Scientists discover body’s fusebox’ to diseases
Genetic recipe for human book of life’
They’ve done it! An international group of scientists from England, the United States, Canada, Sweden, and Japan gave the world a millennium present last month by announcing that the first human chromosome had been mapped.
Although the researchers were able to map only 97% of the chromosome’s genetic material, the results are considered complete for now. There are 23 pairs of chromosomes — a molecular chain within a cell carrying hereditary characteristics — containing all the human deoxyribonucleic acid (DNA). The human genome, or genetic pattern, is a biological map consisting of the 3 billion pairs of chemicals within the DNA of each cell.
While the impact on hospital ethics committees may not be immediate in terms of providing diagnostic testing, the achievement means committees will need more education. Syndromes and diseases will be linked to one of 23 chromosomes, and ethics committees, along with genetic counselors, will have to be well-versed in each "chapter" of the human book of life, experts predict.
Chromosome 22 is the second smallest, but it was chosen because of its influence on the human body’s functioning. The chromosome is one of the most densely packed, with 33.5 million pieces, or chemical components. More than 30 human disorders, however, are associated with changes in the genetic makeup of this chromosome.
Previous research has revealed that chromosome 22 is instrumental in the workings of the immune system, congenital heart disease, schiz ophrenia, mental retardation, and several cancers, including leukemia. (For a complete list, see chart, p. 4.)
"For the first time we can see the entire landscape of a human chromosome, the basic unit of human inheritance, how the genes are organized, how they’re laid out on the chromosome," says Francis Collins, MD, chair of the National Human Genome Research Institute (NHGRI) in Bethesda, MD. The achievement was published in the Dec. 2 issue of Nature.1 NHGRI is a joint effort by the National Institutes of Health and the U.S. Department of Energy.
"I think this is probably the most important scientific effort that mankind has ever mounted. That includes splitting the atom and going to the moon," Collins says.
"This is the first time that we have been able to see the organization of a chromosome at the base-pair level. This immediately suggests new experiments and avenues of research which can be pursued," says Ian Dunham, MD, senior research fellow and principal scientist at the Sanger Centre in Hinxton, Cambridge, UK, and lead author of the Nature article. The Sanger Centre is the primary research facility in England involved in the international research effort.
One down, 22 to go
The achievement is not an indication for science to rest on its laurels, however. "One down, the others to go," notes Dunham. Researchers are testing gene therapies to correct misfirings and attempt to make cells work correctly. The hope, scientists say, is to create therapies reliable enough to treat diseases without the side effects of some medications.
"You will see buried in all sorts of papers that people have used the sequence already," says Peter Little of Imperial College in London. Little uses the existing map to study a protein on the surface of nerve cells.
The fact that the information is freely available is of major importance, scientists say. The sequence of chromosome 22, for example, includes 298 genes previously unknown in humans, and all are being released without the constraints of patents and fees. Their hope, say Collins and Dunham, is that the knowledge of genetic makeup will be used for the good of humankind.
There is, however, private competition to complete mapping of the entire human genome. (See related story, below.)
"What happens now is a whole host of fascinating experimental challenges to figure out. What do these genes do individually, and how do they work together to do all the things we humans are capable of? Until now, the ability to sequence an entire chromosome was just hypothetical. Having done this for chromosome 22 tells us we will be able to finish the human genome [completely] in another two or three years," explains Collins.
He says the first benefit from mapping human chromosomes will be in diagnosing diseases or syndromes. "In other words, the identification, particularly the early identification, of disease."
The other chromosome mapping projects likely will evolve more quickly, researchers say. The next most likely candidate will be chromosome seven. Researchers expect to have the remaining chromosomes mapped by next spring.
Reference
1. Dunham I, Hunt AR, Collins JE, et al. The DNA sequence of chromosome 22. Nature 1999; 402:489-495.
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