Scientists have made a major leap in unravelling the genetic causes of seven common diseases, including diabetes, arthritis and high blood pressure, by completing the largest analysis of the human genome. The discoveries pave the way for improved treatments and possible cures for the millions of people in the UK who develop the diseases every year.

Using new techniques to examine the DNA of thousands of patients, scientists also found common genetic links in heart disease cases. The findings raise the prospect of improved medical treatment and preventative work with people identified as carrying a genetic risk of disease.

Peter Donnelly of Oxford University, who chaired the £9m research programme funded by the Wellcome Trust, said: "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, to produce more effective, more personalised treatments."

Since the completion of the human genome project in 2000, which mapped every gene in the human body, scientists have quickly identified rare genetic variants that cause major inherited diseases such as cystic fibrosis. Today's development marks a real breakthrough in diseases affecting millions.

"It's been much more challenging to identify the rather common variants in diseases such as diabetes and Crohn's disease, where there are multiple genes involved but the effects of individual genes has been much smaller," said Mark Walport, director of the Wellcome Trust.

By studying the DNA from 17,000 people, the 50 research groups identified 24 new genetic links for bipolar disorder, Crohn's disease, heart disease, type 1 and type 2 diabetes, rheumatoid arthritis and high blood pressure, tripling the number of genes already associated with them.

"This study is a landmark in the field of diabetes research," said Karen Addington of the Juvenile Diabetes Research Foundation. Dr Walport said that the study, one of the largest genetic research projects to date, had carried out genetic analysis at a "scale that's never been done before."

Research into the links between genes and disease has focused on small numbers of samples, often from relatives who share a higher than usual risk of suffering a particular illness. But the new approach pioneered by the research team, known as a genome-wide association study, heralds the future for this kind of research.

In the study, scientists analysed DNA samples from 2,000 patients per disease, comparing them with 3,000 "control" samples from healthy volunteers and looking at around 500,000 genetic differences in each sample. The full results of the Wellcome trust Case Control Project are published today in Nature and Nature Genetics. "Just a few years ago it would have been thought wildly optimistic that it would be possible in the near future to study a thousand genetic variants in each of a thousand people," said Dr Walport.

"This research shows that it is possible to analyse human variation in health and disease on an enormous scale. It shows the importance of studies such as the UK Biobank, which is seeking half a million volunteers aged between 40 and 69, with the aim of understanding the links between health, the environment and genetic variation."

Prof Donnelly said that the gene discoveries would begin a new chapter of research. Genetics was only part of the story. "Many of the most common diseases are very complex, part nature and nurture, with genes interacting with our environment and lifestyles."

Main findings

Crohn's disease: Eight new genetic links were found to increase a person's susceptibility to this illness, which affects between 30,000 and 60,000 people in the UK. Having a single copy of any of the disease variants of these genes increases the risk by up to 40%.

Diabetes: Type 1 diabetes affects around 350,000 people in the UK; 1.9 million people have type 2. The study highlighted four new regions of the genome that increase the risk of type 1 diabetes. The research also confirmed that Type 2 diabetes has a genetic component.

Bipolar disorder: Also known as manic depression. It is marked by extreme mood swings and affects abut 100 million people worldwide. Many of the genes identified in the study seem to play a key role in the way nerve cells in the brain talk to each other.

Coronary heart disease: The study found several genetic regions that increased the risk of heart disease. The risk increased by 50% in people carrying one version of the disease variant. For those carrying both the risk was almost doubled. Coronary disease is Britain's biggest killer, claiming 105,000 lives each year.

Hypertension (high blood pressure): The research suggests that high blood pressure arises because of a wide range of interacting factors, including three genes identified in the study . The disorder affects more than 16 million Britons and a billion people worldwide.

Rheumatoid arthritis: This disease affects almost 400,000 people in the UK. The project identified three locations in the genome that had a possible role in predisposing people to the condition.