Ionis Pharmaceuticals Completes Enrollment in Pivotal Phase 3 REVEAL Study Cohort Evaluating Obudanersen for Angelman Syndrome
Ionis Pharmaceuticals, Inc. has announced the completion of enrollment in the pivotal pediatric cohort of its global Phase 3 REVEAL clinical trial evaluating obudanersen (ION582), an investigational RNA-targeted therapy being developed for the treatment of Angelman syndrome (AS). The milestone represents a significant advancement in the company’s efforts to develop what could become the first disease-modifying therapy for individuals living with this rare and serious neurodevelopmental disorder, for which there are currently no approved treatments.
The completion of enrollment in the pivotal portion of the study marks an important step in the late-stage clinical development of obudanersen, bringing the program closer to generating the data needed to determine whether the therapy can meaningfully improve communication, cognition, motor skills, and other aspects of daily functioning in people affected by Angelman syndrome.
According to Ionis, the pivotal pediatric cohort enrolled 136 participants between the ages of 2 years and less than 18 years who had a confirmed clinical diagnosis of Angelman syndrome supported by genetic confirmation of either a UBE3A gene deletion or UBE3A gene mutation. Enrollment of the adult cohort, which includes participants between 18 and 50 years of age, is expected to be completed during the third quarter of 2026. The company anticipates reporting topline results from the REVEAL study during the second half of 2027.
Advancing a Potential Disease-Modifying Therapy
Angelman syndrome is a rare genetic neurological disorder that affects approximately one in every 12,000 to 20,000 live births worldwide. The condition is caused by the loss of function of the maternally inherited copy of the UBE3A gene in neurons, resulting in profound developmental and neurological impairments.
Individuals living with Angelman syndrome typically experience severe delays in speech and language development, intellectual disability, difficulties with balance and movement, seizures, sleep disturbances, and behavioral characteristics including frequent smiling, laughter, and an unusually happy demeanor.
While supportive therapies—including physical therapy, occupational therapy, speech therapy, and medications for seizure control—can help manage symptoms, no approved medicines currently address the underlying genetic cause of the disease.
Obudanersen has been designed as an RNA-targeted investigational medicine intended to restore expression of the UBE3A protein in neurons, with the goal of modifying the disease process rather than simply treating individual symptoms.
If successful, the therapy could represent an important breakthrough for patients and families who currently have limited therapeutic options.
Enrollment Milestone Reflects Strong Community Participation
Ionis emphasized that completion of enrollment in the pediatric cohort was made possible through extensive collaboration with the global Angelman syndrome community.
Families affected by rare genetic disorders often play a central role in advancing clinical research by participating in trials despite the logistical and emotional challenges associated with long-term study involvement.
The REVEAL study was developed with substantial input from patients, caregivers, advocacy organizations, clinicians, and researchers to ensure that the trial addresses outcomes considered meaningful by the Angelman syndrome community.
According to Holly Kordasiewicz, Ph.D., Executive Vice President and Chief Development Officer at Ionis Pharmaceuticals, the completion of enrollment represents an important milestone toward potentially delivering the first disease-modifying treatment for this complex neurological disorder.
She noted that the trial was intentionally designed to evaluate obudanersen across a broad and diverse population of individuals living with Angelman syndrome, allowing the study to better reflect the range of patients encountered in clinical practice.
Kordasiewicz also expressed appreciation to the participating families, caregivers, investigators, and advocacy organizations whose partnership helped achieve this significant enrollment milestone.
Understanding the REVEAL Phase 3 Trial
REVEAL (ClinicalTrials.gov Identifier: NCT06914609) is a global, randomized, double-blind, controlled Phase 3 clinical trial evaluating the safety and efficacy of obudanersen in individuals with genetically confirmed Angelman syndrome.
The study is expected to enroll approximately 158 participants worldwide and has been structured into two separate cohorts representing pediatric and adult patient populations.
The pediatric cohort serves as the pivotal portion of the study and will provide the primary evidence supporting evaluation of the therapy’s effectiveness.
