Exhibit 99.2 TSHA-102 Rett Syndrome Program Update May 2025

Legal disclosure FORWARD LOOKING STATEMENTS This presentation contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this presentation, including statements regarding the potential of TSHA-102, the durability and reproducibility of the clinical data from the REVEAL trials, the anticipated Part B trial design, our research, development and regulatory plans, and our strategy, future operations, future financial position, future revenues, projected costs, prospects, plans and objectives of management, are forward-looking statements. The words “anticipate,” “believe,” “estimate,” “expect,” “intend,” “may,” “might,” “plan,” “predict,” “project,” “target,” “potential,” “will,” “would,” “could,” “should,” “continue,” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. These forward-looking statements are subject to a number of risks, uncertainties and assumptions. Risks regarding our business are described in detail in our Securities and Exchange Commission filings, including in our Annual Report on Form 10-K for the year ended December 31, 2024, our Quarterly Report on Form 10-Q for the quarter ended March 31, 2025, and our other filings with the SEC, which are available on the SEC’s website at www.sec.gov. We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements we make. The forward-looking statements contained in this presentation reflect our current views with respect to future events, and we assume no obligation to update any forward-looking statements except as required by applicable law. This presentation includes statistical and other industry and market data that we obtained from industry publications and research, surveys and studies conducted by third parties as well as our own estimates of potential market opportunities. All of the market data used in this presentation involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such data. Industry publications and third-party research, surveys and studies generally indicate that their information has been obtained from sources believed to be reliable, although they do not guarantee the accuracy or completeness of such information. Our estimates of the potential market opportunities for our product candidates include several key assumptions based on our industry knowledge, industry publications, third-party research and other surveys, which may be based on a small sample size and may fail to accurately reflect market opportunities. While we believe that our internal assumptions are reasonable, no independent source has verified such assumptions. This presentation shall not constitute an offer to sell or the solicitation of an offer to buy these securities, nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction. This presentation is intended to be viewed by investors in the U.S. only 2

Agenda Rett Syndrome Overview and Natural History Data Analysis FDA Alignment on Key Elements of Pivotal Part B Trial TSHA-102 Clinical Data from Part A of REVEAL Phase 1/2 Trials Developmental Milestones R-MBA CGI-I Safety Data 3

Key investment highlights TSHA-102: potential one-time treatment designed to address the root cause of Rett syndrome o No approved therapies address genetic root cause of disease High Unmet Need and 1 Significant Market Opportunity o 15,000-20,000 patients (U.S., EU+U.K.); 1 of 10,000 female births worldwide Longitudinal Rett Syndrome o Established patients ≥6 years of age are in developmental plateau, with a ~0% likelihood of gaining or regaining a 2 developmental milestone Natural History Data o Single-arm, open-label trial with patients serving as their own control (intend N=15) o Broad enrollment focused on females ≥6 years of age who have reached developmental plateau Written FDA Alignment on Key 3 Elements of Pivotal Trial Design o Primary endpoint: developmental milestone gain or regain o During advanced discussions with FDA, aligned on responder definition: gain/regain of ≥ one defined developmental milestone o 100% of pediatric, adolescent and adult patients gained/regained ≥ one developmental milestone as assessed by multiple independent central raters through video evidence 4 o Dose-dependent response seen across key measures six months post-treatment, with the separation between dose cohorts TSHA-102 Part A Clinical Data increasing over time o No treatment-related SAEs or DLTs following low and high dose of TSHA-102 Next Steps: Expect to submit pivotal trial protocol and SAP as an amendment to the IND application in Q2 2025 Pivotal trial initiation activities expected in Q3 2025 1 Amir, R E et al. “Rett syndrome is caused by mutations in X-linked MECP2, encoding methyl-CpG-binding protein 2.” Nature genetics vol. 23,2 (1999): 185-8. doi:partners. 10.1038/13810. (estimated prevalence of 2 15,000-20,000 patients with typical Rett syndrome caused by a MECP2 mutation). Accessed from International Rett Syndrome Foundation (IRSF). ClinicalTrials.gov: NCT02738281: a prospective cohort of individuals with a pathologic mutation in the MECP2 gene, commonly associated with RTT. Cumulative incidence models of NHS data conducted by third-party statistical partners (llikelihood of gain/regain ranged from 0% to 3 4 <6.7%). Finalization of SAP, including sample size, responder rate and interim analysis, expected to occur following Company’s submission of IND amendment and SAP in Q2 2025. Efficacy data based on May 19, 4 2025, data cutoff (N=10); Safety data based on May 20, 2025, data cutoff (N=12); Patient 11 is 12 weeks post-treatment and Patient 12 is 6 weeks post-treatment. Study is ongoing and data is subject to change. IND=investigational new drug application; SAE=serious adverse event; DLT=dose-limiting toxicity

