Scientists publish map of human variety

US researchers have published a detailed map of key variations in our genetic make-up, information they say will help pinpoint genes involved in many common diseases. The team, based at Californian firm Perlegen Sciences, has identified and studied 1.58 million genetic 'markers' in 71 people from three different populations. The study was presented at the annual meeting of the American Association for the Advancement of Science last week, and is published in the journal Science.

Human Genome Project scientists unveiled the final version of the entire human genetic code in April 2003. However, to understand the role of genetic factors in illnesses such as heart disease, diabetes and depression, researchers need to look for different versions of human genes. To help them do this, Perlegen and others have been studying SNPs (single nucleotide polymorphisms). A SNP is a single chemical unit (base pair) variation in a stretch of DNA. Human DNA is estimated to vary one in every 1000 base pairs between any two people. As well as their role in health and disease, SNPs also influence an individual's response to different medicines.

The scientists looked at DNA from 71 Americans of either European, African or Chinese ancestry, and identified 1.58 million SNPS. Although they represent just some of the estimated 10 million SNPS thought to exist, they appear to be the most common, according to team lead David Cox. He said the goal of the research was 'to be able to use genetic information in a practical way...while I'm still alive'. Perlegen is making its results freely available for other scientists to use.

Another map of human variation is due to be published later this year, by the international HapMap consortium. This project has looked at more than one million SNPs in 270 people from around the world. The HapMap scientists are looking at SNPs that have been inherited together in a block over many generations, indicating that they are physically close to each other. To identify these 'haplotype blocks', researchers will study people originating from China, Nigeria, Japan and the US. Between them, these populations are thought to represent the majority of human genetic variation.