SPTBN4-Related Neurodevelopmental Disorder

Mendelian MONDO:0060496 Pathograph 14 Show in embeddings browser Neurodevelopmental Disorder Autosomal recessive disease

Neurodevelopmental disorder with hypotonia, neuropathy, and deafness (NEDHND) is an autosomal recessive disorder caused by bi-allelic variants in SPTBN4, the gene encoding beta-IV spectrin. It is a disease of one subcellular structure: the submembranous actin-spectrin scaffold that builds the axon initial segment and the node of Ranvier. Beta-IV spectrin is the beta-subunit of that scaffold, binding actin at one end and ankyrin-G at the other, and it is required both to hold the nodal membrane undercoat together and to concentrate the voltage-gated ion channels that make an axon excitable. When it is lost, sodium-channel and KCNQ2/KCNQ3 potassium-channel clusters fail, action-potential initiation and saltatory conduction degrade, and long myelinated motor and auditory axons - the fibres most dependent on that scaffold - degenerate. The clinical result is congenital hypotonia with profound global developmental delay, absent or severely limited speech, a motor axonal neuropathy with areflexia and secondary muscle wasting, feeding and respiratory failure from bulbar weakness, and, in a minority, auditory neuropathy, seizures or a paradoxically epileptiform EEG without clinical seizures. Two features of the entity deserve emphasis at the outset. First, the disease name overstates deafness: the largest series to date counted deafness in 21% of patients and the HPO annotation set for OMIM:617519 records sensorineural hearing impairment at 2/5, although the founding 2018 report named auditory neuropathy as part of the syndrome it described. Second, the "myopathy" reported in the earliest descriptions is now contested - a muscle-specific beta-IV-spectrin knockout showed the protein is not present in skeletal muscle at all, implying the muscle pathology is neurogenic. The published experience remains small; the most recent systematic review counted 38 reported individuals worldwide.

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Classifications

Harrison's Chapter

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Inheritance

Autosomal recessive inheritance HP:0000007

Disease requires two damaging SPTBN4 alleles. Homozygous genotypes dominate the reported literature, reflecting ascertainment through consanguineous families in the Middle East, Iran, Afghanistan and Kurdish populations; compound heterozygotes are a small minority. Heterozygous carriers, including the parents in every reported family, are not described as affected, and no dominant or de novo SPTBN4 mechanism has been established for this phenotype. Penetrance is left unset rather than asserted. No apparently healthy bi-allelic individual has been reported, but neither has any systematic population-database interrogation of SPTBN4 genotypes been published, so complete penetrance would be an inference from ascertainment rather than an observation. Two counts from the 2025 natural-history review bear on the recessive model and are recorded here rather than as separate claims - 31 different pathogenic variants across 38 patients, and compound heterozygosity in only 4 of them. The same review reports two de novo variants in individuals ascertained through ADHD/autism cohorts rather than through NEDHND, which is a different and much weaker genotype-phenotype assertion; those cases are not treated here as evidence for a dominant mechanism in this disease.

Autosomal recessive inheritance

Show evidence (3 references)

PMID:33772159 SUPPORT Human Clinical

"Neurodevelopmental disorder with hypotonia, neuropathy, and deafness (NEDHND, OMIM #617519) is an autosomal recessive disease caused by homozygous or compound heterozygous variants in SPTBN4 coding for type 4 βIV-spectrin, a non-erythrocytic member of the β-spectrin family."

States the mode of inheritance, the OMIM entity number this MONDO term xrefs, and the two admissible bi-allelic genotype configurations.

PMID:32672909 SUPPORT Other

"SPTBN4 disorder is inherited in an autosomal recessive manner."

Independent confirmation from the GeneReviews chapter, which is the source clinical laboratories and counsellors use.

PMID:33772159 SUPPORT Human Clinical

"Most affected individuals reported to date are homozygous."

Supports the statement that homozygous genotypes, rather than compound heterozygosity, dominate the reported series.

Discussions and Knowledge Gaps

What fraction of individuals with SPTBN4 disease actually have clinical seizures, given that the four available sources give figures spanning "very rare" to "more than half"?

KNOWLEDGE GAP OPEN sptbn4-seizure-frequency-conflict

Attached to

pathophysiology#Axonal Hyperexcitability and Epileptiform Discharge

This is not a rounding disagreement. GeneReviews states that half of affected individuals develop seizures. The 2021 cohort report says more than half develop seizures or have a pathological EEG, which is a different and broader endpoint. The 2025 systematic review of 38 patients puts seizures at 21%. The HPO annotation set for OMIM:617519 carries HP:0001250 with the frequency modifier "Very rare", sourced to OMIM. The likely explanation is that the compound endpoint (seizures OR epileptiform EEG) has been propagated as if it were the seizure rate, compounded by ascertainment - EEG was performed in only 12 of 38 patients, and prolonged recording in fewer still, so the epileptiform abnormality is systematically under-detected while clinical seizures are not. Until this is resolved, a clinician cannot give a family a defensible seizure risk, and the entry deliberately asserts no FrequencyEnum band for either the seizure or the EEG phenotype.

Proposed experiments

Prospective prolonged-EEG phenotyping of a molecularly defined cohort

sptbn4-prospective-eeg-cohort

Perform 24- to 72-hour EEG including sleep in every molecularly confirmed SPTBN4 patient in a multicentre registry, irrespective of seizure history, and report clinical seizures and epileptiform abnormality as two separate denominators rather than a compound endpoint.

Is the muscle pathology in SPTBN4 disease a primary myopathy, or is it entirely secondary to denervation?

KNOWLEDGE GAP OPEN sptbn4-myopathy-neurogenic-or-myogenic

Attached to

pathophysiology#Contested Skeletal Muscle Involvement histopathology#Absent beta-IV-spectrin immunostaining in patient muscle

The disorder was first described as a congenital myopathy on the strength of fibre-type disproportion plus sarcolemmal beta-IV-spectrin immunostaining that was present in controls and absent in patient muscle, and a second cohort replicated the immunostaining result and proposed a direct effect on sarcolemmal stability and myofibre depolarisation. A muscle-specific conditional knockout then reported that beta-4 spectrin is not present in muscle at all and that the myopathy must be neurogenic. The disagreement is methodologically tractable rather than philosophical: the human immunohistochemistry was performed without a beta-IV-spectrin-null muscle as an antibody specificity control, and the conditional knockout was performed in mouse rather than human muscle. It matters because it determines whether a normal or myopathic muscle biopsy carries any diagnostic weight, and whether muscle is a legitimate therapeutic target.

Proposed experiments

Antibody specificity control on beta-IV-spectrin-null muscle

sptbn4-muscle-antibody-specificity

Re-run the sarcolemmal immunohistochemistry using the same antibodies on muscle from a beta-IV-spectrin-null mouse alongside human control and patient muscle, to establish whether the sarcolemmal signal reported in controls is beta-IV spectrin or a cross-reacting epitope.

SPTBN4 expression in human skeletal muscle by RNA-seq and proteomics

sptbn4-human-muscle-transcriptomics

Quantify SPTBN4 transcript and beta-IV spectrin peptide abundance in human skeletal muscle and at the human neuromuscular junction, since the conditional-knockout evidence is murine and human expression has been asserted on both sides of the argument.

Does loss of beta-IV spectrin raise or lower neuronal excitability, given that its two clustered channel clients push in opposite directions?

KNOWLEDGE GAP OPEN sptbn4-excitability-direction

Attached to

pathophysiology#Impaired Action Potential Initiation and Saltatory Conduction pathophysiology#Failure of KCNQ2 and KCNQ3 Potassium Channel Clustering

Losing nodal and AIS sodium channels should make neurons harder to fire, and that is what was measured in the dentate gyrus in vivo and at the auditory presynaptic terminal, where action-potential threshold rose. Losing nodal KCNQ2/KCNQ3 should make axons fire spontaneously, and that is what was measured at the diaphragm neuromuscular junction and what the patients' near-continuous epileptiform discharges suggest. Both effects occur in the same mutant animals. The unresolved question is what determines which dominates - axonal compartment, fibre type, developmental stage, or the specific truncation - and the answer would have direct therapeutic implications, since a KCNQ opener and a sodium-channel enhancer are opposite interventions. It is recorded as a knowledge gap rather than resolved in favour of either arm.

Proposed experiments

Compartment-resolved excitability mapping in beta-IV spectrin nulls

sptbn4-compartment-resolved-excitability

Record simultaneously from soma, axon initial segment and node in the same neurons of beta-IV-spectrin-null mice across development, to determine where and when the sodium-channel and KCNQ2 arms dominate.

Does any available model or human material support the cortical mechanism proposed for the intellectual disability, which is the disorder's most disabling feature?

HUMAN MODEL MISMATCH OPEN sptbn4-no-human-cns-tissue

Attached to

pathophysiology#Cortical Network Dysfunction and Impaired Neurodevelopment

This is a model-fidelity problem rather than an absence of evidence, which is why it is recorded as HUMAN_MODEL_MISMATCH. Substantial in vivo evidence exists, but none of it addresses the human cognitive phenotype. No post-mortem CNS tissue, no brain biopsy and no patient-derived iPSC neuronal model from an SPTBN4 individual has been reported; the human tissue evidence in this disorder consists of nerve biopsy, muscle biopsy and fibroblasts. The mouse models reproduce ataxia, tremor, deafness and motor paresis, all of which are minor or absent components of the human phenotype, while intellectual disability - present in nearly every patient - has no characterised murine counterpart. The specific mismatch runs both ways: the mouse is ataxic and the humans generally are not, and the humans are profoundly intellectually disabled and the mouse has not been tested. Every cortical mechanistic claim in this entry is therefore extrapolated from rodent hippocampal and brainstem recordings, and the competing explanation - that the developmental delay is substantially secondary to motor, communicative and sensory deprivation plus recurrent hypoxia - has never been excluded.

Proposed experiments

Patient iPSC-derived cortical neurons and AIS morphometry

sptbn4-ipsc-cortical-neurons

Derive cortical neurons from SPTBN4 patients and controls and measure AIS length and position, ankyrinG and Nav/KCNQ2 clustering, and intrinsic excitability, in the cell type the cognitive phenotype implicates.

Cognitive phenotyping of beta-IV spectrin mutant mice

sptbn4-mouse-cognitive-phenotyping

Run learning, memory and social-behaviour batteries on the existing quivering and gene-trap lines, controlling for their motor and auditory impairment, to establish whether a cognitive phenotype exists in the model at all.

Neuropathological examination through a patient registry

sptbn4-neuropathology-registry

Establish consent for post-mortem CNS examination within a rare-disease registry, since mortality in early childhood is unfortunately common in this disorder and no neuropathology has ever been reported.

Should the OMIM/MONDO label for this disorder continue to name deafness as a cardinal feature when it is present in a minority of patients?

CURATION TODO OPEN sptbn4-deafness-in-the-disease-name

Attached to

phenotypes#Sensorineural hearing impairment (auditory neuropathy)

Both counted series put hearing impairment well below half - 2/5 in the HPO annotation set for OMIM:617519 and 21% in the 38-patient review - while hypotonia, developmental delay, absent speech and poor head control approach 100%. The name derives from the founding single-case report, in which central deafness was one of three presenting features and was the observation that connected the patient to the quivering mouse. The practical harm is real: a clinician using the disease name as a phenotype checklist will under-consider SPTBN4 in the much larger group of hypotonic, areflexic infants with normal hearing. Recorded here rather than acted on, because renaming is an OMIM/MONDO decision and outside the scope of a dismech entry; the correct dismech response is the explicit caveat in the entry-level notes and in the hearing-impairment phenotype.

What are the two reported individuals with SPTBN4 variants whose disease onset was at 48 and 60 years of age?

KNOWLEDGE GAP OPEN sptbn4-late-onset-outliers

Attached to

pathophysiology#Residual-Function Alleles and the Mild End of the Spectrum

A congenital-onset neurodevelopmental disorder with two cases of mid-to-late-adult onset is either two different diseases or a misattribution. The 2025 systematic review records the observation in a single clause with no clinical, molecular or ascertainment detail, and the primary source is not identifiable from the review text alone. The possibilities are distinguishable and consequential: these could be genuinely hypomorphic alleles defining an adult-onset SPTBN4 neuropathy; they could be individuals ascertained through a neuropathy cohort in whom an SPTBN4 variant is incidental; or the ages could be errors of transcription in the review's supplementary table. Until this is resolved, the entry treats congenital-to-early-childhood onset as the disorder's natural history and flags the outliers rather than widening the onset range.

Proposed experiments

Trace and re-phenotype the reported late-onset individuals

sptbn4-late-onset-source-tracing

Identify the primary publications behind the two late-onset entries in the pooled review, obtain their genotypes and phenotypes, and determine whether they represent a distinct adult-onset SPTBN4 phenotype or an artefact of pooling.

⚙

Pathophysiology

Bi-allelic Loss-of-Function SPTBN4 Variants

The primary lesion is bi-allelic damage to SPTBN4 at 19q13.13, reported against transcript NM_020971. The reported allelic spectrum is dominated by truncating variants - nonsense, frameshift, splice-site and at least one multi-exon deletion - with a minority of missense changes. Missense alleles cluster in the spectrin-repeat rod, which is the segment that polymerises the scaffold, and the founding functional study showed that most tested patient alleles behave as loss of function in neurons rather than as subtler hypomorphs. There is no clean genotype-phenotype correlation: the variants are dispersed across the whole gene, and the one clearly milder published family carries an in-frame splice consequence rather than a distinct class of allele.

SPTBN4 hgnc:14896

Downstream

Loss of beta-IV Spectrin from the Axon Initial Segment and Nodal Membrane Skeleton Truncating and most missense alleles remove functional beta-IV spectrin from the axonal membrane skeleton, either by abolishing the protein or by preventing its targeting to the AIS.

Residual-Function Alleles and the Mild End of the Spectrum A parallel, allele-specific arm. In-frame consequences that preserve part of the protein are the proposed explanation for the one published family with axonal neuropathy but normal cognition.

Show evidence (4 references)

PMID:29861105 SUPPORT Human Clinical

"we report bi-allelic pathogenic SPTBN4 variants (three homozygous and two compound heterozygous) that cause a severe neurological syndrome that includes congenital hypotonia, intellectual disability, and motor axonal and auditory neuropathy"

The founding cohort report establishing bi-allelic SPTBN4 variants as the cause of the syndrome curated here.

PMID:29861105 SUPPORT In Vitro

"We introduced these variants into βIV spectrin, expressed these in neurons, and found that 5/7 were loss-of-function variants disrupting AIS localization or abolishing phosphoinositide binding."

Functional testing of the patient alleles themselves, showing that they act by loss of function through two specific molecular routes - failure of AIS targeting and loss of phosphoinositide (PH-domain) binding.

PMID:40781329 SUPPORT Human Clinical

"more than 70% of SPTBN4 variants are located in spectrin repeat domains"

Localises the bulk of the reported allelic spectrum to the spectrin-repeat rod, the segment that builds the scaffold.

+ 1 more reference

Loss of beta-IV Spectrin from the Axon Initial Segment and Nodal Membrane Skeleton

Beta-IV spectrin is the neuron-specific beta-subunit of the submembranous spectrin scaffold, restricted almost entirely to the axon initial segment and the nodes of Ranvier of myelinated neurons. The axonal scaffold it belongs to is a periodic lattice: actin rings spaced roughly 180 to 190 nm apart along the axon, bridged by spectrin tetramers of that same length, with sodium channels distributed in register with the lattice. Beta-IV spectrin is what links that lattice to the membrane at excitable domains. Its longest isoform, beta-IV-Sigma1, is the only one carrying an actin-binding domain and also carries 17 spectrin repeats, the ERQES specific domain and a pleckstrin homology domain; a shorter, N-terminally-truncated isoform, Sigma6, is expressed at much higher levels and carries the sodium-channel-clustering activity. The isoform structure matters clinically, because truncating variants at different positions remove different subsets of isoforms.

myelinated neuron CL:0000540

SPTBN4 hgnc:14896

beta-IV spectrin-containing membrane skeleton GO:0008091

actin binding GO:0003779 ↓ DECREASED structural constituent of cytoskeleton GO:0005200 ↓ DECREASED phosphoinositide binding via the pleckstrin homology domain GO:0035091 ↓ DECREASED

axon initial segment GO:0043194 node of Ranvier GO:0033268 spectrin-associated cytoskeleton GO:0014731

Downstream

Failure of the Reciprocal AnkyrinG-beta-IV Spectrin Scaffold Loss of the beta-subunit removes one half of a mutually stabilising pair, so ankyrin-G is no longer retained at the AIS and node.

Loss of the Dense Nodal Membrane Undercoat The actin-binding Sigma1 isoform is the structural component of the electron-dense coat beneath the nodal membrane; without it the coat disappears.

Show evidence (6 references)

PMID:11086001 SUPPORT In Vitro

"In brain, betaIV spectrin is enriched in myelinated neurons, where it colocalizes with ankyrin(G) 480/270-kD at axon initial segments and nodes of Ranvier."

Establishes the subcellular localisation that defines this disorder - beta-IV spectrin is an AIS and nodal protein of myelinated neurons.

PMID:11086001 SUPPORT In Vitro

"The longest isoform (betaIVSigma1 spectrin) includes an actin-binding domain, followed by 17 spectrin repeats, a specific domain in which the amino acid sequence ERQES is repeated four times, several putative SH3-binding sites and a pleckstrin homology domain."

Defines the domain architecture whose loss the patient alleles cause, including the PH domain whose phosphoinositide binding several patient variants abolish.

PMID:23239625 SUPPORT In Vitro

"Actin formed ringlike structures that wrapped around the circumference of axons and were evenly spaced along axonal shafts with a periodicity of ~180 to 190 nanometers."

Establishes the periodic actin-spectrin lattice architecture of the axon, the structure that beta-IV spectrin builds at excitable domains.

+ 3 more references

Failure of the Reciprocal AnkyrinG-beta-IV Spectrin Scaffold

AnkyrinG and beta-IV spectrin are not arranged in series but in a reciprocal pair. AnkyrinG recruits beta-IV spectrin to the AIS and to nodes through a specific domain in the spectrin, and beta-IV spectrin in turn retains ankyrinG there; deleting either one delocalises the other. That reciprocity is why an SPTBN4 lesion is not merely the loss of one scaffolding activity but the collapse of the adaptor hub through which every clustered channel and adhesion molecule is anchored. Two of the routes by which patient alleles break this hub were demonstrated directly: failure to localise to the AIS, and loss of phosphoinositide binding by the pleckstrin homology domain, which is the membrane-facing half of the linkage.

myelinated neuron CL:0000540

SPTBN4 hgnc:14896

ankyrin binding GO:0030506 ↓ DECREASED

axon initial segment GO:0043194 node of Ranvier GO:0033268

Downstream

Failure of Voltage-Gated Sodium Channel Clustering at the AIS and Node The ankyrinG-spectrin hub is the anchor for nodal and AIS Nav channels; losing it disperses them.

Failure of KCNQ2 and KCNQ3 Potassium Channel Clustering The same hub, acting through regulatory partners rather than by direct binding, positions the nodal KCNQ2/KCNQ3 channels.

Show evidence (5 references)

PMID:11807096 SUPPORT Model Organism

"These results indicate that betaIV-spectrin and ankyrin-G mutually stabilize the membrane protein cluster and the linked membrane cytoskeleton at AIS and NR."

States the reciprocal stabilisation that this node models, from the definitive gene-trap knockout study.

PMID:11807096 SUPPORT Model Organism

"Conversely, in ankyrin-G-null neurons, betaIV-spectrin is not localized to these sites."

Establishes the second direction of the reciprocity, which is the basis for treating ANK3 disease as a mechanistic differential.

PMID:17283186 SUPPORT In Vitro

"We identify a distinct protein domain in betaIV spectrin required for its localization to the AIS, and show that this domain mediates betaIV spectrin's interaction with ankG."

Identifies the specific beta-IV spectrin domain mediating the ankyrinG interaction, the interface that AIS-mislocalising patient variants disrupt.

+ 2 more references

Loss of the Dense Nodal Membrane Undercoat

Beneath the nodal axolemma sits an electron-dense submembranous coat that is thought to be what physically holds the channel cluster in place. Beta-IV-Sigma1 spectrin, the actin-binding isoform, is an essential component of that coat, and removing it alone makes the coat disappear, widens the node, and fills it with organelle-laden membrane dilations. The structural failure is separable from the channel-clustering failure: mice retaining only the short Sigma6 isoform still show waving and swelling of the AIS and nodal membrane while recovering much of their sodium-channel clustering, and mice lacking only Sigma6 do the reverse. So the disorder has two mechanistically distinct arms - a mechanical one and an electrical one - and a given truncating allele may load them unequally.

myelinated neuron CL:0000540

node of Ranvier GO:0033268 cortical cytoskeleton GO:0030863

peripheral nervous system UBERON:0000010

Downstream

Impaired Action Potential Initiation and Saltatory Conduction A structurally disorganised node cannot support the current densities that saltatory conduction requires.

Distal Motor Axonal Degeneration and Neurogenic Muscle Wasting Chronic mechanical destabilisation of nodal membrane, with organelle accumulation and axonal shape change, precedes overt axonal loss.

Show evidence (4 references)

PMID:15381686 SUPPORT Model Organism

"Here, we prove that betaIVSigma1 spectrin, the only betaIV spectrin with an actin-binding domain, is an essential component of this coat."

Identifies the specific isoform whose loss removes the nodal undercoat and states why - it is the only actin-binding beta-IV spectrin.

PMID:15381686 SUPPORT Model Organism

"Removal of betaIVSigma1 alone causes the disappearance of the nodal coat, an increased diameter of the NR, and the presence of dilations filled with organelles."

The direct ultrastructural consequence modelled by this node.

PMID:15317849 SUPPORT Model Organism

"Central nodes of qv(3J) mice, which lack betaIV spectrins, are significantly broader and have prominent vesicle-filled nodal membrane protrusions, whereas axon shape and neurofilament density are dramatically altered."

Independent replication of the nodal structural breakdown, and the source of the CNS-versus-PNS severity asymmetry noted above.

+ 1 more reference

Failure of Voltage-Gated Sodium Channel Clustering at the AIS and Node

Saltatory conduction depends on sodium channels being present at very high density over the short bare stretch of axolemma at each node, and action potential initiation depends on the same arrangement at the axon initial segment. Without beta-IV spectrin, neither ankyrinG nor the sodium channels are correctly clustered at these sites. In human disease this was shown directly: nerve biopsy from an affected individual had reduced nodal sodium channels. The failure is partial rather than absolute, and the reason is a specific compensation - ankyrinR together with beta-I spectrin can substitute at nodes and cluster some sodium channels when the ankyrinG/beta-IV-spectrin pair is gone.

motor neuron CL:0000100 cortical pyramidal neuron CL:4023111

clustering of voltage-gated sodium channels GO:0045162 ↓ DECREASED

voltage-gated sodium channel complex GO:0001518 node of Ranvier GO:0033268 axon initial segment GO:0043194

Downstream

Impaired Action Potential Initiation and Saltatory Conduction Reduced nodal sodium-channel density directly reduces the inward current available to regenerate the impulse at each node.

Show evidence (4 references)

PMID:11807096 SUPPORT Model Organism

"In betaIV-spectrin-null neurons, neither ankyrin-G nor voltage-gated sodium channels (VGSC) are correctly clustered at these sites, suggesting that impaired action potential caused by mislocalization of VGSC leads to the phenotype."

The core loss-of-function result. Removing beta-IV spectrin disperses both the adaptor and the sodium channels, and the authors attribute the organismal phenotype to that mislocalisation.

PMID:29861105 SUPPORT Human Clinical

"Nerve biopsies from an individual with a loss-of-function variant had reduced nodal Na+ channels and no nodal KCNQ2 K+ channels."

Direct human patient-tissue demonstration of the channel-clustering failure, which is what makes this mechanism a human disease mechanism rather than a mouse phenomenon.

PMID:29861105 SUPPORT Model Organism

"Modeling the disease in mice revealed that although ankyrinR (AnkR) and βI spectrin can cluster Na+ channels and partially compensate for the loss of AnkG and βIV spectrin at nodes of Ranvier, AnkR and βI spectrin cannot cluster KCNQ2- and KCNQ3-subunit-containing K+ channels."

Identifies the partial rescue that makes the sodium-channel arm survivable, and simultaneously identifies the potassium-channel arm as the non-compensable one.

+ 1 more reference

Failure of KCNQ2 and KCNQ3 Potassium Channel Clustering

This is the mechanistically distinctive lesion of the disorder and the one that best explains its epilepsy. Nodal KCNQ2/KCNQ3 (Kv7) channels carry the slow M-current that damps repetitive firing. In patient nerve they are not merely reduced but absent, and in the disease mouse model the ankyrinR / beta-I spectrin backup that partially rescues sodium channels cannot cluster KCNQ2/KCNQ3 at all. Beta-IV spectrin does not bind KCNQ2/3 directly, so it must position them through regulatory partners; consistent with that, total KCNQ2 protein is normal in mutant animals and only its localisation fails. The functional consequence measured in mice is axonal hyperexcitability - spontaneous and evoked neuromyotonic and myokymic discharges arising in myelinated axons - which is pharmacologically reversible with the KCNQ2/3 opener retigabine.

motor neuron CL:0000100

clustering of voltage-gated potassium channels GO:0045163 ↓ DECREASED

voltage-gated potassium channel complex GO:0008076 node of Ranvier GO:0033268

Downstream

Axonal Hyperexcitability and Epileptiform Discharge Loss of the nodal M-current brake permits spontaneous repetitive firing in myelinated axons.

Show evidence (5 references)

PMID:29861105 SUPPORT Human Clinical

"Nerve biopsies from an individual with a loss-of-function variant had reduced nodal Na+ channels and no nodal KCNQ2 K+ channels."

The human tissue observation that nodal KCNQ2 is absent, not merely reduced - a qualitatively more severe failure than the sodium-channel arm.

PMID:20962009 SUPPORT Model Organism

"Of interest, KCNQ2 subunit aggregates were undetectable at PNS and CNS nodes, whereas Nav and Kv1.1/Kv1.2 channels were properly concentrated at nodal and juxtaparanodal regions, respectively."

