The future is starting to arrive. The new issue of Nature (online June 26, 2011) and ScienceDaily bring the significant news that scientists have now actually fixed a disease by editing a chromosome in a mouse. In short, they researchers designed a way to target – and then edit (replace) – a particular segment of DNA.
In short, the targeted sequence was missing the instructions to create blood clotting protein. The absence of the clotting protein creates the disease we call hemophilia. The "fix" involved inserting the genetic coding needed to cause the mouse body to generate the clotting factor. An engineered virus was used to find the errant section, cut it out, and then insert new instructions. It worked – the mouse now produces the clotting factor and so is no longer a hemophiliac !
This is just one step down the path for science, but it is a symbolically large step. Key quotes are set out below from ScienceDaily’s summary of the full article.
ScienceDaily (June 26, 2011) — Using an innovative gene therapy technique called genome editing that hones in on the precise location of mutated DNA, scientists have treated the blood clotting disorder hemophilia in mice. This is the first time that genome editing, which precisely targets and repairs a genetic defect, has been done in a living animal and achieved clinically meaningful results.
As such, it represents an important step forward in the decades-long scientific progression of gene therapy — developing treatments by correcting a disease-causing DNA sequence. In this new study, researchers used two versions of a genetically engineered virus (adeno-associated virus, or AAV) — one carrying enzymes that cut DNA in an exact spot and one carrying a replacement gene to be copied into the DNA sequence. All of this occurred in the liver cells of living mice.
"Our research raises the possibility that genome editing can correct a genetic defect at a clinically meaningful level after in vivo delivery of the zinc finger nucleases," said the study leader, Katherine A. High, M.D., a hematologist and gene therapy expert at The Children’s Hospital of Philadelphia. High, a Howard Hughes Medical Institute Investigator, directs the Center for Cellular and Molecular Therapeutics at Children’s Hospital, and has investigated gene therapy for hemophilia for more than a decade.