KCNA2-Related Developmental and Epileptic Encephalopathy

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Inheritance

1

Autosomal Dominant (De Novo) HP:0000006

The disorder arises almost exclusively from de novo heterozygous KCNA2 variants; a single altered allele is sufficient to cause disease, acting either as a dominant-negative loss of function or as a dominant gain of function on the tetrameric Kv1.2 channel.

Autosomal dominant inheritance

Show evidence (2 references)

PMID:29050392 SUPPORT Human Clinical

"de novo occurrence could be shown in 20 patients."

Documents the de novo dominant occurrence of KCNA2 variants in the large genotype-phenotype cohort.

PMID:25751627 SUPPORT Human Clinical

"we identified four different de novo mutations in KCNA2, encoding the potassium channel KV1.2, in six isolated patients with epileptic encephalopathy"

Original identification of de novo heterozygous KCNA2 variants as the cause of the epileptic encephalopathy.

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Discussions and Knowledge Gaps

2

How does a gain of function of the Kv1.2 potassium channel — which hyperpolarizes and electrically silences individual neurons — paradoxically produce a more severe epilepsy than the loss-of-function variants, and is preferential silencing of inhibitory interneurons the correct explanation at the network level?

OPEN QUESTION OPEN gap_kcna2_gof_seizure_paradox

Attached to

pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing pathophysiology#Network Excitation-Inhibition Imbalance and Seizures

At the single-neuron level, increased Kv1.2 conductance hyperpolarizes and silences neurons, yet clinically the gain-of-function variants cause more severe, generalized epilepsy than the loss-of-function variants that produce classic hyperexcitability. The leading resolution is that gain of function preferentially silences inhibitory interneurons, disinhibiting the network, but this cell-type-specific mechanism has not been definitively established in human cortical circuits and remains, in the words of the review literature, an unresolved paradox with direct consequences for whether channel-blocking (4-aminopyridine) versus channel-opening strategies are appropriate for a given variant.

Proposed experiments

Cell-type-resolved test of interneuron silencing in KCNA2 gain of function

cell-type-resolved electrophysiology experiment

exp_kcna2_gof_interneuron_silencing

In human iPSC-derived or mouse cortical networks expressing a KCNA2 gain-of-function variant, measure firing and intrinsic excitability separately in excitatory neurons and inhibitory interneurons, and test whether interneurons are preferentially silenced and whether the resulting network is hyperexcitable, with reversal by 4-aminopyridine.

Perturbations

KCNA2 gain-of-function expression

pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing

Express a gain-of-function KCNA2 variant (e.g. R297Q or L298F) across a cortical network with excitatory and inhibitory neurons distinguished.

KCNA2 hgnc:6220

Readouts

Interneuron versus principal-neuron firing and network activity

pathophysiology#Network Excitation-Inhibition Imbalance and Seizures

regulation of membrane potential GO:0042391 ⚠ ABNORMAL

patch-clamp recording multielectrode array recording

Direction: POSITIVE

Controls

Wild-type KCNA2

Wild-type Kv1.2 expressed in the same network.

4-aminopyridine versus vehicle

Matched networks treated with 4-aminopyridine or vehicle.

Decision criterion

Preferential interneuron silencing is supported if inhibitory interneurons show disproportionately reduced firing while the network becomes hyperexcitable, and if 4-aminopyridine restores interneuron firing and network balance.

Would support

pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing pathophysiology#Network Excitation-Inhibition Imbalance and Seizures

Show evidence (2 references)

PMID:29542386 SUPPORT Other

"This development has been difficult to understand as traditionally potassium channel loss-of-function, not gain-of-function, has been associated with hyperexcitability disorders."

States the core paradox that gain-of-function potassium-channel variants cause epilepsy despite the traditional loss-of-function view of hyperexcitability.

PMID:29542386 SUPPORT Other

"A surprising finding of these efforts is the recognition that gain of function potassium channel variants are actually associated with certain types of epilepsy, such as malignant migrating partial seizures of infancy or early-onset epileptic encephalopathy."

Confirms the association of potassium-channel gain of function with early-onset epileptic encephalopathy, the phenomenon requiring a network-level explanation.

Does the benefit of 4-aminopyridine generalize across all gain-of-function KCNA2 variants and to the gain-and-loss-of-function subgroup, and can functional variant classification prospectively predict which patients respond?

KNOWLEDGE GAP OPEN gap_kcna2_4ap_generalization

Attached to

pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing

The n-of-1 4-aminopyridine trials showed benefit in 9 of 11 gain-of-function patients, but two did not benefit and one worsened, and the gain-and-loss-of-function subgroup — which combines an activation shift with reduced amplitude — was not clearly addressed. Whether response can be predicted prospectively from the precise biophysical fingerprint of each variant, and whether the gain-and-loss group behaves like the gain group for treatment selection, is not established, yet it determines who should receive channel-blocking therapy.

Proposed experiments

Biophysical response map for 4-aminopyridine across KCNA2 variants

genotype-response correlation study

exp_kcna2_4ap_variant_response_map

Across a panel of KCNA2 variants spanning pure gain, gain-and-loss, and loss of function, quantify the biophysical fingerprint (activation shift, amplitude, inactivation) and the in-vitro rescue by 4-aminopyridine, then correlate with clinical response in treated patients to build a prospective response predictor.

Perturbations

KCNA2 variant panel expression

pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing

Express each KCNA2 variant class and characterize its biophysical fingerprint and 4-aminopyridine sensitivity.

KCNA2 hgnc:6220

Readouts

Channel biophysics and 4-aminopyridine rescue

pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing

potassium ion transmembrane transport GO:0071805 ↑ INCREASED

voltage-clamp recording

Direction: NEGATIVE

Controls

Wild-type KCNA2

Wild-type Kv1.2 characterized under identical conditions.

Decision criterion

A predictor is supported if the in-vitro 4-aminopyridine rescue of a variant's biophysical defect correlates with clinical response across the treated cohort, and if the gain-and-loss group segregates predictably.

Would support

pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing

Show evidence (2 references)

PMID:34516822 SUPPORT Human Clinical

"In n-of-1 trials carried out in nine different centers, 9 of 11 patients carrying such variants benefitted from treatment with 4-aminopyridine."

Documents the incomplete response rate that motivates the need for prospective response prediction.

PMID:29050392 SUPPORT Human Clinical

"Our study thus indicates well represented genotype-phenotype associations between three subgroups of patients with KCNA2 encephalopathy according to the electrophysiological features of the mutations."

Establishes the three functional subgroups, including the gain-and-loss-of-function group whose treatment response is uncertain.

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Pathophysiology

6

KCNA2 Variant and Altered Kv1.2 Channel Function

A de novo heterozygous KCNA2 variant alters the voltage-gated potassium channel Kv1.2, the pore-forming subunit of a delayed-rectifier channel expressed across excitatory and inhibitory neurons. Because Kv1.2 assembles as a tetramer, a single variant subunit co-assembles with wild-type subunits and modifies the whole channel, producing either loss or gain of channel function depending on the variant. This is the shared trigger of a bidirectional channelopathy.

neuron CL:0000540

potassium ion transmembrane transport GO:0071805 ⚠ ABNORMAL protein homooligomerization GO:0051260 ⚠ ABNORMAL

brain UBERON:0000955

Downstream

Dominant-Negative Loss of Kv1.2 Delayed-Rectifier Current

Gain-of-Function Kv1.2 Conductance and Neuronal Silencing

Show evidence (2 references)

PMID:25751627 SUPPORT Human Clinical

"we identified four different de novo mutations in KCNA2, encoding the potassium channel KV1.2, in six isolated patients with epileptic encephalopathy"

Establishes de novo KCNA2 variants affecting the Kv1.2 channel as the molecular trigger of the disorder.

