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 s
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Contact: Tony Stephenson
at.stephenson@ic.ac.uk
44-207-594-6712
Imperial College London
19-Dec-2002