STXBP1 Disorder: A Complete Guide

STXBP1-related disorders are a group of rare genetic neurodevelopmental conditions caused by pathogenic variants (mutations) in the STXBP1 gene — full name Syntaxin-Binding Protein 1 — located on chromosome 9q34.11. The gene encodes a protein called Munc18-1, which plays an indispensable role in allowing neurons to communicate with one another.

When STXBP1 is mutated, the molecular machinery governing neurotransmitter release is disrupted. The downstream consequences include early-onset epilepsy, global developmental delay, intellectual disability, and a range of motor and behavioral challenges. STXBP1 disorders were first identified in 2008 when researchers investigating Ohtahara Syndrome — a severe early-onset epileptic encephalopathy — found that mutations in the STXBP1 gene were a major causative factor.

Since that initial discovery, the scope of STXBP1-related disorders has expanded to encompass a broad clinical spectrum: West syndrome, Lennox-Gastaut syndrome, Dravet-like syndrome, and unspecified developmental epileptic encephalopathy. Today, STXBP1 is recognized as one of the five most commonly mutated genes in developmental and epileptic encephalopathies.

Effective October 1, 2025, STXBP1-related disorders have their own dedicated ICD-10 code: QA0.0141. This is a landmark milestone for the STXBP1 community — the result of years of advocacy by the STXBP1 Foundation, over 3,000 petition signers, and more than 125 clinicians.

Before this change, STXBP1 was coded under general diagnoses like “epilepsy” or “developmental delay,” making it nearly impossible to accurately track patients in healthcare systems. With a dedicated code, STXBP1 diagnoses can now be reliably documented, counted, and studied worldwide — strengthening epidemiology, insurance coverage, research, and care coordination for every affected family.

Clinicians: please use code QA0.0141 when documenting an STXBP1 diagnosis. Read the full story →

To understand STXBP1 disorder, it helps to understand what the STXBP1 gene normally does. The STXBP1 gene provides the blueprint for a protein called Munc18-1 (also known as nSec1 or STXBP1 protein). Munc18-1 is a key regulatory component of the SNARE complex — the core molecular machinery that enables neurons to release neurotransmitters.

Neurons communicate across tiny gaps called synapses. To send a signal, a neuron packages neurotransmitters (chemical messengers like glutamate or GABA) into small membrane bubbles called synaptic vesicles. When an electrical impulse arrives, these vesicles must fuse with the neuron’s outer membrane and release their contents into the synapse, where the next neuron picks up the signal.

This vesicle fusion is orchestrated by the SNARE complex — a set of proteins including syntaxin-1, SNAP-25, and synaptobrevin. Munc18-1 (STXBP1 protein) binds directly to syntaxin-1 and is essential for priming the SNARE complex into its active “open” configuration. Without functional Munc18-1, SNARE assembly is impaired, vesicle fusion is disrupted, and neurotransmitter release fails.

Pathogenic variants in the STXBP1 gene operate primarily through haploinsufficiency — meaning that having one functional copy of the gene (with the other copy mutated or deleted) is not enough to produce sufficient Munc18-1 protein. Some missense mutations also cause the protein to misfold, aggregate, and be degraded, further depleting available Munc18-1. The result is a global impairment of neuronal communication throughout the developing brain.

Reduced Munc18-1 activity leads to two interconnected pathologies: disrupted inhibitory signaling (allowing runaway neuronal excitation → seizures) and impaired neurodevelopmental signaling during critical windows of brain maturation (→ intellectual disability and developmental delay).

STXBP1-related disorders manifest across a broad clinical spectrum. The severity and combination of symptoms varies considerably between individuals, even among those with the same type of mutation. Most individuals are described as having a developmental and epileptic encephalopathy (DEE) because they experience both developmental impairment and epilepsy.

Seizures in STXBP1 disorder are diverse and often drug-resistant. Common seizure types include:

• Infantile spasms (West syndrome) — brief, clustered flexion/extension spasms; usually before age 1
• Tonic seizures — sudden stiffening of the body or limbs
• Clonic seizures — rhythmic jerking movements
• Generalized tonic-clonic seizures — full-body convulsions
• Myoclonic seizures — sudden brief muscle jerks
• Focal impaired awareness seizures — blank staring, unresponsiveness
• Absence seizures — brief lapses in awareness

STXBP1 disorder should be suspected in any infant or child presenting with unexplained early-onset epilepsy, especially if accompanied by developmental delay and hypotonia. Because clinical features alone cannot confirm the diagnosis, genetic testing is essential. A diagnosis cannot be made on clinical features alone.

There is currently no approved cure for STXBP1-related disorders. Treatment is focused on managing symptoms — particularly epilepsy — and supporting development through multidisciplinary therapies. Because each patient is affected differently, care plans are highly individualized.

