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February 10, 2001

Now that scientists are beginning to study the intricacies of the human genome, they’re finding out how similar we are to one another. But analyzing the genome to pinpoint our tiny genetic differences may lead to new ways of treating disease. In this week’s Nature magazine, researchers report that for the first time, they will have all the genes in the genome that could be involved in common diseases, like diabetes and high blood pressure. The genome is yielding its secrets faster than scientists had hoped, and some experts are even predicting an era where the cure is as individual as the patients.

Picking up the pace

Six year old Theo Emms lacks just one gene, but because of it, he can’t walk properly. Theo has a genetic disease called Spinal Muscular Atrophy (SMA), where the cells in his spinal cord can’t produce a protein needed to make his motor neurons function properly. But researchers hope that studying the genome will lead to a cure that will help Theo to walk someday.

"We will be able to develop treatment more quickly. So those taking 20 years, they’ll now take five years to disprove or prove that they will work and that now brings that into the realm of the lifetime of the child, particularly in SMA, for example," says Kay Davies, professor and head of human anatomy and genetics at the University of Oxford.

Thanks to the free availability of the human genome information on the web, researchers are unraveling genetic links to disease more quickly than they could have imagined. "I keep track of the disease genes that have been found because of the rapid accumulation over the last year of this sequence of the genome in public databases, where anybody who wants to see it can go and look, and the number is now well over the dozens. It just keeps piling up of new genes that are discovered," says Francis Collins, director of the National Human Genome Research Institute.

More than one gene

Man having blood pressure taken

Theo has a simple genetic disease caused by just one defective gene, but scientists are on the verge of understanding even complex genetic diseases, which involve several genes. These are diseases like diabetes, heart disease, high blood pressure, and even cancer.

Dr. David Altshuler, a research scientist at the Whitehead Center for Genome Research says that right now, he can’t tell his patients why they have diseases like diabetes. "I believe that in my lifetime…we’ll be able to know the answer to that and to tell them why it happened, but more importantly, begin to diagnose it before it actually causes problems."

Researchers believe the key to finding genes connected with disease is the fact that our genomes are 99.9 percent identical. We are more similar to one another than most species on the planet, including fruit flies and chimpanzees. That means that if you were to take any two people at random from the world’s population and sequence their genomes, 999 out of 1,000 letters would be identical. "It’s not that a letter’s missing, it’s not that a letter is added or 10 letters are changed, it’s just one letter that’s different," says Altshuler.

These one-letter differences are known as SNPs, or single nucleotide polymorphisms. "SNPs make up about 90 percent of the genetic difference between any two people whose genomes are compared," says Altshuler. Scientists have already found around half of the three to four million SNPs in the human population. The public Human Genome Project’s report is published in this week’s issue of Nature magazine, while the commercial group’s results, lead by Celera Genomics, are in this week’s Science magazine.

Most of the time, the tiny differences between our genomes are unique and harmless. But sometimes they can be linked to disease. If a lot of people have the same difference at a certain spot in their genomes — say a C instead of a G — it might help disease geneticists design a test where they can analyze how many patients with a particular disease have that same variation, says Altshuler. He says that by tracking such variations, we might be able to build a sort of encyclopedia of information about which genes track with which diseases.

Many people on street

"I believe in a decade, all of us will have the opportunity to learn our own risks of future illness based on looking at our DNA sequence," says Collins. "In instances where there’s something you can do to reduce that risk by medical surveillance or lifestyle or diet, that’s pretty exciting, that’s preventive medicine."

Collins says that studying the genome will transform the way medicine is practiced. "Most of our therapies these days were derived rather empirically," he explains. "You just tried something and some of them worked and most of them didn’t. We can move beyond that now to an approach that’s based on really understanding how things work and how things don’t work when a disease arises, and the therapy, instead of being plucked out of the air, will be designed."

Some experts believe that this will lead to cures being customized for each patient. "What this is going to lead to is a whole new era of medicine," says Michael Dexter, director of the Wellcome Trust. "It’s truly individualized medicine, where we’ll be treating you as an individual, for the right disease, with the right medicine, at the right dose, at the right time."

As for the pace of genome research, Altshuler thinks it will continue to race ahead in the coming years. He says that in our lifetimes, the vast database of information will lead us to understand at a much deeper and fundamental level most of the common diseases of man.

by Jill Max

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