How long do we need gene therapy to last?

Biomarin Pharmaceuticals’ gene therapy for hemophilia A might work well enough to win approval, but the durability of its effects has led to a familiar debate for one-time treatments.

As STAT’s Adam Feuerstein and Matthew Herper write, the latest data are unquestionably positive by one metric: Patients had very few of the bleeding episodes that characterize hemophilia A. The issue is that the gene therapy’s effect on factor VIII, the clotting factor patients are missing, waned over time.

Biomarin believes the data it’s gathering will be enough to convince regulators to approve the therapy by the end of 2020. But just how much payers are willing to shell out for the one-time treatment will depend on how long it can keep hemophilia A patients out of the hospital and free from the need for other expensive drugs.

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