Rett Research & Clinical Trial Overview

More than 25 companies are actively working on treatments to improve the quality of life for individuals with Rett syndrome. Fifteen years ago, there were none. Scroll down to view the major drug development programs and track their progress from discovery to FDA approval. Click on a company to learn more about their approach and status.

Development & Clinical Trial Status

The development of a new therapy for Rett syndrome must follow the path that regulatory bodies have established. This path follows five structured stages spanning pre-clinical and clinical research and can take 10-25 years to complete. From early discovery to post-market safety monitoring, each stage contributes vital data reviewed vigorously to ensure a new therapy is safe and effective, ultimately bringing therapies to patients.

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Stage 5: Post-Market Safety Monitoring

The following companies have successfully completed clinical trials and received regulatory approval for a Rett syndrome treatment. As more data becomes available, regulatory agencies will continue to monitor the outcomes of patients being treated for months to years after approval.

Status: In March 2023, the U.S. Food and Drug Administration (FDA) approved Acadia Pharmaceuticals Inc.’s investigational drug, trofinetide, for the treatment of Rett syndrome. The FDA’s approval was broad and includes all individuals with Rett syndrome – male and female – aged two and older, with no upper limit. The orally administered drug, marketed under the name DAYBUE®, is commercially available via prescription in the United States. In October 2024, Health Canada also granted marketing authorization of Daybue for Rett syndrome in patients 2 years and older. 

Study Results: Clinical data from the open-label extension LILAC-1 (40 weeks) and LILAC-2 (32 months) studies evaluating long-term safety and efficacy was published in July 2024. In both studies, patients treated with DAYBUE experienced improvement in Rett syndrome as measured by the Rett Syndrome Behaviour Questionnaire (RSBQ). In caregiver exit interviews, the most frequently reported improvements observed were engagement with others (46.2%), hand use (42.3%), and eye gaze (30.8%), with approximately 20% of participants acquiring new sounds or words. The most common adverse event was mild to moderate diarrhea (74.7% in LILAC-1 and 53.2% in LILAC-2).

A Phase 4 clinical study of real-world usage of DAYBUE, called LOTUS, is ongoing, following participants for at least 12 months from the start of treatment, with an option to continue for another year. Interim results shared in September 2025 found that most caregivers reported improvements, most frequently in nonverbal communication, alertness, and social interaction. Diarrhea was the most common side effect, and reports of normal stool increased over time. Many participants began treatment on lower-than-labeled doses and titrated up, with most reaching the full approved dose by week 10.

Next Steps: Acadia acquired the global rights to expand access to other countries from Neuren Pharmaceuticals in July 2023. They submitted a Marketing Authorization Application (MAA) to the European Medicines Agency (EMA) to expand into the European Union (EU) in January 2025. Further expansion plans will be announced at a later date.

Recent News & Updates:
9.12.25 – Real World Data from LOTUS Study Evaluating Long-term Efficacy and Tolerability Outcomes of DAYBUE® (trofinetide) in Patients with Rett Syndrome Published in Developmental Medicine and Child Neurology
3.5.25 – Clinical Data from Open-Label DAFFODIL™ Study Evaluating Long-term Safety of DAYBUE® (trofinetide) in Patients with Rett Syndrome Published in Med
1.14.25 – Acadia Pharmaceuticals Submits Marketing Authorization Application to the European Medicines Agency for Trofinetide for the Treatment of Rett Syndrome
10.16.24 – Acadia Pharmaceuticals Announces Health Canada Approval of DAYBUE™ (trofinetide) for the Treatment of Rett Syndrome
10.1.24 – Rett Sibling Scholarship Applications Now Open (Community Letter)
7.18.24 – Clinical Data from Open-Label Extension LILAC-1™ and LILAC-2™ Studies Published in Med
6.18.24 – Real-World Evidence and Additional Data on DAYBUE presented at the 2024 IRSF Annual Scientific Meeting
6.3.24 – A Letter to the Rett Community with Updates on DAYBUE from Acadia
4.22.24 – Trofinetide New Drug Submission Accepted for Filing and Priority Review by Health Canada
7.13.23 – Acadia Acquires International Rights to Trofinetide
4.17.23 – DAYBUE™ (trofinetide) is Now Available for the Treatment of Rett Syndrome
3.10.23 – DAYBUE™ (trofinetide) Approved by FDA for the Treatment of Rett Syndrome
2.28.23 – LILAC-1 Study Topline Results Announced (Community Letter)
9.12.22 – FDA Grants Priority Review to Trofinetide
7.18.22 – ACADIA Submits NDA for Trofinetide
12.6.21 – Positive Phase 3 LAVENDER Trial Results

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Stage 4: Drug Review

The following companies have applied to a regulatory agency like the FDA for permission to market a treatment after clinical trial results indicated the treatment is safe and effective. This stage may take 1-2 years once an NDA is submitted.