Shows the selectivity of the defect - in this allele KCNQ2 clustering fails while sodium and Kv1 channels are spared, isolating the potassium arm.

PMID:20962009 SUPPORT Model Organism

"The protein level of KCNQ2 subunits was normal in mutant animals, suggesting that KCNQ2 subunit absence stems from clustering or trafficking defects in axons."

Establishes that the lesion is one of localisation rather than of channel abundance, which is what makes it a cytoskeletal rather than a channelopathy mechanism.

+ 2 more references

Impaired Action Potential Initiation and Saltatory Conduction

The convergence point of the structural and the channel-clustering arms. With fewer sodium channels at a structurally disorganised AIS and node, the threshold for spike initiation rises, conduction along myelinated fibres slows, and high-frequency firing becomes unreliable. Both features have been measured: in the auditory brainstem, beta-4-spectrin-null mice show an elevated action-potential threshold, increased failures during high-frequency trains, and slowed central conduction; in the hippocampus, beta-IV-spectrin mutants show an impaired input-output relationship and reduced network excitability that a computational model reproduces from sodium-channel loss alone.

motor neuron CL:0000100 cortical pyramidal neuron CL:4023111

neuronal action potential GO:0019228 ↓ DECREASED neuronal action potential propagation GO:0019227 ↓ DECREASED membrane depolarization during action potential GO:0086010 ↓ DECREASED

axon GO:0030424

Downstream

Distal Motor Axonal Degeneration and Neurogenic Muscle Wasting Chronically failing conduction in the longest motor axons precedes and accompanies their degeneration.

Central Auditory Conduction Failure The auditory brainstem pathway depends on submillisecond temporal fidelity and is the first system to fail.

Cortical Network Dysfunction and Impaired Neurodevelopment AIS-dependent spike initiation in cortical pyramidal neurons underlies the cognitive and language phenotype.

Show evidence (3 references)

PMID:35393465 SUPPORT Model Organism

"Presynaptic terminal recordings in Sptbn4geo mice, β4-spectrin null mice, showed an elevated threshold of action potential and increased failures during action potential train at high-frequency."

Direct electrophysiological measurement of the initiation and high-frequency-fidelity failure that this node describes.

PMID:19156852 SUPPORT Model Organism

"This revealed an impaired input-output relationship between stimulus intensity and granule cell population spikes and an enhanced paired-pulse inhibition of population spikes, indicating a reduced ability of granule cells to generate action potentials and decreased network excitability."

In vivo network-level demonstration that the channel-clustering lesion translates into a measurable firing deficit, and the source of the reduced-excitability half of the paradox described in the notes.

PMID:19156852 SUPPORT Computational

"This in silico approach confirmed that the loss of VGSCs is sufficient to explain the electrophysiological changes observed in qv(3j) mice."

A computational model showing that sodium-channel loss alone accounts for the measured network changes, closing the causal chain from clustering failure to firing deficit.

Axonal Hyperexcitability and Epileptiform Discharge

Loss of nodal KCNQ2/3 removes the slow potassium brake on repetitive firing, and the result in mice is spontaneous and evoked neuromyotonic and myokymic discharge originating in myelinated axons distal to the nerve terminal. The human counterpart is the striking, and initially counterintuitive, finding that patients can have abundant to nearly continuous epileptiform discharges on EEG - in one case documented over 72 hours and in another over 24-hour video EEG - with no clinical seizure ever observed. This dissociation between electrographic and clinical epilepsy is a distinctive feature of the disorder and is the reason EEG is worth performing even in a child with no history of fits.

motor neuron CL:0000100 cortical pyramidal neuron CL:4023111

regulation of monoatomic ion transmembrane transport GO:0034765 ⚠ ABNORMAL

Downstream

Cortical Network Dysfunction and Impaired Neurodevelopment Recurrent epileptiform activity is a plausible additional contributor to the developmental phenotype, though causality is not established.

Show evidence (3 references)

PMID:20962009 SUPPORT Model Organism

"The quivering-3J mice show prominent spontaneous and evoked hyperactivities at diaphragm neuromuscular junctions."

The hyperexcitability phenotype produced by nodal KCNQ2 loss in the disease model.

PMID:33772159 SUPPORT Human Clinical

"Additional symptoms comprised horizontal nystagmus, epileptiform discharges in EEG without manifest seizures, and choreoathetosis."

The human electroclinical dissociation - epileptiform EEG without clinical seizures - that this node models.

PMID:33772159 SUPPORT Human Clinical

"As βIV-spectrin plays a role in the clustering of KCNQ2 subunit-containing potassium channels, there could be some degree of overlap of clinical symptoms with early-infantile epileptic encephalopathy type 7 and with benign familial neonatal seizures type 1."

The authors' own statement of the KCNQ2 mechanistic link, which is the basis for curating the two KCNQ2 disorders as mechanistic differentials.

Distal Motor Axonal Degeneration and Neurogenic Muscle Wasting

The peripheral endpoint is a length-dependent motor axonal neuropathy. Electrophysiology in patients shows low-amplitude motor responses with preserved conduction velocities - the signature of axonal rather than demyelinating disease - together with fibrillation potentials, positive sharp waves and enlarged, long-duration motor unit potentials indicating acute and chronic denervation. Clinically this produces areflexia, generalised and distal amyotrophy, and weakness that is severe enough in most individuals to prevent sitting, standing or walking. Muscle biopsy shows the corresponding neurogenic picture in some patients: atrophic fascicles, angulated fibres, and fibre grouping.

alpha motor neuron CL:0008038 denervated skeletal muscle fiber CL:0008002

neuronal action potential propagation GO:0019227 ↓ DECREASED

peripheral nerve UBERON:0001021 skeletal muscle tissue UBERON:0001134

Downstream

Contested Skeletal Muscle Involvement Denervation is the currently favoured explanation for the muscle biopsy abnormalities that were originally interpreted as a primary congenital myopathy.

Show evidence (4 references)

PMID:29861105 SUPPORT Human Clinical

"cause a severe neurological syndrome that includes congenital hypotonia, intellectual disability, and motor axonal and auditory neuropathy"

Names motor axonal neuropathy as a defining component of the syndrome.

PMID:33772159 SUPPORT Human Clinical

"EMG showed signs of acute and chronic denervation such as fibrillation potentials and positive sharp waves, motor unit potentials with increased amplitude and duration, and decreased recruitment."

The electrophysiological denervation signature that establishes the muscle involvement as neurogenic.

PMID:33772159 SUPPORT Human Clinical

"Nerve conduction studies showed normal sensory and motor conduction velocities, with low-amplitude motor responses."

Establishes the axonal rather than demyelinating character of the neuropathy, which is why the module's demyelination arm is explicitly not claimed.

+ 1 more reference

Central Auditory Conduction Failure

Hearing loss in this disorder is a neuropathy, not a cochlear disease. The quivering mouse, which is the natural model of the human condition, is deaf with normal cochlear morphology and normal cochlear potentials but abnormal transmission through the brainstem auditory nuclei - deafness "central in origin". The same pattern was documented in a patient: otoacoustic emissions present, but brainstem evoked response audiometry showing only wave I, localising the block to cochlear nerve conduction. Mechanistically the auditory pathway is the most demanding client of the nodal scaffold because it encodes at submillisecond precision, and beta-4-spectrin-null mice fail specifically at the heminode adjacent to the nerve terminal, with slowed central conduction and absent startle responses despite normal cochlear function.

spiral ganglion neuron CL:0011113

clustering of voltage-gated sodium channels GO:0045162 ↓ DECREASED

cochlear nerve UBERON:0004727 auditory brainstem UBERON:0002028

Show evidence (5 references)

PMID:11528393 SUPPORT Model Organism

"However, responses from brainstem auditory nuclei show abnormal transmission of auditory information, indicating that, in contrast to the many known mutations causing deafness originating in the cochlea, deafness in qv is central in origin."

Establishes the central, non-cochlear origin of the deafness in the model organism that first defined this gene's phenotype.

PMID:11528393 SUPPORT Model Organism

"Ear twitch responses (Preyer's reflex) to sound are absent in homozygous qv/qv mice, although cochlear morphology seems normal and cochlear potentials recorded at the round window are no different from those of control mice."

The specific negative findings - normal cochlear morphology and potentials - that exclude a hair-cell mechanism.

PMID:33772159 SUPPORT Human Clinical

"In brainstem evoked response audiometry (BERA) only wave 1 from the inner ear could be recorded pointing to a defect at the level of cochlear nerve conduction."

The human counterpart of the mouse finding, localising the auditory lesion to cochlear nerve conduction with a preserved inner ear.

+ 2 more references

Cortical Network Dysfunction and Impaired Neurodevelopment

The cognitive and language phenotype is the least mechanistically resolved part of the disorder and also its most severe. The axon initial segment is where a cortical pyramidal neuron decides whether to fire; beta-IV spectrin is one of the two proteins that build it; and beta-IV-spectrin mutant mice have measurably reduced network excitability in vivo. Beyond that the chain is inference. Most affected individuals have severe to profound developmental delay and intellectual disability with absent or single-word speech, and neuroimaging is normal in a substantial minority - 8 of 22 patients with available MRI in the pooled review - so there is no gross structural lesion to which the cognitive phenotype can be attributed. Where MRI is abnormal the findings are non-specific: vermian atrophy, diffuse T2 hyperintensity, enlarged CSF spaces, cerebral atrophy and white matter change.

cortical pyramidal neuron CL:4023111

axon initial segment GO:0043194

cerebral cortex UBERON:0000956 cerebellum UBERON:0002037

Show evidence (3 references)

PMID:29861105 PARTIAL Human Clinical

"βIV spectrin links ankyrinG (AnkG) and clustered ion channels at axon initial segments (AISs) and nodes of Ranvier to the axonal cytoskeleton."

Marked PARTIAL because it states the molecular premise - beta-IV spectrin builds the AIS - but says nothing about how an AIS defect produces intellectual disability, which is the step this node cannot evidence.

PMID:19156852 PARTIAL Model Organism

"Taken together, our findings demonstrate that betaIV-spectrin is required for normal granule cell firing and for physiological levels of network excitability in the mouse dentate gyrus in vivo."

The strongest available support for a primary CNS network mechanism, but marked PARTIAL because it is rodent hippocampal physiology standing alone for a human cognitive phenotype.

PMID:40781329 SUPPORT Human Clinical

"Such abnormalities included vermian atrophy, diffuse T2-hyperintensity, mildly enlarged CSF spaces, cerebral atrophy, and white matter abnormalities."

Documents the non-specific and inconsistent imaging findings, which is why no structural lesion is proposed as the cause of the cognitive phenotype.

Contested Skeletal Muscle Involvement

Whether SPTBN4 disease includes a primary myopathy is unresolved, and the two positions are held by competent groups using different methods. The myogenic case: the founding report described congenital myopathy with incomplete congenital fibre-type disproportion, showed beta-IV-spectrin immunostaining at the sarcolemma of normal human and mouse muscle and its absence in patient and quivering muscle, and found complete absence of type 1 fibres in quivering mouse muscle; a follow-up cohort again found no beta-IV-spectrin staining in patient muscle and type 1 fibre hypotrophy without frank fibre-type disproportion, and hypothesised a direct effect on sarcolemmal stability and on depolarisation along the myofibre and its T-tubular system. The neurogenic case: a muscle-specific conditional knockout showed that beta-4 spectrin does not contribute to muscle function, and that the protein is not present in muscle at all - which would make the sarcolemmal immunostaining a cross-reaction and the muscle pathology entirely secondary to denervation. The 2025 natural-history review sides with the neurogenic reading.

skeletal muscle fiber CL:0008002 type 1 (slow) skeletal muscle fiber CL:0000189

skeletal muscle tissue UBERON:0001134

Show evidence (5 references)

PMID:28540413 SUPPORT Human Clinical

"Immunohistology confirmed expression of βIV-spectrin in normal human and mouse muscle at the sarcolemma and its absence in patient and quivering (qv4J) mouse."

The primary evidence for the myogenic position - sarcolemmal beta-IV-spectrin present in controls and absent in patient muscle.

PMID:33772159 SUPPORT Human Clinical

"We hypothesize that βIV-spectrin deficiency directly impacts the structural stability of the sarcolemma and the initiation or propagation of the depolarization waves along the myofiber and its T-tubular system."

States the proposed myogenic mechanism explicitly, and is labelled by its own authors as a hypothesis.

PMID:33772159 PARTIAL Human Clinical

"We derived that the evidence for a myopathy is mostly from the clinical and histopatholocigal findings, but not from functional studies about the role of SPTBN4 in muscle cells."

The same authors' own statement of the limitation of their myogenic claim. Marked PARTIAL because it qualifies rather than supports the myopathy hypothesis. The misspelling is verbatim from the source.

+ 2 more references

Residual-Function Alleles and the Mild End of the Spectrum

Not every SPTBN4 genotype produces the profound phenotype. Two siblings with a homozygous splice-site variant causing in-frame skipping of exon 19 had muscular hypotonia, myopathic facies with ptosis and axonal neuropathy but no seizures, no feeding or respiratory difficulty and, in the index case, normal cognition and mainstream schooling. The proposed explanation is residual protein activity from an in-frame product rather than complete loss of function. A second, independent observation points the same way: of the patients carrying missense rather than truncating alleles, several had milder symptoms or later onset, and the more severely affected missense carriers had their variants in the calponin-homology, variable-region or pleckstrin-homology domains rather than in the spectrin-repeat rod.

SPTBN4 hgnc:14896

Downstream

Distal Motor Axonal Degeneration and Neurogenic Muscle Wasting Even at the mild end the axonal neuropathy is present, making it the most penetrant consequence of the lesion.

Show evidence (3 references)

PMID:31857255 SUPPORT Human Clinical

"Here we report on two siblings with a homozygous splice-site mutation in the SPTBN4 gene, lacking previously reported features of the disorder such as seizures, feeding difficulties, respiratory difficulties or profound intellectual disability."

Establishes that a genuinely milder end of the phenotypic spectrum exists and defines what it lacks.

PMID:31857255 SUPPORT Human Clinical

"Our findings indicate that muscular hypotonia, myopathic facies with ptosis and axonal neuropathy can be the core clinical features in the SPTBN4 disorder and suggest that SPTBN4 mutation analysis should be considered in infants with marked axonal neuropathy."

Defines the minimal core phenotype at the mild end, which is the presentation most likely to be missed diagnostically.

PMID:33772159 PARTIAL Human Clinical

"Patients generally suffer from severe developmental delay and intellectual disability, although two individuals in one family had a milder phenotype, including one individual with normal cognitive development."

Confirms the existence of the mild family but marked PARTIAL because the same report states there is no clear genotype-phenotype correlation, so it supports the observation without supporting the allele-severity model.

Extraneural beta-IV Spectrin Expression and Reported Cardiac Involvement

Beta-IV spectrin is not exclusively neuronal. It is abundantly transcribed in pancreatic islets as well as brain, and a substantial separate literature places it in cardiomyocytes and cardiac fibroblasts as a scaffold for the cardiac sodium channel and as a signalling partner. Two individuals with SPTBN4 disease have been reported with cardiac disease: one with non-obstructive hypertrophic cardiomyopathy alongside mitochondrial dysfunction and optic atrophy, and one with congenital heart defects but no available neuromuscular data. This node exists to mark the possibility without over-reading it: two cardiac cases out of 38 reported individuals is not an established disease feature, and no cardiac surveillance recommendation follows from it in the GeneReviews chapter.

heart UBERON:0000948

Show evidence (2 references)

PMID:33986717 SUPPORT Human Clinical

"This is the first report of a severe form of ßIV-spectrin deficiency with hypertrophic cardiomyopathy and mitochondrial dysfunction."

The single reported case of cardiomyopathy with mitochondrial dysfunction in this disorder, presented by its own authors as a first report.

PMID:11086001 SUPPORT In Vitro

"Northern blots revealed an abundant expression of betaIV spectrin transcripts in brain and pancreatic islets."

Documents that expression is not confined to neurons, which is the premise for asking whether extraneural disease exists - although no islet or endocrine phenotype has been reported in patients.

✶

Histopathology

Type 1 fiber hypotrophy without frank fiber-type disproportion

ATPase pH 4.3 staining in patient muscle shows selective reduction of type 1 fibre diameter relative to type 2, quantified by minimal Feret diameter, without the complete fibre-type disproportion classically defined for congenital myopathies. The founding case was described as having incomplete congenital fibre-type disproportion, and the corresponding quivering mouse muscle showed complete absence of type 1 fibres.

Show evidence (1 reference)

PMID:33772159 SUPPORT Human Clinical

"ATPase pH 4.3 staining and IHC with an antibody directed against myosin heavy chain slow (MHC neonatal, NCL-MHCn, Novocastra, 1:20) revealed a reduction of type 1 fiber diameters but no manifest fiber-type disproportion"

The precise histological finding, including the explicit negative for frank fibre-type disproportion.

Neurogenic changes with atrophic fascicles and angulated fibers

In other patients the biopsy is unambiguously neurogenic: atrophic fascicles, small angulated fibres of both types next to fibres of preserved diameter, and fibre grouping. The coexistence of this picture with the type 1 hypotrophy picture in different patients from the same cohort is the empirical basis of the myopathy-versus-neuropathy debate.

Show evidence (1 reference)

PMID:33772159 SUPPORT Human Clinical

"H&E/Gömöri-trichrome staining of a muscle biopsy sample from Patient 5 showed clear signs of neurogenic changes with atrophic fascicles, dark fibers (type 1) as well as brighter fibers (type 2) small and angulated fibers next to populations of muscle fibers with preserved diameter and groups of..."

The neurogenic biopsy pattern, which is what the current mechanistic reading predicts should be the universal finding.

Absent beta-IV-spectrin immunostaining in patient muscle

Immunohistochemistry with an anti-beta-IV-spectrin antibody shows no signal in patient muscle where age-matched control muscle stains, while a pan-beta-spectrin antibody stains the sarcolemma normally in both. This was the original evidence that beta-IV spectrin is a sarcolemmal protein whose loss could cause myopathy directly.

Show evidence (1 reference)

PMID:33772159 PARTIAL Human Clinical

"IHC with an antibody directed against the non-erythrocytic βIV-spectrin subtype 4 (sc-368195, H-85, Santa-Cruz, 1:100) showed no staining in Patient 3, while staining was preserved in age-matched control muscle."

Marked PARTIAL rather than SUPPORT. The observation is real, but a subsequent muscle-specific conditional knockout reported that beta-4 spectrin is not present in muscle at all (PMID:38441922), which implies the control-muscle signal these antibodies detect may not be beta-IV spectrin. Neither study included a knockout-muscle antibody control at the time the human staining was performed.

⬡

Pathograph

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

●

Phenotypes

Digestive 1

Feeding difficulties and dysphagia Feeding difficulties HP:0011968

HPO annotation for OMIM:617519 records HP:0011968 Feeding difficulties at 6/6, HP:0002033 Poor suck at 6/6, HP:0002015 Dysphagia at 5/5, HP:0002020 Gastroesophageal reflux at 3/3 and HP:0011471 Gastrostomy tube feeding in infancy at 4/5, sourced to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). The 2025 review reports gastrointestinal problems in 15 patients (54%). The review does not state the denominator for that percentage; 15/54% back-calculates to about 28, not the 38 patients tabulated overall, so the fraction is a curator inference.

Show evidence (2 references)

PMID:40781329 SUPPORT Human Clinical

"dysphagia, and gastrostomy tube feeding during infancy were reported in 15 patients (54%)"

Quantifies the gastrointestinal burden across the pooled published cohort.

PMID:32672909 SUPPORT Other

"Most affected individuals require tube feeding for nutrition."

The GeneReviews statement of the usual outcome, which is the basis for anticipatory gastrostomy planning.

Ear 1

Sensorineural hearing impairment (auditory neuropathy) Sensorineural hearing impairment HP:0000407

HPO annotation for OMIM:617519 records HP:0000407 Sensorineural hearing impairment at 2/5, sourced to PMID:33772159 (retrieved 2026-08-01); the 2025 natural-history review of 38 patients reports deafness in 21%. Both figures are far below what the disease name implies. In the 2021 cohort three of five patients were recorded as clinically unaffected without formal audiology, so the true figure is likely between the two. HPO has no term for auditory neuropathy - searches of `sqlite:obo:hp` for both `l~auditory neuropathy` and free-text `auditory neuropathy` returned nothing on 2026-08-01 - so the sensorineural term is bound and the neuropathic character is carried by the separate absent-brainstem-response phenotype below.

Show evidence (2 references)

PMID:40781329 SUPPORT Human Clinical

"Nevertheless, scoliosis, deafness, and seizure are still present in some of the affected individuals (25%, 21%, and 21%, respectively)."

The largest available denominator for hearing loss in this disorder, and the source of the statement that deafness is a minority feature.

PMID:32672909 SUPPORT Other

"Cortical visual impairment and auditory neuropathy have also been reported."

GeneReviews classifies the hearing loss specifically as auditory neuropathy rather than as cochlear deafness.

Head and Neck 1

Myopathic facies Myopathic facies HP:0002058

HPO annotation for OMIM:617519 records HP:0002058 Myopathic facies at 6/6 and HP:0000218 High palate at 5/6, sourced to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). The term label says "myopathic" but on the current mechanistic reading the weakness is neurogenic; the HPO label is retained unchanged because it is the canonical term.

Show evidence (1 reference)

PMID:31857255 SUPPORT Human Clinical

"Our findings indicate that muscular hypotonia, myopathic facies with ptosis and axonal neuropathy can be the core clinical features in the SPTBN4 disorder"

Places myopathic facies among the minimal core features, present even at the mild end of the spectrum.

Musculoskeletal 3

Congenital and generalized hypotonia Generalized hypotonia HP:0001290

HPO annotation for OMIM:617519 records HP:0001290 Generalized hypotonia at 5/5 and HP:0001319 Neonatal hypotonia at 5/5, both sourced to PMID:33772159 (retrieved 2026-08-01). No FrequencyEnum band is asserted; see the entry-level notes.

Show evidence (2 references)

PMID:32672909 SUPPORT Other

"Affected individuals typically have congenital hypotonia that may transition to hypertonia."

The GeneReviews characterisation of the tone abnormality, including its evolution, which is not captured by the single HPO term.

PMID:29861105 SUPPORT Human Clinical

"a severe neurological syndrome that includes congenital hypotonia, intellectual disability, and motor axonal and auditory neuropathy"

Names congenital hypotonia as one of the three defining components of the syndrome.

Generalized amyotrophy Generalized amyotrophy HP:0003700

HPO annotation for OMIM:617519 records HP:0003700 Generalized amyotrophy at 5/6 and HP:0003693 Distal amyotrophy at 4/5, sourced to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). Note that the 2021 cohort's own table labels HP:0009055 as "Generalized muscle atrophy"; the canonical HPO label for HP:0009055 verified with OAK on 2026-08-01 is "Generalized limb muscle atrophy", so the broader HP:0003700 used by the HPO annotation set is bound here instead.

Show evidence (1 reference)

PMID:33772159 SUPPORT Human Clinical

"EMG showed signs of acute and chronic denervation such as fibrillation potentials and positive sharp waves"

The denervation evidence that makes the wasting neurogenic rather than myopathic.

Scoliosis Scoliosis HP:0002650

HPO annotation for OMIM:617519 records HP:0002650 Scoliosis at 3/6, sourced to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01); the 2025 review reports 25%.

Show evidence (1 reference)

PMID:40781329 SUPPORT Human Clinical

"Nevertheless, scoliosis, deafness, and seizure are still present in some of the affected individuals (25%, 21%, and 21%, respectively)."

The pooled-cohort frequency for scoliosis alongside deafness and seizures.

Nervous System 7

Severe to profound intellectual disability Severe intellectual disability HP:0010864

HPO annotation for OMIM:617519 records HP:0010864 Severe intellectual disability at 5/5, sourced to PMID:33772159 (retrieved 2026-08-01). The 2018 cohort title uses "profound" (HP:0002187) and GeneReviews uses "severe-to-profound"; HP:0010864 is bound rather than HP:0002187 because it is the term the HPO annotation set actually carries for this OMIM entity, and because the two are sibling severity grades rather than parent-and-child, so choosing the more severe one on the strength of a paper title would overstate the annotation.

Show evidence (1 reference)

PMID:32672909 SUPPORT Other

"SPTBN4 disorder is typically characterized by severe-to-profound developmental delay and/or intellectual disability, although two individuals in one family had a milder phenotype, including one individual with normal cognitive development."

States both the typical severity and the documented exception, which is the whole content of this phenotype's description.

Absent or severely limited speech Absent speech HP:0001344

HPO annotation for OMIM:617519 records HP:0001344 Absent speech at 5/5, sourced to PMID:33772159 (retrieved 2026-08-01).

Show evidence (1 reference)

PMID:33772159 SUPPORT Human Clinical

"All patients presented with the key features of NEDHND; severe muscular hypotonia, dysphagia, absent speech, gross motor, and mental retardation."

Absent speech is listed among the key features present in all patients of this cohort.

Delayed gross motor development Delayed gross motor development HP:0002194

HPO annotation for OMIM:617519 records HP:0002194 Delayed gross motor development at 5/5 and HP:0002421 Poor head control at 6/6, sourced to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01).

Show evidence (1 reference)

PMID:32672909 SUPPORT Other

"Affected individuals rarely achieve head control. Most are unable to sit, stand, or walk."

Quantifies the motor ceiling that defines the disorder's functional impact.

Areflexia Areflexia HP:0001284

HPO annotation for OMIM:617519 records HP:0001284 Areflexia at 5/6, sourced to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). One patient in the 2021 cohort had brisk reflexes without clonus, which is the basis for the qualification in the description and is full-text rather than abstract content.

Show evidence (1 reference)

PMID:32672909 SUPPORT Other

"Axonal motor neuropathy leads to hyporeflexia/areflexia and weakness"

Attributes the reflex loss directly to the axonal neuropathy, which is the causal claim this phenotype makes.

