Larimar Therapeutics, Inc. (LRMR) Business

ITEM 1. BUSINESS

Overview

We are a clinical-stage biotechnology company focused on developing treatments for patients suffering from complex rare diseases using our novel cell penetrating peptide (“CPP”) technology platform. Our lead product candidate, nomlabofusp, is a subcutaneously administered, recombinant fusion protein intended to deliver frataxin (“FXN”), an essential protein, to the mitochondria of patients with Friedreich's ataxia (“FA”). FA is a rare, progressive, and fatal disease in which patients are unable to produce sufficient FXN due to a genetic abnormality. Currently, there are no treatment options that address the core deficit of FA, low levels of FXN. Nomlabofusp represents the first potential therapy designed to systemically increase FXN levels in patients with FA.

We believe that our CPP platform, which enables a therapeutic molecule to cross a cell membrane in order to reach intracellular targets, also has the potential to enable the treatment of other rare and orphan diseases. We intend to use our proprietary platform to target additional orphan indications characterized by deficiencies in or alterations of intracellular content or activity.

Since our inception, we have devoted substantially all of our resources to developing nomlabofusp, building our intellectual property portfolio, developing third-party manufacturing capabilities, business planning, raising capital, and providing general and administrative support for such operations.

As of December 31, 2025, we had cash, cash equivalents, and marketable securities of $136.9 million, which, together with the net proceeds of $107.6 million from our February 2026 public offering of common stock, we anticipate will fund operations into the second quarter of 2027.

Nomlabofusp Program Update

We have Orphan Drug Designation, Fast Track Designation, Pediatric Rare Disease Designation and Breakthrough Therapy Designation from the FDA and have been granted Orphan Drug Designation and access to the European Medicines Agency’s (“EMA’s”) Priority Medicines Program (“PRIME”) scheme in the European Union (the “EU”). We have also received access in the United Kingdom (the “UK”) to the Medicines and Healthcare Regulatory Agency’s (“MHRA”) Innovative Licensing and Access Pathway (“ILAP”). These programs are designed to facilitate development of certain therapeutics such as those for rare and serious diseases, and those that have the potential to meet an unmet medical need.

The FDA’s Center for Drug Evaluation and Research selected nomlabofusp as one of a few drug development programs for participation in the Support for Clinical Trials Advancing Rare Disease Therapeutics (“START”) Pilot Program. The objective of the program is to accelerate the development of drugs for rare diseases that lead to significant disability or death by facilitating frequent advice and regular communication with the FDA staff to expedite the review process of biologics and drugs.

We have engaged in multiple discussions and interactions with the FDA in connection with our clinical development of nomlabofusp and communications remain ongoing. We have also had numerous interactions with the EMA, the MHRA, and Canada’s Health Canada regarding the clinical development of nomlabofusp.

We have completed four clinical studies: (i) two Phase 1 clinical studies in adults, (ii) a Phase 2 dose exploration study in adults and (iii) a Phase 1 pharmacokinetic (“PK”) run-in study in adolescents (12-17 years old). We currently have an ongoing open label ("OL") study (previously referred to as the Open Label Extension, (“OLE”) study) in adults and adolescents with FA. Approximately 8,000 doses of nomlabofusp have been administered to patients throughout the clinical development program.

Recent significant developments are as follows:

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In December 2024, we reported initial data from our ongoing OL study. This data included safety, FXN levels, clinical and PK data in 14 participants administered 25 mg nomlabofusp daily for up to 260 days (mean 99 days). Tissue FXN levels increased and were maintained at day 90 and there were early trends towards improvement in clinical outcomes observed at day 90. The most common adverse events were injection site reactions and two participants experienced serious adverse events (one seizure and one

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anaphylactic reaction) that resolved within 24 hours and they were withdrawn from the study. Also in December 2024, we announced that we were increasing the dose in the OL study to 50 mg of nomlabofusp daily for then currently enrolled participants and would be starting all new patients on 50 mg daily and in March 2025 we announced that all participants had transitioned to the 50 mg daily dose. In March 2025 we also announced that our Safety Monitoring Team had identified anaphylaxis as an adverse drug reaction likely associated with nomlabofusp.

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In January 2025, we initiated dosing of adolescents (12-17 years old) in a PK run-in study for pediatric patients with FA. Study participants in the PK run-in study were randomized 2:1 to receive either nomlabofusp at a weight-base dose expected to match the PK of adults receiving the 50 mg dose, or placebo, daily for seven days. We completed dosing in 14 adolescents in March 2025. The PK and exposure data were similar to adults and the participants became eligible to enroll in the OL study. The PK results from the adolescent cohort also supported the predictive value of our exposure modeling and will facilitate direct enrollment of children (2-11 years old) into the OL study which would eliminate any pause in study drug administration between the PK study and the OL study. Therefore, it was not necessary to perform a cohort for children in the PK study and we terminated the study. We are now planning to initiate enrollment of children directly into the ongoing OL study.

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In February 2025, the FDA accepted the data supporting the comparability of the lyophilized drug product to the frozen solution and agreed with our plans to introduce the lyophilized product into our clinical development program. In July 2025, we began introducing the lyophilized product formulation into the OL study. This is the formulation intended for commercialization.

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In March 2025, we announced that the FDA stated as part of the START pilot program, that it is open to considering the use of FXN concentration as a reasonably likely surrogate endpoint (“RLSE”) and the acceptability of FXN concentration as an RLSE to support accelerated approval will be a matter of review in a future marketing application. The FDA recommended focusing on assessments of skin FXN concentrations rather than buccal FXN concentrations due to more consistent sampling and less variability. The FDA acknowledged that data we submitted appeared to support a relationship between increased FXN concentrations in skin and relevant tissues such as the heart, dorsal root ganglion and skeletal muscle. The FDA also acknowledged that the nonclinical studies we submitted were performed at relevant human doses. The FDA also suggested that we consider exploring the relationship between increases in FXN in skin and changes in pharmacodynamic (“PD”) markers such as lipid profiles and/or clinical measures to provide additional support for the use of FXN as an RLSE.

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In June 2025, the FDA provided recommendations regarding the safety data set that might be needed to support a Biologics License Application (“BLA”) seeking accelerated approval, which included evaluating safety in at least 30 participants with continuous study drug exposure for six months and a subset of at least 10 of those participants with continuous study drug exposure for one year, with the large majority of data coming from participants receiving the 50 mg dose.

