medical Advisory Board and has an equity position in the company.

Chronix also is conducting studies on its approach for cancer diagnostics. The firm said that it intends to offer its serum DNA-based assays in a CLIA laboratory setting.

DNAWellnessinfo.com Resource:  http://www.genomeweb.com/dxpgx/chronix-study-supports-use-circulating-dna-monitoring-disease-status

Vital cues for cancer prevention through DNA repairing gene

Naveen Kumar, TNN, Mar 6, 2010, 10.23pm IST

VARANASI: Now, the study of DNA repairing gene using single nucleotide polymorphism (SNP) marker would provide vital cue for cancer prevention, especially neck and head that comprises of as many as seven different types of cancer in the facial region. In addition, the study would also enable early prediction of much feared breast cancer in women.

While a team of scientists is studying the genomics in cancer, especially the squamous cell carcinoma in neck, head and breast region under the Hap Map project, the case studies in the last five years have revealed interesting contribution of DNA repairing genes including P53 associated genes, where SNP can be used as a marker for prompt diagnostic purpose.

Senior scientist Central Drug Research Institute Lucknow Dr SK Rath told TOI on Saturday, “The studies have shown that P53 associated genes play a vital role in DNA repair and act as tumour suppressor. It changes the DNA repair scene and plays pivotal role in protection against mutagenic and cytotoxic effects of DNA damage that also prevents cancer.” Similarly, SNP could also provide vital cue for DNA repairing in BRAC 1 and 2 genes that are believed to cause breast cancer in women, he added.

It is to be mentioned here that Dr Rath is a key member of the team that studied genotype of cancerous and non-cancerous cells under the project in the Xth five-year plan. Now, the team is researching on SNP of different people including smokers and non-smokers, drinkers and non-drinkers, where the cause of cancer

could not be ascertained.

Saying that million of SNPs exist in human genome that occur in gene within the regulatory region, Dr Rath emphasised that the method detects the most common type of variation in the genome, as it cater to small alteration, providing better scope for prediction. The SNP markers are preferred for population genomic disease association and are good indicators of squamous cell carcinoma in neck and head region that includes cancers of oral cavity, pharynx, nasopharynx, oropharynx, hypopharynx and tongue, he added.

Stressing that cancers of neck and head region are growing at alarming rate in states like UP, he said the case studies in Lucknow revealed that out of 100 cancer patients, the number of patients with cancer in the neck and head region increased from 30 to 49 (150 per cent increase) in the last five years. Worldwide, it is the fifth most common type of cancer affecting over one million population annually, he concluded.

DNAWellnessinfo.com Resource:  http://timesofindia.indiatimes.com/city/varanasi/-Vital-cues-for-cancer-prevention-through-DNA-repairing-gene/articleshow/5648729.cms

A First: Diagnosis By DNA

Matthew Herper, 02.25.10, 11:20 AM EST
Forbes Magazine dated March 15, 2010

Last year a five-month-old boy in Turkey stopped gaining weight and became dehydrated despite getting plenty of liquids. Specialists in Istanbul suspected Bartter’s syndrome, a potentially fatal kidney disorder that afflicts one in 100,000 babies, causing dangerously low levels of potassium and salt.

To confirm their hunch they sent a blood sample to Yale Medical School geneticist Richard Lifton. They asked him to determine whether the baby had the gene defect implicated in Bartter’s. But Lifton thought that Bartter’s might not be the culprit. So he did something that would have been prohibitively expensive a few years ago. He deciphered the DNA letters for all the baby’s genes. The gene scan revealed that the baby’s problem was not Bartter’s but something else called congenital chloride diarrhea, which also lowers salt levels. The result means that the baby, now doing better on a special diet, could be treated with drugs if his condition gets worse.

The case, published in the Proceedings of the National Academies of the Sciences in October, may be the first in which the results of DNA sequencing have altered treatment of a patient. Does this herald the beginning of a new kind of medicine in which patients with unexplained symptoms get their DNA sequenced? Yes, says Lifton: “This will be a court of last resort to try and identify causes of disease.”

