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Inheritance

2

Autosomal dominant HP:0000006

Heterozygous and usually de novo for the gain-of-function missense variants and duplications.

Autosomal dominant inheritance

Show evidence (1 reference)

PMID:27164707 SUPPORT Human Clinical

"A de novo heterozygous missense mutation was identified in the FHF1 gene (FHF1AR114H, FHF1BR52H) in the 2 affected siblings"

Establishes the de novo heterozygous mechanism. Note the variant was de novo yet present in two siblings, which implies parental germline mosaicism and is relevant to recurrence-risk counselling.

Autosomal recessive HP:0000007

A separate, later-recognised biallelic loss-of-function route to the same clinical syndrome, established by long-read sequencing in an exome-negative patient. This is not a variant of the dominant mechanism but its inverse.

Autosomal recessive inheritance

Show evidence (1 reference)

PMID:37286232 SUPPORT Human Clinical

"FGF12 heterozygous recurrent missense variants with gain-of-function or heterozygous entire duplication of FGF12 are known causes of epilepsy, but biallelic SNVs/SVs have never been described"

States both the established dominant mechanisms and the novelty of the biallelic route at the time of report.

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Discussions and Knowledge Gaps

3

Does promptly starting a sodium channel blocker improve neurodevelopmental outcome in FGF12-related epilepsy, or does outcome track the variant and phenotype regardless of when treatment starts?

CONTROVERSY OPEN controversy_does_prompt_sodium_channel_blockade_change_outcome

Attached to

pathophysiology#Depolarizing Shift in Nav1.6 Fast Inactivation pathophysiology#Early-Onset Refractory Seizures

Three cohorts now speak to this question and they do not agree. Two published within a year of each other reach opposite conclusions. One reports that eight patients promptly started on sodium channel blockers became seizure-free with good developmental outcomes while four developed encephalopathy, and frames early precision therapy as consequential. The other looked for exactly this association and states that it did not find a clear correlation between sodium-channel-blocker treatment, its timing, and neurodevelopmental outcome. The mechanistic rationale is strong and undisputed - the dominant lesion is a sodium channel gain of function, so blocking the channel is the rational target - which makes it easy to assume the clinical benefit follows. It may not. The competing explanation is confounding by severity: milder variants produce both better outcomes and easier seizure control, so treatment responsiveness could be a marker of a mild phenotype rather than a cause of a good outcome. A third cohort of 27 patients reports sodium channel blockers commonly associated with clinical improvement, but it declines to overclaim - responses are described as heterogeneous and the authors call for systematic studies - and it speaks to seizure improvement rather than to the developmental outcome the other two dispute, so it does not break the tie. All three cohorts are small and none is randomised. This matters more than a typical unresolved question because it bears directly on what clinicians do at diagnosis, and because a precision-therapy claim that turns out to be confounded is harder to retract than one never made. The entry therefore curates the supporting cohort as SUPPORT and the null cohort as REFUTE on the same treatment, so the disagreement is visible in the structured data rather than only in prose. Note that the deep-research report used to build this entry asserted the optimistic version as a quote attributed to both papers; its own validator flagged that quote as unsupported, and inspection showed one of the two papers states the opposite.

Proposed experiments

Severity-stratified analysis of treatment timing

exp_severity_stratified_treatment_timing

Pool the published FGF12 cohorts and stratify outcome by variant and by pre-treatment seizure burden before testing the effect of sodium-channel-blocker timing. If the timing effect survives stratification by baseline severity, the precision-therapy claim is supported; if it disappears, the association was confounding by severity and the claim should be withdrawn.

How do gain-of-function and loss-of-function FGF12 variants produce the same clinical syndrome?

KNOWLEDGE GAP OPEN gap_opposite_direction_variants_converge_on_one_syndrome

Attached to

pathophysiology#FGF12 Gain-of-Function Missense Variant pathophysiology#Biallelic FGF12 Loss of Function

Heterozygous missense variants increase FHF1-mediated modulation of sodium channel inactivation; biallelic structural and single-nucleotide variants reduce or remove it, confirmed by expression analysis, structural reasoning and a Drosophila assay. Both cause developmental and epileptic encephalopathy. The entry keeps them as separate trigger nodes converging on the clinical endpoint rather than routing the recessive arm through the dominant chain, because nothing establishes that they pass through the same intermediate states - and if they did, the direction of the channel change would have to be the same, which it is not. The practical stake is therapeutic: a sodium channel blocker is mechanistically indicated for the gain-of-function arm and potentially harmful for the loss-of-function arm, so treating the two as one disease for management purposes could be actively wrong.

Proposed experiments

Channel-level comparison of loss- and gain-of-function FGF12 alleles

exp_loss_versus_gain_channel_phenotype

Measure Nav1.6 and Nav1.2 inactivation kinetics and neuronal excitability in the same preparation for a gain-of-function missense allele and for FHF1 depletion, and determine whether excitability rises in both cases or whether the loss-of-function arm reaches seizures through a different excitability change. The answer directly determines whether sodium channel blockade is rational for biallelic patients.

Can a model in which every animal dies within a month inform a disorder that includes drug-responsive epilepsy with normal cognition?

HUMAN MODEL MISMATCH OPEN mismatch_uniformly_lethal_mouse_versus_a_broad_human_spectrum

Attached to

pathophysiology#Cardiac Arrhythmia

Every Fhf1R52H/+ mouse experiences seizures or seizure-like episodes ending lethally between 12 and 26 days of age. The human spectrum carrying the same recurrent variant class now extends to patients aged up to 38 years with favourable cognitive outcomes. The model is a faithful and valuable representation of the severe pole - it is the source of the cardiac and sudden-death findings, which would be hard to establish any other way - but it cannot be used to reason about the milder end, and that is precisely where the open clinical question about treatment timing now lies. The mismatch also has a specific consequence for the cardiac arm: because the model dies young and uniformly, it cannot tell us the lifetime arrhythmia risk for a patient who survives infancy, which is the number a cardiologist would want.

Proposed experiments

Cardiac screening in older FGF12 patients

exp_cardiac_screening_in_surviving_patients

Systematically screen the surviving FGF12 cohort, including the adults at the favourable-outcome pole, with ECG and ambulatory rhythm monitoring, to establish whether the cardiac arm demonstrated in the mouse is present in humans who live beyond infancy and whether it warrants surveillance.

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Pathophysiology

9

FGF12 Gain-of-Function Missense Variant

The dominant lesion, most often p.Arg52His in the FHF1B isoform (equivalently p.Arg114His in FHF1A). Whole-gene duplication is an alternative dominant route acting through increased dosage rather than altered protein. FHFs were candidate epilepsy genes precisely because they bind Nav channels, which is how the gene was found.

Downstream

Weakened FHF1 Binding to the Nav Cytoplasmic Tail The variant's first measured consequence is on the protein-protein interaction.

Show evidence (2 references)

PMID:27164707 SUPPORT Human Clinical

"A de novo heterozygous missense mutation was identified in the FHF1 gene (FHF1AR114H, FHF1BR52H) in the 2 affected siblings"

Identifies the recurrent variant in both isoform numbering systems.

PMID:27164707 SUPPORT In Vitro

"Our data demonstrate that gain-of-function FHF mutations can cause neurologic disorder, and expand the repertoire of genetic causes (FHF1) and mechanisms (altered Nav gating) underlying EOEE and cerebellar atrophy"

The founding study's own statement of the gain-of-function mechanism and of altered Nav gating as the mechanistic class.

Weakened FHF1 Binding to the Nav Cytoplasmic Tail

The counterintuitive step, and the reason it is curated as its own node. The gain-of-function effect is predicted to arise from a *weaker* interaction between mutant FHF1 and the sodium channel cytoplasmic tail - a loss of binding producing a gain of channel function. Collapsing this into the downstream channel node would hide the fact that the direction of the binding change is opposite to the direction of the functional change.

sodium channel regulator activity GO:0017080 ⚠ ABNORMAL

Downstream

Depolarizing Shift in Nav1.6 Fast Inactivation Altered binding changes the channel's inactivation behaviour.

Show evidence (1 reference)

PMID:27164707 SUPPORT In Vitro

"Surprisingly, the gain-of-function effect is predicted to result from weaker interaction of mutant FHF1 with the Nav cytoplasmic tail"

States the inverted relationship between binding strength and functional outcome, including the authors' own note that it is surprising.

Depolarizing Shift in Nav1.6 Fast Inactivation

The channel-level readout: mutant FHF1 enhances the depolarizing shift in the voltage-dependence of Nav1.6 fast inactivation, so channels remain available at potentials where they would normally be inactivated.

regulation of sodium ion transmembrane transport GO:1902305 ↕ DYSREGULATED

voltage-gated sodium channel activity GO:0005248 ↑ INCREASED

Downstream

Increased Intrinsic Neuronal Excitability Greater sodium channel availability raises the excitability of the neuron.

Show evidence (1 reference)

PMID:27164707 SUPPORT In Vitro

"The mutant FHF1 proteins had a strong gain-of-function phenotype in transfected Neuro2A cells, enhancing the depolarizing shifts in Nav1.6 voltage-dependent fast inactivation, predicting increased neuronal excitability"

The direct biophysical measurement, together with the excitability consequence the authors predict from it.

Increased Intrinsic Neuronal Excitability

Neurons carrying the variant are expected to fire more readily. Kept separate from the channel biophysics node because excitability is a cell-level property rather than a channel property. The status of this node is weaker than the nodes on either side of it: the founding study measured channel gating in Neuro2A cells and *predicted* increased excitability rather than recording it, so this is curated as a predicted step. No cell type is bound, because the supporting measurement was made in a neuroblastoma line rather than in an identified neuronal population.

Downstream

Epileptiform Network Activity Hyperexcitable neurons generate epileptiform network discharge.

Show evidence (1 reference)

PMID:27164707 SUPPORT In Vitro

"enhancing the depolarizing shifts in Nav1.6 voltage-dependent fast inactivation, predicting increased neuronal excitability"

The excitability claim as stated by the founding study. Curated as predicted rather than directly measured at this point in the literature.

Epileptiform Network Activity

Spontaneous epileptiform discharge at the network level, demonstrated by cortical EEG in the genotype-matched knock-in mouse.

Animal models

Fhf1 p.Arg52His knock-in mouse Mouse recapitulates Spontaneous epileptiform events on cortical EEG in a genotype-matched animal.

Downstream

Early-Onset Refractory Seizures Network discharge manifests as the clinical seizure disorder.

Cardiac Arrhythmia The demonstrated route. Heart rate falls abruptly within seconds of seizure onset, attributed to a parasympathetic surge - so the arrhythmia in this model is seizure-triggered rather than a standing consequence of the cardiac channel defect.

Show evidence (1 reference)

PMID:33982289 SUPPORT Model Organism

"Spontaneous epileptiform events in Fhf1R52H/+ mice were assessed by cortical electroencephalography (EEG) and video monitoring"

Establishes that spontaneous epileptiform activity is the measured endpoint in the knock-in mouse.

Altered Cardiac Sodium Channel Function

FHF1 binds Nav1.5 in cardiomyocytes by the same mechanism it uses on neuronal channels, so the variant has a direct cardiac substrate independent of seizures. This node is drawn from the variant rather than from the neuronal chain, because the two organs are affected in parallel by one molecular lesion.

cardiac muscle cell CL:0000746

voltage-gated sodium channel activity involved in cardiac muscle cell action potential GO:0086006 ⚠ ABNORMAL

Downstream

Cardiac Arrhythmia Downgraded from a direct edge. The cardiac channel defect is demonstrable, but the same paper reports that heart rhythm is normal in these animals before a seizure, so the channel change is not sufficient on its own to produce arrhythmia. It is curated as a permissive substrate rather than a direct cause.