Rett Syndrome Overview and Natural History Data Analysis Natural History Data accessed from the International Rett Syndrome Foundation (IRSF). We thank IRSF and the governance committee for their partnership.

There are no approved disease-modifying treatments that address the genetic root cause of Rett syndrome High Unmet Medical Need Significant Market Opportunity o Estimated 15,000 and 20,000 patients in Current standard of care focused on 3 1 major global markets (U.S., EU+U.K.) symptom management 3 o 1 of every 10,000 female births worldwide Patients typically require 24/7 care and o Commercial launch and uptake of DAYBUE 2 lifelong assistance 4 highlights market demand High caregiver burden with significant impact 2 on quality of life and activities of daily living 1 2 Fu, Cary et al. “Consensus guidelines on managing Rett syndrome across the lifespan.” BMJ paediatrics open vol. 4,1 e000717. 13 Sep. 2020, doi:10.1136/bmjpo-2020-000717. Coenraads, Monica et al. “Voice of the Patient Report: Rett 3 Syndrome Externally-Led Patient-Focused Drug Development Meeting.” 9 Aug. 2022, https://rettpfdd.org/site/assets/files/1/2022-rett-syndrome-voice-of-the-patient-report.pdf. Amir, R E et al. “Rett syndrome is caused by mutations in X-linked 4 MECP2, encoding methyl-CpG-binding protein 2.” Nature genetics vol. 23,2 (1999): 185-8. doi:10.1038/13810. (estimated prevalence of 15,000-20,000 patients with typical Rett syndrome caused by a MECP2 mutation). Based on net product 6 sales for the three months ended March 31, 2025 (source: Acadia Pharmaceuticals Reports First Quarter 2025 Financial Results and Operating Overview).

Rett syndrome caregiver research indicates improved function or achievement of developmental milestones would significantly improve quality of life “If she can actually tell me what she wants, or make a choice Communication between two things, even if it's just Gained or improved communication of basic needs—through looking at something purposefully…because now I don’t eye gaze, gestures, or words—would enable self-advocacy know what's going on.” and strengthen social connections – Caregiver of 20-year-old o Ex: follow a command without a gesture, pointed for something they wanted, use word(s) with meaning, identify body parts (pointed with eyes or fingers) “Feeding herself, entertaining Fine Motor Function herself…being able to flip pages or purposefully hold a book, change the Gained or improved hand function would restore a sense of channel on a remote...would be a control and purpose, and enable play and social engagement game changer for us.” o Ex: finger feed, use fork or spoon to eat without assistance, reached for a toy, – Caregiver of 8-year-old drank from a cup held without assistance Gross Motor Function “If we got a safe and secure sitting position from her, that would be a win. Gained or improved gross motor function would foster We would be able to have her sitting and independence and reduce the physical burden of caregiving not have to be right next to her. We could o Ex: walked independently or with support, stood while holding on, sat without have her at the dining table with us.” support, climbed up stairs without help – Caregiver of 5-year-old Results from caregiver research conducted in October 2024 by independent third-party research firm with 22-U.S.-based caregivers of females with RTT (aged 5-39). These findings have identified key developmental milestones that may provide an 7 important foundation for selection of endpoints in future Rett syndrome gene therapy trials.

