Scientists removed and replaced gene causing muscular dystrophy in mice.
Most diseases are really complex. Not just when it comes to symptoms and outward appearance, but also considering their tangled genetic roots. Often, many genes are involved, as well as numerous interactions between them. Some, however, have a simpler foundation consisting of only one or a few genes.
Wouldn’t it be great if we could remove and replace those genes? Wait a minute. People are already working on it.
The newest example concerns Duchenne muscular dystrophy, an inherited muscle disease that, since it’s linked to the X-chromosome, affects mostly boys and causes progressive weakening of the muscles. In most cases, the symptoms appear in early childhood and life expectancy estimates are centered around the tender age of 25. Sadly, there is no effective treatment.
A new study on mice, performed by researchers at the University of Texas Southwestern Medical Center and published in the journal Science, details the use of the CRISPR/Cas9 system to edit the genome of mice that have been engineered to develop the disease. To put it simply, CRISPR/Cas9 is a cut-and-paste tool at the genetic level: it allows researchers to target a defected gene and replace it with its faultless version.
Implementing the CRIPR/Cas9 method, the scientists were able to select the ‘broken’ gene (the healthy version of which encodes the protein dystrophin, required for muscle fiber integrity) in the germline of affected mice. This is the cell line that gives rise to egg or sperm cells and, consequently, the next generation of small squeaking rodents. The gene was cut out and the correct version was pasted in its genomic place. The mice that sprang forth from the resulting germ cells contained between 2 and 100% of the corrected cells. Interestingly, even mice with a small percentage of cells that had incorporated the flawless gene version performed quite well, which probably reflects an advantage of carrying at least some normally functioning cells for overall muscle performance.
Unfortunately, this techniques is not yet refined enough to use in human beings. Nevertheless, the authors speculate that technological advances in the foreseeable future could enable the eradication of diseases with a relatively simple genomic basis. Cutting defected genes and pasting the right ones in their place is a burgeoning technique with many potential applications in medicine and beyond. Of course, the ethics of intervening in the genome, and especially the germline (which would make the changes heritable), should not be neglected. Nor should the possible benefits.
After all, it’s a brave new world over there, at the cusp of scientific progress.
Long C, McAnally JR, Shelton JM, Mireault AA, Bassel-Duby R, & Olson EN (2014). Prevention of muscular dystrophy in mice by CRISPR/Cas9-mediated editing of germline DNA. Science (New York, N.Y.), 345 (6201), 1184-8 PMID: 25123483
genome, disease, duchenne, CRIPR/Cas9, muscular dystrophy, germline