Show evidence (1 reference)

PMID:33982289 SUPPORT In Vitro

"Although ectopic overexpression of FHF1BR52H in cardiomyocytes induced a 15-mV depolarizing shift in voltage of steady-state sodium channel inactivation and slowed the rate of channel inactivation, heart rhythm was normal in Fhf1R52H/+ mice prior to seizure"

Establishes the cardiac channel effect and, in the same sentence, its limit: the channel change is real but does not by itself produce a resting rhythm disturbance. Classified IN_VITRO because the channel measurement is ectopic adenoviral overexpression in cardiomyocytes, not an intact-animal observation.

Cardiac Arrhythmia

Arrhythmia and bradycardia in the knock-in mouse, contributing to sudden death. The cardiac arm is what distinguishes this disorder's risk profile from most other developmental and epileptic encephalopathies, because the same lesion acts on the heart and the brain.

Animal models

Fhf1 p.Arg52His knock-in mouse Mouse recapitulates Ictal bradyarrhythmia. Basal rhythm is explicitly normal, so the model shows a seizure-triggered cardiac event rather than a standing cardiac phenotype - the two readouts below record that contrast directly.

Show evidence (2 references)

PMID:33982289 SUPPORT Model Organism

"Within 2-53 s after lethal seizure onset, heart rate abruptly declined from 572 +/- 16 bpm to 108 +/- 15 bpm, suggesting a parasympathetic surge accompanying seizures that may have contributed to SUDEP"

The actual arrhythmia result and its proposed mechanism, with the timing that establishes it as seizure-triggered. This replaces an earlier citation of the paper's methods sentence, which described what was measured rather than what was found.

PMID:33982289 SUPPORT Model Organism

"All Fhf1R52H/+ mice experienced seizure or seizurelike episodes with lethal ending between 12 and 26 days of age"

Records the uniform lethal outcome in the model within a narrow age window.

Early-Onset Refractory Seizures

Seizures beginning in the neonatal or early infantile period. In the severe DEE47 phenotype they are refractory and accompanied by developmental impairment; at the milder end of the spectrum they respond to medication.

Show evidence (1 reference)

PMID:40488543 SUPPORT Human Clinical

"All developed epilepsy before 5 months, with 70% achieving seizure remission by 6 months with antiseizure medication (ASM), leading to good neurodevelopmental outcomes"

Establishes the early onset shared across the spectrum, and simultaneously documents the drug-responsive pole with a remission figure.

Biallelic FGF12 Loss of Function

A separate, recessive route to the same clinical syndrome. Biallelic intragenic structural variants, and a biallelic single-nucleotide variant, reduce or remove FHF1 function - the opposite direction of effect to the dominant missense variants. Curated as its own trigger node rather than folded into the gain-of-function chain, because both increased and decreased FHF1-mediated channel modulation destabilise network excitability and the entry should not imply they act through the same intermediate states.

Downstream

Early-Onset Refractory Seizures Reaches the same clinical endpoint by an opposite-direction molecular route. Marked indirect with unknown intermediates because no source establishes the intervening steps for the recessive arm.

Show evidence (2 references)

PMID:37286232 SUPPORT Human Clinical

"We discovered biallelic intragenic structural variations (SVs) in FGF12 by applying long-read whole genome sequencing to an exome-negative patient with developmental and epileptic encephalopathy (DEE)"

Establishes the biallelic structural-variant route and the sequencing technology that was required to see it.

PMID:37286232 SUPPORT In Vitro

"highly sensitive gene expression analyses using lymphoblastoid cells from the patient with biallelic SVs, structural considerations, and Drosophila in vivo functional analysis of the SNV were performed, confirming loss-of-function"

Confirms the direction of effect as loss of function across three independent lines of evidence.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

5

Cardiovascular 1

Cardiac Arrhythmia HP:0011675

Show evidence (2 references)

PMID:40897676 SUPPORT Human Clinical

"We report the first known case of a 9-year-old male with early-onset epilepsy, syncope, and ictal asystole-requiring pacemaker implantation at the age of seven-associated with a pathogenic variant in FGF12"

A human cardiac event in a genotype-confirmed patient, severe enough to require a pacemaker. This is a single case report, so it establishes that the cardiac arm occurs in humans without establishing how often.

PMID:40897676 SUPPORT Human Clinical

"A holter ECG confirmed a 25-s peri-ictal asystole in an ambulatory record"

Documents the asystole objectively and shows it is peri-ictal, matching the seizure-triggered mechanism described in the mouse.

Nervous System 4

Early-Onset Seizures HP:0001250

Show evidence (2 references)

PMID:40488543 SUPPORT Human Clinical

"All developed epilepsy before 5 months"

Establishes the upper bound on age at onset across the cohort.

PMID:40488543 SUPPORT Human Clinical

"We aim to refine the electroclinical phenotype and outcomes of 10 unpublished patients (2-38 years old) with these recurrent pathogenic variants in the FGF12 gene without DEE"

Establishes that patients carrying the same recurrent variants can reach adulthood without developmental and epileptic encephalopathy, which is what broadens the phenotype beyond the original lethal description.

Developmental and Epileptic Encephalopathy Global developmental delay HP:0001263

Show evidence (1 reference)

PMID:40488543 SUPPORT Human Clinical

"have repeatedly been associated with developmental and epileptic encephalopathy-47 (DEE47; Mendelian Inheritance in Man #617166) with poor outcome"

Records the severe, poor-outcome phenotype the recurrent variants were originally associated with.

Intellectual Disability FREQUENT HP:0001249

Show evidence (1 reference)

PMID:42057324 SUPPORT Human Clinical

"79.1% of patients exhibited moderate to severe intellectual disability"

Quantifies moderate-to-severe intellectual disability across a 27-patient pooled cohort. 79.1% sits at the top of the 30-79% FREQUENT band rather than in VERY_FREQUENT, so the band is assigned conservatively.

Cerebellar Atrophy HP:0001272

Show evidence (3 references)

PMID:27164707 SUPPORT Human Clinical

"we performed whole-exome sequencing in a family quintet with 2 siblings with a lethal disease characterized by EOEE and cerebellar atrophy"

Records cerebellar atrophy as part of the phenotype in the founding family, quoted from the abstract body rather than from the paper's title.

PMID:40488543 SUPPORT Human Clinical

"patients with favorable neurodevelopmental outcomes and FGF12 pathogenic variants showed no signs of cerebellar atrophy"

Establishes that cerebellar atrophy is absent at the favourable-outcome pole, making it severity-associated rather than universal.

PMID:42057324 SUPPORT Human Clinical

"Brain MRI showed mild cerebral and/or cerebellar atrophy in 41.6% of cases"

Supplies the pooled frequency across 27 patients, consistent with a severity-associated rather than universal finding.

🧬

Genetic Associations

1

FGF12 (FGF12 encodes fibroblast growth factor homologous factor 1 (FHF1), an intracellular, non-secreted FGF that modulates voltage-gated sodium channel inactivation. Three variant classes cause disease: recurrent heterozygous gain-of-function missense variants (p.Arg52His, p.Gly50Ser), whole-gene duplication, and - separately - biallelic loss-of-function structural or single-nucleotide variants.)

Gene: FGF12 hgnc:3668 relationship_type: CAUSATIVE

Show evidence (1 reference)

PMID:37286232 SUPPORT Human Clinical

"FGF12 heterozygous recurrent missense variants with gain-of-function or heterozygous entire duplication of FGF12 are known causes of epilepsy, but biallelic SNVs/SVs have never been described"

Enumerates the dominant variant classes and marks the biallelic route as newly described.

💊

Medical Actions

1

Sodium Channel Blocker Therapy

Action: Pharmacotherapy NCIT:C15986

Agent: carbamazepine CHEBI:3387 phenytoin CHEBI:8107 lamotrigine CHEBI:6367 oxcarbazepine CHEBI:7824

Because the dominant mechanism is a sodium channel gain of function, sodium channel blockers are the mechanistically indicated treatment, and this is one of relatively few developmental and epileptic encephalopathies with a candidate precision therapy. Whether prompt treatment actually improves developmental outcome is disputed between two recent cohorts - see the controversy discussion, which this treatment entry should be read alongside.

Mechanism Target:

INHIBITS Depolarizing Shift in Nav1.6 Fast Inactivation — Sodium channel blockers act on the channel whose inactivation the variant shifts.

Show evidence (4 references)

PMID:42185328 SUPPORT Human Clinical

"8 patients promptly started on sodium channel blockers became seizure-free with good developmental outcomes while 4 developed DEE"

The cohort supporting a benefit from prompt sodium-channel-blocker therapy.

PMID:40488543 REFUTE Human Clinical

"we did not find a clear correlation between treatment with sodium channel blockers, its timing, and neurodevelopmental outcome"

The cohort that looked for the same association and did not find it. Curated as REFUTE against the precision-therapy claim so that the disagreement is visible on the treatment itself rather than only in prose.

PMID:42057324 SUPPORT Human Clinical

"While treatment responses were heterogeneous, sodium channel blockers were commonly associated with clinical improvement"

A third cohort, curated PARTIAL rather than SUPPORT because it reports an association with seizure improvement while explicitly describing responses as heterogeneous - and because association with clinical improvement is a weaker claim than the developmental-outcome benefit the other two cohorts disagree about.

+ 1 more reference

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Diagnosis

1

Long-Read Genome Sequencing

Standard exome sequencing does not resolve every FGF12 case. The biallelic structural variants were found only by applying long-read whole genome sequencing to a patient whose exome was negative, so a negative exome does not exclude the gene.

Whole Genome Sequencing NCIT:C101294

Show evidence (1 reference)

PMID:37286232 SUPPORT Human Clinical

"We discovered biallelic intragenic structural variations (SVs) in FGF12 by applying long-read whole genome sequencing to an exome-negative patient with developmental and epileptic encephalopathy (DEE)"

Directly supports the claim that a negative exome does not exclude FGF12 and that long-read sequencing has additional diagnostic yield here.

🐁

Animal Models

1

Fhf1 p.Arg52His knock-in mouse

CRISPR knock-in carrying the recurrent human variant. The model that establishes the cardiac arm of the disorder, and the reason sudden death is treated as mechanistically linked rather than incidental.

Species

Mouse

Genotype

Fhf1R52H/+

Publication

PMID:33982289

Pathograph links

Epileptiform Network Activity recapitulates fidelity: high Spontaneous epileptiform events on cortical EEG in a genotype-matched animal.

Readouts

Cortical EEG epileptiform events

Direction: INCREASED

Interpretation: Spontaneous epileptiform activity assessed by EEG with video monitoring.

Show evidence (1 reference)

PMID:33982289 SUPPORT Model Organism

"Spontaneous epileptiform events in Fhf1R52H/+ mice were assessed by cortical electroencephalography (EEG) and video monitoring"

The electrophysiological measurement behind this readout.

Show evidence (1 reference)

PMID:33982289 SUPPORT Model Organism

"The Arg52His mutation was introduced into fertilized eggs by CRISPR (clustered regularly interspaced short palindromic repeats) editing to generate Fhf1R52H/F+ mice"

Establishes that the model carries the actual human variant rather than a surrogate lesion.

Cardiac Arrhythmia recapitulates fidelity: moderate Ictal bradyarrhythmia. Basal rhythm is explicitly normal, so the model shows a seizure-triggered cardiac event rather than a standing cardiac phenotype - the two readouts below record that contrast directly.

Limitations: The mouse phenotype is uniformly lethal between 12 and 26 days of age, whereas the human disorder spans a lethal encephalopathy through to drug-responsive epilepsy with favourable cognitive outcome. The model therefore represents the severe pole only and cannot speak to the milder end of the spectrum, which is where the treatment question now sits.

Readouts

Basal heart rhythm prior to seizure

Direction: UNCHANGED

Interpretation: No intrinsic cardiac phenotype between seizures. This is a real negative result and is what makes the downgrade of the channel-to-arrhythmia edge correct: the cardiac sodium channel defect is demonstrable in vitro yet produces no measurable resting rhythm abnormality in the intact animal.

