LXEO

Finalized SUNRISE-FA 2 open-label, pivotal trial protocol and SAP for LX2006 in support of accelerated approval pathway; topline data expected in second half of 2027 Initiated SUNRISE-FA 2 with first patient enrolled into pivotal study in June; site activation efforts ongoing CLARITY-FA enrollment continues to advance, supporting identification of eligible participants for SUNRISE-FA 2 FDA granted RMAT designation for LX2020 based on recent interim clinical data in PKP2-ACM Cash, cash equivalents and investments of $234.2 million expected to provide operational runway into 2028 NEW YORK, Aug. 12, 2026 (GLOBE NEWSWIRE) -- Lexeo Therapeutics, Inc. (Nasdaq: LXEO), a clinical stage genetic medicine company dedicated to pioneering novel treatments for cardiovascular diseases, today provided business updates across its portfolio and reported financial results for the second quarter 2026. “We closed the second quarter with significant momentum, highlighted by the initiation of SUNRISE-FA 2, the pivotal study for LX2006 in Friedreich ataxia cardiomyopathy,” said R. Nolan Townsend, Chief Executive Officer of Lexeo Therapeutics. “With SUNRISE-FA 2 now underway, we are focused on execution and advancing what we believe could be the first disease-modifying gene therapy for FA cardiomyopathy. Beyond LX2006, we continue to advance LX2020 in PKP2 arrhythmogenic cardiomyopathy and are pleased to have recently received RMAT designation from the FDA, an important milestone that reinforces the strength of the emerging clinical evidence and supports the potential expedited development of the program. With multiple value-driving catalysts ahead and a strong balance sheet to support our key clinical and regulatory milestones, we believe Lexeo is well positioned to deliver on our mission of transforming the treatment of genetically defined diseases.” Program Updates and Recent Progress LX2006 in Friedreich Ataxia (FA) In June 2026, Lexeo finalized the SUNRISE-FA 2 pivotal trial protocol and statistical analysis plan (SAP) for LX2006 under the accelerated approval pathway. In June 2026, Lexeo announced publication of LX2006 data in the Journal of the American Medical Association (JAMA) Cardiology demonstrating LX2006 is generally well tolerated, with signs of efficacy in Phase I/II studies. In April 2026, Lexeo presented data at ASGCT highlighting LX2006’s continued positive clinical profile, along with preclinical and CMC data supporting potential sequential dosing strategies and the Company’s scalable manufacturing platform. Presentations and publications from ASGCT 2026 can be found here. Anticipated milestones for the program include: LX2020 in PKP2 Arrhythmogenic Cardiomyopathy (PKP2-ACM) In August 2026, Lexeo received Regenerative Medicine Advanced Therapy (RMAT) designation for LX2020 from the FDA based on recent interim data from its ongoing Phase I/II clinical trial in PKP2-ACM. RMAT designation provides opportunities for increased FDA interaction and may help expedite the development of LX2020. LX2020 remains generally well tolerated across ten participants dosed with no clinically significant complement activation to date. Anticipated milestones for the program include: Pre-Clinical Assets In May 2026, Lexeo presented preclinical data for LX2022 at ASGCT demonstrating proof-of-concept efficacy for TNNI3 gene replacement in a newly developed porcine model of hypertrophic cardiomyopathy. Presentations and publications from ASGCT 2026 can be found here. Second Quarter 2026 Financial Results Cash Position: As of June 30, 2026, cash, cash equivalents, and investments in marketable securities were $234.2 million, which Lexeo believes will be sufficient to fund operations into 2028. Research & Development Expenses: Research and Development expenses were $19.0 million for the three months ended June 30, 2026, compared to $14.7 million for the three months ended June 30, 2025. General & Administrative Expenses: General and Administrative expenses were $9.0 million for the three months ended June 30, 2026, compared to $16.0 million for the three months ended June 30, 2025. Net Loss: Net loss was $25.9 million or $0.30 per share (basic and diluted) for the three months ended June 30, 2026, compared to $26.1 million or $0.60 per share (basic and diluted) for the three months ended June 30, 2025. About Lexeo TherapeuticsLexeo Therapeutics is a New York City-based, clinical stage genetic medicine company dedicated to reshaping heart health by applying pioneering science to fundamentally change how cardiovascular diseases are treated. The Company is advancing a portfolio of therapeutic candidates that take aim at the underlying genetic causes of conditions, including LX2006 in Friedreich ataxia (FA), LX2020 in plakophilin-2 (PKP2) arrhythmogenic cardiomyopathy, and others in devastating diseases with high unmet need. Cautionary Note Regarding Forward-Looking StatementsCertain statements in this press release may constitute “forward-looking statements” within the meaning of the federal securities laws, including, but not limited to, Lexeo’s expectations and plans regarding its current product candidates and programs, the anticipated benefits of its current product candidates, the timing for receipt and announcement of data from its clinical trials, the timing and likelihood of potential regulatory developments, trial design changes and approval, and expectations regarding the time period over which Lexeo’s capital resources will be sufficient to fund its anticipated operations and estimates regarding Lexeo’s financial condition. Words such as “may,” “might,” “will,” “objective,” “intend,” “should,” “could,” “can,” “would,” “expect,” “believe,” “design,” “estimate,” “predict,” “potential,” “develop,” “plan” or the negative of these terms, and similar expressions, or statements regarding intent, belief, or current expectations, are forward-looking statements. While Lexeo believes these forward-looking statements are reasonable, undue reliance should not be placed on any such forward-looking statements. These forward-looking statements are based upon current information available to the company as well as certain estimates and assumptions and are subject to various risks and uncertainties (including, without limitation, those set forth in Lexeo’s filings with the U.S. Securities and Exchange Commission (SEC)), many of which are beyond the company’s control and subject to change. Actual results could be materially different from those indicated by such forward-looking statements as a result of many factors, including but not limited to: risks and uncertainties related to global macroeconomic conditions and related volatility; the outcome of ongoing discussions with the U.S. Food and Drug Administration (FDA) regarding the design of our pivotal trial for accelerated approval pathway and the design of our confirmatory study for obtaining full approval; expectations regarding the initiation, progress, and expected results of Lexeo’s preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; delays in submission of regulatory filings or failure to receive regulatory approval; liquidity and capital resources; and other risks and uncertainties identified in Lexeo’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2026, filed with the SEC on May 11, 2026, and subsequent future filings Lexeo may make with the SEC. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Lexeo claims the protection of the Safe Harbor contained in the Private Securities Litigation Reform Act of 1995 for forward-looking statements. Lexeo expressly disclaims any obligation to update or alter any statements whether as a result of new information, future events or otherwise, except as required by law. Media Response:[email protected] Investor Response:Ashley Kaplowitz        [email protected]