PMID:25751627 SUPPORT Human Clinical

"These results establish KCNA2 as a new gene involved in human neurodevelopmental disorders through two different mechanisms, predicting either hyperexcitability or electrical silencing of KV1.2-expressing neurons."

Defines the two divergent functional mechanisms (loss versus gain of function) that branch from this trigger.

Dominant-Negative Loss of Kv1.2 Delayed-Rectifier Current

Loss-of-function variants (e.g. P405L, I263T) reduce delayed-rectifier potassium current, and because the mutant subunit poisons the tetramer they act dominant-negatively, lowering current below the level expected from simple haploinsufficiency. Kv1.2 normally enables efficient repolarization of the neuronal membrane after each action potential, so its loss impairs repolarization.

neuron CL:0000540

potassium ion transmembrane transport GO:0071805 ↓ DECREASED membrane repolarization GO:0086009 ↓ DECREASED

Downstream

Neuronal Membrane Hyperexcitability

Show evidence (3 references)

PMID:25751627 SUPPORT In Vitro

"Functional studies of the two mutations associated with this phenotype showed almost complete loss of function with a dominant-negative effect."

Demonstrates near-complete loss of Kv1.2 function with a dominant-negative mechanism for the loss-of-function variant class.

PMID:25751627 SUPPORT In Vitro

"both P405L and I263T exert a clear dominant-negative effect on WT KV1.2 channels."

Identifies the specific loss-of-function variants and confirms the dominant-negative reduction of channel current.

PMID:25751627 SUPPORT Other

"KV1.2 belongs to the delayed rectifier class of potassium channels enabling efficient neuronal repolarization following an action potential."

Establishes the normal delayed-rectifier/repolarization role of Kv1.2 that the loss-of-function variants degrade.

Neuronal Membrane Hyperexcitability

Impaired repolarization from reduced delayed-rectifier Kv1.2 current leaves the neuronal membrane hyperexcitable and prone to repetitive, prolonged firing. This is the classic loss-of-function route to hyperexcitability shared with other potassium-channelopathies and corroborated by the seizure phenotype of the Kcna2 knockout mouse.

neuron CL:0000540

neuronal action potential GO:0019228 ⚠ ABNORMAL regulation of membrane potential GO:0042391 ⚠ ABNORMAL

Downstream

Network Excitation-Inhibition Imbalance and Seizures

Show evidence (1 reference)

PMID:25751627 SUPPORT Other

"Loss-of-function mutations predict hyperexcitable neuronal membranes and repetitive neuronal firing due to impaired repolarization."

States the mechanistic link from Kv1.2 loss of function to membrane hyperexcitability and repetitive firing.

Gain-of-Function Kv1.2 Conductance and Neuronal Silencing

Gain-of-function variants (e.g. R297Q, L298F) shift voltage-dependent activation strongly in the hyperpolarizing direction and increase current amplitude, leaving Kv1.2 channels permanently open at physiological membrane potentials. The excess potassium conductance hyperpolarizes the membrane and electrically silences the affected neuron. Because Kv1.2 is expressed in both excitatory and inhibitory neurons, silencing of inhibitory interneurons is the leading hypothesis for how a potassium-channel gain of function paradoxically produces network hyperexcitability and severe epilepsy.

neuron CL:0000540 interneuron CL:0000099

potassium ion transmembrane transport GO:0071805 ↑ INCREASED regulation of membrane potential GO:0042391 ⚠ ABNORMAL

Downstream

Network Excitation-Inhibition Imbalance and Seizures

Cerebellar and Cortical Dysfunction

Show evidence (2 references)

PMID:25751627 SUPPORT In Vitro

"Two further individuals presented with a different and more severe epileptic encephalopathy phenotype. They carried mutations inducing a drastic gain-of-function effect leading to permanently open channels."

Establishes the gain-of-function variant class with permanently open channels and its more severe phenotype.

PMID:25751627 SUPPORT In Vitro

"R297Q and L298F predict permanently open channels at physiological membrane potentials, and electrical silencing by membrane hyperpolarization (as observed in oocytes)."

Shows the gain-of-function variants hyperpolarize and electrically silence neurons through excess potassium conductance.

Network Excitation-Inhibition Imbalance and Seizures

Both arms of the channelopathy converge on a disturbance of cortical excitatory/inhibitory balance producing neuronal hyperexcitability and hypersynchronous discharges. Loss-of-function variants tend to produce predominantly focal seizures with sleep-activated multifocal epileptiform discharges, whereas gain-of-function variants tend to produce generalized seizures; clinically this manifests as an early-onset epileptic encephalopathy.

neuron CL:0000540

regulation of membrane potential GO:0042391 ⚠ ABNORMAL

neocortex UBERON:0001950

Downstream

Epilepsy

Show evidence (2 references)

PMID:29050392 SUPPORT Human Clinical

"The main differences were (i) predominant focal (loss-of-function) versus generalized (gain-of-function) seizures and corresponding epileptic discharges with prominent sleep activation in most cases with loss-of-function mutations"

Links the two functional variant classes to focal versus generalized seizure semiology and the sleep-activated discharges of the loss-of-function group.

PMID:25751627 SUPPORT Human Clinical

"Four individuals presented with febrile and multiple afebrile, often focal seizure types, multifocal epileptiform discharges strongly activated by sleep, mild to moderate intellectual disability, delayed speech development and sometimes ataxia."

Documents the focal seizure semiology and sleep-activated multifocal discharges of the loss-of-function presentation.

Cerebellar and Cortical Dysfunction

Kv1.2 dysfunction, most prominently in the gain-of-function group, disturbs cerebellar and cortical circuit function and is accompanied in about half of gain-of-function patients by atrophy of the cerebellum or even the whole brain. The resulting circuit dysfunction underlies the ataxia, intellectual disability, and delayed speech that accompany the epilepsy.

neuron CL:0000540

regulation of membrane potential GO:0042391 ⚠ ABNORMAL

cerebellum UBERON:0002037

Downstream

Ataxia

Intellectual Disability

Show evidence (1 reference)

PMID:29050392 SUPPORT Human Clinical

"more severe epilepsy, developmental problems and ataxia, and atrophy of the cerebellum or even the whole brain in about half of the patients with gain-of-function mutations"

Documents cerebellar/whole-brain atrophy and prominent ataxia in the gain-of-function subgroup, supporting cerebellar and cortical dysfunction.

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Pathograph

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Phenotypes

8

Nervous System 6

Focal-Onset Seizures HP:0007359

Show evidence (1 reference)

PMID:25751627 SUPPORT Human Clinical

"Four individuals presented with febrile and multiple afebrile, often focal seizure types, multifocal epileptiform discharges strongly activated by sleep, mild to moderate intellectual disability, delayed speech development and sometimes ataxia."

Documents focal seizure types with sleep-activated multifocal discharges.

Febrile Seizures Febrile seizure (within the age range of 3 months to 6 years) HP:0002373

Show evidence (1 reference)

PMID:25751627 SUPPORT Human Clinical

"Four individuals presented with febrile and multiple afebrile, often focal seizure types, multifocal epileptiform discharges strongly activated by sleep, mild to moderate intellectual disability, delayed speech development and sometimes ataxia."

Documents febrile seizures within the loss-of-function seizure spectrum.

Intellectual Disability HP:0001249

Show evidence (1 reference)

PMID:25751627 SUPPORT Human Clinical

"Four individuals presented with febrile and multiple afebrile, often focal seizure types, multifocal epileptiform discharges strongly activated by sleep, mild to moderate intellectual disability, delayed speech development and sometimes ataxia."

Documents mild to moderate intellectual disability in the loss-of-function presentation.

Ataxia HP:0001251

Show evidence (1 reference)

PMID:29050392 SUPPORT Human Clinical

"more severe epilepsy, developmental problems and ataxia, and atrophy of the cerebellum or even the whole brain in about half of the patients with gain-of-function mutations"

Documents prominent ataxia with cerebellar/whole-brain atrophy in the gain-of-function subgroup.