Gene researchers have talked for years about how sequencing will transform medicine. Now that sequencing is cheap this transformation is under way. The cost of deciphering all 6 billion letters in the human genome has dropped from $1 million in 2007 to less than $20,000 today. Lifton used a two-step method to extract and sequence only the 1% of those letters that contain known genes, lowering the price to $2,500. New DNA sequencers just introduced by Illumina ( ILMN – news – people ) (whose model Lifton used) and Life Technologies ( LIFE – news – people ) could lower the cost of sequencing a whole genome to below $3,000 by year-end.

DNA sequencers haven’t been approved for use in medical testing, and insurers don’t pay for sequencing. But peering into DNA is becoming an option for wealthy patients with rare and scary diseases. Knome, a privately held company in Cambridge, Mass., started out in 2008 charging $350,000 to arrange sequencing and interpret the data for wealthy patrons as a vanity project. Now it offers the scans for as little as $25,000. Chief Executive Jorge Conde says several patients hoping to improve their care are among his customers.

The $600 million annual market for DNA sequencers is still all about research, with Illumina holding a 60% market share. But numerous companies are already jockeying for position in anticipation of a big future medical-test market.

Cancer patients may be among the first to benefit from DNA sequencing technology. In one early example of how this may work, Marco Marra, a researcher at the Michael Smith Genome Sciences Centre in Vancouver, last year sequenced the genes from a tumor that had spread from an 80-year-old patient’s tongue to his lungs. There is no standard therapy for this type of tumor. But the gene scan found the tumor was making large amounts of a growth-promoting protein called RET. When the patient’s medicine was switched to Pfizer ( PFE – news – people )’s Sutent, a drug that blocks this protein, the tumor shrank, according to a report in Nature.

A looming question is how the Food & Drug Administration will regulate sequencing technology. It could treat DNA sequencing like genetic tests and require separate approvals for each use. Some equipment makers hope for a faster path in which doctors practicing a new medical specialty emerge to evaluate and interpret gene scans, as radiologists do with X-rays. Clifford Reid, chief executive of Complete Genomics, which has finished 50 genomes, is skeptical that it will be that easy. “The FDA has been very quiet up until now,” he says. “We all have to expect the FDA to be intimately involved with these new tests.”

DNAWellnessinfo.com Resource:  http://www.forbes.com/forbes/2010/0315/health-illumina-genome-cancer-diagnosis-by-dna.html

Scientists develop universal DNA reader to advance faster, cheaper sequencing efforts

2/11/10 – physorg.com

Led by ASU Regents’ Professor Stuart Lindsay, director of the Biodesign Institute’s Center for Single Molecule Biophysics, the ASU team is one of a handful that has received stimulus funds for a National Human Genome Research Initiative, part of the National Institutes of Health, to make DNA genome sequencing as widespread as a routine medical checkup.

The broad goal of this “$1000 genome” initiative is to develop a next-generation DNA sequencing technology to usher in the age of personalized medicine, where knowledge of an individual’s complete, 3 billion-long code of DNA information, or genome, will allow for a more tailored approach to disease diagnosis and treatment. With current technologies taking almost a year to complete at a cost of several hundreds of thousands of dollars, less than 20 individuals on the planet have had their whole genomes sequenced to date.

To make their research dream a reality, Lindsay’s team has envisioned building a tiny, nanoscale DNA reader that could work like a supermarket checkout scanner, distinguishing between the four chemical letters of the DNA genetic code, abbreviated by A, G, C, and T, as they rapidly pass by the reader.

To do so, they needed to develop the nanotechnology equivalent of threading the eye of a needle. In this case, the DNA would be the thread that could be recognized as it moved past the reader ‘eye.’ During the past few years, Lindsay’s team has made steady progress, and first demonstrated the ability to read individual DNA sequences in 2008—but this approach was limited because they had to use four separate readers to recognize each of the DNA bases. More recently, they demonstrated the ability to thread DNA sequences through the narrow hole of a fundamental building block of nanotechnology, the carbon nanotube.