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In July 2025, we announced the publication of nonclinical data evaluating the mechanism of action, pharmacodynamics and pharmacology of nomlabofusp as a novel FXN protein replacement therapy designed to address the underlying cause of FA in two peer-reviewed articles. These data were included in the briefing package reviewed by the FDA in support of using skin FXN concentrations as a RLSE for our registrational program seeking accelerated approval for nomlabofusp.

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In September 2025, we announced positive 25 mg and 50 mg data from the OL study evaluating daily subcutaneous injections of nomlabofusp self-administered or administered by a caregiver in participants with FA. Ten out of 10 participants with data at six months achieved skin FXN levels that were higher than 50% of median levels in healthy volunteers and similar to levels expected in asymptomatic carriers. We also observed consistent directional improvements across four key clinical outcomes relative to a worsening in a Friedreich's Ataxia Clinical Outcomes Measure study (“FACOMS”) natural history study reference population. In participants receiving long term continuous treatment, including 14 participants on nomlabofusp for at least six months, eight of whom continued to be on nomlabofusp for over one year, daily administration of nomlabofusp was generally well-tolerated. Anaphylaxis was reported in seven participants, with most events occurring on the initial day of administration and all occurring within the first 6 weeks of dosing. As a result, we consulted experts and decided to modify the starting dose regimen

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and the FDA agreed with our approach. The most common adverse events continued to be local injection site reactions that are mostly mild, brief in duration and self-limited.

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In September 2025 we also announced that we amended the previous OLE study protocol (which had only included participants from previous clinical trials of nomlabofusp) to include adolescent and adult patients who have not previously participated in a prior nomlabofusp study and the study is now being referred to as the OL study. In addition to risk mitigation measures against anaphylaxis that are already in place such as pre-medicating with antihistamines and supplying epinephrine auto-injectors to study participants, we introduced a new dosing regimen in which participants initially receive a 5 mg dose followed by a 25 mg dose one hour later under observation. Nomlabofusp 25 mg is then administered once daily through day 30 and then the dose is increased to 50 mg once daily.

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In February 2026, the FDA granted the nomlabofusp program Breakthrough Therapy Designation (“BTD”). BTD is intended to expedite the development and regulatory review of a drug intended to treat a serious condition. A drug is eligible for BTD if preliminary clinical evidence indicates that the drug may demonstrate substantial improvement over available treatments in one or more clinically significant endpoints.

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Also in February 2026, as a result of a START pilot program meeting with the FDA, we announced continued alignment with the FDA to consider the use of skin FXN as a novel surrogate endpoint reasonably likely to predict clinical benefit to support a planned Biologics License Application (BLA) submission seeking accelerated approval and that the use of FXN as a novel surrogate endpoint to support accelerated approval. There was also agreement on the type of analyses required to support the exposure response relationships for the nomlabofusp program. The FDA stated that the adequacy of the safety database will be a matter of review at the time of BLA submission.

We are targeting to provide topline study data from our OL study in the second quarter of 2026 and we plan to submit a BLA seeking accelerated approval in June 2026.

For our global confirmatory Phase 3 study, we are planning sites in the U.S., E.U., U.K., Canada and Australia. We have obtained feedback from both the FDA and the EMA on the study protocol. Our clinical trial application was recently approved by Health Canada Authorities and now will undergo Ethics Committee review. We have also filed our CTIS application with the EMA and it is currently under review. Submission to the U.K. regulatory authorities is expected to follow soon. We plan to initiate screening in the U.S.for the study in the second quarter of 2026, with dosing of the first patient expected in mid-2026.

Our Strategy

Our strategy is to become a leader in the treatment of rare diseases by leveraging our CPP technology platform and applying our management team’s know-how and expertise to the development of nomlabofusp and other future pipeline programs. Key elements of our strategy include:

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Advance nomlabofusp through clinical development and regulatory approval in the United States the European Union and other foreign jurisdictions. We have completed two Phase 1 clinical trials in adults along with a Phase 1 PK run-in study in adolescents and a Phase 2 dose exploration trial in adults with FA. We also have an ongoing OL study in adults and adolescents with FA in which participants receive 50 mg nomlabofusp daily. Enrollment in this study is now open to adolescents and adult patients regardless of whether they participated in a previous nomlabofusp trial. We are continuing to develop and execute a clinical development plan for regulatory approval of nomlabofusp in the United States, the European Union, the United Kingdom (“UK”), Australia, Canada and potentially other countries. We have obtained feedback from both FDA and EMA on the global Phase 3 confirmatory study protocol and continue to qualify sites in the U.S., E.U., U.K, Canada, and Australia and we plan to initiate screening in this Phase 3 study in the second quarter of 2026, with dosing of the first patient expected in mid-2026. We are targeting nomlabofusp BLA submission in June 2026 seeking accelerated approval using tissue FXN levels as a novel surrogate endpoint.

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If nomlabofusp receives regulatory approval(s), we intend to commercialize nomlabofusp in the United States, the European Union, and other relevant countries independently or with third parties. We intend to evaluate commercialization options in the United States, the European Union, the United Kingdom and in other foreign jurisdictions throughout the world where FA patients can benefit, if we are successful in obtaining regulatory approval for nomlabofusp. We may build our own internal sales force, partner with a contract sales organization, enter into a joint marketing partnership with another pharmaceutical or biotechnology company, or we may seek to out-license nomlabofusp.

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Expand our product candidate pipeline to treat a variety of rare diseases. We intend to expand our pipeline to treat additional rare diseases. A key component of this strategy is to utilize our novel protein replacement therapy platform technology to deliver FXN or other molecules to intracellular targets. We employ a rational approach to selecting disease targets, and take into account many scientific, business, and indication specific factors before choosing each indication.

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Continue to improve our novel protein replacement therapy platform. We continue to improve the scientific understanding of our platform, including how our technology allows enhanced delivery of cargo proteins, thereby impacting the biological processes associated with the diseases we seek to treat. In addition, with our expertise in the use of a CPP to effectively deliver proteins to intracellular targets, we believe that our scientists are well positioned to design and develop additional therapies that will address unmet medical needs associated with other rare diseases and develop other therapeutics with potentially disease modifying therapeutic action. We also plan to continue to build our intellectual property portfolio to expand our protein replacement therapy platform.