Delayed Speech and Language Development HP:0000750

Show evidence (1 reference)

PMID:25751627 SUPPORT Human Clinical

"Four individuals presented with febrile and multiple afebrile, often focal seizure types, multifocal epileptiform discharges strongly activated by sleep, mild to moderate intellectual disability, delayed speech development and sometimes ataxia."

Documents delayed speech development in the KCNA2 phenotype.

Cerebellar Atrophy HP:0001272

Show evidence (1 reference)

PMID:29050392 SUPPORT Human Clinical

"more severe epilepsy, developmental problems and ataxia, and atrophy of the cerebellum or even the whole brain in about half of the patients with gain-of-function mutations"

Documents cerebellar (and whole-brain) atrophy in the gain-of-function subgroup.

Other 2

Epilepsy Epileptic encephalopathy HP:0200134

Show evidence (1 reference)

PMID:25751627 SUPPORT Human Clinical

"we identified four different de novo mutations in KCNA2, encoding the potassium channel KV1.2, in six isolated patients with epileptic encephalopathy"

Establishes epileptic encephalopathy as the core presentation of KCNA2 disease.

Progressive Microcephaly HP:0000253

Show evidence (1 reference)

PMID:27117551 SUPPORT Human Clinical

"The patient presented since birth with intractable seizures, progressive microcephaly, developmental delay, and progressive brain atrophy."

Documents progressive microcephaly and brain atrophy in a severe early-onset KCNA2 case.

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Genetic Associations

1

KCNA2 (De Novo Loss-of-Function and Gain-of-Function Variants)

Gene: KCNA2 hgnc:6220 variant_origin: GERMLINE

Autosomal Dominant (De Novo)

Show evidence (2 references)

PMID:29050392 SUPPORT Human Clinical

"Recently, de novo mutations in the gene KCNA2, causing either a dominant-negative loss-of-function or a gain-of-function of the voltage-gated K+ channel Kv1.2, were described to cause a new molecular entity within the epileptic encephalopathies."

Establishes the two opposing functional mechanisms of de novo KCNA2 variants.

PMID:29050392 SUPPORT Human Clinical

"Our study thus indicates well represented genotype-phenotype associations between three subgroups of patients with KCNA2 encephalopathy according to the electrophysiological features of the mutations."

Documents three functional subgroups (loss, gain, and gain-and-loss of function) with correlated phenotypes.

💊

Medical Actions

4

4-Aminopyridine (Gain-of-Function Precision Therapy)

Action: Pharmacotherapy NCIT:C15986

Agent: 4-aminopyridine CHEBI:34385

For patients carrying gain-of-function KCNA2 variants, the potassium-channel blocker 4-aminopyridine (fampridine) is a mechanism-tailored therapy: it antagonizes the gain-of-function defect in vitro and, in n-of-1 trials, benefitted 9 of 11 patients with gain-of-function variants, improving seizures, gait, ataxia, alertness, cognition, or speech. It is not appropriate for loss-of-function variants, where blocking residual Kv1.2 current would be expected to worsen hyperexcitability.

Show evidence (2 references)

PMID:34516822 SUPPORT In Vitro

"we show for KCNA2-encephalopathy that the K+ channel blocker 4-aminopyridine can antagonize gain-of-function defects caused by variants in the KV1.2 subunit in vitro, by reducing current amplitudes and negative shifts of steady-state activation and increasing the firing rate of transfected neurons."

Demonstrates the mechanistic rationale — 4-aminopyridine antagonizes the gain-of-function Kv1.2 defect in vitro.

PMID:34516822 SUPPORT Human Clinical

"In n-of-1 trials carried out in nine different centers, 9 of 11 patients carrying such variants benefitted from treatment with 4-aminopyridine."

Documents clinical benefit of 4-aminopyridine in gain-of-function KCNA2 patients.

Antiseizure Medication

Action: Pharmacotherapy NCIT:C15986

Agent: valproic acid CHEBI:39867

Seizures are managed with antiseizure medications with variable response. Choice may be informed by the functional variant class; response is often incomplete, and some loss-of-function patients become seizure-free over childhood.

Show evidence (1 reference)

PMID:25751627 SUPPORT Human Clinical

"Seizures and ataxia responded poorly to antiepileptic drugs (topiramate, oxcarbazepine, valproic acid, bromide), including acetazolamide (known to be effective in EA1 caused by mutations in KCNA1"

Documents the variable/incomplete response of KCNA2 seizures to conventional antiseizure medications including valproic acid.

Genetic Counseling

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Genetic counseling addresses the de novo dominant mechanism, the generally low recurrence risk (with attention to rare parental mosaicism), and the prognostic and treatment implications of the functional variant class.

Supportive and Developmental Care

Action: Supportive Care NCIT:C15747

Multidisciplinary supportive care — developmental therapies and management of intellectual disability, ataxia, and speech delay — is a mainstay given the neurodevelopmental impairment.

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Diagnosis

3

KCNA2 Molecular Diagnosis

Diagnosis is established by identifying a heterozygous pathogenic KCNA2 variant, typically de novo, in a child with early-onset epileptic encephalopathy, intellectual disability, and often ataxia. Functional classification of the variant (loss versus gain of function) informs prognosis and, for gain-of-function variants, candidacy for 4-aminopyridine.

molecular genetic testing NCIT:C19770

Results: A heterozygous pathogenic KCNA2 variant establishes the diagnosis.

Show evidence (1 reference)

PMID:27117551 SUPPORT Human Clinical

"Whole-exome sequencing showed a novel de novo mutation in the KCNA2 gene: c.1120A > G (p.Thr374Ala)."

Illustrates molecular genetic (exome) confirmation of a de novo KCNA2 variant establishing the diagnosis.

EEG and Seizure Phenotyping

EEG documents the epileptic encephalopathy and helps distinguish the functional subgroups — multifocal discharges with prominent sleep activation in loss-of-function disease versus generalized discharges in gain-of-function disease.

electroencephalography NCIT:C38054

Results: Multifocal sleep-activated (loss-of-function) or generalized (gain-of-function) epileptiform discharges.

Show evidence (1 reference)

PMID:29050392 SUPPORT Human Clinical

"The main differences were (i) predominant focal (loss-of-function) versus generalized (gain-of-function) seizures and corresponding epileptic discharges with prominent sleep activation in most cases with loss-of-function mutations"

Documents the EEG differences that phenotype the two functional subgroups.

Brain MRI

Brain MRI assesses for cerebellar or whole-brain atrophy, which is seen in about half of gain-of-function patients, and excludes structural causes.

magnetic resonance imaging procedure NCIT:C16809

Results: May show cerebellar or whole-brain atrophy, especially with gain-of-function variants.

Show evidence (1 reference)

PMID:29050392 SUPPORT Human Clinical

"more severe epilepsy, developmental problems and ataxia, and atrophy of the cerebellum or even the whole brain in about half of the patients with gain-of-function mutations"

Documents the cerebellar/whole-brain atrophy seen on imaging in the gain-of-function subgroup.

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Progression

2

Infancy to Early Childhood

Onset is typically in infancy or early childhood with epilepsy and evolving developmental impairment; severe gain-and-loss-of-function presentations may begin in the neonatal period.

Show evidence (1 reference)

PMID:29050392 SUPPORT Human Clinical

"Our study thus indicates well represented genotype-phenotype associations between three subgroups of patients with KCNA2 encephalopathy according to the electrophysiological features of the mutations."

The three functional subgroups differ in onset and severity, framing the disease trajectory.

Childhood onward

In milder loss-of-function disease seizures may remit in childhood while intellectual disability and ataxia persist; gain-of-function disease tends to a more severe, progressive course with cerebellar or whole-brain atrophy.

