On-Demand, Prophy, Gene Therapy, Gene Editing: What’s the Difference?

Megan Procario, PhD candidate in the department of Microbiology and Immunology at the University of Michigan Medical School

(Originally published in HFM’s Spring 2019 issue of The Artery)

There are many treatment options for patients with hemophilia, with even more being developed in scientific laboratories. I’d like to use an analogy to outline the broad principles of some of these therapies. I’d like you to picture a neighborhood full of houses. Normally, all of these houses would be well-lit once evening falls. These houses are lit because they have power supplied by the local electric company. Within this neighborhood, however, there is one house that is unlike the others. This house can’t utilize the power from the electric company due to faulty wiring connecting the house to the power cables. Once the residents of the house identified the cause of their power deficit, they were able to talk with some engineers who specialized in this sort of problem.

This group of engineers presented the following list of options to the homeowners.

• Don’t do anything. Accept that the house doesn’t have electricity and all of the complications that come with that problem.

• Purchase a short-term power source to temporarily supply electricity to the house. These power sources usually last about 3-4 days before running out. There is both an option to buy these power sources as needed or to have them delivered on a regular schedule, twice a week.

• Purchase a large generator to supply electricity to the house. This isn’t exactly the same as the other houses in the neighborhood but is functionally very similar.

• Hire technicians to come to the house and repair the faulty wiring connecting it to the cables from the electric company. This should allow the house to finally (and permanently) utilize the power supplied by the electric company.

As you may have guessed, this story is an analogy for the different treatment options currently (or potentially) available to patients with hemophilia A or B. The power/electricity is the missing clotting factor, while the faulty wiring represents the mutation in the gene for the factor. The missing clotting factor can be temporarily supplemented via infusions, either on demand or on a prophylactic schedule, just like the short-term power source in the analogy. A more recent therapy that is in trial for patients with hemophilia is gene therapy. Very simply, this consists of adding a functional version of the gene for the missing clotting factor to the body. This doesn’t replace the mutated gene, which is still there, but instead allows the body to make factor using the additional gene. Just like in the analogy, where the generator didn’t change the faulty wiring, it performs its function in a slightly different way. The final therapy that this analogy refers to is not yet available for hemophilia patients but is currently being researched in the laboratory. This therapy is called ‘gene-editing’ and is precisely what it sounds like. Just like a technician fixing faulty wiring, this therapy allows scientists/doctors to change a patient’s mutated clotting factor gene to restore its function.

While there are many more details about these therapeutic options than I have discussed here, hopefully this will establish a good foundation. As always, if you have questions about your current hemophilia treatment, please reach out to your treatment team at your hemophilia treatment center.


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The Hemophilia Foundation of Michigan strives to improve the quality of life for all people affected by hemophilia, von Willebrand disease, other coagulation disorders, and related complications.

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