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GTX-102

Phase 3

Angelman Syndrome | Small molecule | Rare Disease |Ultragenyx Pharmaceutical Inc.|Last Updated: Aug 7, 2026

Success Probability

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Market & Valuation

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Trial Design

RandomizedDouble-BlindSHAM_CONTROLLEDDMC
Total Trials4
Total Enrollment518

FDA Designations

BREAKTHROUGH_THERAPY

Clinical trial landscape

GTX-102 · 4 trials · 1 indication

Phase 3 2Phase 2 1Phase 1 1
NCT06617429Phase 3 Efficacy and Safety Study of GTX-102 in Pediatric Subjects With Angelman Syndrome (AS)Angelman Syndrome
ACTIVE NOT_RECRUITING129 Analytics
NCT06415344Long-term Extension of GTX-102 in Angelman SyndromeAngelman Syndrome
ENROLLING BY_INVITATION255 Analytics
PHASE3ACTIVE NOT_RECRUITING
Phase 3 Efficacy and Safety Study of GTX-102 in Pediatric Subjects With Angelman Syndrome (AS)
Angelman SyndromeUnlock trial analytics
PHASE3ENROLLING BY_INVITATION
Long-term Extension of GTX-102 in Angelman Syndrome
Angelman SyndromeUnlock trial analytics

Study Endpoints

Primary Endpoints

Change from Baseline in Bayley-4 Cognitive Raw Score Without Caregiver Input at Day 338
Baseline, Day 338
Incidence of Treatment Emergent Adverse Events (TEAEs)
Up to 5 Years
Subprotocol A/B/C/D: Number of Participants with Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Events (SAEs), Severe Events, and Events Related to Investigational Product, Procedure, and Premedication
Up to Day 506
Subprotocol A Only: Bayley-4 Cognitive Without Caregiver Input Raw Score Change from Baseline at Day 338
Baseline, Day 338
Subprotocol B/D Only: Multidomain Responder Index (MDRI) Net Response at Day 338
Baseline, Day 338

The following assessments will be included to calculate the MDRI net response: Bayley-4 Cognitive and Receptive Communication, Aberrant Behavior Checklist- Community (ABC-C) Hyperactivity/Noncompliance (H/N), Angelman Severity Assessment (ASA) Sleep, ASA Gross Motor. For each assessment a meaningful score difference (MSD) is defined. A single net response score per participant will be derived accordingly, and a summary measure of net response will then be calculated across all participants.

Subprotocol C Only: MDRI Net Response at Day 338
Baseline, Day 338

The following assessments will be included to calculate the MDRI net response: Vineland-3 Expressive and Receptive Communication, ABC-C Irritability, ASA Gross Motor. For each assessment a meaningful score difference (MSD) is defined. A single net response score per participant will be derived accordingly, and a summary measure of net response will then be calculated across all participants.

Number of Participants with Adverse Events (AEs), Serious AEs (SAEs), Adverse Events of Special Interest (AESIs), AEs Leading to Discontinuation and Severity of AEs
Up to Day 337

Secondary Endpoints

Net Response in Multidomain Responder Index (MDRI)
Day 338
Change from Baseline in ABC-C Hyperactivity/Noncompliance Subscale Score at Day 338
Baseline, Day 338
Change from Baseline in Bayley-4 Receptive Communication Raw Score at Day 338
Baseline, Day 338
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Study Design & Arms