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Stage 3: Active Clinical Trials & Research

The following companies are actively conducting clinical trials in individuals with Rett syndrome. This stage may take 6-7 years to complete the 3 phases of clinical trials depending on factors including participant recruitment, length of patient monitoring, and the clarity of results.

Status: In January 2024, Anavex announced topline results from the EXCELLENCE Phase 2/3 study in girls ages 5-17 with Rett syndrome in Australia, Canada, and the U.K. At 12 weeks, the study showed improvement that did not reach statistical significance on the key co-primary endpoint Rett Syndrome Behaviour Questionnaire (RSBQ) between treated and placebo groups and failed to meet the co-primary endpoint on the Clinical Global Impression – Improvement scale (CGI-I). There were no new SAEs reported, and over 91% of trial participants continued into the 48-week open-label study.

Anavex Life Sciences Corp. has also completed a Phase 3 adult study in Australia and the U.K., with topline results expected soon. Previously, they’ve announced that adult patients enrolled in its long-term Phase 2 clinical study in the U.S. showed statistically significant reductions in Rett syndrome severity as well as continued improvement from the drug compared to placebo patients as measured by the RSBQ over 36 weeks of treatment. The drug has previously received Fast Track designation, Rare Pediatric Disease designation, and Orphan Drug designation from the FDA for the treatment of Rett syndrome. Anavex 2-73 (blarcamesine) is an activator of the sigma-1 receptor and is taken as a liquid once a day.

Recent News & Updates:
1.2.24 – Anavex Announces Topline Results from Phase 2/3 EXCELLENCE Clinical Study in Pediatric Rett Syndrome
6.28.23 – Long-term Clinical Study Demonstrates Disease-Modifying Effects of ANAVEX®2-73 for Rett Syndrome
6.6.23 – Completion of ANAVEX®2-73 (blarcamesine) EXCELLENCE Phase 2/3 Rett Syndrome Clinical Trial
2.1.22 – ANAVEX®2-73 (Blarcamesine) AVATAR Phase 3 Trial met Primary and Secondary Efficacy Endpoints
12.15.20 – Anavex Life Sciences Announces ANAVEX®2-73 Meets Primary and Secondary Endpoints in Clinical Trial
6.5.19 – Anavex Life Sciences Announces First Patient Dosed in Phase 2 Clinical Trial of ANAVEX®2-73

Status: In July 2025, UCB announced plans to initiate a Phase 3 clinical program for fenfluramine (Fintepla) in Rett syndrome, expected to begin in the first half of 2026. Fintepla is an FDA-approved treatment for Dravet syndrome and Lennox-Gastaut syndrome, rare epileptic disorders. In these approved uses, fenfluramine significantly reduced monthly seizure frequency and improved overall clinical impressions compared with placebo. The drug acts as a serotonin 5-HT2 receptor agonist, meaning it helps boost serotonin activity in the brain, a chemical that supports communication between nerve cells and helps regulate mood, movement, and other brain functions. Fenfluramine is also being studied in CDKL5 deficiency disorder.

Recent News & Updates:
7.31.25 UCB Announces Plans for Phase 3 Rett Syndrome Trial 

Status: NGN-401 is a gene replacement therapy that delivers the full-length human MECP2 gene under the control of Neurogene’s EXACT™ technology. This is done through an injection directly into a ventricle in the brain, where the AAV-9 virus carries the MECP2 gene to cells in the brain. NGN-401 has received RMAT designation and been selected for the START Pilot Program by the FDA, Priority Medicines (PRIME) designation by the European Medicines Agency (EMA), and Australian HREC approval.

In November 2023, Neurogene announced the dosing of the first pediatric patients. The Phase 1/2 clinical trial was initially split into a low dose (1E15 vg) and high dose (3E15 vg) cohort. The high-dose level was discontinued in November 2024 after the 3rd high-dose patient passed away after experiencing signs of a systemic hyperinflammatory syndrome, a rare and life-threatening immune response that has been reported with systemic exposure to high doses of AAV. This phase of the trial is fully enrolled with 5 participants at the 1E15 vg dose with updated clinical efficacy and safety data expected in the second half of 2025.

