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Researchers develop guidelines to establish identity of genes responsible for common, complex diseases

December 18, 2002

Scientists from Imperial College London, the Medical Research Council, Case Western Reserve University, USA and the Hammersmith Hospital have developed guidelines which scientists can use as a benchmark for proof of identification of the multiple genes responsible for common, complex diseases.

Predisposition to common conditions such as asthma, cancer, Type 2 diabetes, mental illness and Crohn's disease, are all determined partly by multiple genes, and partly by environmental factors. This makes it difficult to identify the genes involved in these diseases.

Although some of the many genes contributing to complex traits such as Alzheimer's and Type 1 Diabetes have been discovered in the last few years, researchers have faced a difficult task in deciding what represents definitive proof of a particular gene's action.

As well as looking at human illness and disease, the authors of the review paper published in Science today also looked at the multiple gene traits in cows, tomatoes and flowers, and the effects of the environment upon them. Through these methods researchers are now able to predict the milk yield in cows, the size tomatoes will grow to, the flowering period in commercial breeds of flowers and many other "genetically complex traits".

Professor Timothy Aitman, from the MRC Clinical Sciences Centre, based at Imperial College London at the Hammersmith Hospital comments: "Where diseases and illnesses have been caused by a single gene, it has been relatively straightforward to identify that gene, but where multiple genes, and environmental factors have all had an effect it has proved much more difficult. We hope our guidelines will allow scientists to say when they have conclusively identified the genes behind these complex traits, or diseases, more effectively."

Over the last 25 years, scientists have identified over 1000 single gene disorders or illnesses. Diseases caused by a single gene, such as haemophilia and sickle cell disease, have been identified, but it has proven difficult to identify genes which interact in more complex disorders. Since the decoding of the human genome, the task of identifying these multiple interacting genes has become much easier.

The researchers have described a four-stage process through which a disease caused by multiple genes can be identified; linkage and association, fine-mapping, sequence analysis, and functional tests of candidate genes. This process will ensure that there is robust proof of the identity of genes underlying complex diseases.

Dr Anne Glazier, from the MRC Clinical Sciences Centre, Imperial College London at the Hammersmith Hospital adds: "The criteria we have established will provide a means to evaluate the nature of the candidate genes identified to date, and demonstrate the insights that can be expected from the accelerating pace of gene discovery."

Imperial College, University of London