Natural History Study of Patients With Succinic Semialdehyde Dehydrogenase (SSADH) Deficiency

January 12, 2026 updated by: Phillip Pearl, Boston Children's Hospital

Succinic Semialdehyde Dehydrogenase deficiency (SSADHD) is a rare autosomal recessive disease that interferes with the catabolism of the major inhibitory neurotransmitter gamma-amino butyric acid (GABA) and furthermore leads to accumulation of various potential toxic metabolites, most prominently gamma hydroxybutyric acid (GHB). Current research indicates that there is developmental delay and significant neurophysiological and biochemical alterations in SSADHD patients, but whether disease presentation varies with age is not known. The investigators propose to determine the natural course of the clinical presentation of SSADHD; to determine the natural course of neurophysiological and biochemical indices known to be altered in SSADHD; and to identify neurophysiological and biochemical predictors of clinical severity.

The overall objective is to define the natural course of the clinical, neurophysiological and biochemical spectrum of SSADHD. Secondary objectives include the identification of biomarkers that correlate with disease phenotype and predict clinical outcomes, and the creation of an international SSADHD data repository for future investigation of pathogenesis and therapy.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Detailed Description

The study will be conducted by 4 academic institutions: Washington State University (WSU), Boston Children's Hospital (BCH), University of South Florida (USF), and University Children's Hospital Heidelberg (iNTD). The design of the study is mixed, with longitudinal and cross-sectional assessments over a period of 5 years.

Patients will be separated into three cohorts. The Boston Children's cohort will be a total of 20 patients evaluated at Boston Children's Hospital in the United States. These patients will be followed for five years, and attend a visit to the hospital in years 1,3 and 5 where assessments including history/physical, neuropsychological testing, EEG, TMS, and bio-specimen collection will be completed. Each patient will have an MRI of the brain done with special GABA sequencing one time over the five years. Each visit will take place over the course of two days. At BCH, the goal will be to schedule visits every other year with questionnaires and surveys sent out up to every 6 months, and bio-specimen collection every year. The BCH team will also ask for two follow up phone calls occurring 12 months after each onsite visit. Visits will consist of clinical assessments (demographics, medical history, physical examination, neurological exam, medication history, neuropsychological assessments, and clinical severity score), neurophysiological assessments (Brain MRI/MRS/DTI, Electroencephalogram, and Transcranial magnetic stimulation), and yearly bio-specimen collection (blood, urine, saliva, hair, stool, and skin biopsy). Bio-specimens will be sent to Washington State University for testing and addition to a biorepository. The iNTD (international NeuroTransmitters Disorders) cohort will be comprised of 15 patients who are seen at European sites who will have approval through their ethics committee to share de-identified information. Bio-specimens will be attempted to be collected at each visit from patients and sent to Washington State University. At the iNTD sites and for patients followed outside of iNTD, visits and bio-specimen collections will depend on the patients' follow-up schedules with electronic, web-based survey sent on a regular schedule (every 6 months). The standard of care cohort will be comprised of 10 patients throughout the world who provide consent to share de-identified information to the database.

The data will be stored in a database on the University of South Florida server. The server is password protected, and each member of the study personal will have a unique log in to have access to the site. Subjects will also be given specialized access to complete follow up electronic web based surveys twice a year over the course of 5 years. The team at USF will assist with data analysis.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Observational

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
55

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Locations

  • Germany
    • Heidelberg
      • Heidelberg, Heidelberg, Germany
  • Spain
      • Barcelona, Spain
        • Active, not recruiting
        • Sant Joan de Deu Hospital Barcelona
  • United Kingdom
      • Birmingham, United Kingdom
        • Not yet recruiting
        • Birmingham Children's Hospital NHS Foundation Trust
        • Contact:
        • Principal Investigator:
          • Evangeline Wassmer
  • United States
    • Massachusetts
      • Boston, Massachusetts, United States, 02115

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Child
  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Sampling Method

Non-Probability Sample

Study Population

Children and adults diagnosed with Succinic Semialdehyde Dehydrogenase (SSADH) deficiency.