Longitudinal natural history data informed key elements of TSHA-102 pivotal trial design 1 Natural History Study (NHS) Dataset Developed Age- and Time-Based Models 1 of Developmental Milestone NHS Data o N = ~1100 females with confirmed Rett syndrome diagnosis; up to 14 years follow-up o Cumulative incidence models demonstrated distinct age- and time-based trends in developmental o Captures longitudinal data on the functional gain, loss milestone acquisition that: and regain of developmental milestones across core domains of Rett syndrome: ü Strengthened understanding of longitudinal disease progression in Rett syndrome Communication Ex: Pointed for something they wanted | Used word(s) with meaning ü Contextualized and substantiated disease-modifying potential of TSHA-102 Fine Motor Function Ex: Finger feed | Drank from a cup held without assistance ü Informed our discussions with the U.S. FDA on proposed pivotal trial design for TSHA-102 Gross Motor Function Ex: Sat without support | Walked with support o These functional skills and activities of daily living are highly important to caregivers 1 Accessed from International Rett Syndrome Foundation (IRSF). ClinicalTrials.gov: NCT02738281: a prospective cohort of 8 individuals with a pathologic mutation in the MECP2 gene, commonly associated with RTT. Cumulative incidence models of NHS data conducted by third-party statistical partners.

NHS cumulative incidence models showed that the likelihood of gaining/regaining 1 28 defined developmental milestones is predictable in the age ≥ 6 population Communication Milestones Fine Motor Milestones Gross Motor Milestones Ex: of patients who learn to use word(s) with Ex: of patients who learn to drink from a cup held Ex: of patients who learn to walk with support, meaning, ~0% ever learn after age 6 without assistance, ~0% ever learn after age 6 ~0% ever learn after age 6 We leveraged these findings to establish the “Developmental Plateau Population” 1 Accessed from International Rett Syndrome Foundation (IRSF). ClinicalTrials.gov: NCT02738281: a prospective cohort of individuals with a pathologic mutation in the MECP2 gene, commonly associated with RTT. Incidence models of NHS data 9 conducted by third-party statistical partners.

Identified 28 developmental milestones from the NHS dataset that would reflect: 1 meaningful functional gains to caregivers, with a ~0% likelihood of being achieved after ≥6 years if untreated Communication Fine Motor Gross Motor o Reached for toy o Come to sitting o Pointed for something they o Holds bottle unpropped wanted o Sat without support o Used raking grasp to retrieve an o Stood while holding on o Waved “Bye-Bye” object o Pulled to standing o Followed a command with a o Used pincer grasp (refined or o Stood independently gesture modified) o Walked with support o Identified body parts (pointed o Transferred an object from one with eyes or fingers) o Walked independently hand to another o Climbed up stairs with help o Followed a command without a o Finger fed o Climbed down stairs with help gesture o Drank from a cup held without o Climbed up stairs without help o Used word(s) with meaning assistance o Climbed down stairs without help o Spoke in phrases (2 words or o Used a fork or spoon to eat with more) with meaning o Ran 10 feet without falling assistance o Used a fork or spoon to eat without assistance 1 Accessed from International Rett Syndrome Foundation (IRSF). ClinicalTrials.gov: NCT02738281: a prospective cohort of individuals with a pathologic mutation in the MECP2 10 gene, commonly associated with RTT. Cumulative incidence models of NHS data conducted by third-party statistical partners. Likelihood in this population ranged from 0-3%. NHS=natural history study

Rett syndrome NHS data analysis demonstrated that after 6 years of age, 1 there is ~0% likelihood of gaining or regaining developmental milestones Graph is for illustrative purposes only and is not derived from natural history data. The gain of new By age 6, there is a ~0% skills or restoration probability that untreated of previously lost individuals with Rett syndrome: skills presents an 1. Gain new milestones objective, data- driven way to assess 2. Regain milestones that were lost the efficacy of TSHA- after a defined number of years 102 in a broad Rett syndrome population ~0% AGE:0 1 2 3 4 5 10 15 20 25 >30 Pre-Developmental Plateau Population (age 0-6 years): Developmental Plateau Population (age ≥6 years): demonstrate ongoing development gain or regain of developmental milestones is unexpected 1 Accessed from International Rett Syndrome Foundation (IRSF). ClinicalTrials.gov: NCT02738281: a prospective cohort of individuals with a pathologic mutation in the MECP2 gene, commonly associated with RTT. Cumulative incidence models of NHS 11 data conducted by third-party statistical partners. NHS=natural history study Probability of Gaining/Regaining Developmental Milestones

Pivotal Part B Trial Design for TSHA-102: data-driven assessment of functional gains in a broad Rett syndrome population