Show evidence (2 references)

PMID:33982289 SUPPORT Model Organism

"heart rhythm was normal in Fhf1R52H/+ mice prior to seizure"

States the negative basal result directly.

+ 1 more reference

Ictal heart rate

Direction: DECREASED

Interpretation: An abrupt fall in heart rate within seconds of seizure onset, attributed to a parasympathetic surge.

Show evidence (1 reference)

PMID:33982289 SUPPORT Model Organism

"Within 2-53 s after lethal seizure onset, heart rate abruptly declined from 572 +/- 16 bpm to 108 +/- 15 bpm, suggesting a parasympathetic surge accompanying seizures that may have contributed to SUDEP"

The ictal measurement, with the timing that establishes it as following seizure onset rather than preceding it.

Show evidence (1 reference)

PMID:33982289 SUPPORT Model Organism

"All Fhf1R52H/+ mice experienced seizure or seizurelike episodes with lethal ending between 12 and 26 days of age"

Supports the model as informative for sudden death, and records the narrow age window that also defines its limitation.

{ }

Source YAML

click to show

name: FGF12-Related Developmental and Epileptic Encephalopathy
creation_date: "2026-08-20T00:20:00Z"
category: Mendelian
synonyms:
- Developmental and epileptic encephalopathy 47
- DEE47
- EIEE47
- FHF1-related epileptic encephalopathy
- FGF12-related epilepsy
description: >-
  FGF12-related developmental and epileptic encephalopathy (DEE47) is caused by
  heterozygous de novo gain-of-function variants in FGF12, most often the recurrent
  p.Arg52His change, and also by whole-gene duplication. Despite its name FGF12 is not a
  secreted growth factor: it encodes fibroblast growth factor homologous factor 1 (FHF1),
  an intracellular protein that binds the cytoplasmic C-terminal tail of voltage-gated
  sodium channels Nav1.6 and Nav1.2 and tunes their inactivation. The disorder is
  therefore a sodium channelopathy acting through a channel-binding partner rather than
  through the channel itself, which places it alongside the SCN2A and SCN8A entries in
  this knowledge base while remaining mechanistically distinct from them. Seizures begin
  in the neonatal or early infantile period. The phenotype has broadened considerably:
  what was described as a lethal encephalopathy now spans that severe form and a
  drug-responsive epilepsy with favourable cognitive outcome.
disease_term:
  preferred_term: developmental and epileptic encephalopathy, 47
  term:
    id: MONDO:0014949
    label: developmental and epileptic encephalopathy, 47
parents:
- Epilepsy
- Neurological Disease
inheritance:
- name: Autosomal dominant
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    Heterozygous and usually de novo for the gain-of-function missense variants and
    duplications.
  evidence:
  - reference: PMID:27164707
    reference_title: "Gain-of-function FHF1 mutation causes early-onset epileptic encephalopathy with cerebellar atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A de novo heterozygous missense mutation was identified in the FHF1 gene
      (FHF1AR114H, FHF1BR52H) in the 2 affected siblings"
    explanation: >-
      Establishes the de novo heterozygous mechanism. Note the variant was de novo yet
      present in two siblings, which implies parental germline mosaicism and is relevant
      to recurrence-risk counselling.

- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    A separate, later-recognised biallelic loss-of-function route to the same clinical
    syndrome, established by long-read sequencing in an exome-negative patient. This is
    not a variant of the dominant mechanism but its inverse.
  evidence:
  - reference: PMID:37286232
    reference_title: "Biallelic structural variations within FGF12 detected by long-read sequencing in epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "FGF12 heterozygous recurrent missense variants with gain-of-function or
      heterozygous entire duplication of FGF12 are known causes of epilepsy, but biallelic
      SNVs/SVs have never been described"
    explanation: >-
      States both the established dominant mechanisms and the novelty of the biallelic
      route at the time of report.

pathophysiology:

- name: FGF12 Gain-of-Function Missense Variant
  biological_scale: MOLECULAR
  description: >-
    The dominant lesion, most often p.Arg52His in the FHF1B isoform (equivalently
    p.Arg114His in FHF1A). Whole-gene duplication is an alternative dominant route acting
    through increased dosage rather than altered protein. FHFs were candidate epilepsy
    genes precisely because they bind Nav channels, which is how the gene was found.
  evidence:
  - reference: PMID:27164707
    reference_title: "Gain-of-function FHF1 mutation causes early-onset epileptic encephalopathy with cerebellar atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A de novo heterozygous missense mutation was identified in the FHF1 gene
      (FHF1AR114H, FHF1BR52H) in the 2 affected siblings"
    explanation: >-
      Identifies the recurrent variant in both isoform numbering systems.
  - reference: PMID:27164707
    reference_title: "Gain-of-function FHF1 mutation causes early-onset epileptic encephalopathy with cerebellar atrophy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Our data demonstrate that gain-of-function FHF mutations can cause
      neurologic disorder, and expand the repertoire of genetic causes (FHF1) and
      mechanisms (altered Nav gating) underlying EOEE and cerebellar atrophy"
    explanation: >-
      The founding study's own statement of the gain-of-function mechanism and of altered
      Nav gating as the mechanistic class.
  downstream:
  - target: Weakened FHF1 Binding to the Nav Cytoplasmic Tail
    causal_link_type: DIRECT
    description: >-
      The variant's first measured consequence is on the protein-protein interaction.

- name: Weakened FHF1 Binding to the Nav Cytoplasmic Tail
  biological_scale: MOLECULAR
  description: >-
    The counterintuitive step, and the reason it is curated as its own node. The
    gain-of-function effect is predicted to arise from a *weaker* interaction between
    mutant FHF1 and the sodium channel cytoplasmic tail - a loss of binding producing a
    gain of channel function. Collapsing this into the downstream channel node would hide
    the fact that the direction of the binding change is opposite to the direction of the
    functional change.
  molecular_functions:
  - preferred_term: sodium channel regulator activity
    modifier: ABNORMAL
    term:
      id: GO:0017080
      label: sodium channel regulator activity
  evidence:
  - reference: PMID:27164707
    reference_title: "Gain-of-function FHF1 mutation causes early-onset epileptic encephalopathy with cerebellar atrophy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Surprisingly, the gain-of-function effect is predicted to result from weaker
      interaction of mutant FHF1 with the Nav cytoplasmic tail"
    explanation: >-
      States the inverted relationship between binding strength and functional outcome,
      including the authors' own note that it is surprising.
  downstream:
  - target: Depolarizing Shift in Nav1.6 Fast Inactivation
    causal_link_type: DIRECT
    description: >-
      Altered binding changes the channel's inactivation behaviour.

- name: Depolarizing Shift in Nav1.6 Fast Inactivation
  biological_scale: MOLECULAR
  description: >-
    The channel-level readout: mutant FHF1 enhances the depolarizing shift in the
    voltage-dependence of Nav1.6 fast inactivation, so channels remain available at
    potentials where they would normally be inactivated.
  molecular_functions:
  - preferred_term: voltage-gated sodium channel activity
    modifier: INCREASED
    term:
      id: GO:0005248
      label: voltage-gated sodium channel activity
  biological_processes:
  - preferred_term: regulation of sodium ion transmembrane transport
    modifier: DYSREGULATED
    term:
      id: GO:1902305
      label: regulation of sodium ion transmembrane transport
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Ion Channel and Synaptic Dysfunction"
  evidence:
  - reference: PMID:27164707
    reference_title: "Gain-of-function FHF1 mutation causes early-onset epileptic encephalopathy with cerebellar atrophy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The mutant FHF1 proteins had a strong gain-of-function phenotype in
      transfected Neuro2A cells, enhancing the depolarizing shifts in Nav1.6
      voltage-dependent fast inactivation, predicting increased neuronal excitability"
    explanation: >-
      The direct biophysical measurement, together with the excitability consequence the
      authors predict from it.
  downstream:
  - target: Increased Intrinsic Neuronal Excitability
    causal_link_type: DIRECT
    description: >-
      Greater sodium channel availability raises the excitability of the neuron.

- name: Increased Intrinsic Neuronal Excitability
  biological_scale: CELLULAR
  description: >-
    Neurons carrying the variant are expected to fire more readily. Kept separate from the
    channel biophysics node because excitability is a cell-level property rather than a
    channel property. The status of this node is weaker than the nodes on either side of
    it: the founding study measured channel gating in Neuro2A cells and *predicted*
    increased excitability rather than recording it, so this is curated as a predicted
    step. No cell type is bound, because the supporting measurement was made in a
    neuroblastoma line rather than in an identified neuronal population.
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Neuronal Hyperexcitability and Hypersynchrony"
  evidence:
  - reference: PMID:27164707
    reference_title: "Gain-of-function FHF1 mutation causes early-onset epileptic encephalopathy with cerebellar atrophy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "enhancing the depolarizing shifts in Nav1.6 voltage-dependent fast
      inactivation, predicting increased neuronal excitability"
    explanation: >-
      The excitability claim as stated by the founding study. Curated as predicted rather
      than directly measured at this point in the literature.
  downstream:
  - target: Epileptiform Network Activity
    causal_link_type: DIRECT
    description: >-
      Hyperexcitable neurons generate epileptiform network discharge.

- name: Epileptiform Network Activity
  biological_scale: CELLULAR
  description: >-
    Spontaneous epileptiform discharge at the network level, demonstrated by cortical EEG
    in the genotype-matched knock-in mouse.
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Seizure Generation and Epileptogenesis"
  evidence:
  - reference: PMID:33982289
    reference_title: "Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Spontaneous epileptiform events in Fhf1R52H/+ mice were assessed by cortical
      electroencephalography (EEG) and video monitoring"
    explanation: >-
      Establishes that spontaneous epileptiform activity is the measured endpoint in the
      knock-in mouse.
  downstream:
  - target: Early-Onset Refractory Seizures
    causal_link_type: DIRECT
    description: >-
      Network discharge manifests as the clinical seizure disorder.
  - target: Cardiac Arrhythmia
    causal_link_type: DIRECT
    description: >-
      The demonstrated route. Heart rate falls abruptly within seconds of seizure onset,
      attributed to a parasympathetic surge - so the arrhythmia in this model is
      seizure-triggered rather than a standing consequence of the cardiac channel defect.

- name: Altered Cardiac Sodium Channel Function
  biological_scale: MOLECULAR
  description: >-
    FHF1 binds Nav1.5 in cardiomyocytes by the same mechanism it uses on neuronal
    channels, so the variant has a direct cardiac substrate independent of seizures. This
    node is drawn from the variant rather than from the neuronal chain, because the two
    organs are affected in parallel by one molecular lesion.
  molecular_functions:
  - preferred_term: voltage-gated sodium channel activity involved in cardiac muscle cell action potential
    modifier: ABNORMAL
    term:
      id: GO:0086006
      label: voltage-gated sodium channel activity involved in cardiac muscle cell action potential
  cell_types:
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  evidence:
  - reference: PMID:33982289
    reference_title: "Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Although ectopic overexpression of FHF1BR52H in cardiomyocytes induced a
      15-mV depolarizing shift in voltage of steady-state sodium channel inactivation and
      slowed the rate of channel inactivation, heart rhythm was normal in Fhf1R52H/+ mice
      prior to seizure"
    explanation: >-
      Establishes the cardiac channel effect and, in the same sentence, its limit: the
      channel change is real but does not by itself produce a resting rhythm disturbance.
      Classified IN_VITRO because the channel measurement is ectopic adenoviral
      overexpression in cardiomyocytes, not an intact-animal observation.
  downstream:
  - target: Cardiac Arrhythmia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Downgraded from a direct edge. The cardiac channel defect is demonstrable, but the
      same paper reports that heart rhythm is normal in these animals before a seizure, so
      the channel change is not sufficient on its own to produce arrhythmia. It is curated
      as a permissive substrate rather than a direct cause.