SUNRISE-FA 2 open-label, pivotal trial protocol and SAP for LX2006 submitted to FDA in Q1 2026; Awaiting final FDA feedback Multiple presentations highlighting progress across cardiac genetic medicine pipeline and optimized, Sf9-baculovirus AAV manufacturing platform to be presented at ASGCT 2026 Appointed Laura Sepp-Lorenzino, Ph.D. to Board of Directors Cash, cash equivalents and investments of $227.6 million expected to provide operational runway into 2028 NEW YORK, May 11, 2026 (GLOBE NEWSWIRE) -- Lexeo Therapeutics, Inc. (Nasdaq: LXEO), a clinical stage genetic medicine company dedicated to pioneering novel treatments for cardiovascular diseases, today provided business updates across its portfolio and reported financial results for the first quarter 2026. “We continued to make steady progress across our key priorities in the first quarter of 2026. As we work with the FDA to finalize the SUNRISE‑FA 2 pivotal study protocol, we are advancing site readiness and patient identification activities to ensure we are prepared to initiate the study promptly once the protocol is complete,” said R. Nolan Townsend, Chief Executive Officer of Lexeo Therapeutics. “We will also have a meaningful scientific presence at ASGCT this week, where we will share updates from our LX2006 program as well as new preclinical data for LX2022. We remain committed to advancing our pipeline toward meaningful therapies for patients and look forward to providing further updates as our programs continue to progress.” Program Updates and Recent Progress LX2006 in Friedreich Ataxia (FA) In May 2026, Lexeo will share multiple presentations on LX2006 at the 29th American Society of Gene and Cell Therapies (ASGCT) Annual Meeting: Phase I/II interim clinical data of LX2006 continue to show sustained or deepening improvements across both cardiac and neurologic measures of FA, including statistically significant improvement in mean mFARS scores for LX2006-treated participants compared to a propensity-matched control cohort from the UNIFAI natural history study (n=17; p=0.003). LX2006 remains generally well tolerated with no Grade 3+ SAEs to date. Nonhuman primate research with LX2006 conducted by researchers at Weill Cornell Medicine demonstrates the potential of sequential dosing strategies to treat FA. Eight weeks following systemic intravenous administration of LX2006, nonhuman primates were administered LX2006 directly to the cerebellum or cerebral spinal fluid (CSF), and potentially therapeutic levels of cerebellar vector genome copies were detected via both routes of administration despite pre-existing immunity to the therapeutic vector. CMC comparability data for LX2006 between adherent HEK293 and Sf9 baculovirus suspension processes highlight Lexeo’s optimized manufacturing platform that can maintain purity and potency while significantly improving scalability of production and reducing cost. In February 2026, Lexeo submitted the final registrational trial design and statistical analysis plan (SAP) for the SUNRISE‑FA 2 pivotal study to the FDA following a Type B meeting. The company is in contact with the FDA and is awaiting final feedback on the study protocol. Lexeo plans to provide an update when the protocol and SAP are finalized. Anticipated milestones for the remainder of 2026 include: FDA feedback on protocol submission expected in Q2 2026 Initiation of SUNRISE-FA 2 pivotal trial in Q2 2026 LX2020 in PKP2 Arrhythmogenic Cardiomyopathy (PKP2-ACM) In January 2026, Lexeo reported positive interim clinical data from the HEROIC-PKP2 Phase I/II clinical trial evaluating LX2020. LX2020 remains generally well tolerated across ten participants dosed with no clinically significant complement activation to date. Anticipated milestones for the remainder of 2026 include: 12-month data update for all high dose participants in Q4 2026 Regulatory engagement with the FDA expected in 2026 Pre-Clinical Assets In May 2026, Lexeo will present preclinical data for LX2022 at the ASGCT Annual Meeting, demonstrating proof‑of‑concept efficacy for TNNI3 replacement in a newly developed porcine model of hypertrophic cardiomyopathy. This novel model closely recapitulates severe disease physiology and mortality and was specifically developed by Lexeo to evaluate TNNI3‑targeted therapies. TNNI3‑related disease is estimated to account for approximately 1-3% of genetic cardiomyopathies. Corporate Updates Appointed Laura Sepp Lorenzino, Ph.D., as an independent, non-executive director to the Board of Directors. Laura was the former Chief Scientific Officer at Intellia Therapeutics and previously held senior research leadership roles at Alnylam Pharmaceuticals and Vertex Pharmaceuticals. She currently serves on the boards of AskBio, Taysha Gene Therapies, Ursa Medicines, the American Society of Gene & Cell Therapy (ASGCT) and the Oligonucleotide Therapeutics Society, and contributes to multiple scientific advisory boards including Inverna Therapeutics, Thermo Fisher Scientific, Arsenal Capital Partners and the UK Nucleic Acid Therapy Accelerator. First Quarter 2026 Financial Results Cash Position: As of March 31, 2026, cash, cash equivalents, and investments in marketable securities were $227.6 million, which Lexeo believes will be sufficient to fund operations into 2028. Research & Development Expenses: Research and Development expenses were $15.7 million for the three months ended March 31, 2026, compared to $17.2 million for the three months ended March 31, 2025. General & Administrative Expenses: General and Administrative expenses were $6.6 million for the three months ended March 31, 2026, compared to $16.6 million for the three months ended March 31, 2025. Net Loss: Net loss was $20.2 million or $0.25 per share (basic and diluted) for the three months ended March 31, 2026, compared to $32.7 million or $0.99 per share (basic and diluted) for the three months ended March 31, 2025. About Lexeo Therapeutics Lexeo Therapeutics is a New York City-based, clinical stage genetic medicine company dedicated to reshaping heart health by applying pioneering science to fundamentally change how cardiovascular diseases are treated. The Company is advancing a portfolio of therapeutic candidates that take aim at the underlying genetic causes of conditions, including LX2006 in Friedreich ataxia (FA), LX2020 in plakophilin-2 (PKP2) arrhythmogenic cardiomyopathy, and others in devastating diseases with high unmet need. Cautionary Note Regarding Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the federal securities laws, including, but not limited to, Lexeo’s expectations and plans regarding its current product candidates and programs and the timing for receipt and announcement of data from its clinical trials, the timing and likelihood of potential regulatory developments and approval, expectations regarding the time period over which Lexeo’s capital resources will be sufficient to fund its anticipated operations and estimates regarding Lexeo’s financial condition. Words such as “may,” “might,” “will,” “objective,” “intend,” “should,” “could,” “can,” “would,” “expect,” “believe,” “design,” “estimate,” “predict,” “potential,” “develop,” “plan” or the negative of these terms, and similar expressions, or statements regarding intent, belief, or current expectations, are forward-looking statements. While Lexeo believes these forward-looking statements are reasonable, undue reliance should not be placed on any such forward-looking statements. These forward-looking statements are based upon current information available to the company as well as certain estimates and assumptions and are subject to various risks and uncertainties (including, without limitation, those set forth in Lexeo’s filings with the U.S. Securities and Exchange Commission (SEC)), many of which are beyond the company’s control and subject to change. Actual results could be materially different from those indicated by such forward-looking statements as a result of many factors, including but not limited to: risks and uncertainties related to global macroeconomic conditions and related volatility; expectations regarding the initiation, progress, and expected results of Lexeo’s preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; delays in submission of regulatory filings or failure to receive regulatory approval; liquidity and capital resources; and other risks and uncertainties identified in Lexeo’s Annual Report on Form 10-K for the annual period ended December 31, 2025, filed with the SEC on March 30, 2026, and subsequent future filings Lexeo may make with the SEC. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Lexeo claims the protection of the Safe Harbor contained in the Private Securities Litigation Reform Act of 1995 for forward-looking statements. Lexeo expressly disclaims any obligation to update or alter any statements whether as a result of new information, future events or otherwise, except as required by law. Media Response: [email protected] Investor Response: Ashley Kaplowitz [email protected] Lexeo Therapeutics, Inc. Selected Financial Information (Unaudited, in thousands, except share and per share amounts) Statements of Operations Balance Sheet Data