Lindsay’s team relies on the eyes of nanotechnology, scanning tunneling- (STM) and atomic force- (ATM) microscopes, to make their measurements. The microscopes have a delicate electrode tip that is held very close to the DNA sample.

In their latest innovation, Lindsay’s team made two electrodes, one on the end of microscope probe, and another on the surface, that had their tiny ends chemically modified to attract and catch the DNA between a gap like a pair of chemical tweezers. The gap between these functionalized electrodes had to be adjusted to find the chemical bonding sweet spot, so that when a single chemical base of DNA passed through a tiny, 2.5 nanometer gap between two gold electrodes, it momentarily sticks to the electrodes and a small increase in the current is detected. Any smaller, and the molecules would be able to bind in many configurations, confusing the readout, any bigger and smaller bases would not be detected.

“What we did was to narrow the number of types of bound configurations to just one per DNA base,” said Lindsay. “The beauty of the approach is that all the four bases just fit the 2.5 nanometer gap, so it is one size fits all, but only just so!”

At this scale, which is just a few atomic diameters wide, quantum phenomena are at play where the electrons can actually leak from one electrode to the other, tunneling through the DNA bases in the process.

Each of the chemical bases of the DNA genetic code, abbreviated A, C, T or G, gives a unique electrical signature as they pass between the gap in the electrodes. By trial and error, and a bit of serendipity, they discovered that just a single chemical modification to both electrodes could distinguish between all 4 DNA bases.

“We’ve now made a generic DNA sequence reader and are the first group to report the detection of all 4 DNA bases in one tunnel gap,” said Lindsay. “Also, the control experiments show that there is a certain (poor) level of discrimination with even bare electrodes (the control experiments) and this is in itself, a first too.”

“We were quite surprised about binding to bare electrodes because, like many physicists, we had always assumed that the bases would just tumble through. But actually, any surface chemist will tell you that the bases have weak chemical interactions with metal surfaces.”

Next, Lindsay’s group is hard at work trying to adapt the reader to work in water-based solutions, a critically practical step for DNA sequencing applications. Also, the team would like to combine the reader capabilities with the carbon nanotube technology to work on reading short stretches of DNA.

More information: The Nano Letters research article can be accessed online at URL: http://pubs.acs.org/doi/pdfplus/10.1021/nl1001185

Provided by Arizona State University (news : web)

DNAWellnessinfo.com Resource:  http://www.physorg.com/news185129971.html

A new theory of how low doses of antibioitics create antibiotic resistance

Feb 11, 2010 – usatoday.com

E.coli bacteria is seen under a microscope.

CAPTION

By Centers for Disease Control

Exposure to low levels of antibiotics increases mutations in E. coli and Staphylococcus bacteria hundreds of time more than normal, making the creation of drug-resistance strains more likely, says a paper in today’s edition of the journal Molecular Cell.

This finding adds to concerns about antibiotic resistance brought on by poor prescriptions practices among doctors, patients who don’t take all their medicine and even low doses of antibiotics given to help animals grow faster.

The researchers found that while low levels of antibiotics may not be enough to kill off the bacteria, they still stress them. That stress causes them to produce free radicals, says James Collins, a biomedical engineer at Boston University and one of the paper’s authors.

Those free radicals are produced by oxidation, a process that’s known to damage cells. In the case of bacteria, the free radicals damage the bacteria’s DNA, causing some of the affected bugs to mutate.

Two and a half years ago Collins’ group began looking at how bacteria respond to antibiotics. It was then that they discovered that antibiotics can stimulate the pathways that create free radicals in bacteria.

A year ago they started considering what other implications their discovery might have.

“We wondered whether sub-lethal levels still produce free radicals. We know the cells wouldn’t die, but we know that free radicals can damage DNA, and that increases mutenigenesis,” he says.

And that’s exactly what they found. Basically, if the antibiotic dose isn’t high enough to kill every bacteria in sight, “you could be creating a zoo with a wide range of mutations,” he says.

