The Lily Foundation statement on accessing experimental treatments overseas

We understand why people affected by mitochondrial disease and their families may wish to explore experimental treatments, particularly where there are currently few or no established treatment options. Early research into potential new therapies is important and can provide genuine reasons for hope. However, promising early findings do not necessarily mean that a treatment has been proven to be safe or effective.

This is particularly important when results come from small, early-stage studies without an untreated comparison group. Without an appropriate comparison, it can be difficult to know whether changes seen following treatment are due to the treatment itself, the natural course of the condition or other factors.

These concerns are shared by an international group of mitochondrial disease experts. In August 2026, 24 clinicians and researchers from across the international mitochondrial disease community contributed to a published commentary examining the evidence for nucleoside therapy in mitochondrial DNA depletion and deletion syndromes beyond TK2 deficiency. The commentary includes seven named authors and a further 17 international experts who contributed on behalf of the TK2d collaborators.

The experts recognise the importance of this early research and do not argue against further investigation, compassionate use or carefully conducted individual studies. However, they caution that the evidence currently available from studies in conditions including POLG-related disease should be considered preliminary. They highlight important limitations including small and clinically varied groups of patients, the lack of untreated comparison groups, limited disease-specific preclinical evidence and uncertainty around how apparent treatment effects should be interpreted.

Importantly, the experts distinguish between early evidence that an experimental treatment may be feasible to give, appears reasonably safe in a small number of patients or shows possible biological activity, and robust evidence that it’s clinically effective. They also emphasise the need for rigorous clinical evaluation, systematic collection of outcomes and transparent reporting of uncertainty as this research progresses.

Read the full open-access commentary

When considering travelling overseas to access an experimental treatment, we would encourage families to discuss this with their specialist mitochondrial disease team and to make sure they have clear answers to a number of important questions before making a decision.

These include whether the treatment is being provided as part of a formally approved and registered clinical trial or through another recognised regulatory route; what evidence exists in terms of its safety profile and potential benefit; and whether there is appropriate independent ethical and regulatory oversight.

It’s also important to understand exactly what product will be given. Families should be able to establish who manufactures the product, where it’s manufactured, the quality standards under which it’s produced, and what testing is undertaken to confirm its identity, purity, strength and consistency. This is particularly important for experimental treatments that have not been approved for routine clinical use.

Appropriate medical monitoring is equally important. Families should understand what assessments will take place before treatment, what monitoring will be undertaken while they are overseas, how potential side effects or complications will be identified and managed, and how long they will remain under the care of the treating team.

There should also be a clear plan for what happens after the patient returns home. This should include what ongoing monitoring is required, who will be responsible for providing it, how the overseas team will communicate with the patient’s UK clinical team, and what arrangements are in place if an adverse reaction or unexpected deterioration occurs. Families should not assume that specialist NHS teams will necessarily be able to provide monitoring for an experimental treatment initiated elsewhere without prior discussion and agreement.

We would also encourage families to ask how outcomes and adverse events are being systematically recorded and reported, and whether the results of treatment, including unsuccessful outcomes and side effects, will contribute to the wider scientific evidence. This is particularly important in very rare conditions, where information from every person treated can contribute to understanding whether an experimental approach is genuinely safe and effective.

Choosing whether to pursue an experimental treatment is an extremely personal decision. Our intention is not to discourage families from exploring emerging therapies, but to help ensure that decisions are based on reliable information and that appropriate safeguards are in place.

Where possible, we strongly encourage families to involve their existing specialist mitochondrial disease team before committing to treatment overseas.

The Lily Foundation, September 2026