• Epilepsy
  • seizure type and severity varies by phenotypic subgroup
• Developmental delay
  • Intellectual disability
  • present in over 90% of individuals in large cohorts
• Autism spectrum disorder (29% > than 2 years)
• Movement disorders
  • including dystonia, chorea, dyskinesia, stereotypies, episodic ataxia, and choreoathetosis
• Hypotonia (68%)

Phenotypic subgroups are recognized based on age of seizure onset and variant function:

• Early-onset (EO) epilepsy
• Late-onset (LO) phenotypes (seizure onset ≥3 months or no epilepsy): Typically caused by loss-of-function (LoF) variants. Includes late-onset epilepsy with mid-infancy onset (often [infantile spasms](https://www.openevidence.com/rare-disease/west-syndrome)), late-onset epilepsy with childhood onset, and ID/ASD without epilepsy. Sodium channel blockers are rarely effective and may worsen seizures.

Developmental outcomes vary widely. In a cohort of 100 individuals, 62% could sit independently, 55% could walk, and only 31% spoke more than 1–5 single words. Adaptive behavior composite scores on the Vineland Adaptive Behavior Scales were generally low across all subgroups.

• Cortical/cerebral visual impairment (45%)
  • Most common in neonatal-onset and infantile-onset phenotypic groups and decreased in frequency in later-onset and ASD/ID groups.
• Strabismus
  • reported in multiple cohorts; Howell et al. identified strabismus in 4 of 17 patients with SCN2A encephalopathy.
• Optic atrophy
  • reported in individual cases. Baasch et al. described a patient with a de novo SCN2A missense mutation (p.R1882L) presenting with intractable seizures, severe intellectual disability, and optic atrophy alongside brain abnormalities and muscular hypotonia.
• Oculogyric crises
  • paroxysmal conjugate tonic deviation of the eyes, typically upward, has been noted as part of the movement disorder spectrum in SCN2A-related disorders.

Biological basis for visual involvement: NaV1.2 (encoded by SCN2A) is expressed in the retina, where it is found in retinal ganglion cell axons and in a subset of ON cone bipolar cells. In retinal ganglion cells, NaV1.2 is essential for action potential initiation and regeneration, and its expression is predominantly localized to intraretinal axons.[2][8] In bipolar cells, NaV1.2 may serve to amplify neurotransmitter release during rapid depolarization, thereby accelerating light responses.[7] NaV1.2 is also expressed in horizontal cells and amacrine cell processes within the inner plexiform layer.[1][9] This widespread retinal expression of NaV1.2 provides a plausible biological mechanism for the visual dysfunction observed in SCN2A-related disorders, potentially affecting both retinal signal processing and optic nerve function.

Beyond epilepsy, developmental disability, and eye findings, SCN2A-related disorders are associated with a range of additional clinical features:

• Movement disorders: dystonia, chorea, dyskinesia, stereotypies, choreoathetosis (especially in LO-MI subgroup), and episodic ataxia
• Spasticity (reported in ~22% of individuals)
• Acquired microcephaly
• Structural brain abnormalities: cerebral atrophy, hypoplastic corpus callosum, and cortical dysplasia
• Malformation of cortical development has been described in association with specific GoF variants

• Constipation, gastroesophageal reflux, chronic diarrhea
• Feeding difficulties requiring nasogastric or gastrostomy tube (22% requiring G-tube for most or all nutrition)

• Scoliosis (reported in 22%)

• Episodic hyperventilation, breath-holding spells
• Autonomic dysfunction (tachycardia, temperature instability)

• Extreme irritability
• Auditory startle
• Vulnerability to secondary psychiatric disorders including bipolar disorder in adults with SCN2A-related ASD

No specific facial gestalt is recognized, although dysmorphic features were noted in approximately 27% of patients in one cohort

SCN2A-related neurodevelopmental disorder follows an autosomal dominant inheritance pattern. The vast majority of pathogenic variants causing severe phenotypes arise de novo (i.e., are not inherited from parents), while inherited variants are more commonly associated with the milder, self-limited epilepsy phenotypes.[2][4]

The SCN2A gene is located on chromosome 2q24.3 and encodes the NaV1.2 voltage-gated sodium channel alpha subunit. The channel consists of four homologous domains, each with six transmembrane segments. The S4 segment acts as the voltage sensor, and the S5–S6 segments form the ion selectivity pore.[4]

