A disease concept model for STXBP1-related disorders

"Living with" CACNA1A-related hemiplegic migraine, a disease concept model

Introduction

CACNA1A-related Hemiplegic Migraine (HM) is a rare neurological disorder distinguished by paroxysmal episodes of hemiparesis/hemiplegia with and without headache. Clinical features have been widely characterized, yet the impacts of the paroxysmal events on the patient and caregiver have not been thoroughly explored. Disease concept models are formal frameworks used to describe the lived experiences of patients and their families, offering a source for surrogate endpoints for clinical trials.

Methods

We completed 13 semi-structured interviews with caregivers of 12 individuals diagnosed with CACNA1A-related HM. We methodically coded themes, grouping concepts into three domains. We measured the occurrence of concepts throughout all interviews and subgroups stratified by age categories.

Results

Over 11 h of interviews yielded 2,018 references to 27 distinct concepts. Established symptoms such as seizures (87 references; including status epilepticus 27 references), hemiparesis/hemiplegia (24 references), and unconsciousness (17 references) were referenced, as well as previously underreported symptoms such as apneic episodes (32 references), lost ability to eat (13 references), and vascular access challenges (10 references). The symptom impacts were largely medical (294 references), followed by health (101 references), emotional (36 references), daily living (28 references), and social (26 references). Caregiver impacts were the most referenced domain (995 references), with the pivotal effects seen in caregiver requirements (355 references), emotional (245 references), HM treatments (179 references), daily living (148 references), and health support (135 references).

Discussion

CACNA1A-related HM is a complex disorder defined by serious paroxysmal events that affects a broad range of social and clinical domains. We systematically classified symptoms and impacts from HM episodes, creating a disease concept model to help develop surrogate endpoints for future clinical trials, and identified two opportunities to improve patient management, including a written emergency protocol and a transition plan for adolescents approaching adulthood.

Novel Splice Site Pathogenic Variant in STXBP1 Gene in a Child with Intellectual Disability, Epilepsy, and Autism Spectrum Disorder: A Case Report

Introduction

Pathogenic variants in the STXBP1 gene are associated to a large spectrum of severe early onset developmental and epileptic encephalopathies (OMIM #612164). They were also identified in various other neurodevelopmental disorders. This gene encodes for the syntaxin-binding protein 1, a member of the SEC-1 family of membrane-transport proteins that modulate the presynaptic vesicular fusion by interacting with soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). However, the physiopathology of STXBP1 pathogenic variants is not yet fully understood.

Case Presentation

Herein, we report a patient presenting intellectual disability, early onset seizures, and autism. Clinical exome sequencing identified a novel monoallelic splice pathogenic variant STXBP1(NM_001032221.6):c.38-2A>G.

Discussion

Splice-site pathogenic variants in the STXBP1 gene are mostly associated with West syndrome, early onset epilepsy and encephalopathy, and Ohtahara syndrome. Our findings extend clinical and molecular spectrum of STXBP1 gene variants by reporting the first splice-site variant associated with autism along with early onset epilepsy and, and intellectual disability in a patient.

Accelerating therapeutic development and clinical trial readiness for STXBP1 and SYNGAP1 disorders

Gene-targeted therapies for genetic neurodevelopmental disorders (NDDs) are becoming a reality. The Center for Epilepsy and Neurodevelopmental Disorders (ENDD) is currently focused on the development of therapeutics for STXBP1 and SYNGAP1 disorders. Here we review the known clinical features of these disorders, highlight the biological role of STXBP1 and SYNGAP1, and discuss our current understanding of pathogenic mechanisms and therapeutic development. Finally, we provide our perspective as scientists and parents of children with NDDs, and comment on the current challenges for both clinical and basic science endeavors.

Advances in big data and omics: Paving the way for discovery in childhood epilepsies

The insights gained from big data and omics approaches have transformed the field of childhood genetic epilepsy. With an increasing number of individuals receiving genetic testing for seizures, we are provided with an opportunity to identify clinically relevant subgroups and extract meaningful observations from this large-scale clinical data. However, the volume of data from electronic medical records and omics (e.g., genomics, transcriptomics) is so vast that standardized methods, such as the Human Phenotype Ontology, are necessary for reliable and comprehensive characterization. Here, we explore the integration of clinical and omics data, highlighting how these approaches pave the way for discovery in childhood epilepsies.

Early life seizures and epileptic spasms in STXBP1-related disorders

OBJECTIVE

Individuals with disease-causing variants in STXBP1 frequently have epilepsy onset in the first year of life with a variety of seizure types, including epileptic spasms. However, the impact of early onset seizures and antiseizure medication (ASM) on the risk of developing epileptic spasms and impact on their trajectory are poorly understood, limiting informed and anticipatory treatment, as well as trial design.