SUNRISE-FA 2 open-label, pivotal trial protocol and SAP for LX2006 submitted to FDA in Q1 2026 following Type B meeting; study initiation on track for 1H 2026 First CMC Development and Readiness Program (CDRP) meeting for LX2006 in Q1 2026; aligned with FDA on flexible approach to process validation such as reduced PPQ manufacturing batches Late-breaking oral presentations at the American College of Cardiology (ACC) Annual Meeting demonstrate continued, encouraging efficacy and safety data across LX2006 and LX2020 programs Established research collaboration with Johnson & Johnson to explore targeted cardiac delivery of AAV gene therapy using novel, localized routes of administration Strengthened leadership team with addition of new Chief Medical Officer and senior appointments bolstering cardiac expertise Cash, cash equivalents and investments of $246.6 million expected to provide operational runway into 2028 NEW YORK, March 30, 2026 (GLOBE NEWSWIRE) -- Lexeo Therapeutics, Inc. (Nasdaq: LXEO), a clinical stage genetic medicine company dedicated to pioneering novel treatments for cardiovascular diseases, today provided business updates across its portfolio and reported financial results for the fourth quarter and full year 2025. “Over the past year we have made meaningful progress across our cardiac pipeline, including significant advancements for both LX2006 and LX2020,” said R. Nolan Townsend, Chief Executive Officer of Lexeo Therapeutics. “Most recently, we were pleased to be selected for two Late-Breaker presentations at the American College of Cardiology and appreciate the opportunity to engage the cardiology community around the future of precision medicine in cardiovascular care. Looking ahead, we remain focused on disciplined execution as we continue to advance our pipeline toward key milestones. With additional resources from our October financing, the expansion of our cardiac leadership team, and multiple announced preclinical research collaborations, we believe Lexeo is well positioned to drive significant long-term value for patients and shareholders.” Program Updates and Recent Progress LX2006 in Friedreich Ataxia (FA) In October 2025, Lexeo announced progress in FDA discussions and reported positive interim clinical data from both ongoing Phase I/II studies of LX2006 demonstrating an encouraging safety profile and evidence of meaningful cardiac and functional benefit. LX2006 was generally well tolerated and associated with improvements in cardiac structure, biomarkers, and functional outcomes, including reduced left ventricular mass index (LVMI) and improved modified Friedreich Ataxia Rating Scale (mFARS) scores across participants with more than six months of follow‑up. In November 2025, FDA approved the analytical comparability report establishing comparability between LX2006 HEK293 and Sf9 manufacturing processes, endorsing use of the optimized, Sf9 final commercial manufacturing process for LX2006 in the planned pivotal study and clearing comparability requirements to begin dosing patients. In February 2026, Lexeo submitted the final registrational trial design and statistical analysis plan (SAP) for the SUNRISE‑FA 2 pivotal study to the FDA following a Type B meeting. The proposed open-label study is generally consistent with previously communicated guidance on key design elements, such as study size, duration, patient population, and the LVMI primary endpoint, and incorporates FDA feedback on minimizing bias, including physician selection bias of study participants. Lexeo expects to receive final feedback from the FDA in the second quarter of 2026 and plans to provide a more detailed update at that time. In March 2026, Lexeo conducted an initial Chemistry, Manufacturing and Controls (CMC) Development and Readiness Program (CDRP) meeting with the FDA for LX2006, during which the agency reiterated its support for a flexible validation approach including potential for reduced process performance qualification (PPQ) runs and concurrent process validation. Lexeo is proceeding with validation and commercial manufacturing readiness activities to support the Biologic License Application (BLA) submission for LX2006. In March 2026, Lexeo shared updated interim clinical data for LX2006 at the ACC Annual Meeting. Phase I/II interim clinical data continue to show sustained or deepening improvements across both cardiac and neurologic measures of FA, including statistically significant improvement in mean mFARS scores for LX2006-treated participants compared to a propensity-matched control cohort from the UNIFAI natural history study. LX2006 remains generally well tolerated with no Grade 3+ SAEs to date. Anticipated milestones for the remainder of 2026 include: FDA feedback on protocol submission expected in Q2 2026 Initiate SUNRISE-FA 2 pivotal trial in the first half of 2026 LX2020 in PKP2 Arrhythmogenic Cardiomyopathy (PKP2-ACM) In January 2026, Lexeo reported positive interim clinical data from the HEROIC PKP2 Phase I/II clinical trial evaluating LX2020. Clinical data from the program were presented at the ACC Annual Meeting in March 2026. Cardiac biopsy assessments demonstrated dose dependent increases in PKP2 protein expression, vector copy number, and transgene mRNA. In high-dose cohorts, mean arrythmia burden was reduced at the latest visit and the majority of participants reported symptom improvement. LX2020 remains generally well tolerated across ten participants dosed with no clinically significant complement activation to date. Anticipated milestones for the remainder of 2026 include: 12-month data update for all high dose participants in Q4 2026 Regulatory engagement with the FDA expected in 2026 Corporate Updates Strengthened cardiovascular and commercial expertise through key leadership appointments, including the appointment of Narinder Bhalla, MD, as Chief Medical Officer. Dr. Bhalla brings deep experience building and scaling global medical and clinical development organizations and leading successful product launches, most recently at Bristol Myers Squibb and at AstraZeneca. Additional senior leadership appointments further underscore Lexeo’s expanding capabilities in cardiovascular medicine and late-stage clinical development. Established research collaboration with Johnson & Johnson to explore targeted cardiac delivery of AAV gene therapy. Collaboration combines Lexeo’s expertise in cardiac genetic medicine with Johnson & Johnson’s expertise in cardiovascular therapeutics and circulatory technologies, including Impella™ heart pumps, to enable the accelerated development of a preclinical cardiac target using novel, localized routes of viral gene therapy administration. Executed $154 million equity financing in October 2025 to further advance development of the company’s cardiac pipeline and to support registrational readiness activities for LX2006. Fourth Quarter and Full Year 2025 Financial Results Cash Position: As of December 31, 2025, cash, cash equivalents, and investments in marketable securities were $246.6 million, which Lexeo believes will be sufficient to fund operations into 2028. Research & Development Expenses: Research and Development expenses were $16.2 million for the three months ended December 31, 2025, compared to $18.4 million for the three months ended December 31, 2024. Research and Development expenses were $63.8 million for the year ended December 31, 2025, compared to $74.1 million for the year ended December 31, 2024. General & Administrative Expenses: General and Administrative expenses were $6.9 million for the three months ended December 31, 2025, compared to $9.0 million for the three months ended December 31, 2024. General and Administrative expenses were $45.5 million for the year ended December 31, 2025, compared to $31.7 million for the year ended December 31, 2024. Net Loss: Net loss was $20.9 million or $0.27 per share (basic and diluted) for the three months ended December 31, 2025, compared to $25.9 million or $0.78 per share (basic and diluted) for the three months ended December 31, 2024. Net loss was $100.0 million or $1.86 per share (basic and diluted) for the year ended December 31, 2025, compared to $98.3 million or $3.09 per share (basic and diluted) for the year ended December 31, 2024. About Lexeo Therapeutics Lexeo Therapeutics is a New York City-based, clinical stage genetic medicine company dedicated to reshaping heart health by applying pioneering science to fundamentally change how cardiovascular diseases are treated. The Company is advancing a portfolio of therapeutic candidates that take aim at the underlying genetic causes of conditions, including LX2006 in Friedreich ataxia (FA), LX2020 in plakophilin-2 (PKP2) arrhythmogenic cardiomyopathy, and others in devastating diseases with high unmet need. Cautionary Note