The adult cohort will generate additional information regarding the safety and clinical activity of obudanersen in older individuals living with Angelman syndrome.
By including both pediatric and adult participants, the study aims to better understand how treatment may perform across a broad age spectrum.
The global nature of the trial also increases the diversity of participating patients while supporting broader evaluation across different healthcare systems and geographic regions.
Pediatric Cohort Forms the Basis for Primary Analysis
The pivotal pediatric cohort includes children between the ages of 2 years and less than 18 years.
These participants have received a confirmed clinical diagnosis of Angelman syndrome together with genetic confirmation demonstrating either deletion or mutation of the UBE3A gene.
This cohort serves as the primary population for evaluating the study’s efficacy endpoints.
Data generated from these participants will be used to determine whether obudanersen demonstrates statistically and clinically meaningful improvements compared with the study’s control group.
Completion of enrollment ensures that all required participants have entered the study, allowing investigators to continue scheduled treatment administration and follow-up assessments.
As participants progress through the study protocol, researchers will collect extensive clinical data measuring multiple aspects of neurological function and daily living.
Adult Cohort Continues Enrollment
Alongside the pediatric cohort, Ionis is also enrolling adults between 18 and 50 years of age into the second portion of the REVEAL study.
Enrollment for this adult cohort is expected to conclude during the third quarter of 2026.
Including adults provides valuable information regarding treatment effects in individuals who have lived with Angelman syndrome for many years and whose disease characteristics may differ from younger patients.
The adult data may also help physicians better understand the potential role of obudanersen across the broader Angelman syndrome population should the therapy eventually receive regulatory approval.
Primary Endpoint Focuses on Communication
One of the distinguishing features of the REVEAL study is its emphasis on expressive communication.
Communication impairment represents one of the defining characteristics of Angelman syndrome.
Many affected individuals speak few or no words throughout their lifetime, creating significant challenges for social interaction, education, independence, and overall quality of life.
Ionis selected improvement in expressive communication as the primary endpoint following discussions with caregivers and the broader Angelman syndrome community regarding the outcomes considered most meaningful.
The primary endpoint will be assessed using the Bayley Scales of Infant and Toddler Development, Fourth Edition (Bayley-4), an objective clinician-administered assessment that evaluates developmental functioning.
By using a standardized and validated clinical instrument, investigators aim to measure changes in expressive communication with consistency across participating study sites.
Evaluating Multiple Aspects of Daily Function
Beyond communication, the REVEAL study includes numerous secondary endpoints designed to provide a comprehensive assessment of treatment benefit.
Researchers will evaluate overall disease severity together with cognitive functioning, communication abilities, sleep quality, motor performance, and activities of daily living.
Sleep disturbances are common among individuals with Angelman syndrome and often contribute to significant caregiver burden.
Motor impairments affecting balance, coordination, and walking also substantially influence daily independence.
Similarly, improvements in cognitive abilities or adaptive functioning could translate into meaningful enhancements in quality of life for both patients and families.
The inclusion of multiple clinical endpoints reflects the complex, multisystem nature of Angelman syndrome and acknowledges that meaningful therapeutic benefit may extend beyond a single symptom domain.
Investigators will also collect exploratory data that may provide additional insight into how obudanersen influences neurological function over time.
RNA-Targeted Therapeutic Approach
Obudanersen represents one of a new generation of RNA-targeted medicines designed to address genetic diseases at their molecular origin.
Unlike conventional medications that primarily manage symptoms, RNA-based therapeutics seek to modify the underlying biological mechanisms responsible for disease.
In Angelman syndrome, the paternal copy of the UBE3A gene remains naturally silenced within neurons.
Obudanersen has been developed with the goal of unsilencing this paternal gene, enabling production of functional UBE3A protein despite loss of the maternal copy.
Restoring expression of this essential protein could potentially improve neuronal function and alter the course of the disease.
This mechanism differentiates obudanersen from supportive therapies currently used in clinical practice and supports its potential as a disease-modifying treatment.
