A UK collaboration of scientists has identified three new genes that predispose individuals to develop type 2 diabetes, bringing scientists a step closer towards understanding what causes this complex disease.
The study, jointly led by researchers at the University of Oxford and the Peninsula Medical School, Exeter, and forming part of the Wellcome Trust Case Control Consortium looked at over 2 billion pieces of genetic data and 6,000 people with type 2 diabetes and 8,000 controls to track down these three genes. In addition, they confirmed the link between the disease and a further two previously-identified genes.
The findings, published online today in the journal Science, bring the total number of genes known to be involved in type 2 diabetes to nine, including the FTO gene reported by the same UK group two weeks ago. The FTO gene influences individual risk of type 2 diabetes through its effect on weight and obesity.
Type 2 diabetes occurs as a result of a failure of the body to produce enough insulin to maintain normal levels of glucose (sugar) in the blood. This failure is usually compounded by a reduction in the capacity of the insulin released to work properly in tissues such as muscle and fat (known as insulin resistance). It is a major cause of heart disease and stroke, as well as blindness and kidney failure.
There are currently around 200 million people who have type 2 diabetes worldwide, yet its underlying cause is poorly understood, limiting both treatment and prevention. Lifestyle factors, such as poor diet and lack of exercise have been known for some time to increase risk of developing the disease, but scientists are becoming increasingly aware of the role played by genetics.
For each of the three genes described in the paper, the researchers have found that there are two common "versions", one of which is associated with an increased risk of developing type 2 diabetes, and the other with reduced risk. Each high-risk version increases the risk of type 2 diabetes by between 10 and 20 percent. All are common in the general population.
"This research helps us to understand that, for most people at least, an individual’s risk of developing diabetes as they get older is influenced by a number of genes, as well as by their environment," says Professor Mark McCarthy from the University of Oxford, one of the lead authors of the paper. "Clearly, the more ‘high risk’ alleles a person inherits, the higher the likelihood that they will go on to develop diabetes."
The exact role of the genes that have been implicated by these studies is still uncertain. However, two of them appear to be involved in the development, function and regeneration of insulin-producing beta cells, found within the pancreas. This finding is likely to help to answer a long-standing controversy in the diabetes field concerning the extent to which a reduced number of pancreatic beta-cells (as opposed to reduced function) contributes to the development of diabetes.
"We now have significantly more pieces to the jigsaw that will help us understand the mechanisms behind type 2 diabetes," says Professor Andrew Hattersley of the Peninsula Medical School, also a lead author on the paper. "Each piece of new knowledge takes us a step closer towards a future with improved prevention and treatment of this very significant condition."
The first important clues to the identities of these genes came from a genome-wide analysis conducted in 2,000 people with type 2 diabetes and 3,000 controls as part of the Wellcome Trust Case Control Consortium2. The Consortium is one of the biggest projects ever undertaken to identify the genetic variations that predispose people to or protect them from major diseases.
Professor Peter Donnelly of the University of Oxford, who heads the consortium said: "This landmark study reveals the power of the strategy that the Wellcome Trust Case Control Consortium has adopted to study diabetes and several other common diseases. It is clear that these and other findings which the Consortium will shortly be reporting will have a major impact on our understanding of the mechanisms behind many diseases of global importance."
These initial findings were then confirmed by studying a further 9,000 samples from the UK (the majority of them from the Dundee area collected by researchers from the Ninewells Hospital and Medical School.
The research has been conducted in close collaboration with two other groups from the US and Scandinavia, who were undertaking similar research studies in samples from Sweden and Finland. Their results, which have also identified the same three genes, are published today alongside the UK study. In a unique collaboration, these three international groups chose to combine forces rather than compete, resulting in the largest ever collaborative study of type 2 diabetes, involving over 32,000 subjects.
"The extraordinary achievements of this research project have only been made possible through the unique international collaboration," says Dr Mark Walport, Director the Wellcome Trust, which funded the UK study. "By sharing data and working together, the researchers have made significant progress in understanding the genetics underlying type 2 diabetes in a very short time."
Iain Frame, Research Manager at Diabetes UK, said: "Diabetes UK welcomes these exciting findings. It’s important to remember that Type 2 diabetes is a genetic condition and not just associated with lifestyle factors. This discovery will help us get closer to unravelling the genetics of the condition. If we can understand more about the genetics we can make real progress towards the prevention and treatment of Type 2 diabetes.
"Diabetes UK funded the original collection of samples at the beginning of this study. It is thanks to the collaborative efforts of Diabetes UK, a number of excellent researchers and the Wellcome Trust that this discovery has been possible."
Wellcome Trust. April 2007.