Taysha receives go-ahead for early dose escalation in adolescent and adult Rett syndrome gene therapy trial 


Yesterday, 19th March 2024, Taysha Gene Therapies published a press release with an update to their Rett syndrome gene therapy program TSHA-102. 

The company announced that having reviewed the data, the Independent Data Monitoring Committee (IDMC) has approved the company’s request to move to the higher dose for their adults and adolescents Rett syndrome gene therapy trial earlier than planned. 

Taysha also announced that the IDMC has approved the dosing of the second US paediatric patient in the low dose group of the children’s Rett syndrome gene therapy trial. The second patient has now been identified and the dosing is scheduled to take place this quarter. 

Taysha announced MHRA approval for the UK arm of the TSHA-102 children’s trial to start back in January. The company’s UK focus is now on initiating their first UK trial site. Taysha also announced yesterday that they have received MHRA ILAP approval which is designed to help speed up the development of new and innovative treatments for diseases for which there are no or limited treatments. 

Read Taysha’s full press release here

Read Taysha’s letter to Community Leaders below. 

Here are our key takeaways: 

Adults and adolescents trial –Canada and USA 

  • There have been no serious adverse events or safety issues in adult patients 1 and 2 as of 35 weeks and 19 weeks post dosing. 
  • The IDMC has approved dose escalation which means moving to a higher dose earlier than planned.  
  • Based on the latest data taken at 6 months (patient 1) and 12 weeks (patient 2) post dosing, both patients are showing sustained and new clinical improvements.  

Children’s trial –USA and UK 

  • One patient has been dosed in the USA.  
  • The IDRC has approved dosing of patient 2.  
  • Patient 2 has been identified. 
  • Dosing is scheduled to take place this quarter. 
  • The UK regulator, the MHRA, has granted Taysha ILAP approval. 
  • The current focus in the UK is on site initiation. 

Next milestones to look for: 

  • Data from cohort 1 (low dose) of the children’s trial mid-year 2023. 
  • Initial data from cohort 2 (high dose) of the adult and adolescent trial in second half of 2024. 


What is the U.K. MHRA Innovative Licensing and Access Pathway (ILAP)?  

The ILAP designation aims to make it easier and quicker for UK patients to access new treatments by speeding the time it takes to get new treatments to market by enhancing interactions with the UK regulator and other relevant bodies involved in the process.  

What improvements were seen in the adult and adolescent group? 

Taysha has shared information about patients 1 and 2 and their symptoms before and after treatment, along with statements to clarify that whilst they did not expect to see any efficacy in adult patients with stage 4 disease, no conclusions can be made based on interim findings of a clinical trial until all the patients are dosed and evaluated for the duration of the study and all data has been collected and analysed.  

More information about patients 1 and 2 and their before and after symptoms can be found in the press release, community letter and by listening to Taysha’s most recent investor call here. https://ir.tayshagtx.com/news-events/events-presentations 

Has the UK children’s trial started yet? 

Although Taysha has received clearance from the UK regulator, the MHRA, the first UK trial site has not been activated and is not yet recruiting. More information about the UK children’s trial including inclusion and exclusion criteria can be found here. https://clinicaltrials.gov/study/NCT06152237  

In the first instance, numbers needed for UK Rett syndrome gene therapy trials will be very small and clinicians are likely to recruit from their patient list. As trials expand, it is likely that Reverse Rett will support trial recruitment through the Rett Registry UK. If the person you care for (of any age) is not registered, please register today. http://rettregistry.uk and email to express interest in gene therapy trials [email protected]  

Will families who live outside the UK be eligible to participate?  

Ultimately the lead doctor at any given trial site will decide the eligibility of an individual patient for the clinical trial. Though this varies site to site, participants are typically selected for enrolment using several considerations, including how close they live to the clinical trial site.  

Rett families and/or their treating physician may contact a participating site directly to ask about potential trial participation.  

At Reverse Rett, we encourage patients outside the UK who wish to take part in clinical trials and/or access emerging treatments to register on the Rett Registry UK so that we are able to gather and share information about where there are concentrations of patients with companies and other relevant bodies.