- name: Cardiac Arrhythmia
  biological_scale: ORGANISM
  description: >-
    Arrhythmia and bradycardia in the knock-in mouse, contributing to sudden death. The
    cardiac arm is what distinguishes this disorder's risk profile from most other
    developmental and epileptic encephalopathies, because the same lesion acts on the
    heart and the brain.
  evidence:
  - reference: PMID:33982289
    reference_title: "Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Within 2-53 s after lethal seizure onset, heart rate abruptly declined from
      572 +/- 16 bpm to 108 +/- 15 bpm, suggesting a parasympathetic surge accompanying
      seizures that may have contributed to SUDEP"
    explanation: >-
      The actual arrhythmia result and its proposed mechanism, with the timing that
      establishes it as seizure-triggered. This replaces an earlier citation of the
      paper's methods sentence, which described what was measured rather than what was
      found.
  - reference: PMID:33982289
    reference_title: "Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "All Fhf1R52H/+ mice experienced seizure or seizurelike episodes with lethal
      ending between 12 and 26 days of age"
    explanation: >-
      Records the uniform lethal outcome in the model within a narrow age window.

- name: Early-Onset Refractory Seizures
  biological_scale: ORGANISM
  description: >-
    Seizures beginning in the neonatal or early infantile period. In the severe DEE47
    phenotype they are refractory and accompanied by developmental impairment; at the
    milder end of the spectrum they respond to medication.
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Recurrent Unprovoked Seizures"
  evidence:
  - reference: PMID:40488543
    reference_title: "Broadening the phenotype associated with pathogenic variants in the FGF12 gene: From developmental and epileptic encephalopathy to drug-responsive epilepsy with favorable cognitive outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All developed epilepsy before 5 months, with 70% achieving seizure remission
      by 6 months with antiseizure medication (ASM), leading to good neurodevelopmental
      outcomes"
    explanation: >-
      Establishes the early onset shared across the spectrum, and simultaneously documents
      the drug-responsive pole with a remission figure.

- name: Biallelic FGF12 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    A separate, recessive route to the same clinical syndrome. Biallelic intragenic
    structural variants, and a biallelic single-nucleotide variant, reduce or remove FHF1
    function - the opposite direction of effect to the dominant missense variants. Curated
    as its own trigger node rather than folded into the gain-of-function chain, because
    both increased and decreased FHF1-mediated channel modulation destabilise network
    excitability and the entry should not imply they act through the same intermediate
    states.
  evidence:
  - reference: PMID:37286232
    reference_title: "Biallelic structural variations within FGF12 detected by long-read sequencing in epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We discovered biallelic intragenic structural variations (SVs) in FGF12 by
      applying long-read whole genome sequencing to an exome-negative patient with
      developmental and epileptic encephalopathy (DEE)"
    explanation: >-
      Establishes the biallelic structural-variant route and the sequencing technology
      that was required to see it.
  - reference: PMID:37286232
    reference_title: "Biallelic structural variations within FGF12 detected by long-read sequencing in epilepsy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "highly sensitive gene expression analyses using lymphoblastoid cells from
      the patient with biallelic SVs, structural considerations, and Drosophila in vivo
      functional analysis of the SNV were performed, confirming loss-of-function"
    explanation: >-
      Confirms the direction of effect as loss of function across three independent lines
      of evidence.
  downstream:
  - target: Early-Onset Refractory Seizures
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Reaches the same clinical endpoint by an opposite-direction molecular route. Marked
      indirect with unknown intermediates because no source establishes the intervening
      steps for the recessive arm.

phenotypes:

- category: Neurological
  name: Early-Onset Seizures
  description: >-
    Seizures begin in the neonatal period or early infancy - before five months in every
    patient of the broadened cohort. Types reported include tonic, focal, migrating focal
    and spasms.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:40488543
    reference_title: "Broadening the phenotype associated with pathogenic variants in the FGF12 gene: From developmental and epileptic encephalopathy to drug-responsive epilepsy with favorable cognitive outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All developed epilepsy before 5 months"
    explanation: >-
      Establishes the upper bound on age at onset across the cohort.
  - reference: PMID:40488543
    reference_title: "Broadening the phenotype associated with pathogenic variants in the FGF12 gene: From developmental and epileptic encephalopathy to drug-responsive epilepsy with favorable cognitive outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We aim to refine the electroclinical phenotype and outcomes of 10
      unpublished patients (2-38 years old) with these recurrent pathogenic variants in
      the FGF12 gene without DEE"
    explanation: >-
      Establishes that patients carrying the same recurrent variants can reach adulthood
      without developmental and epileptic encephalopathy, which is what broadens the
      phenotype beyond the original lethal description.

- category: Neurological
  name: Developmental and Epileptic Encephalopathy
  description: >-
    The severe pole of the spectrum: refractory epilepsy with developmental impairment and
    poor outcome, which is the presentation the disorder was originally defined by.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:40488543
    reference_title: "Broadening the phenotype associated with pathogenic variants in the FGF12 gene: From developmental and epileptic encephalopathy to drug-responsive epilepsy with favorable cognitive outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "have repeatedly been associated with developmental and epileptic
      encephalopathy-47 (DEE47; Mendelian Inheritance in Man #617166) with poor outcome"
    explanation: >-
      Records the severe, poor-outcome phenotype the recurrent variants were originally
      associated with.

- category: Neurological
  name: Intellectual Disability
  description: >-
    Moderate to severe intellectual disability in the large majority of patients across
    the pooled literature, though the broadened phenotype now includes patients with
    favourable cognitive outcome.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:42057324
    reference_title: "FGF12-Related Early-Onset Epileptic Encephalopathies: Therapeutic Response to Sodium Channel Blockers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "79.1% of patients exhibited moderate to severe intellectual disability"
    explanation: >-
      Quantifies moderate-to-severe intellectual disability across a 27-patient pooled
      cohort. 79.1% sits at the top of the 30-79% FREQUENT band rather than in
      VERY_FREQUENT, so the band is assigned conservatively.

- category: Neuroimaging
  name: Cerebellar Atrophy
  description: >-
    Cerebellar atrophy was part of the original phenotype definition. Notably it tracks
    severity rather than genotype: patients at the favourable-outcome end of the spectrum
    showed none, which makes it a potential imaging correlate of prognosis rather than a
    constant feature of the disorder.
  phenotype_term:
    preferred_term: Cerebellar atrophy
    term:
      id: HP:0001272
      label: Cerebellar atrophy
  evidence:
  - reference: PMID:27164707
    reference_title: "Gain-of-function FHF1 mutation causes early-onset epileptic encephalopathy with cerebellar atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we performed whole-exome sequencing in a family quintet with 2 siblings with
      a lethal disease characterized by EOEE and cerebellar atrophy"
    explanation: >-
      Records cerebellar atrophy as part of the phenotype in the founding family, quoted
      from the abstract body rather than from the paper's title.
  - reference: PMID:40488543
    reference_title: "Broadening the phenotype associated with pathogenic variants in the FGF12 gene: From developmental and epileptic encephalopathy to drug-responsive epilepsy with favorable cognitive outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "patients with favorable neurodevelopmental outcomes and FGF12 pathogenic
      variants showed no signs of cerebellar atrophy"
    explanation: >-
      Establishes that cerebellar atrophy is absent at the favourable-outcome pole, making
      it severity-associated rather than universal.
  - reference: PMID:42057324
    reference_title: "FGF12-Related Early-Onset Epileptic Encephalopathies: Therapeutic Response to Sodium Channel Blockers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain MRI showed mild cerebral and/or cerebellar atrophy in 41.6% of cases"
    explanation: >-
      Supplies the pooled frequency across 27 patients, consistent with a
      severity-associated rather than universal finding.

- category: Cardiovascular
  name: Cardiac Arrhythmia
  description: >-
    Arrhythmia is established in the knock-in mouse, where it accompanies seizures and
    contributes to sudden death, and a human case of peri-ictal asystole requiring a
    pacemaker is now on record. The human frequency is not established - one case report
    shows the cardiac arm occurs in patients, not how commonly - so no frequency band is
    curated here.
  phenotype_term:
    preferred_term: Arrhythmia
    term:
      id: HP:0011675
      label: Arrhythmia
  evidence:
  - reference: PMID:40897676
    reference_title: "Ictal Asystole in a Patient With DEE due to an FGF12 Pathogenic Variant: A Reminder to Monitor Cardiac Function."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report the first known case of a 9-year-old male with early-onset
      epilepsy, syncope, and ictal asystole-requiring pacemaker implantation at the age of
      seven-associated with a pathogenic variant in FGF12"
    explanation: >-
      A human cardiac event in a genotype-confirmed patient, severe enough to require a
      pacemaker. This is a single case report, so it establishes that the cardiac arm
      occurs in humans without establishing how often.
  - reference: PMID:40897676
    reference_title: "Ictal Asystole in a Patient With DEE due to an FGF12 Pathogenic Variant: A Reminder to Monitor Cardiac Function."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A holter ECG confirmed a 25-s peri-ictal asystole in an ambulatory record"
    explanation: >-
      Documents the asystole objectively and shows it is peri-ictal, matching the
      seizure-triggered mechanism described in the mouse.

genetic:
- name: FGF12
  gene_term:
    preferred_term: FGF12
    term:
      id: hgnc:3668
      label: FGF12
  relationship_type: CAUSATIVE
  association: >-
    FGF12 encodes fibroblast growth factor homologous factor 1 (FHF1), an intracellular,
    non-secreted FGF that modulates voltage-gated sodium channel inactivation. Three
    variant classes cause disease: recurrent heterozygous gain-of-function missense
    variants (p.Arg52His, p.Gly50Ser), whole-gene duplication, and - separately -
    biallelic loss-of-function structural or single-nucleotide variants.
  evidence:
  - reference: PMID:37286232
    reference_title: "Biallelic structural variations within FGF12 detected by long-read sequencing in epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "FGF12 heterozygous recurrent missense variants with gain-of-function or
      heterozygous entire duplication of FGF12 are known causes of epilepsy, but biallelic
      SNVs/SVs have never been described"
    explanation: >-
      Enumerates the dominant variant classes and marks the biallelic route as newly
      described.
  notes: >-
    The recurrent p.Arg52His variant is numbered in the FHF1B isoform; the same change is
    p.Arg114His in FHF1A, and both numberings appear in the literature for one variant.
    In the founding family the variant was de novo yet shared by two affected siblings,
    which implies parental germline mosaicism - relevant to recurrence-risk counselling
    even though a de novo finding would ordinarily suggest low recurrence risk.
    Scope note: FGF12 also appears in the cardiac arrhythmia literature as a minor Brugada
    syndrome gene, and the GeneReviews chapter that mentions FGF12 is the Brugada Syndrome
    chapter, not a chapter about this disorder. That cardiac-channelopathy literature is a
    separate disease context and is deliberately not curated into this entry; the cardiac
    content here comes only from DEE47-genotype sources.

diagnosis:
- name: Long-Read Genome Sequencing
  description: >-
    Standard exome sequencing does not resolve every FGF12 case. The biallelic structural
    variants were found only by applying long-read whole genome sequencing to a patient
    whose exome was negative, so a negative exome does not exclude the gene.
  diagnosis_term:
    preferred_term: Whole Genome Sequencing
    term:
      id: NCIT:C101294
      label: Whole Genome Sequencing
  evidence:
  - reference: PMID:37286232
    reference_title: "Biallelic structural variations within FGF12 detected by long-read sequencing in epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We discovered biallelic intragenic structural variations (SVs) in FGF12 by
      applying long-read whole genome sequencing to an exome-negative patient with
      developmental and epileptic encephalopathy (DEE)"
    explanation: >-
      Directly supports the claim that a negative exome does not exclude FGF12 and that
      long-read sequencing has additional diagnostic yield here.