Obtained written alignment from the FDA on key elements of pivotal Part B REVEAL trial design NHS models provide data-driven, objective approach to assessing functional gains in a single arm trial Study Overview o Study Design: Single-arm, open-label trial, using patient as own control Company Believes REVEAL Part A Data Continues to Support Advancement to Pivotal Trial 15 o Dose: Intend 1x10 total vg (high dose) o Sample Size: Intend 15 females with Rett syndrome age ≥6 years 1 Responder rate = 100% (developmental plateau population) (N = 10) across all patients o Primary Endpoint: Developmental milestone gain or regain treated with TSHA-102 post- o During advanced discussions with FDA, aligned on the definition of a 2 treatment 1 responder: gain/regain of ≥ one defined developmental milestone o Video-based determination of milestone gain/regain will be performed by independent, blinded central raters 1 Next Steps o 12-month primary analysis; intend 6-month interim analysis ⚬ In written correspondence, the FDA advised Company to o Safety of TSHA-102 will be evaluated in females with Rett syndrome submit pivotal trial protocol and SAP as an amendment 2-6 years of age with efficacy extrapolated from developmental plateau to the IND application; expected in Q2 2025 population 1 Finalization of SAP, including sample size, responder rate and interim analysis, expected to occur following Company’s submission of IND amendment and SAP. 2 Based on May 19, 2025, data cutoff. Study is ongoing, and data is subject to change. 13 NHS=natural history study; SAP=statistical analysis plan; IND=investigational new drug

Primary endpoint: milestone gain is an objective, clinically meaningful and inherently individualized assessment of function in the developmental plateau population Gain or regain of ≥ one of 28 defined developmental probability of milestone gain/regain milestones post-TSHA-102 ~0% 1 after age 6 in the untreated population ü Represent meaningful functional improvement based on caregiver Supported by cumulative incidence models from 2 research longitudinal NHS developmental milestone data ü Directly reflects activities of daily Fine motor, gross motor, and communication living developmental milestones captured as binary ü Inherently individualized to show (yes/no) measures improvements in a heterogeneous disease ü FDA-endorsed primary endpoint 1 Incidence models derived from NHS data; accessed from International Rett Syndrome Foundation (IRSF). ClinicalTrials.gov: NCT02738281: a prospective cohort of individuals with a pathologic mutation in the 2 14 MECP2 gene, commonly associated with RTT. Cumulative incidence models of NHS data conducted by third-party statistical partners. Results from caregiver research conducted in October 2024 by independent third-party research firm with 22-US-based caregivers of females with RTT (aged 5 to 39). NHS=natural history study

TSHA-102 Clinical Data from Part A of REVEAL Phase 1/2 Trials

100% of patients (n=10) gained/regained ≥ one defined developmental milestone post-TSHA-102 1 with a ~0% likelihood of being achieved without treatment based on NHS data Cohort 1: Low Dose Cohort 2: High Dose 14 15 5.7x10 total vg 1x10 total vg LD:P1 LD:P2 LD:P3 LD:P4 HD:P1 HD:P2 HD:P3 HD:P4 HD:P5 HD:P6 AGE AT DOSING 20 21 6 7 15 21 16 8 6 7 (years): POST- TREATMENT 18 mos. 18 mos. 12 mos. 12 mos. 9 mos. 9 mos. 6 mos. 6 mos. 6 mos. 3 mos. FOLLOW UP: Developmental Milestone Gained Post-TSHA-102 Developmental Milestone Gained Post-TSHA-102 Developmental milestone gains and regains were assessed by multiple independent central raters, who evaluated functional skills through video evidence at baseline and post-treatment, applying predefined binary criteria. 1 Based on May 19, 2025, data cutoff (N=10). Data presented reflects current data in the Electronic Data Capture System, subject to change. Incidence models derived from NHS data; 16 accessed from International Rett Syndrome Foundation (IRSF). ClinicalTrials.gov: NCT02738281: a prospective cohort of individuals with a pathologic mutation in the MECP2 gene, commonly associated with RTT. Cumulative incidence models of NHS data conducted by third-party statistical partners.

