know that CRISPR-Cas9 technology works in both cells and germ cells and in both primate and human embryos.” George Church (2015) Encourage the innovators Nature 528, 3 December, Page S7 “There is no technical reason why gene therapy could not be deployed to alter the human germ line” “We already know that germline-editing is unlikely to cause dangerous, unforeseen mutations” “so far CRISPR-Cas9 seems capable of less than 1 error in 300 trillion base pairs, and techniques to reduce these off-target effects using CRISPR pairs might cut this by many factors of ten” Michael Eisenstein (2015) Closing the door on HIV Nature 528, 3 December, Page S8-S9 Virginia Gewin (2015) Expanding possibilities Nature 528, 3 December, Page S10-S11 “In late 2013, Hans Clevers isolated intestinal stem cells from two children with cystic fibrosis … He used these stem cells to grow gut tissue…. And introduced a healthy version of the gene that is disrupted in people with cystic fibrosis … The results were impressive; the faulty gene was corrected in about half of the miniguts that Clevers tested. “ “The consensus is that monogenc diseases – those involving only one gene – are the low lying fruit of the field” “Thedelivery hurdle is so substantial that researchers are trying to work around it, rather than over come it.” Easiest are problems with the bone marrow including HIV, sickle cell anemia, disorders and genetic diseases affecting the eye. Also easier are diseases in which the patient has one mutant gene and one healthy gene where witching off the mutant gene solves the problem. Trickier is inserting a corrected copy of the gene in place of the defective copy.
That new method is CRISPR, uses RNA-guided enzymes to snip out or add segments of DNA to a cell. In the first time it has been applied to Huntingtons disease, says neuroscientist Nicole Déglon of the University of Lausanne in Switzerland, who led the mouse study, results of which she and her co-researcher Nicolas Merienne shared yesterday at the Society for Neuroscience Conference in Chicago, Illinois. As neurological diseases go, Huntingtons is an ideal candidate for CRISPR therapy, because the disease is determined by a single gene, Déglon notes. A mutation in the gene, which codes for a normally helpful brain protein called huntingtin, consists of different numbers of “tandem repeats,” repeating segments of DNA that cause the protein to fold into a shape that is toxic to the brain. Déglon and her team wondered whether CRISPR could halt production of this dangerous molecule. Using a virus as a delivery vehicle, the researchers infected two separate groups of healthy adult mice with a mutant huntingtin gene, but only one group received the therapy: a CRISPR “cassette,” which includes DNA for the gene-editing enzyme Cas9 and the RNA to target the huntingtin gene. CRISPR-Cas9 works by “silencing” the part of the huntingtin gene that signals protein production. Researchers hypothesized that by cutting into these so-called “start sites,” they would be able to permanently pause synthesis of the huntingtin protein. If this were true, the mice treated with the CRISPR cassette would have little to no buildup of mutated proteins, and that’s exactly what Déglon and her team saw. After only 3 weeks, the two groups of mice showed a striking contrast: Those without the CRISPR treatment had large areas of protein aggregation, and those with the treatment had almost editing had prevented nearly 90% of the rogue proteins. “Having reached about 90% [blockage of production] changes the story [of Huntingtons therapy] completely,” she says. “It opens new treatment strategies that are based in DNA, and so would have a permanent benefit for the rest of someone’s life.” Abdellatif Benraiss, a translational neuroscientist at the University of Rochester in New York who is not involved with the research, cautions that the current technique is not poised for that kind of longevity. Because CRISPR cannot yet discriminate between mutant and healthy