As great as this scenario may sound, once nature is tampered with, there may be no turning back should things go awry. Altering an entire population of mosquitos, or eliminating them altogether, could have drastic and unknown consequences for an ecosystem: It might mean that other pests emerge, for example, or it could affect predators higher up the food chain. Hypothetically, a guide RNA could mutate over time such that it targets a different part of the genome. This mutation could then race through the population, with unpredictable effects.9,10 Not only could gene drives doom species to extinction or change the course of evolution, bioterrorists could alter the genomes of disease-causing organisms to make them more lethal or more infectious and use gene drives to spread that trait throughout a population. Someone with nefarious intentions and $10,000—the estimated cost of materials to construct a gene drive—can wreak considerable havoc. This has caught the attention of the United Nations office that oversees the biological weapons treaty, as well as that of the FBI’s Weapons of Mass Destruction directorate.10
In an effort to identify possible ramifications of gene drives, the National Academy of Sciences has convened a panel of experts to assess current regulations and recommend what additional oversight will be needed.
Designer Humans
Can CRISPR excise deleterious genes from our genome? It is one thing for scientists to genetically modify bacterial cultures so that our yogurt tastes fresher or our cheese pizza is tastier, but what about modifying genes that control risks for certain cancers, infections or even autoimmune diseases? What about editing embryos?
This latter possibility ratchets things up a few notches, because germ line, unlike somatic cell modifications, are heritable, and they could have an unpredictable effect on future generations. In a world first, Chinese scientists have recently reported editing the genomes of human embryos.11 The researchers tried to head off ethical concerns by using “non-viable” embryos obtained from local fertility clinics that were carrying an extra set of chromosomes, which prevented maturation and live birth. They studied the ability of the CRISPR/Cas9 system to edit a gene called HBB, which encodes the human β-globin protein. Mutations in the gene are responsible for β-thalassemia.
A fascinating discovery that allows for the easy manipulation of an organism’s genome has rocked the world of biology. [It] has the potential to alter our genomes, & so the use or misuse of this technology will have profound implications for society.
The team injected 86 embryos. Of the 71 embryos that survived, 54 were genetically tested. This revealed that just 28 were successfully spliced and that only a fraction of those contained the replacement genetic material. Most worrisome, they observed a surprising number of off-target mutations assumed to be introduced by the CRISPR/Cas9 complex acting on other parts of the genome. This effect is one of the main safety concerns surrounding germ line gene editing, because these unintended mutations could be harmful. The rates of such mutations were much higher than those observed in gene-editing studies of mouse embryos or human adult cells. And the investigators conceded that they likely detected just a fraction of the unintended mutations because their study looked only at a portion of the genome, known as the exome.