METHODS

We retrospectively reconstructed seizure and medication histories in weekly intervals for individuals with STXBP1 developmental and epileptic encephalopathy (DEE) with epilepsy onset in the first year of life and quantitatively analyzed longitudinal seizure histories and medication response.

RESULTS

We included 61 individuals with early onset seizures, 29 of whom had epileptic spasms. Individuals with neonatal seizures were likely to have continued seizures after the neonatal period (25/26). The risk of developing epileptic spasms was not increased in individuals with neonatal seizures or early infantile seizures (21/41 vs. 8/16, odds ratio [OR] = 1, 95% confidence interval [CI] = .3-3.9, p = 1). We did not find any ASM associated with the development of epileptic spasms following prior seizures. Individuals with prior seizures (n = 16/21, 76%) had a higher risk of developing refractory epileptic spasms (n = 5/8, 63%, OR = 1.9, 95% CI = .2-14.6, p = .6). Individuals with refractory epileptic spasms had a later onset of epileptic spasms (n = 20, median = 20 weeks) compared to individuals with nonrefractory epileptic spasms (n = 8, median = 13 weeks, p = .08).

SIGNIFICANCE

We provide a comprehensive assessment of early onset seizures in STXBP1-DEE and show that the risk of epileptic spasms is not increased following a prior history of early life seizures, nor by certain ASMs. Our study provides baseline information for targeted treatment and prognostication in early life seizures in STXBP1-DEE.

STXBP1: fast-forward to a brighter future - a patient organization perspective

Syntaxin-binding protein 1 related disorder (STXBP1-RD) is a rare neurologic disorder associated with global neurodevelopmental delay, intellectual disability, early-onset epilepsy, motor abnormalities, and autism. The underlying pathophysiology stems from a de novo mutation in the STXBP1 gene, which codes for the STXBP1 protein. The STXBP1 protein is involved in synaptic vesicle fusion and neurotransmitter release. Pathogenic variants in the STXBP1 gene generally result in haploinsufficiency, an impairment in neurotransmitter release, and subsequent dysfunction in neuronal communication. The STXBP1 Foundation was founded in 2017 to support families of children with STXBP1-RD and accelerate the development of effective therapies and, ultimately, a cure for the disorder. The Foundation initially supported research aimed at better understanding the complex phenotypic presentation of the disease as well as the development of animal and cellular models usable by the research community to more fully characterize STXBP1 function and disease pathogenicity. In 2023, the Foundation embarked on its STXBP1 Fast Forward Strategic Plan, which includes a prospective natural history study and substantive biomarker work to drive forward the development of new precision therapies for STXBP1-RD.

STXBP1-Related Disorders: Clinical Presentation, Molecular Function, Treatment, and Future Directions

In recent years, the affordability and availability of genetic testing have led to its increased use in clinical care. The increased frequency of testing has led to STXBP1 variants being identified as one of the more common variants associated with neurological disorders. In this review, we aim to summarize the common clinical phenotypes associated with STXBP1 pathogenic variants, provide an overview of their known natural history, and discuss current research into the genotype to phenotype correlation. We will also provide an overview of the suspected normal function of the STXBP1-encoded Munc18-1 protein, animal models, and experimental techniques that have been developed to study its function and use this information to try to explain the diverse phenotypes associated with STXBP1-related disorders. Finally, we will explore current therapies for STXBP1 disorders, including an overview of treatment goals for STXBP1-related disorders, a discussion of the current evidence for therapies, and future directions of personalized medications for STXBP1-related disorders.

