Skip to Content

Gene Therapy Stops Bleeding in Hemophilia Patients

December 7, 2017

By infusing hemophilia sufferers with safe, redesigned viruses, it’s possible to get their livers making clotting agents that are otherwise missing from their body.

Patients with hemophilia B lack a gene that helps create factor IX, a protein that clots blood, making it difficult for even small bleeds to stop. A promising gene therapy developed by Spark Therapeutics promises to solve that by administering an infusion of viruses carrying the missing factor IX gene. In a handful of patients, early results appeared to be promising (see “Gene Therapy Is Curing Hemophilia”).

Now, a modestly sized trial suggests that Spark may really be onto something. In results published in the New England Journal of Medicine, 10 patients received viruses designed to deliver the missing gene to their livers. Eighteen months after the treatment, on average their livers made 34 percent of the normal level of the clotting agent. That may sound low, but it was enough for nine patients to have no bleeding, and eight didn’t require regular injections of clotting agent.

Some question marks still hang over the therapy. First, the trial is still small, and larger tests will be required before the treatment really proves itself. Another major concern  is how long the effect will last beyond the 18 months of the trial. It’s hoped that it will be a one-time cure, but it might need to be if it’s going to be viable—given the high cost of gene therapies, multiple treatments over a lifetime may not be feasible.

Deep Dive


Our best illustrations of 2022

Our artists’ thought-provoking, playful creations bring our stories to life, often saying more with an image than words ever could.

How CRISPR is making farmed animals bigger, stronger, and healthier

These gene-edited fish, pigs, and other animals could soon be on the menu.

The Download: the Saudi sci-fi megacity, and sleeping babies’ brains

This is today’s edition of The Download, our weekday newsletter that provides a daily dose of what’s going on in the world of technology. These exclusive satellite images show Saudi Arabia’s sci-fi megacity is well underway In early 2021, Crown Prince Mohammed bin Salman of Saudi Arabia announced The Line: a “civilizational revolution” that would house up…

10 Breakthrough Technologies 2023

Every year, we pick the 10 technologies that matter the most right now. We look for advances that will have a big impact on our lives and break down why they matter.

Stay connected

Illustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at with a list of newsletters you’d like to receive.