Expanding Development Through the CHAMPION Study
In addition to the REVEAL trial, Ionis announced plans to initiate another Phase 3 clinical study known as CHAMPION.
Whereas REVEAL primarily evaluates patients with UBE3A deletions or mutations, CHAMPION will focus on individuals with Angelman syndrome resulting from uniparental disomy (UPD) or imprinting defects (ID).
Although these genetic mechanisms account for a smaller proportion of Angelman syndrome cases, affected individuals also experience significant neurological impairment.
By expanding clinical development into these additional genetic subtypes, Ionis aims to evaluate obudanersen across a broader spectrum of patients living with Angelman syndrome.
The company expects to initiate the CHAMPION Phase 3 study before the end of 2026.
Successful completion of both studies could ultimately support a broader treatment indication encompassing multiple genetic forms of the disease.
Completion of enrollment in the pivotal pediatric cohort of the Phase 3 REVEAL study marks a major milestone in Ionis Pharmaceuticals’ development program for obudanersen. With 136 children and adolescents now enrolled, the company has moved an important step closer to determining whether its investigational RNA-targeted therapy can deliver meaningful improvements in communication and other key aspects of daily functioning for individuals living with Angelman syndrome.
As follow-up continues and enrollment of the adult cohort progresses toward completion, attention will turn to the anticipated topline results expected in the second half of 2027. Together with the planned CHAMPION Phase 3 study, these programs reflect Ionis’ broader commitment to advancing innovative RNA-based therapies for rare neurological disorders.
For families affected by Angelman syndrome, where no approved disease-modifying treatments currently exist, the continued progress of obudanersen represents an encouraging development in the pursuit of therapies that address the underlying genetic cause of this devastating condition rather than simply managing its symptoms.
About obudanersen (ION582)
Obudanersen (ION582) is an investigational RNA-targeted antisense medicine designed to inhibit the expression of the UBE3A antisense transcript (UBE3A-ATS) and increase production of UBE3A protein, for the potential treatment of Angelman syndrome (AS). The U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) granted Orphan Drug designation to obudanersen for the treatment of AS. Additionally, the FDA granted Fast Track and Rare Pediatric designations to obudanersen for the treatment of AS.
About Angelman Syndrome (AS)
AS is a rare, genetic neurological disease that affects an estimated 1 in 21,000 people worldwide and is caused by the loss of function of the maternal UBE3A gene. AS typically presents in infancy and is characterized by profound intellectual disability, balance issues, motor impairment and debilitating seizures.
Most people with AS are unable to speak. Individuals with AS have a normal lifespan but require complete care from a caregiver. Some symptoms can be managed with existing medicines; however, there are no approved disease modifying therapies.
About Ionis Neurology
Ionis has been at the forefront of discovering and developing leading neurological disease medicines, including SPINRAZA® (nusinersen), the first approved treatment for spinal muscular atrophy, WAINUA® (eplontersen), a medicine to treat hereditary transthyretin-mediated amyloid polyneuropathy (ATTRv-PN), and QALSODY® (tofersen) for SOD1-ALS.
The clinical-stage portfolio includes 13 investigational medicines, of which six are wholly owned by Ionis. Ionis’ investigational portfolio includes medicines for which there are few or no disease modifying treatments, such as rare diseases including Alexander disease, Angelman syndrome, prion disease, multiple system atrophy and Huntington’s disease, as well as more common conditions such as Alzheimer’s disease.
About Ionis Pharmaceuticals, Inc.
For more than three decades, Ionis has invented medicines that bring better futures to people with serious diseases. Ionis currently has marketed medicines and a leading pipeline in neurology, cardiometabolic disease and select areas of high patient need.
As the pioneer in RNA-targeted medicines, Ionis continues to drive innovation in RNA therapies in addition to advancing new approaches in gene editing. A deep understanding of disease biology and industry-leading technology propels our work, coupled with a passion and urgency to deliver life-changing advances for patients.