Ask the Mito Doc – March 2026: Updates on TK2d Therapy Kygevvi
All answers today are based on personal experience of the participants. As always, please consult your personal physician prior to taking any action.
Speakers:
· Sarah Chang, PhD, Medical Strategy Lead, UCB
· Cristy Balcells, RN, MSN, Global Patient Engagement Lead, UCB
Q: Is treatment available as preventative medicine, or do symptoms have to be present? Is the goal to prevent symptoms, or treat them once they exist?
A: Cristy Balcells, RN: Symptom onset is explicitly stated in the FDA approval: Kygevvi is indicated for the treatment of thymidine kinase 2 deficiency (TK2d) in adults and pediatric patients with an age of symptom onset on or before 12 years.
Q: Has Kygevvi ever been used in a patient with the TK2D variant mutation that has yet to be symptomatic?
A: Sarah Chang PhD: Our clinical study looked at symptomatic patients. It’s a really good question because it is an ultra rare disease. There’s a lot we don’t know. The people we hear about, we’re hearing about because they have symptoms. And we’ll see what the future of genetics holds because we are entering into this era where we’re getting so much information and we might be able to identify people earlier before symptoms happen. So at this point, no, but we’ll see what the future holds.
Q: The young patients that I know have very dramatic symptoms, so it’s hard to miss when they are little. What would your advice be to a person who is at the geneticist today and they get a diagnosis of TK2D for their very young child? What steps do you think they should take?
A: Sarah Chang PhD: Well, I think they should work with their geneticist to understand the implications of that test result and then work with their healthcare team to understand if the patient is symptomatic and if they want to pursue treatment. I would recommend having that conversation with the healthcare provider.
Q: What about PolG in this treatment? TK2D is not the same as PolG, correct?
A: Sarah Chang PhD: You are correct. And we get this question a lot. There is a lot of interest in the community because there aren’t a lot of treatments available for people with mitochondrial disease. Kygevvi was studied specifically for people living with TK2D, and they did have confirmed mutations in the TK2 gene; we don’t have an indication for people with PolG.
Q: Can PolG lead to TK2d like symptoms? Since PolG also can have mitochondrial deletion, would that or could that lead to deletion of the genes needed or responsible for the TK2d enzyme? I ask because this drug is currently being studied in Canada for PolG treatment. Will be meeting that Doctor sometime this year. Is there any evidence that the treatment is beneficial prior to symptoms? The issue I’m running into is that progression is apparently measured by symptoms, which aren’t necessarily indicative of mitochondrial decline or mitochondrial function.
A: Cristy Balcells, RN: PolG can look like TK2d deficiency but it is caused by a different gene, even though they both share a mitochondrial pathway. The clinical trial for Kygevvi assessed the survival benefit of treatment only in people with genetically-confirmed TK2d who had already begun to show symptoms. These pre-symptom questions being explored in the field by clinicians, as you mention, but was not answered in the Kygevvi clinical trial.
Q: When a patient is determined to need this medicine what is it going to look like? Do they just go to their local Walgreens and get it? I know the answer to this question, but I think everybody else needs to know too, that it’s not so easy or not so straightforward.
A: Sarah Chang, PhD: We at UCB have partnered with what’s called a specialty pharmacy. Their name is Panther Rx Rare. They focus exclusively on rare diseases, and they ship directly to the patient’s home. And you would work with your healthcare provider to get that prescription. Panther would be the pharmacy that then ships it out to the patients and families. The specialty pharmacy, along with the folks at UCB, can help families determine how their insurance might work and how to take care of that part of the equation. Panther would work directly with your doctor, help coordinate with the insurance provider during the approval process, and then if there were any questions, UCB Cares can always point you in the right direction as well.
Q: What about now that the trial is over and the medicine is commercially available? What about those who maybe live somewhere else or that where there isn’t an approval, how would they access the medicine? Would it be the same as it’s always been?
A: Sarah Chang, PhD: If a person is living outside of the US, they would work with their healthcare providers. We do have expanded access programs running in other countries. There are eligibility requirements. It would be recommended that the patient work with their health care provider to understand if they are eligible and then that health care provider would put in a request.
Q: How can people describe and report any side effects? And if they were to report to the FDA where would they do that?
A: Sarah Chang, PhD: They can go to the UCB Cares website to do that or call 1-844-599-CARE, which is 2273. They can also report side effects to the FDA. Their number is 1-800-FDA-1088.
Q: Is use of Kygevvi for other mtDNA depletion syndromes being studied?
A: Sarah Chang, PhD: At this time, no, we have not studied it in other mitochondrial DNA depletion syndromes.
Q: What did this approval mean to your team at UCB and how do you feel now that this has happened?
A: Sarah Chang, PhD: I tell everyone I’ve worked in the pharmaceutical industry in various capacities for over 20 years now. For me, this experience has been personally the most rewarding. It’s because of the connectedness with the community. It is unlike any other community that I’ve worked with. The team at UMDF, the patients, the families, everyone is so engaged and so authentic and genuine. And our team at UCB we call tiny but mighty. We are all deeply engaged and we’re driven by the mission to support better outcomes for people living with mitochondrial disease and TK2D specifically. When we got the approval, there was joy, there were tears. It was a very emotional response, I would say.
Q: I know once the approval happens, there’s a lot that has to go on. So when did the drug officially become commercially available?
A: Sarah Chang, PhD: That’s a very timely question, Margaret, because that just happened on Monday this week.
A: Margaret Moore, UMDF Support: So it’s very exciting that we’re here and now the work begins on making sure that patients can get this that need it, and that all of that goes as smoothly as possible. It’s going to be a little bumpy, I think, at first because we’re all getting used to this. But just know that behind the scenes we’ve been trying to figure out how to best support patient families as they walk through this journey. And I encourage anyone that is moving from the clinical trial to the medicine or getting the medicine for the first time to please reach out to us and we’ll get you on the right path to make sure that it’s as smooth of a road as possible.