Seizures Seizure HP:0001250

The four sources disagree. GeneReviews: half of affected individuals develop seizures. The 2021 cohort report: more than half develop seizures or have a pathological EEG - a compound endpoint, not the same claim. The 2025 natural-history review of 38 patients: seizures in 21%. The HPO annotation set for OMIM:617519 (retrieved 2026-08-01): HP:0001250 with frequency modifier "Very rare", sourced to OMIM. No FrequencyEnum band is asserted, and the discrepancy is recorded as an explicit knowledge-gap discussion rather than averaged away.

Show evidence (2 references)

PMID:32672909 SUPPORT Other

"Half of affected individuals develop seizures."

The GeneReviews estimate, one of the four mutually inconsistent figures recorded in the notes.

PMID:40781329 PARTIAL Human Clinical

"The disorder is highlighted with neuropathy, muscle weakness, and infrequent appearance of seizures in the affected individuals."

Marked PARTIAL because it directly contradicts the GeneReviews estimate quoted above. Both are retained so the disagreement is visible in the data rather than resolved by curator preference.

Choreoathetosis Choreoathetosis HP:0001266

HPO annotation for OMIM:617519 records HP:0001266 Choreoathetosis at 1/5, sourced to PMID:33772159 (retrieved 2026-08-01).

Show evidence (1 reference)

PMID:33772159 SUPPORT Human Clinical

"the variably present features of areflexia, axonal motor neuropathy, nystagmus, epileptiform activity in EEG without clinical correlation, and a movement disorders with choreoathetosis."

The authors' own statement that choreoathetosis is a variably present addition to the phenotype.

Ataxia Ataxia HP:0001251

Not present in the HPO annotation set for OMIM:617519 as retrieved on 2026-08-01. Curated from the 2025 natural-history review, in which ataxia was present in 2 of 10 patients, both in family 1, and had never previously been reported in the disorder. The same family also had cerebellar vermian atrophy on MRI.

Show evidence (1 reference)

PMID:40781329 SUPPORT Human Clinical

"Ataxia was never reported in any NEDHND patients; however, two patients in our cohort suffered from ataxia"

Documents both the novelty of ataxia in this disorder and its rarity, which is the basis for the human-model mismatch recorded below.

Other 9

Poor head control Poor head control HP:0002421

HPO annotation for OMIM:617519 records HP:0002421 at 6/6, sourced to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). The cached abstract of neither source names head control, so no evidence item is attached rather than a snippet that does not support the claim.

Peripheral axonal neuropathy Peripheral axonal neuropathy HP:0003477

HPO annotation for OMIM:617519 records HP:0003477 Peripheral axonal neuropathy at 2/6 and HP:0007002 Motor axonal neuropathy at 1/1, while HP:0007108 Demyelinating peripheral neuropathy is recorded at 0/5, all sourced to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). The low numerator for the axonal term reflects how few patients had electrophysiology, not how many had neuropathy.

Show evidence (2 references)

PMID:29861105 SUPPORT Human Clinical

"cause a severe neurological syndrome that includes congenital hypotonia, intellectual disability, and motor axonal and auditory neuropathy"

Establishes motor axonal neuropathy as a defining component of the syndrome.

PMID:33772159 SUPPORT Human Clinical

"Nerve conduction studies showed normal sensory and motor conduction velocities, with low-amplitude motor responses."

The electrophysiological pattern that defines the neuropathy as axonal rather than demyelinating.

Absent brainstem auditory evoked responses Absent brainstem auditory responses HP:0004463

HPO annotation for OMIM:617519 records HP:0004463 at 1/2, sourced to PMID:33772159 (retrieved 2026-08-01). The denominator of 2 reflects how few patients were tested.

Show evidence (1 reference)

PMID:33772159 SUPPORT Human Clinical

"Otoacoustic emissions were present. In brainstem evoked response audiometry (BERA) only wave 1 from the inner ear could be recorded pointing to a defect at the level of cochlear nerve conduction."

The paired result - preserved emissions with absent central waves - that defines the deficit as auditory neuropathy rather than cochlear hearing loss.

Recurrent aspiration and respiratory insufficiency Recurrent infections due to aspiration HP:0004891

HPO annotation for OMIM:617519 records HP:0004891 Recurrent infections due to aspiration at 5/5, sourced to PMID:33772159 (retrieved 2026-08-01). The 2025 review reports respiratory difficulties in 17 patients (61%), of whom 10 had recurrent pneumonia, 2 progressed to restrictive lung disease and 2 died of respiratory failure.

Show evidence (2 references)

PMID:40781329 SUPPORT Human Clinical

"Respiratory difficulties were seen in 17 patients (61%)."

Quantifies the respiratory burden in the pooled cohort.

PMID:40781329 SUPPORT Human Clinical

"Two of the 17 patients died at age of 14 months and 3 years due to respiratory failure."

Establishes respiratory failure as the mode of death in this disorder.

Epileptiform EEG without clinical seizures Interictal epileptiform activity HP:0011182

HP:0011182 is bound rather than its parent HP:0002353 EEG abnormality because its HPO definition ("Interictal epileptiform activity refers to such activity that occurs in the absence of a clinical or subclinical seizure") names exactly the finding described here; ancestry confirmed with `runoak -i sqlite:obo:hp ancestors -p i HP:0011182`, which lists HP:0002353. The HPO annotation set for OMIM:617519 records only the parent, HP:0002353 EEG abnormality, at 2/2, sourced to PMID:33772159 (retrieved 2026-08-01); since no FrequencyEnum band is asserted anywhere in this entry that parent-level count is recorded here rather than driving the binding. Whether such discharges warrant antiseizure treatment in a child with no clinical events is not addressed anywhere in the literature and is not asserted here.

Show evidence (3 references)

PMID:33772159 SUPPORT Human Clinical

"Though two of our patients did not exhibit clinically manifest seizures, their EEGs showed highly pathologic epileptiform discharges."

States both halves of this phenotype in a single sentence - absence of clinically manifest seizures together with the presence of highly pathologic epileptiform discharges on EEG.

PMID:33772159 SUPPORT Human Clinical

"Seventy-two-hour EEG showed abundant to nearly continuous centro-parietal sharp/spike/poly-spike wave discharges during sleep without clinical correlation to manifest seizures."

The 72-hour recording in Patient 3, which is the source of the "abundant to nearly continuous" characterisation used in the description.

PMID:33772159 SUPPORT Human Clinical

"No clinical seizures were observed in a 24-h video EEG recording. The parents had never observed any type of fits or seizures."

The second patient, and the source of the explicit parental confirmation that no fits had ever occurred.

Horizontal nystagmus Horizontal nystagmus HP:0000666

HPO annotation for OMIM:617519 records HP:0000666 Horizontal nystagmus at 2/5, sourced to PMID:33772159 (retrieved 2026-08-01). The 2025 review reports ocular abnormalities of any kind in 43% of patients.

Show evidence (1 reference)

PMID:33772159 SUPPORT Human Clinical

"Additional symptoms comprised horizontal nystagmus, epileptiform discharges in EEG without manifest seizures, and choreoathetosis."

Names horizontal nystagmus among the features that expanded the recognised phenotype.

Cerebral visual impairment Cerebral visual impairment HP:0100704

HPO annotation for OMIM:617519 records HP:0100704 Cerebral visual impairment sourced to OMIM:617519 itself, with no frequency (retrieved 2026-08-01). GeneReviews recommends ophthalmology review every one to two years in those with optic atrophy, which implies optic atrophy is expected to occur but does not quantify it.

Show evidence (1 reference)

PMID:32672909 SUPPORT Other

"Cortical visual impairment and auditory neuropathy have also been reported."

The GeneReviews statement recording cortical visual impairment as part of the phenotype.

Type 1 muscle fiber atrophy Type 1 muscle fiber atrophy HP:0011807

HPO annotation for OMIM:617519 records HP:0011807 Type 1 muscle fiber atrophy at 3/3 and HP:0003554 Type 2 muscle fiber atrophy at 1/2, sourced to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). Muscle biopsy was performed in only 8 of the 38 patients in the pooled review (21.1%), so these denominators describe who was biopsied, not who has the finding.

Show evidence (1 reference)

PMID:28540413 SUPPORT Human Clinical

"the human phenotype of βIV-spectrin deficiency included a myopathy with incomplete congenital fiber-type disproportion"

The original description of the muscle finding, which is the claim later disputed on mechanistic grounds.

Cerebellar vermis atrophy Cerebellar vermis atrophy HP:0006855

Not present in the HPO annotation set for OMIM:617519 as retrieved on 2026-08-01. Curated from the 2025 natural-history review, which found abnormal MRI in 14 of 22 patients with imaging available and lists vermian atrophy first among the abnormalities.

Show evidence (1 reference)

PMID:40781329 SUPPORT Human Clinical

"Such abnormalities included vermian atrophy, diffuse T2-hyperintensity, mildly enlarged CSF spaces, cerebral atrophy, and white matter abnormalities."

Names vermian atrophy among the reported structural findings.

🧬

Genetic Associations

SPTBN4 (Bi-allelic loss-of-function variants; predominantly homozygous truncating alleles in consanguineous families)

Gene: SPTBN4 hgnc:14896 relationship_type: CAUSATIVE

Show evidence (4 references)

PMID:28540413 SUPPORT Human Clinical

"We found a homozygous nonsense mutation in SPTBN4"

The first human SPTBN4 disease allele. The full sentence in the source gives the allele, transcript and protein accessions in square brackets (c.1597C>T, NM_020971.2, p.(Q533*), NP_066022.2); the bracketed span is omitted from the quoted snippet because the reference validator strips bracketed text as a citation marker, and the detail is recorded in this section's notes instead.

PMID:40781329 SUPPORT Human Clinical

"Thirty-one different SPTBN4 pathological variants have been discovered in 38 patients."

Quantifies the allelic heterogeneity of the disorder - close to one distinct variant per reported individual, which is why no founder allele is asserted.

PMID:40781329 SUPPORT Human Clinical

"the variant leads to an aberrant mRNA transcript with a shorter product"

RNA-level confirmation that a splice-site allele produces an aberrant transcript, which is the evidence standard this entry treats as sufficient for a splicing claim.

+ 1 more reference

💊

Medical Actions

Multidisciplinary supportive care

Category: Therapeutic Action: supportive care Ontology label: Supportive Care NCIT:C15747

No disease-modifying therapy exists. Management follows the components of the phenotype: developmental, educational and communication support; physiotherapy and orthotics for weakness, contractures and scoliosis; and surveillance for the complications that determine survival.

Show evidence (1 reference)

PMID:32672909 SUPPORT Other

"standard treatment for developmental delay / intellectual disability, epilepsy, cortical vision impairment, constipation, and spasticity / joint contractures"

The GeneReviews management recommendation, which is explicitly standard supportive care rather than anything disorder-specific.

Nutritional management (feeding therapy and gastrostomy)

Category: Therapeutic Action: enteral nutritional support Ontology label: Nutritional Support NCIT:C15433

Feeding therapy and, when aspiration risk or growth failure persists, gastrostomy placement. Anticipating this rather than reacting to a pneumonia is part of the practical core of care in this disorder, because dysphagia and recurrent aspiration are what precipitate the respiratory failure that is the usual cause of death.

Show evidence (1 reference)

PMID:32672909 SUPPORT Other

"feeding therapy and consideration of gastrostomy tube placement for persistent feeding difficulties and/or concern about aspiration"

The GeneReviews recommendation for the feeding and aspiration problem.

Ventilatory support

Category: Therapeutic Action: ventilatory support Ontology label: Respiratory Therapy NCIT:C15322

Non-invasive or invasive ventilatory support for respiratory distress, with tracheostomy in the most affected. This is the intervention that most directly changes survival, since neuromuscular respiratory failure is the usual cause of death.

Show evidence (1 reference)

PMID:32672909 SUPPORT Other

"ventilator support (e.g., BiPAP) for respiratory distress"

The GeneReviews recommendation for the complication that drives mortality.

Hearing support with amplification

Category: Therapeutic Action: supportive care Ontology label: Supportive Care NCIT:C15747

Hearing aids are recommended for those with hearing loss, but the neuropathic character of the deficit tempers the expectation: in auditory neuropathy the cochlea works and the nerve does not, so amplification addresses the wrong part of the pathway. The paired otoacoustic-emission and brainstem-response testing that should precede a decision about amplification is a diagnostic action and is curated separately under diagnosis ("Auditory brainstem response with otoacoustic emissions"); this entry covers only the amplification/hearing-support intervention.

Show evidence (1 reference)

PMID:32672909 SUPPORT Other

"Hearing aids may be helpful for those with hearing loss"

The only published management statement about hearing in this disorder.

Surveillance

Category: Screening Action: structured surveillance schedule Ontology label: Disease Screening NCIT:C15419

Structured surveillance is the one place where GeneReviews gives disorder-specific guidance: neurological and developmental review, growth and nutrition, constipation and joint mobility at each visit; ophthalmology every one to two years in those with optic atrophy; audiology as clinically indicated; and a sleep study every one to two years, which is the item most easily overlooked and most directly relevant to neuromuscular respiratory failure.

Show evidence (1 reference)

PMID:32672909 SUPPORT Other

"ophthalmology evaluation every one to two years in those with optic atrophy; audiology evaluation as clinically indicated; sleep study every one to two years"

The published surveillance schedule for this disorder.

Genetic counselling and reproductive options

Category: Counseling / Informational Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Autosomal recessive recurrence-risk counselling with a 25% risk to each subsequent pregnancy, carrier testing for the specific familial alleles once identified, and prenatal or preimplantation testing. This carries unusual weight in this disorder because the reported population is heavily consanguineous and because the disorder is severe, untreatable and often lethal in early childhood; the 2025 Saudi natural-history study frames its entire rationale around enabling preimplantation and carrier-screening programmes.

Show evidence (2 references)

PMID:32672909 SUPPORT Other

"At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier."

The quantitative recurrence risk that the counselling recommendation rests on.

PMID:32672909 SUPPORT Other

"Once the SPTBN4 pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives, prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing are possible."

States the reproductive options available once the familial alleles are known.

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from SPTBN4-Related Neurodevelopmental Disorder:

Spinal muscular atrophy type 1 Not Yet Curated MONDO:0009669

Overlapping Features The dominant clinical mimic and the diagnosis SPTBN4 patients are actually tested for first. A floppy infant with profound weakness, areflexia, poor suck, tongue involvement, respiratory compromise and denervation on EMG is SMA type 1 until proven otherwise, and both the 2021 cohort and the 2026 sibling report describe SMA testing being sent and returning negative before SPTBN4 was found. The distinction is now urgent rather than academic: approved disease-modifying therapy exists for SMA and none exists for SPTBN4 disease, so misdiagnosis in either direction has direct consequences. (No reference cached for this entry states the SMA treatment landscape; the claim is general clinical background, not a sourced assertion.)

Distinguishing Features

SMN1 testing (deletion/dosage) resolves the question directly and should precede or accompany exome sequencing in any floppy infant.
Cognition is typically normal in SMA type 1 but severely impaired in most SPTBN4 disease, so intellectual disability argues for SPTBN4.
Auditory neuropathy and an epileptiform EEG are not features of SMA and, when present, point strongly to SPTBN4.
Nystagmus, choreoathetosis and cerebral visual impairment occur in SPTBN4 disease and not in SMA.
Muscle biopsy in SMA shows large-group fascicular atrophy with hypertrophic type 1 fibres; SPTBN4 biopsies more often show type 1 hypotrophy or patchy neurogenic change.

Show evidence (1 reference)

PMID:42068471 SUPPORT Human Clinical

"Both patients exhibited severe failure to thrive, hypotonia, dysphagia, and global developmental delay, initially suggesting spinal muscular atrophy (SMA)."

Documents that SMA was the working diagnosis in a real SPTBN4 family, which is why this differential is listed first.

KCNQ2 developmental and epileptic encephalopathy MONDO:0013387

Overlapping Features A mechanistic rather than a clinical differential, and the closest thing this disorder has to a pathway relative. KCNQ2 encodes the channel subunit that beta-IV spectrin positions at the node; SPTBN4 disease produces nodes with no detectable KCNQ2. The 2021 cohort report proposed exactly this overlap when explaining the epileptiform EEGs. The two disorders converge on absent nodal M-current from opposite directions - one by losing the channel, the other by losing the scaffold that places it.

Distinguishing Features

KCNQ2-DEE is a de novo dominant channelopathy; SPTBN4 disease is autosomal recessive, so unaffected consanguineous parents favour SPTBN4.
Seizures dominate the KCNQ2-DEE presentation from the neonatal period, whereas in SPTBN4 disease hypotonia and weakness dominate and the epileptiform activity is frequently subclinical.
Peripheral axonal neuropathy, areflexia and auditory neuropathy are features of SPTBN4 disease and not of KCNQ2-DEE.
Sodium-channel blockers are a rational therapy in KCNQ2 gain-of-function disease; no analogous targeted option exists for SPTBN4 disease.

Show evidence (1 reference)

PMID:33772159 SUPPORT Human Clinical

The authors' own proposal of this mechanistic overlap, which is the reason the differential is curated.

ANK3-related intellectual disability-hypotonia-spasticity-sleep disorder syndrome Not Yet Curated MONDO:0014210

Overlapping Features The other half of the scaffold. AnkyrinG and beta-IV spectrin stabilise each other reciprocally at the axon initial segment and node, so losing either delocalises the other, and the recessive ANK3 syndrome accordingly pairs intellectual disability with hypotonia. Curating the pair makes the point that the AIS/nodal scaffold is a disease module rather than a set of unrelated genes.

Distinguishing Features

Spasticity and a prominent sleep disorder characterise the ANK3 syndrome and are not core features of SPTBN4 disease.
Motor axonal neuropathy with areflexia and auditory neuropathy are characteristic of SPTBN4 disease and are not the ANK3 phenotype.
ANK3 also has a separate dominant neurodevelopmental/psychiatric association, so the inheritance pattern must be established before the phenotype is interpreted.
The two are distinguished definitively by the causal gene, not clinically.

SPTAN1-related developmental and epileptic encephalopathy 5 Not Yet Curated MONDO:0013277

Overlapping Features The alpha-spectrin partner. Alpha-II spectrin, encoded by SPTAN1, is the obligate alpha-subunit that pairs with beta-spectrins to form the axonal tetramer, and it forms the periodic AIS cytoskeleton alongside beta-IV spectrin. Its dominant variants cause a severe epileptic encephalopathy with hypomyelination, and heterozygous loss of function has more recently been linked to a distal myopathy with neurogenic features - a phenotypic convergence with SPTBN4 that is not coincidental.

Distinguishing Features

SPTAN1-DEE is autosomal dominant, usually de novo, with in-frame dominant-negative variants; SPTBN4 disease is recessive loss of function.
Infantile spasms with hypsarrhythmia and progressive brain atrophy with hypomyelination characterise SPTAN1-DEE; SPTBN4 imaging is normal in a substantial minority and shows only non-specific change when abnormal.
Auditory neuropathy and areflexic motor axonal neuropathy point to SPTBN4 rather than SPTAN1.

Show evidence (1 reference)

PMID:36697767 SUPPORT Other

"Pathogenic variants in SPTAN1, SPTBN1, SPTBN2 and SPTBN4, four of the six genes encoding neuronal spectrins, cause neurological disorders."

Establishes the neuronal spectrinopathies as a coherent gene family whose members must be distinguished from one another.

SPTBN1-related developmental delay, impaired speech, and behavioral abnormalities Not Yet Curated MONDO:0859178

Overlapping Features The beta-II spectrin sibling disorder. Beta-II spectrin is the general axonal beta-subunit, present along the axon shaft rather than concentrated at excitable domains, and its dominant variants cause developmental delay with impaired speech and behavioural abnormalities. Together with SPTBN2 ataxia and SPTBN5 disease it illustrates why beta-spectrin paralogues, all building the same lattice, produce non-overlapping diseases: they differ in where in the neuron they are deployed.

Distinguishing Features

SPTBN1 disease is autosomal dominant; SPTBN4 disease is recessive.
Autism and behavioural abnormality dominate the SPTBN1 phenotype; profound motor disability, areflexia and neuropathy dominate SPTBN4.
Congenital hypotonia with feeding and respiratory failure is not the SPTBN1 presentation.

Show evidence (1 reference)

PMID:36697767 SUPPORT Other

"Despite their structural similarity and shared role as molecular organizers at the cell membrane, spectrins vary in expression, subcellular localization and specialization in neurons, and this variation partly underlies non-overlapping disease presentations across spectrinopathies."

States the principle that separates the spectrinopathies from one another, which is the substance of this differential.

Congenital fiber-type disproportion myopathy Not Yet Curated MONDO:0009711

Overlapping Features The differential that the muscle biopsy creates. A hypotonic infant whose biopsy shows small type 1 fibres will be labelled congenital fibre-type disproportion, and the first SPTBN4 patient was described in exactly those terms. Because the current mechanistic reading holds that the muscle pathology in SPTBN4 disease is neurogenic, this is a differential that exists because of a shared histological appearance rather than a shared mechanism.

Distinguishing Features

Congenital fibre-type disproportion is genetically heterogeneous (ACTA1, TPM3, RYR1, SELENON and others) and is a histological label, not a single disease.
Areflexia, denervation on EMG and auditory neuropathy point away from a primary congenital myopathy and towards SPTBN4.
Severe intellectual disability is not a feature of the classical congenital myopathies and is present in most SPTBN4 patients.
In SPTBN4 disease the fibre-type disproportion is characteristically incomplete or absent, with type 1 hypotrophy only.

{ }

Source YAML

click to show

name: SPTBN4-Related Neurodevelopmental Disorder
creation_date: "2026-08-01T00:00:00Z"
category: Mendelian
disease_term:
  preferred_term: neurodevelopmental disorder with hypotonia, neuropathy, and deafness
  term:
    id: MONDO:0060496
    label: neurodevelopmental disorder with hypotonia, neuropathy, and deafness
description: >-
  Neurodevelopmental disorder with hypotonia, neuropathy, and deafness (NEDHND)
  is an autosomal recessive disorder caused by bi-allelic variants in SPTBN4,
  the gene encoding beta-IV spectrin. It is a disease of one subcellular
  structure: the submembranous actin-spectrin scaffold that builds the axon
  initial segment and the node of Ranvier. Beta-IV spectrin is the beta-subunit
  of that scaffold, binding actin at one end and ankyrin-G at the other, and it
  is required both to hold the nodal membrane undercoat together and to
  concentrate the voltage-gated ion channels that make an axon excitable. When
  it is lost, sodium-channel and KCNQ2/KCNQ3 potassium-channel clusters fail,
  action-potential initiation and saltatory conduction degrade, and long
  myelinated motor and auditory axons - the fibres most dependent on that
  scaffold - degenerate. The clinical result is congenital hypotonia with
  profound global developmental delay, absent or severely limited speech, a
  motor axonal neuropathy with areflexia and secondary muscle wasting, feeding
  and respiratory failure from bulbar weakness, and, in a minority, auditory
  neuropathy, seizures or a paradoxically epileptiform EEG without clinical
  seizures. Two features of the entity deserve emphasis at the outset. First,
  the disease name overstates deafness: the largest series to date counted
  deafness in 21% of patients and the HPO annotation set for OMIM:617519
  records sensorineural hearing impairment at 2/5, although the founding 2018
  report named auditory neuropathy as part of the syndrome it described.
  Second, the "myopathy" reported
  in the earliest descriptions is now contested - a muscle-specific
  beta-IV-spectrin knockout showed the protein is not present in skeletal
  muscle at all, implying the muscle pathology is neurogenic. The published
  experience remains small; the most recent systematic review counted 38
  reported individuals worldwide.
parents:
- Neurodevelopmental Disorder
- Autosomal recessive disease
synonyms:
- NEDHND
- SPTBN4 disorder
- beta-IV spectrinopathy
- betaIV spectrin deficiency
- neurodevelopmental disorder with hypotonia, neuropathy, and deafness
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    notes: >-
      Every organ system affected in this disorder is affected through the
      nervous system. The cardinal features - congenital hypotonia, profound
      developmental delay and intellectual disability, absent speech, motor
      axonal neuropathy with areflexia, auditory neuropathy, seizures and
      epileptiform EEG - are all neurological. The gastrointestinal and
      respiratory morbidity (dysphagia, aspiration, ventilatory failure) is
      bulbar and neuromuscular rather than primary organ disease. The muscle
      involvement, historically reported as a congenital myopathy, is now
      argued to be neurogenic (PMID:38441922), which strengthens rather than
      weakens the single NEUROLOGIC assignment. Cardiomyopathy has been
      reported in two individuals and is not the disorder's centre of gravity.
    evidence:
    - reference: PMID:33772159
      reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Variants in SPTBN4 disrupt the cytoskeletal machinery that controls proper localization of ion channels and the function of axonal domains, thereby generating severe neurological dysfunction."
      explanation: The authors characterise the whole disorder as neurological dysfunction arising from an axonal cytoskeletal lesion, which is the basis for the NEUROLOGIC chapter assignment.
notes: >-
  Entity verification, done before any content was written. `runoak -i
  sqlite:obo:mondo info MONDO:0060496 -O obo` returns xref OMIM:617519,
  MEDGEN:1382171, GARD:0027987, UMLS:C4479603, synonym NEDHND, and
  `is_a: MONDO:0100500 (Mendelian neurodevelopmental disorder)`. `runoak -i
  sqlite:obo:mondo relationships -p RO:0004003 MONDO:0060496` returns exactly
  one gene, `HGNC:14896 SPTBN4`. `runoak -i sqlite:obo:hgnc search "l^SPTBN4"`
  confirms hgnc:14896 as the symbol SPTBN4. All three anchors - gene, OMIM
  number and MONDO label - agree with the dominant gene in every source used
  below, so the NEC gate passes.