In October 2025, Neurogene announced that the FDA provided written agreement on key elements of the registrational Embolden™ trial of its investigational gene therapy NGN-401.  In November, the company announced the dosing of the first patient at one of 13 planned sites. 

Recent News & Updates:
11.6.25 – Neurogene Announces First Participant Dosed in Embolden™ Registrational Trial of NGN-401 Gene Therapy for Rett Syndrome
10.9.25 Neurogene Announces Positive Regulatory Update for NGN-401 Gene Therapy in Rett Syndrome
6.30.25 – Neurogene Announces Registrational Trial Design for Embolden™ Study of NGN-401 Gene Therapy for Rett Syndrome | (Community Letter)
6.18.25 – Community Letter
11.21.24 – Community Letter
11.18.24 – Neurogene Provides Update on NGN-401 Gene Therapy Clinical Trial for Rett Syndrome | (Community Letter)
11.11.24 – Neurogene Reports Positive Interim Efficacy Data from First Four Low-Dose Pediatric Participants in NGN-401 Gene Therapy Clinical Trial for Rett Syndrome | (Community Letter)
8.7.24 – Neurogene Announces RMAT Designation for NGN-401 Investigational Gene Therapy for Rett Syndrome
6.18.24 – First Patient Dosed in High-Dose Cohort
6.3.24 – NGN-401 Gene Therapy for Rett Syndrome Selected by FDA for START Pilot Program
5.10.24 – Neurogene Received Australian HREC Approval for Trial
5.7.24 – Neurogene Presents Favorable Safety Data from Phase 1/2 Trial of NGN-401 Gene Therapy for Rett Syndrome during ASGCT Annual Meeting
3.4.24 – Neurogene expands clinical trial and removes staggered dosing protocol
1.5.24 – Updates on the U.S. pediatric trial and expansion to the U.K. from Neurogene’s Business Update and 2024 Outlook
12.19.23 – Neurogene closes merger with Neoleukin Therapeutics (Community Letter 7.18.23)
11.30.23 – 1st pediatric patients dosed in U.S. trial of NGN-401
6.12.23 – Neurogene Announces Locations & Opens Enrollment for US Gene Therapy Clinical Trial
4.18.23 – Update for Rett Syndrome Community and Clarification Concerning Trofinetide
1.23.23 – Neurogene Announces First Rett Syndrome Gene Therapy Trial in U.S.
5.18.22 – Neurogene announces new development program for Rett syndrome, NGN-401 (Community Letter)

Status: TSHA-102 is a gene replacement therapy intended to deliver a functioning copy of MECP2 to the cells in the brain. The one-time injection into the spinal canal includes the AAV-9 virus, which carries the miniMECP2 gene product to the cells for the body to make more MeCP2 protein. TSHA-102 is currently being evaluated in the Phase 1/2 REVEAL Adolescent & Adult and REVEAL Pediatric Study in Canada, the U.K., and the U.S.

In February 2025, Taysha announced that the dosing of the 10 patients in Part A of both REVEAL trials has been completed. This included six patients in cohort two (high dose, 1×1015 total vector genomes (vg)) and four patients in cohort one (low dose, 5.7×1014 total vg). TSHA-102 was generally well tolerated with no treatment-related serious adverse events (SAEs) or dose-limiting toxicities (DLTs) in these patients as of the February 17, 2025, data cutoff. Taysha anticipates sharing more data and an update on the Part B pivotal trial design in the first half of 2025.

The FDA granted TSHA-102 Regenerative Medicine Advanced Therapy (RMAT) Designation in May 2024. In the U.K., TSHA-102 received Innovative Licensing and Access Pathway (ILAP) designation, and the Medicines and Healthcare Products Regulatory Agency (MHRA) has authorized the Clinical Trial Application (CTA) to expand into the country in Part B of the study.

Adolescent & Adult Study: Interim data shared in June 2024 from the first two patients in cohort one showed no serious adverse events (SAEs) reported at 52- and 36 weeks post-administration. The patients also showed clinical improvement in multiple clinician and caregiver-assessed efficacy measures. Clinical observations reported by the Pl include new improvements in motor skills, communication/socialization, autonomic function, and seizures.

