Dna-based Chips Diagnose Disease-- And Raise Hackles The Sacramento Bee
It looks like a run-of-the-mill silicon computer chip. It's flat, dark gray and no bigger than a thumbnail. But this is a very special chip: Its job is to find out whether people are likely to get cancer.
Similar chips are being made for other diseases, including AIDS, leukemia and tuberculosis, and eventually there will be chips that will even predict the behavioral traits of unborn babies.
DNA chip technology is a burgeoning new area of medicine and genetics that promises to revolutionize disease diagnosis. But it is also generating growing controversy, with calls for international controls to make sure it is not abused.
Current laboratory techniques for detecting genetic mutations that are responsible for disease are time-consuming and expensive, taking months, even years. In contrast, a DNA chip takes minutes, or at most hours, to seek out disease-causing mutations in genes.
Though the technology is complex, the theory behind the process is simple. Instead of having intricate microelectronic circuits etched onto their surfaces, these tiny chips are coated with DNA sequences, some of which are associated with a healthy gene while others are known disease-causing mutations.
The sequences, up to 400,000 on a single tiny chip, line up in the squares of a grid on the surface of the chip. A sample of the patient's DNA is then put onto the chip and each sequence pairs off with its opposite number. Whether or not they are exactly the same as their partner is then detected by a laser.
A patient whose DNA exactly matches with a known mutation on the chip may be at risk from that particular disease. If the DNA fails to match with a known healthy sequence, that can also indicate potential problems.
"It is incredibly rapid. What you are relying on is that you will
recognize differences between the DNA on the chip and DNA you are
looking at. In terms of a quick screen, it is masterful because it
gives you a quick answer and it is cheap," says Dr. Gareth Evans,
consultant geneticist at Christie's Hospital in Manchester, England.
Half a dozen companies are now working on producing variations of these chips and California-based Affymetrix has launched three for use by researchers. The jewel in the crown at present is a chip that works on a gene called p53 that is abnormal in more than half of all types of cancers.
At the Houston Advanced Researcher Center, Dr. Dat Dao and a team of researchers are working on chips that will be able to pinpoint antibiotic-resistant strains of TB. Another chip detecting mutations linked to breast cancer is in the pipeline, and the center is also working on one that will take some of the uncertainty out of matching donor tissue for bone marrow transplants.
"This genosensor technology is going to create a host of benefits for
the diagnosis of cancer as well as genetic and infectious diseases.
It is going to be the diagnostic tool of the future," says Dao.
Dr. Mike Ramsay of the Oak Ridge National laboratory in Tennessee, who also works with DNA chips, agrees: "This technology could be used to screen for people carrying genes that predispose them to getting breast cancer, becoming obese, or having children with cystic fibrosis. To make such an analysis we eventually hope to require only a few white blood cells or skin cells."
But the rapidly evolving technology is seen by some as a Pandora's box, with almost as many ethical dilemmas as benefits. One of the biggest fears is that the chips will be seen as the ideal tool for the establishment of widespread genetic screening of all types and for all kinds of motives.
"Today's supply of screening for young couples is restricted to
cystic fibrosis and a few rare diseases that are confined to specific
populations. The chip, however, will broaden the spectrum of
analyzable parental traits practically ad libitum," says Dr. Wolfram
Henn, a clinical geneticist at the University of Hamburg in Germany
who raised concerns about the technology in this month's Journal of
Medical Ethics.
The chief area for concern is prenatal screening, where DNA chips, the developers claim, will make it possible to test for every disease and trait in an unborn baby.
"The subjective choice of genetic traits that are considered as
prenatal selection criteria may blur the distinction between
preventative medicine and striving for the perfectly designed child,"
he says.
(Copyright 1999)
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Publication Date: April 22, 1999
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