The  finding is important “within the context of our understanding — or lack of understanding — of how bacteria become resistant to antibiotics,” says Deborah Hung, a molecular biologist at Massachusetts General Hospital, who wrote an accompanying Perspective piece on the article.

The  truth is that no one really knows exactly how bacteria become resistant to antibiotics, says Hung. So knowing that low levels of antibiotics might potentially increase the random chance that bacteria might mutate into resistant forms could have important implications for medicine.

By Elizabeth Weise

DNAWellnessinfo.com Resource:  http://content.usatoday.com/communities/sciencefair/post/2010/02/a-new-theory-of-how-low-doses-of-antibioitics-create-antibiotic-resistance/1

Living fast? Scientists show lifespan is linked to DNA

Ian Sample, science correspondent
guardian.co.uk, Sunday 7 February 2010 19.55 GMT

Scientists have isolated a gene sequence that appears to determine how fast our bodies age, the first time a link between DNA and human lifespan has been found.

The discovery could have a profound impact on public health and raises the best hope yet for drugs that prevent the biological wear and tear behind common age-related conditions such as heart disease and certain cancers.

The work is expected to pave the way for screening programmes to spot people who are likely to age fast and be more susceptible to heart problems and other conditions early in life. People who test positive for the gene variant in their 20s could be put on cholesterol-lowering statin drugs and encouraged to exercise, eat healthily and avoid smoking.

The breakthrough is unlikely to lead to drugs that dramatically extend lifespan, but doctors say it may help prolong the lives of patients whose genes make them susceptible to dying young.

The research gives the kind of insight into the biology of ageing that has not emerged from work on other strategies that claim to extend lifespan, such as consuming vast quantities of antioxidants or pursuing a severely calorie-restricted diet.

“This may help us identify patients who are at a greater risk of developing common age-related diseases so we can focus more attention on them,” said Professor Nilesh Samani, a cardiologist at the University of Leicester, who led the research.

The research highlights the difference between chronological age and biological age, the latter of which is determined by our genetic makeup and lifestyle factors, such as diet and smoking. Two people of the same age can have biological ages that differ by more than 10 years.

A team led by Samani and Professor Tim Spector at King’s College, London found a common sequence of DNA was strongly linked to a person’s biological age. In a study of nearly 3,000 people, around 38% inherited one copy of the gene variant and were biologically three to four years older than those who did not carry the sequence.

A minority of 7% inherited two copies of the DNA sequence and were on average six to seven biological years older. The majority of the population, 55%, do not carry any copies of the variant.

The study, published in the journal Nature Genetics, was prompted by the huge variability in the age at which people develop medical problems that are often considered diseases of the elderly.

“I see patients in their 80s with high blood pressure who have healthy coronary arteries and I see people in their 40s who don’t seem to have any risk factors yet have advanced heart disease,” Samani said. “We think this kind of variability must have something to do with premature ageing.”

Most of the cells in our bodies contain long molecules of DNA called chromosomes that have protective caps at either end called telomeres. Every time a cell divides, the telomeres shorten, like plastic tips fraying on a shoelace. When the telomeres become very short, the cell starts to malfunction and show signs of ageing.

From blood samples, Samani and Spector found a particular gene sequence was more common in people who had unusually short telomeres for their age. The section of DNA was found on chromosome three, next to a gene called TERC, which makes an enzyme that repairs telomeres when they shorten.

People who carry one or two copies of the genetic sequence probably make less of the enzyme, called telomerase, when they are growing in the womb. This means they are born with shorter telomeres, and so are prone to ageing more quickly.

“The effect may be built in at a very early stage in life. If you’re born with shorter telomeres, there’s evidence you will be prone to heart disease and other age-related diseases,” Samani said.

Scientists are unlikely to reverse the ageing process by boosting telomerase in people’s bodies. Telomerase is almost completely deactivated after birth, but is switched back on in cancer cells so they can divide endlessly without dying. “Introducing telomerase might protect you from heart disease, but if you turn it on willy nilly you could cause cancer instead,” Samani said.

DNAWellnessinfo.com Resource:  http://www.guardian.co.uk/science/2010/feb/07/ageing-genetics