Regarding Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the federal securities laws, including, but not limited to, Lexeo’s expectations and plans regarding its current product candidates and programs and the timing for receipt and announcement of data from its clinical trials, the timing and likelihood of potential regulatory developments and approval, expectations regarding the time period over which Lexeo’s capital resources will be sufficient to fund its anticipated operations and estimates regarding Lexeo’s financial condition. Words such as “may,” “might,” “will,” “objective,” “intend,” “should,” “could,” “can,” “would,” “expect,” “believe,” “design,” “estimate,” “predict,” “potential,” “develop,” “plan” or the negative of these terms, and similar expressions, or statements regarding intent, belief, or current expectations, are forward-looking statements. While Lexeo believes these forward-looking statements are reasonable, undue reliance should not be placed on any such forward-looking statements. These forward-looking statements are based upon current information available to the company as well as certain estimates and assumptions and are subject to various risks and uncertainties (including, without limitation, those set forth in Lexeo’s filings with the U.S. Securities and Exchange Commission (SEC)), many of which are beyond the company’s control and subject to change. Actual results could be materially different from those indicated by such forward-looking statements as a result of many factors, including but not limited to: risks and uncertainties related to global macroeconomic conditions and related volatility; expectations regarding the initiation, progress, and expected results of Lexeo’s preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; delays in submission of regulatory filings or failure to receive regulatory approval; liquidity and capital resources; and other risks and uncertainties identified in Lexeo’s Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2025, filed with the SEC on November 5, 2025, and subsequent future filings Lexeo may make with the SEC. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Lexeo claims the protection of the Safe Harbor contained in the Private Securities Litigation Reform Act of 1995 for forward-looking statements. Lexeo expressly disclaims any obligation to update or alter any statements whether as a result of new information, future events or otherwise, except as required by law. Media Response: [email protected] Investor Response: Ashley Kaplowitz [email protected]

FDA open to pooling data from ongoing Phase I/II studies of LX2006 with data from pivotal trial, and to earlier co-primary endpoint assessment, to support a Biologics License Application FDA approved comparability report between LX2006 HEK and Sf9 manufacturing processes in November 2025, endorsing use of Sf9 final commercial manufacturing process to begin dosing patients in upcoming pivotal study LX2006 interim clinical data show clinically meaningful improvements across cardiac and neurologic measures of Friedreich ataxia, including left ventricular mass index and the modified Friedreich Ataxia Rating Scale Completed enrollment of LX2020 HEROIC-PKP2 Phase I/II trial with ten participants dosed; interim data from low-dose cohort reported and additional clinical data from high-dose cohorts on track for January 2026 $154 million equity financing to support LX2006 registrational activities and further development of cardiac pipeline; in addition to Q3-25 end cash, cash equivalents and investments, expected to fund operations into 2028 NEW YORK, Nov. 05, 2025 (GLOBE NEWSWIRE) -- Lexeo Therapeutics, Inc. (Nasdaq: LXEO), a clinical stage genetic medicine company dedicated to pioneering novel treatments for cardiovascular diseases, today provided business updates across its portfolio and reported third quarter 2025 financial results. “We continue to build significant momentum across our cardiac pipeline, and the recent financing strengthens our ability to execute on essential manufacturing and commercial activities for LX2006 as we look towards registrational readiness,” said R. Nolan Townsend, Chief Executive Officer of Lexeo Therapeutics. “Interim clinical data for LX2006 demonstrate meaningful benefit across measures of cardiac health and neurologic function, including improvements in the modified Friedreich Ataxia Rating Scale (mFARS), and we believe this therapy could represent a transformational step forward in the standard of care for FA. Furthermore, with enrollment complete in the HEROIC-PKP2 Phase I/II trial, we look forward to sharing new clinical data for LX2020 in January.” Business and Program Updates LX2006 in Friedreich Ataxia (FA): Regulatory Progress: In response to questions regarding the possibility of a faster path to a Biologics License Application (BLA), the FDA has indicated openness to a BLA submission for accelerated approval that includes clinical data from the ongoing Phase I/II studies of LX2006 pooled with new clinical data to be generated in the planned pivotal study. To enable pooling of these data to support licensure, Lexeo plans to submit enhanced manufacturing comparability data and additional nonclinical data. The FDA also previously agreed to evaluate the co-primary endpoint of left ventricular mass index (LVMI) at a time point earlier than 12 months. Lexeo continues to engage with the FDA on the pivotal trial protocol and enhanced comparability. There have been no changes to the previously disclosed alignment with FDA on key parameters related to the LX2006 planned registrational study to date. Interim Clinical Data: In October 2025, Lexeo shared interim clinical data from both ongoing Phase I/II studies of LX2006, which continue to show encouraging safety and efficacy: 18% mean improvement in LVMI at 6 months and 23% mean improvement at 12 months in participants with abnormal baseline LVMI (n=6), exceeding the 10% FDA-aligned efficacy threshold for the planned pivotal study Improvement or stabilization in secondary cardiac biomarkers high-sensitivity troponin I and lateral wall thickness in 14 of 16 participants (n=16) 2.0-point mean improvement in mFARS from baseline at latest visit across all participants with >6-months of follow-up (n=16) Previously reported cardiac biopsy data from the SUNRISE-FA trial (n=8) showed that all study participants achieved increases in frataxin protein expression from baseline at 3 months, exceeding FDA-aligned efficacy threshold for frataxin expression Treatment with LX2006 has been generally well tolerated with no Grade 3+ SAEs to date, no clinically significant complement activation, and minimal, transient liver function test (LFT) elevations Analytical Comparability: In November 2025, FDA approved the analytical comparability report establishing comparability between LX2006 HEK293 and Sf9 manufacturing processes. This approval endorses use of the optimized, Sf9 final commercial manufacturing process for LX2006 in the planned pivotal study and clears comparability requirements to begin dosing patients. In October 2025, Lexeo shared manufacturing data from this report demonstrating similar frataxin expression in vitro between the two processes, as well as the high quality of the Sf9 material with minimal residual DNA. Next Steps: Lexeo plans to initiate a registrational study in the first half of 2026, pending finalization of the trial protocol in early 2026. LX2020 in PKP2-ACM: Dosing Update: Enrollment is complete with ten participants dosed in the HEROIC-PKP2 Phase I/II clinical trial, including three participants in Cohort 1 at the low dose (2×1013 vg/kg), three participants in Cohort 2 at the high dose (6×1013 vg/kg), and four participants in dose-expansion Cohort 3 at the high dose (6×1013 vg/kg). Low-dose (Cohort 1) Interim Update: In October 2025, Lexeo shared interim clinical data for the three participants dosed in Cohort 1 (n=2 at 12 months; n=1 at 9 months), assessing multiple cardiac parameters at latest visit relative to baseline: Arrythmia burden: premature ventricular contractions (PVCs) were reduced in one of three participants and non-sustained ventricular tachycardia (NSVT) was reduced or stable in two of three participants Electrical activity: QRS duration was normalized or stable in two of three participants and T-wave inversions were reduced in two of three participants Cardiac function: left ventricular ejection fraction (LVEF) and right ventricular ejection fraction (RVEF) were stable in three of three participants Safety: LX2020 continues to be generally well tolerated across participants with no clinically