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Opportunistically evaluate enabling, adjacent or potential competing technologies, and where advantageous, seek licenses or collaborations regarding those technologies, to advance our platform. We will continue to evaluate technologies that may enable or enhance our product candidates or our rare disease focus. To facilitate the advancement of our CPP platform, we periodically engage in partnering and licensing discussions with a range of biotechnology or pharmaceutical companies and academic institutions and maintain awareness of complementary technologies, synergistic opportunities and “tuck-in” options.

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Continue to strengthen key relationships. We partner with experts in every aspect of development. We believe this expertise, along with our technology platform, will provide us with the ability to develop and commercialize the drug and biologic candidates we have under development and to maximize the value of our platform. In addition to partnering with experts in drug and biologic development, we collaborate with key opinion leaders, academic institutions, experts in the field of rare diseases and with patient advocacy groups associated with the diseases that are being targeted. We have established a scientific advisory board and we regularly seek advice and input from these experienced thought leaders on matters related to our research and development programs. The members of our scientific advisory board consist of distinguished research scientists, professors and industry experts recognized as key opinion leaders in the fields of rare disease, pediatrics and mitochondrial disease. We build these relationships to enhance our knowledge of the patient’s needs and utilize that knowledge to design development programs intended to address unmet medical needs and add value for potential patients.

Platform Technology for Treatment of Rare Genetic Diseases

There are estimated to be over 9,500 rare genetic diseases, which, collectively affect hundreds of millions of people worldwide. Of the hundreds of millions of individuals suffering from these rare genetic diseases, only approximately 5% have therapeutic options available to manage their disease. Many of these diseases result from a deficiency in the amount or the function of a particular target molecule, often a protein. Particularly challenging to treat are those diseases that result from the deficiency of a molecule that is active within a cell or within a cell-based organelle. The challenge to providing treatment of these diseases is the need to improve the amount or function of the therapeutic target by transporting a therapeutic element across the cell membrane and potentially the membrane of the organelle where the target is active in the diseased patients.

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The ability to transport therapeutic proteins across biological membranes has, to date, not been reproducibly achieved. The collective population of people with rare diseases stands to benefit from the emergence of a scalable treatment platform that can transport therapeutic proteins across cell membranes to deliver them to the intracellular site of activity. In addition, traditionally, medical treatment for each rare genetic disorder has been approached on a disease-by-disease basis. This approach is inefficient, as there are thousands of diseases, each with a distinct patient population, that cannot be addressed by traditional therapeutic approaches and are in need of treatment options. Our understanding of our platform and our bioengineering capabilities support the concept that product candidates based on our platform technology could significantly impact common pathological mechanisms in various diseases with comparable etiologies. We are utilizing this approach to identify therapeutic opportunities where our molecules and technology are more likely to be impactful.

Nomlabofusp For the Treatment of Friedreich’s ataxia

Friedreich’s ataxia

FA is a rare genetic disease that is the most commonly inherited ataxia in humans, with approximately 20,000 individuals living with Friedreich’s ataxia globally, and of these individuals, approximately 5,000 are in the United States and the majority of the remaining individuals are primarily in Europe. Friedreich’s ataxia results from a deficiency of the mitochondrial protein, frataxin, (“FXN”). FXN is an essential and phylogenetically conserved protein that is found in cells throughout the body, with higher levels found in the heart, spinal cord, liver, pancreas, and skeletal muscle. FXN is encoded in the nucleus of the cell, expressed in the cytoplasm and transported into the mitochondria, where it is processed to the mature form. As part of this process the mitochondrial targeting sequence is cleaved off in the mitochondria by a naturally occurring enzyme.

Friedreich’s ataxia is a progressive multi-symptom disease typically presenting in mid-childhood that affects the functioning of multiple organs and systems. It is a debilitating neurodegenerative disease that results in poor coordination of legs and arms, progressive loss of the ability to walk, generalized weakness, loss of sensation, scoliosis, diabetes and cardiomyopathy as well as impaired vision, hearing and speech. Patients suffer from progressive neurologic and cardiac dysfunction. Key among these is a primary neurodegeneration of the dorsal root ganglia and the dentate nucleus of the cerebellum, which leads to the hallmark clinical findings of progressive limb ataxia and dysarthria. A hypertrophic cardiomyopathy is common and associated with early mortality, typically between 30 and 50 years of age. Omaveloxolone, the first drug approved for the treatment of FA, was approved by the FDA and the European Commission in February 2023 and February 2024, respectively.

Nomlabofusp

Nomlabofusp, an investigational biologic fusion protein that is administered subcutaneously, consists of a CPP genetically fused to human FXN, and includes a mitochondrial targeting sequence. Using our proprietary peptide delivery technology, nomlabofusp is designed to carry the molecule from the intravascular space across the cell membrane and into the mitochondria where the CPP and the mitochondrial targeting sequence are cleaved off by the mitochondrial processing peptidase (“MPP”) enzyme to yield mature FXN. See Figure 1.

Figure 1.

We have completed two Phase 1 clinical trials and a Phase 2 dose exploration trial in adults with FA, along with a Phase 1 PK run-in study in adolescents with FA (12-17 years old). We also have our ongoing Phase 2 OL trial in adults and adolescents with FA in which participants receive 50 mg nomlabofusp daily. Enrollment in this study is now open to adolescents and adult patients regardless of whether they participated in a previous nomlabofusp trial.

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Based on the results of our non-clinical development program as well as results from our Phase 2 clinical trials, we believe that administering nomlabofusp may increase FXN levels in the mitochondria of patients with Friedreich’s ataxia and they could potentially experience:

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improved cellular function;

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a positive impact on Friedreich’s ataxia symptoms; and

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a slowing of progression of the disease, potentially prolonging life.