Patients in both cohorts will be evaluated over the next 60+ months. The trial is currently recruiting female participants aged 12 and older in Montreal, Canada, and as follows in the United States:
– Open for Recruitment: UC San Diego (La Jolla, CA) & Rush University Medical Center (Chicago, IL)
– Coming Soon: Boston Children’s Hospital (Boston, MA), Gillette Children’s Hospital (St. Paul, MN), & University of Texas Southwestern (Dallas, TX)

To learn more about enrolling or to express interest in the REVEAL Adult & Adolescent Phase 1/2 Study, click here.

Pediatric Study: Taysha has dosed two of six Part A female pediatric patients ages 5-8 years old in cohort one (low dose). Interim data shared in June 2024 from two female pediatric patients ages 5-8 years old in cohort one (low dose) showed no serious adverse events (SAEs) related to TSHA-102 reported at 22- and 11 weeks post-administration. The patients also showed clinical improvement in multiple clinician and caregiver-assessed efficacy measures. Clinical observations reported by the PI include new improvements in motor skills, communication/socialization, autonomic function, and seizures.

Taysha plans to expand the pediatric study to up to 21 additional patients ages 3-8 years old in Part B of the study. The trial is currently recruiting female participants aged 5-8 in Montreal, Canada, and as follows in the United States:
– Open for Recruitment: Rush University Medical Center (Chicago, IL), Gillette Children’s Hospital (St. Paul, MN), & Washington University in St. Louis (St. Louis, MO)
– Coming Soon: UC San Diego (La Jolla, CA), Boston Children’s Hospital (Boston, MA), Children’s Hospital of Philadelphia (Philadelphia, PA), Vanderbilt Kennedy Center (Nashville, TN), & University of Texas Southwestern (Dallas, TX).

To learn more about enrolling or to express interest in the REVEAL Pediatric Phase 1/2 Study, click here.

Next Steps: In October 2025, Taysha announced new supplemental data from Part A of the REVEAL Phase 1/2 trials of TSHA-102 in adults, adolescents, and children with Rett syndrome. The analysis showed that 100% of patients (n=10) gained multiple additional functional skills beyond the 28 predefined developmental milestones from the Natural History Study. A total of 165 new skills and improvements were observed across communication, fine motor, gross motor, and autonomic function domains. These included pointing to desired objects, waving goodbye, using meaningful words or phrases, grasping and feeding with utensils, as well as standing, walking, and climbing stairs with support or independently.

Recent News & Updates:

10.9.25 Taysha Gene Therapies Presents New Supplemental Data Analysis from Part A of the REVEAL Phase 1/2 Trials
10.9.25 CNS 2025 Developmental Milestones and Broad Restoration of Function Poster
10.2.25 – Taysha Gene Therapies Announces FDA Breakthrough Therapy Designation and Provides Positive Regulatory Update on TSHA-102 in Rett Syndrome | Community Letter
8.12.25 – Taysha Gene Therapies Reports Second Quarter 2025 Financial Results and Provides Corporate Update | Community Letter
6.19.25 – Community Letter on Part A Results & Part B Design
5.28.25 – Taysha Gene Therapies Announces Pivotal Part B Trial Design Details for TSHA-102 in Rett Syndrome Enabled by IRSF Natural History Data and Positive Clinical Data from Part A of the REVEAL Adult/Adolescent and Pediatric Trials Evaluating TSHA-102
2.26.25 – Taysha Gene Therapies Reports Full-Year 2024 Financial Results and Provides Corporate Update
11.13.24 – Taysha Gene Therapies Reports Third Quarter 2024 Financial Results and Provides Corporate Update
8.12.24 – Updates from 2nd Quarter 2024 Financial Results
6.18.24 – Taysha Gene Therapies Announces Positive Clinical Data Across Adult and Pediatric Patients from Low Dose Cohort
5.14.24 – Corporate and Program Updates in First Quarter 2024 Financial Results
5.2.24 – Taysha Gene Therapies Announces Regenerative Medicine Advanced Therapy (RMAT) Designation Granted by U.S. FDA for TSHA-102 in Rett Syndrome
3.19.24 – Interim Clinical Data from Cohort One Shared on FY23 Financial Results Call
2.29.24 – Study expanded to adolescents and adults in the U.S. and dosing of the 1st adult cohort is complete
1.10.24 – First Pediatric Patient Dosed in U.S. Gene Therapy Clinical Trial

Status: In March 2025, Minoryx, a late-stage biotech company focused on the development of therapies for orphan central nervous system (CNS) disorders, announced the dosing of the first patient in its phase 2a clinical study of leriglitazone. Leriglitazone is a selective PPAR-γ agonist, with high oral bioavailability and CNS penetration. It showed pre-clinical proof-of-concept in Rett syndrome models by improving mitochondrial function and reducing oxidative stress and inflammation, resulting in an amelioration of the phenotype in Rett mice in both general condition and exploratory activity.