significant complement activation. One Grade 3 serious adverse event of sustained ventricular tachycardia (VT) was observed three months after dosing in a single participant in the high dose cohort and assessed as possibly treatment related. The participant was successfully treated with anti-arrhythmic medication and was discharged with no additional intervention required. Next Steps: Lexeo expects to provide a substantive LX2020 data update in January. This data update is expected to include safety data for all ten participants dosed, clinical efficacy data for five high-dose participants at >6 months of follow up and three low-dose participants at >12 months of follow up, and cardiac biopsy data from five participants in high-dose Cohorts 2 and 3. Closed $154 Million Equity Financing: In October 2025, Lexeo announced the closing of an oversubscribed $154 million equity financing to further advance development of its cardiac pipeline and to support registrational readiness activities for LX2006. Third Quarter Financial Results Cash Position: As of September 30, 2025, cash, cash equivalents, and investments in marketable securities were $122.8 million, excluding the $153.8 million of proceeds from the October 2025 public offering and concurrent PIPE which Lexeo believes will be sufficient to fund operations into 2028. Research and Development Expenses: Research and Development expenses were $15.7 million for the three months ended September 30, 2025, compared to $23.4 million for the three months ended September 30, 2024. General and Administrative Expenses: General and Administrative expenses were $6.0 million for the three months ended September 30, 2025, compared to $8.1 million for the three months ended September 30, 2024. Net Loss: Net loss was $20.3 million or $0.33 per share (basic and diluted) for the three months ended September 30, 2025, compared to $29.5 million or $0.89 per share (basic and diluted) for the three months ended September 30, 2024. About Lexeo Therapeutics Lexeo Therapeutics is a New York City-based, clinical stage genetic medicine company dedicated to reshaping heart health by applying pioneering science to fundamentally change how cardiovascular diseases are treated. The Company is advancing a portfolio of therapeutic candidates that take aim at the underlying genetic causes of conditions, including LX2006 in Friedreich ataxia (FA), LX2020 in plakophilin-2 (PKP2) arrhythmogenic cardiomyopathy, and others in devastating diseases with high unmet need. Cautionary Note Regarding Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the federal securities laws, including, but not limited to, Lexeo’s expectations and plans regarding its current product candidates and programs and the timing for receipt and announcement of data from its clinical trials, the timing and likelihood of potential regulatory developments and approval, expectations regarding the time period over which Lexeo’s capital resources will be sufficient to fund its anticipated operations and estimates regarding Lexeo’s financial condition. Words such as “may,” “might,” “will,” “objective,” “intend,” “should,” “could,” “can,” “would,” “expect,” “believe,” “design,” “estimate,” “predict,” “potential,” “develop,” “plan” or the negative of these terms, and similar expressions, or statements regarding intent, belief, or current expectations, are forward-looking statements. While Lexeo believes these forward-looking statements are reasonable, undue reliance should not be placed on any such forward-looking statements. These forward-looking statements are based upon current information available to the company as well as certain estimates and assumptions and are subject to various risks and uncertainties (including, without limitation, those set forth in Lexeo’s filings with the U.S. Securities and Exchange Commission (SEC)), many of which are beyond the company’s control and subject to change. Actual results could be materially different from those indicated by such forward-looking statements as a result of many factors, including but not limited to: risks and uncertainties related to global macroeconomic conditions and related volatility; expectations regarding the initiation, progress, and expected results of Lexeo’s preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; delays in submission of regulatory filings or failure to receive regulatory approval; liquidity and capital resources; and other risks and uncertainties identified in Lexeo’s Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2025, filed with the SEC on August 14, 2025, and subsequent future filings Lexeo may make with the SEC. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Lexeo claims the protection of the Safe Harbor contained in the Private Securities Litigation Reform Act of 1995 for forward-looking statements. Lexeo expressly disclaims any obligation to update or alter any statements whether as a result of new information, future events or otherwise, except as required by law. Media Response: [email protected] Investor Response: Carlo Tanzi, Ph.D. [email protected] Condensed Balance Sheet Data

Breakthrough Therapy designation granted for LX2006 based on interim data from Phase I/II trials demonstrating clinically meaningful improvements in cardiac and neurologic measures of Friedreich ataxia LX2006 selected for FDA Chemistry, Manufacturing, and Controls Development and Readiness Pilot (CDRP) program, created to facilitate CMC registrational readiness and support faster patient access Eight participants dosed in Phase I/II clinical trial (HEROIC-PKP2) of LX2020 for PKP2-ACM; interim clinical data update on track for second half of 2025 Strategic partnership announced with Perceptive Xontogeny Venture Funds and venBio Partners to advance non-viral, RNA-based therapeutics for genetic cardiac diseases $80 million equity financing to support development of clinical stage pipeline; cash, cash equivalents and investments in marketable securities of $152.5 million expected to provide operational runway into 2028 Louis Tamayo appointed Chief Financial Officer NEW YORK, Aug. 14, 2025 (GLOBE NEWSWIRE) -- Lexeo Therapeutics, Inc. (Nasdaq: LXEO), a clinical stage genetic medicine company dedicated to pioneering novel treatments for cardiovascular diseases, today provided business updates across its portfolio and reported second quarter 2025 financial results. “Over the last several months, Lexeo has made significant progress advancing our clinical stage programs, diversifying our pipeline through a strategic partnership that we believe enables us to stay on the cusp of leading-edge cardiovascular science, and further strengthening our balance sheet,” said R. Nolan Townsend, Chief Executive Officer of Lexeo Therapeutics. “FDA Breakthrough Therapy designation for LX2006 underscores the potential of this gene therapy candidate, and we are moving as quickly as possible in close partnership with patient advocates, clinicians, and the FA community to initiate a registrational study early next year. We are also continuing to advance our LX2020 program for arrhythmogenic cardiomyopathy with eight participants dosed to date and data updates expected in the second half of this year.” Business and Program Updates LX2006 in Friedreich Ataxia (FA): Regulatory Updates: In July 2025, Lexeo received Breakthrough Therapy designation from the U.S. Food and Drug Administration (FDA) for LX2006 based on interim clinical data demonstrating clinically meaningful improvements in cardiac and neurologic measures of FA. LX2006 has also been selected to participate in the FDA Chemistry, Manufacturing, and Controls (CMC) Development Readiness Pilot (CDRP) program, created to accelerate CMC registrational readiness for therapies with expedited clinical development timelines. Lexeo expects final alignment with FDA on the LX2006 registrational study in late Q3 to early Q4 2025. Natural History: The CLARITY-FA natural history study is currently enrolling and is expected to serve as a concurrent external control arm for the planned registrational study. Safety: LX2006 continues to be generally well tolerated with no clinically significant complement activation, and no new treatment-related serious adverse events to report. Next Steps: Lexeo expects to initiate a registrational study in early 2026 with a potential efficacy readout in 2027. LX2020 in PKP2-ACM: Dosing Update: Eight participants have been dosed to date in the HEROIC-PKP2 Phase I/II clinical trial, including three participants in Cohort 1 at the low dose (2x1013 vg/kg), three participants in Cohort 2 at the high dose (6x1013 vg/kg), and