The goal of the prospective treatment, which is not yet in clinical trials, is to repair a faulty gene that causes hemophilia A, the more common of two main types of the disease. If the therapy is perfected, a single dose could last for years, improving quality of life for patients, who currently must inject themselves with treatments two or three times per week.

Dimension Therapeutics, a Cambridge biotechnology startup, has struck a deal worth up to $252 million with the pharmaceutical giant Bayer HealthCare to develop a gene therapy to treat hemophilia, a rare disease that prevents blood from clotting.


Under the agreement with Bayer, Dimension will get $20 million upfront, followed by development and commercialization milestone payments that could total $232 million. Bayer will fund clinical trials and handle regulatory submissions. In exchange, it will have worldwide rights to commercialize the resulting therapy, should it go to market, though Bayer would continue to pay royalties to Dimension.

For Dimension, founded less than a year ago, the deal represents rapid validation of its research.

"It's quite rewarding to understand the level of confidence that they've put in us to get us to this extraordinary deal," said chief executive Thomas R. Beck.

Beck declined to offer a timetable for beginning clinical trials, and both companies acknowledged it will be years before the gene therapy could become readily available.

Hemophilia is caused by defective genes that are unable to produce the proteins that enable blood to clot. The disease can cause even minor wounds to bleed profusely.

Because of the way genes are passed down, hemophilia affects males almost exclusively. About 20,000 people in the United States are living with the disorder, according to the Centers for Disease Control, with roughly 80 percent suffering from hemophilia A.

After nearly two decades without a new treatment for the disease, Cambridge-based Biogen Idec received FDA approval this spring for two new drugs, one for hemophilia A and one for hemophilia B, that allow patients to go as long as five days between injections.


Bayer's large bet on Dimension is the latest endorsement of gene therapy, which is back in vogue after having fallen short of lofty expectations more than a decade ago.

A new technique that uses a class of viruses known as adeno-associated viruses to carry proteins in the body has helped revive interest in gene therapy, which promises long-lasting relief from hard-to-treat diseases by targeting the root cause — bad genes — instead of only the symptoms.

Several Boston-area companies are at the forefront of gene therapy, including Cambridge-based Voyager Therapeutics, which received $45 million in venture funding in February for its programs targeting ALS and Parkinson's disease.

In addition, bluebird bio, also of Cambridge, raised more than $100 million in an initial public stock offering a year ago. It is developing therapies for multiple blood and central nervous system disorders.

Bayer has steered clear of gene therapy for hemophilia since an unsuccessful project in the 1990s, during the first wave interest in the strategy.

Hans Duerr, who heads Bayer's global hematology business, recalled a promising treatment for hemophilia B that worked in animal trials but proved ineffective in humans.

"Gene therapy has always been a promise out there, and we've been intrigued by the possibilities, but it comes with a lot of challenges, and we wondered if the right time to get back in would ever come," Duerr said. "Technology has advanced, and we feel now is the right time to reenter."


In the meantime, Bayer has developed a leading hemophilia drug that replaces a protein called Factor VIII, which enables blood to clot but is missing in people with hemophilia A. It is effective, but must be readministered by injection every few days.

A newer version, in development, could reduce the frequency of injections to once per week, Duerr said.

"But the gene therapy would be a huge leap," Duerr added. "Maybe not for a lifetime, but certainly for many years."

Callum Borchers

can be reached at callum.borchers@globe.com. Follow him on Twitter @callumborchers.