Patients gained/regained developmental milestones across the core functional domains of Rett syndrome post-TSHA-102 22 developmental milestones were achieved across 10 patients treated with TSHA-102 Communication Gross Motor Fine Motor Spoke in phrases (2 words or more) Holds bottle unpropped Walked with support with meaning Used word(s) with meaning Finger fed Stood while holding on Followed a command without a gesture Reached for a toy Pulled to standing Followed a command with a gesture Transferred an object from Sat without support one hand to another Pointed for something they wanted Identified body parts Enable expression of Enhance mobility and Reflect self-care skills and needs, preferences, independence, and reduce purposeful hand use that emotions, and foster social the physical burden of enable independence connections caregiving Based on May 19, 2025, data cutoff (N=10). Developmental milestone gains and regains were assessed by multiple 17 independent central raters through video evidence.

REVEAL caregiver testimonials post-TSHA-102 highlight the impact of functional developmental milestone gains on quality of life “All of our days are better. Her improvements “She’s gained multiple words – ‘no,’ ‘yeah,’ ‘mom,’ ‘dad’ are much beyond anything we had expected – makes consistent sounds with meaning – and even or hoped for.” says some phrases – ‘ok, bye’ and ‘no more.’” “She’s a lot easier to care for. She can point a lot more deliberately to make choices and show us what she wants, and she will keep gesturing until we get it for her. And she pushes away what she doesn’t want.” “[Standing while holding on] has been a godsend when it comes to toileting while out in the community because now, I can have her stand and hang on to my arm to toilet or wipe her… and the consistency of keeping her hand down [without constant stereotypies] allows us to practice more with a walker, which has been huge.” “Her hands are more relaxed, and she tries to grab everything with a raking grasp. She can follow directions in a snap, like if we say, ‘let’s go,’ she gets up, heads to the door. She’s babbling now, which she didn’t do before, and is definitely trying to tell us something.” Based on documented testimonials from caregivers of participants treated with TSHA-102 in REVEAL Phase 1/2 trials, as of 18 May 19, 2025, data cutoff.

High dose TSHA-102 achieved 100% responder result at a 25% faster rate compared to low dose TSHA-102 Responder Rate: Time to Response Responder Rate: Time to Response 100% ⚬ Accelerated functional benefit seen 75% with high dose TSHA-102 50% ⚬ Early clinical response may increase the likelihood of reversing the disease 25% trajectory and may be predictive of long- term clinical outcomes in Rett syndrome 0% Baseline 1 mos. 3 mos. 6 mos. 9 mos. 12 mos. ⚬ Consistent pattern of early gains that are Low Dose (N=4) High Dose (N=6) Low Dose sustained, with new achievements 25% 75% 75% 75% 100% TSHA-102 continuing to emerge over time following High Dose TSHA-102 33% 67% 83% 100% TSHA-102 1 Natural History (Developmental Plateau Population) = ~0% Based on May 19, 2025, data cutoff (N=10). Data presented reflects current data in the Electronic Data Capture System, subject to change. Low Dose N=4 across all time points; High Dose N=6 at 1-3 months., 1 19 N=5 at 6 months, N=2 at 9 months, based on available follow up. Accessed from International Rett Syndrome Foundation (IRSF). ClinicalTrials.gov: NCT02738281: a prospective cohort of individuals with a pathologic mutation in the MECP2 gene, commonly associated with RTT.Cumulative incidence models of NHS data conducted by third-party statistical partners.

Overview of Revised Motor Behavior Assessment (R-MBA) R-MBA Questionnaire Scale Very Severe or Constant Normal or Never ⚬ Clinician-reported assessment that measures the 0 1 2 3 4 onset of disease regression, growth, motor and communication skills, and disease behaviors for Moderate or Occasional 1 individuals with Rett syndrome ⚬ Associated with developmental milestone acquisition and function impacting quality of life 24-item questionnaire across five domains: ⚬ Measures the severity or frequency of a diverse set 1. Motor Dysfunction of symptoms to capture phenotypic variability 2. Functional Skills 2 ⚬ Assessed in Rett syndrome natural history study 3. Social Skills 4. Aberrant Behavior 5. Respiratory Behavior 1 Raspa, M. et al. A Psychometric Evaluation of the Motor-Behavioral Assessment Scale for Use as an Outcome Measure in Rett Syndrome. 2 Nov 2020. MBA natural history data converted to R-MBA; Accessed from International Rett Syndrome Foundation (IRSF). ClinicalTrials.gov: 20 NCT02738281: a prospective cohort of individuals with a pathologic mutation in the MECP2 gene, commonly associated with RTT.