The placebo-controlled randomised TREE Study will be conducted in Spain and evaluate leriglitazone’s safety, tolerability and efficacy (assessing multiple Rett syndrome scales) over a 36-week period in 24 Rett syndrome pediatric patients up to 17 years old with confirmed MECP2 mutations.

Recent News & Updates:

3.4.25 – Minoryx announces dosing of the first patient with leriglitazone in the phase 2a study in Rett syndrome (TREE study)

Status: Neurotech reported positive results from their ongoing Phase I/II clinical trial in Australia of NTI164, a broad-spectrum medical cannabinoid drug therapy for the treatment of Rett syndrome, in May 2024. After 12 weeks with no SAEs, the company reported that 93% of participants showed improvement based on the CGI-I scale and that the mean improvement from week 4 to 12 on the RSBQ was 205% in symptoms including communication, hand behaviors, anxiety/mood, and quality of life. The trial will evaluate 14 female participants with Rett syndrome ages 5-18 in Australia. An extension of the trial was announced in March 2024 with all trial participants enrolling in the 52-week extension phase. Neurotech received U.S. Orphan Drug Designation (ODD) from the FDA in November 2024 and received ODD from the European Medicines Agency’s (EMA) Committee for Orphan Medicinal Products (COMP) in March 2025.

 

In October 2025, the US FDA granted NTI164 Rare Pediatric Disease Designation (RPDD) for the treatment of Rett syndrome. In June 2025, Rett syndrome clinical trial results were published in the Journal of Paediatrics and Child Health.

Recent News & Updates:

10.8.25 US FDA Rare Pediatric Disease Designation for NTI164 in Rett syndrome
6.26.25 Neurotech’s Rett Syndrome Clinical Trial Results Published in Scientific Journal
3.31.25 – European Commission grants NTI164 Orphan Drug Designation for Rett Syndrome
11.26.24 – Neurotech Receives US Orphan Drug Designation in Rett Syndrome 
8.30.24 – Neurotech Files for US Orphan Drug Designation in Rett Syndrome 
5.6.24 – Neurotech Reports Significant Clinical Benefits and Safety in Phase I/II Rett Syndrome Clinical Trial
3.13.24 – All Phase I/II Rett Syndrome Patients to Receive NTI164 Treatment for a Total of 52 Weeks
9.26.23 – Neurotech Completes Patient Recruitment in Phase I/II Rett Syndrome Clinical Trial
3.20.23 – Neurotech to Launch Phase II Clinical Trial in Rett Syndrome

Status: Vorinostat (RVL-001) is a small molecule oral therapeutic identified by Unravel’s proprietary drug prediction platform as potentially beneficial for patients with Rett Syndrome. In 2024, Unravel initiated clinical trial material manufacturing for use in potential clinical trials in the U.S. and Colombia and was announced as one of the drugs to be evaluated in an umbrella trial led by Dr. Jeffrey Neul at VUMC. RVL-001 was granted Orphan Drug Designation from FDA in May 2024.

In April 2025, Unravel Biosciences announced plans to initiate a clinical study in early summer for its Rett syndrome program at the Universidad de Antioquia’s Center for Technological Development, a designated INVIMA clinical trial site in Medellín, Colombia. The RVL-001 proof-of-concept study is designed as a placebo-controlled, “n-of-1” trial with a target enrollment of 15 patients with Rett syndrome.

Recent News & Updates:
4.29.25 Unravel Biosciences Announces Submission of RVL-001 Clinical Study Applications for Rett Syndrome to Colombian Health Regulatory Authority

Status: In March 2024, DepYmed received clearance from the U.S. FDA to initiate a Phase 1 clinical trial for DPM-1003 for the treatment of Rett syndrome. It had previously been granted Orphan Drug designation and conditionally designated under the FDA’s Rare Pediatric Disease program. DPM-1003 is an orally bioavailable small molecule inhibitor that targets the protein tyrosine phosphatase (PTP) family of enzymes that are disrupted in diseases like Rett.