  Named-entity risks specific to this gene, checked rather than assumed. (1)
  SPTBN4 sits in a five-member beta-spectrin family (SPTBN1, SPTBN2, SPTBN4,
  SPTBN5, plus SPTB) whose members each cause distinct neurological disease;
  a PubMed sweep on 2026-08-01 for `SPTBN4[TIAB] OR "betaIV spectrin"[TIAB] OR
  "beta-IV-spectrin"[TIAB]` returned 100+ records of which a substantial
  minority were about SPTBN1/SPTBN2/SPTBN5 or about cardiac and endothelial
  beta-IV spectrin biology. Every sibling-gene paper encountered was excluded
  from the evidence base and the sibling disorders were instead curated
  explicitly as differentials with OAK-verified MONDO terms. (2) A large
  contemporary literature uses beta-IV spectrin as a *cardiac* and *tumour
  angiogenesis* scaffold (CaMKII-beta-IV-spectrin-STAT3 axis, VEGFR2
  signalling, cardiac fibroblasts). Those papers are real SPTBN4 papers but
  they are not about this disease, and none is cited as evidence for a human
  neurological claim here. (3) The mouse gene has historically been called
  Spnb4 and the protein beta4-spectrin or beta-spectrin 4; the quivering (qv)
  mouse literature uses those names exclusively. Those papers ARE about this
  gene and are cited as model-organism evidence, with the naming stated
  explicitly so a reader does not mistake them for a different locus.

  Two OMIM/MONDO neighbours were checked and deliberately NOT curated as
  subtypes: `runoak -i sqlite:obo:mondo relationships --direction down
  HGNC:14896` returns MONDO:0060496 as the only SPTBN4 disease term, so unlike
  several other spectrinopathies this gene carries a single MONDO entity and
  the milder "axonal neuropathy without intellectual disability" presentation
  (PMID:31857255) belongs inside it rather than beside it.

  Disease-name caveat, recorded because it changes how the entry should be
  read. The MONDO/OMIM label names deafness as one of three cardinal features,
  but no cohort supports that weighting. The HPO annotation set for OMIM:617519
  (retrieved 2026-08-01 from https://ontology.jax.org/api/network/annotation/
  OMIM:617519) records HP:0000407 Sensorineural hearing impairment at 2/5,
  sourced to PMID:33772159; the 2025 natural-history review counted deafness in
  21% of patients. Hypotonia and neuropathy are near-universal; deafness is
  not. The name is a historical artefact of the founding single-case report
  (PMID:28540413), in which "central deafness" was one of the three presenting
  features and provided the link to the quivering mouse.

  Frequency bands are deliberately omitted from every phenotype in this entry.
  The HPO annotation set for OMIM:617519 draws on exactly two publications
  (PMID:33772159 and PMID:28540413) with denominators of 1 to 6, so a single
  reclassified individual moves most features across a FrequencyEnum boundary.
  Where a larger denominator exists it comes from the 2025 natural-history
  review, whose own percentages rest on inconsistent denominators (38 patients
  overall, but its gastrointestinal and respiratory percentages imply a
  denominator of about 28 - 15/54% and 17/61% both back-calculate to 28, a
  curator inference; the review does not state that denominator - and fewer
  still for imaging and biopsy). Each phenotype's `notes:` therefore carries
  the exact counts and their source instead of a band. Per
  docs/frequency-evidence-guidelines.md, omitting the band is preferred to
  manufacturing justification for one.

  Structured-source evidence was unavailable in this checkout: `data/orphadata/`
  and `data/clingen/` contain only `MANIFEST.yaml` with no downloaded payload,
  and `grep -ril SPTBN4 references_cache/` returns only PMID caches. No
  Orphanet prevalence class and no ClinGen gene-disease-validity classification
  could therefore be quoted. Per the scope rules the manifests were not
  touched. This is recorded as a gap, not as a claim that no such record
  exists.

  Reference-cache limits. Four references are cached with full text -
  PMID:33772159 (`content_type: full_text_xml`) and PMID:40781329,
  PMID:33986717 and PMID:35393465 (`content_type: full_text_pdf`); every other
  reference is cached abstract-only. Facts drawn from the body of a PDF-derived cache are quoted
  only where the extracted text is free of line-break hyphenation, and
  everything else is recorded in `notes:` rather than dressed up as a snippet.
  PMID:40842327 (De Winter et al., J Physiol 2025, "Loss-of-function variants
  in SPTAN1 and SPTBN4 cause early-onset hereditary myopathy") and
  PMID:30602540 (a commentary) were both fetched on 2026-08-01 and returned no
  abstract text at all, so neither can be quoted and neither is cited as
  evidence anywhere in this entry, despite the first being directly on topic.
  Their empty cache files were removed rather than committed.
inheritance:
- name: Autosomal recessive inheritance
  description: >-
    Disease requires two damaging SPTBN4 alleles. Homozygous genotypes
    dominate the reported literature, reflecting ascertainment through
    consanguineous families in the Middle East, Iran, Afghanistan and Kurdish
    populations; compound heterozygotes are a small minority. Heterozygous
    carriers, including the parents in every reported family, are not described
    as affected, and no dominant or de novo SPTBN4 mechanism has been
    established for this phenotype.

    Penetrance is left unset rather than asserted. No apparently healthy
    bi-allelic individual has been reported, but neither has any systematic
    population-database interrogation of SPTBN4 genotypes been published, so
    complete penetrance would be an inference from ascertainment rather than
    an observation. Two counts from the 2025 natural-history review bear on the
    recessive model and are recorded here rather than as separate claims - 31
    different pathogenic variants across 38 patients, and compound
    heterozygosity in only 4 of them. The same review reports two de novo
    variants in individuals ascertained through ADHD/autism cohorts rather than
    through NEDHND, which is a different and much weaker genotype-phenotype
    assertion; those cases are not treated here as evidence for a dominant
    mechanism in this disease.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurodevelopmental disorder with hypotonia, neuropathy, and deafness (NEDHND, OMIM #617519) is an autosomal recessive disease caused by homozygous or compound heterozygous variants in SPTBN4 coding for type 4 βIV-spectrin, a non-erythrocytic member of the β-spectrin family."
    explanation: States the mode of inheritance, the OMIM entity number this MONDO term xrefs, and the two admissible bi-allelic genotype configurations.
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SPTBN4 disorder is inherited in an autosomal recessive manner."
    explanation: Independent confirmation from the GeneReviews chapter, which is the source clinical laboratories and counsellors use.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most affected individuals reported to date are homozygous."
    explanation: Supports the statement that homozygous genotypes, rather than compound heterozygosity, dominate the reported series.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: NOT_YET_DOCUMENTED
  notes: >-
    No population prevalence or incidence estimate of any kind has been
    published for NEDHND, and no ORPHA code with an epidemiology table was
    available in this checkout, so there is no source to band and
    `NOT_YET_DOCUMENTED` is used rather than a qualitative `ULTRA_RARE` tier.
    `rate_per_100000` is deliberately omitted rather than set to 0.0: no rate
    has been estimated, and a numeric zero would be read downstream as an
    assertion that the disorder does not occur. The only quantity that can be
    sourced is a
    case tally: the 2025 systematic natural-history review counted 38 reported
    individuals worldwide, including its own 10 Saudi patients, across all
    publications to that date. Ascertainment is heavily consanguinity-driven -
    17 of the 38 were Arab, of whom 13 were Saudi - so the reported ethnic
    distribution reflects which health systems run autozygosity-guided exome
    sequencing, and must not be read as a population restriction.
  evidence:
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "there are only 38 patients (including our 10 cases) reported to carry deleterious variants of SPTBN4"
    explanation: Establishes the total published case count for this disorder at the time of curation, which is the only quantitative occurrence figure available.
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Arabs harbor significantly higher number of patients (n = 17) and 13 of them being Saudis."
    explanation: Documents the consanguinity-driven ascertainment skew that makes the reported ethnic distribution uninformative about true population frequency.
clinical_burden:
  burden_level: HIGH
  rationale: >-
    The typical course is profound and lifelong. Most affected individuals
    never achieve head control and cannot sit, stand or walk; speech is absent
    or limited to single words; tube feeding is usually required; and
    respiratory failure from neuromuscular and bulbar weakness is the usual
    cause of death. Two of seventeen patients with respiratory involvement in
    the 2025 review died at 14 months and 3 years of respiratory failure, and a
    2026 report describes two siblings who died at 18 months and 31 months.
    Management is entirely supportive. Burden is assigned HIGH rather than
    VARIABLE despite the existence of a mild end (PMID:31857255), because the
    mild presentations are a small minority of a small literature.
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Affected individuals rarely achieve head control. Most are unable to sit, stand, or walk."
    explanation: GeneReviews summary of typical functional outcome, which is the basis for a HIGH burden assignment.
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two of the 17 patients died at age of 14 months and 3 years due to respiratory failure."
    explanation: Documents mortality from the disorder's dominant complication, respiratory failure secondary to neuromuscular and bulbar weakness.
progression:
- phase: Onset
  age_range: Birth to early childhood
  notes: >-
    Presentation is congenital or neonatal in most reported individuals -
    hypotonia noted at birth, poor suck and feeding difficulty in the newborn
    period. The HPO annotation set for OMIM:617519 records HP:0003623 Neonatal
    onset at 4/6 and HP:0003577 Congenital onset at 2/5 (retrieved 2026-08-01).
    The 2025 natural-history review found that of 29 patients with onset data,
    presentation was most often at birth.
  evidence:
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the age at presentation was mostly at birth (n = 15)"
    explanation: Establishes birth as the modal age of presentation across the pooled published cohort.
- phase: Course
  age_range: Childhood onward
  notes: >-
    The published course is static or slowly progressive rather than
    relentlessly degenerative: developmental milestones are not lost, but they
    are largely not gained either. Two individuals in the pooled review had
    disease onset only at 48 and 60 years of age, which is difficult to
    reconcile with a congenital-onset neurodevelopmental disorder and is
    flagged as a knowledge gap rather than smoothed into the natural history.
    The clinically important trajectory is the secondary one: progressive
    bulbar weakness leads to dysphagia, aspiration and recurrent pneumonia, and
    thence to restrictive lung disease, tracheostomy and death. Scoliosis and
    joint contractures accumulate with immobility.
  evidence:
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "only two cases have late disease onset at the ages of 48 and 60 years old"
    explanation: >-
      Marked PARTIAL because the observation is quoted for what it is - an
      unexplained outlier within the pooled review - rather than as support for
      a late-onset form of this disorder. The review gives no clinical or
      molecular detail for these two individuals.
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Respiratory difficulties were seen in 17 patients (61%)."
    explanation: Quantifies the respiratory morbidity that drives the disorder's late course and mortality.
pathophysiology:
- name: Bi-allelic Loss-of-Function SPTBN4 Variants
  biological_scale: MOLECULAR
  description: >-
    The primary lesion is bi-allelic damage to SPTBN4 at 19q13.13, reported
    against transcript NM_020971. The reported allelic spectrum is dominated by
    truncating variants - nonsense, frameshift, splice-site and at least one
    multi-exon deletion - with a minority of missense changes. Missense alleles
    cluster in the spectrin-repeat rod, which is the segment that polymerises
    the scaffold, and the founding functional study showed that most tested
    patient alleles behave as loss of function in neurons rather than as
    subtler hypomorphs. There is no clean genotype-phenotype correlation: the
    variants are dispersed across the whole gene, and the one clearly milder
    published family carries an in-frame splice consequence rather than a
    distinct class of allele.
  genes:
  - preferred_term: SPTBN4
    term:
      id: hgnc:14896
      label: SPTBN4
  mechanism_confidence: ESTABLISHED
  notes: >-
    Two quantitative statements about the allelic spectrum come from different
    counting exercises and are recorded here rather than reconciled. The 2021
    report counted 15 pathogenic variants in total (10 truncating, 4 missense,
    1 splice-site, 1 multi-exon deletion - the arithmetic in the source sums to
    16 because the multi-exon deletion is also listed separately). The 2025
    natural-history review counted 31 different pathogenic variants across 38
    patients and reported that more than 70% of them sit in spectrin-repeat
    domains. These are different literature cut-offs, not a contradiction.
  evidence:
  - reference: PMID:29861105
    reference_title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we report bi-allelic pathogenic SPTBN4 variants (three homozygous and two compound heterozygous) that cause a severe neurological syndrome that includes congenital hypotonia, intellectual disability, and motor axonal and auditory neuropathy"
    explanation: The founding cohort report establishing bi-allelic SPTBN4 variants as the cause of the syndrome curated here.
  - reference: PMID:29861105
    reference_title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We introduced these variants into βIV spectrin, expressed these in neurons, and found that 5/7 were loss-of-function variants disrupting AIS localization or abolishing phosphoinositide binding."
    explanation: >-
      Functional testing of the patient alleles themselves, showing that they
      act by loss of function through two specific molecular routes - failure
      of AIS targeting and loss of phosphoinositide (PH-domain) binding.
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "more than 70% of SPTBN4 variants are located in spectrin repeat domains"
    explanation: Localises the bulk of the reported allelic spectrum to the spectrin-repeat rod, the segment that builds the scaffold.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is the first description of a multi-exon deletion in the SPTBN4 gene and it shows that larger SPTBN4 deletions may account for a part of SPTBN4-related disorder."
    explanation: Documents copy-number loss as part of the allelic spectrum, which is the reason sequencing alone can miss a second allele.
  downstream:
  - target: Loss of beta-IV Spectrin from the Axon Initial Segment and Nodal Membrane Skeleton
    description: >-
      Truncating and most missense alleles remove functional beta-IV spectrin
      from the axonal membrane skeleton, either by abolishing the protein or by
      preventing its targeting to the AIS.
  - target: Residual-Function Alleles and the Mild End of the Spectrum
    description: >-
      A parallel, allele-specific arm. In-frame consequences that preserve part
      of the protein are the proposed explanation for the one published family
      with axonal neuropathy but normal cognition.
- name: Loss of beta-IV Spectrin from the Axon Initial Segment and Nodal Membrane Skeleton
  biological_scale: MOLECULAR
  description: >-
    Beta-IV spectrin is the neuron-specific beta-subunit of the submembranous
    spectrin scaffold, restricted almost entirely to the axon initial segment
    and the nodes of Ranvier of myelinated neurons. The axonal scaffold it
    belongs to is a periodic lattice: actin rings spaced roughly 180 to 190 nm
    apart along the axon, bridged by spectrin tetramers of that same length,
    with sodium channels distributed in register with the lattice. Beta-IV
    spectrin is what links that lattice to the membrane at excitable domains.
    Its longest isoform, beta-IV-Sigma1, is the only one carrying an
    actin-binding domain and also carries 17 spectrin repeats, the ERQES
    specific domain and a pleckstrin homology domain; a shorter,
    N-terminally-truncated isoform, Sigma6, is expressed at much higher levels
    and carries the sodium-channel-clustering activity. The isoform structure
    matters clinically, because truncating variants at different positions
    remove different subsets of isoforms.
  genes:
  - preferred_term: SPTBN4
    term:
      id: hgnc:14896
      label: SPTBN4
  protein_complexes:
  - preferred_term: beta-IV spectrin-containing membrane skeleton
    modifier: DECREASED
    term:
      id: GO:0008091
      label: spectrin
  cellular_components:
  - preferred_term: axon initial segment
    term:
      id: GO:0043194
      label: axon initial segment
  - preferred_term: node of Ranvier
    term:
      id: GO:0033268
      label: node of Ranvier
  - preferred_term: spectrin-associated cytoskeleton
    term:
      id: GO:0014731
      label: spectrin-associated cytoskeleton
  molecular_functions:
  - preferred_term: actin binding
    modifier: DECREASED
    term:
      id: GO:0003779
      label: actin binding
  - preferred_term: structural constituent of cytoskeleton
    modifier: DECREASED
    term:
      id: GO:0005200
      label: structural constituent of cytoskeleton
  - preferred_term: phosphoinositide binding via the pleckstrin homology domain
    modifier: DECREASED
    term:
      id: GO:0035091
      label: phosphatidylinositol binding
  cell_types:
  - preferred_term: myelinated neuron
    term:
      id: CL:0000540
      label: neuron
  mechanism_confidence: ESTABLISHED
  notes: >-
    Two independent patient-material demonstrations that the protein is
    actually lost, from different tissues and different laboratories: Western
    blot showing absence of the full-length isoform in muscle and of a 72 kDa
    isoform in fibroblasts (PMID:28540413), and immunohistochemistry showing no
    beta-IV-spectrin signal in patient muscle where control muscle stained
    (PMID:33772159). Both were performed on muscle, which is precisely the
    tissue whose beta-IV spectrin expression was later disputed
    (PMID:38441922); see the "Contested Skeletal Muscle Involvement" node. The
    protein-loss claim for neurons rests on the founding functional study's
    neuronal expression experiments rather than on patient neural tissue, since
    no post-mortem CNS material from an affected individual has been reported.

