LOS ANGELES — Researchers have found more than 15 million places in the human genome where the genetic code differs from person to person, providing a catalog of hotspots for genetic change that should speed the search for genetic causes of such complex disorders as diabetes, Alzheimer’s and heart disease.
Only 10 years after scientists laboriously unraveled the first sequence of a human genome, an international team said Wednesday they have sequenced the bulk of the genomes from more than 800 people in the pilot stage of the so-called 1000 Genomes Project that aims to complete 2,500 sequences by the end of 2012 at a cost of $120 million.
More than 99 percent of the human genome is identical in all of the Earth’s nearly 7 billion inhabitants; it is in that minuscule 1 percent left over that individual physical characteristics, such as eye color, height, and disease propensity lie hidden. The research team reported that it has now identified 95 percent of the individual places in the genome where such information is stored and is well on their way to discovering all of them.
The key to this progress is the development of powerful new DNA-sequencing machines that enable researchers to accomplish in hours feats that used to require months or even years at a fraction of the cost.
“In the last 10 years, DNA sequencing technology has advanced dramatically so that it becomes feasible to systematically sequence many people to find genetic variants and build a catalog which we can use as a basis for investigations into disease genetics and which variants may be functional,” Dr. Richard Durbin of the Wellcome Trust Sanger Institute in England, co-chair of the project, said at a news conference.
The human genetic blueprint, or genome, is composed of an estimated 20,000 to 25,000 genes encoded in a chain of about 3.1 billion individual chemicals called bases. The initial effort to decode, or sequence, the genome of one individual took more than 10 years and cost more than $3 billion.
But researchers reported Wednesday in the journal Nature that their pilot project now includes the entire genomes of 179 people of European, West African and East Asian ancestry as well as the gene-coding regions of another 697 people. The resulting information on more than 4.5 trillion bases of DNA sequences is enough to fill 400,000 books the size of the New York City telephone directory.
The results so far have produced a number of surprises.
Among the individuals whose genomes were fully sequenced were two families of father, mother and daughter. The team found that each daughter had about 60 genetic variants that were not inherited from either parent and apparently arose on their own.
The team also discovered that, on average, each person carries between 250 and 300 genetic changes that would cause a gene to stop working normally, and about 50 to 100 genetic variations that have already been associated with an inherited disease. No person carries a perfect set of genes — the fact that everyone has two copies of each gene prevents most of those variations from being problems.
The complete list of genetic variants will give researchers powerful new tools not only for discovering the genetic roots of diseases but for identifying mutations in tumors and other disorders such as heart disease that will respond to specific drugs, theoretically opening a new era of targeted treatments, the researchers said.
In a separate study released online Wednesday by the journal Science, geneticist Evan Eichler of the University of Washington and his colleagues reported that they had found a way to identify multiple copies of genes, a feat which is not achievable by conventional sequencing.
They found that the presence of multiple copies of some genes may be associated with an increased tendency to develop certain diseases. The accumulation of extra copies of genes associated with brain development may have helped humans evolved from lower primates, they found.
Talk to us
> Give us your news tips.
> Send us a letter to the editor.
> More Herald contact information.