Recent News & Updates:
3.19.24 – DepYmed Receives Clearance from U.S. Food and Drug Administration to Initiate Phase 1 Clinical Trial for DPM-1003 for the Treatment of Rett Syndrome

Status: In March and April 2025, Marvel reported new data from a Rett syndrome mouse study comparing MB-204 with trofinetide (Daybue). After two weeks of treatment and three weeks of follow-up, mice treated with MB-204 showed greater improvement in social behaviors than those treated with trofinetide, and these benefits were sustained throughout the monitoring period. In March 2025, Marvel announced plans to file for Orphan Drug Designation with the FDA for MB-204, as a potential treatment for Rett syndrome. MB-204 is a modified version of istradefylline (Nourianz), an FDA-approved drug used with other medications to treat Parkinson’s disease. It acts as an adenosine A2A receptor antagonist, helping to restore balance in adenosine signaling in the brain, which has been shown to be compromised in Rett syndrome.

Recent News & Updates:
04.30.25 Marvel Announces the Second of Two Final Data Sets from Rett Syndrome Study
03.17.25 Marvel Biosciences to File for Orphan Drug Designation with the U.S. FDA for MB-204 as a Treatment for Rett Syndrome
03.13.25 Marvel Announces First of Two Final Data Sets from Rett Syndrome Study
11.26.24 Marvel Biosciences Announces New Data from Rett Syndrome Study and Plans to Discuss Orphan and Rare Disease Status with the FDA

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Stage 2: Pre-Clinical Research & Development

The following companies have a treatment that showed promise during the discovery stage, and is now being more vigorously tested in cell cultures and animal models following regulatory agency mandated requirements. This process lasts 3-5 years and if successful, results in an IND application to begin clinical trials.

ACTX-101 is an AAV9-delivered X-reactivation gene therapy for the treatment of Rett syndrome. In May 2022, Alcyone presented preclinical data showing that ACTX-101 safely and effectively reactivates the inactive X chromosome in a Rett syndrome mouse model and is safe in a preliminary nonhuman primate study.

XGR-101 (previously referred to as ACTX-101) is an AAV9-delivered X-reactivation gene therapy for the treatment of Rett syndrome. In May 2022, Alcyone presented preclinical data showing that ACTX-101 safely and effectively reactivates the inactive X chromosome in a Rett syndrome mouse model and is safe in a preliminary nonhuman primate study.

Recent News & Updates:
5.18.22 – Alcyone Presents Preclinical Data on Gene Therapy Programs

​NQ-13 is a novel peptide-based compound that mimics Insulin-Like Growth Factor Binding Protein 2 (IGFBP2), a protein involved in neurogenesis, synaptic function, and cognition. In a rat model of Rett syndrome, NQ-13 treatment reversed movement, breathing, and cognitive dysfunction, and restored brain MeCP2 levels to normal values.

AMO-4 is a glutamate modulator that has shown significant promise as a potential treatment for Rett syndrome based on extensive drug discovery screen in a mouse model completed through IRSF’s Scout Program. In June 2018, the U.S. FDA granted Orphan Drug Designation to AMO-04 for the treatment of Rett syndrome.

Recent News & Updates:
6.13.18 – AMO Pharma Receives FDA Orphan Drug Designation for AMO-04 in Treatment of Rett Syndrome
AMO-04 – Rettsyndrome.org Q&A

KIT-13, a synthetic derivative of plasmalogen, a type of phospholipid that is present in the membranes of cells throughout the body including the brain. It has shown strong anti-inflammatory effects by inhibiting the nuclear accumulation of p65, suppressing the expression of IL-1B, and inducing phosphorylation of ERK, suggesting promise for treating Rett syndrome. KIT-13 was granted Rare Pediatric Disease Designation and Orphan Drug Designation from the U.S. FDA in March 2023.

In June 2025, the European Medicines Agency (EMA) granted Orphan Drug Designation (ODD) in the European Union for KIT-14, for the treatment of Rett syndrome.

