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March 20, 2015
A new way of creating genetically modified insects could wipe out many mosquito-borne diseases such as malaria within a few years but it could also unleash potentially devastating unintended consequences, scientists have warned.
Researchers have devised a method of bypassing a fundamental barrier to the rapid spread of genes within a population. They believe that it could be used to spread malaria-resistant genes in mosquitoes to prevent transmission of disease to people.
However, it could also be used to spread harmful genes rapidly in the wild, which has led other researchers to call for the imposition of strict safety controls over such research in case of an accidental escape from a laboratory.
A child plays under a mosquito net in Nairobi. A way to spread (EPA)
The scientists have already demonstrated that it works in fruit flies reared in a high-security laboratory. When a genetically modified fly was mated with a normal fly, the mutated gene was passed on to about 97 per cent of the offspring, instead of the usual one-in-three proportion dictated by classical genetics.
The technique works because the genetically modified DNA includes a “cassette” of other genetic elements that made sure the intended mutation is passed from one chromosome to another within the same organism in what the scientists have called a “mutagenic chain reaction”.
This ensures that almost all offspring born as a result of the genetically modified mosquito mating with wild mosquitoes are born with the ability to pass on the mutated gene. This would enable malaria resistance to spread completely within a single breeding season, said Ethan Bier of the University of California, San Diego.
“In the case of malaria, several groups have created genetic cassettes that when introduced into mosquitoes prevent the malarial parasite from propagating thereby blocking infection,” Dr Bier said.
“A major challenge in the field, however, has been devising a way to disseminate these gene cassettes throughout the mosquito populations. MCR offers an obvious solution to this problem since the incorporation of an anti-malaria gene cassette into an MCR element should result in the rapid spread of the gene cassette through the target population,” he said.
“For example, if one in 100 individuals initially carried the cassette, the cassette should spread to virtually all individuals in as few as 10 generations, which is less than one season for mosquitoes,” he added.
The chain reaction, described in a study published in the journal Science, uses a new method for precision editing of genes, called Crispr. This has an enzyme that cuts and splices chromosomes, enabling a modified gene to be passed between one chromosome and other in the same organism.
However, other scientists have warned about carrying out experimental work without taking adequate precautions against the possibility of escape from laboratories carrying out so-called “gene drive” research.
“We have published methods by which gene drives can be kept confined not only by physical means but ecological and molecular methods,” said George Church of Harvard University.
“All of these should be employed especially with flying organisms and for organisms common in the wild near the lab,” Dr Church said.
Valentino Gantz at San Diego, the co-author of the study, said that the technique could be adapted to target human cells that carry mutated genes, such as cancer cells or cells infected with viruses similar to HIV.
“Since MCR works by targeting specific DNA sequences, in cases where diseased cells have altered DNA as in HIV-infected individuals or some types of cancer, MCR-based methods should be able to distinguish diseases from healthy cells and then be used to selectively either destroy or modify the diseased cells,” Dr Gantz said.