A COMPREHENSIVE chart of the genetic differences between human beings has been drawn up for the first time, promising breakthroughs in the hunt for the genes that influence common diseases such as cancer, asthma and diabetes.

The International Haplotype Map, or HapMap, provides an index to the human genetic code, allowing scientists to identify inherited variations that affect human health with much greater speed and simplicity. This will transform the development of new drugs and diagnostic tests, and could open a new era of bespoke medicine in which patients can be prescribed treatments that correspond best to their individual genetic make-up.

While the Human Genome Project has sequenced the 99.9 per cent of DNA that is shared by every person, the HapMap has started to plot the other 0.1 per cent — the individual idiosyncracies that make people different and often underlie ill health.

“The human genome sequence provided us with the list of many of the parts to make a human,” Peter Donnelly, Professor of Statistical Science at Oxford University and one of the project’s leaders, said.

“The HapMap provides us with indicators — like Post-It notes — which we can focus on in looking for genes involved in common disease. This report describes a remarkable step in our journey to understand human biology and disease.”

Panos Deloukas of the Wellcome Trust Sanger Centre near Cambridge, which conducted much of the work, said: “Humans are genetically 99.9 per cent identical: it is the tiny percentage that is different that holds the key to why some of us are more susceptible to common diseases such as diabetes and hypertension or respond differently to treatment with certain drugs.”

The full first draft of the HapMap is published today in the journal Nature, but the data sets on which it is based have been made available on the internet have already provided important help to genetic researchers. In March, an American team used HapMap data to identify a gene that may trigger up to half the cases of age-related macular degeneration, the most common cause of blindness in the elderly.

The £80million HapMap project, which involves more than 200 scientists drawn from Britain, the US, Canada, China, Japan and Nigeria, has focused on variations in the human code known as single nucleotide polymorphisms or SNPs — pronounced “snips”. Each SNP represents a “spelling mistake” in the genetic code, in which one DNA “letter” is substituted for another.

Although some SNPs do little to change a gene’s function, others are implicated in disease. Each of us has about three million SNPs that differ from others. Some occur randomly, many more are passed on in blocks known as haplotypes, which are more common among populations that share a genetic inheritance. Comparisons between haplotypes, now possible with the HapMap, allow scientists to identify SNPs that are linked to disease much more quickly and easily.

Most common haplotypes occur across all human ethnic groups, but there are slight differences in frequency across populations. Haplotypes from four populations — Americans of European origin from Utah; the Yoruba tribe of Nigeria; Han Chinese from the Beijing area; and Japanese — have been scanned to cover all the bases, making the map relevant to people all over the world.

Mark Walport, director of the Wellcome Trust, which funded the British element of the project, said: “The HapMap is a remarkable resource that will accelerate the search for genes involved in common ailments, such as heart disease and obesity. It is freely available to researchers around the globe and is already being exploited to answer important questions about health and disease.”

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