French and American scientists have mapped chromosome 14, the longest sequenced to date and the site of more than 60 disease genes, including one linked to early onset Alzheimer's.
The feat enlisting nearly 100 researchers marks the fourth of the 24 human chromosomes mapped so far as part of an international effort.
Scientists at Genoscope, the French national sequencing center, said the chromosome is comprised of more than 87 million pairs of DNA, all of which have been sequenced so that the chromosome's map includes no gaps.
``At the present time, this is the longest piece of contiguous DNA that has been sequenced. We made an effort to close all the gaps,'' said Genoscope's director, Jean Weissenbach.
The researchers describe chromosome 14 and its 87,410,661 pairs of DNA _ a fraction of the total 3 billion pairs found in human genome _ in a paper to be published online Thursday by the journal Nature.
The project was led by Genoscope, with contributions from scientists at Seattle's Institute for Systems Biology and the Washington University School of Medicine in St. Louis.
The scientists identified 1,050 genes and gene fragments, among them more than 60 disease genes. Those include genes linked to early onset Alzheimer's, spastic paraplegia, NiemannPick disease and a severe form of Usher syndrome.
Although the accomplishment is noteworthy, it does not mean science is any closer to conquering Alzheimer's, said Bill Thies, vice president for medical and scientific affairs for the Alzheimer's Association in Chicago.
He said the chromosome 14 gene linked to early onset Alzheimer's accounts for only a fraction of cases of the degenerative brain disease. Several genes, as well as environmental factors, are known to play a role in a person's risk of developing Alzheimer's, Thies said.
During the last three years, nearly complete sequences of chromosomes 22, 21, 20 _ and now chromosome 14 _ have been published.
By April, researchers around the globe hope to complete the sequencing of the remaining 20 chromosomes, said Mark Guyer, director of the division of extramural research at the National Human Genome Research Institute.
April is also the 50th anniversary of the publication of James D. Watson and Francis H.C. Crick's 1953 paper in Nature describing DNA's double-helix structure.
Guyer said the institute, one of the National Institutes of Health, intends to mark the occasions by publishing a paper outlining its vision of the future human genetics studies.
``Once we've sequenced the chromosomes, that is essentially just the basic set of instructions. We still need to learn how to read the instructions and understand what they mean,'' he said.