In our Phase 1 clinical trials, nomlabofusp appeared to increase FXN levels in the peripheral tissues that were tested (buccal cells, skin biopsies and platelets) and data from our Phase 2 dose exploration study demonstrated dose dependent increases in FXN levels in all evaluated tissues (skin and buccal cells) after daily dosing of 14 days followed by every other day dosing until day 28 in the 25 mg and 50 mg cohorts. Data from the ongoing OL study showed increases in skin FXN levels in 10 of 10 participants with data at six months. These skin FXN levels were higher than 50% of median levels in healthy volunteers similar to levels expected in asymptomatic carriers. We also observed consistent directional improvement across four key clinical outcomes after one year of nomlabofusp treatment relative to a worsening observed in a FACOMS natural history study reference population. The most common adverse events were mild/moderate injection site reactions and we have identified anaphylaxis as an adverse event likely associated with nomlabofusp administration and have implemented several risk mitigation measures. We believe that our technology may allow us to address other rare genetic diseases that either require the replacement of molecules that need to target specific intracellular organelles, or that share similar clinical symptoms that overlap with Friedreich’s ataxia. Finally, the use of nomlabofusp to improve mitochondrial function in other rare diseases that demonstrate evidence of mitochondrial dysfunction is also being explored.

Development of Nomlabofusp

Non-clinical Pharmacology

Following nomlabofusp dosing in multiple non-clinical studies in rodents and non-human primates (“NHPs”), human FXN was found to be distributed into all tissues tested, as shown in Figure 2.

Figure 2.

In a study in Sprague Dawley rats in which nomlabofusp was administered daily via SC injection for 7 days, a dose‑dependent increase in hFXN was observed in skin and disease-related target tissues (heart, dorsal root ganglion and skeletal muscle). Furthermore, increases in rat skin hFXN after administration of nomlabofusp were correlated with increases in hFXN in these tissues. These results demonstrate that changes in skin FXN concentrations can be used to predict changes in FXN concentrations of other tissues following administration of nomlabofusp. Correlations were observed not only with skin, but also between tissues, corroborating that hFXN measurements in one tissue are indicative of concentrations in other tissues (De Toni, F., Ragaglia, V., Schecter, D. et al. Pharmacokinetics and Pharmacodynamics of Nomlabofusp in Non-clinical Studies of Friedreich’s Ataxia. AAPS J 27, 112 (2025)).

Nomlabofusp was demonstrated to prolong the life of knock-out (“KO”) mice whose heart and skeletal muscles were deficient in FXN. These mice, when untreated, develop a severe hypertrophic cardiomyopathy similar to patients with Friedreich’s ataxia and, like many Friedreich’s ataxia patients, die early in life. In non-clinical studies of nomlabofusp, the median survival in animals treated with vehicle of 98 days was extended to a median survival of 166 days in animals treated with nomlabofusp subcutaneously three times per week (p=0.0001).

Furthermore, 87.5% of mice treated with nomlabofusp survived beyond the mean age of death in the vehicle treated group (107.5 days) whereas only 33% of vehicle treated animals survived. Results are reflected in Figure 3.

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Figure 3.

In a separate study conducted at an independent laboratory, a similar mouse model was studied. In this study doses of 2 mg/kg, 10 mg/kg, 30 mg/kg, 60 mg/kg and 100 mg/kg administered subcutaneously every other day were compared to vehicle. After 2 weeks of dosing, mitochondrial extracts from cardiac tissue were analyzed for the presence of human FXN. In addition, activity of succinate dehydrogenase (“SDH”), an enzyme whose activity is dependent on the presence of FXN, was also analyzed. Human FXN was found in the mitochondria of the cardiomyocytes and increased with increasing dose. SDH activity which was suppressed to near zero in vehicle treated animals was also suppressed to near zero in the 2 mg/kg dose group. In the 10 mg/kg dose group activity was increased and in the 30 mg/kg dose group the activity was returned to that of wild type animals. There was no further increase in activity when the animals were dosed with 60 mg/kg or 100 mg/kg but the effect was maintained at levels equivalent to that of wild type animals. See Figures 4 and 5.

Figure 4.

Figure 5.

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Another study, also performed at an independent laboratory, demonstrated the maintenance of cardiac function when the same KO mouse model was studied. These mice were treated with nomlabofusp at doses of 10 mg/kg every other day for 6 weeks. Echocardiograms were performed prior to initiating dosing and after 4 weeks of dosing. When compared to vehicle, mice treated with nomlabofusp maintained their left ventricular volume and ejection fraction while vehicle treated mice deteriorated over the same 4-week period. See Figures 6 and 7.

Figure 6.

Figure 7.

Using a neurologic mouse model, treatment with nomlabofusp prevented the development of ataxia in mice whose nervous system was deficient in FXN compared to those treated with placebo.

In other non-clinical pharmacology studies it was demonstrated that SC administration of nomlabofusp distributed in a dose-dependent manner to several organs known to be predominantly affected in FA, including the dorsal root ganglion, heart, and skeletal muscle, as well as to other tissues, including skin. Plasma nomlabofusp concentrations correlated with levels of human FXN delivered by nomlabofusp into tissues, and the increases in frataxin were correlated amongst tissues, especially with skin. In KO mice, the pharmacokinetics and processing of nomlabofusp were comparable with wild type animals and treatment with nomlabofusp halted the progression of cardiac dysfunction and significantly increased survival. Together, the findings from these non-clinical studies demonstrate that nomlabofusp exposure increased hFXN in FA-relevant tissues and provide evidence of pharmacologic effects. (De Toni, F., Ragaglia, V., Schecter, D. et al. Pharmacokinetics and Pharmacodynamics of Nomlabofusp in Non-clinical Studies of Friedreich’s Ataxia. AAPS J 27, 112 (2025)).

Non-Human Primate and Rat Toxicology Studies

We previously conducted 28-day and 13-week GLP toxicology studies of nomlabofusp in two species, rat and NHP. In the rat studies, some injection sites showed edema and erythema with associated histologic changes localized to the injection site. The rat studies showed no significant clinical observations and no significant systemic histopathological findings. In the NHP studies, some injection sites were raised and firm with dose dependent histologic changes localized to the injection sites. The NHP 28-day study showed no systemic toxicity. The NHP 13-week study showed no systemic toxicity in the low and mid-dose groups, and minimal to mild histopathological

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findings in the high dose group. There were also several episodes of occasional transient muscle rigidity in some animals observed immediately after dosing in the two highest dose groups at very high exposures. These clinical observations resolved with no intervention and all of the NHPs who experienced these clinical observations received all doses and completed the in-life portion of the study.