Show evidence (1 reference)

PMID:29050392 SUPPORT Human Clinical

"more severe epilepsy, developmental problems and ataxia, and atrophy of the cerebellum or even the whole brain in about half of the patients with gain-of-function mutations"

Documents the more severe, atrophy-associated trajectory of the gain-of-function subgroup.

📊

Prevalence

1

Worldwide

Unknown Rare

KCNA2-related developmental and epileptic encephalopathy is individually rare; in the original screen de novo KCNA2 variants accounted for roughly 1.7% of cases across mixed epileptic-encephalopathy cohorts, and a precise population prevalence has not been established.

Show evidence (1 reference)

PMID:25751627 SUPPORT Human Clinical

"we identified de novo mutations in KCNA2 causing mild to severe epileptic encephalopathy in roughly 1.7% of cases across our different cohorts."

Quantifies the fraction of screened epileptic-encephalopathy cases attributable to KCNA2, supporting a rare single-gene DEE.

🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from KCNA2-Related Developmental and Epileptic Encephalopathy:

Other potassium-channel developmental and epileptic encephalopathies

Overlapping Features DEEs from other voltage-gated potassium channel genes (KCNQ2, KCNB1, KCNT1, KCNA1) overlap through early-onset epilepsy and developmental impairment and are distinguished by molecular testing and channel-specific electrophysiology.

Distinguishing Features

A de novo pathogenic KCNA2 variant favors this disorder.
A causal variant in a different potassium-channel gene favors that channelopathy.

Show evidence (1 reference)

PMID:29542386 SUPPORT Other

"we describe the current state of the field regarding the gain-of-function potassium channel variants associated with epilepsy (KCNA2, KCNB1, KCND2, KCNH1, KCNH5, KCNJ10, KCNMA1, KCNQ2, KCNQ3, and KCNT1)"

Lists the potassium-channel epilepsy genes that constitute the molecular differential diagnosis.

Dravet syndrome and myoclonic-atonic epilepsy

Overlapping Features The loss-of-function KCNA2 presentation with febrile and focal seizures can resemble Dravet syndrome (SCN1A) or myoclonic-atonic epilepsy, but focal seizures and sleep-activated multifocal discharges are atypical for those syndromes and molecular testing distinguishes them.

Distinguishing Features

Multifocal epileptiform discharges strongly activated by sleep favor KCNA2.
An SCN1A variant favors Dravet syndrome.

🐁

Animal Models

1

Kcna2 loss-of-function (Pingu) and Kcna2 knockout Mouse (Mus musculus)

The Pingu mouse, carrying a Kcna2 loss-of-function mutation close to the human P405L residue, shows ataxia and growth retardation, and Kcna2 knockout mice have severe seizures and premature death — recapitulating the hyperexcitability predicted for the loss-of-function arm of the human disease.

Species

Mouse (Mus musculus)

Genotype

Kcna2 loss-of-function (Pingu) and Kcna2 knockout

Show evidence (1 reference)

PMID:25751627 SUPPORT Model Organism

"the Pingu mouse presenting with ataxia and growth retardation carries a Kcna2 loss-of-function mutation, p.Ile402Thr, in close proximity to P405L; Kcna2 knock-out mice present with severe seizures and premature death"

Mouse Kcna2 loss-of-function and knockout models reproduce ataxia and seizures, supporting the loss-of-function hyperexcitability mechanism.