TSHA-102 demonstrated a statistically significant mean R-MBA score improvement compared to natural history at both 6 and 12 months 1 Lower score = improvement; R-MBA assessed in Rett syndrome NHS at ~6 months and ~12 months R-MBA Score Mean Change From R-MBA Score Mean Change From R-MBA Score Mean Change From Baseline: R-MBA Score Mean Change From Baseline: 6 Months Baseline: 12 Months 6 Months Baseline: 12 Months -0.81 -0.62 p = 0.0123 p < 0.0001 -11.1 -12.8 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 REVEAL Mean Change Natural History Mean Change REVEAL Mean Change Natural History Mean Change TSHA-102 Mean Natural History TSHA-102 Mean Natural History (N=9, age ≥6 years) (N=75, age ≥6 years) (N=4, age ≥6 years) (N=196, age ≥6 years) StDev=11.9 StDev=5.97 StDev=4.92 StDev=5.73 Statistical analyses are based on May 19, 2025, data cutoff: TSHA-102 R-MBA mean 6 months: N=9 (Low dose cohort: N=4, High dose cohort: N=5). TSHA-102 R-MBA mean 12 months: N=4, Low dose cohort. 1 MBA natural history data converted to R-MBA; mean scores reported were calculated from baseline to 6 and 12 months: Accessed from International Rett Syndrome Foundation (IRSF). ClinicalTrials.gov: 21 NCT02738281: a prospective cohort of individuals with a pathologic mutation in the MECP2 gene, commonly associated with RTT.

Overview of Clinical Global Impression-Improvement 1 (CGI-I) rating with Rett syndrome-specific anchors Score CGI-I 1 Very much improved CGI-I: Clinician-rated scale assessing improvement from baseline 2 Much improved o Designed as a global clinical assessment 3 Minimally improved o Factors considered to determine change included duration, onset, durability of change and the context 4 No change of sign/symptom change across the Rett syndrome 5 specific domains of the CGI Minimally worse 6 Much worse 7 Very much worse 1 Neul, Jeffrey L et al. “Improving Treatment Trial Outcomes for Rett Syndrome: The Development of Rett-specific Anchors for 22 the Clinical Global Impression Scale.” Journal of child neurology vol. 30,13 (2015): 1743-8. doi:10.1177/0883073815579707

TSHA-102 demonstrated early global improvement, with dose-dependent effects deepening over time in CGI-I Average CGI-I score of 1.0 (very much improved) in high dose cohort vs. average CGI-I score of 2.8 in low dose cohort at ≥9 months post-TSHA-102 Low Dose: Average 3.0 2.3 3.0 3.3 2.0 CGI-I Score (N=4) (N=4) (N=2) (N=4) (N=2) High Dose: Average 2.7 2.0 1.0 CGI-I Score (N=6) (N=5) (N=2) Time Post TSHA-102: 3 months 6 months 9 months 12 months 18 months Based on May 19, 2025, data cutoff. Data presented reflects current data in the Electronic Data Capture System, subject to change. 23 CGI-I average scores based on latest assessment for each patient. No data available at 12 and 18 months in high dose cohort.

Consistent dose response observed across key measures at 6 months post-TSHA-102, with the separation between dose cohorts increasing over time Endpoint Low Dose Cohort High Dose Cohort Dose-Dependent Response? 100% 100% Responder Rate (%) by 12 months by 9 months Developmental Milestones Responder Rate at 6 Months 75% 83% (%) Patients with R-MBA 100% 100% Improvement (%) at latest visit Mean Score Improvement at 6 1 R-MBA -9.8 -12.2 Months Mean Score Improvement at ≥9 -11.5 -18.0 Months Patients with CGI-I 75% 100% Improvement (%) at latest visit CGI-I Mean CGI-I Score at 6 Months 2.3 2.0 Mean CGI-I Score at ≥9 Months 2.8 1.0 Patients with CGI-S CGI-S 25% 33% Improvement (%) at latest visit Data cut through May 19, 2025. Study is ongoing and data is subject to change. 24 Low dose data: N=4. High dose data: N=5 at 6 months; N=2 at ≥9 months. 1 R-MBA mean score change post-TSHA-102 is relative to baseline; lower score=improvement from baseline.

