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HemophiliaDecember 2017Summary reviewed July 2026

A One-Time Gene Therapy Gave 6 of 7 Hemophilia Patients Normal Blood Clotting

Researchers tested a one-time gene therapy infusion in nine men with severe hemophilia A. Six of seven people who got the highest dose reached normal clotting factor levels that lasted a full year, and bleeding events dropped dramatically.

What the trial was testing

The trial enrolled 15 patients with hemophilia. The study was sponsored by BioMarin Pharmaceutical and tracked outcomes across the full group of patients who matched the trial's eligibility profile.

It was an early-stage trial — researchers are still confirming safety and getting an early look at how well the treatment works. Trials at this stage are designed to produce evidence regulators and physicians can act on — not just observations to follow up later.

What the results showed

Six of seven participants reached normal clotting factor levels that lasted one year.

The New England journal of medicine · 2017 · NCT02576795

These findings — that participants who got the high dose achieved normal clotting factor levels for a year — were published in the The New England journal of medicine and represent the headline result of the study.

Researchers tracked outcomes across 15 patients enrolled in the trial. The result was consistent enough across the group that the team felt confident reporting it.

What this means for patients

For patients with hemophilia, this result changes the calculus on what to ask their care team about. Whether it changes day-to-day care depends on factors like disease subtype, prior treatments, and where the patient is in their care journey.

What you can do now

This was an early-stage study with only nine people. The gene therapy (valoctocogene roxaparvovec) later gained FDA approval in 2023 under the brand name Roctavian for adults with severe hemophilia A. Ask your doctor if this treatment is right for you.

Eligibility for the treatments mentioned above depends on specific test results and clinical history. Bring this summary, the trial name, and your most recent labs or pathology report to your next visit.