    Isoform nomenclature is a live source of confusion and is stated
    explicitly. The original description names four alternatively spliced
    isoforms Sigma1 to Sigma4 and reports the longest as a 250 kD band;
    subsequent work adds Sigma6 as the dominant short isoform; and the first
    clinical report describes the full-length isoform as 288 kDa. These are the
    same gene product family described with different antibodies, species and
    conventions, and the discrepancy in stated molecular weight is not resolved
    in the literature. It is recorded rather than averaged.
  evidence:
  - reference: PMID:11086001
    reference_title: "betaIV spectrin, a new spectrin localized at axon initial segments and nodes of ranvier in the central and peripheral nervous system."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In brain, betaIV spectrin is enriched in myelinated neurons, where it colocalizes with ankyrin(G) 480/270-kD at axon initial segments and nodes of Ranvier."
    explanation: Establishes the subcellular localisation that defines this disorder - beta-IV spectrin is an AIS and nodal protein of myelinated neurons.
  - reference: PMID:11086001
    reference_title: "betaIV spectrin, a new spectrin localized at axon initial segments and nodes of ranvier in the central and peripheral nervous system."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The longest isoform (betaIVSigma1 spectrin) includes an actin-binding domain, followed by 17 spectrin repeats, a specific domain in which the amino acid sequence ERQES is repeated four times, several putative SH3-binding sites and a pleckstrin homology domain."
    explanation: Defines the domain architecture whose loss the patient alleles cause, including the PH domain whose phosphoinositide binding several patient variants abolish.
  - reference: PMID:23239625
    reference_title: "Actin, spectrin, and associated proteins form a periodic cytoskeletal structure in axons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Actin formed ringlike structures that wrapped around the circumference of axons and were evenly spaced along axonal shafts with a periodicity of ~180 to 190 nanometers."
    explanation: Establishes the periodic actin-spectrin lattice architecture of the axon, the structure that beta-IV spectrin builds at excitable domains.
  - reference: PMID:23239625
    reference_title: "Actin, spectrin, and associated proteins form a periodic cytoskeletal structure in axons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Sodium channels in axons were distributed in a periodic pattern coordinated with the underlying actin-spectrin-based cytoskeleton."
    explanation: Directly links the spectrin lattice geometry to sodium-channel placement, which is the mechanistic bridge from a cytoskeletal lesion to a channel-clustering failure.
  - reference: PMID:17197442
    reference_title: "Specific role of the truncated betaIV-spectrin Sigma6 in sodium channel clustering at axon initial segments and nodes of ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "betaIV-Spectrin, an essential component of the membrane skeleton at these sites, has an N-terminal-truncated isoform, Sigma6, which is expressed at much higher levels than the full-length isoform Sigma1."
    explanation: Establishes the isoform structure that determines which functions a given truncating variant removes.
  - reference: PMID:28540413
    reference_title: "A recessive mutation in beta-IV-spectrin (SPTBN4) associates with congenital myopathy, neuropathy, and central deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Western blot confirmed the absence of the full-length 288 kDa isoform in muscle and of a specific 72 kDa isoform in fibroblasts."
    explanation: Patient-material demonstration that a nonsense allele abolishes the protein rather than merely altering it.
  downstream:
  - target: Failure of the Reciprocal AnkyrinG-beta-IV Spectrin Scaffold
    description: >-
      Loss of the beta-subunit removes one half of a mutually stabilising pair,
      so ankyrin-G is no longer retained at the AIS and node.
  - target: Loss of the Dense Nodal Membrane Undercoat
    description: >-
      The actin-binding Sigma1 isoform is the structural component of the
      electron-dense coat beneath the nodal membrane; without it the coat
      disappears.
- name: Failure of the Reciprocal AnkyrinG-beta-IV Spectrin Scaffold
  biological_scale: MOLECULAR
  description: >-
    AnkyrinG and beta-IV spectrin are not arranged in series but in a
    reciprocal pair. AnkyrinG recruits beta-IV spectrin to the AIS and to nodes
    through a specific domain in the spectrin, and beta-IV spectrin in turn
    retains ankyrinG there; deleting either one delocalises the other. That
    reciprocity is why an SPTBN4 lesion is not merely the loss of one
    scaffolding activity but the collapse of the adaptor hub through which
    every clustered channel and adhesion molecule is anchored. Two of the
    routes by which patient alleles break this hub were demonstrated directly:
    failure to localise to the AIS, and loss of phosphoinositide binding by the
    pleckstrin homology domain, which is the membrane-facing half of the
    linkage.
  genes:
  - preferred_term: SPTBN4
    term:
      id: hgnc:14896
      label: SPTBN4
  molecular_functions:
  - preferred_term: ankyrin binding
    modifier: DECREASED
    term:
      id: GO:0030506
      label: ankyrin binding
  cellular_components:
  - preferred_term: axon initial segment
    term:
      id: GO:0043194
      label: axon initial segment
  - preferred_term: node of Ranvier
    term:
      id: GO:0033268
      label: node of Ranvier
  cell_types:
  - preferred_term: myelinated neuron
    term:
      id: CL:0000540
      label: neuron
  mechanism_confidence: ESTABLISHED
  notes: >-
    The reciprocity has a direct consequence for how this disorder relates to
    ANK3 disease. Because ankyrinG-null neurons lose beta-IV spectrin from the
    AIS and node, and beta-IV-spectrin-null neurons lose ankyrinG from the same
    sites, the two genes converge on one lesion; ANK3-related
    intellectual-disability-hypotonia-spasticity-sleep-disorder syndrome
    (MONDO:0014210, verified with OAK) is curated below as a mechanistic
    differential on that basis. The asymmetry is also informative: a
    dominant-negative ankyrinG construct displaced beta-IV spectrin without
    displacing endogenous ankyrinG or sodium channels, so beta-IV spectrin is
    the more downstream and more dispensable partner for the initial assembly
    step, and its role is retention and stabilisation rather than nucleation.
  evidence:
  - reference: PMID:11807096
    reference_title: "[Beta]IV-spectrin regulates sodium channel clustering through ankyrin-G at axon initial segments and nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These results indicate that betaIV-spectrin and ankyrin-G mutually stabilize the membrane protein cluster and the linked membrane cytoskeleton at AIS and NR."
    explanation: States the reciprocal stabilisation that this node models, from the definitive gene-trap knockout study.
  - reference: PMID:11807096
    reference_title: "[Beta]IV-spectrin regulates sodium channel clustering through ankyrin-G at axon initial segments and nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Conversely, in ankyrin-G-null neurons, betaIV-spectrin is not localized to these sites."
    explanation: Establishes the second direction of the reciprocity, which is the basis for treating ANK3 disease as a mechanistic differential.
  - reference: PMID:17283186
    reference_title: "betaIV spectrin is recruited to axon initial segments and nodes of Ranvier by ankyrinG."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We identify a distinct protein domain in betaIV spectrin required for its localization to the AIS, and show that this domain mediates betaIV spectrin's interaction with ankG."
    explanation: Identifies the specific beta-IV spectrin domain mediating the ankyrinG interaction, the interface that AIS-mislocalising patient variants disrupt.
  - reference: PMID:17283186
    reference_title: "betaIV spectrin is recruited to axon initial segments and nodes of Ranvier by ankyrinG."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Finally, using adenovirus for transgene delivery into myelinated neurons, we demonstrate that betaIV spectrin recruitment to nodes of Ranvier also depends on binding to ankG."
    explanation: Extends the same recruitment mechanism from the AIS to the node of Ranvier, the second domain whose failure produces the neuropathy.
  - reference: PMID:29861105
    reference_title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "found that 5/7 were loss-of-function variants disrupting AIS localization or abolishing phosphoinositide binding"
    explanation: Shows that the disease alleles break this scaffold specifically at the two interfaces modelled here - AIS targeting and membrane phosphoinositide binding.
  downstream:
  - target: Failure of Voltage-Gated Sodium Channel Clustering at the AIS and Node
    description: The ankyrinG-spectrin hub is the anchor for nodal and AIS Nav channels; losing it disperses them.
  - target: Failure of KCNQ2 and KCNQ3 Potassium Channel Clustering
    description: >-
      The same hub, acting through regulatory partners rather than by direct
      binding, positions the nodal KCNQ2/KCNQ3 channels.
- name: Loss of the Dense Nodal Membrane Undercoat
  biological_scale: CELLULAR
  description: >-
    Beneath the nodal axolemma sits an electron-dense submembranous coat that
    is thought to be what physically holds the channel cluster in place.
    Beta-IV-Sigma1 spectrin, the actin-binding isoform, is an essential
    component of that coat, and removing it alone makes the coat disappear,
    widens the node, and fills it with organelle-laden membrane dilations. The
    structural failure is separable from the channel-clustering failure: mice
    retaining only the short Sigma6 isoform still show waving and swelling of
    the AIS and nodal membrane while recovering much of their sodium-channel
    clustering, and mice lacking only Sigma6 do the reverse. So the disorder
    has two mechanistically distinct arms - a mechanical one and an electrical
    one - and a given truncating allele may load them unequally.
  cellular_components:
  - preferred_term: node of Ranvier
    term:
      id: GO:0033268
      label: node of Ranvier
  - preferred_term: cortical cytoskeleton
    modifier: ABNORMAL
    term:
      id: GO:0030863
      label: cortical cytoskeleton
  cell_types:
  - preferred_term: myelinated neuron
    term:
      id: CL:0000540
      label: neuron
  locations:
  - preferred_term: peripheral nervous system
    term:
      id: UBERON:0000010
      label: peripheral nervous system
  mechanism_confidence: ESTABLISHED
  notes: >-
    All the ultrastructural evidence for this node is murine. No nerve or brain
    ultrastructure from a human SPTBN4 patient has been published; the closest
    human evidence is the nerve biopsy in the founding cohort, which was
    assayed for channel content rather than for nodal ultrastructure. The
    structural arm of the mechanism is therefore well established in mouse and
    inferred in human. Note also the CNS/PNS asymmetry seen in the mouse
    allelic series: central nodes were far more severely affected than
    peripheral ones for the milder qv3J allele, whereas the more complete qv4J
    truncation damaged peripheral nodes too - a dose-dependence that is a
    plausible, untested explanation for why some human alleles produce
    neuropathy with normal cognition.
  evidence:
  - reference: PMID:15381686
    reference_title: "BetaIVSigma1 spectrin stabilizes the nodes of Ranvier and axon initial segments."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Here, we prove that betaIVSigma1 spectrin, the only betaIV spectrin with an actin-binding domain, is an essential component of this coat."
    explanation: Identifies the specific isoform whose loss removes the nodal undercoat and states why - it is the only actin-binding beta-IV spectrin.
  - reference: PMID:15381686
    reference_title: "BetaIVSigma1 spectrin stabilizes the nodes of Ranvier and axon initial segments."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Removal of betaIVSigma1 alone causes the disappearance of the nodal coat, an increased diameter of the NR, and the presence of dilations filled with organelles."
    explanation: The direct ultrastructural consequence modelled by this node.
  - reference: PMID:15317849
    reference_title: "BetaIV spectrins are essential for membrane stability and the molecular organization of nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Central nodes of qv(3J) mice, which lack betaIV spectrins, are significantly broader and have prominent vesicle-filled nodal membrane protrusions, whereas axon shape and neurofilament density are dramatically altered."
    explanation: Independent replication of the nodal structural breakdown, and the source of the CNS-versus-PNS severity asymmetry noted above.
  - reference: PMID:17197442
    reference_title: "Specific role of the truncated betaIV-spectrin Sigma6 in sodium channel clustering at axon initial segments and nodes of ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We conclude that the truncated betaIV-spectrin isoform Sigma6 plays a specific role in clustering voltage-gated sodium channels, whereas it is dispensable for membrane stabilization at axon initial segments and nodes of Ranvier."
    explanation: >-
      Establishes that the mechanical (membrane-stabilising) and electrical
      (channel-clustering) arms of beta-IV spectrin function are genetically
      separable, which is why they are modelled as two nodes rather than one.
  downstream:
  - target: Impaired Action Potential Initiation and Saltatory Conduction
    description: A structurally disorganised node cannot support the current densities that saltatory conduction requires.
  - target: Distal Motor Axonal Degeneration and Neurogenic Muscle Wasting
    description: >-
      Chronic mechanical destabilisation of nodal membrane, with organelle
      accumulation and axonal shape change, precedes overt axonal loss.
- name: Failure of Voltage-Gated Sodium Channel Clustering at the AIS and Node
  biological_scale: CELLULAR
  description: >-
    Saltatory conduction depends on sodium channels being present at very high
    density over the short bare stretch of axolemma at each node, and action
    potential initiation depends on the same arrangement at the axon initial
    segment. Without beta-IV spectrin, neither ankyrinG nor the sodium channels
    are correctly clustered at these sites. In human disease this was shown
    directly: nerve biopsy from an affected individual had reduced nodal
    sodium channels. The failure is partial rather than absolute, and the
    reason is a specific compensation - ankyrinR together with beta-I spectrin
    can substitute at nodes and cluster some sodium channels when the
    ankyrinG/beta-IV-spectrin pair is gone.
  biological_processes:
  - preferred_term: clustering of voltage-gated sodium channels
    modifier: DECREASED
    term:
      id: GO:0045162
      label: clustering of voltage-gated sodium channels
  cellular_components:
  - preferred_term: voltage-gated sodium channel complex
    modifier: ABNORMAL
    term:
      id: GO:0001518
      label: voltage-gated sodium channel complex
  - preferred_term: node of Ranvier
    term:
      id: GO:0033268
      label: node of Ranvier
  - preferred_term: axon initial segment
    term:
      id: GO:0043194
      label: axon initial segment
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  - preferred_term: cortical pyramidal neuron
    term:
      id: CL:4023111
      label: cerebral cortex pyramidal neuron
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:11807096
    reference_title: "[Beta]IV-spectrin regulates sodium channel clustering through ankyrin-G at axon initial segments and nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In betaIV-spectrin-null neurons, neither ankyrin-G nor voltage-gated sodium channels (VGSC) are correctly clustered at these sites, suggesting that impaired action potential caused by mislocalization of VGSC leads to the phenotype."
    explanation: >-
      The core loss-of-function result. Removing beta-IV spectrin disperses
      both the adaptor and the sodium channels, and the authors attribute the
      organismal phenotype to that mislocalisation.
  - reference: PMID:29861105
    reference_title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nerve biopsies from an individual with a loss-of-function variant had reduced nodal Na+ channels and no nodal KCNQ2 K+ channels."
    explanation: Direct human patient-tissue demonstration of the channel-clustering failure, which is what makes this mechanism a human disease mechanism rather than a mouse phenomenon.
  - reference: PMID:29861105
    reference_title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Modeling the disease in mice revealed that although ankyrinR (AnkR) and βI spectrin can cluster Na+ channels and partially compensate for the loss of AnkG and βIV spectrin at nodes of Ranvier, AnkR and βI spectrin cannot cluster KCNQ2- and KCNQ3-subunit-containing K+ channels."
    explanation: Identifies the partial rescue that makes the sodium-channel arm survivable, and simultaneously identifies the potassium-channel arm as the non-compensable one.
  - reference: PMID:19156852
    reference_title: "Reduced excitability in the dentate gyrus network of betaIV-spectrin mutant mice in vivo."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Quivering (qv(3j)) mice lack functional betaIV-spectrin and have reduced voltage-gated sodium channel (VGSC) immunoreactivity at the axon initial segment and nodes of Ranvier."
    explanation: Independent confirmation of reduced nodal and AIS sodium-channel content in a second beta-IV spectrin mutant line.
  downstream:
  - target: Impaired Action Potential Initiation and Saltatory Conduction
    description: Reduced nodal sodium-channel density directly reduces the inward current available to regenerate the impulse at each node.
- name: Failure of KCNQ2 and KCNQ3 Potassium Channel Clustering
  biological_scale: CELLULAR
  description: >-
    This is the mechanistically distinctive lesion of the disorder and the one
    that best explains its epilepsy. Nodal KCNQ2/KCNQ3 (Kv7) channels carry the
    slow M-current that damps repetitive firing. In patient nerve they are not
    merely reduced but absent, and in the disease mouse model the ankyrinR /
    beta-I spectrin backup that partially rescues sodium channels cannot
    cluster KCNQ2/KCNQ3 at all. Beta-IV spectrin does not bind KCNQ2/3
    directly, so it must position them through regulatory partners; consistent
    with that, total KCNQ2 protein is normal in mutant animals and only its
    localisation fails. The functional consequence measured in mice is axonal
    hyperexcitability - spontaneous and evoked neuromyotonic and myokymic
    discharges arising in myelinated axons - which is pharmacologically
    reversible with the KCNQ2/3 opener retigabine.
  biological_processes:
  - preferred_term: clustering of voltage-gated potassium channels
    modifier: DECREASED
    term:
      id: GO:0045163
      label: clustering of voltage-gated potassium channels
  cellular_components:
  - preferred_term: voltage-gated potassium channel complex
    modifier: DECREASED
    term:
      id: GO:0008076
      label: voltage-gated potassium channel complex
  - preferred_term: node of Ranvier
    term:
      id: GO:0033268
      label: node of Ranvier
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  mechanism_confidence: ESTABLISHED
  notes: >-
    The mechanistic significance of this node is that it is where the SPTBN4
    phenotype touches the KCNQ2 phenotypes. KCNQ2 loss of function causes both
    developmental and epileptic encephalopathy 7 (MONDO:0013387) and benign
    familial neonatal seizures 1 (MONDO:0007365), both verified with OAK and
    both already curated in this knowledge base; a disorder that fails to
    cluster the same channel is expected to share features with them, and the
    2021 cohort report makes exactly that argument. Retigabine is discussed in
    this entry only as an experimental probe in mice: it has never been tested
    in SPTBN4 disease, it was withdrawn from clinical use for retinal and skin
    pigmentation, and it is therefore NOT curated as a treatment.
  evidence:
  - reference: PMID:29861105
    reference_title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nerve biopsies from an individual with a loss-of-function variant had reduced nodal Na+ channels and no nodal KCNQ2 K+ channels."
    explanation: The human tissue observation that nodal KCNQ2 is absent, not merely reduced - a qualitatively more severe failure than the sodium-channel arm.
  - reference: PMID:20962009
    reference_title: "The C-terminal domain of ßIV-spectrin is crucial for KCNQ2 aggregation and excitability at nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Of interest, KCNQ2 subunit aggregates were undetectable at PNS and CNS nodes, whereas Nav and Kv1.1/Kv1.2 channels were properly concentrated at nodal and juxtaparanodal regions, respectively."
    explanation: Shows the selectivity of the defect - in this allele KCNQ2 clustering fails while sodium and Kv1 channels are spared, isolating the potassium arm.
  - reference: PMID:20962009
    reference_title: "The C-terminal domain of ßIV-spectrin is crucial for KCNQ2 aggregation and excitability at nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The protein level of KCNQ2 subunits was normal in mutant animals, suggesting that KCNQ2 subunit absence stems from clustering or trafficking defects in axons."
    explanation: Establishes that the lesion is one of localisation rather than of channel abundance, which is what makes it a cytoskeletal rather than a channelopathy mechanism.
  - reference: PMID:20962009
    reference_title: "The C-terminal domain of ßIV-spectrin is crucial for KCNQ2 aggregation and excitability at nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Retigabine, an activator of KCNQ2/3 channels, attenuated the repetitive activities in quivering-3J mice, suggesting that depletion of KCNQ2 subunits at nodes initiates neuromyotonic/myokymic discharges."
    explanation: Pharmacological confirmation that the hyperexcitability is caused by the KCNQ2 clustering failure rather than being an unrelated epiphenomenon.
  - reference: PMID:33986717
    reference_title: "Severe Form of ßIV-Spectrin Deficiency With Mitochondrial Dysfunction and Cardiomyopathy-A Case Report."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Together with ankyrin G, ßIV-spectrin is responsible for the clustering of KCNQ2/3-potassium channels and NaV-sodium channels."
    explanation: >-
      States the dual channel-clustering role in a clinical review context.
      Classified OTHER because this sentence is the case report's introductory
      statement of established cell biology rather than an observation of its
      own.
  downstream:
  - target: Axonal Hyperexcitability and Epileptiform Discharge
    description: Loss of the nodal M-current brake permits spontaneous repetitive firing in myelinated axons.
- name: Impaired Action Potential Initiation and Saltatory Conduction
  biological_scale: CELLULAR
  description: >-
    The convergence point of the structural and the channel-clustering arms.
    With fewer sodium channels at a structurally disorganised AIS and node, the
    threshold for spike initiation rises, conduction along myelinated fibres
    slows, and high-frequency firing becomes unreliable. Both features have
    been measured: in the auditory brainstem, beta-4-spectrin-null mice show an
    elevated action-potential threshold, increased failures during
    high-frequency trains, and slowed central conduction; in the hippocampus,
    beta-IV-spectrin mutants show an impaired input-output relationship and
    reduced network excitability that a computational model reproduces from
    sodium-channel loss alone.
  biological_processes:
  - preferred_term: neuronal action potential
    modifier: DECREASED
    term:
      id: GO:0019228
      label: neuronal action potential
  - preferred_term: neuronal action potential propagation
    modifier: DECREASED
    term:
      id: GO:0019227
      label: neuronal action potential propagation
  - preferred_term: membrane depolarization during action potential
    modifier: DECREASED
    term:
      id: GO:0086010
      label: membrane depolarization during action potential
  cellular_components:
  - preferred_term: axon
    term:
      id: GO:0030424
      label: axon
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  - preferred_term: cortical pyramidal neuron
    term:
      id: CL:4023111
      label: cerebral cortex pyramidal neuron
  mechanism_confidence: ESTABLISHED
  notes: >-
    There is a real tension in this node that the entry does not smooth over.
    The sodium-channel arm predicts REDUCED excitability, and that is what was
    measured in the dentate gyrus in vivo. The KCNQ2 arm predicts INCREASED
    excitability, and that is what was measured at the diaphragm neuromuscular
    junction and in peripheral axons, and what the epileptiform EEGs in
    patients suggest. Both are true of the same mutant animals. The resolution
    is presumably compartmental - which channel's loss dominates depends on the
    axonal domain, the fibre type and the developmental stage - but no study
    has tested that directly, and it is recorded as an open question rather
    than asserted. This is also why the entry does NOT declare conformance to
    `epilepsy_excitation_inhibition_imbalance`: the direction of the
    excitability shift is not uniform across the nervous system in this
    disorder.
  evidence:
  - reference: PMID:35393465
    reference_title: "Loss of β4-spectrin impairs Na(v) channel clustering at the heminode and temporal fidelity of presynaptic spikes in developing auditory brain."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Presynaptic terminal recordings in Sptbn4geo mice, β4-spectrin null mice, showed an elevated threshold of action potential and increased failures during action potential train at high-frequency."
    explanation: Direct electrophysiological measurement of the initiation and high-frequency-fidelity failure that this node describes.
  - reference: PMID:19156852
    reference_title: "Reduced excitability in the dentate gyrus network of betaIV-spectrin mutant mice in vivo."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "This revealed an impaired input-output relationship between stimulus intensity and granule cell population spikes and an enhanced paired-pulse inhibition of population spikes, indicating a reduced ability of granule cells to generate action potentials and decreased network excitability."
    explanation: In vivo network-level demonstration that the channel-clustering lesion translates into a measurable firing deficit, and the source of the reduced-excitability half of the paradox described in the notes.
  - reference: PMID:19156852
    reference_title: "Reduced excitability in the dentate gyrus network of betaIV-spectrin mutant mice in vivo."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "This in silico approach confirmed that the loss of VGSCs is sufficient to explain the electrophysiological changes observed in qv(3j) mice."
    explanation: A computational model showing that sodium-channel loss alone accounts for the measured network changes, closing the causal chain from clustering failure to firing deficit.
  downstream:
  - target: Distal Motor Axonal Degeneration and Neurogenic Muscle Wasting
    description: Chronically failing conduction in the longest motor axons precedes and accompanies their degeneration.
  - target: Central Auditory Conduction Failure
    description: The auditory brainstem pathway depends on submillisecond temporal fidelity and is the first system to fail.
  - target: Cortical Network Dysfunction and Impaired Neurodevelopment
    description: AIS-dependent spike initiation in cortical pyramidal neurons underlies the cognitive and language phenotype.
- name: Axonal Hyperexcitability and Epileptiform Discharge
  biological_scale: CELLULAR
  description: >-
    Loss of nodal KCNQ2/3 removes the slow potassium brake on repetitive
    firing, and the result in mice is spontaneous and evoked neuromyotonic and
    myokymic discharge originating in myelinated axons distal to the nerve
    terminal. The human counterpart is the striking, and initially
    counterintuitive, finding that patients can have abundant to nearly
    continuous epileptiform discharges on EEG - in one case documented over 72
    hours and in another over 24-hour video EEG - with no clinical seizure ever
    observed. This dissociation between electrographic and clinical epilepsy is
    a distinctive feature of the disorder and is the reason EEG is worth
    performing even in a child with no history of fits.
  biological_processes:
  - preferred_term: regulation of monoatomic ion transmembrane transport
    modifier: ABNORMAL
    term:
      id: GO:0034765
      label: regulation of monoatomic ion transmembrane transport
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  - preferred_term: cortical pyramidal neuron
    term:
      id: CL:4023111
      label: cerebral cortex pyramidal neuron
  mechanism_confidence: PROVISIONAL
  notes: >-
    Marked PROVISIONAL rather than ESTABLISHED for a specific reason: the
    causal link from KCNQ2 declustering to hyperexcitability is established in
    mouse peripheral axons, and the epileptiform EEG is established in
    patients, but nothing connects the two directly in human tissue. The mouse
    readout is neuromyotonia and myokymia at the neuromuscular junction, which
    is a peripheral phenomenon, whereas the patient readout is a cortical EEG.
    Whether the patients' discharges arise by the same KCNQ2-declustering
    mechanism, or instead from the cortical AIS pathology, is untested.

    Seizure frequency is genuinely inconsistent across sources and is not
    averaged here. GeneReviews states that half of affected individuals develop
    seizures; the 2021 cohort report says more than half develop seizures or
    have a pathological EEG; the 2025 natural-history review of 38 patients
    puts seizures at 21%; and the HPO annotation set for OMIM:617519 records
    HP:0001250 Seizure with the frequency modifier "Very rare", sourced to OMIM
    (retrieved 2026-08-01). These four sources cannot all be right. The
    discrepancy is recorded as a knowledge-gap discussion.
  evidence:
  - reference: PMID:20962009
    reference_title: "The C-terminal domain of ßIV-spectrin is crucial for KCNQ2 aggregation and excitability at nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The quivering-3J mice show prominent spontaneous and evoked hyperactivities at diaphragm neuromuscular junctions."
    explanation: The hyperexcitability phenotype produced by nodal KCNQ2 loss in the disease model.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Additional symptoms comprised horizontal nystagmus, epileptiform discharges in EEG without manifest seizures, and choreoathetosis."
    explanation: The human electroclinical dissociation - epileptiform EEG without clinical seizures - that this node models.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "As βIV-spectrin plays a role in the clustering of KCNQ2 subunit-containing potassium channels, there could be some degree of overlap of clinical symptoms with early-infantile epileptic encephalopathy type 7 and with benign familial neonatal seizures type 1."
    explanation: The authors' own statement of the KCNQ2 mechanistic link, which is the basis for curating the two KCNQ2 disorders as mechanistic differentials.
  downstream:
  - target: Cortical Network Dysfunction and Impaired Neurodevelopment
    description: Recurrent epileptiform activity is a plausible additional contributor to the developmental phenotype, though causality is not established.
- name: Distal Motor Axonal Degeneration and Neurogenic Muscle Wasting
  biological_scale: TISSUE
  description: >-
    The peripheral endpoint is a length-dependent motor axonal neuropathy.
    Electrophysiology in patients shows low-amplitude motor responses with
    preserved conduction velocities - the signature of axonal rather than
    demyelinating disease - together with fibrillation potentials, positive
    sharp waves and enlarged, long-duration motor unit potentials indicating
    acute and chronic denervation. Clinically this produces areflexia,
    generalised and distal amyotrophy, and weakness that is severe enough in
    most individuals to prevent sitting, standing or walking. Muscle biopsy
    shows the corresponding neurogenic picture in some patients: atrophic
    fascicles, angulated fibres, and fibre grouping.
  conforms_to: "peripheral_axonal_degeneration#Distal Axonal Degeneration and Demyelination"
  biological_processes:
  - preferred_term: neuronal action potential propagation
    modifier: DECREASED
    term:
      id: GO:0019227
      label: neuronal action potential propagation
  cell_types:
  - preferred_term: alpha motor neuron
    term:
      id: CL:0008038
      label: alpha motor neuron
  - preferred_term: denervated skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  locations:
  - preferred_term: peripheral nerve
    term:
      id: UBERON:0001021
      label: nerve
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  mechanism_confidence: ESTABLISHED
  notes: >-
    Conformance caveat. This node declares conformance to the central effector
    step of the `peripheral_axonal_degeneration` module, which bundles axonal
    degeneration with Schwann-cell demyelination. Only the axonal arm applies
    here: the HPO annotation set for OMIM:617519 records HP:0007108
    Demyelinating peripheral neuropathy at 0/5 (retrieved 2026-08-01), sensory
    and motor conduction velocities were normal in the patients in whom they
    were measured, and no myelin pathology has been reported. The module's
    upstream axonal-transport and mitochondrial nodes are also NOT claimed: no
    transport or mitochondrial assay has been done in SPTBN4 disease, and the
    upstream lesion here is a nodal cytoskeletal and channel-clustering
    failure, not a transport failure. The conformance is therefore asserted at
    the effector node only.