{ }

Source YAML

click to show

name: KCNA2-Related Developmental and Epileptic Encephalopathy
creation_date: "2026-07-25T00:00:00Z"
description: >-
  A developmental and epileptic encephalopathy (DEE 32) caused by de novo
  heterozygous variants in KCNA2, which encodes the pore-forming alpha subunit
  of the voltage-gated potassium channel Kv1.2, a delayed-rectifier channel that
  drives neuronal repolarization after an action potential. KCNA2-related
  disease is a distinctive bidirectional channelopathy: some variants cause
  dominant-negative loss of Kv1.2 current, producing hyperexcitable neuronal
  membranes and repetitive firing, whereas others cause a gain of function with
  permanently open channels that hyperpolarize and electrically silence
  neurons. The two functional classes map onto partly distinct clinical
  pictures — loss-of-function variants tend to produce predominantly focal
  seizures with sleep-activated multifocal discharges and milder outcome, while
  gain-of-function variants tend to produce a more severe, ataxia-prominent
  encephalopathy with generalized seizures and cerebellar or whole-brain
  atrophy, and a third gain-and-loss-of-function group has the most severe,
  earliest-onset phenotype. Affected individuals present in infancy or early
  childhood with epilepsy, intellectual disability, delayed speech, and ataxia.
  The gain-of-function arm has become an early example of precision epilepsy
  therapy, as the potassium-channel blocker 4-aminopyridine can antagonize the
  gain-of-function defect and has benefitted patients carrying such variants.
category: Mendelian
parents:
- Neurodevelopmental Disorder
- Epileptic Encephalopathy
disease_term:
  preferred_term: KCNA2-related developmental and epileptic encephalopathy
  term:
    id: MONDO:0014607
    label: developmental and epileptic encephalopathy, 32
inheritance:
- name: Autosomal Dominant (De Novo)
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    The disorder arises almost exclusively from de novo heterozygous KCNA2
    variants; a single altered allele is sufficient to cause disease, acting
    either as a dominant-negative loss of function or as a dominant gain of
    function on the tetrameric Kv1.2 channel.
  evidence:
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      de novo occurrence could be shown in 20 patients.
    explanation: >-
      Documents the de novo dominant occurrence of KCNA2 variants in the large
      genotype-phenotype cohort.
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we identified four different de novo mutations in KCNA2, encoding the
      potassium channel KV1.2, in six isolated patients with epileptic
      encephalopathy
    explanation: >-
      Original identification of de novo heterozygous KCNA2 variants as the
      cause of the epileptic encephalopathy.
prevalence:
- population: Worldwide
  measure_type: UNKNOWN
  prevalence_class: RARE
  notes: >-
    KCNA2-related developmental and epileptic encephalopathy is individually
    rare; in the original screen de novo KCNA2 variants accounted for roughly
    1.7% of cases across mixed epileptic-encephalopathy cohorts, and a precise
    population prevalence has not been established.
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we identified de novo mutations in KCNA2 causing mild to severe epileptic
      encephalopathy in roughly 1.7% of cases across our different cohorts.
    explanation: >-
      Quantifies the fraction of screened epileptic-encephalopathy cases
      attributable to KCNA2, supporting a rare single-gene DEE.
references:
- reference: PMID:25751627
  title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
- reference: PMID:29050392
  title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
- reference: PMID:34516822
  title: "4-Aminopyridine is a promising treatment option for patients with gain-of-function KCNA2-encephalopathy."
- reference: PMID:27117551
  title: "Severe early-onset epileptic encephalopathy due to mutations in the KCNA2 gene: Expansion of the genotypic and phenotypic spectrum."
- reference: PMID:29542386
  title: "Potassium Channel Gain of Function in Epilepsy: An Unresolved Paradox."
pathophysiology:
- name: KCNA2 Variant and Altered Kv1.2 Channel Function
  description: >-
    A de novo heterozygous KCNA2 variant alters the voltage-gated potassium
    channel Kv1.2, the pore-forming subunit of a delayed-rectifier channel
    expressed across excitatory and inhibitory neurons. Because Kv1.2 assembles
    as a tetramer, a single variant subunit co-assembles with wild-type
    subunits and modifies the whole channel, producing either loss or gain of
    channel function depending on the variant. This is the shared trigger of a
    bidirectional channelopathy.
  role: trigger
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: potassium ion transmembrane transport
    term:
      id: GO:0071805
      label: potassium ion transmembrane transport
    modifier: ABNORMAL
  - preferred_term: protein homooligomerization
    term:
      id: GO:0051260
      label: protein homooligomerization
    modifier: ABNORMAL
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we identified four different de novo mutations in KCNA2, encoding the
      potassium channel KV1.2, in six isolated patients with epileptic
      encephalopathy
    explanation: >-
      Establishes de novo KCNA2 variants affecting the Kv1.2 channel as the
      molecular trigger of the disorder.
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These results establish KCNA2 as a new gene involved in human
      neurodevelopmental disorders through two different mechanisms, predicting
      either hyperexcitability or electrical silencing of KV1.2-expressing
      neurons.
    explanation: >-
      Defines the two divergent functional mechanisms (loss versus gain of
      function) that branch from this trigger.
  downstream:
  - target: Dominant-Negative Loss of Kv1.2 Delayed-Rectifier Current
    causal_link_type: DIRECT
  - target: Gain-of-Function Kv1.2 Conductance and Neuronal Silencing
    causal_link_type: DIRECT
- name: Dominant-Negative Loss of Kv1.2 Delayed-Rectifier Current
  description: >-
    Loss-of-function variants (e.g. P405L, I263T) reduce delayed-rectifier
    potassium current, and because the mutant subunit poisons the tetramer they
    act dominant-negatively, lowering current below the level expected from
    simple haploinsufficiency. Kv1.2 normally enables efficient repolarization
    of the neuronal membrane after each action potential, so its loss impairs
    repolarization.
  role: central_effector
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: potassium ion transmembrane transport
    term:
      id: GO:0071805
      label: potassium ion transmembrane transport
    modifier: DECREASED
  - preferred_term: membrane repolarization
    term:
      id: GO:0086009
      label: membrane repolarization
    modifier: DECREASED
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Functional studies of the two mutations associated with this phenotype
      showed almost complete loss of function with a dominant-negative effect.
    explanation: >-
      Demonstrates near-complete loss of Kv1.2 function with a dominant-negative
      mechanism for the loss-of-function variant class.
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      both P405L and I263T exert a clear dominant-negative effect on WT KV1.2
      channels.
    explanation: >-
      Identifies the specific loss-of-function variants and confirms the
      dominant-negative reduction of channel current.
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      KV1.2 belongs to the delayed rectifier class of potassium channels
      enabling efficient neuronal repolarization following an action potential.
    explanation: >-
      Establishes the normal delayed-rectifier/repolarization role of Kv1.2 that
      the loss-of-function variants degrade.
  downstream:
  - target: Neuronal Membrane Hyperexcitability
    causal_link_type: DIRECT
- name: Neuronal Membrane Hyperexcitability
  description: >-
    Impaired repolarization from reduced delayed-rectifier Kv1.2 current leaves
    the neuronal membrane hyperexcitable and prone to repetitive, prolonged
    firing. This is the classic loss-of-function route to hyperexcitability
    shared with other potassium-channelopathies and corroborated by the seizure
    phenotype of the Kcna2 knockout mouse.
  role: effector
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: neuronal action potential
    term:
      id: GO:0019228
      label: neuronal action potential
    modifier: ABNORMAL
  - preferred_term: regulation of membrane potential
    term:
      id: GO:0042391
      label: regulation of membrane potential
    modifier: ABNORMAL
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Loss-of-function mutations predict hyperexcitable neuronal membranes and
      repetitive neuronal firing due to impaired repolarization.
    explanation: >-
      States the mechanistic link from Kv1.2 loss of function to membrane
      hyperexcitability and repetitive firing.
  downstream:
  - target: Network Excitation-Inhibition Imbalance and Seizures
    causal_link_type: DIRECT
- name: Gain-of-Function Kv1.2 Conductance and Neuronal Silencing
  description: >-
    Gain-of-function variants (e.g. R297Q, L298F) shift voltage-dependent
    activation strongly in the hyperpolarizing direction and increase current
    amplitude, leaving Kv1.2 channels permanently open at physiological
    membrane potentials. The excess potassium conductance hyperpolarizes the
    membrane and electrically silences the affected neuron. Because Kv1.2 is
    expressed in both excitatory and inhibitory neurons, silencing of inhibitory
    interneurons is the leading hypothesis for how a potassium-channel gain of
    function paradoxically produces network hyperexcitability and severe
    epilepsy.
  role: central_effector
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: interneuron
    term:
      id: CL:0000099
      label: interneuron
  biological_processes:
  - preferred_term: potassium ion transmembrane transport
    term:
      id: GO:0071805
      label: potassium ion transmembrane transport
    modifier: INCREASED
  - preferred_term: regulation of membrane potential
    term:
      id: GO:0042391
      label: regulation of membrane potential
    modifier: ABNORMAL
