The study will assess the acceptability and feasibility of a randomised controlled trial of 6-12 sessions of remotely-delivered Acceptance and Commitment Therapy (ACT) versus waitlist control. Waitlist control will involve a delay in the offer of ACT sessions for 12 weeks. Participants may access all services as usual in this time. Follow-up assessments will be conducted at 12-, 24 and 48 weeks post-randomisation to measure effectiveness.

Tuberous Sclerosis Complex (TSC) is a genetic disease caused by mutations in the tumour suppressor genes TSC1 and TSC2. The clinical hallmarks of the disease are the growth of benign tumours in various organs such as the brain, kidneys and skin. Seizures are present in around 60% of the population and neurodevelopmental problems such as attention deficit disorder and autism are common. Anxiety and depressive disorders are similarly linked and at the psychosocial level, there is increasing evidence of the effect of TSC on self-esteem, family functioning and peer relationships resulting in poorer quality of life. Despite these difficulties, no unique treatments, and almost no effective evidenced psychological treatments for TSC are available.

This trial aims to assess the feasibility and acceptability of Acceptance and Commitment Therapy (ACT) as a psychological treatment to improve quality of life among adolescents and young adults with TSC. ACT is a cognitive behavioural therapy that helps participants accept difficulties that they are unable to change. There is strong evidence for ACT's clinical effectiveness amongst patients with chronic diseases. The intervention will be delivered to participants aged 11-24 with TSC and sufficient cognitive and speech capabilities to take part. This will be delivered remotely via secure video-conferencing software. Our primary hypothesis is that ACT will be acceptable and feasible delivered remotely and may yield clinical improvements in health and quality of life.

The study will be a 12-week, waitlist controlled randomised clinical trial. Participants will be randomised to receive 12-weeks treatment either immediately or following a 12-week wait. The treatment will be ACT adapted for 11-24-year olds who have TSC. Treatment will involve 6 to 12 weekly sessions of ACT of up to one hour each in length. Clinical outcomes will be assessed unblinded at baseline, 12, 24 and 48 weeks from randomisation. As a feasibility and acceptability study a range of physical and mental health outcomes are assessed. All clinical outcomes focus on health, wellbeing and quality of life from baseline to 12 week (3-month) follow-up amongst those offered ACT immediately versus waitlist controls.

Inclusion Criteria:

• Aged 11 to 24 years.
• Diagnosis of Tuberous Sclerosis Complex.
• Sufficient understanding of English to engage with the intervention (spoken and written), as judged by the assessing clinician.
• Sufficient cognitive, sensory and speech capabilities to take part in the intervention.
• Participants (or their parents if under 16) give verbal or written informed consent to participate in the study.
• Participants give verbal or written assent if under 16.
• Receiving treatment over video-conferencing will be the default modality for delivery, so access to the internet is a requirement.

Exclusion Criteria:

• Previous structured behavioural intervention within last 6 months.
• Previous or current alcohol/substance dependence, psychosis, suicidality, or anorexia nervosa.
• Moderate or severe intellectual disability.
• Immediate risk to self or others.
• Parent or child not able to speak, read or write English.

The study design is an unblinded, waitlist-controlled, randomised controlled trial (RCT). Randomisation will be conducted using established randomisation software RedCap. Researchers will not be blind to trial arm allocation.