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Sick Kids scientists repair genetic errors in mice with muscular dystrophy

Sick Kids scientists wielding a “breakthrough” gene editing technology have snipped out a genetic defect in mice that causes a severe form of muscular dystrophy, eliminating all signs of paralysis in the animals. Science magazine hailed the gene editing tool, CRISPR, as the breakthrough of the year in 2015. The new research is part of a wave of effort to push CRISPR from its early experimental promise toward real-life therapies. “It’s not just something that happens in a petri dish. And it happened in such a remarkable way,” said Dr. Ronald Cohn, the principal investigator of the new study and a senior scientist at Sick Kids. Much work remains before the technique can be tested in humans. But success in animal experiments allows researchers to begin exploring that next step. “For the first time it’s possible to think about — and this is still at the thinking stage, let’s be clear — the possibilities of gene correction in humans with these diseases,” said Janet Rossant, a senior scientist in the stem cell and developmental biology program at Sick Kids who was not involved in the research. Rossant called the new study “really important.”Article Continued BelowThe mice in the study have a rare and severe form of congenital muscular dystrophy known as MDC1A. Humans afflicted with the disease are typically diagnosed as infants, lose muscle function as they develop, and die in their late teens or early 20s. “I couldn’t believe it. I don’t want to be dramatic, but I couldn’t believe it,” says Dr. Ronald Cohn, the principal investigator of the study and a senior scientist at Sick Kids, of the degree of recovery he saw in the mice.  (Anne-Marie Jackson / Toronto Star) | Order this photo  The illness is caused by a splice site mutation: a genetic error makes cellular messengers misread a critical section of DNA, like the scratch that makes a record skip.Researchers in Cohn’s lab used CRISPR to cut out the scratch. Natural cell repair mechanisms stitched the remaining strands of DNA back together, allowing the whole genetic sequence to be read normally.

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