Background:
Thymidine Kinase 2 deficiency (TK2d) is an ultra-rare inherited mitochondrial disorder affecting roughly 50 patients worldwide, although the exact number is unknown. ​

In this autosomal recessive disorder, alterations to the TK2 gene lead to partial or full lack of function of the TK2d enzyme. This results in the inability recycle thymidine nucleotides, and therefore mitochondrial DNA cannot be repaired or replicated. As a result, mitochondrial function ins greatly affected and there is a lack of energy production, cells that require high energy production are the most affected.

Symptoms can begin in infancy, childhood, or adulthood and there is a spectrum of symptoms which depend on severity of disease and age of onset, symptoms often worsen over time but the earlier the onset the higher the likelihood of critical disease. Symptoms may include loss of muscle mass, difficulty with mobility, difficultly breathing and difficulty swallowing.​ As a result of symptoms, patients are often referred for genetic testing or for a muscle biopsy that will lead to diagnosis​

In the United Kingdom, there is no approved treatment for TK2d, and clinicians aim to manage symptoms.

Aim:
This piece of work aimed to further understand the lived experience of people living with or caring for or have cared for people living with TK2d. ​

The insight gained from this study will be used to form part of the evidence basis for a patient group submission to NICE for the approval of Doxecitine–doxribtimine for treating thymidine kinase 2 deficiency in people of any age [ID6484]