The hidden impact of Thymidine Kinase 2 Deficiency

When we speak with families living with thymidine kinase 2 deficiency (TK2d), we are reminded that the clinical description; an ultra-rare, genetic mitochondrial disease causing progressive muscle weakness, only just begins to capture the reality. Behind every diagnosis is a child struggling to walk, a caregiver staying awake to watch out for breathing difficulties, or an adult adapting to the loss of independence.

I want to share what we are learning from individuals and families who live with TK2d, and why their voices help change how we think about this disease.

First symptoms and early progression

Most people first notice something is wrong before they turn 12. In a recent UCB-led online forum with patients and caregivers, eight out of ten participants reported their first symptoms appeared by that age - typically muscle weakness, unexplained falls, or what was described as ‘floppiness’.

The trajectory of TK2d rarely stays still. Children with early-onset disease may decline rapidly, with a life expectancy of around four years from onset. Adolescents and adults face new and often frightening symptoms such as respiratory difficulty, swallowing problems, and a steady loss of mobility that survey participants described as the most significant turning point in their disease.

A burden that families carry largely on their own

TK2d does not stop with the person living with the condition. It reshapes entire households. New research presented at EUROMIT 2026 found that the cost and care burden of TK2d in children may exceed even spinal muscular atrophy and Duchenne muscular dystrophy.

As the disease progresses, support needs grow; starting with home adaptations, to round-the-clock care, and ultimately hospice placement. Families face workforce loss and significant out-of-pocket costs for these home modifications, as well as travel and assistive devices.

Those living with the disease describe the same picture from the inside, noting increased reliance on equipment and a daily impact on the things that matter most to them - mobility, daily activities, and independence.

Why earlier diagnosis matters

Because TK2d can progress quickly, particularly in children, reducing the time from first symptoms to diagnosis is critical. Earlier recognition is seen as a turning point that opens the door to earlier specialist input, better-coordinated care, and appropriate treatment and management options.

Those living with the condition tell us the same thing in their own words. For some forum participants, simply receiving their TK2d diagnosis was recognized as a positive turning point in their journey - an answer after years of uncertainty, and the start of a more directed care pathway. Access to treatment was also frequently described as the most positive turning point, made all the more poignant because, until recently, there were no approved treatment options.

Earlier recognition depends on greater awareness across the healthcare community, particularly among the pediatricians, neurologists, and other specialists most likely to see early presentations of childhood muscle weakness. The clearer those early signals are to the wider clinical community, the sooner families can move from searching for answers to receiving an accurate diagnosis and appropriate care.

Turning commitment into action

Our role at UCB is to keep listening to those living with TK2d, their caregivers, and healthcare professionals - translating what we hear into research, education, and support for earlier diagnosis. The voices behind these new findings are a reminder of why we do this work.

Together, with continued collaboration and a sharper focus on what families experience every day, we can give people living with TK2d more opportunities to feel heard - and more reasons to hope.

I invite you to learn more here Thymidine Kinase deficiency type 2 | UCB