Description

Inclusion Criteria:

  • 4-hydroxybutyric aciduria (γ-hydroxybutyric aciduria)
  • documented pathogenic ALDH5A1 (aldehyde dehydrogenase 5A1 gene) mutation
  • 0-99 years

Exclusion Criteria:

  • active or recent substance abuse or dependence within the past year.
  • inability to participate in the study procedures.
  • any condition that makes the study subject, in the opinion of the investigator, unsuitable for the study.
  • patients will be excluded from the MRI section of the study if they have: implanted cardiac pacemaker or autodefibrillators, implanted neural pacemakers, cochlear implants, metallic foreign bodies in the eye or Central Nervous System (CNS), any implanted wire or metal device that may concentrate radio frequency fields.
  • patients less than age two years will be excluded from the TMS procedure.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Observational Models: Cohort
  • Time Perspectives: Prospective

Cohorts and Interventions

Group / Cohort

Group / Cohort

A group or subgroup of participants in an observational study that is assessed for biomedical or health outcomes.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
BCH Cohort
Patients enrolled at BCH will travel to BCH every 2 years at a minimum for comprehensive evaluation taking place over a 48 hour period. Visits to BCH may occur within ± 2 months of the scheduled visit date. Electronic surveys will be sent out every 6 months.Visits will consist of clinical assessments (demographics, medical history, physical examination, neurological exam, medication history, neuropsychological assessments, and clinical severity score), neurophysiological assessments (Brain Magnetic resonance imaging [MRI/MRS/DTI], Electroencephalogram [EEG], and Transcranial magnetic stimulation [TMS]), and yearly bio-specimen collection.
Device: Transcranial magnetic stimulation (TMS)
Transcranial magnetic stimulation (TMS) is a method for noninvasive electrical cortical stimulation, where small intracranial currents are generated by a powerful, fluctuating, extracranial magnetic field. TMS is unique in its capacity for experimental, diagnostic, and therapeutic utility. Single pulse (spTMS) and paired-pulse TMS (ppTMS) have been used extensively to study, measure, and modulate cortical excitability and plasticity.
Other Names:
  • Nexstim Navigated Brain Stimulation (NBS) System 4
Device: Magnetic resonance imaging (MRI)
These will be outpatient MRI studies that are planned without sedation. Subjects enrolled at BCH will undergo brain MRI, including volumetric MRI, MRS, and diffusion tensor imaging (DTI). The data will help define the natural history of brain volume, brain myelination and spectroscopic (e.g. GABA) abnormalities.
Device: Electroencephalogram (EEG)
These will be outpatient EEG recordings that span 20-60 minutes and done without sedation. Recordings will be performed using electrode locations specified by the international 10-20 system for standard clinical practice.
Other Names:
  • Natus
Procedure: Bio-specimen Collection
Bio-specimen collection will include blood, urine, saliva, hair, stool, and a skin biopsy. Blood, urine, saliva, blood spots, and hair samples will also be banked for to-be-determined (TBD) studies.
iNTD Cohort
Patients enrolled at iNTD sites will travel to their iNTD site according to standard of care requirements. Data collection includes clinical history and relevant laboratory-chemical, therapeutic, instrumental and neuropsychological parameters by the study centers. Data collection takes place within the framework of elective outpatient visits. The collected parameters are congruent with the current standard investigations. Electronic surveys will be sent out every 6 months. Imaging and neurophysiological data will be collected if performed during the clinical visit or if performed as part of the site's ongoing research. Yearly bio-specimen collection will be attempted after consent is obtained from the family.
Procedure: Bio-specimen Collection
Bio-specimen collection will include blood, urine, saliva, hair, stool, and a skin biopsy. Blood, urine, saliva, blood spots, and hair samples will also be banked for to-be-determined (TBD) studies.
Standard of Care Cohort
Patients enrolled at other sites will attend their visit at their regular clinical site as mandated by standard of care. Data collection includes medical history, family history, medications, and all clinical and neuropsychological assessments listed. Imaging and neurophysiological data will be collected if performed during the clinical visit or if performed as part of the clinical site's ongoing research. Yearly bio-specimen collection will be attempted.
Procedure: Bio-specimen Collection
Bio-specimen collection will include blood, urine, saliva, hair, stool, and a skin biopsy. Blood, urine, saliva, blood spots, and hair samples will also be banked for to-be-determined (TBD) studies.