two participants in dose-expansion Cohort 3 at the high dose (6x1013 vg/kg). Cohort 3 is still enrolling and up to two additional participants may be dosed in this cohort. Safety: LX2020 has been generally well tolerated with no clinically significant complement activation, and no treatment-related serious adverse events to date across all dose cohorts. Next Steps: Lexeo expects to share an interim clinical data update in the second half of 2025. Closed $80 Million Equity Financing: In May 2025, Lexeo announced the closing of an $80 million equity financing to further advance development of its clinical stage genetic medicine candidates. Lexeo anticipates that current cash, cash equivalents and marketable securities will be sufficient to fund operating and capital expenditures into 2028, through a potential efficacy readout for the registrational study of LX2006 in 2027. Research Collaboration with Perceptive Xontogeny Venture Funds and venBio Partners: In June 2025, Lexeo announced a strategic partnership to develop therapies for genetic cardiac diseases utilizing a novel non-viral RNA platform. PXV Funds and venBio will contribute up to $40 million in private equity financing to a new entity addressing cardiac genetic diseases that existing AAV platforms are unable to treat. Lexeo is contributing expertise and know-how in cardiac genetic medicines, preclinical intellectual property and technology to the partnership, with a double-digit percentage equity position in the new entity at transaction close alongside entitlement to future milestone payments, royalties, and opt-in rights to certain program(s). New Leadership Appointment: Lexeo announced today that Louis Tamayo has been appointed Chief Financial Officer. Mr. Tamayo succeeds Kyle Rasbach who remains an advisor to Lexeo. Mr. Tamayo will support Lexeo’s late-stage clinical and commercialization plans as LX2006 development accelerates and LX2020 development continues, alongside strategic planning, portfolio management, capital allocation, and other financial operations. Mr. Tamayo brings extensive commercial finance experience, having previously served as Senior Vice President at Siemens Healthineers AG, responsible for driving revenue growth and market expansion for the company’s $5 billion global diagnostics division. In this role, he built and led high-performing finance organizations that supported multiple global product launches and strategic partnerships, directed R&D capital allocation, and oversaw large-scale transformation initiatives. Prior to Siemens Healthineers, Mr. Tamayo was the Business Unit CFO for Becton, Dickinson and Company’s $1.2 billion global diabetes care business. Mr. Tamayo began his career at Pfizer where he held a series of financial, strategic, and analytical leadership roles across U.S. and international markets. Mr. Tamayo holds a BBA in Finance and Marketing from Northeastern University. Recent Data Presentations: Lexeo presented new data at the 28th American Society of Gene & Cell Therapy (ASGCT) Annual Meeting on AAV manufacturing optimization via the Company’s Sf9-baculovirus process. Data presentations reviewed the high purity and potency of Lexeo yields with improved scalability of production and reduced cost. Lexeo also presented data at the Global Cell and Gene Therapy Summit reviewing the favorable complement profile of AAVrh10 based on clinical monitoring experience across the three gene therapy studies in FA and PKP2 in which no clinically significant events related to complement activation have been observed to date. Second Quarter Financial Results Cash Position: As of June 30, 2025, cash, cash equivalents, and investments in marketable securities were $152.5 million, which Lexeo believes will be sufficient to fund operations into 2028. Research and Development Expenses: Research and Development expenses were $14.7 million for the three months ended June 30, 2025, compared to $16.6 million for the three months ended June 30, 2024. General and Administrative Expenses: General and Administrative expenses were $16.0 million for the three months ended June 30, 2025, compared to $7.0 million for the three months ended June 30, 2024. Net Loss: Net loss was $26.1 million or $0.60 per share (basic and diluted) for the three months ended June 30, 2025, compared to $21.2 million or $0.64 per share (basic and diluted) for the three months ended June 30, 2024. About Lexeo Therapeutics Lexeo Therapeutics is a New York City-based, clinical stage genetic medicine company dedicated to reshaping heart health by applying pioneering science to fundamentally change how cardiovascular diseases are treated. The Company is advancing a portfolio of therapeutic candidates that take aim at the underlying genetic causes of conditions, including LX2006 in Friedreich ataxia (FA) cardiomyopathy, LX2020 in plakophilin-2 (PKP2) arrhythmogenic cardiomyopathy, and others in devastating diseases with high unmet need. Cautionary Note Regarding Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the federal securities laws, including, but not limited to, Lexeo’s expectations and plans regarding its current product candidates and programs and the timing for receipt and announcement of data from its clinical trials, the timing and likelihood of potential regulatory developments and approval, expectations regarding the time period over which Lexeo’s capital resources will be sufficient to fund its anticipated operations and estimates regarding Lexeo’s financial condition. Words such as “may,” “might,” “will,” “objective,” “intend,” “should,” “could,” “can,” “would,” “expect,” “believe,” “design,” “estimate,” “predict,” “potential,” “develop,” “plan” or the negative of these terms, and similar expressions, or statements regarding intent, belief, or current expectations, are forward-looking statements. While Lexeo believes these forward-looking statements are reasonable, undue reliance should not be placed on any such forward-looking statements. These forward-looking statements are based upon current information available to the company as well as certain estimates and assumptions and are subject to various risks and uncertainties (including, without limitation, those set forth in Lexeo’s filings with the U.S. Securities and Exchange Commission (SEC)), many of which are beyond the company’s control and subject to change. Actual results could be materially different from those indicated by such forward-looking statements as a result of many factors, including but not limited to: risks and uncertainties related to global macroeconomic conditions and related volatility; expectations regarding the initiation, progress, and expected results of Lexeo’s preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; delays in submission of regulatory filings or failure to receive regulatory approval; liquidity and capital resources; and other risks and uncertainties identified in Lexeo’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2025, filed with the SEC on May 12, 2025, and subsequent future filings Lexeo may make with the SEC. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Lexeo claims the protection of the Safe Harbor contained in the Private Securities Litigation Reform Act of 1995 for forward-looking statements. Lexeo expressly disclaims any obligation to update or alter any statements whether as a result of new information, future events or otherwise, except as required by law. Media Response: [email protected] Investor Response: Carlo Tanzi, Ph.D. [email protected] Condensed Statements of Operations Condensed Balance Sheet Data