To support extended dosing of patients with nomlabofusp, we conducted a 26-week NHP toxicology study in 2021. In May 2021, we notified the FDA of certain mortalities which occurred at the two highest dose levels in the then-ongoing study. On May 25, 2021, the FDA placed a clinical hold on the nomlabofusp clinical program. In the clinical hold letter, the FDA stated that it needed to review a full study report from the then-ongoing NHP study and that we could not initiate additional interventional clinical trials until we submitted such report and received notification from the FDA that additional clinical trials could commence. At the time of the FDA clinical hold, we had no interventional clinical trials with patients enrolled or enrolling.

In July 2021, we completed dosing in the 26-week NHP toxicology study. The study included four dose groups in addition to vehicle. Data from the study were collected throughout the second half of 2021 and included in the complete response to the clinical hold submitted to the FDA in January 2022. After additional interactions and submission of additional information requested by FDA, in September 2022, the FDA lifted its full clinical hold on the nomlabofusp clinical development program and imposed a partial clinical hold. Following additional interactions and submission of clinical data, in May 2024, the FDA removed the partial clinical hold on the development of nomlabofusp.

Clinical Development

Non-Interventional Study

In 2021, we conducted a non-interventional study that enrolled 60 healthy adults to examine the range of tissue FXN concentrations in individuals who are homozygous for the normal FXN gene. Tissue samples in these studies were collected using the same sampling techniques and proprietary assay used in the interventional studies. Enrollment in this study was completed in 2022 and data has been used for comparison purposes in the Phase 2 clinical study described below. See Figure 8.

Figure 8.

FXN concentrations were measured in skin and buccal cells from 60 homozygous healthy volunteers utilizing the same sampling technique and assay as clinical trials of nomlabofusp; FXN levels measured via detection of peptide derived from mature FXN; FXN concentrations normalized to total cellular protein content in each sample. 1. E.C. Deutsch et al. Molecular Genetics and Metabolism 101 (2010) 238–245. 2. Friedreich’s Ataxia Research Alliance.

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Clinical Trials

Completed Phase 1 and Phase 2 Clinical Studies in Adults with Friedreich’s Ataxia

In 2019, we submitted our Investigational New Drug application (“IND”) application for nomlabofusp and began Phase 1 clinical trials in 2019 in patients with FA. We have completed three clinical studies in adult patients, with FA; a Phase 1 SAD study (completed in 2020), a Phase 1 MAD study (completed in 2021), and a Phase 2 Dose Exploration study (completed in 2023). The primary objective for the phase 1 SAD and MAD studies was to assess the tolerability of nomlabofusp at doses ranging from 25 mg to 100 mg administered via SC injection. The secondary objectives were to establish the PK of nomlabofusp administration in humans and to explore the PD of nomlabofusp administration by measuring tissue FXN concentrations in accessible tissues, namely buccal and skin cells, and in platelets. In the MAD study, patients in the 25 mg cohort were dosed once a day for the first 4 days followed by 1 dose every third day through day 13 for a total of 7 doses, while the patients in the 50 mg cohort were dosed once a day for the first 7 days followed by 1 dose every other day through day 13 for a total of 10 doses, and patients in the 100 mg cohort were dosed once a day for 13 days consecutively for a total of 13 doses. Administration of nomlabofusp via SC injection appeared to be well tolerated up to doses of 100 mg administered daily for up to 13 days. No SAEs were reported in either study. The most common treatment emergent adverse events (“TEAEs”) were injection site reactions (“ISRs”) that were generally mild, self-limited, and usually resolved within approximately 1 hour. There was rapid uptake of nomlabofusp into the circulation following subcutaneous injection, and exposure appeared to be proportional to dose. Increased FXN concentrations were observed in buccal cells, skin, and platelets, with higher and more frequent nomlabofusp administration.

The Phase 2 randomized, double-blind, placebo-controlled dose exploration study evaluated the safety, tolerability, PK and PD of two doses of nomlabofusp. Cohort 1 evaluated 25 mg and Cohort 2 evaluated 50 mg. Participants in either the 25 mg or 50 mg cohorts were randomized 2:1 to receive daily SC injections of either nomlabofusp or placebo for 14 days, and then every other day for an additional 14 days for a total 28-day dosing period.

Substantial increases in tissue FXN concentrations were observed after daily SC administration of both the 25 mg and 50 mg doses. The majority of treated patients in both cohorts with quantifiable levels of frataxin at baseline and day 14 achieved at least a 100% increase in tissue frataxin in skin cells, and at least a 30% increase in tissue frataxin levels in buccal cells. Participants treated with 50 mg for 14 days daily had frataxin levels in skin cells increase from less than 17% at baseline relative to healthy volunteers, to 33% to 59% of healthy volunteers after 14 days of treatment. Patients treated with placebo showed no increase in their frataxin levels during this period. Increases in skin and buccal FXN concentrations were dose-dependent and the increases were not maintained when the dosing regimen was changed to alternate day dosing. Abnormal lipid profiles were identified in adults with FA at baseline with directional dose-dependent normalization observed post nomlabofusp treatment.

Nineteen adults with FA received nomlabofusp in the Phase 2 study and 9 received placebo. There were no serious adverse events reported. There was one allergic reaction which was considered to be a severe adverse event in the 25 mg cohort that resolved with standard treatment. This participant withdrew from the trial. The most common adverse events reported were mild and moderate injection site reactions which resolved without any intervention and there were no study discontinuations due to injection site reactions. Consistent with findings in our Phase 1 study, nomlabofusp demonstrated quick absorption after SC administration and had dose proportional increases in exposure.

Completed Phase 1 PK Run-In Study in Adolescents (12-17 years old) with FA

In January 2025, we initiated dosing of adolescents (12-17 years old) in a PK run-in study for pediatric patients with FA. Study participants in the PK run-in study were randomized 2:1 to receive either nomlabofusp at a weight-based dose expected to match the PK of adults receiving the 50 mg dose, or placebo, daily for seven days. We completed dosing in 14 adolescents in March 2025. The PK and exposure data were similar to adults and the participants became eligible to enroll in the OL study. The PK results from the adolescent cohort also supported the predictive value of our exposure modeling and thus the planned dosing of a cohort of children (2-11 years of age) will facilitate direct enrollment of children (2-11 years old) was cancelled and will now be enrolled directly into the OL study, This eliminates any pause in study drug administration between the PK study and the open label study.