treatments:
- name: Sodium Channel Blocker Therapy
  description: >-
    Because the dominant mechanism is a sodium channel gain of function, sodium channel
    blockers are the mechanistically indicated treatment, and this is one of relatively
    few developmental and epileptic encephalopathies with a candidate precision therapy.
    Whether prompt treatment actually improves developmental outcome is disputed between
    two recent cohorts - see the controversy discussion, which this treatment entry should
    be read alongside.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: carbamazepine
      term:
        id: CHEBI:3387
        label: carbamazepine
    - preferred_term: phenytoin
      term:
        id: CHEBI:8107
        label: phenytoin
    - preferred_term: lamotrigine
      term:
        id: CHEBI:6367
        label: lamotrigine
    - preferred_term: oxcarbazepine
      term:
        id: CHEBI:7824
        label: oxcarbazepine
  target_mechanisms:
  - target: Depolarizing Shift in Nav1.6 Fast Inactivation
    treatment_effect: INHIBITS
    description: >-
      Sodium channel blockers act on the channel whose inactivation the variant shifts.
  evidence:
  - reference: PMID:42185328
    reference_title: "Expanding the phenotypic spectrum of FGF12-epilepsy-does prompt precision therapy affect outcomes?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "8 patients promptly started on sodium channel blockers became seizure-free
      with good developmental outcomes while 4 developed DEE"
    explanation: >-
      The cohort supporting a benefit from prompt sodium-channel-blocker therapy.
  - reference: PMID:40488543
    reference_title: "Broadening the phenotype associated with pathogenic variants in the FGF12 gene: From developmental and epileptic encephalopathy to drug-responsive epilepsy with favorable cognitive outcome."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "we did not find a clear correlation between treatment with sodium channel
      blockers, its timing, and neurodevelopmental outcome"
    explanation: >-
      The cohort that looked for the same association and did not find it. Curated as
      REFUTE against the precision-therapy claim so that the disagreement is visible on
      the treatment itself rather than only in prose.
  - reference: PMID:42057324
    reference_title: "FGF12-Related Early-Onset Epileptic Encephalopathies: Therapeutic Response to Sodium Channel Blockers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "While treatment responses were heterogeneous, sodium channel blockers were
      commonly associated with clinical improvement"
    explanation: >-
      A third cohort, curated PARTIAL rather than SUPPORT because it reports an
      association with seizure improvement while explicitly describing responses as
      heterogeneous - and because association with clinical improvement is a weaker claim
      than the developmental-outcome benefit the other two cohorts disagree about.
  - reference: PMID:42057324
    reference_title: "FGF12-Related Early-Onset Epileptic Encephalopathies: Therapeutic Response to Sodium Channel Blockers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These findings support cautious consideration of sodium channel targeting
      therapies in FGF12-DEE and underscore the need for systematic studies to better
      define genotype treatment relationships"
    explanation: >-
      The same cohort's own hedge. Quoted because the word "cautious" and the call for
      systematic studies are the authors positioning their result as suggestive rather
      than as settling the question.

animal_models:
- name: Fhf1 p.Arg52His knock-in mouse
  species: Mouse
  genotype: Fhf1R52H/+
  publication: PMID:33982289
  description: >-
    CRISPR knock-in carrying the recurrent human variant. The model that establishes the
    cardiac arm of the disorder, and the reason sudden death is treated as mechanistically
    linked rather than incidental.
  modeled_mechanisms:
  - target: Epileptiform Network Activity
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Spontaneous epileptiform events on cortical EEG in a genotype-matched animal.
    readouts:
    - name: Cortical EEG epileptiform events
      target: Epileptiform Network Activity
      direction: INCREASED
      interpretation: >-
        Spontaneous epileptiform activity assessed by EEG with video monitoring.
      evidence:
      - reference: PMID:33982289
        reference_title: "Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Spontaneous epileptiform events in Fhf1R52H/+ mice were assessed by
          cortical electroencephalography (EEG) and video monitoring"
        explanation: >-
          The electrophysiological measurement behind this readout.
    evidence:
    - reference: PMID:33982289
      reference_title: "Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The Arg52His mutation was introduced into fertilized eggs by CRISPR
        (clustered regularly interspaced short palindromic repeats) editing to generate
        Fhf1R52H/F+ mice"
      explanation: >-
        Establishes that the model carries the actual human variant rather than a
        surrogate lesion.
  - target: Cardiac Arrhythmia
    relationship: RECAPITULATES
    fidelity: MODERATE
    limitations: >-
      The mouse phenotype is uniformly lethal between 12 and 26 days of age, whereas the
      human disorder spans a lethal encephalopathy through to drug-responsive epilepsy
      with favourable cognitive outcome. The model therefore represents the severe pole
      only and cannot speak to the milder end of the spectrum, which is where the
      treatment question now sits.
    description: >-
      Ictal bradyarrhythmia. Basal rhythm is explicitly normal, so the model shows a
      seizure-triggered cardiac event rather than a standing cardiac phenotype - the two
      readouts below record that contrast directly.
    readouts:
    - name: Basal heart rhythm prior to seizure
      target: Cardiac Arrhythmia
      direction: UNCHANGED
      interpretation: >-
        No intrinsic cardiac phenotype between seizures. This is a real negative result and
        is what makes the downgrade of the channel-to-arrhythmia edge correct: the cardiac
        sodium channel defect is demonstrable in vitro yet produces no measurable resting
        rhythm abnormality in the intact animal.
      evidence:
      - reference: PMID:33982289
        reference_title: "Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "heart rhythm was normal in Fhf1R52H/+ mice prior to seizure"
        explanation: >-
          States the negative basal result directly.
      - reference: PMID:33982289
        reference_title: "Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "average basal heart rates recorded over a 6-hour period were not
          significantly different"
        explanation: >-
          The quantitative form of the same negative result, over a six-hour recording
          rather than a spot measurement.
    - name: Ictal heart rate
      target: Cardiac Arrhythmia
      direction: DECREASED
      interpretation: >-
        An abrupt fall in heart rate within seconds of seizure onset, attributed to a
        parasympathetic surge.
      evidence:
      - reference: PMID:33982289
        reference_title: "Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Within 2-53 s after lethal seizure onset, heart rate abruptly declined
          from 572 +/- 16 bpm to 108 +/- 15 bpm, suggesting a parasympathetic surge
          accompanying seizures that may have contributed to SUDEP"
        explanation: >-
          The ictal measurement, with the timing that establishes it as following seizure
          onset rather than preceding it.
    evidence:
    - reference: PMID:33982289
      reference_title: "Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "All Fhf1R52H/+ mice experienced seizure or seizurelike episodes with lethal
        ending between 12 and 26 days of age"
      explanation: >-
        Supports the model as informative for sudden death, and records the narrow age
        window that also defines its limitation.

discussions:

- discussion_id: controversy_does_prompt_sodium_channel_blockade_change_outcome
  kind: CONTROVERSY
  status: OPEN
  attaches_to:
  - pathophysiology#Depolarizing Shift in Nav1.6 Fast Inactivation
  - pathophysiology#Early-Onset Refractory Seizures
  prompt: >-
    Does promptly starting a sodium channel blocker improve neurodevelopmental outcome in
    FGF12-related epilepsy, or does outcome track the variant and phenotype regardless of
    when treatment starts?
  rationale: >-
    Three cohorts now speak to this question and they do not agree. Two published within a
    year of each other reach opposite conclusions. One reports that eight patients promptly started on sodium channel
    blockers became seizure-free with good developmental outcomes while four developed
    encephalopathy, and frames early precision therapy as consequential. The other looked
    for exactly this association and states that it did not find a clear correlation
    between sodium-channel-blocker treatment, its timing, and neurodevelopmental outcome.
    The mechanistic rationale is strong and undisputed - the dominant lesion is a sodium
    channel gain of function, so blocking the channel is the rational target - which makes
    it easy to assume the clinical benefit follows. It may not. The competing explanation
    is confounding by severity: milder variants produce both better outcomes and easier
    seizure control, so treatment responsiveness could be a marker of a mild phenotype
    rather than a cause of a good outcome. A third cohort of 27 patients reports
    sodium channel blockers commonly associated with clinical improvement, but it declines
    to overclaim - responses are described as heterogeneous and the authors call for
    systematic studies - and it speaks to seizure improvement rather than to the
    developmental outcome the other two dispute, so it does not break the tie. All three
    cohorts are small and none is randomised. This matters more than a typical unresolved question because it bears
    directly on what clinicians do at diagnosis, and because a precision-therapy claim
    that turns out to be confounded is harder to retract than one never made. The entry
    therefore curates the supporting cohort as SUPPORT and the null cohort as REFUTE on
    the same treatment, so the disagreement is visible in the structured data rather than
    only in prose. Note that the deep-research report used to build this entry asserted
    the optimistic version as a quote attributed to both papers; its own validator flagged
    that quote as unsupported, and inspection showed one of the two papers states the
    opposite.
  proposed_experiments:
  - experiment_id: exp_severity_stratified_treatment_timing
    name: Severity-stratified analysis of treatment timing
    description: >-
      Pool the published FGF12 cohorts and stratify outcome by variant and by
      pre-treatment seizure burden before testing the effect of sodium-channel-blocker
      timing. If the timing effect survives stratification by baseline severity, the
      precision-therapy claim is supported; if it disappears, the association was
      confounding by severity and the claim should be withdrawn.

- discussion_id: gap_opposite_direction_variants_converge_on_one_syndrome
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#FGF12 Gain-of-Function Missense Variant
  - pathophysiology#Biallelic FGF12 Loss of Function
  prompt: >-
    How do gain-of-function and loss-of-function FGF12 variants produce the same clinical
    syndrome?
  rationale: >-
    Heterozygous missense variants increase FHF1-mediated modulation of sodium channel
    inactivation; biallelic structural and single-nucleotide variants reduce or remove it,
    confirmed by expression analysis, structural reasoning and a Drosophila assay. Both
    cause developmental and epileptic encephalopathy. The entry keeps them as separate
    trigger nodes converging on the clinical endpoint rather than routing the recessive
    arm through the dominant chain, because nothing establishes that they pass through the
    same intermediate states - and if they did, the direction of the channel change would
    have to be the same, which it is not. The practical stake is therapeutic: a sodium
    channel blocker is mechanistically indicated for the gain-of-function arm and
    potentially harmful for the loss-of-function arm, so treating the two as one disease
    for management purposes could be actively wrong.
  proposed_experiments:
  - experiment_id: exp_loss_versus_gain_channel_phenotype
    name: Channel-level comparison of loss- and gain-of-function FGF12 alleles
    description: >-
      Measure Nav1.6 and Nav1.2 inactivation kinetics and neuronal excitability in the
      same preparation for a gain-of-function missense allele and for FHF1 depletion, and
      determine whether excitability rises in both cases or whether the loss-of-function
      arm reaches seizures through a different excitability change. The answer directly
      determines whether sodium channel blockade is rational for biallelic patients.