• Gain-of-function (GoF) variants: Typically missense mutations that increase sodium channel activity through mechanisms such as slowing of fast inactivation, acceleration of recovery from inactivation, or increased persistent sodium current. These are associated with early-onset epilepsy phenotypes
• Loss-of-function (LoF) variants: Include both missense and truncating (nonsense, frameshift) mutations that reduce NaV1.2 channel activity. Mechanisms include reduced protein expression (haploinsufficiency via nonsense-mediated decay), protein instability, depolarizing shift of voltage-dependent activation, or hyperpolarizing shift of channel availability. These are associated with later-onset epilepsy, ID, and/or ASD. Sodium channel blockers are typically ineffective and may worsen seizures.
• 2q24.3 copy number variants (CNVs): Deletions encompassing SCN2A (and sometimes neighboring SCN1A and SCN3A) can also cause SCN2A-related phenotypes, often with severe developmental outcomes.

Patient-derived iPSC neurons have confirmed that LoF variants result in reduced NaV1.2 protein levels, decreased sodium current density, and impaired action potential firing, while GoF/epilepsy-associated variants show impaired sodium channel inactivation without changes in protein levels.

1. Goad BS, Rodda J, Allen M, et al. Development and Adaptive Function in Individuals With SCN2A-Related Disorders. //Neurology//.2025.
2. Wolff M, Brunklaus A, Zuberi SM. Phenotypic Spectrum and Genetics of SCN2A-related Disorders, Treatment Options, and Outcomes in Epilepsy and Beyond. //Epilepsia//. 2019;60 Suppl 3:S68-S80
3. Tan M, Goad BS, Allen M, et al. Mechanisms of SCN2A loss of function do not predict presence or phenotype of epilepsy. //Epilepsia//. 2026.
4. Richardson R, Baralle D, Bennett C, et al. Further delineation of phenotypic spectrum of SCN2A-related disorder. //Am J Med Genet A//. 2022;188(3):898-914.
5. Wolff M, Johannesen KM, Hedrich UBS, et al. Genetic and Phenotypic Heterogeneity Suggest Therapeutic Implications in SCN2A-related Disorders. //Brain//. 2017;140(5):1316-1336
6. Berg AT, Nili AN, Evans L, et al. Assessing Communication Impairments in a Rare Neurodevelopmental Disorder: The SCN2A Clinical Trials Readiness Study. //Neurol Clin Pract//. 2025;15(1):e200399
7. Howell KB, McMahon JM, Carvill GL, et al. SCN2A Encephalopathy: A Major Cause of Epilepsy of Infancy With Migrating Focal Seizures. //Neurology//. 2015;85(11):958-966
8. Baasch AL, Hüning I, Gilissen C, et al. Exome Sequencing Identifies a De Novo SCN2A Mutation in a Patient With Intractable Seizures, Severe Intellectual Disability, Optic Atrophy, Muscular Hypotonia, and Brain Abnormalities. //Epilepsia//. 2014;55(4):e25-e29
9. Risner ML, McGrady NR, Pasini S, et al. Elevated Ocular Pressure Reduces Voltage-Gated Sodium Channel NaV1.2 Protein Expression in Retinal Ganglion Cell Axons. //Exp Eye Res//. 2020;190:107873
10. Kawai F, Ohkuma M, Horiguchi M, et al. A Subset of Cone Bipolar Cells Expresses the Na Channel SCN2A in the Human Retina. //Exp Eye Res//. 2021;202:108367
11. Mojumder DK, Frishman LJ, Otteson DC, Sherry DM. Voltage-Gated Sodium Channel Alpha-Subunits Nav1.1, Nav1.2, and Nav1.6 in the Distal Mammalian Retina. //Mol Vis//. 2007;13:2163-2182
12. Corradi A, Riva A, Sterlini B, et al. Functional Characterization of a De Novo SCN2A Mixed Variant Linked to [Early Infantile Developmental and Epileptic Encephalopathy](https://www.openevidence.com/rare-disease/early-infantile-developmental-and-epileptic-encephalopathy). //Neurol Genet//. 2026;12(1):e200234
13. Hedrich UBS, Lauxmann S, Lerche H. SCN2A Channelopathies: Mechanisms and Models. //Epilepsia//. 2019;60 Suppl 3:S68-S80
14. Clatot J, Thompson CH, Sotardi S, et al. Rare Dysfunctional SCN2A Variants Are Associated With Malformation of Cortical Development. //Epilepsia//. 2025;66(3):e30-e37
15. Asadollahi R, Delvendahl I, Muff R, et al. Pathogenic SCN2A Variants Cause Early-Stage Dysfunction in Patient-Derived Neurons. //Hum Mol Genet//. 2023;32(13):2192-2204

