A spotlight on TK2d: why earlier answers matter for families living with an ultra-rare disease
This is an advertorial sponsored by UCB.
Cristy Balcells, Global Patient Engagement Lead, Rare Diseases at UCB, and Fabian Somers, Vice President Asset Head Rare and Ultra-Rare Diseases at UCB, discuss the human impact of thymidine kinase 2 deficiency (TK2d), the importance of listening to those affected, and why genetic testing can be a critical step towards earlier diagnosis and more appropriate care
TK2d: an ultra-rare mitochondrial disease
Thymidine kinase 2 deficiency (TK2d) is an ultra-rare, life-threatening, genetic mitochondrial disease that can affect the parts of the body that need the most energy—the muscles, heart and brain, and often results in premature death.1–6 Characterised by progressive and severe muscle weakness known as myopathy,
TK2d can make everyday activities, like walking, eating and even breathing, increasingly difficult and sometimes impossible.2-6
The condition can present differently from person to person, with symptoms beginning at different ages and progressing at varying speeds.1,2,4,5 That variability, alongside similarities to other neuromuscular and mitochondrial diseases, is partly why TK2d can be difficult to recognise and why reaching the right diagnosis can be such an important step for families and healthcare teams.1,2,4 Due to its rarity, TK2d awareness within the medical community remains low, further complicating diagnosis.1,4
TK2d Awareness Day in September helps bring greater attention to this little-known condition, offering an important moment to reflect on why recognition and understanding can make such a difference for families navigating the path to diagnosis.
The reality behind the symptoms
For many people affected by a rare disease, the hardest part can be not knowing what is happening to yourself or a loved one. As a mother of a child born with a rare mitochondrial disease, and as someone who personally works with the TK2d community, Cristy understands first-hand the everyday uncertainties that families face living with an unfamiliar disease.
“Families are often trying to explain something that others cannot easily see or understand,” Cristy says. “I think that we need to understand, from the people themselves, what that looks like. I’m very interested in qualitative representation of communities and what that experience for them looks like.”
From working closely with the community and hearing the lived experiences of those with TK2d, Fabian reflects on the true impact of the disease:
“TK2d is a very rare but also a very harsh disease—one that takes a huge toll on patients and their families. TK2d robs patients of their ability to do the most basic things, like standing up, sitting, eating, breathing—all things we take for granted.”
A search for answers: why genetic testing matters
Genetic testing looks for changes in a person’s genes that may help explain their symptoms. In TK2d, molecular genetic testing can confirm the diagnosis by identifying disease-causing changes in both copies of the TK2 gene.2,7–9
Earlier consideration of TK2d and appropriate genetic testing could help families move from uncertainty towards clearer conversations about care, support and next steps.
“Genetic testing is more than a laboratory step,” Fabian states. “For families, it can be the moment the story starts to make sense, and the moment healthcare teams can begin to ask more targeted questions to hopefully lead to the right answers.”
Cristy adds that these answers can also help families advocate for themselves.
“Educating and empowering people so that they can have those seats at the table to be part of their own healthcare decisions, that’s important to me,” she says. “Really making decisions with the people who are going to be most affected and trying to understand what’s important to them.”
For those living with TK2d and their caregivers, an earlier diagnosis can also reduce the emotional and physical burden of searching for an explanation. It allows them to move forward in understanding what they are facing and getting access to the right care.
Listening to families: first-hand lived experiences matter
Cristy believes awareness work must begin by collaborating with the community, rather than simply speaking to it. She believes engagement is most meaningful when it reflects what people living with TK2d and caregivers say they need at different points in the journey.
“Support has to be specific,” she says. “A family newly searching for answers may need something very different from a family already managing long-term care. If we want to be patient-centred, we must be precise about what we are offering and when.”
Fabian agrees that progress depends on partnership.“We need to make sure we elevate everyone’s role in a partnership that’s there to benefit patients in ways that matter to them, such as more rapid diagnosis.”
Turning awareness into action
September brings both TK2d Tuesday and World Mitochondrial Disease Week, important milestones in raising the visibility of TK2d and the realities of mitochondrial diseases. But awareness must also lead to action, recognising possible signs, considering TK2d earlier and understanding the role genetic testing can play in confirming the diagnosis.
For Fabian, the call to action is simple:
“Diagnosis is the starting point for patients to get the proper care they deserve. Supporting disease awareness, while also improving access to genetic testing and counselling for a timely and accurate diagnosis, is definitely a priority.”
For Cristy, the message is also about empowerment.
“Families should not have to fight to be heard. The more we raise awareness of TK2d, the more we can help families move towards answers and a care conversation that recognises the full reality of their lived experience. The lived experience of TK2d is holistic by nature, so solutions should also be holistic.”
This sponsored article was developed by UCB, with contributions from Cristy Balcells and Fabian Somers.
GL-DA-2600915
Date of preparation: August 2026
© UCB Biopharma SRL, 2026. All rights reserved.
References:
[1] Garone C, et al. Retrospective natural history of thymidine kinase 2 deficiency. J Med Genet. 2018;55(8):515-21.
[2] Wang J, El-Hattab AW, Wong LJC. TK2-Related Mitochondrial DNA Maintenance Defect, Myopathic Form. 2012 Dec 6 [Updated 2018 Jul 26]. In: Adam MP, Bick S, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2026. Available from: https://www.ncbi.nlm.nih.gov/books/NBK114628/.
[3] Cleveland Clinic. Mitochondrial Diseases. https://my.clevelandclinic.org/health/diseases/15612-mitochondrial-diseases. Accessed August 2026.
[4] Berardo A, et al. Advances in Thymidine Kinase 2 Deficiency: Clinical Aspects, Translational Progress, and Emerging Therapies. J Neuromuscul Dis. 2022;9(2):225-35.
[5] Domínguez-González C, et al. Late-onset thymidine kinase 2 deficiency: a review of 18 cases. Orphanet J Rare Dis. 2019;14(1):100.
[6] National Institutes of Health. TK2-related mitochondrial DNA depletion syndrome, myopathic form. https://medlineplus.gov/genetics/condition/tk2-related-mitochondrial-dna-depletion-syndrome-myopathic-form/#genes. Accessed August 2026.
[7] Parikh S, et al. Diagnosis and management of mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society. Genet Med. 2015;17(9):689–701.
[8] de Barcelos IP, Emmanuele V, Hirano M. Advances in primary mitochondrial myopathies (PMM). Curr Opin Neurol. 2019;32(5):715-721.
[9] Dominguez-Gonzalez C, et al. Muscle MRI characteristic pattern for late‑onset TK2 deficiency diagnosis. J Neurol. 2022;269:3550–3562.