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Open Label Study

In January 2024, we initiated the OL trial evaluating daily SC injections of 25 mg of nomlabofusp self-administered or administered by a caregiver, with the first patient dosed in March 2024. Participants who completed treatment in the Phase 2 dose exploration study, or who previously completed a prior clinical trial of nomlabofusp, were eligible to screen for the OL study. Subjects were allowed to take omaveloxolone during the trial. The OL study is evaluating the safety and tolerability, PK, and FXN levels in peripheral tissues as well as other exploratory PD markers (lipid profiles and gene expression data) following long-term subcutaneous administration of nomlabofusp. In addition, clinical assessments collected during the study will be compared to data from a matched control arm derived from participants in the FACOMS database.

In December 2024, we reported positive initial data from our ongoing OLE study. This data included safety, FXN levels, clinical, PK data and dose escalation:

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Nomlabofusp was generally well tolerated for up to 260 days in subjects. The most common adverse events were injection site reactions, with most being mild, brief in duration, and self-limited. Two participants had serious adverse events (one seizure and one anaphylactic reaction) that resolved within 24 hours and these participants withdrew from the study;

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Long-term 25 mg tissue FXN levels showed positive mean change from baseline of 1.32 pg/μg in buccal cells and 9.28 pg/μg in skin cells at Day 90 and that 25 mg of nomlabofusp increased and maintained tissue FXN levels over time, increasing from a mean level of 15% of HV at baseline to 30% in buccal cells and from 16% to 72% in skin cells at Day 90;

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Tissue FXN levels appear to reach steady-state levels by Day 30 in buccal cells;

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Early clinical data showed trends toward improvement across a number of clinical outcomes for long-term 25 mg daily nomlabofusp including: (1) decreased values indicating early trends towards improvement in the Modified Friedreich Ataxia Rating Scale (mFARS) and the FARS-Activities of Daily Living (“ADL”), Modified Fatigue Impact Scale and nine hole peg test at 90 days relative to baseline;

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Key PK data showed rapid absorption after SC administration with exposure appearing to reach steady state in plasma by day 30 with no further accumulation, which is consistent with data from our Phase 1 and Phase 2 studies.

Also in December 2024, we announced that we were increasing the dose in the OL study to 50 mg of nomlabofusp daily for then currently enrolled and all future study participants. In March 2025, we announced that our Safety Monitoring Team has deemed anaphylaxis as an adverse drug reaction likely associated with nomlabofusp. To reduce the risk of allergic reactions, including anaphylaxis, we amended the OL study protocol to administer premedication for the first month of dosing.

In June 2025, the FDA provided recommendations regarding the safety data that might be needed to support a Biologics License Application.(“BLA”) seeking accelerated approval, which included evaluating safety in at least 30 participants with continuous study drug exposure for six months and a subset of at least 10 of those participants with continuous study drug exposure for one year, with the large majority of data coming from participants receiving the 50 mg dose.

In July 2025, we announced the publication of two peer-reviewed articles highlighting nonclinical data on the therapeutic potential, pharmacology, and mechanism of action of nomlabofusp as a novel FXN protein replacement therapy designed to address the underlying cause of FA. These data were included in the briefing package reviewed by the FDA in support of potentially using skin FXN concentrations as a RLSE for Larimar’s registrational program seeking accelerated approval for nomlabofusp.

In September 2025, we announced additional data from the ongoing OL study:

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In 4 completed studies and the ongoing OL study, 65 participants received at least 1 dose of nomlabofusp.

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Of the 65 participants receiving at least one dose of nomlabofusp, 39 have been dosed as part of the open label study, with 14 on treatment for at least 6 months and 8 for over 1 year in the OL study.

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Consistent directional improvement was observed across 4 key clinical outcomes (mFARS, FARS-ADL, 9-HPT, MFIS) after 1 year of nomlabofusp treatment relative to a worsening in a FACOMS natural history study reference population. See Figure 8.

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10/10 participants with data at 6 months achieved skin FXN levels over 50% of median levels in healthy volunteers (which is similar to levels in asymptomatic carriers). See Figure 9.

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Of the 39 participants in the OL study (and of 65 total participants who received at least 1 dose in all nomlabofusp studies), 7 experienced anaphylaxis in the first 6 weeks of dosing and returned to their usual state of health after standard treatment. In the OL study, of the 10 participants who had not had prior exposure to nomlabofusp, only 1 experienced anaphylaxis. Excluding these events, long term dosing of nomlabofusp was generally well tolerated, including 14 on treatment for at least 6 months and 8 on treatment for over 1 year.

Figure 8.

IQR = interquartile range

1 - Based on the range of baseline characteristics of participants in the OL study, Larimar identified patients from the FACOMS dataset with similar characteristics using data recorded over the last 4 years for each patient.

2 - Modified Fatigue scale presented here is at Month 24 because it was not assessed at Month 12.

Note: Data presented is based on the September 2025 data release.

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Figure 9.

*Data include all participants with quantifiable levels at each measurement point who had received 25 mg, 50 mg or had the dose increased from 25 mg to 50 mg.

**8.2 pg/µg represents 50% of the average FXN concentration average FXN concentration of healthy volunteers.

Note: Data presented is based on the September 2025 data release.

We believe that these data, as well as the improvement in abnormal lipid profiles observed in prior completed studies, provide support that nomlabofusp increases FXN in patients with FA and that the strategy of FXN replacement has the potential to result in a clinical benefit. Changes observed in skin FXN levels, and clinical outcomes after nomlabofusp administration across diverse participants with FA including individuals with advanced disease, are all directionally consistent and suggest a potential treatment effect.

In addition to the risk mitigation measures for anaphylaxis already in place such as pre-medicating with antihistamines and supplying epinephrine auto-injectors to study participants, we have introduced a new dosing regimen in which participants initially receive a 5 mg dose followed by a 25 mg dose 1 hour later under observation. Nomlabofusp 25 mg is then administered once daily through Day 30 and then the dose is increased to 50 mg once daily.