    Neuropathy is not detectable in every patient. In the 2021 cohort,
    electrophysiology showed obvious neuropathy in only one of five; one
    patient (Patient 3) had entirely normal nerve conduction studies and EMG,
    and a second (Patient 4) had normal sensory and motor action potentials
    with no EMG reported - so a normal
    neurophysiological study does not exclude the diagnosis, and the HPOA
    denominator for HP:0003477 Peripheral axonal neuropathy is correspondingly
    low (2/6).
  evidence:
  - reference: PMID:29861105
    reference_title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "cause a severe neurological syndrome that includes congenital hypotonia, intellectual disability, and motor axonal and auditory neuropathy"
    explanation: Names motor axonal neuropathy as a defining component of the syndrome.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "EMG showed signs of acute and chronic denervation such as fibrillation potentials and positive sharp waves, motor unit potentials with increased amplitude and duration, and decreased recruitment."
    explanation: The electrophysiological denervation signature that establishes the muscle involvement as neurogenic.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nerve conduction studies showed normal sensory and motor conduction velocities, with low-amplitude motor responses."
    explanation: Establishes the axonal rather than demyelinating character of the neuropathy, which is why the module's demyelination arm is explicitly not claimed.
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Axonal motor neuropathy leads to hyporeflexia/areflexia and weakness, which can result in respiratory difficulties requiring ventilatory support."
    explanation: Connects the neuropathy to its two dominant clinical consequences, areflexic weakness and ventilatory failure.
  downstream:
  - target: Contested Skeletal Muscle Involvement
    description: >-
      Denervation is the currently favoured explanation for the muscle biopsy
      abnormalities that were originally interpreted as a primary congenital
      myopathy.
- name: Central Auditory Conduction Failure
  biological_scale: TISSUE
  description: >-
    Hearing loss in this disorder is a neuropathy, not a cochlear disease. The
    quivering mouse, which is the natural model of the human condition, is deaf
    with normal cochlear morphology and normal cochlear potentials but abnormal
    transmission through the brainstem auditory nuclei - deafness "central in
    origin". The same pattern was documented in a patient: otoacoustic
    emissions present, but brainstem evoked response audiometry showing only
    wave I, localising the block to cochlear nerve conduction. Mechanistically
    the auditory pathway is the most demanding client of the nodal scaffold
    because it encodes at submillisecond precision, and beta-4-spectrin-null
    mice fail specifically at the heminode adjacent to the nerve terminal, with
    slowed central conduction and absent startle responses despite normal
    cochlear function.
  cell_types:
  - preferred_term: spiral ganglion neuron
    term:
      id: CL:0011113
      label: spiral ganglion neuron
  locations:
  - preferred_term: cochlear nerve
    term:
      id: UBERON:0004727
      label: cochlear nerve
  - preferred_term: auditory brainstem
    term:
      id: UBERON:0002028
      label: hindbrain
  biological_processes:
  - preferred_term: clustering of voltage-gated sodium channels
    modifier: DECREASED
    term:
      id: GO:0045162
      label: clustering of voltage-gated sodium channels
  mechanism_confidence: ESTABLISHED
  notes: >-
    This node is the reason the entry does NOT declare conformance to the
    `sensorineural_hair_cell_loss` module. That module's central effector is
    hair cell mechanotransduction failure and death, and the evidence here
    points the opposite way: cochlear function is preserved in both the mouse
    and the reported patients, and the lesion is in the first-order auditory
    neuron and its central projection. Curating this as hair-cell disease would
    be a category error, and would also mislead about management, since
    auditory neuropathy responds poorly to conventional amplification.
    HP:0000407 Sensorineural hearing impairment is nonetheless the phenotype
    term used, because HPO has no "auditory neuropathy" term - searches for
    both `l~auditory neuropathy` and a free-text `auditory neuropathy` against
    `sqlite:obo:hp` returned nothing on 2026-08-01 - and HP:0004463 Absent
    brainstem auditory responses is bound alongside it to carry the
    neuropathic character.
  evidence:
  - reference: PMID:11528393
    reference_title: "Mutant beta-spectrin 4 causes auditory and motor neuropathies in quivering mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "However, responses from brainstem auditory nuclei show abnormal transmission of auditory information, indicating that, in contrast to the many known mutations causing deafness originating in the cochlea, deafness in qv is central in origin."
    explanation: Establishes the central, non-cochlear origin of the deafness in the model organism that first defined this gene's phenotype.
  - reference: PMID:11528393
    reference_title: "Mutant beta-spectrin 4 causes auditory and motor neuropathies in quivering mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Ear twitch responses (Preyer's reflex) to sound are absent in homozygous qv/qv mice, although cochlear morphology seems normal and cochlear potentials recorded at the round window are no different from those of control mice."
    explanation: The specific negative findings - normal cochlear morphology and potentials - that exclude a hair-cell mechanism.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In brainstem evoked response audiometry (BERA) only wave 1 from the inner ear could be recorded pointing to a defect at the level of cochlear nerve conduction."
    explanation: The human counterpart of the mouse finding, localising the auditory lesion to cochlear nerve conduction with a preserved inner ear.
  - reference: PMID:35393465
    reference_title: "Loss of β4-spectrin impairs Na(v) channel clustering at the heminode and temporal fidelity of presynaptic spikes in developing auditory brain."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Sptbn4geo mice exhibited a slower central conduction and showed no startle responses, but had normal cochlear function."
    explanation: Independent confirmation in a second null line that the auditory deficit is central and conduction-based with preserved cochlear function.
  - reference: PMID:35393465
    reference_title: "Loss of β4-spectrin impairs Na(v) channel clustering at the heminode and temporal fidelity of presynaptic spikes in developing auditory brain."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We found during postnatal development, β4-spectrin is critical for voltage-gated sodium channel (Nav) clustering at the heminode along the nerve terminal, but not for the formation of nodal and AIS structures in the auditory brainstem."
    explanation: Localises the auditory lesion to a specific axonal subdomain, the heminode, and shows that nodal and AIS assembly per se can be spared there.
- name: Cortical Network Dysfunction and Impaired Neurodevelopment
  biological_scale: ORGANISM
  description: >-
    The cognitive and language phenotype is the least mechanistically resolved
    part of the disorder and also its most severe. The axon initial segment is
    where a cortical pyramidal neuron decides whether to fire; beta-IV spectrin
    is one of the two proteins that build it; and beta-IV-spectrin mutant mice
    have measurably reduced network excitability in vivo. Beyond that the chain
    is inference. Most affected individuals have severe to profound
    developmental delay and intellectual disability with absent or
    single-word speech, and neuroimaging is normal in a substantial minority -
    8 of 22 patients with available MRI in the pooled review - so there is no
    gross structural lesion to which the cognitive phenotype can be attributed.
    Where MRI is abnormal the findings are non-specific: vermian atrophy,
    diffuse T2 hyperintensity, enlarged CSF spaces, cerebral atrophy and white
    matter change.
  cell_types:
  - preferred_term: cortical pyramidal neuron
    term:
      id: CL:4023111
      label: cerebral cortex pyramidal neuron
  locations:
  - preferred_term: cerebral cortex
    term:
      id: UBERON:0000956
      label: cerebral cortex
  - preferred_term: cerebellum
    term:
      id: UBERON:0002037
      label: cerebellum
  cellular_components:
  - preferred_term: axon initial segment
    term:
      id: GO:0043194
      label: axon initial segment
  mechanism_confidence: HYPOTHETICAL
  notes: >-
    Marked HYPOTHETICAL deliberately, and it is the weakest link in the
    pathograph. There is no human neuropathology in SPTBN4 disease - no
    autopsy, no biopsy of CNS tissue, no iPSC-derived neuronal model has been
    reported. The cortical AIS mechanism is imported wholesale from rodent
    hippocampal and brainstem recordings. The competing explanations are not
    excluded: the developmental delay could be substantially secondary to
    profound motor and communicative impairment plus recurrent hypoxia from
    aspiration, rather than a primary cortical lesion, and no study has tried
    to separate these. The cerebellar findings are a further complication -
    ataxia was reported in only one Saudi family, yet cerebellar vermian
    atrophy appears in the imaging series and ataxia is a cardinal feature of
    the quivering mouse, so the cerebellum may be involved more often than the
    clinical phenotype suggests.
  evidence:
  - reference: PMID:29861105
    reference_title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "βIV spectrin links ankyrinG (AnkG) and clustered ion channels at axon initial segments (AISs) and nodes of Ranvier to the axonal cytoskeleton."
    explanation: >-
      Marked PARTIAL because it states the molecular premise - beta-IV spectrin
      builds the AIS - but says nothing about how an AIS defect produces
      intellectual disability, which is the step this node cannot evidence.
  - reference: PMID:19156852
    reference_title: "Reduced excitability in the dentate gyrus network of betaIV-spectrin mutant mice in vivo."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "Taken together, our findings demonstrate that betaIV-spectrin is required for normal granule cell firing and for physiological levels of network excitability in the mouse dentate gyrus in vivo."
    explanation: >-
      The strongest available support for a primary CNS network mechanism, but
      marked PARTIAL because it is rodent hippocampal physiology standing alone
      for a human cognitive phenotype.
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Such abnormalities included vermian atrophy, diffuse T2-hyperintensity, mildly enlarged CSF spaces, cerebral atrophy, and white matter abnormalities."
    explanation: Documents the non-specific and inconsistent imaging findings, which is why no structural lesion is proposed as the cause of the cognitive phenotype.
- name: Contested Skeletal Muscle Involvement
  biological_scale: TISSUE
  description: >-
    Whether SPTBN4 disease includes a primary myopathy is unresolved, and the
    two positions are held by competent groups using different methods. The
    myogenic case: the founding report described congenital myopathy with
    incomplete congenital fibre-type disproportion, showed beta-IV-spectrin
    immunostaining at the sarcolemma of normal human and mouse muscle and its
    absence in patient and quivering muscle, and found complete absence of type
    1 fibres in quivering mouse muscle; a follow-up cohort again found no
    beta-IV-spectrin staining in patient muscle and type 1 fibre hypotrophy
    without frank fibre-type disproportion, and hypothesised a direct effect on
    sarcolemmal stability and on depolarisation along the myofibre and its
    T-tubular system. The neurogenic case: a muscle-specific conditional
    knockout showed that beta-4 spectrin does not contribute to muscle
    function, and that the protein is not present in muscle at all - which
    would make the sarcolemmal immunostaining a cross-reaction and the muscle
    pathology entirely secondary to denervation. The 2025 natural-history
    review sides with the neurogenic reading.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  - preferred_term: type 1 (slow) skeletal muscle fiber
    term:
      id: CL:0000189
      label: slow muscle cell
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  mechanism_confidence: HYPOTHETICAL
  notes: >-
    Deliberately curated as one node holding a live disagreement rather than as
    two confident nodes, and marked HYPOTHETICAL because the currently best
    controlled experiment - a tissue-specific conditional knockout with
    knockout-validated antibody controls - argues against the myogenic arm. The
    practical consequence is diagnostic: a muscle biopsy showing type 1 fibre
    atrophy in a hypotonic infant should not be read as excluding SPTBN4
    disease, nor as establishing a primary myopathy within it. The 2025
    review's framing is quoted below rather than paraphrased because it is a
    reversal of the disorder's original description. Note that neither
    the founding report nor the follow-up cohort had access to a
    beta-IV-spectrin-null muscle as an antibody control, which is the specific
    methodological gap the conditional-knockout study fills.
  evidence:
  - reference: PMID:28540413
    reference_title: "A recessive mutation in beta-IV-spectrin (SPTBN4) associates with congenital myopathy, neuropathy, and central deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Immunohistology confirmed expression of βIV-spectrin in normal human and mouse muscle at the sarcolemma and its absence in patient and quivering (qv4J) mouse."
    explanation: The primary evidence for the myogenic position - sarcolemmal beta-IV-spectrin present in controls and absent in patient muscle.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We hypothesize that βIV-spectrin deficiency directly impacts the structural stability of the sarcolemma and the initiation or propagation of the depolarization waves along the myofiber and its T-tubular system."
    explanation: States the proposed myogenic mechanism explicitly, and is labelled by its own authors as a hypothesis.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "We derived that the evidence for a myopathy is mostly from the clinical and histopatholocigal findings, but not from functional studies about the role of SPTBN4 in muscle cells."
    explanation: >-
      The same authors' own statement of the limitation of their myogenic
      claim. Marked PARTIAL because it qualifies rather than supports the
      myopathy hypothesis. The misspelling is verbatim from the source.
  - reference: PMID:38441922
    reference_title: "Postsynaptic β1 spectrin maintains Na(+) channels at the neuromuscular junction."
    supports: REFUTE
    evidence_source: MODEL_ORGANISM
    snippet: "In addition, we show β4 spectrin is not present in muscle, indicating the previously reported myopathy associated with pathogenic SPTBN4 variants is neurogenic in origin."
    explanation: >-
      Directly refutes the primary-myopathy interpretation using a
      muscle-specific conditional knockout, which is the best-controlled
      experiment addressing the question.
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "contrary to prior assumptions, β4 spectrin is likely not required for skeletal muscle health or function; myopathy previously associated with SPTBN4 mutations is possibly neurogenic rather than myogenic."
    explanation: The most recent systematic review adopts the neurogenic interpretation, which is why this node is marked HYPOTHETICAL rather than carrying a confident myopathy claim.
- name: Residual-Function Alleles and the Mild End of the Spectrum
  biological_scale: MOLECULAR
  description: >-
    Not every SPTBN4 genotype produces the profound phenotype. Two siblings
    with a homozygous splice-site variant causing in-frame skipping of exon 19
    had muscular hypotonia, myopathic facies with ptosis and axonal neuropathy
    but no seizures, no feeding or respiratory difficulty and, in the index
    case, normal cognition and mainstream schooling. The proposed explanation
    is residual protein activity from an in-frame product rather than complete
    loss of function. A second, independent observation points the same way:
    of the patients carrying missense rather than truncating alleles, several
    had milder symptoms or later onset, and the more severely affected missense
    carriers had their variants in the calponin-homology, variable-region or
    pleckstrin-homology domains rather than in the spectrin-repeat rod.
  genes:
  - preferred_term: SPTBN4
    term:
      id: hgnc:14896
      label: SPTBN4
  mechanism_confidence: PROVISIONAL
  notes: >-
    The residual-activity model is an inference, not a measurement: no assay of
    residual beta-IV-spectrin function has been performed on any of the milder
    genotypes, and the 2021 cohort report explicitly states that the reported
    variants are dispersed across the gene with no clear genotype-phenotype
    correlation. The two published assertions of an allele-severity gradient
    therefore sit against a third assertion that no gradient exists. This entry
    records the gradient as provisional and does not use it for prognostic
    claims. A separate observation from the natural-history review complicates
    it further: two aberrant-splicing variants are known, and the milder of the
    two families had complete skipping of one exon while the more severely
    affected family had a partial 48 bp in-frame deletion within an exon, which
    is the opposite of what a simple "more in-frame product, milder disease"
    model predicts.
  evidence:
  - reference: PMID:31857255
    reference_title: "A novel homozygous splice-site mutation in the SPTBN4 gene causes axonal neuropathy without intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we report on two siblings with a homozygous splice-site mutation in the SPTBN4 gene, lacking previously reported features of the disorder such as seizures, feeding difficulties, respiratory difficulties or profound intellectual disability."
    explanation: Establishes that a genuinely milder end of the phenotypic spectrum exists and defines what it lacks.
  - reference: PMID:31857255
    reference_title: "A novel homozygous splice-site mutation in the SPTBN4 gene causes axonal neuropathy without intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings indicate that muscular hypotonia, myopathic facies with ptosis and axonal neuropathy can be the core clinical features in the SPTBN4 disorder and suggest that SPTBN4 mutation analysis should be considered in infants with marked axonal neuropathy."
    explanation: Defines the minimal core phenotype at the mild end, which is the presentation most likely to be missed diagnostically.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients generally suffer from severe developmental delay and intellectual disability, although two individuals in one family had a milder phenotype, including one individual with normal cognitive development."
    explanation: >-
      Confirms the existence of the mild family but marked PARTIAL because the
      same report states there is no clear genotype-phenotype correlation, so
      it supports the observation without supporting the allele-severity model.
  downstream:
  - target: Distal Motor Axonal Degeneration and Neurogenic Muscle Wasting
    description: >-
      Even at the mild end the axonal neuropathy is present, making it the most
      penetrant consequence of the lesion.
- name: Extraneural beta-IV Spectrin Expression and Reported Cardiac Involvement
  biological_scale: TISSUE
  description: >-
    Beta-IV spectrin is not exclusively neuronal. It is abundantly transcribed
    in pancreatic islets as well as brain, and a substantial separate
    literature places it in cardiomyocytes and cardiac fibroblasts as a
    scaffold for the cardiac sodium channel and as a signalling partner. Two
    individuals with SPTBN4 disease have been reported with cardiac disease:
    one with non-obstructive hypertrophic cardiomyopathy alongside
    mitochondrial dysfunction and optic atrophy, and one with congenital heart
    defects but no available neuromuscular data. This node exists to mark the
    possibility without over-reading it: two cardiac cases out of 38 reported
    individuals is not an established disease feature, and no cardiac
    surveillance recommendation follows from it in the GeneReviews chapter.
  locations:
  - preferred_term: heart
    term:
      id: UBERON:0000948
      label: heart
  mechanism_confidence: HYPOTHETICAL
  notes: >-
    Explicitly marked HYPOTHETICAL and deliberately not connected to the main
    causal chain. The cardiac beta-IV spectrin literature is large and
    mechanistically detailed but is almost entirely about the mouse and rat
    heart and about acquired cardiac disease rather than about SPTBN4 patients;
    importing it here would be exactly the named-entity error this entry's
    preflight was designed to avoid. The mitochondrial dysfunction reported in
    one patient is likewise a single observation with no proposed mechanism
    linking it to beta-IV spectrin, and is not curated as a mechanism node.
  evidence:
  - reference: PMID:33986717
    reference_title: "Severe Form of ßIV-Spectrin Deficiency With Mitochondrial Dysfunction and Cardiomyopathy-A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is the first report of a severe form of ßIV-spectrin deficiency with hypertrophic cardiomyopathy and mitochondrial dysfunction."
    explanation: The single reported case of cardiomyopathy with mitochondrial dysfunction in this disorder, presented by its own authors as a first report.
  - reference: PMID:11086001
    reference_title: "betaIV spectrin, a new spectrin localized at axon initial segments and nodes of ranvier in the central and peripheral nervous system."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Northern blots revealed an abundant expression of betaIV spectrin transcripts in brain and pancreatic islets."
    explanation: Documents that expression is not confined to neurons, which is the premise for asking whether extraneural disease exists - although no islet or endocrine phenotype has been reported in patients.
genetic:
- name: SPTBN4
  association: Bi-allelic loss-of-function variants; predominantly homozygous truncating alleles in consanguineous families
  relationship_type: CAUSATIVE
  gene_term:
    preferred_term: SPTBN4
    term:
      id: hgnc:14896
      label: SPTBN4
  notes: >-
    Nomenclature and identifiers. HGNC:14896 is SPTBN4, spectrin beta,
    non-erythrocytic 4, at 19q13.13. The gene identity and the gene-disease
    edge were both taken from OAK rather than from memory: `runoak -i
    sqlite:obo:mondo relationships -p RO:0004003 MONDO:0060496` returns
    HGNC:14896 SPTBN4, and `runoak -i sqlite:obo:hgnc search "l^SPTBN4"`
    returns hgnc:14896. Note the repo convention that HGNC CURIEs are written
    lowercase in YAML. The mouse orthologue appears in the older literature as
    Spnb4 and the protein as beta-spectrin 4 or beta4-spectrin; the founding
    localisation paper places the human gene at 19q13.13 and the mouse gene on
    chromosome 7.

    Reference transcript. Clinical variants are reported against NM_020971
    (versions .2 and .3 both appear in the literature). Representative alleles,
    each traceable to a cited publication: c.1597C>T p.(Gln533Ter) homozygous,
    the founding Kurdish case; c.3375_3393del p.(Asp1126Thrfs*39),
    c.1247del p.(Leu417Tyrfs*5), c.737G>C p.(Arg246Pro), c.1149dup
    p.(Asn384Glnfs*17) and a maternal deletion of exons 6-11, from the 2021
    cohort; c.1665+2T>C, c.1217T>C p.(Leu406Pro), c.2535_2554del
    p.(Gly846Alafs*13) and the novel c.2265G>A p.(Trp755Ter), from the four
    Saudi families; and c.508A>T p.(Lys170Ter) from the 2026 lethal sibling
    pair. Two aberrant-splicing alleles have been characterised at the RNA
    level, c.1665+2T>C (48 bp skipped within exon 12) and c.3949-1G>A.

    Copy-number matters for diagnosis. At least one reported patient carries a
    multi-exon deletion in trans to a point variant, so a single heterozygous
    SPTBN4 variant in a compatible phenotype should prompt a search for a
    second, structural allele.