SCN2A-related neurodevelopmental disorder (SCN2A-NDD) is caused by pathogenic variants in the SCN2A gene, which encodes the alpha subunit of the voltage-gated sodium channel Nav1.2. This channel is critical for generating neuronal action potentials throughout the central nervous system. Depending on whether a variant causes a gain-of-function or loss-of-function effect on channel activity, patients present with a broad and variable clinical spectrum, including:

• Neonatal or infantile-onset epilepsy, ranging from benign familial infantile seizures to severe developmental and epileptic encephalopathies (e.g., Ohtahara syndrome, infantile spasms, epilepsy of infancy with migrating focal seizures, Lennox-Gastaut syndrome)
• Developmental delay and intellectual disability, often significant
• Autism spectrum disorder — SCN2A is considered one of the highest-confidence single-gene causes of autism
• Movement disorders, including choreoathetosis and ataxia
• Hypotonia

SCN2A-NDD is one of the more commonly identified monogenic causes of both neonatal-onset epilepsy and autism spectrum disorder.

Visual and ocular abnormalities are common in SCN2A-NDD and are increasingly recognized as a core feature rather than an incidental finding.

• Cortical (cerebral) visual impairment (CVI) — the most clinically significant ocular finding, reflecting impaired visual processing in the brain rather than a structural eye problem. CVI has been reported in roughly 40% or more of individuals with SCN2A-related disorder.
• Broader visual problems (including visuomotor, depth perception, and distance-related difficulties) are reported in a majority of affected individuals in emerging research cohorts.
• Strabismus
• Nystagmus
• Refractive errors (myopia, hyperopia, astigmatism)
• Reduced visual acuity

Because CVI is a brain-based visual impairment, standard eye exams (including visual acuity testing and structural exam) may appear relatively normal even when functional vision is significantly affected. A functional vision assessment (FVA), ideally performed by a clinician experienced with CVI, is recommended in addition to routine ophthalmologic evaluation, since CVI-related accommodations (e.g., use of color, movement, reduced visual clutter, positioning) can meaningfully improve a child's ability to use vision functionally.

• Gastrointestinal issues, including feeding difficulties and gastroesophageal reflux; some children require gastrostomy tube feeding
• Sleep disturbances
• Behavioral and sensory processing differences, including atypical responses to sensory stimuli
• Speech and language impairment
• Orthopedic issues related to hypotonia or movement disorder
• Autonomic dysfunction in some individuals

SCN2A-NDD is caused by heterozygous, typically de novo, pathogenic variants in the SCN2A gene (OMIM #182390) located on chromosome 2q24.3. The gene encodes Nav1.2, a voltage-gated sodium channel expressed throughout excitatory neurons of the central nervous system.

• Gain-of-function variants tend to increase neuronal excitability and are associated with early-onset (neonatal/infantile), often more severe, epileptic encephalopathies.
• Loss-of-function variants tend to decrease neuronal excitability and are more often associated with later-onset seizures (or no seizures), autism spectrum disorder, and intellectual disability.

This genotype-function-phenotype relationship is an active area of research and is beginning to guide precision treatment approaches, including selection of sodium-channel-targeted anti-seizure medications based on predicted variant function.

• SCN2A-related disorders - Wikipedia
• SCN2A-Related Disorders - Cambridge Elements
• Cortical Vision Impairment (CVI)-informed assessment and treatment of challenging behavior in a child with SCN2A-related disorder - PMC
• Electrophysiological features: The next precise step for SCN2A developmental epileptic encephalopathy - PMC
• Clinical Information - FamilieSCN2A Foundation