Map of human gene variations is unveiled

WASHINGTON — In a major step toward one day offering gene-based customized medicine, scientists on Thursday unveiled the first map of common human genetic variations — patterns of DNA differences that may help forecast people's disease risks and best treatments.

This map, created by California-based Perlegen Sciences Inc., is essentially the first chapter in the quest to identify tiny bits of genetic information, known as SNPs or "snips," believed key in creating gene-based medicine. A more detailed version is expected later this year.

"It is a dramatic advance," said Barbara Jasny, a senior editor at the journal Science, which published the research Thursday. The study also was presented at a meeting of the American Association for the Advancement of Science.

Public health experts view it "with a lot of excitement," agreed Lawrence Lesko, who heads the Food and Drug Administration's division of gene-based medicine.

Even unrelated people share DNA that is 99.9 percent similar. Variations in that last remaining bit are what make us individual, determining traits from our hair color to our risk of different diseases.

Until now, most genetics breakthroughs have come when a mutation in a single gene causes illness. But the most common health problems, such as heart disease, diabetes or depression, are caused by complex interactions between numerous genes and environmental or behavioral risks. Teasing out the genetic culprits under such conditions has been almost impossible.

Enter SNPs, single-nucleotide polymorphisms. DNA is made up of precise orders of chemicals identified with the letters A, T, C or G. SNPs are the most common type of genetic variation, sort of a spelling error — one of those letters gets out of order.

Even that tiny a difference may have profound effects.

Consider Lesko's example: Only a fraction of smokers get lung cancer, and only about 10 percent of those patients respond to lung-cancer therapy — but no one knows why, or can predict who will be the unlucky.

SNPs may hold some of those answers. The SNP map, Lesko said, gives scientists a way to study such questions and design better drug treatment.

Perlegen scientists examined the DNA of 71 Americans of European, African or Chinese ancestry, and identified 1.58 million SNPs — most of them shared across the three populations.

They're a fraction of the estimated 10 million SNPs thought to exist. But they appear to be the most common ones, said lead researcher David R. Cox.