    Not asserted, deliberately. No gnomAD constraint metric (pLI, o/e LoF,
    missense Z), no allele frequency, no ClinVar classification counts and no
    ClinGen gene-disease-validity classification are recorded anywhere in this
    entry. None was available from a cached source in this checkout, and
    populating them from memory is exactly the failure mode the repository's
    evidence rules exist to prevent. No founder allele, modifier locus,
    methylation episignature or somatic mechanism has been established.
  evidence:
  - reference: PMID:28540413
    reference_title: "A recessive mutation in beta-IV-spectrin (SPTBN4) associates with congenital myopathy, neuropathy, and central deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found a homozygous nonsense mutation in SPTBN4"
    explanation: >-
      The first human SPTBN4 disease allele. The full sentence in the source
      gives the allele, transcript and protein accessions in square brackets
      (c.1597C>T, NM_020971.2, p.(Q533*), NP_066022.2); the bracketed span is
      omitted from the quoted snippet because the reference validator strips
      bracketed text as a citation marker, and the detail is recorded in this
      section's notes instead.
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thirty-one different SPTBN4 pathological variants have been discovered in 38 patients."
    explanation: Quantifies the allelic heterogeneity of the disorder - close to one distinct variant per reported individual, which is why no founder allele is asserted.
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the variant leads to an aberrant mRNA transcript with a shorter product"
    explanation: RNA-level confirmation that a splice-site allele produces an aberrant transcript, which is the evidence standard this entry treats as sufficient for a splicing claim.
  - reference: PMID:42068471
    reference_title: "Severe SPTBN4-Related Neurodevelopmental Disorder: Case Report of Two Siblings with Lethal Outcomes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "whole genome sequencing (WGS) revealed a novel homozygous nonsense c.508 A > T p. (Lys170*) variant in the SPTBN4 gene in the younger sibling"
    explanation: A recent novel truncating allele, and an illustration that reclassification of a VUS after sibling testing can convert a presumed diagnosis into an actionable one.
phenotypes:
- name: Congenital and generalized hypotonia
  category: Neurologic
  diagnostic: true
  description: >-
    Hypotonia present at birth is the entry point to the diagnosis and the
    first-named feature in the disease label. It is generalized rather than
    axial-predominant, and it does not remit; GeneReviews notes that it may
    transition to hypertonia over time in some individuals, and spasticity was
    recorded in two of the ten Saudi patients.
  phenotype_term:
    preferred_term: Generalized hypotonia
    term:
      id: HP:0001290
      label: Generalized hypotonia
  notes: >-
    HPO annotation for OMIM:617519 records HP:0001290 Generalized hypotonia at
    5/5 and HP:0001319 Neonatal hypotonia at 5/5, both sourced to PMID:33772159
    (retrieved 2026-08-01). No FrequencyEnum band is asserted; see the
    entry-level notes.
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Affected individuals typically have congenital hypotonia that may transition to hypertonia."
    explanation: The GeneReviews characterisation of the tone abnormality, including its evolution, which is not captured by the single HPO term.
  - reference: PMID:29861105
    reference_title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a severe neurological syndrome that includes congenital hypotonia, intellectual disability, and motor axonal and auditory neuropathy"
    explanation: Names congenital hypotonia as one of the three defining components of the syndrome.
- name: Severe to profound intellectual disability
  category: Neurologic
  diagnostic: true
  description: >-
    Intellectual disability is severe to profound in the great majority of
    affected individuals and is, with hypotonia, the feature that separates
    this disorder from an isolated hereditary neuropathy. The important
    exception is the sibling pair with a splice-site allele in whom cognition
    was normal, which is why the disorder must be considered in an infant with
    axonal neuropathy even when development appears cognitively appropriate.
  phenotype_term:
    preferred_term: Severe intellectual disability
    term:
      id: HP:0010864
      label: Severe intellectual disability
  notes: >-
    HPO annotation for OMIM:617519 records HP:0010864 Severe intellectual
    disability at 5/5, sourced to PMID:33772159 (retrieved 2026-08-01). The
    2018 cohort title uses "profound" (HP:0002187) and GeneReviews uses
    "severe-to-profound"; HP:0010864 is bound rather than HP:0002187 because it
    is the term the HPO annotation set actually carries for this OMIM entity,
    and because the two are sibling severity grades rather than
    parent-and-child, so choosing the more severe one on the strength of a
    paper title would overstate the annotation.
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SPTBN4 disorder is typically characterized by severe-to-profound developmental delay and/or intellectual disability, although two individuals in one family had a milder phenotype, including one individual with normal cognitive development."
    explanation: States both the typical severity and the documented exception, which is the whole content of this phenotype's description.
- name: Absent or severely limited speech
  category: Neurologic
  description: >-
    Speech is absent or restricted to single words in nearly every reported
    individual. It is not separable from the global developmental delay, but it
    is recorded separately because it is the feature families notice and
    because it is one of the few domains in which supportive intervention
    (augmentative and alternative communication) has a defined role.
  phenotype_term:
    preferred_term: Absent speech
    term:
      id: HP:0001344
      label: Absent speech
  notes: >-
    HPO annotation for OMIM:617519 records HP:0001344 Absent speech at 5/5,
    sourced to PMID:33772159 (retrieved 2026-08-01).
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients presented with the key features of NEDHND; severe muscular hypotonia, dysphagia, absent speech, gross motor, and mental retardation."
    explanation: Absent speech is listed among the key features present in all patients of this cohort.
- name: Delayed gross motor development
  category: Neurologic
  description: >-
    Gross motor development is severely delayed from the outset. Most affected
    individuals never achieve head control, and most never sit, stand or walk.
    Where motor skills are gained they are not subsequently lost, which
    distinguishes the disorder from a progressive degenerative process.
  phenotype_term:
    preferred_term: Delayed gross motor development
    term:
      id: HP:0002194
      label: Delayed gross motor development
  notes: >-
    HPO annotation for OMIM:617519 records HP:0002194 Delayed gross motor
    development at 5/5 and HP:0002421 Poor head control at 6/6, sourced to
    PMID:33772159 and PMID:28540413 (retrieved 2026-08-01).
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Affected individuals rarely achieve head control. Most are unable to sit, stand, or walk."
    explanation: Quantifies the motor ceiling that defines the disorder's functional impact.
- name: Poor head control
  category: Neurologic
  description: >-
    Failure of antigravity neck control is the single most consistent physical
    sign, present in every individual in whom it has been assessed, and is a
    direct consequence of combined axial hypotonia and neurogenic weakness.
  phenotype_term:
    preferred_term: Poor head control
    term:
      id: HP:0002421
      label: Poor head control
  notes: >-
    HPO annotation for OMIM:617519 records HP:0002421 at 6/6, sourced to
    PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). The cached abstract
    of neither source names head control, so no evidence item is attached
    rather than a snippet that does not support the claim.
- name: Peripheral axonal neuropathy
  category: Neurologic
  diagnostic: true
  description: >-
    A motor-predominant axonal neuropathy with areflexia is the feature that
    points specifically at SPTBN4 rather than at a generic
    hypotonia-plus-delay syndrome. It is axonal, not demyelinating: motor and
    sensory conduction velocities are normal while motor amplitudes are low.
    Crucially, it is not detectable in every patient - neurophysiology was
    entirely normal in some - so a normal study does not exclude the diagnosis.
  phenotype_term:
    preferred_term: Peripheral axonal neuropathy
    term:
      id: HP:0003477
      label: Peripheral axonal neuropathy
  notes: >-
    HPO annotation for OMIM:617519 records HP:0003477 Peripheral axonal
    neuropathy at 2/6 and HP:0007002 Motor axonal neuropathy at 1/1, while
    HP:0007108 Demyelinating peripheral neuropathy is recorded at 0/5, all
    sourced to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). The low
    numerator for the axonal term reflects how few patients had
    electrophysiology, not how many had neuropathy.
  evidence:
  - reference: PMID:29861105
    reference_title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "cause a severe neurological syndrome that includes congenital hypotonia, intellectual disability, and motor axonal and auditory neuropathy"
    explanation: Establishes motor axonal neuropathy as a defining component of the syndrome.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nerve conduction studies showed normal sensory and motor conduction velocities, with low-amplitude motor responses."
    explanation: The electrophysiological pattern that defines the neuropathy as axonal rather than demyelinating.
- name: Areflexia
  category: Neurologic
  description: >-
    Absent deep tendon reflexes accompany the motor axonal neuropathy and are
    the bedside sign most likely to redirect a hypotonic infant's differential
    from central hypotonia towards a neuropathy. Brisk reflexes have
    nonetheless been recorded in individual patients, so areflexia is usual but
    not obligatory.
  phenotype_term:
    preferred_term: Areflexia
    term:
      id: HP:0001284
      label: Areflexia
  notes: >-
    HPO annotation for OMIM:617519 records HP:0001284 Areflexia at 5/6, sourced
    to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). One patient in
    the 2021 cohort had brisk reflexes without clonus, which is the basis for
    the qualification in the description and is full-text rather than abstract
    content.
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Axonal motor neuropathy leads to hyporeflexia/areflexia and weakness"
    explanation: Attributes the reflex loss directly to the axonal neuropathy, which is the causal claim this phenotype makes.
- name: Generalized amyotrophy
  category: Neurologic
  description: >-
    Generalized and distal muscle wasting develops as a consequence of chronic
    denervation, and is the visible counterpart of the EMG denervation
    signature. It is recorded here as a neurogenic rather than a myopathic
    phenotype, consistent with the conditional-knockout evidence that beta-IV
    spectrin is not expressed in skeletal muscle.
  phenotype_term:
    preferred_term: Generalized amyotrophy
    term:
      id: HP:0003700
      label: Generalized amyotrophy
  notes: >-
    HPO annotation for OMIM:617519 records HP:0003700 Generalized amyotrophy at
    5/6 and HP:0003693 Distal amyotrophy at 4/5, sourced to PMID:33772159 and
    PMID:28540413 (retrieved 2026-08-01). Note that the 2021 cohort's own table
    labels HP:0009055 as "Generalized muscle atrophy"; the canonical HPO label
    for HP:0009055 verified with OAK on 2026-08-01 is "Generalized limb muscle
    atrophy", so the broader HP:0003700 used by the HPO annotation set is bound
    here instead.
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "EMG showed signs of acute and chronic denervation such as fibrillation potentials and positive sharp waves"
    explanation: The denervation evidence that makes the wasting neurogenic rather than myopathic.
- name: Sensorineural hearing impairment (auditory neuropathy)
  category: Otologic
  description: >-
    Hearing loss in this disorder is an auditory neuropathy: outer hair cell
    function is preserved (otoacoustic emissions present) while brainstem
    auditory conduction fails. It is a minority feature despite being named in
    the disease label - present in roughly a fifth to two fifths of reported
    individuals depending on the series and on whether it was formally tested.
    Its neuropathic character matters practically, because auditory neuropathy
    responds poorly to conventional amplification.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  notes: >-
    HPO annotation for OMIM:617519 records HP:0000407 Sensorineural hearing
    impairment at 2/5, sourced to PMID:33772159 (retrieved 2026-08-01); the
    2025 natural-history review of 38 patients reports deafness in 21%. Both
    figures are far below what the disease name implies. In the 2021 cohort
    three of five patients were recorded as clinically unaffected without
    formal audiology, so the true figure is likely between the two. HPO has no
    term for auditory neuropathy - searches of `sqlite:obo:hp` for both
    `l~auditory neuropathy` and free-text `auditory neuropathy` returned
    nothing on 2026-08-01 - so the sensorineural term is bound and the
    neuropathic character is carried by the separate absent-brainstem-response
    phenotype below.
  evidence:
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nevertheless, scoliosis, deafness, and seizure are still present in some of the affected individuals (25%, 21%, and 21%, respectively)."
    explanation: The largest available denominator for hearing loss in this disorder, and the source of the statement that deafness is a minority feature.
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Cortical visual impairment and auditory neuropathy have also been reported."
    explanation: GeneReviews classifies the hearing loss specifically as auditory neuropathy rather than as cochlear deafness.
- name: Absent brainstem auditory evoked responses
  category: Otologic
  description: >-
    Absent or grossly abnormal auditory brainstem responses with preserved
    otoacoustic emissions is the electrophysiological signature of auditory
    neuropathy and is the objective test that establishes the site of the
    lesion. It is feasible in infants in whom behavioural audiometry is not.
  phenotype_term:
    preferred_term: Absent brainstem auditory responses
    term:
      id: HP:0004463
      label: Absent brainstem auditory responses
  notes: >-
    HPO annotation for OMIM:617519 records HP:0004463 at 1/2, sourced to
    PMID:33772159 (retrieved 2026-08-01). The denominator of 2 reflects how few
    patients were tested.
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Otoacoustic emissions were present. In brainstem evoked response audiometry (BERA) only wave 1 from the inner ear could be recorded pointing to a defect at the level of cochlear nerve conduction."
    explanation: The paired result - preserved emissions with absent central waves - that defines the deficit as auditory neuropathy rather than cochlear hearing loss.
- name: Feeding difficulties and dysphagia
  category: Gastrointestinal
  description: >-
    Bulbar weakness produces poor suck from the newborn period, then dysphagia,
    gastro-oesophageal reflux and failure to thrive. Most affected individuals
    eventually require gastrostomy feeding. This is the phenotype that drives
    the disorder's dominant complication, aspiration pneumonia, and is
    therefore the single most actionable feature in management.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  notes: >-
    HPO annotation for OMIM:617519 records HP:0011968 Feeding difficulties at
    6/6, HP:0002033 Poor suck at 6/6, HP:0002015 Dysphagia at 5/5,
    HP:0002020 Gastroesophageal reflux at 3/3 and HP:0011471 Gastrostomy tube
    feeding in infancy at 4/5, sourced to PMID:33772159 and PMID:28540413
    (retrieved 2026-08-01). The 2025 review reports gastrointestinal problems
    in 15 patients (54%). The review does not state the denominator for that
    percentage; 15/54% back-calculates to about 28, not the 38 patients
    tabulated overall, so the fraction is a curator inference.
  evidence:
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "dysphagia, and gastrostomy tube feeding during infancy were reported in 15 patients (54%)"
    explanation: Quantifies the gastrointestinal burden across the pooled published cohort.
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Most affected individuals require tube feeding for nutrition."
    explanation: The GeneReviews statement of the usual outcome, which is the basis for anticipatory gastrostomy planning.
- name: Recurrent aspiration and respiratory insufficiency
  category: Respiratory
  description: >-
    Recurrent aspiration pneumonia follows directly from bulbar weakness and a
    weak cough, and progresses in some individuals to restrictive lung disease
    requiring tracheostomy and home ventilation. It is the usual cause of death
    in this disorder.
  phenotype_term:
    preferred_term: Recurrent infections due to aspiration
    term:
      id: HP:0004891
      label: Recurrent infections due to aspiration
  notes: >-
    HPO annotation for OMIM:617519 records HP:0004891 Recurrent infections due
    to aspiration at 5/5, sourced to PMID:33772159 (retrieved 2026-08-01). The
    2025 review reports respiratory difficulties in 17 patients (61%), of whom
    10 had recurrent pneumonia, 2 progressed to restrictive lung disease and 2
    died of respiratory failure.
  evidence:
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Respiratory difficulties were seen in 17 patients (61%)."
    explanation: Quantifies the respiratory burden in the pooled cohort.
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two of the 17 patients died at age of 14 months and 3 years due to respiratory failure."
    explanation: Establishes respiratory failure as the mode of death in this disorder.
- name: Seizures
  category: Neurologic
  description: >-
    Clinical seizures occur in a substantial minority and are refractory to
    medication in some. They coexist with a distinct and probably more common
    finding, an abundantly epileptiform EEG in a child who has never had a
    clinical fit. Reported seizure frequency varies more than fourfold across
    sources and no single figure is asserted here.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  notes: >-
    The four sources disagree. GeneReviews: half of affected individuals
    develop seizures. The 2021 cohort report: more than half develop seizures
    or have a pathological EEG - a compound endpoint, not the same claim. The
    2025 natural-history review of 38 patients: seizures in 21%. The HPO
    annotation set for OMIM:617519 (retrieved 2026-08-01): HP:0001250 with
    frequency modifier "Very rare", sourced to OMIM. No FrequencyEnum band is
    asserted, and the discrepancy is recorded as an explicit knowledge-gap
    discussion rather than averaged away.
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Half of affected individuals develop seizures."
    explanation: The GeneReviews estimate, one of the four mutually inconsistent figures recorded in the notes.
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "The disorder is highlighted with neuropathy, muscle weakness, and infrequent appearance of seizures in the affected individuals."
    explanation: >-
      Marked PARTIAL because it directly contradicts the GeneReviews estimate
      quoted above. Both are retained so the disagreement is visible in the
      data rather than resolved by curator preference.
- name: Epileptiform EEG without clinical seizures
  category: Neurologic
  description: >-
    Abundant to nearly continuous epileptiform discharges recorded on
    prolonged EEG in individuals who have never had an observed clinical
    seizure. In one patient this was documented on 72-hour EEG and in another
    on 24-hour video EEG with explicit parental confirmation that no fits had
    ever occurred. It is modelled as a distinct phenotype from clinical
    seizures because it has different management implications and because it
    is the human observation that most directly reflects the nodal KCNQ2
    clustering failure.
  phenotype_term:
    preferred_term: Interictal epileptiform activity
    term:
      id: HP:0011182
      label: Interictal epileptiform activity
  notes: >-
    HP:0011182 is bound rather than its parent HP:0002353 EEG abnormality
    because its HPO definition ("Interictal epileptiform activity refers to
    such activity that occurs in the absence of a clinical or subclinical
    seizure") names exactly the finding described here; ancestry confirmed with
    `runoak -i sqlite:obo:hp ancestors -p i HP:0011182`, which lists
    HP:0002353. The HPO annotation set for OMIM:617519 records only the parent,
    HP:0002353 EEG abnormality, at 2/2, sourced to PMID:33772159 (retrieved
    2026-08-01); since no FrequencyEnum band is asserted anywhere in this entry
    that parent-level count is recorded here rather than driving the binding.
    Whether such discharges
    warrant antiseizure treatment in a child with no clinical events is not
    addressed anywhere in the literature and is not asserted here.
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Though two of our patients did not exhibit clinically manifest seizures, their EEGs showed highly pathologic epileptiform discharges."
    explanation: States both halves of this phenotype in a single sentence - absence of clinically manifest seizures together with the presence of highly pathologic epileptiform discharges on EEG.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seventy-two-hour EEG showed abundant to nearly continuous centro-parietal sharp/spike/poly-spike wave discharges during sleep without clinical correlation to manifest seizures."
    explanation: The 72-hour recording in Patient 3, which is the source of the "abundant to nearly continuous" characterisation used in the description.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No clinical seizures were observed in a 24-h video EEG recording. The parents had never observed any type of fits or seizures."
    explanation: The second patient, and the source of the explicit parental confirmation that no fits had ever occurred.
- name: Horizontal nystagmus
  category: Ophthalmologic
  description: >-
    Horizontal nystagmus is the commonest eye movement abnormality reported and
    sits within a broader ocular phenotype that ranges from nystagmus and
    cortical visual impairment to blindness from optic atrophy.
  phenotype_term:
    preferred_term: Horizontal nystagmus
    term:
      id: HP:0000666
      label: Horizontal nystagmus
  notes: >-
    HPO annotation for OMIM:617519 records HP:0000666 Horizontal nystagmus at
    2/5, sourced to PMID:33772159 (retrieved 2026-08-01). The 2025 review
    reports ocular abnormalities of any kind in 43% of patients.
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Additional symptoms comprised horizontal nystagmus, epileptiform discharges in EEG without manifest seizures, and choreoathetosis."
    explanation: Names horizontal nystagmus among the features that expanded the recognised phenotype.
- name: Cerebral visual impairment
  category: Ophthalmologic
  description: >-
    Cortical (cerebral) visual impairment is recorded in the OMIM phenotype
    description and in GeneReviews. Optic atrophy has been reported separately
    in at least one severely affected individual, so visual loss in this
    disorder can be pre-geniculate, post-geniculate or both.
  phenotype_term:
    preferred_term: Cerebral visual impairment
    term:
      id: HP:0100704
      label: Cerebral visual impairment
  notes: >-
    HPO annotation for OMIM:617519 records HP:0100704 Cerebral visual
    impairment sourced to OMIM:617519 itself, with no frequency (retrieved
    2026-08-01). GeneReviews recommends ophthalmology review every one to two
    years in those with optic atrophy, which implies optic atrophy is expected
    to occur but does not quantify it.
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Cortical visual impairment and auditory neuropathy have also been reported."
    explanation: The GeneReviews statement recording cortical visual impairment as part of the phenotype.
- name: Myopathic facies
  category: Craniofacial
  description: >-
    A mask-like face with weak facial musculature, tented upper lip and often a
    high arched palate is present in essentially every reported individual and
    is a useful gestalt cue. It reflects facial and bulbar neurogenic weakness
    rather than a dysmorphic syndrome.
  phenotype_term:
    preferred_term: Myopathic facies
    term:
      id: HP:0002058
      label: Myopathic facies
  notes: >-
    HPO annotation for OMIM:617519 records HP:0002058 Myopathic facies at 6/6
    and HP:0000218 High palate at 5/6, sourced to PMID:33772159 and
    PMID:28540413 (retrieved 2026-08-01). The term label says "myopathic" but
    on the current mechanistic reading the weakness is neurogenic; the HPO
    label is retained unchanged because it is the canonical term.
  evidence:
  - reference: PMID:31857255
    reference_title: "A novel homozygous splice-site mutation in the SPTBN4 gene causes axonal neuropathy without intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings indicate that muscular hypotonia, myopathic facies with ptosis and axonal neuropathy can be the core clinical features in the SPTBN4 disorder"
    explanation: Places myopathic facies among the minimal core features, present even at the mild end of the spectrum.
- name: Type 1 muscle fiber atrophy
  category: Musculoskeletal
  description: >-
    Muscle biopsy, where performed, most often shows selective atrophy or
    hypotrophy of type 1 (slow) fibres, sometimes described as incomplete
    congenital fibre-type disproportion. Whether this is a primary myopathic
    change or the consequence of chronic denervation is contested; see the
    "Contested Skeletal Muscle Involvement" pathophysiology node.
  phenotype_term:
    preferred_term: Type 1 muscle fiber atrophy
    term:
      id: HP:0011807
      label: Type 1 muscle fiber atrophy
  notes: >-
    HPO annotation for OMIM:617519 records HP:0011807 Type 1 muscle fiber
    atrophy at 3/3 and HP:0003554 Type 2 muscle fiber atrophy at 1/2, sourced
    to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01). Muscle biopsy
    was performed in only 8 of the 38 patients in the pooled review (21.1%), so
    these denominators describe who was biopsied, not who has the finding.
  evidence:
  - reference: PMID:28540413
    reference_title: "A recessive mutation in beta-IV-spectrin (SPTBN4) associates with congenital myopathy, neuropathy, and central deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the human phenotype of βIV-spectrin deficiency included a myopathy with incomplete congenital fiber-type disproportion"
    explanation: The original description of the muscle finding, which is the claim later disputed on mechanistic grounds.
- name: Scoliosis
  category: Musculoskeletal
  description: >-
    Scoliosis develops secondary to axial hypotonia and immobility rather than
    as a primary skeletal feature, and accumulates with age.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  notes: >-
    HPO annotation for OMIM:617519 records HP:0002650 Scoliosis at 3/6, sourced
    to PMID:33772159 and PMID:28540413 (retrieved 2026-08-01); the 2025 review
    reports 25%.
  evidence:
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nevertheless, scoliosis, deafness, and seizure are still present in some of the affected individuals (25%, 21%, and 21%, respectively)."
    explanation: The pooled-cohort frequency for scoliosis alongside deafness and seizures.
- name: Choreoathetosis
  category: Neurologic
  description: >-
    Choreoathetoid movements of the arms, sometimes with intermittent dystonia,
    were described in one patient and expanded the recognised phenotype to
    include a hyperkinetic movement disorder. It is uncommon and its
    relationship to the nodal mechanism is unexplained.
  phenotype_term:
    preferred_term: Choreoathetosis
    term:
      id: HP:0001266
      label: Choreoathetosis
  notes: >-
    HPO annotation for OMIM:617519 records HP:0001266 Choreoathetosis at 1/5,
    sourced to PMID:33772159 (retrieved 2026-08-01).
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the variably present features of areflexia, axonal motor neuropathy, nystagmus, epileptiform activity in EEG without clinical correlation, and a movement disorders with choreoathetosis."
    explanation: The authors' own statement that choreoathetosis is a variably present addition to the phenotype.
- name: Ataxia
  category: Neurologic
  description: >-
    Ataxia is the most surprising feature in the phenotypic spectrum, because
    it is cardinal in the quivering mouse yet was absent from every human
    report until two siblings in one Saudi family were described. Its rarity in
    humans, set against its prominence in the mouse, is one of the clearest
    human-model mismatches in this disorder.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  notes: >-
    Not present in the HPO annotation set for OMIM:617519 as retrieved on
    2026-08-01. Curated from the 2025 natural-history review, in which ataxia
    was present in 2 of 10 patients, both in family 1, and had never previously
    been reported in the disorder. The same family also had cerebellar vermian
    atrophy on MRI.
  evidence:
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ataxia was never reported in any NEDHND patients; however, two patients in our cohort suffered from ataxia"
    explanation: Documents both the novelty of ataxia in this disorder and its rarity, which is the basis for the human-model mismatch recorded below.
- name: Cerebellar vermis atrophy
  category: Neurologic
  description: >-
    Vermian atrophy is one of the non-specific MRI abnormalities reported, and
    is the imaging correlate of the ataxia described in the one affected
    family. Neuroimaging is normal in a substantial minority of patients
    overall, so a normal MRI does not argue against the diagnosis.
  phenotype_term:
    preferred_term: Cerebellar vermis atrophy
    term:
      id: HP:0006855
      label: Cerebellar vermis atrophy
  notes: >-
    Not present in the HPO annotation set for OMIM:617519 as retrieved on
    2026-08-01. Curated from the 2025 natural-history review, which found
    abnormal MRI in 14 of 22 patients with imaging available and lists vermian
    atrophy first among the abnormalities.
  evidence:
  - reference: PMID:40781329
    reference_title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Such abnormalities included vermian atrophy, diffuse T2-hyperintensity, mildly enlarged CSF spaces, cerebral atrophy, and white matter abnormalities."
    explanation: Names vermian atrophy among the reported structural findings.
histopathology:
- name: Type 1 fiber hypotrophy without frank fiber-type disproportion
  description: >-
    ATPase pH 4.3 staining in patient muscle shows selective reduction of type
    1 fibre diameter relative to type 2, quantified by minimal Feret diameter,
    without the complete fibre-type disproportion classically defined for
    congenital myopathies. The founding case was described as having incomplete
    congenital fibre-type disproportion, and the corresponding quivering mouse
    muscle showed complete absence of type 1 fibres.
  diagnostic: false
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ATPase pH 4.3 staining and IHC with an antibody directed against myosin heavy chain slow (MHC neonatal, NCL-MHCn, Novocastra, 1:20) revealed a reduction of type 1 fiber diameters but no manifest fiber-type disproportion"
    explanation: The precise histological finding, including the explicit negative for frank fibre-type disproportion.
  notes: >-
    Recorded as a finding, not as a mechanism. Whether this appearance is
    primary or denervation-driven is the subject of the "Contested Skeletal
    Muscle Involvement" pathophysiology node. Muscle biopsy was performed in
    only 8 of 38 reported patients.
- name: Neurogenic changes with atrophic fascicles and angulated fibers
  description: >-
    In other patients the biopsy is unambiguously neurogenic: atrophic
    fascicles, small angulated fibres of both types next to fibres of preserved
    diameter, and fibre grouping. The coexistence of this picture with the
    type 1 hypotrophy picture in different patients from the same cohort is the
    empirical basis of the myopathy-versus-neuropathy debate.
  diagnostic: false
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "H&E/Gömöri-trichrome staining of a muscle biopsy sample from Patient 5 showed clear signs of neurogenic changes with atrophic fascicles, dark fibers (type 1) as well as brighter fibers (type 2) small and angulated fibers next to populations of muscle fibers with preserved diameter and groups of small fibers"
    explanation: The neurogenic biopsy pattern, which is what the current mechanistic reading predicts should be the universal finding.
- name: Absent beta-IV-spectrin immunostaining in patient muscle
  description: >-
    Immunohistochemistry with an anti-beta-IV-spectrin antibody shows no signal
    in patient muscle where age-matched control muscle stains, while a
    pan-beta-spectrin antibody stains the sarcolemma normally in both. This was
    the original evidence that beta-IV spectrin is a sarcolemmal protein whose
    loss could cause myopathy directly.
  diagnostic: false
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "IHC with an antibody directed against the non-erythrocytic βIV-spectrin subtype 4 (sc-368195, H-85, Santa-Cruz, 1:100) showed no staining in Patient 3, while staining was preserved in age-matched control muscle."
    explanation: >-
      Marked PARTIAL rather than SUPPORT. The observation is real, but a
      subsequent muscle-specific conditional knockout reported that beta-4
      spectrin is not present in muscle at all (PMID:38441922), which implies
      the control-muscle signal these antibodies detect may not be beta-IV
      spectrin. Neither study included a knockout-muscle antibody control at
      the time the human staining was performed.
diagnosis:
- name: Exome or genome sequencing with bi-allelic SPTBN4 variant interpretation
  description: >-
    Diagnosis is molecular. In a hypotonic infant with global developmental
    delay, exome or genome sequencing identifying bi-allelic SPTBN4 variants
    against transcript NM_020971 establishes the diagnosis. Three
    interpretation points follow from the published series. First, parental
    testing is required to confirm the variants are in trans, since
    heterozygotes are unaffected. Second, if only one variant is found, look
    for a structural second allele: a multi-exon deletion has been reported in
    trans to a point variant. Third, splice-site variants of uncertain effect
    should be resolved at RNA level where patient material allows, as has been
    done for two SPTBN4 alleles.
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The diagnosis of SPTBN4 disorder is established in a proband with congenital hypotonia and biallelic pathogenic (or likely pathogenic) variants in SPTBN4 identified by molecular genetic testing."
    explanation: The formal diagnostic criterion from GeneReviews.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Screening for large genomic SPTBN4 rearrangements should improve molecular diagnostic rates for this population, in particular for patients where only a single variant that affects function has been identified."
    explanation: Supports the specific recommendation to pursue copy-number analysis when only one sequence variant is found.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "it seems rational that SPTBN4 genetic testing should also be considered in patients with early-onset hypotonia, motor developmental delay, and intellectual disability, especially in the presence of axonal neuropathy, deafness, or pathological discharge patterns on the EEG"
    explanation: Defines the clinical trigger for testing, including the three features that raise the pre-test probability.
- name: Neurophysiology (nerve conduction studies and EMG)
  description: >-
    Nerve conduction studies and EMG establish the axonal, motor-predominant
    character of the neuropathy: low-amplitude motor responses with preserved
    conduction velocities, plus fibrillation potentials, positive sharp waves
    and enlarged motor unit potentials. The important caveat is that
    neurophysiology can be entirely normal in affected individuals, so it
    supports but does not gate the diagnosis.
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nerve conduction studies showed normal sensory and motor conduction velocities, with low-amplitude motor responses."
    explanation: The characteristic axonal pattern that neurophysiology is performed to detect.
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Electrophysiology revealed signs of obvious neuropathy only in Patient 5."
    explanation: >-
      Marked PARTIAL because it qualifies the test's sensitivity: only one of
      five patients in this cohort had an unambiguously neuropathic study, so a
      normal result does not exclude the diagnosis.
- name: Auditory brainstem response with otoacoustic emissions
  description: >-
    Because the hearing loss is an auditory neuropathy, the pairing of tests
    matters more than either alone: otoacoustic emissions test the cochlea and
    auditory brainstem responses test the nerve and brainstem pathway.
    Preserved emissions with absent or wave-I-only brainstem responses
    localises the lesion and predicts poor benefit from simple amplification.
    This is feasible in infants who cannot cooperate with behavioural
    audiometry.
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Otoacoustic emissions were present. In brainstem evoked response audiometry (BERA) only wave 1 from the inner ear could be recorded pointing to a defect at the level of cochlear nerve conduction."
    explanation: The worked example of the paired testing strategy and its interpretation in this disorder.
- name: Prolonged EEG
  description: >-
    Prolonged or overnight EEG is worth performing even without a history of
    clinical seizures, because abundant epileptiform discharge has been
    documented in patients whose parents had never observed a fit. Its
    therapeutic implications are undefined, but it changes the interpretation
    of paroxysmal events and of developmental plateauing.
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seventy-two-hour EEG showed abundant to nearly continuous centro-parietal sharp/spike/poly-spike wave discharges during sleep without clinical correlation to manifest seizures."
    explanation: Demonstrates that the epileptiform abnormality is only detectable on prolonged recording and is sleep-activated.
  notes: >-
    The 2025 natural-history review found EEG data available for only 12 of 38
    patients, of whom 5 were abnormal. That denominator is small and
    ascertainment-biased towards patients with clinical events, which is one
    reason the reported seizure frequency varies so widely across sources.
differential_diagnoses:
- name: Spinal muscular atrophy type 1
  disease_term:
    preferred_term: spinal muscular atrophy, type 1
    term:
      id: MONDO:0009669
      label: spinal muscular atrophy, type 1
  description: >-
    The dominant clinical mimic and the diagnosis SPTBN4 patients are actually
    tested for first. A floppy infant with profound weakness, areflexia, poor
    suck, tongue involvement, respiratory compromise and denervation on EMG is
    SMA type 1 until proven otherwise, and both the 2021 cohort and the 2026
    sibling report describe SMA testing being sent and returning negative
    before SPTBN4 was found. The distinction is now urgent rather than
    academic: approved disease-modifying therapy exists for SMA and none
    exists for SPTBN4 disease, so misdiagnosis in either direction has direct
    consequences. (No reference cached for this entry states the SMA treatment
    landscape; the claim is general clinical background, not a sourced
    assertion.)
  distinguishing_features:
  - SMN1 testing (deletion/dosage) resolves the question directly and should precede or accompany exome sequencing in any floppy infant.
  - Cognition is typically normal in SMA type 1 but severely impaired in most SPTBN4 disease, so intellectual disability argues for SPTBN4.
  - Auditory neuropathy and an epileptiform EEG are not features of SMA and, when present, point strongly to SPTBN4.
  - Nystagmus, choreoathetosis and cerebral visual impairment occur in SPTBN4 disease and not in SMA.
  - Muscle biopsy in SMA shows large-group fascicular atrophy with hypertrophic type 1 fibres; SPTBN4 biopsies more often show type 1 hypotrophy or patchy neurogenic change.
  notes: >-
    MONDO:0009669 was verified with OAK (`runoak -i sqlite:obo:mondo
    relationships --direction down HGNC:11117` returns it as an SMN1 disease
    with the label "spinal muscular atrophy, type 1"); SMN1 is hgnc:11117, also
    verified. The existing dismech entry `kb/disorders/Spinal_Muscular_Atrophy.yaml`
    is bound to the broader MONDO:0001516, not to this type-specific term, so
    the two are not the same entity and no content was copied.
  evidence:
  - reference: PMID:42068471
    reference_title: "Severe SPTBN4-Related Neurodevelopmental Disorder: Case Report of Two Siblings with Lethal Outcomes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both patients exhibited severe failure to thrive, hypotonia, dysphagia, and global developmental delay, initially suggesting spinal muscular atrophy (SMA)."
    explanation: Documents that SMA was the working diagnosis in a real SPTBN4 family, which is why this differential is listed first.
- name: KCNQ2 developmental and epileptic encephalopathy
  disease_term:
    preferred_term: developmental and epileptic encephalopathy, 7
    term:
      id: MONDO:0013387
      label: developmental and epileptic encephalopathy, 7
  description: >-
    A mechanistic rather than a clinical differential, and the closest thing
    this disorder has to a pathway relative. KCNQ2 encodes the channel subunit
    that beta-IV spectrin positions at the node; SPTBN4 disease produces nodes
    with no detectable KCNQ2. The 2021 cohort report proposed exactly this
    overlap when explaining the epileptiform EEGs. The two disorders converge
    on absent nodal M-current from opposite directions - one by losing the
    channel, the other by losing the scaffold that places it.
  distinguishing_features:
  - KCNQ2-DEE is a de novo dominant channelopathy; SPTBN4 disease is autosomal recessive, so unaffected consanguineous parents favour SPTBN4.
  - Seizures dominate the KCNQ2-DEE presentation from the neonatal period, whereas in SPTBN4 disease hypotonia and weakness dominate and the epileptiform activity is frequently subclinical.
  - Peripheral axonal neuropathy, areflexia and auditory neuropathy are features of SPTBN4 disease and not of KCNQ2-DEE.
  - Sodium-channel blockers are a rational therapy in KCNQ2 gain-of-function disease; no analogous targeted option exists for SPTBN4 disease.
  notes: >-
    MONDO:0013387 was verified with OAK (`runoak -i sqlite:obo:mondo
    relationships --direction down HGNC:6296` returns MONDO:0013387
    "developmental and epileptic encephalopathy, 7" and MONDO:0007365
    "seizures, benign familial neonatal, 1"); KCNQ2 is hgnc:6296, also
    verified. MONDO:0013387 matches the disease_term already bound in
    `kb/disorders/KCNQ2_Developmental_and_Epileptic_Encephalopathy.yaml`, and
    MONDO:0007365 appears in `kb/disorders/Benign_Neonatal_Seizures.yaml` only
    as a `has_subtypes` subtype_term - that file's own disease_term is
    MONDO:0016027 `benign neonatal seizures`. No content was copied from
    either.
  evidence:
  - reference: PMID:33772159
    reference_title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "As βIV-spectrin plays a role in the clustering of KCNQ2 subunit-containing potassium channels, there could be some degree of overlap of clinical symptoms with early-infantile epileptic encephalopathy type 7 and with benign familial neonatal seizures type 1."
    explanation: The authors' own proposal of this mechanistic overlap, which is the reason the differential is curated.
- name: ANK3-related intellectual disability-hypotonia-spasticity-sleep disorder syndrome
  disease_term:
    preferred_term: intellectual disability-hypotonia-spasticity-sleep disorder syndrome
    term:
      id: MONDO:0014210
      label: intellectual disability-hypotonia-spasticity-sleep disorder syndrome
  description: >-
    The other half of the scaffold. AnkyrinG and beta-IV spectrin stabilise
    each other reciprocally at the axon initial segment and node, so losing
    either delocalises the other, and the recessive ANK3 syndrome accordingly
    pairs intellectual disability with hypotonia. Curating the pair makes the
    point that the AIS/nodal scaffold is a disease module rather than a set of
    unrelated genes.
  distinguishing_features:
  - Spasticity and a prominent sleep disorder characterise the ANK3 syndrome and are not core features of SPTBN4 disease.
  - Motor axonal neuropathy with areflexia and auditory neuropathy are characteristic of SPTBN4 disease and are not the ANK3 phenotype.
  - ANK3 also has a separate dominant neurodevelopmental/psychiatric association, so the inheritance pattern must be established before the phenotype is interpreted.
  - The two are distinguished definitively by the causal gene, not clinically.
  notes: >-
    MONDO:0014210 was verified with OAK (`runoak -i sqlite:obo:mondo
    relationships --direction down HGNC:494` returns it as the only ANK3
    disease term); ANK3 is hgnc:494, also verified. There is no ANK3 entry in
    kb/disorders/ at the time of curation, so no cross-entry consistency check
    was possible. No evidence item is attached: the contrast is a reasoned
    mechanistic cross-reference rather than a quotable finding.
- name: SPTAN1-related developmental and epileptic encephalopathy 5
  disease_term:
    preferred_term: developmental and epileptic encephalopathy, 5
    term:
      id: MONDO:0013277
      label: developmental and epileptic encephalopathy, 5
  description: >-
    The alpha-spectrin partner. Alpha-II spectrin, encoded by SPTAN1, is the
    obligate alpha-subunit that pairs with beta-spectrins to form the axonal
    tetramer, and it forms the periodic AIS cytoskeleton alongside beta-IV
    spectrin. Its dominant variants cause a severe epileptic encephalopathy
    with hypomyelination, and heterozygous loss of function has more recently
    been linked to a distal myopathy with neurogenic features - a phenotypic
    convergence with SPTBN4 that is not coincidental.
  distinguishing_features:
  - SPTAN1-DEE is autosomal dominant, usually de novo, with in-frame dominant-negative variants; SPTBN4 disease is recessive loss of function.
  - Infantile spasms with hypsarrhythmia and progressive brain atrophy with hypomyelination characterise SPTAN1-DEE; SPTBN4 imaging is normal in a substantial minority and shows only non-specific change when abnormal.
  - Auditory neuropathy and areflexic motor axonal neuropathy point to SPTBN4 rather than SPTAN1.
  notes: >-
    MONDO:0013277 was verified with OAK (`runoak -i sqlite:obo:mondo
    relationships --direction down HGNC:11273` returns four SPTAN1 disease
    terms, of which MONDO:0013277 "developmental and epileptic encephalopathy,
    5" is the classic one; the others are MONDO:0957813, MONDO:0957815 and
    MONDO:0957875); SPTAN1 is hgnc:11273, also verified. Note that the
    SPTAN1/SPTBN4 myopathy paper found in the literature search
    (PMID:40842327) returned no abstract text when fetched, so the myopathy
    convergence mentioned in this description is stated in the description only
    and is not supported by a snippet.
  evidence:
  - reference: PMID:36697767
    reference_title: "Spectrins: molecular organizers and targets of neurological disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Pathogenic variants in SPTAN1, SPTBN1, SPTBN2 and SPTBN4, four of the six genes encoding neuronal spectrins, cause neurological disorders."
    explanation: Establishes the neuronal spectrinopathies as a coherent gene family whose members must be distinguished from one another.
- name: SPTBN1-related developmental delay, impaired speech, and behavioral abnormalities
  disease_term:
    preferred_term: developmental delay, impaired speech, and behavioral abnormalities
    term:
      id: MONDO:0859178
      label: developmental delay, impaired speech, and behavioral abnormalities
  description: >-
    The beta-II spectrin sibling disorder. Beta-II spectrin is the general
    axonal beta-subunit, present along the axon shaft rather than concentrated
    at excitable domains, and its dominant variants cause developmental delay
    with impaired speech and behavioural abnormalities. Together with SPTBN2
    ataxia and SPTBN5 disease it illustrates why beta-spectrin paralogues, all
    building the same lattice, produce non-overlapping diseases: they differ in
    where in the neuron they are deployed.
  distinguishing_features:
  - SPTBN1 disease is autosomal dominant; SPTBN4 disease is recessive.
  - Autism and behavioural abnormality dominate the SPTBN1 phenotype; profound motor disability, areflexia and neuropathy dominate SPTBN4.
  - Congenital hypotonia with feeding and respiratory failure is not the SPTBN1 presentation.
  notes: >-
    MONDO:0859178 was verified with OAK (`runoak -i sqlite:obo:mondo
    relationships --direction down HGNC:11275` returns it as the only SPTBN1
    disease term); SPTBN1 is hgnc:11275, also verified. Sibling
    beta-spectrin disorders that were looked up but NOT curated as separate
    differentials, to avoid padding: SPTBN2 spinocerebellar ataxia type 5
    (MONDO:0010848) and autosomal recessive spinocerebellar ataxia 14
    (MONDO:0014159), both verified against hgnc:11276. They are cerebellar
    ataxias with no hypotonia-neuropathy-deafness overlap.
  evidence:
  - reference: PMID:36697767
    reference_title: "Spectrins: molecular organizers and targets of neurological disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Despite their structural similarity and shared role as molecular organizers at the cell membrane, spectrins vary in expression, subcellular localization and specialization in neurons, and this variation partly underlies non-overlapping disease presentations across spectrinopathies."
    explanation: States the principle that separates the spectrinopathies from one another, which is the substance of this differential.
- name: Congenital fiber-type disproportion myopathy
  disease_term:
    preferred_term: congenital fiber-type disproportion myopathy
    term:
      id: MONDO:0009711
      label: congenital fiber-type disproportion myopathy
  description: >-
    The differential that the muscle biopsy creates. A hypotonic infant whose
    biopsy shows small type 1 fibres will be labelled congenital fibre-type
    disproportion, and the first SPTBN4 patient was described in exactly those
    terms. Because the current mechanistic reading holds that the muscle
    pathology in SPTBN4 disease is neurogenic, this is a differential that
    exists because of a shared histological appearance rather than a shared
    mechanism.
  distinguishing_features:
  - Congenital fibre-type disproportion is genetically heterogeneous (ACTA1, TPM3, RYR1, SELENON and others) and is a histological label, not a single disease.
  - Areflexia, denervation on EMG and auditory neuropathy point away from a primary congenital myopathy and towards SPTBN4.
  - Severe intellectual disability is not a feature of the classical congenital myopathies and is present in most SPTBN4 patients.
  - In SPTBN4 disease the fibre-type disproportion is characteristically incomplete or absent, with type 1 hypotrophy only.
  notes: >-
    MONDO:0009711 was verified with OAK; note that a second, obsolete term
    (MONDO:0000865 "obsolete congenital fiber-type disproportion") also matches
    the search string and was deliberately not used. No evidence item is
    attached; the contrast is a reasoned histological comparison rather than a
    quoted finding.
treatments:
- name: Multidisciplinary supportive care
  description: >-
    No disease-modifying therapy exists. Management follows the components of
    the phenotype: developmental, educational and communication support;
    physiotherapy and orthotics for weakness, contractures and scoliosis; and
    surveillance for the complications that determine survival.
  action_category: THERAPEUTIC
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: BEHAVIORAL
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "standard treatment for developmental delay / intellectual disability, epilepsy, cortical vision impairment, constipation, and spasticity / joint contractures"
    explanation: The GeneReviews management recommendation, which is explicitly standard supportive care rather than anything disorder-specific.
- name: Nutritional management (feeding therapy and gastrostomy)
  description: >-
    Feeding therapy and, when aspiration risk or growth failure persists,
    gastrostomy placement. Anticipating this rather than reacting to a
    pneumonia is part of the practical core of care in this disorder, because
    dysphagia and recurrent aspiration are what precipitate the respiratory
    failure that is the usual cause of death.
  action_category: THERAPEUTIC
  treatment_term:
    preferred_term: enteral nutritional support
    term:
      id: NCIT:C15433
      label: Nutritional Support
  therapeutic_modality: DEVICE
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "feeding therapy and consideration of gastrostomy tube placement for persistent feeding difficulties and/or concern about aspiration"
    explanation: The GeneReviews recommendation for the feeding and aspiration problem.
- name: Ventilatory support
  description: >-
    Non-invasive or invasive ventilatory support for respiratory distress, with
    tracheostomy in the most affected. This is the intervention that most
    directly changes survival, since neuromuscular respiratory failure is the
    usual cause of death.
  action_category: THERAPEUTIC
  treatment_term:
    preferred_term: ventilatory support
    term:
      id: NCIT:C15322
      label: Respiratory Therapy
  therapeutic_modality: DEVICE
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ventilator support (e.g., BiPAP) for respiratory distress"
    explanation: The GeneReviews recommendation for the complication that drives mortality.
- name: Hearing support with amplification
  description: >-
    Hearing aids are recommended for those with hearing loss, but the
    neuropathic character of the deficit tempers the expectation: in auditory
    neuropathy the cochlea works and the nerve does not, so amplification
    addresses the wrong part of the pathway. The paired otoacoustic-emission
    and brainstem-response testing that should precede a decision about
    amplification is a diagnostic action and is curated separately under
    diagnosis ("Auditory brainstem response with otoacoustic emissions");
    this entry covers only the amplification/hearing-support intervention.
  action_category: THERAPEUTIC
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: DEVICE
  notes: >-
    The caveat about amplification in auditory neuropathy is a mechanistic
    inference from this entry's own "Central Auditory Conduction Failure" node,
    not a recommendation found in any SPTBN4 source, and is deliberately
    written into the description rather than attached to a snippet.
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Hearing aids may be helpful for those with hearing loss"
    explanation: The only published management statement about hearing in this disorder.
- name: Surveillance
  description: >-
    Structured surveillance is the one place where GeneReviews gives
    disorder-specific guidance: neurological and developmental review, growth
    and nutrition, constipation and joint mobility at each visit; ophthalmology
    every one to two years in those with optic atrophy; audiology as
    clinically indicated; and a sleep study every one to two years, which is
    the item most easily overlooked and most directly relevant to
    neuromuscular respiratory failure.
  action_category: SCREENING
  treatment_term:
    preferred_term: structured surveillance schedule
    term:
      id: NCIT:C15419
      label: Disease Screening
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ophthalmology evaluation every one to two years in those with optic atrophy; audiology evaluation as clinically indicated; sleep study every one to two years"
    explanation: The published surveillance schedule for this disorder.
- name: Genetic counselling and reproductive options
  description: >-
    Autosomal recessive recurrence-risk counselling with a 25% risk to each
    subsequent pregnancy, carrier testing for the specific familial alleles
    once identified, and prenatal or preimplantation testing. This carries
    unusual weight in this disorder because the reported population is heavily
    consanguineous and because the disorder is severe, untreatable and often
    lethal in early childhood; the 2025 Saudi natural-history study frames its
    entire rationale around enabling preimplantation and carrier-screening
    programmes.
  action_category: COUNSELING_INFORMATIONAL
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier."
    explanation: The quantitative recurrence risk that the counselling recommendation rests on.
  - reference: PMID:32672909
    reference_title: "SPTBN4 Disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Once the SPTBN4 pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives, prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing are possible."
    explanation: States the reproductive options available once the familial alleles are known.
animal_models:
- species: Mus musculus
  genotype: quivering (qv) allelic series - spontaneous Sptbn4 (Spnb4) loss-of-function alleles including qv3J and qv4J
  category: Spontaneous loss-of-function allelic series
  description: >-
    The quivering mouse is the reason this gene was ever connected to human
    disease. It arose spontaneously in 1953 and produces progressive ataxia
    with hindlimb paralysis, deafness and tremor; when the founding human case
    was described, the resemblance to quivering is what prompted the authors to
    examine muscle in both. The allelic series is unusually informative because
    the alleles truncate the protein at different points: qv3J removes the
    C-terminal specific and pleckstrin homology domains, qv4J additionally
    removes the ankyrinG-binding domain and abolishes detectable protein, and
    the two produce graded severity with central nodes affected before
    peripheral ones. The series is what established the separability of the
    mechanical (nodal undercoat) and electrical (channel clustering) arms of
    beta-IV spectrin function.

