New mitochondrial disease treatment available through UK early access scheme
A new treatment for a mitochondrial disease, thymidine kinase 2 deficiency (TK2d) is now available in the UK through the Early Access to Medicines Scheme. Doxecitine-doxribtimine is the first medicine developed specifically to target the underlying cause of TK2d. While not yet fully licensed in the UK, the scheme allows certain patients to access the treatment while it continues through the UK’s licensing process.
For the first time, some people with a type of mitochondrial disease called thymidine kinase 2 deficiency, or TK2d, may now be able to access a new treatment designed specifically for their condition through something called the Early Access to Medicines Scheme.
The treatment, called doxecitine-doxribtimine but is also known by the brand name Kygevvi in the USA and the EU. Doxecitine-doxribtimine is already approved in the USA and EU but not yet fully licensed in the UK.
What families need to know
Although doxecitine-doxribtimine isn’t yet fully licensed in the UK, some children and adults with genetically confirmed TK2d may now be able to access it through the UK’s Early Access to Medicines Scheme if their symptoms began at or before the age of 12. This refers to the age when symptoms first appeared, not the person’s current age.
Families should speak to their mitochondrial specialist team, as access cannot be arranged directly through Metabolic Support or via the manufacturer.
What is doxecitine-doxribtimine?
Doxecitine-doxribtimine is the first medicine developed to target the underlying cause of TK2d. While not a cure, it aims to address the specific biological problem that leads to the condition.
It provides substances that the body uses to make and maintain mitochondrial DNA. This may help muscle cells produce energy more effectively and could slow the progression of the condition.
Evidence so far suggests that the treatment may improve survival and help some patients maintain or regain physical abilities. However, TK2d is extremely rare, and the evidence comes from a relatively small number of patients, so people receiving it will continue to be monitored carefully.
What is TK2d?
TK2d is a very rare inherited mitochondrial disease. It mainly affects the muscles and can cause progressive muscle weakness, loss of movement, breathing difficulties and problems with eating and swallowing.
The condition affects people in different ways and can be life-limiting, particularly when symptoms begin in infancy or childhood.
You can find more information about its causes, symptoms, diagnosis and management on our TK2d information page.
What is the Early Access to Medicines Scheme?
Before a treatment can be routinely prescribed on the NHS in the UK, it must receive a licence.
The Early Access to Medicines Scheme allows some patients with serious or life-threatening conditions to access promising new medicines before they receive a full UK license, where there’s a clear unmet medical need and the potential benefits outweigh the risks.
The UK medicines regulator, the MHRA, has reviewed the available evidence and believes the potential benefits of Doxecitine-doxribtimine are greater than the known risks for patients who meet the scheme’s criteria.
A positive Early Access to Medicines Scheme decision is not the same as full UK approval, however, and it doesn’t mean that everyone with TK2d will be eligible for and benefit from the treatment.
You can read the official MHRA information about doxecitine-doxribtimine and TK2d on the GOV.UK website.
Could this treatment help people with other inherited metabolic disorders?
Doxecitine-doxribtimine has been developed specifically for TK2d. It works by addressing the particular problem caused by changes in the TK2 gene.
Other inherited metabolic disorders are caused by different genetic changes and affect the body in different ways. There’s currently no evidence that this treatment would be safe or effective for those conditions.
This early access scheme is therefore limited to eligible people with genetically confirmed TK2d and cannot be used to provide the treatment for other inherited metabolic disorders.
Why is doxecitine-doxribtimine approved in the USA and Europe, but not here?
Medicines must be assessed separately by the regulators responsible for different countries and regions.
Doxecitine-doxribtimine was approved in the United States in November 2025 and in the European Union in March 2026. Following the UK’s departure from the European Union, EU approval doesn’t automatically apply here.
Doxecitine-doxribtimine still needs to go through a separate UK approval process. Early Access to Medicines Scheme provides a route for some eligible patients to access it while it remains unlicensed here.
What happens next?
Specialist mitochondrial disease teams can now consider whether eligible patients may be suitable for treatment.
Patients who receive doxecitine-doxribtimine through Early Access to Medicines Scheme will need regular monitoring, which may include blood tests and other checks recommended by their clinical team.
Further decisions will be needed before the treatment can become fully licensed and routinely available through the NHS. There’s no confirmed timetable for this yet.
What is Metabolic Supports role?
Metabolic Support has worked closely with The Lily Foundation, a patient organisation dedicated to those with mitochondrial disorder and with people affected by TK2d to make sure patients’ experiences are understood as this treatment has developed.
This has included gathering evidence about the impact of TK2d on patients and carers, and helping to make sure their experiences inform decisions about access to treatment. You can read more about our research here.
We’ll continue to provide clear information, support families and represent the inherited metabolic disorder community as decisions are made about longer-term UK access.
Metabolic Support cannot decide whether someone is eligible for doxecitine-doxribtimine, prescribe the treatment or guarantee access. These decisions must be made by a patient’s specialist clinical team.
How can patients and families access doxecitine-doxribtimine?
Families should speak to their mitochondrial specialist team.
A specialist doctor will need to confirm whether the patient meets the Early Access to Medicines Scheme criteria and whether the treatment is suitable for them.
Anyone affected by TK2d who would like more information or support can contact Katie, the Head of Patient Support and Advocacy at the Lily Foundation, at katie@thelilyfoundation.org.uk. For information and support about other inherited metabolic disorders, please contact Helen, the Support and Advice Manager at Metabolic Support, at contact@metabolicsupport.org.
Questions about individual patient treatment should always be discussed with your mitochondrial specialist.