Announced positive interim data for LX2006 from Phase 1/2 studies in Friederich ataxia (FA) cardiomyopathy; frataxin expression and LVMI improvement exceeded co-primary target thresholds for planned registrational study LX2006 registrational study expected to begin by early 2026; commencing enrollment in prospective natural history study, CLARITY-FA, in Q2 2025 to serve as concurrent external control Phase 1/2 clinical trial of LX2020 (HEROIC-PKP2) currently enrolling patients in Cohort 3; interim clinical data update on track for second half of 2025 Redeployed $20 million to focus on clinical-stage programs; cash, cash equivalents and investments of $106.9 million expected to provide operational runway into 2027 NEW YORK, May 12, 2025 (GLOBE NEWSWIRE) -- Lexeo Therapeutics, Inc. (Nasdaq: LXEO), a clinical stage genetic medicine company dedicated to pioneering novel treatments for cardiovascular diseases, today provided business updates across its portfolio and reported first quarter 2025 financial results. “Based on the highly encouraging clinical data shared to date, we believe LX2006 could be transformational and establish a new standard of care in FA cardiomyopathy,” said R. Nolan Townsend, Chief Executive Officer of Lexeo Therapeutics. “We look forward to beginning enrollment in the CLARITY-FA natural history study imminently and moving as quickly as possible to initiate a registrational study for LX2006 by early 2026. We were also proud to share the promising, early data for LX2020 for the treatment of PKP2-associated arrhythmogenic cardiomyopathy and we look forward to sharing additional clinical updates later in 2025 for this program.” Business and Program Updates LX2006 for the Treatment of FA Cardiomyopathy: In April 2025, Lexeo announced positive interim data of LX2006 across both the Lexeo-sponsored SUNRISE-FA Phase 1/2 clinical trial (NCT05445323) and the Weill Cornell Medicine investigator-initiated Phase 1A trial (NCT05302271). Efficacy: Clinically meaningful improvements were observed across cardiac biomarkers and functional measures in the majority of participants across both studies. Participants with abnormal left ventricular mass index (LVMI) at baseline achieved 25% mean reduction in LVMI by 12 months or sooner, exceeding the 10% target reduction in LVMI by 12 months aligned with the U.S. Food and Drug Administration (FDA) for the planned registrational study. Protein Expression: Increases in cardiac frataxin expression were observed in all SUNRISE-FA participants at 3-months post treatment, with an average increase of 115% over baseline observed in the high-dose cohort. Safety: LX2006 continues to be generally well tolerated with no new treatment-related serious adverse events to report. Regulatory Plans: Lexeo expects final alignment with FDA on the LX2006 planned pivotal study protocol and statistical analysis plan in 2025. Lexeo previously aligned with FDA on co-primary endpoints for the study and measurement thresholds: greater than 10% reduction in LVMI as measured by cardiac MRI, and any increase from baseline cardiac frataxin expression as measured by liquid chromatography mass spectrometry (LCMS). Next Steps: In Q2 2025, Lexeo expects to begin enrollment in a prospective natural history study serving as a concurrent external control arm for the registrational study. The Company expects to initiate a registrational study by early 2026 with a potential efficacy readout in 2027. LX2020 for the Treatment of PKP2-ACM: In March 2025, Lexeo shared positive interim data of LX2020 from the low-dose cohort in the HEROIC-PKP2 Phase 1/2 clinical trial. Cohort 1 Interim Update: At 3-months post-treatment, cardiac biopsies from two participants in cohort 1 showed 71% and 115% increases, respectively, in PKP2 protein expression from baseline; the third cohort 1 participant elected not to undergo a post-treatment biopsy. The first participant evaluated 6-months post treatment experienced a 67% reduction in premature ventricular contractions (PVCs) from baseline. Safety: LX2020 has been generally well tolerated with no treatment-related serious adverse events to date across both dose cohorts. Next Steps: Currently enrolling cohort 3 of LX2020 HEROIC-PKP2 (n=4), with an interim clinical data update expected in the second half of 2025. Capital Redeployment and Cash Runway: In April 2025, Lexeo identified approximately $20 million in capital to redeploy towards the Company’s lead cardiac programs, LX2006 and LX2020. This capital was redeployed from preclinical and non-cardiac pipeline activities and included a limited reduction in force impacting approximately 15% of employees. The updated capital structure is expected to enable the Company to execute against key milestones for its clinical-stage pipeline, accelerate work to initiate a registrational study for LX2006 by early 2026, and maintain operational runway into 2027. First Quarter Financial Results Cash Position: As of March 31, 2025, cash, cash equivalents, and investments were $106.9 million, which Lexeo believes will be sufficient to fund operations into 2027. Research and Development Expenses: Research and Development expenses were $17.2 million for the three months ended March 31, 2025, compared to $15.7 million for the three months ended March 31, 2024. General and Administrative Expenses: General and Administrative expenses were $16.6 million for the three months ended March 31, 2025, compared to $7.5 million for the three months ended March 31, 2024. Net Loss: Net loss was $32.7 million or $0.99 per share (basic and diluted) for the three months ended March 31, 2025, compared to $21.7 million or $0.77 per share (basic and diluted) for the three months ended March 31, 2024. About Lexeo Therapeutics Lexeo Therapeutics is a New York City-based, clinical stage genetic medicine company dedicated to reshaping heart health by applying pioneering science to fundamentally change how cardiovascular diseases are treated. The Company is advancing a portfolio of therapeutic candidates that take aim at the underlying genetic causes of conditions, including LX2006 for the treatment of Friedreich ataxia (FA) cardiomyopathy, LX2020 for the treatment of plakophilin-2 (PKP2) arrhythmogenic cardiomyopathy, and others for devastating diseases with high unmet need. Cautionary Note Regarding Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the federal securities laws, including, but not limited to, Lexeo’s expectations and plans regarding its current product candidates and programs and the timing for receipt and announcement of data from its clinical trials, the timing and likelihood of potential regulatory developments and approval, expectations regarding the time period over which Lexeo’s capital resources will be sufficient to fund its anticipated operations and estimates regarding Lexeo’s financial condition. Words such as “may,” “might,” “will,” “objective,” “intend,” “should,” “could,” “can,” “would,” “expect,” “believe,” “design,” “estimate,” “predict,” “potential,” “develop,” “plan” or the negative of these terms, and similar expressions, or statements regarding intent, belief, or current expectations, are forward-looking statements. While Lexeo believes these forward-looking statements are reasonable, undue reliance should not be placed on any such forward-looking statements. These forward-looking statements are based upon current information available to the company as well as certain estimates and assumptions and are subject to various risks and uncertainties (including, without limitation, those set forth in Lexeo’s filings with the U.S. Securities and Exchange Commission (SEC)), many of which are beyond the company’s control and subject to change. Actual results could be materially different from those indicated by such forward-looking statements as a result of many factors, including but not limited to: risks and uncertainties related to global macroeconomic conditions and related volatility; expectations regarding the initiation, progress, and expected results of Lexeo’s preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; delays in submission of regulatory filings or failure to receive regulatory approval; liquidity and capital resources; and other risks and uncertainties identified in Lexeo’s Annual Report on Form 10-K for the annual period ended December 31, 2024, filed with the SEC on March 24, 2025, and subsequent future filings Lexeo may make with the SEC. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Lexeo claims the protection of the Safe Harbor contained in the Private Securities Litigation Reform Act of 1995 for forward-looking statements. Lexeo expressly disclaims any obligation to update or alter any statements whether as a result of new information, future events or otherwise, except as required by law. Media Response: [email protected] Investor Response: Carlo Tanzi, Ph.D. [email protected]

