Scientists decipher third human chromosome

Fresh medical advances could be on the way after British scientists deciphered the entire genetic code of chromosome number 20 – the third human chromosome to be decoded as part of the international human genome project.

Medical researchers hope that the feat will lead to a new understanding of a range of illnesses associated with defects of the chromosome, including diabetes, obesity, cataracts and eczema.

It is the largest chromosome yet to be unravelled and constituents some 2 per cent of the genome, which is composed of 23 pairs of chromosomes and some 3 billion "letters" of the genetic alphabet.

The Sanger Institute near Cambridge, which is funded by the Wellcome Trust, the world's biggest medical research charity, describe the decoded chromosome as a "treasure trove for biomedical sciences". The information will be made freely available for scientists throughout the world.

One intriguing facet of the discovery, published today in the journal Nature, is that in two out of every five people, chromosome 20 has an additional "chunk" of DNA containing at least one extra gene. Scientists have yet to discover the purpose, if any, of this extra genetic material.

Chromosome 20 also carries the genes involved in Creutzfeldt-Jakob disease, heart disease, stroke and dermatitis. The scientists found it contains 30,000 tiny "point" mutations that are involved in genetically distinguishing one person from another. Michael Dexter, director of the Wellcome Trust, said: "This is one more completed chapter of our genomic anatomy textbook. Medical research will be using this information for decades to come in its quest to tackle our common diseases."

The painstaking work of deciphering the code and re-checking the results was done by a team led by Panos Deloukas of the Sanger Institute, who will now attempt to understand the purpose and function of the deciphered genes.

Allan Bradley, director of the institute, said: "This high-quality sequence is like a finely tuned engine that will drive researchers towards medical benefits more rapidly and more smoothly."

Scientists plan to finish decoding the human genome in 2003, to coincide with the 50th anniversary of the discovery of the DNA double helixby the Cambridge Nobel laureates Francis Crick and Jim Watson.