Scientists reveal genetic map that will unlock the secrets of human diversity

The first genetic "map" of human diversity is published today by scientists who describe it as a landmark achievement that will revolutionise medicine.

More than 200 researchers from six countries have spent three years and more than £80m deconstructing the human genome to discover the precise genetic differences between people. Whereas the human genome - the basic genetic blueprint - showed that everyone shares 99.9 per cent of their genes, it is the 0.1 per cent difference that can hold clues to illnesses such as asthma, diabetes, dementia, heart disease and cancer.

Scientists have completed the first phase of an ambitious project to tease apart these minute differences to begin to explain why some people develop serious diseases while others with a similar lifestyle remain healthy.

The map of human diversity could also be used to identify patients who respond better to certain drugs as well as explaining the evolutionary origins of humankind by shedding light on the ancient migrations of our ancestors from Africa.

"This represents a milestone for medical research," said David Altshuler of Harvard University, one of the leaders of the team to draw up the genetic map, published in the journal Nature. He said that the map provides a powerful new tool for exploring the root causes of the many common diseases that have a genetic as well as lifestyle component.

"Such understanding is required for researchers to develop new and much-needed approaches to prevent, diagnose and treat diseases such as diabetes, bipolar disorder, cancer and many others," he said.

The scientists built up the map of genetic diversity from a detailed analysis of the DNA from 269 volunteers drawn from four different ethnic groups - the Yoruba tribe from Nigeria, residents of Tokyo, the Han Chinese from Beijing and European Americans from Utah.

By painstakingly comparing the smallest possible mutations - single nucleotide polymorphisms - in each of the volunteer's DNA, the scientists produced the first comprehensive catalogue of human genetic variation.

Panos Deloukas, a senior investigator at the Wellcome Trust Sanger Institute in Cambridge, said that a map of such differences will ultimately prove invaluable in understanding the many life-threatening diseases affecting people today.

"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 drugs," Dr Deloukas said.

The new genetic map is based on relatively large fragments of DNA - called haplotypes - that contain a unique battery of single mutations which tend to be inherited together as a block.

Scientists have called the study "HapMap" because it is based on these human haplotypes. More than a million single mutations have so far been mapped to their respective haplotypes.

The researchers estimated that the study will increase by 20-fold the speed at which it is possible to search for the genes responsible for disease. "This report describes a remarkable step in our journey to understand human biology and disease," said Professor Peter Donnelly of Oxford University, another senior member of the research team.

The study - which was funded by governments and private industry - is available on the internet. "The HapMap is a remarkable resource that will accelerate the search for genes involved in common ailments, such as heart disease and obesity," said Mark Wolport, director of the Wellcome Trust, which helped to fund the project.

The battle to decipher our code

The human genome is like a recipe for making a man or woman and is composed of three billion individual "letters" that make up the long genetic code written within our genes.

When the full sequence or map of the human genome was published it was clear that 99.9 per cent of the code was identical for all people of any ethnic group in the world.

But the 0.1 per cent of the code that is different not only accounts for why people look dissimilar, it can also explain why each of us can have different destinies in health.

"Any two unrelated humans have millions of genetic differences, making them look and even behave differently," say geneticists David Goldstein and Gianpiero Cavalleri in Nature. "This variation is the magnificient legacy of our evolutionary past, but it comes at a price.

"Along with making us different in benign and interesting ways, genetics also influences health."

There are some 10 million kinds of mutations or variations in our genes that result from a single change or "polymorphism" to the long code of our DNA.

These single nucleotide polymorphisms, called SNPs or "snips", form the heart of the search for genetic differences that can account for why two people living similar lives can experience very different outcomes in terms of their health.

Snips can also help to separate people who respond differently to drugs.

By building up a map of Snips, and seeing which ones are linked with responding well or responding badly to a particular drug, it should be possible to give patients tailor-made prescriptions that result in few, if any, side-effects.

If the genome sequence can be described as a road map of the human DNA landscape, then a map of our snips - the HapMap - is like a map of the potholes and road works that can provide the vital signs of danger.