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Two further individuals presented with a different and more severe
      epileptic encephalopathy phenotype. They carried mutations inducing a
      drastic gain-of-function effect leading to permanently open channels.
    explanation: >-
      Establishes the gain-of-function variant class with permanently open
      channels and its more severe phenotype.
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      R297Q and L298F predict permanently open channels at physiological
      membrane potentials, and electrical silencing by membrane hyperpolarization
      (as observed in oocytes).
    explanation: >-
      Shows the gain-of-function variants hyperpolarize and electrically silence
      neurons through excess potassium conductance.
  downstream:
  - target: Network Excitation-Inhibition Imbalance and Seizures
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Preferential silencing of inhibitory interneurons producing network disinhibition.
  - target: Cerebellar and Cortical Dysfunction
    causal_link_type: DIRECT
- name: Network Excitation-Inhibition Imbalance and Seizures
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Neuronal Hyperexcitability and Hypersynchrony"
  description: >-
    Both arms of the channelopathy converge on a disturbance of cortical
    excitatory/inhibitory balance producing neuronal hyperexcitability and
    hypersynchronous discharges. Loss-of-function variants tend to produce
    predominantly focal seizures with sleep-activated multifocal epileptiform
    discharges, whereas gain-of-function variants tend to produce generalized
    seizures; clinically this manifests as an early-onset epileptic
    encephalopathy.
  role: amplifier
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: regulation of membrane potential
    term:
      id: GO:0042391
      label: regulation of membrane potential
    modifier: ABNORMAL
  locations:
  - preferred_term: neocortex
    term:
      id: UBERON:0001950
      label: neocortex
  evidence:
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The main differences were (i) predominant focal (loss-of-function) versus
      generalized (gain-of-function) seizures and corresponding epileptic
      discharges with prominent sleep activation in most cases with
      loss-of-function mutations
    explanation: >-
      Links the two functional variant classes to focal versus generalized
      seizure semiology and the sleep-activated discharges of the
      loss-of-function group.
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Four individuals presented with febrile and multiple afebrile, often focal
      seizure types, multifocal epileptiform discharges strongly activated by
      sleep, mild to moderate intellectual disability, delayed speech
      development and sometimes ataxia.
    explanation: >-
      Documents the focal seizure semiology and sleep-activated multifocal
      discharges of the loss-of-function presentation.
  downstream:
  - target: Epilepsy
    causal_link_type: DIRECT
- name: Cerebellar and Cortical Dysfunction
  description: >-
    Kv1.2 dysfunction, most prominently in the gain-of-function group, disturbs
    cerebellar and cortical circuit function and is accompanied in about half of
    gain-of-function patients by atrophy of the cerebellum or even the whole
    brain. The resulting circuit dysfunction underlies the ataxia,
    intellectual disability, and delayed speech that accompany the epilepsy.
  role: effector
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: regulation of membrane potential
    term:
      id: GO:0042391
      label: regulation of membrane potential
    modifier: ABNORMAL
  locations:
  - preferred_term: cerebellum
    term:
      id: UBERON:0002037
      label: cerebellum
  evidence:
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      more severe epilepsy, developmental problems and ataxia, and atrophy of
      the cerebellum or even the whole brain in about half of the patients with
      gain-of-function mutations
    explanation: >-
      Documents cerebellar/whole-brain atrophy and prominent ataxia in the
      gain-of-function subgroup, supporting cerebellar and cortical dysfunction.
  downstream:
  - target: Ataxia
    causal_link_type: DIRECT
  - target: Intellectual Disability
    causal_link_type: DIRECT
phenotypes:
- name: Epilepsy
  category: Clinical
  description: >-
    Early-onset epilepsy is a defining feature, ranging from focal seizures in
    the loss-of-function group to generalized seizures in the gain-of-function
    group, within an epileptic encephalopathy.
  diagnostic: true
  phenotype_term:
    preferred_term: Epileptic encephalopathy
    term:
      id: HP:0200134
      label: Epileptic encephalopathy
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we identified four different de novo mutations in KCNA2, encoding the
      potassium channel KV1.2, in six isolated patients with epileptic
      encephalopathy
    explanation: >-
      Establishes epileptic encephalopathy as the core presentation of KCNA2
      disease.
- name: Focal-Onset Seizures
  category: Clinical
  description: >-
    Focal (often febrile and afebrile) seizures with multifocal epileptiform
    discharges strongly activated by sleep predominate in the loss-of-function
    group.
  phenotype_term:
    preferred_term: Focal-onset seizure
    term:
      id: HP:0007359
      label: Focal-onset seizure
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Four individuals presented with febrile and multiple afebrile, often focal
      seizure types, multifocal epileptiform discharges strongly activated by
      sleep, mild to moderate intellectual disability, delayed speech
      development and sometimes ataxia.
    explanation: >-
      Documents focal seizure types with sleep-activated multifocal discharges.
- name: Febrile Seizures
  category: Clinical
  description: >-
    Febrile seizures are part of the seizure spectrum, often at or near disease
    onset in the loss-of-function group.
  phenotype_term:
    preferred_term: Febrile seizure
    term:
      id: HP:0002373
      label: Febrile seizure (within the age range of 3 months to 6 years)
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Four individuals presented with febrile and multiple afebrile, often focal
      seizure types, multifocal epileptiform discharges strongly activated by
      sleep, mild to moderate intellectual disability, delayed speech
      development and sometimes ataxia.
    explanation: >-
      Documents febrile seizures within the loss-of-function seizure spectrum.
- name: Intellectual Disability
  category: Clinical
  description: >-
    Intellectual disability ranges from mild to moderate in the loss-of-function
    group to more severe developmental problems in the gain-of-function group.
  diagnostic: true
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Four individuals presented with febrile and multiple afebrile, often focal
      seizure types, multifocal epileptiform discharges strongly activated by
      sleep, mild to moderate intellectual disability, delayed speech
      development and sometimes ataxia.
    explanation: >-
      Documents mild to moderate intellectual disability in the loss-of-function
      presentation.
- name: Ataxia
  category: Clinical
  description: >-
    Ataxia is a frequent feature and is especially prominent and severe in the
    gain-of-function group, in which cerebellar or whole-brain atrophy occurs.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      more severe epilepsy, developmental problems and ataxia, and atrophy of
      the cerebellum or even the whole brain in about half of the patients with
      gain-of-function mutations
    explanation: >-
      Documents prominent ataxia with cerebellar/whole-brain atrophy in the
      gain-of-function subgroup.
- name: Delayed Speech and Language Development
  category: Clinical
  description: >-
    Delayed speech and language development accompanies the developmental delay
    and intellectual disability.
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Four individuals presented with febrile and multiple afebrile, often focal
      seizure types, multifocal epileptiform discharges strongly activated by
      sleep, mild to moderate intellectual disability, delayed speech
      development and sometimes ataxia.
    explanation: >-
      Documents delayed speech development in the KCNA2 phenotype.
- name: Cerebellar Atrophy
  category: Imaging
  description: >-
    Atrophy of the cerebellum, and in some patients of the whole brain, is seen
    in about half of individuals with gain-of-function variants.
  phenotype_term:
    preferred_term: Cerebellar atrophy
    term:
      id: HP:0001272
      label: Cerebellar atrophy
  evidence:
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      more severe epilepsy, developmental problems and ataxia, and atrophy of
      the cerebellum or even the whole brain in about half of the patients with
      gain-of-function mutations
    explanation: >-
      Documents cerebellar (and whole-brain) atrophy in the gain-of-function
      subgroup.
- name: Progressive Microcephaly
  category: Clinical
  description: >-
    In severe early-onset presentations, progressive microcephaly with
    progressive brain atrophy has been reported.
  phenotype_term:
    preferred_term: Progressive microcephaly
    term:
      id: HP:0000253
      label: Progressive microcephaly
  evidence:
  - reference: PMID:27117551
    reference_title: "Severe early-onset epileptic encephalopathy due to mutations in the KCNA2 gene: Expansion of the genotypic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patient presented since birth with intractable seizures, progressive
      microcephaly, developmental delay, and progressive brain atrophy.
    explanation: >-
      Documents progressive microcephaly and brain atrophy in a severe
      early-onset KCNA2 case.
genetic:
- name: KCNA2
  gene_term:
    preferred_term: KCNA2
    term:
      id: hgnc:6220
      label: KCNA2
  association: De Novo Loss-of-Function and Gain-of-Function Variants
  presence: Positive
  variant_origin: GERMLINE
  inheritance:
  - name: Autosomal Dominant (De Novo)
    inheritance_term:
      preferred_term: Autosomal dominant inheritance
      term:
        id: HP:0000006
        label: Autosomal dominant inheritance
  notes: >-
    De novo heterozygous KCNA2 variants act through two opposing molecular
