An unprecedented selection of genes that contribute to common diseases has been identified by the biggest survey of the human genome. The discovery promises to transform treatment and diagnosis of everyday health problems.

The study, which screened DNA samples from 17,000 British volunteers, has identified 24 genetic variants that influence six common conditions that together affect tens of millions of people.

Half the genes have effects that are new to science, and the findings open new approaches to research into type 1 and type 2 diabetes, heart disease, Crohn’s disease, bipolar disorder and rheumatoid arthritis.

Genetic variants that may affect a seventh disorder, high blood pressure, have also been highlighted, though these links have yet to be confirmed.

The discovery by the Wellcome Trust Case Control Consortium is a landmark in humanity’s ability to understand our genetic code, illustrating how variations in DNA make different people susceptible to diseases. As the seven studied conditions and the genes that influence them are common, the results should help scientists to design therapies and screening techniques from which millions will benefit.

Many of the new genes lie in areas of the genome that were not previously thought to be related to the diseases in question. As all the variants have small effects, which predispose to disorders rather than inevitably causing them, the study should also reveal environmen-tal factors that matter as well.

“We have known for a long time that genes play a large role in common human diseases such as heart disease, diabetes and many psychiatric disorders,” said Professor Peter Donnelly, of the University of Oxford, who led the research team. “What we have not known is which parts of the genome are involved.”

“Many of the most common diseases are very complex, part nature and nurture, with genes interacting with our environment and lifestyles. By identifying the genes underlying these conditions, our study should enable scientists to understand better how disease occurs, which people are most at risk and, in time, produce more effective, more personalised treatments.”

In the study, published in the journal Nature, more than 200 scientists took DNA samples from 2,000 individuals with each of the seven diseases and from 3,000 healthy control subjects. The study compared 500,000 genetic markers to identify which were more common in people with disease.

This technique, whole genome association, can find genetic variants that have small effects. The new variants are carried by between 5 per cent and 40 per cent of the population.

Most raise the risk of developing a disease by up to 40 per cent if one copy is inherited, and by double this in people with two copies.

Details of several genes identified by the consortium have already been published, including the FTO gene that influences obesity and a cluster that affects type 2 diabetes.

The most exciting results concern type 1 diabetes and Crohn’s disease, a bowel disorder. Specialists in each disease will be watching progress in the others in search of clues. “If there is a breakthrough in Crohn’s disease, we will be looking at it in type 1 diabetes,” said Professor John Todd, of the University of Cambridge, who led the type 1 diabetes arm of the research.

Mark Walport, director of the Wellcome Trust, said: “This research shows that it is possible to analyse human variation in health and disease on an enormous scale.”

Hope for six conditions

Bipolar disorder Psychiatric illness that affects 100 million people worldwide. One new genetic area reliably linked. Many other genes likely to have a small effect on risk

Coronary heart disease Britain’s biggest killer, causing 105,000 deaths annually. Genetic area on chromosome 9 doubles risk in the 20 per cent of people who have two copies, increases risk by 50 per cent in the 50 per cent of people with one copy of the variant

Crohn’s disease Inflammatory bowel disorder that affects up to 60,000 people in Britain. Three new genes discovered that raise the risk by 40 per cent. The study confirms six other previously identified genes are also linked

Rheumatoid arthritis Auto-immune condition affecting 387,000 people in Britain. One genetic region confirmed to have impact on women

Type 1 diabetes Insulin-dependent form of the condition that usually begins in childhood, affecting 350,000 people in Britain. Four genes found that have an effect, raising risk by up to 40 per cent when people have one copy. Effect of three other genes confirmed

Type 2 diabetes Adult-onset form of the condition, affecting 1.9 million people in Britain. Three new genes that affect risk identified, including the FTO gene that contributes to the risk of obesity

Sources: Wellcome Trust/Nature

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