We have amended the open label extension (“OLE”) study protocol to include adolescent and adult patients who have not previously participated in a prior nomlabofusp study and the study is now being referred to as the open label (“OL”) study. We are also making plans to enroll children (2 to 11 years old) directly into the OL study.

In February 2026, we announced that the FDA granted Breakthrough Therapy Designation to nomlabofusp for the treatment of adults and children with FA. Additionally, following a START pilot program meeting with FDA, we announced continued alignment with the FDA to consider the use of skin FXN concentration as a novel surrogate endpoint reasonably likely to predict clinical benefit to support a planned BLA, seeking accelerated approval. The FDA stated that the adequacy of the safety data base will be a matter of review at the time of the BLA submission, which is targeted for June 2026.

Intellectual Property

Our success depends in large part upon our ability to obtain and maintain proprietary protection for our current and future products and technologies, and to operate without infringing the proprietary rights of others. Our policy is to protect our proprietary position by, among other methods, filing for patent applications on inventions that are important to the development and conduct of our business with the U.S. Patent and Trademark Office and its foreign counterparts. We also intend to rely on market and data exclusivities, which is separate and distinct from the protection afforded by patents, to protect our products. We further protect our proprietary information by requiring our employees, consultants, contractors and other advisors to execute nondisclosure and assignment of invention agreements upon commencement of their respective employment or engagement. Agreements with our employees

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also prevent them from bringing the proprietary rights of third parties to us. In addition, we require confidentiality or service agreements from third parties that receive our confidential information or materials.

As of March 17, 2026, our intellectual property portfolio was composed of numerous international Patent Cooperation Treaty (“PCT”), foreign, United States non-provisional patent applications, issued United States patents, one EU patent and United States provisional patent applications that we own or co-own, and four issued United States patents and additional non-provisional patent applications in the United States and in certain foreign jurisdictions that we license from academic institutions. The issued patents in the United States and the E.U. licensed by us, which include issued patents covering the composition of matter for nomlabofusp and methods for treating FA, have expiration dates between 2033 and 2040 without taking potential patent term extension into consideration. The international and the United States non-provisional patent applications licensed by us relate to composition of matter and methods of use for nomlabofusp.

The additional patent applications we own or co-own, which include PCT, foreign and United States non-provisional patent applications, United States patents, and United States provisional patent applications are related to the development of nomlabofusp, including methods of use of nomlabofusp, and to our peptide-delivery platform technology.

A provisional patent application allows for an effective filing date to be established with regard to an invention, but once a provisional patent application is filed, either a corresponding non-provisional patent application or a petition to convert the provisional patent application into a non-provisional patent application must be filed within 12 months or such effective filing date will be lost. If we or our licensor timely files non-provisional patent applications in the United States and in countries outside of the United States with regard to our provisional patent applications and these non-provisional patent applications result in issued patents, such patents are expected to expire in 2046, without taking potential patent term adjustment or patent term extension into consideration.

Nomlabofusp is covered by licensed issued patents (composition of matter and methods of use) in the United States and the E.U., which, if properly maintained, will expire in 2040, excluding any patent term extensions that might be available following the grant of marketing authorizations. We also possess an exclusive license to non-provisional applications in the United States and certain countries outside the United States for nomlabofusp (composition of matter and methods of use). If these patent applications in the United States and other countries result in issued patents, those patents would be expected to expire in 2040. This estimated expiration excludes any patent term adjustment that might be available following the grant of the patent and any patent term extensions that might be available following the grant of marketing authorizations. We cannot predict whether the patent applications we and our licensors are currently pursuing will issue as patents in any particular jurisdiction or whether the claims of any issued patents will provide sufficient protection from competitors or other third parties.

Patents extend for varying periods according to the date of patent filing or grant and the legal term of patents in various countries where patent protection is obtained. The actual protection afforded by a patent, which can vary from country to country, depends on the type of patent, the scope of its coverage and the availability of legal remedies in the country.

We also use other forms of protection besides patent protection and market and data exclusivity, such as trademark, copyright, and trade secret protection, to enhance our intellectual property, particularly where we do not believe patent protection is appropriate or obtainable. We aim to take advantage of all of the intellectual property rights that are available to us and believe that this comprehensive approach will provide us with proprietary exclusive positions for our product candidates, such as nomlabofusp, where available.

In-License Agreements

We are party to a License Agreement dated November 30, 2016, as amended, with Indiana University (“IU”). Such agreements provide for a transferable, worldwide license to certain patent rights regarding technology used by us with respect to the development of nomlabofusp.

In partial consideration for the right and license granted under these agreements, we will pay IU a royalty of a low single digit percentage of net sales of licensed products depending on whether there is a valid patent covering such products. As additional consideration for this agreement, we are obligated to pay IU certain milestone payments of up to $2.0 million in the aggregate upon the achievement of certain developmental milestones, commencing on the enrollment of the first patient in a Phase 1 clinical trial. We will also pay IU sublicensing fees ranging up to a low double-digit percentage of sublicense consideration depending on our achievement of certain

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regulatory milestones as of the time of receipt of the sublicense consideration. We are also obligated to reimburse IU for patent-related expenses. In the event that we dispute the validity of any of the licensed patents, the royalty rate would be tripled during such dispute. We are also obligated to pay to IU a minimum annual royalty of less than $0.1 million per annum starting in the 2020 calendar year for the term of the agreement.

We were previously a party to License Agreement dated November 30, 2016, with Wake Forest University Health Sciences (“WFUHS”), which licensed certain patent rights regarding technology used by us with respect to the development of nomlabofusp in consideration for an obligation to pay WFUHS a royalty of a low single digit percentage of net sales of licensed products, certain milestones, and certain sublicensing revenue. The WFUHS license expired in December 2025 with the last to expire licensed patent.