- discussion_id: mismatch_uniformly_lethal_mouse_versus_a_broad_human_spectrum
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Cardiac Arrhythmia
  prompt: >-
    Can a model in which every animal dies within a month inform a disorder that includes
    drug-responsive epilepsy with normal cognition?
  rationale: >-
    Every Fhf1R52H/+ mouse experiences seizures or seizure-like episodes ending lethally
    between 12 and 26 days of age. The human spectrum carrying the same recurrent variant
    class now extends to patients aged up to 38 years with favourable cognitive outcomes.
    The model is a faithful and valuable representation of the severe pole - it is the
    source of the cardiac and sudden-death findings, which would be hard to establish any
    other way - but it cannot be used to reason about the milder end, and that is
    precisely where the open clinical question about treatment timing now lies. The
    mismatch also has a specific consequence for the cardiac arm: because the model dies
    young and uniformly, it cannot tell us the lifetime arrhythmia risk for a patient who
    survives infancy, which is the number a cardiologist would want.
  proposed_experiments:
  - experiment_id: exp_cardiac_screening_in_surviving_patients
    name: Cardiac screening in older FGF12 patients
    description: >-
      Systematically screen the surviving FGF12 cohort, including the adults at the
      favourable-outcome pole, with ECG and ambulatory rhythm monitoring, to establish
      whether the cardiac arm demonstrated in the mouse is present in humans who live
      beyond infancy and whether it warrants surveillance.

notes: >-
  Module conformance deliberately skips the epilepsy module's Excitation-Inhibition
  Imbalance node. The chain here runs from a channel-gating change to network epileptiform
  activity without an evidenced excitatory-inhibitory balance measurement, and the
  intervening excitability node is itself curated as predicted rather than measured, so
  attaching there would assert a balance claim no source makes. This is a decision, not an
  oversight.
  Items raised in review and deliberately deferred, with the reasoning recorded so they
  are not re-litigated: the zebrafish model and the patient iPSC line are both real and
  relevant but neither carries a measurement this entry currently makes a node for, so
  adding them would produce disconnected list entries rather than pathograph links; the
  reported association of FGF12 duplication with West syndrome is described in secondary
  sources but no primary source available here states it quotably; and seizure semiology
  is curated at the level of HP:0001250 Seizure rather than split into tonic, focal and
  migrating-focal subtypes, because the pooled cohort reports semiology counts without a
  per-patient denominator that would support frequency bands on the subtypes.
  Scope: this entry curates DEE47 and the broader FGF12-related epilepsy spectrum that the
  same recurrent variants produce. FGF12 also appears as a minor gene in the Brugada
  syndrome literature; that is a separate disease context and is not curated here. The
  only GeneReviews chapter returned by a search for FGF12 is the Brugada Syndrome chapter,
  in which FGF12 is a mentioned gene rather than the subject, so it is not the
  GeneReviews baseline for this disorder and is deliberately not tagged as one.

📚

References & Deep Research

Deep Research

1

Claude Code ▸

FGF12-Related Developmental and Epileptic Encephalopathy: Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 24 citations 2026-08-20T03:56:18.201433

FGF12-Related Developmental and Epileptic Encephalopathy: Comprehensive Research Report

1. Disease Information

Overview. FGF12-related developmental and epileptic encephalopathy (also designated Developmental and Epileptic Encephalopathy 47, DEE47, and historically "Early Infantile Epileptic Encephalopathy 47, EIEE47") is a severe, early-onset genetic epilepsy syndrome caused by heterozygous, typically de novo, pathogenic variants in FGF12 (fibroblast growth factor 12, also called FHF1, fibroblast growth factor homologous factor 1). It belongs to the growing family of sodium-channel-regulatory-protein epileptic encephalopathies, alongside SCN1A/SCN2A/SCN8A and FGF13(FHF2)-related disorders. Seizures typically begin in the first days to weeks of life and are intractable, with variable developmental regression (OMIM #617166; Siekierska et al. 2016, Neurology, PMID:27164707).

Key identifiers: - OMIM gene: 601513 (FGF12); OMIM phenotype: #617166 DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 47 (DEE47) - HGNC gene symbol: FGF12 (also known as FHF1, FGF12B) - Chromosomal location: 3q28 (some sources cite 3q28-q29) - Orphanet: listed under "FGF12-fibroblast growth factor 12" gene page, associated with non-specific early-onset epileptic encephalopathy* (Orphanet) - MONDO: developmental and epileptic encephalopathy, 47 (cross-referenced via NORD/MONDO: rarediseases.org) - Synonyms: EIEE47; Early Infantile Epileptic Encephalopathy 47; FHF1 epileptic encephalopathy; DEE47

Evidence source note: Most published data derive from individual patient case reports and small case series (aggregated into cohorts of up to ~27 patients), supplemented by animal-model (mouse, zebrafish) and cell-based electrophysiological studies — i.e., a mix of individual clinical observation and structured multi-patient cohort synthesis, not large-scale registries.

2. Etiology

Disease causal factors — genetic, monogenic. DEE47 is caused by heterozygous, usually de novo, gain-of-function missense variants in FGF12, which encodes an intracellular fibroblast growth factor homologous factor (FHF1) that binds the C-terminal cytoplasmic tail of neuronal voltage-gated sodium channels (Nav1.2/SCN2A, Nav1.6/SCN8A, and cardiac Nav1.5/SCN5A) to modulate channel inactivation (Siekierska et al. 2016, PMID:27164707; Life Science Alliance 2023, PMID:37286232).

Recurrent causal variants: - p.Arg52His (R52H in the B-isoform; equivalently R114H in the A-isoform) — the most frequently reported de novo missense variant, at a highly conserved residue that contacts the Nav cytoplasmic tail, disrupting fast-inactivation modulation (OMIM #617166; Siekierska et al. 2016; Villeneuve et al. 2016, Neurol Genet, PMID:27830185). - p.Gly50Ser / p.Gly112Ser — a second recurrent variant, reported to have a distinct, more explosive/later-onset seizure phenotype compared with R52H (Pierret et al. 2025, Epilepsia, PMID:40488543). - c.334G>A / c.341G>A and other private missense variants reported in individual case reports (e.g., seizure-free on VPA+topiramate combination therapy; PMID:34020858; iPSC line generation from a c.334G>A patient, PMID:37331110). - p.Ser8Pro (S8P) — a novel variant reported in a patient with autism spectrum disorder and developmental delay without seizures, illustrating the phenotypic breadth beyond classic DEE (modulating effects case series, PMID:36029553). - Copy number variants (whole-gene or intragenic duplications) — de novo intragenic tandem duplications (e.g., exons 1–4) and full-gene duplications produce a phenytoin-responsive epileptic encephalopathy phenotype, including via complex chromosomal rearrangements causing West syndrome (Neurol Genet 2017, PMC7371371; Uehara et al. 2019, J Hum Genet, PMID:31311986; Willemsen et al. 2020, PMID:32524056; long-read sequencing of recurrent duplications, PMID:40838839). - Biallelic (recessive) structural/loss-of-function variants — a 2023 report using long-read sequencing identified the first biallelic intragenic structural variants in FGF12, causing DEE via a loss-of-function mechanism, contrasting with the dominant gain-of-function paradigm (PMID:37286232).

Risk factors: - Genetic: de novo occurrence is the norm; germline mosaicism has been reported in at least one family, carrying recurrence-risk implications for genetic counseling. - No established environmental, infectious, or lifestyle risk factors — this is a monogenic ion-channel-regulatory disorder. - Protective factors: none specifically documented; early recognition and use of sodium-channel-blocking antiseizure medications appears to modify (improve) outcome rather than prevent disease.

Gene-environment interactions: None reported; this is a purely monogenic condition with expression driven by the underlying channelopathy mechanism.

3. Phenotypes

Core phenotype — epilepsy (symptom/clinical sign): - Onset: neonatal to early infantile — "the first days or weeks of life" in the classic severe form (OMIM #617166); all patients in the broadened cohort developed epilepsy before 5 months of age (Pierret et al. 2025, PMID:40488543). - Seizure types: tonic seizures are the most common seizure type reported; also focal seizures, migrating focal seizures of infancy (EIMFS phenotype), infantile spasms/hypsarrhythmia, and generalized seizures. - Diagnoses spanned: early infantile epileptic encephalopathy (EIEE/Ohtahara-spectrum), epilepsy of infancy with migrating focal seizures (EIMFS), West syndrome (infantile spasms), and — in the milder/broadened spectrum — drug-responsive focal epilepsy without encephalopathy. - Severity/course: historically described as intractable/refractory with developmental regression; more recent broader ascertainment shows a spectrum from severe DEE to drug-responsive epilepsy with favorable cognitive outcome — ~70% of patients in one 10-patient cohort achieved seizure remission within 6 months of antiseizure medication, with favorable long-term neurodevelopmental outcome over median 6.8-year follow-up (PMID:40488543). - EEG: background slowing, multifocal epileptiform spikes; may show hypsarrhythmia.

Neurodevelopmental/cognitive phenotype: - Development is typically normal before seizure onset in the classic form. - Developmental regression after seizure onset is common in the severe phenotype; persistent intellectual disability and neurologic impairment of variable severity. - One larger-cohort synthesis: 79.1% of patients showed moderate-to-severe intellectual disability (cohort context: PMID:42057324/related reviews). - Milder end of spectrum: normal to near-normal cognitive outcome when seizures are well controlled early. - Autism spectrum disorder has been reported (in a patient with a novel S8P variant, without seizures) (PMID:36029553).

Neuroimaging phenotype: - Mild cerebral and/or cerebellar atrophy reported in a substantial minority (~41.6%) of cases, correlating with more severe phenotype; the original Siekierska et al. report specifically described "cerebellar atrophy" as a feature (PMID:27164707). Patients with favorable outcome/drug-responsive epilepsy show no cerebellar atrophy (PMID:40488543).

Cardiac phenotype (emerging): - Ictal asystole requiring pacemaker implantation has been reported in a 9-year-old with an FGF12 pathogenic variant (PMID:40897676), consistent with the cardiac Nav1.5-modulatory role of FHF1 and the cardiac arrhythmia/SUDEP phenotype demonstrated in mouse models (see Mechanism and Model Organisms below). - Apnea attacks and partial mitochondrial respiratory chain complex II deficiency were reported in one heterogeneous case (PMID:28506426).

Suggested HPO terms: - HP:0011097 Epileptic spasm - HP:0002187 Intractable epilepsy - HP:0032794 Focal-onset seizure - HP:0011146 Focal seizures with impaired awareness - HP:0007186 Cerebellar atrophy - HP:0001263 Global developmental delay - HP:0001249 Intellectual disability - HP:0002194 Delayed gross motor development - HP:0000006 Autosomal dominant inheritance - HP:0011168 Generalized tonic seizure - HP:0011177 Multifocal epileptiform discharges - HP:0011200 EEG with hypsarrhythmia - HP:0000708 Behavioral abnormality (autism) - HP:0001645 Sudden cardiac death / HP:0031547 asystole (context-dependent, cardiac arrhythmia)

Quality of life impact: Not separately quantified in the literature reviewed; qualitatively, the severe end of the spectrum imposes major burden via intractable seizures, developmental regression, and (rarely) SUDEP risk, whereas the drug-responsive end permits favorable developmental trajectories.

4. Genetic / Molecular Information

Gene: FGF12 (HGNC symbol FGF12; also FHF1, FGF12B); located at chromosome 3q28 (some sources: 3q28-q29). Gene structure: 4 introns and 5 coding exons, with alternative splicing producing two isoforms — the shorter isoform B and longer isoform A ("FGF12: biology and function," PMID:38042708).

Protein: Fibroblast growth factor homologous factor 1 (FHF1), a member of the FGF11 subfamily of intracellular FGFs (iFGFs, FHFs 1–4), structurally related to canonical FGFs (β-trefoil fold core domain) but functioning intracellularly rather than as secreted mitogens (though limited non-canonical secretion has recently been reported). FHF1 is highly expressed in excitable cells — neurons (hippocampus, cortex, cerebellum) and cardiomyocytes — where it binds the C-terminal cytoplasmic tail of voltage-gated sodium channel alpha subunits (Nav1.2/SCN2A, Nav1.5/SCN5A, Nav1.6/SCN8A) to modulate fast and long-term inactivation gating (PMID:38042708; PMID:37286232).

