Decoding chromosome 22

An international team of researchers has passed a scientific milestone by deciphering, for the first time, the complete genetic code of a human chromosome. Reporting in last week's Nature, researchers from the Wellcome Trust funded Sanger Centre in Cambridge, Keio University in Japan and various US laboratories announced their success in writing down the 34 million letters that make up the entire sequence that contains all the protein coding genes of chromosome 22.

This is the first human chromosome sequence to be completed and has revealed 679 genes of which 55 per cent were previously unknown in humans. Ian Dunham, who led the team at the Sanger Centre, said: 'This is the first time we have been able to see a whole chromosome in this detail, the organisation of the genes and how they relate to each other'. 'The significance [of this week's publication] is that it shows you can get very good finishing using the clone-by-clone approach,' he added. Michael Morgan, chief executive of the Wellcome Trust's genome campus, one of the main sponsors of the Human Genome Project (HGP), said: 'It is the largest contiguous sequence of DNA, and a major breakthrough'.

Previous research has already revealed that chromosome 22 is implicated in the workings of the immune system, congenital heart disease, schizophrenia, mental retardation and several cancers including leukaemia. The availability of the DNA sequence has the potential for revolutionising the future of research into these diseases. James Scott, professor of molecular medicine at Hammersmith Hospital in London described the availability of the complete sequence of the chromosome as 'a fantastic resource for looking at human population genetics and disease gene susceptibility in a way that has just not really been possible until now.' Work continues to complete the estimated 3 billion letters that make up the whole of the human genome, with a first working draft available by spring 2000 and the finished form before 2003.

The Wellcome Trust has committed £210m towards the Human Genome Project, enabling one third of the work to be completed at the Sanger Centre, the world's largest genome sequencing centre.