schwit1 writes with news that scientists have used a new gene-editing technique called CRISPR to treat mice with defective dystrophin genes. This is the first time that such a method has successfully treated a genetic disease inside a living mammal. The Times reports: "Three research groups, working independently of one another, reported in the journal Science that they had used the Crispr-Cas9 technique to treat mice with a defective dystrophin gene. Each group loaded the DNA-cutting system onto a virus that infected the mice's muscle cells, and excised from the gene a defective stretch of DNA known as an exon. Without the defective exon, the muscle cells made a shortened dystrophin protein that was nonetheless functional, giving all of the mice more strength."