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Three research groups, working independently of one another, reported in the journal Science on Thursday 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.

The teams were led by Charles A. Gersbach of Duke University, Eric N. Olson of the University of Texas Southwestern Medical Center and Amy J. Wagers of Harvard University.

Mosquito-borne disease affecting millions has had no approved vaccine until now

When female Aedes Aegypti mosquito sups on the blood of its human victims it too often deposits the virus that causes dengue, causing as many as 400 million infections per year worldwide. Severe forms of the painful, flu-like disease can be fatal, especially among children. And until recently there has been no truly effective prevention except avoiding getting bit. But the outlook against the disease is looking better.

During the past month Dengvaxia, developed by the French pharmaceutical company Sanofi, has been approved for use in three countries: Mexico and the Philippines approved the vaccine earlier this month. This week, the company also announced the drug has received the green light in Brazil, which has seen more than 1.4 million cases of the disease in 2015. Exactly when the inoculations will be deployed—and at what price—remains unclear as terms of the vaccine are being negotiated between the company and the countries.