Pathogenic variant classes: | Variant type | Example | Mechanism | Reference | |---|---|---|---| | Recurrent missense (dominant, de novo) | p.Arg52His (=R114H isoform A) | Gain of function — weakened FHF1–Nav tail interaction → depolarizing shift in fast inactivation → enhanced Nav1.6/Nav1.2 currents | PMID:27164707, 27830185 | | Recurrent missense | p.Gly50Ser / p.Gly112Ser | Gain of function, distinct kinetic profile (later/more explosive onset) | PMID:40488543 | | Private missense | c.334G>A, c.341G>A, others | Gain of function | PMID:34020858, 37331110 | | Novel missense (non-epilepsy phenotype) | p.Ser8Pro | Mixed loss-/gain-of-function kinetic effects on Nav1.2/Nav1.6 | PMID:36029553 | | Whole-gene / intragenic duplication | exon 1–4 tandem duplication; full-gene duplication | Presumed dosage/gain-of-function; phenytoin-responsive | PMID:31311986, 32524056, 40838839, PMC7371371 | | Biallelic structural variants (recessive) | intragenic SVs, compound state | Loss of function | PMID:37286232 |

Variant classification: Per ACMG/AMP criteria as captured in ClinVar, recurrent variants such as NM_004113.6(FGF12):c.155G>A (p.Arg52His) are classified Pathogenic for "Developmental and epileptic encephalopathy, 47" (ClinVar RCV000258032).

Functional consequences — the central mechanism: In heterologous expression systems (transfected Neuro2A cells), mutant FHF1 (R52H) produces a strong gain-of-function effect: enhanced depolarizing shifts in Nav1.6 voltage-dependent fast inactivation, predicted to increase neuronal excitability. The mechanistic basis is a weaker interaction of mutant FHF1 with the Nav cytoplasmic tail, paradoxically producing gain-of-function kinetics rather than simple loss of channel modulation (bioRxiv/eBioMedicine, PMID:36029553). Other variants (G50S/G112S, S8P) produce a "complex kinetic influence... including loss- as well as gain-of-function changes in fast and slow inactivation" on both Nav1.2 and Nav1.6, explaining phenotypic heterogeneity across variants.

Allele frequency: Not established in population databases (gnomAD) as these are ultra-rare, largely private de novo pathogenic variants; no population carrier frequency data identified.

Modifier genes / epigenetics / chromosomal abnormalities: No modifier genes reported. No specific epigenetic (DNA methylation/histone) studies identified for FGF12-DEE specifically. Chromosomal-level involvement is limited to the described 3q28 duplications/complex rearrangements encompassing FGF12.

Suggested ontology terms: - GO:0005112 Notch binding (not applicable) — more relevant: GO:0044324 regulation of voltage-gated sodium channel activity; GO:0086006 voltage-gated sodium channel activity involved in cardiac muscle cell action potential; GO:0086010 membrane depolarization during action potential - GO:0007507 heart development / GO:0007399 nervous system development (broad context) - CHEBI: n/a (not a small-molecule disease) - UniProt: P61328 (FGF12_HUMAN)

5. Environmental Information

No environmental toxins, lifestyle factors, or infectious triggers have been identified as causal or modifying for FGF12-DEE — it is a monogenic channelopathy. Antiseizure medication choice (see Treatment) is the dominant modifiable factor affecting clinical course, not an "environmental" exposure in the traditional sense.

6. Mechanism / Pathophysiology

Causal chain (trigger → clinical manifestation):

Molecular lesion: De novo heterozygous gain-of-function missense variant (e.g., p.Arg52His) in FGF12/FHF1, or a gene-dosage change (duplication), alters the FHF1 protein's interaction with the intracellular C-terminal tail of neuronal voltage-gated sodium channels.
Channel biophysics: Mutant FHF1 binds Nav1.2 and Nav1.6 (and, for cardiac phenotypes, Nav1.5) with altered affinity, producing a depolarizing shift in the voltage-dependence of fast inactivation and complex effects on slow inactivation and recovery from inactivation — net effect is typically enhanced (gain-of-function) persistent/window sodium current.
Cellular electrophysiology: Increased sodium current availability and delayed fast inactivation increase intrinsic neuronal excitability. This has been directly confirmed by patch-clamp recordings showing increased excitability in hippocampal CA3 pyramidal neurons in a mouse model (FGF12^ΔV52H) (ScienceDirect 2024, "Phenotyping of FGF12^ΔV52H mutation in mouse implies a complex FGF12 network").
Network/circuit level: Hyperexcitable cortical, hippocampal, and cerebellar circuits generate epileptiform activity, demonstrated directly in a zebrafish overexpression/knock-in model showing epileptiform discharges (PMID:27164707).
Cardiac arm: The same FHF1–Nav interaction occurs in cardiomyocytes via Nav1.5, and mouse knock-in models (Fhf1^R52H/+) show cardiac arrhythmia and bradycardia contributing to sudden unexpected death in epilepsy (SUDEP) — paralleling the analogous Scn8a gain-of-function (p.Asn1768Asp) mouse model, supporting a shared "FHF1/Nav1.6 functional axis" in brain and heart (PMID:33982289).
Clinical output: Neonatal/infantile-onset intractable seizures (tonic, focal, migrating focal, spasms), developmental regression/intellectual disability of variable severity, occasional cerebellar/cerebral atrophy on MRI, and — in a subset — cardiac conduction abnormalities/SUDEP risk.

Divergent (loss-of-function) arm: Biallelic structural FGF12 variants instead reduce/eliminate FHF1's normal delay of Nav channel fast inactivation, i.e., a loss-of-function mechanism also producing DEE — indicating that both increased and decreased FHF1-mediated modulation of the same channels can destabilize network excitability, analogous to other channelopathy genes with bidirectional GOF/LOF disease mechanisms (PMID:37286232).

Molecular pathway: Not a classical signaling cascade (Wnt/MAPK/mTOR) — the relevant "pathway" is direct protein–ion channel modulation (FHF1–Nav1.2/1.5/1.6 C-terminal tail interaction), distinguishing FHF1 pathophysiology mechanistically from canonical growth-factor-receptor FGF signaling.

Cell types involved: Cortical and hippocampal excitatory pyramidal neurons (notably CA3), cerebellar neurons (Purkinje cells, by analogy to paralog FGF14/FHF4 biology), and cardiomyocytes (via Nav1.5).

Suggested GO terms: GO:0086010 (membrane depolarization during cardiac muscle cell action potential), GO:1902480 (regulation of the voltage-gated sodium channel), GO:0044309 (neuron spine), GO:0034765 (regulation of ion transmembrane transport) Suggested CL terms: CL:0000598 (pyramidal neuron), CL:0001031 (cerebellar Purkinje cell), CL:0000746 (cardiac muscle cell)

Advanced/omics data: iPSC-derived neuronal models have been generated from a patient carrying c.334G>A (PMID:37331110), enabling future electrophysiological and transcriptomic studies; no large-scale transcriptomic/proteomic/metabolomic datasets specific to FGF12-DEE were identified in this search.

7. Anatomical Structures Affected

Organ level (primary): Central nervous system (brain — cerebral cortex, hippocampus, cerebellum). Secondary: heart (conduction system), via the shared Nav-channel-modulatory mechanism.
Body systems: Nervous system (primary), cardiovascular system (secondary, arrhythmia/SUDEP risk).
Tissue/cell level: Cerebral and cerebellar cortex (mild atrophy on imaging in ~41.6% of more severely affected patients); excitatory pyramidal neurons; cerebellar Purkinje-cell circuitry (by mechanistic analogy with paralog FHF4/FGF14); cardiomyocytes/conduction tissue.
Subcellular level: FHF1 protein localizes intracellularly — nucleus, nucleolus, and cytoplasm — and acts at the plasma membrane at the site of the sodium-channel C-terminal tail (GO Cellular Component: plasma membrane, voltage-gated sodium channel complex).
UBERON suggestions: UBERON:0000955 (brain), UBERON:0002037 (cerebellum), UBERON:0001954 (Ammon's horn/hippocampus), UBERON:0000948 (heart), UBERON:0002382 (cardiac conduction system).
Laterality: Not applicable (diffuse/bilateral CNS process).

8. Temporal Development

Onset: Neonatal to early infantile — seizures typically begin within the first days to weeks of life in the classic severe DEE47 phenotype; all patients in the broadened cohort had epilepsy onset before 5 months of age (PMID:40488543). Development is typically normal before seizure onset.
Onset pattern: Acute onset of seizures, sometimes explosive (particularly with the G50S/G112S variant) versus a more gradual onset pattern (more typical of R52H) (PMID:40488543).
Progression: Variable — ranges from a progressive, refractory course with developmental regression (classic severe DEE47) to stabilization/remission with early, effective antiseizure treatment (milder end of spectrum).
Disease course pattern: Can be intractable/refractory (frequent, difficult-to-control seizures with persistent neurologic impairment) or drug-responsive with seizure remission (up to 70% achieving remission within 6 months on ASMs in a favorable-outcome cohort).
Critical window: Early, precision-guided initiation of sodium-channel-blocking antiseizure medication appears to be a critical intervention window associated with better long-term cognitive/developmental outcome.
Duration: Chronic, lifelong condition; in a minority of severe cases, mortality can occur early via SUDEP-like mechanisms (supported by mouse model data — see below).

9. Inheritance and Population

Prevalence/Incidence: No formal population prevalence or incidence estimates are available; this is an ultra-rare Mendelian condition identified through targeted or exome/genome sequencing in patients with epilepsy, with fewer than ~30–40 patients cumulatively reported in the literature to date (aggregated across the ~27-patient and other smaller cohorts identified in this search).
Inheritance pattern: Autosomal dominant, almost always de novo, for the classic missense gain-of-function and duplication forms. A recessive (biallelic) form has now also been described via loss-of-function structural variants (PMID:37286232) — representing an important, newly recognized second inheritance mode.
Penetrance: Appears high/complete for the recurrent de novo missense variants given consistent early-onset phenotypes, though expressivity (severity) is variable.
Expressivity: Markedly variable — from severe intractable DEE with developmental regression and cerebellar atrophy, to drug-responsive epilepsy with normal-to-near-normal cognitive outcome, to seizure-free autism/developmental-delay presentations (S8P variant).
Germline mosaicism: Reported in at least one family, with implications for recurrence risk counseling in ostensibly "de novo" cases.
Founder effects / geographic distribution: No founder populations identified; cases reported worldwide, including cohorts from Japan (PMID for "Two Japanese cases" report), Turkey (129-patient DEE cohort including FGF12 cases, PMID:41153369), Europe, and North America.
Sex ratio: Not specifically reported as skewed; autosomal gene, no clear sex predilection identified in the literature reviewed.
Consanguinity: Relevant specifically to the newly described biallelic (recessive) form, where both parental alleles must be transmitted.

10. Diagnostics

Genetic testing (primary diagnostic modality): - Whole exome sequencing (WES) / whole genome sequencing (WGS) — the primary route of discovery for de novo missense and many CNV cases; trio WES/WGS is standard for suspected genetic epilepsy/DEE. - Long-read sequencing — specifically valuable for detecting intragenic structural variants/duplications in FGF12 that short-read exome sequencing can miss, as demonstrated in both the biallelic LOF cases (PMID:37286232) and recurrent intragenic duplication cases (PMID:40838839). - Chromosomal microarray (CMA) — can detect larger duplications/complex rearrangements encompassing FGF12 (e.g., West-syndrome-associated 3q28 rearrangement, PMID:31311986). - Gene panels for early-onset/DEE — FGF12 is included in clinical epilepsy gene panels (e.g., Genomics England PanelApp, "Early onset or syndromic epilepsy" panel). - Single-gene testing/Sanger confirmation of recurrent hotspot variants (R52H, G50S/G112S) is reasonable given their recurrence.

Clinical/EEG/imaging: - EEG: background slowing, multifocal epileptiform discharges, possible hypsarrhythmia. - Brain MRI: may show mild cerebral and/or cerebellar atrophy in more severely affected patients (~41.6%); typically normal in the drug-responsive/favorable-outcome subgroup. - Cardiac evaluation (ECG/Holter) — increasingly recommended given emerging reports of ictal asystole and the mouse-model cardiac arrhythmia/SUDEP phenotype; a reasonable diagnostic consideration once the genetic diagnosis is established.

Functional/precision diagnostics: In-vitro electrophysiological characterization of a patient's specific variant (heterologous Nav1.2/Nav1.6 co-expression assays) can clarify gain- vs loss-of-function status, informing precision antiseizure drug selection (PMID:36029553).