6.23.25 KIT-13 Receives EMA Orphan Drug Designation for Rett Syndrome

NLX-101 is a novel compound that activates serotonin 5-HT1A receptors. The administration of NLX-101 in Rett mice reduced the occurrence of apneas and normalized irregular breathing patterns without interfering with other behaviors, suggesting that NLX-101 may represent a promising strategy for treating breathing disturbances in Rett syndrome.

In March 2025, a published study examining the effects of NLX-101 in a Rett syndrome mouse model demonstrated improvements in respiratory impairment and cognitive deficits.

Recent News & Updates:
3.25.25 Transgenic mouse study adds support for development of NLX-101 for treatment of Rett Syndrome
3.3.2014 – European Commission approves Orphan Medicinal Product designation for NLX-101

In June 2025, Ovid Therapeutics announced plans to begin preclinical studies in late 2025 required to file an Investigational New Drug (IND) application for OV4041 as an experimental treatment for Rett syndrome, with IND submission expected in late 2026. OV4041 directly activates KCC2, a key protein that helps restore the balance between excitatory and inhibitory signals in the brain by supporting GABA inhibition. It is an oral medication with anxiolytic (anti-anxiety), antipsychotic, and anticonvulsant activity.

Recent News & Updates:

06.25 Ovid Therapeutics Shares Anticipated Milestones for OV4041 Program

11.13.24 Ovid Therapeutics Shares KCC2 Opportunity & Strategy

Unravel Biosciences is developing RVL-002, a novel small molecule discovered using their AI-driven BioNAV™ drug discovery platform in partnership with COMBINEDBrain’s large patient biosample repository. This approach uses RNA data to identify potential drug targets in rare and ultra-rare diseases. RVL-002 targets mitochondrial metabolism and is planned to be tested as a potential treatment for Rett syndrome.

Recent News & Updates:

2.27.25 Unravel Biosciences and COMBINED Brain Announce Large-Scale Drug Discovery Collaboration for Rare Neurological Diseases with High Unmet Need

5.14.24 Unravel Announces Collaboration with Vanderbilt University Medical Center to Support Upcoming Multicenter U.S. Clinical Study in Rett Syndrome

Axonis Therapeutics is developing medicines that target KCC2, a key protein involved in maintaining inhibitory signaling in the brain. In April 2023, SynGAP Research Fund announced a collaborative grant with the Tang Lab at Boston Children’s Hospital and Axonis Therapeutics. Research led by Dr. Xin Tang has shown that increasing KCC2 expression in neurons derived from Rett syndrome patients and Mecp2 mutant mice can rescue several cellular and behavioral abnormalities, supporting KCC2 as a promising therapeutic target.

Recent News & Updates:

04.05.23 SynGAP Research Fund awards a collaborative grant to Tang Lab & AXONIS Therapeutics

07.14.21 AXONIS Therapeutics Announces $5 Million in Funding; Provides Update on Progress Advancing Novel Therapeutics for Neurological Disorders

Herophilus is a neurotherapeutics startup using robotic automation to “industrialize” the organoid and scale up use of the next-generation human in vitro models in drug discovery experiments for brain diseases. Its lead drug candidate is the first small molecule therapy for Rett Syndrome with the potential to reverse the root cause of the disease, MECP2 deficiency.

Prilenia is continuing preclinical evaluation of pridopidine, a sigma-1 receptor (S1R) agonist with neuroprotective properties administered orally twice daily, for the treatment of Rett syndrome. It is currently in late-stage development and clinical trials for the treatment of Huntington’s disease and ALS.

Shape’s RNAfix® platform uses guide RNAs (gRNAs) to harness the body’s own machinery to therapeutically edit RNA. In May 2025, Shape Therapeutics presented data from a Rett syndrome mouse model, showing that gRNAs targeting the R168X mutation in the MECP2 gene achieved broad brain distribution after IV injection. This resulted in restoration of full-length MECP2 protein in approximately 39% of cells.

5.16.25 Shape Therapeutics Presents Preclinical Data Highlighting Therapeutic Potential of RNA Editing and AAV Delivery Platforms

01

Stage 1: Drug Discovery & Development

The following companies are in the discovery and development stage spanning basic research discoveries in the lab to tests in cell culture or animal models. This stage may include 5-10 years of testing before a new treatment can be developed further.

IAMA Therapeutics is a pharmaceutical company focused on the discovery, development, and commercialization of novel medicines for children affected by brain disorders.