Delineating clinical and developmental outcomes in STXBP1-related disorders

STXBP1-related disorders are among the most common genetic epilepsies and neurodevelopmental disorders. However, the longitudinal epilepsy course and developmental end points, have not yet been described in detail, which is a critical prerequisite for clinical trial readiness. Here, we assessed 1281 cumulative patient-years of seizure and developmental histories in 162 individuals with STXBP1-related disorders and established a natural history framework. STXBP1-related disorders are characterized by a dynamic pattern of seizures in the first year of life and high variability in neurodevelopmental trajectories in early childhood. Epilepsy onset differed across seizure types, with 90% cumulative onset for infantile spasms by 6 months and focal-onset seizures by 27 months of life. Epilepsy histories diverged between variant subgroups in the first 2 years of life, when individuals with protein-truncating variants and deletions in STXBP1 (n = 39) were more likely to have infantile spasms between 5 and 6 months followed by seizure remission, while individuals with missense variants (n = 30) had an increased risk for focal seizures and ongoing seizures after the first year. Developmental outcomes were mapped using milestone acquisition data in addition to standardized assessments including the Gross Motor Function Measure-66 Item Set and the Grasping and Visual-Motor Integration subsets of the Peabody Developmental Motor Scales. Quantification of end points revealed high variability during the first 5 years of life, with emerging stratification between clinical subgroups. An earlier epilepsy onset was associated with lower developmental abilities, most prominently when assessing gross motor development and expressive communication. We found that individuals with neonatal seizures or early infantile seizures followed by seizure offset by 12 months of life had more predictable seizure trajectories in early to late childhood compared to individuals with more severe seizure presentations, including individuals with refractory epilepsy throughout the first year. Characterization of anti-seizure medication response revealed age-dependent response over time, with phenobarbital, levetiracetam, topiramate and adrenocorticotropic hormone effective in reducing seizures in the first year of life, while clobazam and the ketogenic diet were effective in long-term seizure management. Virtual clinical trials using seizure frequency as the primary outcome resulted in wide range of trial success probabilities across the age span, with the highest probability in early childhood between 1 year and 3.5 years. In summary, we delineated epilepsy and developmental trajectories in STXBP1-related disorders using standardized measures, providing a foundation to interpret future therapeutic strategies and inform rational trial design.

Quality of life, socioeconomic and psychological concerns in parents of children with tuberous sclerosis complex, STXBP1 and SYNGAP1 encephalopathies: a mixed method study

Background

Developmental and Epileptic Encephalopathies (DEEs) occur in childhood and are associated with severe epileptic seizures and neurological impairment. The aim of this study was to combine quantitative and qualitative methodologies to comprehensively describe factors related to quality of life, impact on the family and psychosocial factors in parents of children with TSC, STXBP1 and SYNGAP1 variants.

Methods

A convergent parallel mixed design including parents of children with DEE. In the cross-sectional study, 20 parents (10STXBP1, five SYNGAP1, five TSC) were given questionnaires on quality of life, impact on the family and psychological factors. In the descriptive qualitative study, in-depth interviews were conducted with 18 parents (nine STXBP1, five TSC, four SYNGAP1) using a semi-structured questionnaire. A thematic analysis was carried out. The results of the two studies were combined by showing similarities and differences through tables, figures, accounts, and joint displays.

Results

In terms of quality of life, the integrated results were consistent in highlighting the importance of family interaction, although in the qualitative section the influence of the relationship between the children's siblings, the relationship with health professionals and the difficulties in obtaining public aid were highlighted. In terms of impact, the integrated results show that the illness has a significant impact on the family; the financial burden is highlighted, and the experience of the illness is discussed in depth. Finally, the psychological aspects, symptoms such as anxiety, stress and strain, were consistent. Most of the participants reported sleep disturbance, as identified in the questionnaire, although not mentioned in the interviews.

Conclusions

The combined results of the mixed method provide an in-depth analysis of the impact of DEEs on parents of children with STXBP1, SYNGAP1 and TSC.

Early life seizures and epileptic spasms in STXBP1-related disorders

Background and Objectives

Individuals with disease-causing variants in STXBP1 frequently have epilepsy onset in the first year of life with a variety of seizure types, including epileptic spasms. However, the impact of early-onset seizures and anti-seizure medication (ASM) on the risk of developing epileptic spasms and impact on their trajectory is poorly understood, limiting informed and anticipatory treatment, as well as trial design.

Methods

We retrospectively reconstructed seizure and medication histories in weekly intervals for individuals with STXBP1-related disorders with epilepsy onset in the first year of life and quantitatively analyzed longitudinal seizure histories and medication response.

Results

We included 61 individuals with early onset seizures, 29 of whom had epileptic spasms. Individuals with neonatal seizures were likely to have continued seizures after the neonatal period (25/26). The risk of developing epileptic spasms was not increased in individuals with neonatal seizures or early infantile seizures (21/41 vs. 8/16; OR 1, 95% CI 0.3-3.9, p = 1). We did not find any ASM associated with the development of epileptic spasms following prior seizures. Individuals with prior seizures (n = 16/21, 76%) had a higher risk to develop refractory epileptic spasms (n = 5/8, 63%, OR =1.9, 95% CI 0.2-14.6, p = 0.6). Individuals with refractory epileptic spasms had a later onset of epileptic spasms (n = 20, median 20 weeks) compared to individuals with non-refractory epileptic spasms (n = 8, median 13 weeks; p = 0.08). When assessing treatment response, we found that clonazepam (n = 3, OR 12.6, 95% CI 2.2-509.4; p < 0.01), clobazam (n=7, OR 3, 95% CI 1.6-6.2; p < 0.01), topiramate (n=9, OR 2.3, 95% CI 1.4-3.9; p < 0.01), and levetiracetam (n=16, OR 1.7, 95% CI 1.2-2.4; p < 0.01) were more likely to reduce seizure frequency and/or to maintain seizure freedom with regards to epileptic spasms than other medications.