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Clinical Severity Score
Time Frame: 5 Years
A composite score ranging from 5 (profound impairment) to 25 (no impairment) will be calculated using scores from five clinically significant subdomains (cognition, communication, motor skills, psychiatric presentation, and epilepsy), each scored from 1 (worse) to 5 (no impairment).
5 Years
Biochemical - GABA measurement
Time Frame: 5 Years
GABA is measured by electron-capture negative-ion mass fragmentography. The level will be measured in the different bio-specimens.
5 Years
Biochemical - GHB measurement
Time Frame: 5 Years
GHB is measured using gas chromatography-mass spectrometry (GCMS). GHB will be measured in the different bio-specimens.
5 Years
Quantification of GABA related signals on the MRI spectroscopy
Time Frame: 5 Years
MRI spectroscopy with special editing for GABA-related peaks in multi-voxel MRS. Concentrations will be analyzed.
5 Years

Other Outcome Measures

Other Outcome Measures

For clinical trials, a planned measurement described in the protocol that is used to determine the effect of an intervention/treatment on participants. For observational studies, a measurement or observation that is used to describe patterns of diseases or traits, or associations with exposures, risk factors, or treatment. Types of outcome measures include primary outcome measure and secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Quantification of EEG abnormalities (%)
Time Frame: 5 Years
Degree of epileptiform abnormalities will be recorded using the American Clinical Neurophysiology Society guidelines [Continuous (>90%), Abundant (50-89%), Frequent (10-49%), Occasional (1-9%), and Rare (< 1 %)].
5 Years
Extent of altered signal hyperintensities on structural MRI (%)
Time Frame: 5 years
Altered T2 and FLAIR signal hyperintensities will be reported as a percent.
5 years
Degree of myelination on structural MRI (%)
Time Frame: 5 years
Degree of myelination will be reported as a percent.
5 years
Total cerebral volume on structural MRI (cm3)
Time Frame: 5 years
Total cerebral volume will be reported in cubic centimeters (cm3).
5 years
Amplitudes of motor evoked potentials (mm)
Time Frame: 5 years
Intracortical Inhibition (ICI) and Facilitation (ICF) are a paired-pulse TMS measure of cortical excitability. A short Interval interstimuli (2ms) leads to a cortical inhibition, which reflects the GABAergic neurotransmission; whereas a longer interval interstimuli leads to a cortical facilitation, which reflects glutamatergic neurotransmission. Analyzed by obtaining peak-to-peak amplitudes in millimeters (mm).
5 years
Durations of cortical silent period (ms)
Time Frame: 5 years
Cortical Silent Period (CSP) is a single-pulse TMS measure of cortical inhibition, stimulations are applied while subjects are exerting a muscular contraction and lead to a muscular cancellation. Duration of this silence is measured in milliseconds (ms).
5 years

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Boston Children's Hospital

Collaborators

Collaborators

An organization other than the sponsor that provides support for a clinical study. This support may include activities related to funding, design, implementation, data analysis, or reporting.
Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)
University of South Florida
Washington State University
University Hospital Heidelberg

Investigators

Investigators

A researcher involved in a clinical study. Related terms include site principal investigator, site sub-investigator, study chair, study director, and study principal investigator.
  • Study Chair: Phillip L Pearl, MD, Boston Children's Hospital/Harvard Medical School
  • Study Chair: K. Michael Gibson, PhD, Washington State University

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
January 15, 2019

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
May 31, 2029

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
June 1, 2029

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
November 16, 2018

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
November 28, 2018

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
November 29, 2018

Study Record Updates

Last Update Posted (Estimated)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
January 13, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
January 12, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
January 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • IRB-P00029917
  • 1R01HD091142-01A1 (U.S. NIH Grant/Contract)

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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