CHICAGO – Using a newly discovered key to secrets of the genetic code, an international team of more than 200 scientists reported Wednesday that they are on the threshold of finding the genetic variations that make one person different than another, and what in their makeup makes them prone to a particular illness.

Researchers expect that for the first time they will have the power to pinpoint the elusive genetic basis of disease – why some people get sick while others don’t – and why some people are more susceptible to environmental toxins than others, they reported in the British journal Nature.

Their findings are expected to lead to new ways of preventing, treating and curing diseases, they said, though the scientists cautioned it may take a long time before any treatments become available. The new knowledge could also help drug makers achieve their long-sought goal of personalizing medications to avoid genetic reactions, such as allergies.

In the Nature article, scientists unveiled the first edition of a huge catalog of genetic variations that influence such things as height, hair color and susceptibility to disease, primarily in combination with lifestyle and environmental factors.

There are an estimated 10 million of these variations in all. The team cataloged 1 million in the journal, and at a meeting Wednesday in Salt Lake City researchers revealed another 2.5 million.

The variations, called “snips” for single nucleotide polymorphisms or SNPs, make up only about 0.1 percent of the 3 billion nucleic acid units that go into building the approximately 20,000 human genes. Otherwise, any person on Earth is 99.9 percent genetically identical to any other unrelated person.

The breakthrough in deciphering the variations came when scientists from Harvard, McGill University and the University of Montreal accidentally discovered in 2001 that snips tend to be inherited in small pieces or blocks of chromosomes, called haplotypes. In other words, when one variation in a block is found, the others are often present.

In a three-year, $138 million project, scientists from six countries genetically analyzed blood samples of 269 individuals from Africa, Asia and the United States, which represented the European population.

The resulting catalog – called the “HapMap” – identifies the variations, where they occur in our genes and how they are distributed among people within populations and among populations in different parts of the world.

“The power of the modern genomic tool-kit is breathtaking,” Duke University’s David B. Goldstein and Gianpiero L. Cavalleri wrote in a commentary in Nature. “In a few years we have gone from knowing almost nothing … (to) a nearly complete catalog of the common genetic differences among people.”

The map is an offshoot of the human genome project, which sequenced all 3 billion chemical units of the genetic code. Deciphering the human genome was completed in 2003, though it is still being refined.

“The human genome sequence provided us with the list of many of the parts to make a human,” said team member Peter Donnelly of the University of Oxford. “The HapMap provides us with indicators – like Post-it notes – which we can focus on in looking for genes involved in common disease.”

Dr. Francis Collins, director of the Human Genome Research Institute, praised the work in a news conference at the Salt Lake meeting.

“Since the early deliberation about the genome project 20 years ago I have dreamed of the day when we would be able to apply the tools of genomics to the diagnosis, treatment and prevention of those common diseases that fill up our hospitals, clinics and doctors offices,” he said. “Today’s HapMap announcement brings us a major step closer to the realization of that dream.”

For most diseases the basic knowledge of where they come from, and the biological processes that set them in motion, is a complete mystery. Among them are heart disease, cancer, high blood pressure, asthma, diabetes and neurological disorders, which are triggered by complex sets of genes acting together.

“Taking that first step in unlocking the genetics – the root causes of these diseases – could have a profound impact on our understanding of where the diseases come from and our ability to develop treatments for them,” said Harvard geneticist Mark Daly, a member of the research team.

“More often than not, recognizing the genetic causes is simply the first step and it’s going to be a very long haul to turning that into treatments, preventives and cures,” he said. “But it’s a necessary first step because without it we certainly aren’t making progress against a lot of diseases.”

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