Differential diagnosis: Other early-onset DEEs/EIEE genes — SCN1A, SCN2A, SCN8A, KCNQ2, STXBP1, CDKL5, FGF13(FHF2), and syndromes presenting as Ohtahara syndrome, EIMFS, or West syndrome; genetic testing is required to distinguish these clinically overlapping entities.

Screening: No population-level newborn or carrier screening program exists for this ultra-rare condition; diagnosis is reactive, triggered by neonatal/infantile-onset refractory epilepsy.

11. Outcome / Prognosis

Mortality: No formal human mortality statistics are available, but SUDEP is a plausible and mechanistically supported risk, based directly on the Fhf1^R52H/+ mouse model, in which mice die of sudden death with cardiac arrhythmia/bradycardia around postnatal day 16–20, and on the human case report of ictal asystole requiring pacemaker implantation (PMID:33982289; PMID:40897676).
Morbidity/function: Ranges from severe, persistent intellectual disability and neurologic impairment (moderate-to-severe ID reported in ~79% of one cohort) to normal/near-normal developmental outcome in the favorable, drug-responsive subgroup.
Complications: Developmental regression, refractory epilepsy, cerebral/cerebellar atrophy, cardiac arrhythmia/ictal asystole (emerging).
Recovery potential: Substantially improved by early recognition of the genetic diagnosis and prompt initiation of sodium-channel-blocking antiseizure medications — the single most consistent prognostic modifier identified across the literature. In one cohort, patients started promptly on sodium channel blockers achieved seizure freedom with good developmental outcomes in 8/12 cases, versus DEE in the remainder.
Prognostic factors: Specific variant identity (R52H vs G50S/G112S vs biallelic LOF) correlates with onset pattern and severity; presence of cerebellar/cerebral atrophy on MRI correlates with worse prognosis; timing of ASM initiation is a key modifiable prognostic factor.

12. Treatment

Pharmacotherapy — precision, mechanism-guided sodium-channel blockade is the central treatment strategy, reflecting the gain-of-function Nav-channel mechanism:

Phenytoin — repeatedly reported as effective, including in the original discovery families and multiple subsequent case reports; a hallmark "diagnostic-therapeutic" indicator for FGF12-DEE (PMID:38465135; original Neurology Genetics duplication report, e133).
Carbamazepine — the most commonly used agent among achieving-remission patients in the largest recent cohort (used in 6/10 patients; 4/? achieved remission specifically on carbamazepine) (PMID:40488543).
Oxcarbazepine — used successfully in at least one patient achieving remission (PMID:40488543).
High-dose phenobarbital — effective in some early reports (e.g., epilepsy of infancy with migrating focal seizures phenotype responded to phenytoin and high-dose phenobarbital).
Valproic acid (VPA) + topiramate (TPM) combination therapy — reported as effective (seizure freedom in all three probands with the c.341G>A variant), with two patients showing improved motor/cognitive function; the first documented report of this specific combination's efficacy for an FGF12 variant (PMID:34020858).
Lamotrigine — used successfully in at least one remission case in the broadened cohort.
General class: across cohorts, sodium channel blockers as a class are "commonly associated with clinical improvement," and specific FGF12 variants "may be amenable to precision treatment with sodium channel blockers" (PMID:36029553; PMID:42057324/PMID:42185328 review cohorts).

Pharmacogenomic caution: Because the biallelic/structural-variant form of FGF12-DEE operates via a loss-of-function mechanism, sodium-channel-blocker responsiveness cannot necessarily be assumed for all FGF12 variants — precision therapy selection should ideally be informed by variant-specific functional data (gain- vs loss-of-function) rather than gene identity alone.

Advanced/experimental therapeutics: No gene therapy, ASO, or targeted biologic therapies specific to FGF12-DEE were identified in the literature reviewed; the mechanistic/precision approach to date is limited to selection among existing sodium-channel-blocking antiseizure medications.

Supportive/rehabilitative care: Physical, occupational, and speech therapy are standard supportive measures for the neurodevelopmental impairment component, though not specifically studied in this population.

Cardiac monitoring/management: Given the emerging cardiac-arrhythmia/SUDEP signal, cardiac evaluation and, in select cases, pacemaker implantation (as already reported for ictal asystole) may be part of a comprehensive management strategy (PMID:40897676). Atenolol has been shown in the analogous mouse SUDEP model to reduce cardiac-mediated mortality, suggesting a possible (as-yet unstudied in humans) beta-blocker strategy for cardiac risk mitigation (biorxiv 2023, "Atenolol reduces cardiac-mediated mortality in genetic mouse model of sudden unexpected death in epilepsy").

Suggested NCIT terms: - NCIT:C15986 Pharmacotherapy (parent term) - Therapeutic agents (CHEBI/NCIT): phenytoin (CHEBI:8107), carbamazepine (CHEBI:3564), oxcarbazepine (CHEBI:7824), phenobarbital (CHEBI:8069), valproic acid (CHEBI:39867), topiramate (CHEBI:9646), lamotrigine (CHEBI:6367) - NCIT:C15315 Rehabilitation (supportive/rehabilitative care) - NCIT:C15289 Organ Transplantation / device-related — not applicable; pacemaker implantation would fall under NCIT:C15329 Surgical Procedure / device category

Treatment algorithm implication: Because this is a sodium-channelopathy, clinicians and guideline literature explicitly caution against the use of sodium-channel-blocker-contraindicated regimens typical in some other DEEs, mirroring the precision-medicine logic already established for SCN2A/SCN8A gain-of-function epilepsies.

13. Prevention

No primary, secondary, or tertiary prevention strategies specific to FGF12-DEE exist, as it is caused by de novo variants not amenable to population-level prevention. The relevant "prevention" activities identified in the literature are: - Genetic counseling for families with a diagnosed proband, particularly given the documented occurrence of germline mosaicism (recurrence risk counseling) and the newly recognized recessive/biallelic form (carrier-based reproductive risk assessment in consanguineous or carrier-carrier couples). - Prenatal/preimplantation genetic testing could theoretically be offered once a familial variant is identified (mosaicism or biallelic carrier couple), though no specific reports of this were found for FGF12. - Secondary prevention — early genetic diagnosis enabling prompt, mechanism-guided sodium-channel-blocker therapy functions as a de facto "prevention" of the worst neurodevelopmental outcomes, per the outcome data above. - No immunization, public health, or population screening programs apply to this ultra-rare monogenic disorder.

14. Other Species / Natural Disease

No naturally occurring veterinary or wildlife disease attributable to FGF12/FHF1 variants has been reported in the literature reviewed. FGF12 orthologs are broadly conserved across vertebrates (used experimentally in mouse and zebrafish, see below), but no OMIA (Online Mendelian Inheritance in Animals) entries or spontaneous animal disease reports were identified.

15. Model Organisms

Mouse models: - Fhf1^R52H/+ knock-in mice (CRISPR-edited to carry the human-equivalent p.Arg52His mutation) — recapitulate early-onset epilepsy and SUDEP with cardiac arrhythmia. EEG at postnatal day 19–20 confirmed severe tonic seizures immediately preceding loss of brain activity and death; mice die around day 16 (spontaneous seizures and SUDEP), with phenytoin only marginally prolonging survival (to ~day 19) (Velíšková et al. 2021, Epilepsia, PMID:33982289). This model directly parallels the human phenotype and demonstrates a shared FHF1/Nav1.6 functional axis with the analogous Scn8a p.Asn1768Asp gain-of-function mouse model. - FGF12^ΔV52H mice — a related model showing increased excitability in dorsal hippocampal CA3 neurons by patch-clamp recording and seizure susceptibility (without necessarily showing spontaneous seizures), implicating a "complex FGF12 network" (ScienceDirect 2024). - Atenolol intervention study — in the genetic SUDEP mouse model, the beta-blocker atenolol reduced cardiac-mediated mortality, supporting a translatable cardioprotective strategy (bioRxiv 2023). - Neuro2A (N2A) transfection studies — heterologous cell system used to characterize gain-of-function shifts in Nav1.6/Nav1.2 fast-inactivation kinetics induced by mutant FHF1, foundational for establishing the molecular mechanism (PMID:27164707, PMID:36029553).

Zebrafish models: - Zebrafish overexpression/knock-in of mutant FHF1 (R52H/R114H equivalent) — showed increased neuronal excitability and epileptiform activity, directly supporting the gain-of-function disease mechanism in vivo in a second vertebrate model system (Siekierska et al. 2016, PMID:27164707).

Cellular/iPSC models: - Patient-derived induced pluripotent stem cell (iPSC) line generated from a patient carrying the FGF12 c.334G>A variant, intended to enable neuronal differentiation and disease modeling of "developmental epileptic encephalopathy" pathogenesis (PMID:37331110).

Model recapitulation and limitations: The mouse Fhf1^R52H/+ model recapitulates both the seizure phenotype and, notably, the emerging cardiac arrhythmia/SUDEP phenotype now also observed clinically in humans (ictal asystole case, PMID:40897676) — an unusually strong translational correlation. Limitations include the mouse model's very early lethality (~postnatal day 16–20), which may limit study of the milder, drug-responsive, favorable-cognitive-outcome end of the human phenotypic spectrum; and the zebrafish model's inherent differences in nervous system complexity relative to humans.

Summary Table: Key PMIDs Cited

PMID	Study	Key contribution
27164707	Siekierska et al. 2016, Neurology	Original R52H/R114H discovery; zebrafish + cell GOF model; cerebellar atrophy
27830185	Villeneuve et al. 2016, Neurol Genet	3 more R52H patients; infancy-to-adulthood spectrum
33982289	Velíšková et al. 2021, Epilepsia	Fhf1^R52H/+ mouse: SUDEP, cardiac arrhythmia
34020858	—	VPA+TPM combination effective for c.341G>A
36029553	— (eBioMedicine)	Complex GOF/LOF kinetic effects; S8P autism-only variant
37286232	— (Life Science Alliance)	First biallelic/recessive LOF FGF12-DEE, long-read sequencing
37331110	—	iPSC line from FGF12 c.334G>A patient
40488543	Pierret et al. 2025, Epilepsia	10-patient cohort; G50S/R52H; drug-responsive favorable-outcome phenotype
40838839	—	Long-read sequencing of recurrent intragenic duplications
40897676	—	Ictal asystole/pacemaker case
31311986	Uehara et al. 2019, J Hum Genet	Full FGF12 duplication → West syndrome
38042708	—	"FGF12: biology and function" review
42057324 / 42185328	Aldurayhim et al. / related 2026 cohorts	27- and 12-patient cohorts; sodium channel blocker response rates

Sources

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	25
Resolved	25
Unresolved (possible confabulation)	0
Unverifiable	0
Quoted claims checked	6
Quoted claims found in source	3
Quoted claims not found in source	3
References weighed for topical relevance	25
On topic	20
Off topic	0

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

PMID:42057324 (abstract only): "may be amenable to precision treatment with sodium channel blockers"
closest text in source: "While treatment responses were heterogeneous, sodium channel blockers were commonly associated with clinical improvement"
PMID:42185328 (abstract only): "may be amenable to precision treatment with sodium channel blockers"
closest text in source: "8 patients promptly started on sodium channel blockers became seizure-free with good developmental outcomes while 4 developed DEE"
PMID:37331110 (abstract only): "Generation of iPSC line from FGF12 mutation patient"
closest text in source: "This study used non-insertion Sendai virus transfection to establish the induced pluripotent stem cells(iPSCs)line with FGF12 mutation"

FGF12-Related Developmental and Epileptic Encephalopathy

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FGF12-Related Developmental and Epileptic Encephalopathy: Comprehensive Research Report

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic / Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

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11. Outcome / Prognosis

12. Treatment

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14. Other Species / Natural Disease

15. Model Organisms

Summary Table: Key PMIDs Cited

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