se qualcuno vuole farci una news...io sono un po impicciato oggi
************************* da biomednet Denver, Colorado - Just one in a thousand DNA base pairs vary between any two humans. "We have essentially the same genomes," said David Altshuler, who directs the program in medical and population genetics at the Whitehead Institute/Massachusetts Institute of Technology (MIT) Center for Genome Research. "Heterozygosity is relatively limited and largely attributable to common variation," said Altshuler, who was speaking at the annual meeting of the American Academy for the Advancement of Science (AAAS), here. But there's a problem. "If we exaggerate the similarities, we may come to conclusions about disease that will only apply to part of the population," argued Rosenberg, of the University of Southern California. "People are more similar than different, but the differences matter." Those genetic differences may not be numerous, yet they intrigue biomedical researchers who are betting that studying human variation will help them at last figure out the causes of many diseases, learn how to treat them truly effectively, and perhaps even prevent them. But genetic differences are also a political and social minefield. Mindful of the appalling uses to which racial and ethnic categories have been put throughout human history, researchers are struggling with how to define those concepts in ways that will yield the data they want without fostering racism and worse. How should racial and ethnic categories be used to describe research populations, if at all? Does genetic research require the use of these categories? If not, what are the alternatives? Mildred Cho, a bioethicist at Stanford University, posed such questions at an AAAS session she had organized on the implications of human variation studies. Some 90% of human genetic variation originated in the human ancestral population in Africa as long as 400,000 years ago. About 10% is more recent, arising in the last several thousand years during migrations that took the human species around the globe. The question of whether the old or the new variations have more impact on disease is a very hot topic, said Altshuler. He argues that the older ancestral variations are more important, although other researchers focus on recent variations. Another debate centers on how much disease is related to variant proteins resulting from gene regulation by repressors and promoters. This is hard to investigate with rigor, Altshuler notes. A few recent studies have tried to quantify the impact of regulatory activities, and the answer appears to be that a minority of genes vary in their regulation. "How many of these matter is an unanswered question," he said. Rosenberg was first author on a controversial paper published last December in Science that used 377 widely spaced microsatellite loci to cluster 1056 subjects from 52 populations into six main groups. Despite the fact that genetic differences between the groups constituted at most 5% of total variation, five of the six groups corresponded to major geographic regions, subclusters often corresponded to individual populations, and the study subjects' self-reports of their own ancestry often agreed with the microsatellite data. "People have interpreted our study in two ways, as supporting racial categories or as not supporting them," Rosenberg told delegates. "In my view it's almost irrelevant because race is a social category." The groups differed only at small frequencies. Historically, investigators have looked for markers that really distinguish between races, but that approach will work only for a handful of traits that govern physical appearance, he notes. Cho pointed out that racial classifications can be used positively - for example to identify racial disparities in health care and attempt to remedy them. Even academic disciplines use the idea in different ways, she says. Forensic anthropologists want to find genes that will identify ethnicity, but social anthropologists hold that the idea of "race" was discarded decades ago. Whether the categories are real depends on the question being asked, Altshuler argues. For one person's question the right answer might be that there are no biological differences between groups. But the answer would be different for someone trying to track the recent history of human migration. "Is there any biological meaning or correlation to traditional racial categories? The genetic answer is 'yes'. And if you measure that small amount, you can answer some questions," concluded Altshuler. -- ************************************************* * Fabio Sterpone * * e-mail:[EMAIL PROTECTED] * * Adress:DBCM/DSV/CEA Centre d'Etudes Saclay, * * 91191 Gif-sur-Yvette Cedex, France * * Tel: +33-1-69084006 * * Fax: +33-1-69089275 * ************************************************* _______________________________________________ www.e-laser.org [EMAIL PROTECTED]