Additional alignment with FDA on LX2006 planned pivotal study including protein expression co-primary endpoint: based on improvements in LVMI across participants with abnormal LVMI at baseline, frataxin expression to be evaluated for any increase from baseline rather than numerical threshold Interim update from cohort 1 of LX2020 HEROIC-PKP2 Phase 1/2 trial: observed 71% and 115% increases in PKP2 protein expression in first two post-treatment biopsies; first participant evaluated 6-months after dosing experienced 67% reduction in premature ventricular contractions (PVCs) Completed enrollment of cohort 2 of LX2020 HEROIC-PKP2 Phase 1/2 trial; interim clinical data update expected in second half of 2025 LX2020 has been generally well tolerated with no treatment-related serious adverse events to date Cash, cash equivalents and investments of $128.5 million expected to provide operational runway into 2027 NEW YORK, March 24, 2025 (GLOBE NEWSWIRE) -- Lexeo Therapeutics, Inc. (Nasdaq: LXEO), a clinical stage genetic medicine company dedicated to pioneering novel treatments for cardiovascular diseases, today provided business updates across its portfolio and reported fourth quarter and full year 2024 financial results. “We are pleased to share further regulatory clarity for LX2006 for the treatment of Friedreich ataxia (FA) cardiomyopathy, and we appreciate the continued partnership from the FDA on an accelerated approval pathway to support adults and children living with this devastating condition,” said R. Nolan Townsend, Chief Executive Officer of Lexeo Therapeutics. “We are also encouraged by the favorable safety profile and early data observed in participants dosed with LX2020 to date. We look forward to sharing additional clinical updates later in 2025 now that the second cohort of the LX2020 HEROIC-PKP2 Phase 1/2 trial in arrhythmogenic cardiomyopathy is fully enrolled.” Business and Program Updates LX2006 for the Treatment of FA Cardiomyopathy: Regulatory Update: Further alignment on elements of the accelerated development pathway following a Type B RMAT meeting with the U.S. Food and Drug Administration (FDA): Frataxin expression to be evaluated for any increase from baseline rather than numerical threshold, based on improvements to date in LVMI across participants with abnormal LVMI at baseline Inclusion of pediatric cohorts, both adolescents and children, in planned pivotal study Use of prospective natural history data as external control in planned pivotal study Final dose selection and remaining elements of registrational trial alignment expected in 2025 In light of these regulatory updates and anticipated timelines for assay validation, the Company expects to measure frataxin protein expression using liquid chromatography mass spectrometry (LCMS) in the planned registrational trial. Mid-Year Clinical Update Expected to Include: Safety and tolerability data for all participants dosed across both the SUNRISE-FA and Weill Cornell clinical trials (at least 16 participants, including 6 participants with abnormal LVMI at baseline) Pre- and post-treatment cardiac frataxin protein expression measured via LCMS for all four participants at the highest dose (1.2x1012 vg/kg, Cohort 3) Clinical biomarker data, including left ventricular mass index (LVMI), left ventricular wall thickness and high-sensitivity troponin I, for participants with >6-months of follow up Functional and patient-reported outcome data for participants with >6-months of follow up Safety: LX2006 continues to be generally well tolerated with no new treatment-related serious adverse events to report LX2020 for the Treatment of PKP2-ACM: Cohort 1 Interim Update: Post-treatment cardiac biopsies from two participants in cohort 1 showed increases in PKP2 protein expression from baseline; the third cohort 1 participant elected not to undergo a post-treatment biopsy Observed increases in exogenous mRNA and 71% and 115% increases in PKP2 protein levels from baseline First participant evaluated 6-months post treatment experienced 67% reduction in PVCs from baseline (from 861 to 284) and resolution of non-specific intraventricular block (normalization of QRS duration) Enrollment Update: Completed enrollment of cohort 2 of LX2020 HEROIC-PKP2 (n=3), interim clinical data update expected in second half of 2025 Safety: LX2020 has been generally well tolerated with no treatment-related serious adverse events to date across both dose cohorts Regulatory Update: In March 2025 the European Commission granted orphan medicinal product designation for LX2020 for the treatment of PKP2-ACM Fourth Quarter and Full Year Financial Results Cash Position: As of December 31, 2024, cash, cash equivalents, and investments were $128.5 million, which Lexeo believes will be sufficient to fund operations into 2027. R&D Expenses: R&D expenses were $18.4 million for the three months ended December 31, 2024, compared to $8.2 million for the three months ended December 31, 2023. R&D expenses were $74.1 million for the year ended December 31, 2024, compared to $53.1 million for the year ended December 31, 2023. G&A Expenses: G&A expenses were $9.0 million for the three months ended December 31, 2024, compared to $6.8 million for the three months ended December 31, 2023. G&A expenses were $31.7 million for the year ended December 31, 2024, compared to $15.4 million for the year ended December 31, 2023. Net Loss: Net loss was $25.9 million or $0.78 per share (basic and diluted) for the three months ended December 31, 2024, compared to $14.2 million or $0.86 per share (basic and diluted) for the three months ended December 31, 2023. Net loss was $98.3 million or $3.09 per share (basic and diluted) for the year ended December 31, 2024, compared to $66.4 million or $12.40 per share (basic and diluted) for the year ended December 31, 2023. About Lexeo Therapeutics Lexeo Therapeutics is a New York City-based, clinical stage genetic medicine company dedicated to reshaping heart health by applying pioneering science to fundamentally change how cardiovascular diseases are treated. The Company is advancing a portfolio of therapeutic candidates that take aim at the underlying genetic causes of conditions, including LX2006 for the treatment of Friedreich ataxia (FA) cardiomyopathy, LX2020 for the treatment of plakophilin-2 (PKP2) arrhythmogenic cardiomyopathy, and other devastating diseases with high unmet need. Cautionary Note Regarding Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the federal securities laws, including, but not limited to, Lexeo’s expectations and plans regarding its current product candidates and programs and the timing for receipt and announcement of data from its clinical trials, the timing and likelihood of potential regulatory approval, and expectations regarding the time period over which Lexeo’s capital resources will be sufficient to fund its anticipated operations and estimates regarding Lexeo’s financial condition. Words such as “may,” “might,” “will,” “objective,” “intend,” “should,” “could,” “can,” “would,” “expect,” “believe,” “design,” “estimate,” “predict,” “potential,” “develop,” “plan” or the negative of these terms, and similar expressions, or statements regarding intent, belief, or current expectations, are forward-looking statements. While Lexeo believes these forward-looking statements are reasonable, undue reliance should not be placed on any such forward-looking statements. These forward-looking statements are based upon current information available to the company as well as certain estimates and assumptions and are subject to various risks and uncertainties (including, without limitation, those set forth in Lexeo’s filings with the U.S. Securities and Exchange Commission (SEC)), many of which are beyond the company’s control and subject to change. Actual results could be materially different from those indicated by such forward-looking statements as a result of many factors, including but not limited to: risks and uncertainties related to global macroeconomic conditions and related volatility; expectations regarding the initiation, progress, and expected results of Lexeo’s preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; delays in submission of regulatory filings or failure to receive regulatory approval; liquidity and capital resources; and other risks and uncertainties identified in Lexeo’s Annual Report on Form 10-K for the annual period ended December 31, 2023, filed with the SEC on March 11, 2024, Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2024, filed with the SEC on November 13, 2024, and subsequent future filings Lexeo may make with the SEC. Additional information will also be set forth in Lexeo’s Annual Report on Form 10-K for the year ended December 31, 2024. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Lexeo claims the protection of the Safe Harbor contained in the Private Securities Litigation Reform Act of 1995 for forward-looking statements. Lexeo expressly disclaims any obligation to update or alter any statements whether as a result of new information, future events or otherwise, except as required by law. Media Response: [email protected] Investor Response: Carlo Tanzi, Ph.D. [email protected] Lexeo Therapeutics, Inc. Selected Financial Information (in thousands, except share and per share amounts) Statements of Operations Balance Sheet Data