Mapping the human genome

Scientists have completed the first catalogue of common genetic differences between four of the world's ethnic groups.

The Haplotype Map marks a historic step toward the era of customized health care -- in which treatments could be tailor made to a patient's gene type.

Using the DNA of 269 people from China, Japan, Nigeria and the U.S., the project has essentially compiled a new map of the human genome.

This one organizes the book of life encoded in human DNA into paragraphs -- known as haplotypes -- that make it exponentially easier to spot genetic mutations.

For example, the Hap Map has discovered nearly four million mutations and of those, roughly 100 appear in extreme frequency in one group more than another, such as with the lactase gene type of Europeans that allows the lifetime digestion of dairy products, and the mutation that protects sub-Saharan Africans from malaria.

"This helps us to see which genes mattered to the evolution of our species," said Harvard Medical School's David Altshuler, lead author of the Hap Map report also published today in the journal Nature.

In 2001, researchers at the University of Toronto and the Massachusetts Institute of Technology were working on a bowel disease study with 200 Ontario families and discovered the whole genome seems to be arranged in this same block pattern -- like paragraphs in a text.

It seems parents pass down their chromosomes to children in these particular chunks. As well, genetic mutations seem to turn up in the same places in those chunks -- even in different families -- like a library where every book has a typo in the first paragraph of its third page.

In October of 2002, researchers launched the Hap Map that, like an index, would catalogue these blocks and their common mutations in diverse ethnic groups to ensure the haplotype pattern applied broadly.

This way, scientists would no longer have to scan a whole book for a typo, but simply flip to a specific page.

The result is leading to large-scale genetic studies never before possible.

In Canada, researchers are studying 2,500 Ontario residents in the world's largest hunt for genes that increase the risk of colon cancer.

In Britain, thousands of patients are being enrolled in gene studies of eight common conditions -- including heart disease.

A U.S. group has already relied on the Hap Map, which has been uploaded to the Internet as the data came available, to find the gene mutation that increases the risk of macular degeneration, the leading cause of vision loss in the elderly.