Discussion

We provide a comprehensive assessment of early-onset seizures in STXBP1-related disorders and show that the risk of epileptic spasms is not increased following a prior history of early-life seizures, nor by certain ASM. Our study provides baseline information for targeted treatment and prognostication in early-life seizures in STXBP1-related disorders.

A disease concept model for STXBP1-related disorders

OBJECTIVE

STXBP1-related disorders are rare genetic epilepsies and neurodevelopmental disorders, but the impact of symptoms across clinical domains is poorly understood. Disease concept models are formal frameworks to assess the lived experience of individuals and their families and provide a basis for generating outcome measures.

METHODS

We conducted semistructured, qualitative interviews with 19 caregivers of 16 individuals with STXBP1-related disorders and 7 healthcare professionals. We systematically coded themes using NVivo software and grouped concepts into the domains of symptoms, symptom impact, and caregiver impact. We quantified the frequency of concepts throughout the lifespan and across clinical subgroups stratified by seizure history and developmental trajectories.

RESULTS

Over 25 hours of interviews, we coded a total of 3626 references to 38 distinct concepts. In addition to well-recognized clinical features such as developmental delay (n = 240 references), behavior (n = 201), and seizures (n = 147), we identified previously underrepresented symptoms including gastrointestinal (n = 68) and respiratory symptoms (n = 24) and pain (n = 30). The most frequently referenced symptom impacts were autonomy (n = 96), socialization (n = 64), and schooling (n = 61). Emotional impact (n = 354), support (n = 200), and daily life & activities (n = 108) were highly cited caregiver impacts. We found that seizures were more commonly referenced in infancy than in other age groups, while behavior and socialization were more likely to be referred to in childhood. We found that caregivers of individuals with ongoing seizures were less likely to reference developmental delay, possibly due to the relatively high impact of seizures.

SIGNIFICANCE

STXBP1-related disorders are complex conditions affecting a wide range of clinical and social domains. We comprehensively mapped symptoms and their impact on families to generate a comprehensive disease model as a foundation for clinical endpoints in future trials.

Delineating clinical and developmental outcomes in STXBP1-related disorders

STXBP1-related disorders are among the most common genetic epilepsies and neurodevelopmental disorders. However, the longitudinal epilepsy course and developmental endpoints have not yet been described in detail, which is a critical prerequisite for clinical trial readiness. Here, we assessed 1,281 cumulative patient-years of seizure and developmental histories in 162 individuals with STXBP1-related disorders and established a natural history framework. STXBP1-related disorders are characterized by a dynamic pattern of seizures in the first year of life and high variability in neurodevelopmental trajectories in early childhood. Epilepsy onset differed across seizure types, with 90% cumulative onset for infantile spasms by 6 months and focal-onset seizures by 27 months of life. Epilepsy histories diverged between variant subgroups in the first 2 years of life, when individuals with protein-truncating variants and deletions in STXBP1 (n=39) were more likely to have infantile spasms between 5 and 6 months followed by seizure remission, while individuals with missense variants (n=30) had an increased risk for focal seizures and ongoing seizures after the first year. Developmental outcomes were mapped using milestone acquisition data in addition to standardized assessments including the Gross Motor Function Measure-66 Item Set and the Grasping and Visual-Motor Integration subsets of the Peabody Developmental Motor Scales. Quantification of endpoints revealed high variability during the first five years of life, with emerging stratification between clinical subgroups, most prominently between individuals with and without infantile spasms. We found that individuals with neonatal seizures or early infantile seizures followed by seizure offset by 12 months of life had more predictable seizure trajectories in early to late childhood than compared to individuals with more severe seizure presentations, including individuals with refractory epilepsy throughout the first year. Characterization of anti-seizure medication response revealed age-dependent response over time, with phenobarbital, levetiracetam, topiramate, and adrenocorticotropic hormone effective in reducing seizures in the first year of life, while clobazam and the ketogenic diet were effective in long-term seizure management. Virtual clinical trials using seizure frequency as the primary outcome resulted in wide range of trial success probabilities across the age span, with the highest probability in early childhood between 1 year and 3.5 years. In summary, we delineated epilepsy and developmental trajectories in STXBP1-related disorders using standardized measures, providing a foundation to interpret future therapeutic strategies and inform rational trial design.