    mechanisms: dominant-negative loss of function (e.g. P405L, I263T) and
    dominant gain of function (e.g. R297Q, L298F). A third gain-and-loss-of-function
    group combines a hyperpolarizing activation shift with reduced amplitude or
    an additional inactivation shift. The functional class correlates with the
    clinical subgroup.
  evidence:
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recently, de novo mutations in the gene KCNA2, causing either a
      dominant-negative loss-of-function or a gain-of-function of the
      voltage-gated K+ channel Kv1.2, were described to cause a new molecular
      entity within the epileptic encephalopathies.
    explanation: >-
      Establishes the two opposing functional mechanisms of de novo KCNA2
      variants.
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our study thus indicates well represented genotype-phenotype associations
      between three subgroups of patients with KCNA2 encephalopathy according to
      the electrophysiological features of the mutations.
    explanation: >-
      Documents three functional subgroups (loss, gain, and gain-and-loss of
      function) with correlated phenotypes.
diagnosis:
- name: KCNA2 Molecular Diagnosis
  description: >-
    Diagnosis is established by identifying a heterozygous pathogenic KCNA2
    variant, typically de novo, in a child with early-onset epileptic
    encephalopathy, intellectual disability, and often ataxia. Functional
    classification of the variant (loss versus gain of function) informs
    prognosis and, for gain-of-function variants, candidacy for
    4-aminopyridine.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: NCIT:C19770
      label: Molecular Analysis
    qualifiers:
    - predicate:
        preferred_term: has participant
        term:
          id: RO:0000057
          label: has participant
      value:
        preferred_term: KCNA2
        term:
          id: hgnc:6220
          label: KCNA2
  results: A heterozygous pathogenic KCNA2 variant establishes the diagnosis.
  evidence:
  - reference: PMID:27117551
    reference_title: "Severe early-onset epileptic encephalopathy due to mutations in the KCNA2 gene: Expansion of the genotypic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Whole-exome sequencing showed a novel de novo mutation in the KCNA2 gene:
      c.1120A > G (p.Thr374Ala).
    explanation: >-
      Illustrates molecular genetic (exome) confirmation of a de novo KCNA2
      variant establishing the diagnosis.
- name: EEG and Seizure Phenotyping
  description: >-
    EEG documents the epileptic encephalopathy and helps distinguish the
    functional subgroups — multifocal discharges with prominent sleep activation
    in loss-of-function disease versus generalized discharges in gain-of-function
    disease.
  diagnosis_term:
    preferred_term: electroencephalography
    term:
      id: NCIT:C38054
      label: Electroencephalography
  results: Multifocal sleep-activated (loss-of-function) or generalized (gain-of-function) epileptiform discharges.
  evidence:
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The main differences were (i) predominant focal (loss-of-function) versus
      generalized (gain-of-function) seizures and corresponding epileptic
      discharges with prominent sleep activation in most cases with
      loss-of-function mutations
    explanation: >-
      Documents the EEG differences that phenotype the two functional subgroups.
- name: Brain MRI
  description: >-
    Brain MRI assesses for cerebellar or whole-brain atrophy, which is seen in
    about half of gain-of-function patients, and excludes structural causes.
  diagnosis_term:
    preferred_term: magnetic resonance imaging procedure
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  results: May show cerebellar or whole-brain atrophy, especially with gain-of-function variants.
  evidence:
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      more severe epilepsy, developmental problems and ataxia, and atrophy of
      the cerebellum or even the whole brain in about half of the patients with
      gain-of-function mutations
    explanation: >-
      Documents the cerebellar/whole-brain atrophy seen on imaging in the
      gain-of-function subgroup.
differential_diagnoses:
- name: Other potassium-channel developmental and epileptic encephalopathies
  description: >-
    DEEs from other voltage-gated potassium channel genes (KCNQ2, KCNB1, KCNT1,
    KCNA1) overlap through early-onset epilepsy and developmental impairment and
    are distinguished by molecular testing and channel-specific
    electrophysiology.
  distinguishing_features:
  - A de novo pathogenic KCNA2 variant favors this disorder.
  - A causal variant in a different potassium-channel gene favors that channelopathy.
  evidence:
  - reference: PMID:29542386
    reference_title: "Potassium Channel Gain of Function in Epilepsy: An Unresolved Paradox."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      we describe the current state of the field regarding the gain-of-function
      potassium channel variants associated with epilepsy (KCNA2, KCNB1, KCND2,
      KCNH1, KCNH5, KCNJ10, KCNMA1, KCNQ2, KCNQ3, and KCNT1)
    explanation: >-
      Lists the potassium-channel epilepsy genes that constitute the molecular
      differential diagnosis.
- name: Dravet syndrome and myoclonic-atonic epilepsy
  description: >-
    The loss-of-function KCNA2 presentation with febrile and focal seizures can
    resemble Dravet syndrome (SCN1A) or myoclonic-atonic epilepsy, but focal
    seizures and sleep-activated multifocal discharges are atypical for those
    syndromes and molecular testing distinguishes them.
  distinguishing_features:
  - Multifocal epileptiform discharges strongly activated by sleep favor KCNA2.
  - An SCN1A variant favors Dravet syndrome.
animal_models:
- species: Mouse (Mus musculus)
  genotype: Kcna2 loss-of-function (Pingu) and Kcna2 knockout
  description: >-
    The Pingu mouse, carrying a Kcna2 loss-of-function mutation close to the
    human P405L residue, shows ataxia and growth retardation, and Kcna2 knockout
    mice have severe seizures and premature death — recapitulating the
    hyperexcitability predicted for the loss-of-function arm of the human
    disease.
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      the Pingu mouse presenting with ataxia and growth retardation carries a
      Kcna2 loss-of-function mutation, p.Ile402Thr, in close proximity to P405L;
      Kcna2 knock-out mice present with severe seizures and premature death
    explanation: >-
      Mouse Kcna2 loss-of-function and knockout models reproduce ataxia and
      seizures, supporting the loss-of-function hyperexcitability mechanism.
progression:
- phase: Infancy to Early Childhood
  notes: >-
    Onset is typically in infancy or early childhood with epilepsy and evolving
    developmental impairment; severe gain-and-loss-of-function presentations may
    begin in the neonatal period.
  evidence:
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our study thus indicates well represented genotype-phenotype associations
      between three subgroups of patients with KCNA2 encephalopathy according to
      the electrophysiological features of the mutations.
    explanation: >-
      The three functional subgroups differ in onset and severity, framing the
      disease trajectory.
- phase: Childhood onward
  notes: >-
    In milder loss-of-function disease seizures may remit in childhood while
    intellectual disability and ataxia persist; gain-of-function disease tends
    to a more severe, progressive course with cerebellar or whole-brain atrophy.
  evidence:
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      more severe epilepsy, developmental problems and ataxia, and atrophy of
      the cerebellum or even the whole brain in about half of the patients with
      gain-of-function mutations
    explanation: >-
      Documents the more severe, atrophy-associated trajectory of the
      gain-of-function subgroup.
treatments:
- name: 4-Aminopyridine (Gain-of-Function Precision Therapy)
  description: >-
    For patients carrying gain-of-function KCNA2 variants, the potassium-channel
    blocker 4-aminopyridine (fampridine) is a mechanism-tailored therapy: it
    antagonizes the gain-of-function defect in vitro and, in n-of-1 trials,
    benefitted 9 of 11 patients with gain-of-function variants, improving
    seizures, gait, ataxia, alertness, cognition, or speech. It is not
    appropriate for loss-of-function variants, where blocking residual Kv1.2
    current would be expected to worsen hyperexcitability.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: 4-aminopyridine
      term:
        id: CHEBI:34385
        label: 4-aminopyridine
  evidence:
  - reference: PMID:34516822
    reference_title: "4-Aminopyridine is a promising treatment option for patients with gain-of-function KCNA2-encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      we show for KCNA2-encephalopathy that the K+ channel blocker
      4-aminopyridine can antagonize gain-of-function defects caused by variants
      in the KV1.2 subunit in vitro, by reducing current amplitudes and negative
      shifts of steady-state activation and increasing the firing rate of
      transfected neurons.
    explanation: >-
      Demonstrates the mechanistic rationale — 4-aminopyridine antagonizes the
      gain-of-function Kv1.2 defect in vitro.
  - reference: PMID:34516822
    reference_title: "4-Aminopyridine is a promising treatment option for patients with gain-of-function KCNA2-encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In n-of-1 trials carried out in nine different centers, 9 of 11 patients
      carrying such variants benefitted from treatment with 4-aminopyridine.
    explanation: >-
      Documents clinical benefit of 4-aminopyridine in gain-of-function KCNA2
      patients.
- name: Antiseizure Medication
  description: >-
    Seizures are managed with antiseizure medications with variable response.
    Choice may be informed by the functional variant class; response is often
    incomplete, and some loss-of-function patients become seizure-free over
    childhood.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: valproic acid
      term:
        id: CHEBI:39867
        label: valproic acid
  evidence:
  - reference: PMID:25751627
    reference_title: "De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Seizures and ataxia responded poorly to antiepileptic drugs (topiramate,