AllocationRANDOMIZED
MaskingQUADRUPLE
ModelPARALLEL
PurposeTREATMENT

Treatment Arms

ArmTypeDescription
GTX-102EXPERIMENTALParticipants will receive GTX-102 via lumbar puncture (LP) during both the double-blind and open-label period
Sham-LP then GTX-102SHAM_COMPARATORParticipants will receive sham procedure during the double-blind period and then will receive GTX-102 via LP during the open-label period
Subprotocol A GTX-102EXPERIMENTALParticipants with deletion-type Angelman syndrome, ≥1 to \<4 years of age will receive increasing doses of GTX-102 via intrathecal (IT) injection until the target dose is achieved. Dosing occurs every 3 months (Q3M) thereafter.
Subprotocol B GTX-102EXPERIMENTALParticipants with paternal uniparental disomy (UPD)/imprinting center defect (ICD) Angelman syndrome, ≥4 to \<18 years of age will receive increasing doses of GTX-102 via IT injection until the target dose is achieved. Dosing occurs Q3M thereafter.
Subprotocol C GTX-102EXPERIMENTALParticipants with all genotypes of Angelman syndrome, ≥18 to \<65 years of age will receive increasing doses of GTX-102 via IT injection until the target dose is achieved. Dosing occurs Q3M thereafter.
Subprotocol D GTX-102EXPERIMENTALParticipants with mutation-type Angelman syndrome, ≥4 to \<18 years of age will receive increasing doses of GTX-102 via IT injection until the target dose is achieved. Dosing occurs Q3M thereafter.
Subprotocol D No Intervention then GTX-102EXPERIMENTALParticipants with mutation-type Angelman syndrome, ≥4 to \<18 years of age will receive no treatment during the initial period. At the end of the no treatment period, participants will receive increasing doses of GTX-102 via IT injection until the target dose is achieved. Dosing occurs Q3M thereafter.
GTX-102 Cohort 1EXPERIMENTAL3.3 mg starting dose followed by intra-patient dose escalation up to 36 mg and then a maintenance phase (in U.S participants 4 to \<17 years of age)
GTX-102 Cohort 2EXPERIMENTAL10 mg starting dose followed by intra-patient dose escalation up to 36 mg and then a maintenance phase (in U.S participants 4 to \<17 years of age)
GTX-102 Cohort 3EXPERIMENTAL20 mg starting dose followed by intra-patient dose escalation up to 55 mg and then a maintenance phase (in U.S participants 4 to \<17 years of age)
GTX-102 Cohort 4EXPERIMENTAL3.3 mg starting dose followed by slow intra-patient dose escalation up to 5 mg and then a maintenance phase (in Ex-U.S participants 4 to \<8 years of age)
GTX-102 Cohort 5EXPERIMENTAL5 mg starting dose followed by slow intra-patient dose escalation up to 7.5 mg and then a maintenance phase (in Ex-U.S participants ≥ 8 to 17 years of age)
GTX-102 Cohort 6EXPERIMENTAL7.5 mg starting dose followed by slow intra-patient dose escalation up to 10 mg and then a maintenance phase (in Ex-U.S participants 4 to \<8 years of age)
GTX-102 Cohort 7EXPERIMENTAL10 mg starting dose followed by slow intra-patient dose escalation up to 12 mg and then a maintenance phase (in Ex-U.S participants ≥ 8 to 17 years of age)
GTX-102 Cohort USEXPERIMENTAL2 mg for 4 monthly doses followed by a quarterly maintenance regimen
GTX-102 Expanded Enrollment Cohort AEXPERIMENTALSponsor selected dose followed by slow intra-patient dose escalation and then a maintenance phase (in Ex-U.S participants 4 to \<8 years of age)
GTX-102 Expanded Enrollment Cohort BEXPERIMENTALSponsor selected dose followed by slow intra-patient dose escalation and then a maintenance phase (in Ex-U.S participants ≥ 8 to 17 years of age)
GTX-102 Expanded Enrollment Cohort CEXPERIMENTALSponsor selected dose followed by slow intra-patient dose escalation and then a maintenance phase (in U.S participants 4 to \<8 years of age)
GTX-102 Expanded Enrollment Cohort DEXPERIMENTALSponsor selected dose followed by slow intra-patient dose escalation and then a maintenance phase (in U.S participants ≥ 8 to 17 years of age)
GTX-102 Cohort EEXPERIMENTALSponsor selected dose followed by slow intra-patient dose escalation and then a maintenance phase (in participants that transition from GTX-102 US Cohort only)

Interventions

NameTypeDescription
GTX-102DRUGantisense oligonucleotide
Sham-LPPROCEDURESmall needle prick on the lower back at the location where the LP injection is normally made
No interventionOTHERDuring the no treatment period participants do not receive any study drug
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Eligibility Criteria

Age Range4 Years to 17 Years
SexALL
Healthy VolunteersNo
Study Sites28

Key Inclusion Criteria: * Signed informed consent from parent(s) or legal guardian(s) * Confirmed diagnosis of AS with genetic confirmation of full maternal ubiquitin-protein ligase E3A (UBE3A) gene deletion causing AS in the region of 15q11.2 q13 * Able to ambulate independently, or with assistanc...

Countries:United StatesCanadaGermanyJapanPolandSpainAustraliaFranceIsraelUnited KingdomArgentinaBrazilItalyPortugal
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Recent Changes (Last 90 Days)

LOWAug 7, 2026NCT07157254lastUpdatePostDate: changed
LOWAug 7, 2026NCT07157254lastUpdatePostDate: changed
LOWAug 6, 2026NCT06617429primaryCompletionDate: changed
LOWAug 6, 2026NCT06617429primaryCompletionDate: changed
LOWJul 27, 2026NCT07157254lastUpdatePostDate: changed
LOWJul 27, 2026NCT06415344lastUpdatePostDate: changed
LOWJul 27, 2026NCT07157254lastUpdatePostDate: changed
LOWJul 27, 2026NCT06415344lastUpdatePostDate: changed
LOWJul 27, 2026NCT07157254lastUpdatePostDate: changed
LOWJul 27, 2026NCT06415344lastUpdatePostDate: changed
LOWJun 23, 2026NCT07157254lastUpdatePostDate: changed
LOWJun 23, 2026NCT07157254lastUpdatePostDate: changed

Frequently asked questions about GTX-102

What is GTX-102 used for?

GTX-102 is an investigational small molecule being developed for the treatment of Angelman Syndrome, a rare genetic disorder. It is currently in Phase 3 clinical development and has not yet been approved by the FDA. The drug is being studied in pediatric patients with this condition.

Who makes GTX-102?

GTX-102 is being developed by Ultragenyx Pharmaceutical Inc., a biopharmaceutical company traded on the Nasdaq under the ticker symbol RARE. The company is conducting clinical trials to evaluate the safety and efficacy of this investigational therapy for Angelman Syndrome.

What phase is GTX-102 in?

GTX-102 is currently in Phase 3 clinical development for Angelman Syndrome. It has received Breakthrough Therapy designation from the FDA. The drug is investigational and has not been approved for commercial use. Clinical trials are ongoing to assess its safety and efficacy.

What clinical trials is GTX-102 in?

GTX-102 is being studied in four clinical trials. These include a completed Phase 1 study (NCT04259281), a Phase 3 long-term extension study (NCT06415344), a Phase 3 efficacy and safety study (NCT06617429), and a Phase 2 study in deletion- and nondeletion-type Angelman Syndrome (NCT07157254).

Is GTX-102 FDA approved?

No, GTX-102 is not FDA approved. It is an investigational drug currently in Phase 3 clinical trials for Angelman Syndrome. The FDA has granted it Breakthrough Therapy designation, which is intended to expedite development and review, but the drug remains in clinical development.