ProQR is developing AX-2402 using its Axiomer™ RNA editing platform, which uses the body’s own machinery to precisely correct single RNA letters linked to disease. This approach can repair or modify faulty RNA so that cells produce healthy, functional proteins. AX-2402 is designed for people with Rett syndrome who have the R270X mutation in the MECP2 gene, but the technology can also be adapted to target many other MECP2 mutations that affect a large portion of the Rett community. RNA-editing therapies targeting other common MECP2 mutations—including R168X (AX-2403), R255X (AX-2404), R294X (AX-2405), and R133H (AX-2406)—are also in the pipeline.

01.05.24 ProQR and Rett Syndrome Research Trust Join Forces with Axiomer™ RNA Editing Collaboration

12.11.24 ProQR Therapeutics Announces $8.1 Million in New Funding from Rett Syndrome Research Trust to Expand RNA Editing Collaboration

In June 2024, Dewpoint Therapeutics presented new data at the IRSF Scientific Meeting. They treated human neuronal progenitor cells with a small molecule condensate-modifying drug (c-mod), which helped MeCP2 properly localize to chromatin, reducing its mislocalization to the nucleolus—restoring normal cellular function.

6.18.24 Development of a MeCP2 condensate-modifying small molecule for the treatment ​of Rett syndrome – Poster Presentation

Epeius pharma is a cell and gene therapy company developing next generation biological vehicles for delivery of therapeutic proteins into the central nervous system (CNS). They hope to use their novel CNS delivery platform to introduce MECP2 to MECP2 deficient neurons of Rett patients.

Gliachem is developing small molecule therapeutics for rare and neurological diseases. In Rett syndrome, low mTOR activity has been identified as a key driver of impaired brain development and function. Boosting mTOR activity is a promising therapeutic strategy. Gliachem has developed new molecules that block TRPM2, a channel that negatively regulates mTOR and is over-expressed in the Rett brain, with the goal of restoring more normal brain development and function.

11.16.23 Gliachem Discusses Their Technology

GLIACHEM: Small Molecule Therapeutics for Rare and Neurodegenerative Diseases

Palena Therapeutics is developing immunomodulatory peptides, called embedded epitope random peptides (EERPs), designed to selectively inhibit autoimmune responses, similar to the mechanism of Copaxone in multiple sclerosis (MS). Copaxone has been shown to increase BDNF (brain-derived neurotrophic factor), which supports neuronal survival, growth, and plasticity. In Rett syndrome, MeCP2 deficiency leads to reduced BDNF expression, contributing to neurological symptoms. A small open-label study of Copaxone (n=10) in individuals with Rett documented improvements in gait, visual attention, memory, and breath holding index, supporting further exploration of this therapeutic approach.

Vico Therapeutics is exploring taking an RNA editing approach to target Mecp2-R255X. Their therapeutic strategy is based on antisense oligonucleotide-mediated RNA editing to repair mutant MECP2 and reverse symptoms.

Discontinued or Canceled Clinical Programs

The following companies have terminated their Rett syndrome treatment development program.

In October 2021, Novartis terminated its Rett syndrome gene replacement program, OAV201, after pre-clinical data did not support a path forward to human clinical trials per the company’s Q3 2021 Financial Report.

Recent News & Updates:
2.8.21 – IND Submission Update (Community Letter)
8.20.20 – Additional Pre-Clinical Studies Complete (Community Letter)
8.22.19 – AveXis/Novartis Delay Trial and Withdraw IND Application for More Testing (Community Letter)

Due to the challenges presented by COVID-19, GW Pharma discontinued the ARCH Phase 3 global trial of its cannabidiol oral solution for Rett syndrome in November 2020.

Recent News & Updates:
11.12.20 – Trial Closure Announcement (Community Letter)
9.6.19 – Trial Criteria Announcement (Community Letter)
May 2019 – Trial Now Recruiting

In May 2020, Newron canceled its Rett syndrome program after top-line results from its phase 2 STARS clinical study of sarizotan did not demonstrate efficacy on primary and secondary endpoints.

Recent News & Updates:
5.4.20 – Top-Line Results from STARS Study
4.12.19 – Clinical Trial Enrollment Complete & Thank You (Community Letter)

Lucy Therapeutics is a private biotech company developing therapies based on mitochondrial small-molecule treatments and biomarkers for neurological diseases.

In 2025, Founder & CEO, Amy Ripka, announced the closure of Lucy Therapeutics.

Rett syndrome no longer a disease area of Stoke Therapeutics.

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