      oxcarbazepine, valproic acid, bromide), including acetazolamide (known to
      be effective in EA1 caused by mutations in KCNA1
    explanation: >-
      Documents the variable/incomplete response of KCNA2 seizures to
      conventional antiseizure medications including valproic acid.
- name: Genetic Counseling
  description: >-
    Genetic counseling addresses the de novo dominant mechanism, the generally
    low recurrence risk (with attention to rare parental mosaicism), and the
    prognostic and treatment implications of the functional variant class.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
- name: Supportive and Developmental Care
  description: >-
    Multidisciplinary supportive care — developmental therapies and management
    of intellectual disability, ataxia, and speech delay — is a mainstay given
    the neurodevelopmental impairment.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
discussions:
- discussion_id: gap_kcna2_gof_seizure_paradox
  prompt: >-
    How does a gain of function of the Kv1.2 potassium channel — which
    hyperpolarizes and electrically silences individual neurons — paradoxically
    produce a more severe epilepsy than the loss-of-function variants, and is
    preferential silencing of inhibitory interneurons the correct explanation at
    the network level?
  kind: OPEN_QUESTION
  status: OPEN
  attaches_to:
  - pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing
  - pathophysiology#Network Excitation-Inhibition Imbalance and Seizures
  rationale: >-
    At the single-neuron level, increased Kv1.2 conductance hyperpolarizes and
    silences neurons, yet clinically the gain-of-function variants cause more
    severe, generalized epilepsy than the loss-of-function variants that produce
    classic hyperexcitability. The leading resolution is that gain of function
    preferentially silences inhibitory interneurons, disinhibiting the network,
    but this cell-type-specific mechanism has not been definitively established
    in human cortical circuits and remains, in the words of the review
    literature, an unresolved paradox with direct consequences for whether
    channel-blocking (4-aminopyridine) versus channel-opening strategies are
    appropriate for a given variant.
  evidence:
  - reference: PMID:29542386
    reference_title: "Potassium Channel Gain of Function in Epilepsy: An Unresolved Paradox."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      This development has been difficult to understand as traditionally
      potassium channel loss-of-function, not gain-of-function, has been
      associated with hyperexcitability disorders.
    explanation: >-
      States the core paradox that gain-of-function potassium-channel variants
      cause epilepsy despite the traditional loss-of-function view of
      hyperexcitability.
  - reference: PMID:29542386
    reference_title: "Potassium Channel Gain of Function in Epilepsy: An Unresolved Paradox."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      A surprising finding of these efforts is the recognition that gain of
      function potassium channel variants are actually associated with certain
      types of epilepsy, such as malignant migrating partial seizures of infancy
      or early-onset epileptic encephalopathy.
    explanation: >-
      Confirms the association of potassium-channel gain of function with
      early-onset epileptic encephalopathy, the phenomenon requiring a
      network-level explanation.
  proposed_experiments:
  - experiment_id: exp_kcna2_gof_interneuron_silencing
    name: Cell-type-resolved test of interneuron silencing in KCNA2 gain of function
    description: >-
      In human iPSC-derived or mouse cortical networks expressing a KCNA2
      gain-of-function variant, measure firing and intrinsic excitability
      separately in excitatory neurons and inhibitory interneurons, and test
      whether interneurons are preferentially silenced and whether the resulting
      network is hyperexcitable, with reversal by 4-aminopyridine.
    experiment_type:
      preferred_term: cell-type-resolved electrophysiology experiment
    perturbations:
    - name: KCNA2 gain-of-function expression
      target: pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing
      genes:
      - preferred_term: KCNA2
        term:
          id: hgnc:6220
          label: KCNA2
      description: >-
        Express a gain-of-function KCNA2 variant (e.g. R297Q or L298F) across a
        cortical network with excitatory and inhibitory neurons distinguished.
    readouts:
    - name: Interneuron versus principal-neuron firing and network activity
      target: pathophysiology#Network Excitation-Inhibition Imbalance and Seizures
      biological_processes:
      - preferred_term: regulation of membrane potential
        term:
          id: GO:0042391
          label: regulation of membrane potential
        modifier: ABNORMAL
      assays:
      - preferred_term: patch-clamp recording
      - preferred_term: multielectrode array recording
      direction: POSITIVE
    controls:
    - name: Wild-type KCNA2
      description: Wild-type Kv1.2 expressed in the same network.
    - name: 4-aminopyridine versus vehicle
      description: Matched networks treated with 4-aminopyridine or vehicle.
    decision_criterion: >-
      Preferential interneuron silencing is supported if inhibitory interneurons
      show disproportionately reduced firing while the network becomes
      hyperexcitable, and if 4-aminopyridine restores interneuron firing and
      network balance.
    would_support:
    - pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing
    - pathophysiology#Network Excitation-Inhibition Imbalance and Seizures
- discussion_id: gap_kcna2_4ap_generalization
  prompt: >-
    Does the benefit of 4-aminopyridine generalize across all gain-of-function
    KCNA2 variants and to the gain-and-loss-of-function subgroup, and can
    functional variant classification prospectively predict which patients
    respond?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing
  rationale: >-
    The n-of-1 4-aminopyridine trials showed benefit in 9 of 11 gain-of-function
    patients, but two did not benefit and one worsened, and the
    gain-and-loss-of-function subgroup — which combines an activation shift with
    reduced amplitude — was not clearly addressed. Whether response can be
    predicted prospectively from the precise biophysical fingerprint of each
    variant, and whether the gain-and-loss group behaves like the gain group for
    treatment selection, is not established, yet it determines who should receive
    channel-blocking therapy.
  evidence:
  - reference: PMID:34516822
    reference_title: "4-Aminopyridine is a promising treatment option for patients with gain-of-function KCNA2-encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In n-of-1 trials carried out in nine different centers, 9 of 11 patients
      carrying such variants benefitted from treatment with 4-aminopyridine.
    explanation: >-
      Documents the incomplete response rate that motivates the need for
      prospective response prediction.
  - reference: PMID:29050392
    reference_title: "Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our study thus indicates well represented genotype-phenotype associations
      between three subgroups of patients with KCNA2 encephalopathy according to
      the electrophysiological features of the mutations.
    explanation: >-
      Establishes the three functional subgroups, including the
      gain-and-loss-of-function group whose treatment response is uncertain.
  proposed_experiments:
  - experiment_id: exp_kcna2_4ap_variant_response_map
    name: Biophysical response map for 4-aminopyridine across KCNA2 variants
    description: >-
      Across a panel of KCNA2 variants spanning pure gain, gain-and-loss, and
      loss of function, quantify the biophysical fingerprint (activation shift,
      amplitude, inactivation) and the in-vitro rescue by 4-aminopyridine, then
      correlate with clinical response in treated patients to build a
      prospective response predictor.
    experiment_type:
      preferred_term: genotype-response correlation study
    perturbations:
    - name: KCNA2 variant panel expression
      target: pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing
      genes:
      - preferred_term: KCNA2
        term:
          id: hgnc:6220
          label: KCNA2
      description: >-
        Express each KCNA2 variant class and characterize its biophysical
        fingerprint and 4-aminopyridine sensitivity.
    readouts:
    - name: Channel biophysics and 4-aminopyridine rescue
      target: pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing
      biological_processes:
      - preferred_term: potassium ion transmembrane transport
        term:
          id: GO:0071805
          label: potassium ion transmembrane transport
        modifier: INCREASED
      assays:
      - preferred_term: voltage-clamp recording
      direction: NEGATIVE
    controls:
    - name: Wild-type KCNA2
      description: Wild-type Kv1.2 characterized under identical conditions.
    decision_criterion: >-
      A predictor is supported if the in-vitro 4-aminopyridine rescue of a
      variant's biophysical defect correlates with clinical response across the
      treated cohort, and if the gain-and-loss group segregates predictably.
    would_support:
    - pathophysiology#Gain-of-Function Kv1.2 Conductance and Neuronal Silencing

📚

References & Deep Research

References

5

PMID:25751627

De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy.

No top-level findings curated for this source.

PMID:29050392

Clinical spectrum and genotype-phenotype associations of KCNA2-related encephalopathies.

No top-level findings curated for this source.

PMID:34516822

4-Aminopyridine is a promising treatment option for patients with gain-of-function KCNA2-encephalopathy.

No top-level findings curated for this source.

PMID:27117551

Severe early-onset epileptic encephalopathy due to mutations in the KCNA2 gene: Expansion of the genotypic and phenotypic spectrum.

No top-level findings curated for this source.

PMID:29542386

Potassium Channel Gain of Function in Epilepsy: An Unresolved Paradox.

No top-level findings curated for this source.

KCNA2-Related Developmental and Epileptic Encephalopathy

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