TSHA-102 was generally well tolerated at the low and high dose with no treatment-related SAEs or DLTs o All TEAEs related to TSHA-102 were mild- moderate in severity, with the most common Number of Events Across 12 Pediatric, Adolescent and Adult Patients being elevated liver enzymes* (N=4, 33%), Dosed in Part A of REVEAL Phase 1/2 Trials pyrexia (N=3, 25%), lethargy (N=2, 17%), and elevated levels of NfL in CSF (clinically Low Dose High Dose Total 14 15 5.7x10 vg 1x10 vg insignificant) (N=2, 17%) (N=12) (N=4) (N=8) o Expected transaminase elevations observed N E N E N E - Majority experience mild elevations <2x ULN - Acute excursions (>5x ULN) less common, TEAE Related to TSHA-102: 4 [10] 5 [14] 9 [24] clinically asymptomatic and steroid treatment- responsive Serious TEAE Unrelated to TSHA-102: 2 [7] 4 [6] 6 [13] ⚬ Seizures have generally been well controlled Serious TEAE Related to TSHA-102: 0 0 0 0 0 0 following TSHA-102 *Includes the following: hepatic enzyme increased, hypertransaminasemia, transaminases increased and liver function test increased 1 Data cut through May 20, 2025 (N=12); Patient 11 is 12 weeks post-treatment and Patient 12 is 6 weeks post-treatment. Study is ongoing and data are subject to change. 25 SAE=Serious adverse event; TEAE=Treatment-emergent AE; DLT=Dose-limiting toxicity; N=Number of participants; E=Number of event; CSF=Cerebrospinal fluid; ULN=Upper limit normal; NFL=Neurofilament light chain

Thank you May 2025

Appendix May 2025

Option Agreement with Astellas ⚬ In October 2022, we granted Astellas an exclusive option to an exclusive license of certain rights related to TSHA-102 (the “Rett Option”). Subject to certain limited extensions, Astellas may exercise the Rett Option, at its sole discretion, through a specified period of time (the “Rett Option Period”), following Astellas’ receipt of certain clinical data from the female pediatric trial (the “Rett Data Package”). We expect to deliver the Rett Data Package to Astellas in mid-2025. The Rett Option Period expires 90 days after Astellas receives the Rett Data Package. ⚬ Under the Option Agreement, we also granted to Astellas certain rights with respect to a change of control of our company during the Rett Option Period, including a right of first offer in the event that we receive an offer or proposal from a third party that would result in a change of control, and we have agreed to (A) not solicit or encourage any inquiries, offers or proposals for, or that could reasonably be expected to lead to, a change of control, or (B) otherwise initiate a process for a potential change of control, in each case, without first notifying Astellas and offering Astellas the opportunity to submit an offer or proposal to us for a transaction that would result in a change of control. If Astellas fails or declines to submit any such offer within a specified period after the receipt of such notice, we will have the ability to solicit third party bids for a change of control transaction. If during the Rett Option Period, Astellas submits an offer for a transaction that would result in a change of control of our company, we will negotiate with Astellas in good faith the potential terms and conditions of such a transaction for 45 days. If we are unable to mutually agree on such terms, such right of first offer will expire. We have granted Astellas certain additional rights related to a change of control, which are discussed in our SEC filings. ⚬ Because we are substantially dependent on TSHA-102, which is our sole product candidate in clinical development, we believe that if Astellas exercises the Rett Option, it would constitute an offer for the sale of substantially all of the assets of our company, which would result in a change of control requiring stockholder approval. If it were determined this exercise of the Rett Option is not an offer that would result in a change of control, the parties shall negotiate the terms of the license agreement in good faith. If the parties are unable to mutually agree on such terms within 120 days, the terms of such license agreement may, at Astellas’ discretion, be determined by “baseball arbitration,” wherein each party is required to submit a proposed final license agreement to arbitrators, and the arbitrators are required to select one of the proposed license agreements without modification. ⚬ It is possible that, if Astellas exercises the Rett Option, Astellas will not agree that the exercise of the Rett Option for the exclusive license of TSHA-102 would result in a change of control, and we cannot predict whether or how the parties would resolve such dispute. While it is inherently difficult to assess the potential outcome of any such dispute, we may be exposed to additional risks as a result, including, but not limited to, reputational harm and litigation, and we can provide no assurances that we will prevail in such litigation. 28

Taysha Gene Therapies, Inc. 8-K/A