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article imageGene-editing technology repairs mutation for muscular dystrophy

By Tim Sandle     Oct 5, 2017 in Science
A new way to deliver gene-editing technology inside has repaired the mutation that causes Duchenne muscular dystrophy, which is a severe muscle-wasting disease, in mice. The delivery system is CRISPR-Gold.
The development comes from the University of California, Berkeley. Success with the new delivery system saw an 18-times-higher correction rate together with a two-fold increase in a strength and agility test, when the treated mice were compared with control groups.
For the method, lead researchers Jennifer Doudna and Emmanuelle Charpentier repurposed a protein called Cas9 protein to develop a low-cost, precise and straightforward gene editor. This adds to growing evidence that therapies based on CRISPR-Cas9 can revolutionize the treatment of genetic diseases.
The conduction focused on in the animal model — Duchenne muscular dystrophy — is a severe type of muscular dystrophy. Symptoms include muscle weakness, with muscle loss in humans occurring first in the upper legs and pelvis followed by those of the upper arms. The condition can be associated with intellectual disability. The genetic disease affects males.
CRISPR is an acronym for “Clustered regularly-interspaced short palindromic repeats” and it is a genome editing tool that functions much like molecular scissors. The technique enables scientists to modify an organism’s DNA. This gene editing technique is an efficient way of disabling genes, by introducing small mutations that disrupt the code of a DNA sequence and also to repair genes. To read more about this see Digital Journal’s article “Essential Science: First U.S. case of human embryo gene editing.”
Established CRISPR/Cas9 corrects gene mutations by slicing the mutated DNA, which triggers homology-directed DNA repair. The problem is that the means of safely delivering the necessary components (Cas9, guide RNA, plus donor DNA) into cells needs to be worked on in order for the technology to reach its potential. The standard technique to deliver CRISPR-Cas9 into cells uses viruses. Here this method has led to complications. The new CRISPR-Gold technique does not use viruses.
The new method is called CRISPR-Gold since gold nanoparticles are a component. The method delivers Cas9, which is the protein that binds and cuts DNA, into the cells of a living organism to fix a specified gene mutation.
The specific repair process is termed homology-directed repair. This is complex since it requires activity to be going on at the same place and time as Cas9 protein. The method also needs an RNA guide to recognize the mutation together with donor DNA to correct the mutation. To achieve this, the researchers designed a delivery vessel to binds each of the components together. The vessel then releases each component once it inside a wide variety of cell types. This triggers the homology directed repair. The gold nanoparticles coat the donor DNA and bind Cas9.
The initial success with mice led the researchers to tell Controlled Environments magazine: “These experiments suggest that it will be possible to develop non-viral CRISPR therapeutics that can safely correct gene mutations, via the process of homology-directed repair, by simply developing nanoparticles that can simultaneously encapsulate all of the CRISPR components.”
The research has been published in the journal Nature Biomedical Engineering, with the paper titled “Nanoparticle delivery of Cas9 ribonucleoprotein and donor DNA in vivo induces homology-directed DNA repair.”
More about Crispr, CRISPRgold, Muscular dystrophy, Genes, Genetics
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