Slow but Steady Progress Toward Gene Editing for Hunter Syndrome and Hurler Syndrome

Gene Editing

What is gene editing? It’s been a hot topic over the last few years, but basically the concept is this: instead of disabling a malfunctioning gene, researchers are working on ways to replace or correct it. DNA changes achieved with gene editing are not passed to future generations.

Preliminary efficacy of gene editing has just been documented in patients with Hunter syndrome and Hurler syndrome. These conditions are the result of one missing gene. This gene is responsible for making an enzyme that helps the body break down sugar compounds. As a result, sugars build up and cause organ damage. Many people with these conditions don’t live past their teens.

Unfortunately, it’s not yet clear whether or not this editing will be successful in improving patient outcomes. However, these recent study has shown promise, researchers say.

The Study

The first Hunter syndrome patient to ever receive this form of gene editing was Brian Madeux. He received the treatment in 2017 through IV. He was given both copies of the corrected gene as well as zinc finger nucleases which are an editing tool used to help insert the gene into his DNA. The therapy was created by Sangamo Therapeutics.

Seven other Hunter syndrome patients later received this treatment as well as three individuals diagnosed with Hurler syndrome. From these individuals, preliminary safety of the therapy was documented. All of the adverse events experienced by patients were unrelated to the treatment.


All three of the Hurler syndrome patients achieved normal levels of the missing enzyme. However, even with that success, researchers explain that the key test in determining if the gene editing has been effective is seeing whether or not the patients’ bodies can produce the enzyme on their own after they stop enzyme therapy.

As for the Hunter syndrome patients, a few patients reached higher levels of the enzyme than they had previously had, but none achieved normalcy. The patient who experienced the largest increase also experienced an immune response to the therapy. However, additional treatment resolved this issue.

Of all patients in the study, three have gone off of their treatments. However, one later resumed due to rising sugar levels.

Researchers know that these patients must be studied for a much longer period of time in order to properly assess their outcomes. But overall, preliminary results indicate promise.

The Future

Researchers will continue this investigation. They have built a foundation which they can now use to develop better treatments. Ultimately, their goal is to find an effective way to provide gene editing for children with rare conditions, not just adults– therefore stopping symptoms before the disease can cause substantial damage.

Sangamo is working to produce a stronger version of this treatment. The company hopes to include teenagers with Hunter syndrome in future studies, utilizing this more potent therapy. The participation of minors is only possible thanks to the safety of the treatment indicated by the first cohort of patients. However, this examination will not begin for a little while. Before it starts, researchers want to examine the prolonged effects of the treatment on the first group, and therefore need to monitor them for a longer period of time.

You can read more about this ongoing research here.

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