The STXBP1 research landscape is moving rapidly. The dominant pathomechanism of haploinsufficiency makes STXBP1 a strong candidate for gene-based interventions aimed at restoring Munc18-1 protein levels. Multiple therapeutic strategies are currently being explored:

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  Gene augmentation therapy

  Uses a viral vector (typically AAV) to deliver a functional copy of the STXBP1 gene directly to neurons. Because the primary mechanism is haploinsufficiency — insufficient Munc18-1 — restoring gene expression is a particularly rational strategy. Preclinical studies in mouse models have shown promise.

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  Antisense oligonucleotides (ASOs)

  Short synthetic DNA strands designed to modulate STXBP1 gene expression. ASOs can potentially upregulate the healthy copy of STXBP1 to compensate for the mutant copy, or correct aberrant splicing. This approach has shown success in other neurological diseases (e.g. spinal muscular atrophy) and is actively being explored for STXBP1. Rafa’s Moonshot’s Rafa002 program pursues this approach.

• ✂️
  CRISPR-Cas9 gene editing

  Precision gene editing tools that could directly correct the causative mutation in an individual patient’s genome. CRISPR technology is advancing rapidly and holds potential for permanent correction of specific STXBP1 variants, though delivery to neurons and safety remain active research challenges.

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  Chemical chaperones & drug repurposing

  Some STXBP1 missense mutations cause protein misfolding and aggregation. Chemical chaperones such as glycerol phenylbutyrate can stabilize misfolded proteins and restore function. Glycerol phenylbutyrate is FDA-approved for urea cycle disorders and is currently in a clinical trial for STXBP1. Rafa’s Moonshot’s Rafa001 (Beta-NMN) and Rafa003 small molecule programs are also active.

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  Disease models & natural history studies

  Rafa’s Moonshot has funded over $500,000 in organoid and rat chimera research at the Hebrew University of Jerusalem (Dr. Omer Revah’s lab) and mouse model development at Tel Aviv University (Prof. Illana Gozes — R292C model). The 2022 Xian et al. study of 534 individuals and Stamberger et al. adult natural history study are landmark contributions enabling future clinical trials.

STXBP1 Mutational Spectrum

Pathogenic variants in STXBP1 can occur throughout the gene, though certain positions are more frequently mutated (“hotspots”). The 2022 landmark study by Xian et al. (Brain) characterized variants in 534 individuals and provides the most comprehensive mutational landscape to date. All variant types converge on a common pathomechanism: haploinsufficiency — reduction of functional Munc18-1 protein below the threshold needed for normal synaptic neurotransmitter release.

• Missense variants — single amino acid changes; most common type. May cause protein misfolding or impaired syntaxin-1 binding.
• Frameshift variants — insertions or deletions that shift the reading frame, leading to truncated or non-functional protein.
• Nonsense variants — premature stop codons that result in a truncated, non-functional protein.
• Splice-site variants — alter mRNA splicing, often causing exon skipping or intron retention.
• Intragenic deletions — remove one or more exons of the STXBP1 gene.
• Whole-gene deletions — the entire STXBP1 gene is deleted; detected by chromosomal microarray.

• STXBP1 Foundation
• ENDD Center for Epilepsy and NeuroDevelopmental Disorders
• NORD Rare Disease Database
• STXBP1 webpage at VU University in Amsterdam
• STXBP1 webpage from Children’s Hospital of Philadelphia
• Epicare leaflet and patient journey
• Child Neurology Foundation
• Epilepsy Foundation — STXBP1 PDF
• Beyond the Ion Channel blog by Ingo Helbig’s lab
• Gene Reviews — STXBP1 Encephalopathy with Epilepsy
• MedlinePlus Genetics — STXBP1 Encephalopathy
• GeneCards — STXBP1
• Rafa’s Moonshot Glossary

1. Saitsu H, Kato M, Mizuguchi T, et al. De novo mutations in the gene encoding STXBP1 (MUNC18-1) cause early infantile epileptic encephalopathy. Nature Genetics. 2008;40(6):782–788.
2. Xian J, Parthasarathy S, Ruggiero SM, et al. Assessing the landscape of STXBP1-related disorders in 534 individuals. Brain. 2022;145(5):1668–1683. doi:10.1093/brain/awab327
3. Stamberger H, Crosiers D, Balagura G, et al. Natural History Study of STXBP1-Developmental and Epileptic Encephalopathy Into Adulthood. Neurology. 2022;99(3):e221–e233. doi:10.1212/WNL.0000000000200715
4. Stamberger H, Nikanorova M, Willemsen MH, et al. STXBP1 encephalopathy: A neurodevelopmental disorder including epilepsy. Neurology. 2016;86(10):954–962.
5. Lopez-Rivera JA, Leu C, Macnee M, et al. The contribution of rare variant associations to epilepsy and its comorbidities. medRxiv. 2020. (Incidence estimate 1:30,000)
6. Verhage M, Maia AS, Plomp JJ, et al. Synaptic assembly of the brain in the absence of neurotransmitter secretion. Science. 2000;287(5454):864–869.
7. Patzke C, Han Y, Covy J, et al. Analysis of conditional heterozygous STXBP1 mutations in human neurons. J Clin Invest. 2015;125(9):3560–71.

This page was last reviewed and updated in April 2026. Content is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment decisions.