Scientists near breakthrough in predicting illness based on DNA

PHILADELPHIA – We are all 99.9 percent genetically identical, but scientists are rapidly mapping out that critical .1 percent that makes us different. On Wednesday, an international consortium announced it had isolated a million spots on the human genome that tend to vary from person to person – the first phase of a project called HapMap.

The project promises to predict who is more likely to suffer from common diseases such as diabetes, arthritis, heart disease and some cancers. Eventually, the knowledge gained from HapMap could lead to new therapies that better target the root causes of these illnesses.

The findings also offer insights into how human beings evolved over the last 100,000 years and add to the body of evidence suggesting there’s little biological difference between so-called races.

Genetic information is carried in long strands of DNA that string together four chemical bases, serving as letters in a four-character alphabet. Each person carries a sequence of 3 billion of these in each cell, chopped up into 23 pairs of chromosomes in each.

These sequences look almost identical from person to person, but differences occur at about 10 million specific places. Scientists call these places single nucleotide polymorphisms, or SNPs, because they amount to a single letter in the code.

SNPs are not spelling errors, per se, but spelling variants. There is no standard, correct human genetic sequence any more than there’s a normal body type or eye color.

In a press conference, researchers said they’d completed the first phase of their project by mapping the first million of these SNPs, and had already made headway into the second phase, which will find several million more.

The scientists consider HapMap an intermediate step between the Human Genome Project, completed several years ago, and the use of that information to improve human health.

The genome project took DNA from just a small handful of people and read out their entire 3 billion letter codes. It didn’t say much about how we differ from one another or how those differences predispose us to different illnesses.

That’s the job of HapMap, carried out by an international consortium for about $160 million. The scientists collected DNA from 269 people from four countries – the United States, Nigeria, China and Japan.

Because the researchers released their data as it was collected, other scientists have already begun to use it, said Stacy Gabriel, one of the project scientists from the Broad Institute, in Cambridge, Mass.

“It’s already been used to study a form of blindness called macular degeneration,” she said. Researchers at Yale have found a variant that puts people at risk, though there’s no cure.