New gene therapy gel is the 1st approved treatment for rare and painful 'butterfly disease'

A new gene therapy gel is the first-ever approved treatment for the most severe forms of "butterfly disease," a rare and painful skin blistering condition, the U.S. Food and Drug Administration (FDA) announced Friday (May 19).

Dystrophic epidermolysis bullosa (DEB) is a genetic condition that makes skin prone to blisters and chronic, painful wounds. The wounds raise the risk of life-threatening infections, limb deformities and a skin cancer called squamous cell carcinoma. 

Due to a genetic mutation, patients cannot make a specific type of collagen in their skin. This collagen would normally anchor different layers of skin to one another and thus prevent them from rubbing against each other and erupting in blisters.   

The newly approved gene therapy, called Vyjuvek (generic name beremagene geperpavec), works by delivering working copies of the defective collagen gene directly into patients' cells. The treatment itself is a gel that contains a version of the cold sore virus, herpes simplex virus 1, that's been modified so it can't replicate in human cells and carries two copies of the collagen gene: COL7A1.

Related: Gene therapy: What is it and how does it work? 

The gel's effectiveness was tested in two clinical trials that together included roughly 40 adults and children with either the dominant or recessive form of DEB, the latter of which causes much more severe symptoms than the former. In both trials, the gel significantly improved the rate at which patients' wounds closed, compared to a placebo gel. The treatment also helped prevent the skin from immediately blistering again, as working copies of COL7A1 hung around in the skin cells for some time.

The most common side effects included itching, chills, redness, rash, cough and runny nose, according to the FDA.

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The gene therapy gel is now approved for use in DEB patients who are at least 6 months old, and the treatment can be applied by a healthcare professional either in a clinic or in the patients' home, according to Krystal Biotech, the sponsor of the trials. 

"Until now, doctors and nurses had no way to stop blisters and wounds from developing on dystrophic EB patient skin and all we could do was to give them bandages and helplessly watch as new blisters formed," trial leader Dr. M. Peter Marinkovich, director of the Blistering Disease Clinic at Stanford Health Care and an associate professor of dermatology at the Stanford University School of Medicine, said in the Krystal Biotech statement. 

"Because [the drug is] safe and easy to apply directly to wounds, it doesn't require a lot of supporting technology or specialized expertise, making VYJUVEK highly accessible even to patients who live far away from specialized centers," he said. There are experimental EB therapies that involve skin grafts and engineered stem cells, which of course are far more involved than applying a topical gel to the skin, Marinkovich previously told Live Science.