Competition

The biopharmaceutical industry is characterized by intense and dynamic competition to develop new technologies and proprietary therapies. Any product candidates that we successfully develop into products and commercialize may compete with existing therapies and new therapies that may become available in the future. While we believe that our platform technology, product candidates and scientific expertise in the field of rare diseases provide competitive advantages, we face competition from various sources, including larger and better-funded pharmaceutical companies, specialty pharmaceutical companies and biotechnology companies, as well as from academic institutions, governmental agencies and public and private research institutions. We expect to compete with Biogen’s SKYCLARYSTM (omaveloxolone), which was approved for the treatment of FA in adults and adolescents aged 16 and older by the FDA and the European Commission in February 2023 and February 2024, respectively. Other competitors currently developing therapeutics to treat FA include, but are not limited to Design Therapeutics, Lexeo Therapeutics, Neurocrine Biosciences/Voyager Therapeutics, Solid Biosciences and PTC Therapeutics ("PTC"). On August 19, 2025, PTC received a complete response letter and was not approved by the FDA. PTC had a Type C meeting with the FDA in December, 2025 and were advised that an additional study (open label or single arm study with natural history control) would be necessary to support NDA resubmission. Many of our competitors have significantly greater name recognition, longer operating histories and financial, technical manufacturing, marketing and human resources than we do. Mergers and acquisitions in the pharmaceutical and biotechnology industries may result in even more resources being concentrated amongst a smaller number of our competitors. Our commercial opportunity could be reduced or eliminated if our competitors develop or market products or other novel therapies that are more effective, safer or less costly than our product candidates or obtain regulatory approval for their products more rapidly than we may obtain approval for our product candidates.

Manufacturing and Supply

Nomlabofusp is a biologic fusion protein that is produced in E. coli. We have worked with contract manufacturers and research organizations to develop, in accordance with current Good Manufacturing Practices (“cGMP”) a manufacturing process and analytical methods for drug substance and drug product to support clinical trials. We also use third party manufacturers for the clinical packaging, storage and distribution of nomlabofusp. We rely on third parties to store the nomlabofusp master cell bank and working cell bank, each stored at a different location. We continue to advance the manufacturing of nomlabofusp, obtain stability data, and produce drug product for future clinical trials. We are continually trying to optimize our manufacturing process to increase yields, decrease costs and increase reliability in supply chains. We are currently at full scale for the US launch and filing but will need to scale up one more time to have adequate supply for the expansion into other territories.

The drug substance which is in frozen liquid form for nomlabofusp is currently manufactured for us by KBI Biopharma, Inc. (“KBI”). We are party to a Master Services Agreement, as amended, with KBI, pursuant to which KBI provides biological development and clinical manufacturing services with respect to nomlabofusp. We are producing a lyophilized version of the drug product from the same KBI drug substance at another supplier. The drug product previously used in our clinical studies has been in a frozen solution dosage form. In February 2025, FDA accepted the data supporting the comparability of a lyophilized drug product to the frozen solution and we are currently integrating the lyophilized formulation into the OL study. The lyophilized drug product is the formulation that we intend for the long-term commercialization of nomlabofusp, if approved. Process performance qualification (PPQ) of the commercial scale drug substance and drug product manufacturing is nearing completion in preparation for the BLA submission and these batches are planned to support the U.S. commercial launch demand, if nomlabofusp is approved.

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We intend to further scale up our manufacturing process to support potential worldwide commercial demand, if nomlabofusp is approved. We have selected Lonza to support this scale-up effort. We have completed tech transferring and scale-up of the process to Lonza. We are party to a Master Services Agreement with Lonza, pursuant to which Lonza provides manufacturing services with respect to nomlabofusp. Additional comparability of the drug substance manufactured by Lonza will need to be performed and reviewed by the FDA and other regulatory authorities in order to use the Lonza-manufactured drug substance in clinical and commercial activities.

We have received concurrence from the FDA that our proposed potency control strategy appears reasonable, pending review of the BLA.

Human Capital Resources

Employees and Compensation

In order to achieve the goals and expectations of our Company, it is crucial that we continue to attract and retain top talent. To facilitate talent attraction and retention, we strive to make our company a safe and rewarding workplace, with opportunities for our employees to grow and develop in their careers, supported by strong compensation, benefits, paid time-off and health and wellness programs, including programs that build connections between our employees.

As of December 31, 2025, we employed 71 full-time employees in the United States, of which 55 are directly engaged in research and development with the rest providing administrative, business, commercial and operations support. None of our employees are represented by a labor organization or under any collective-bargaining arrangements. We consider our employee relations to be good.

Our human capital resources objectives include, as applicable, identifying, recruiting, retaining, incentivizing and integrating our existing and new employees, advisors and consultants. The principal purposes of our equity and cash incentive plans are to attract, retain and reward personnel through the granting of stock-based and cash-based compensation awards, in order to increase stockholder value and the success of our company by motivating such individuals to perform to the best of their abilities and achieve our objectives.

Scientific Advisors

We have established a scientific advisory board and we regularly seek advice and input from these experienced thought leaders on matters related to our research and development programs. The members of our scientific advisory board consist of distinguished research scientists, professors and industry experts recognized as key opinion leaders in the fields of rare disease, pediatrics and mitochondrial disease. Their scientific perspectives will be invaluable to determine our strategic scientific pathway and support the development of other potential treatments for complex rare diseases to help fill unmet medical needs in this space. We intend to continue to leverage the broad expertise of our advisors by seeking their counsel on important topics relating to our product development and clinical development programs. Our scientific advisors are not our employees and may have commitments to, or consulting or advisory contracts with, other entities that may limit their availability to us. In addition, our scientific advisors may have arrangements with other companies to assist those companies in developing products or technologies that may compete with ours. All of our scientific advisors are affiliated with other entities and devote only a small portion of their time to us.

Our scientific advisors are set forth in the table below:

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Facilities

We currently lease office and laboratory space, which consists of approximately 8,000 square feet and 4,000 square feet located in Bala Cynwyd, PA and King of Prussia, PA, respectively. On November 24, 2025, we entered into a lease for an additional 7,100 square feet of office space through January 31, 2030 in our Bala Cynwyd PA location and extended the term of all our other Bala Cynwyd space through January 31, 2030. We expect to occupy the additional 7,100 of additional office space when renovations are complete, which is expected to be around April 1, 2026.

As part of the Merger (as defined below) with Zafgen, Inc (“Zafgen”), we acquired a non-cancellable operating lease for approximately 17,705 square feet of office space at 3 Center Plaza, Boston, Massachusetts (the “Boston Lease”). The Boston Lease expires on October 30, 2029. On October 27, 2020, we entered into a sublease agreement whereby we subleased all 17,705 square feet of office space leased under the Boston Lease until October 30, 2029.