    Fidelity is good but not complete, and the mismatches run in both
    directions. Ataxia and tremor are cardinal in the mouse and were absent
    from every human report until 2025, when two siblings in one Saudi family
    were found to have ataxia. Conversely, intellectual disability - the most
    severe feature in humans - has no straightforward murine readout and the
    mouse cognitive phenotype has not been characterised. Muscle fibre-type
    findings differ too - the quivering mouse showed complete type 2 fibre
    uniformity, whereas human biopsies show only incomplete type 1 hypotrophy.
  genes:
  - preferred_term: SPTBN4
    term:
      id: hgnc:14896
      label: SPTBN4
  associated_phenotypes:
  - Progressive ataxia with hindlimb paralysis
  - Tremor
  - Central (non-cochlear) deafness with abnormal brainstem auditory transmission
  - Broadened nodes of Ranvier with vesicle-filled membrane protrusions
  - Reduced nodal and AIS sodium channel immunoreactivity
  - Absent nodal KCNQ2 aggregates with neuromyotonic and myokymic discharge
  evidence:
  - reference: PMID:11528393
    reference_title: "Mutant beta-spectrin 4 causes auditory and motor neuropathies in quivering mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The autosomal recessive mouse mutation quivering (qv), which arose spontaneously in 1953, produces progressive ataxia with hind limb paralysis, deafness and tremor."
    explanation: Defines the quivering phenotype, three of whose four components map onto the human disorder.
  - reference: PMID:11528393
    reference_title: "Mutant beta-spectrin 4 causes auditory and motor neuropathies in quivering mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Here we report that quivering mice carry loss-of-function mutations in the mouse beta-spectrin 4 gene (Spnb4) that cause alterations in ion channel localization in myelinated nerves; this provides a rationale for the auditory and motor neuropathies of these mice."
    explanation: Establishes the gene identity of the quivering locus and the ion-channel-localisation mechanism, seventeen years before the human disorder was described.
  - reference: PMID:15317849
    reference_title: "BetaIV spectrins are essential for membrane stability and the molecular organization of nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These results show that quivering mutations disrupt betaIV spectrin retention and stability at nodes and that distinct protein domains regulate nodal structural integrity and molecular organization."
    explanation: Establishes the domain-resolved, allele-graded structure of the model that makes the series informative about human truncating variants.
  - reference: PMID:28540413
    reference_title: "A recessive mutation in beta-IV-spectrin (SPTBN4) associates with congenital myopathy, neuropathy, and central deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical symptoms of the patient largely corresponded to those described for the quivering mouse, a loss-of-function animal model."
    explanation: The explicit human-to-mouse phenotype correspondence that drove the original gene discovery.
- species: Mus musculus
  genotype: Sptbn4 gene-trap null (Sptbn4geo) and betaIVSigma1-specific knockout
  category: Targeted knockout
  description: >-
    Engineered nulls complement the spontaneous series. A gene-trap null was
    the basis for the demonstration that beta-IV spectrin and ankyrin-G stabilise
    each other reciprocally and that both are required for nodal sodium-channel
    clustering; the same line was later used to show the auditory heminode
    defect and the loss of presynaptic spike fidelity. A separate,
    isoform-specific knockout removing only betaIVSigma1 showed that the
    actin-binding isoform is the one that builds the nodal undercoat. A third
    strand of work used timed re-expression of beta-IV spectrin in vivo to show
    that nodal reorganisation and functional recovery in the CNS are possible
    only within a critical developmental window - the closest thing to a
    therapeutic proof of concept that exists for this disorder.

    The re-expression experiment is the reason this entry treats the disorder
    as potentially tractable rather than as fixed at birth. Two caveats
    prevent that being read as a therapeutic claim. First, re-expression in the
    mouse was achieved genetically at chosen developmental time points, not by
    any deliverable agent, and no gene-therapy or ASO approach to SPTBN4 has
    been reported. Second, the critical window closed in the CNS, which is
    where the most disabling component of the human phenotype - intellectual
    disability - resides, so the arm of the disease most in need of treatment
    is the arm the mouse says is hardest to rescue.
  genes:
  - preferred_term: SPTBN4
    term:
      id: hgnc:14896
      label: SPTBN4
  associated_phenotypes:
  - Tremor and hindlimb contraction
  - Loss of ankyrinG and sodium channel clustering at AIS and nodes
  - Disappearance of the nodal membrane undercoat with widened nodes
  - Elevated action potential threshold and high-frequency transmission failure in auditory brainstem
  - Absent startle response with normal cochlear function
  evidence:
  - reference: PMID:11807096
    reference_title: "[Beta]IV-spectrin regulates sodium channel clustering through ankyrin-G at axon initial segments and nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We have generated mice carrying a null mutation in the betaIV-spectrin gene using gene trapping in embryonic stem cells."
    explanation: Identifies the gene-trap null line that underpins most of the mechanistic work cited in this entry.
  - reference: PMID:11807096
    reference_title: "[Beta]IV-spectrin regulates sodium channel clustering through ankyrin-G at axon initial segments and nodes of Ranvier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mice homozygous for the mutation exhibit tremors and contraction of hindlimbs."
    explanation: The organismal phenotype of the engineered null, matching the spontaneous quivering alleles.
  - reference: PMID:29907663
    reference_title: "Reorganization of Destabilized Nodes of Ranvier in βIV Spectrin Mutants Uncovers Critical Timelines for Nodal Restoration and Prevention of Motor Paresis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In the PNS, restoration of nodes occurs within 1 month regardless of the time of βIV spectrin re-expression. In contrast, the CNS nodal reorganization and functional restoration occurs within a critical time window; after that, nodal reorganization diminishes, leading to less efficient motor recovery."
    explanation: >-
      The single most therapeutically relevant animal result in this
      literature: the lesion is reversible by restoring the protein, but only
      inside a developmental window in the CNS.
  - reference: PMID:29907663
    reference_title: "Reorganization of Destabilized Nodes of Ranvier in βIV Spectrin Mutants Uncovers Critical Timelines for Nodal Restoration and Prevention of Motor Paresis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Loss of murine βIV spectrin allows the initial nodal organization, but causes gradual nodal destabilization."
    explanation: Establishes that the defect is one of maintenance rather than of initial assembly, which is what makes post-natal restoration conceivable at all.
discussions:
- discussion_id: sptbn4-seizure-frequency-conflict
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    What fraction of individuals with SPTBN4 disease actually have clinical
    seizures, given that the four available sources give figures spanning
    "very rare" to "more than half"?
  rationale: >-
    This is not a rounding disagreement. GeneReviews states that half of
    affected individuals develop seizures. The 2021 cohort report says more
    than half develop seizures or have a pathological EEG, which is a different
    and broader endpoint. The 2025 systematic review of 38 patients puts
    seizures at 21%. The HPO annotation set for OMIM:617519 carries HP:0001250
    with the frequency modifier "Very rare", sourced to OMIM. The likely
    explanation is that the compound endpoint (seizures OR epileptiform EEG)
    has been propagated as if it were the seizure rate, compounded by
    ascertainment - EEG was performed in only 12 of 38 patients, and prolonged
    recording in fewer still, so the epileptiform abnormality is
    systematically under-detected while clinical seizures are not. Until this
    is resolved, a clinician cannot give a family a defensible seizure risk,
    and the entry deliberately asserts no FrequencyEnum band for either the
    seizure or the EEG phenotype.
  attaches_to:
  - "pathophysiology#Axonal Hyperexcitability and Epileptiform Discharge"
  proposed_experiments:
  - experiment_id: sptbn4-prospective-eeg-cohort
    name: Prospective prolonged-EEG phenotyping of a molecularly defined cohort
    description: >-
      Perform 24- to 72-hour EEG including sleep in every molecularly confirmed
      SPTBN4 patient in a multicentre registry, irrespective of seizure
      history, and report clinical seizures and epileptiform abnormality as two
      separate denominators rather than a compound endpoint.
- discussion_id: sptbn4-myopathy-neurogenic-or-myogenic
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Is the muscle pathology in SPTBN4 disease a primary myopathy, or is it
    entirely secondary to denervation?
  rationale: >-
    The disorder was first described as a congenital myopathy on the strength
    of fibre-type disproportion plus sarcolemmal beta-IV-spectrin
    immunostaining that was present in controls and absent in patient muscle,
    and a second cohort replicated the immunostaining result and proposed a
    direct effect on sarcolemmal stability and myofibre depolarisation. A
    muscle-specific conditional knockout then reported that beta-4 spectrin is
    not present in muscle at all and that the myopathy must be neurogenic. The
    disagreement is methodologically tractable rather than philosophical: the
    human immunohistochemistry was performed without a beta-IV-spectrin-null
    muscle as an antibody specificity control, and the conditional knockout
    was performed in mouse rather than human muscle. It matters because it
    determines whether a normal or myopathic muscle biopsy carries any
    diagnostic weight, and whether muscle is a legitimate therapeutic target.
  attaches_to:
  - "pathophysiology#Contested Skeletal Muscle Involvement"
  - "histopathology#Absent beta-IV-spectrin immunostaining in patient muscle"
  proposed_experiments:
  - experiment_id: sptbn4-muscle-antibody-specificity
    name: Antibody specificity control on beta-IV-spectrin-null muscle
    description: >-
      Re-run the sarcolemmal immunohistochemistry using the same antibodies on
      muscle from a beta-IV-spectrin-null mouse alongside human control and
      patient muscle, to establish whether the sarcolemmal signal reported in
      controls is beta-IV spectrin or a cross-reacting epitope.
  - experiment_id: sptbn4-human-muscle-transcriptomics
    name: SPTBN4 expression in human skeletal muscle by RNA-seq and proteomics
    description: >-
      Quantify SPTBN4 transcript and beta-IV spectrin peptide abundance in
      human skeletal muscle and at the human neuromuscular junction, since the
      conditional-knockout evidence is murine and human expression has been
      asserted on both sides of the argument.
- discussion_id: sptbn4-excitability-direction
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Does loss of beta-IV spectrin raise or lower neuronal excitability, given
    that its two clustered channel clients push in opposite directions?
  rationale: >-
    Losing nodal and AIS sodium channels should make neurons harder to fire,
    and that is what was measured in the dentate gyrus in vivo and at the
    auditory presynaptic terminal, where action-potential threshold rose.
    Losing nodal KCNQ2/KCNQ3 should make axons fire spontaneously, and that is
    what was measured at the diaphragm neuromuscular junction and what the
    patients' near-continuous epileptiform discharges suggest. Both effects
    occur in the same mutant animals. The unresolved question is what
    determines which dominates - axonal compartment, fibre type, developmental
    stage, or the specific truncation - and the answer would have direct
    therapeutic implications, since a KCNQ opener and a sodium-channel enhancer
    are opposite interventions. It is recorded as a knowledge gap rather than
    resolved in favour of either arm.
  attaches_to:
  - "pathophysiology#Impaired Action Potential Initiation and Saltatory Conduction"
  - "pathophysiology#Failure of KCNQ2 and KCNQ3 Potassium Channel Clustering"
  proposed_experiments:
  - experiment_id: sptbn4-compartment-resolved-excitability
    name: Compartment-resolved excitability mapping in beta-IV spectrin nulls
    description: >-
      Record simultaneously from soma, axon initial segment and node in the
      same neurons of beta-IV-spectrin-null mice across development, to
      determine where and when the sodium-channel and KCNQ2 arms dominate.
- discussion_id: sptbn4-no-human-cns-tissue
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Does any available model or human material support the cortical mechanism
    proposed for the intellectual disability, which is the disorder's most
    disabling feature?
  rationale: >-
    This is a model-fidelity problem rather than an absence of evidence, which
    is why it is recorded as HUMAN_MODEL_MISMATCH. Substantial in vivo evidence
    exists, but none of it addresses the human cognitive phenotype. No
    post-mortem CNS tissue, no brain biopsy and no patient-derived iPSC
    neuronal model from an SPTBN4 individual has been reported; the human
    tissue evidence in this disorder consists of nerve biopsy, muscle biopsy
    and fibroblasts. The mouse models reproduce ataxia, tremor, deafness and
    motor paresis, all of which are minor or absent components of the human
    phenotype, while intellectual disability - present in nearly every patient
    - has no characterised murine counterpart. The specific mismatch runs both
    ways: the mouse is ataxic and the humans generally are not, and the humans
    are profoundly intellectually disabled and the mouse has not been tested.
    Every cortical mechanistic claim in this entry is therefore extrapolated
    from rodent hippocampal and brainstem recordings, and the competing
    explanation - that the developmental delay is substantially secondary to
    motor, communicative and sensory deprivation plus recurrent hypoxia - has
    never been excluded.
  attaches_to:
  - "pathophysiology#Cortical Network Dysfunction and Impaired Neurodevelopment"
  proposed_experiments:
  - experiment_id: sptbn4-ipsc-cortical-neurons
    name: Patient iPSC-derived cortical neurons and AIS morphometry
    description: >-
      Derive cortical neurons from SPTBN4 patients and controls and measure AIS
      length and position, ankyrinG and Nav/KCNQ2 clustering, and intrinsic
      excitability, in the cell type the cognitive phenotype implicates.
  - experiment_id: sptbn4-mouse-cognitive-phenotyping
    name: Cognitive phenotyping of beta-IV spectrin mutant mice
    description: >-
      Run learning, memory and social-behaviour batteries on the existing
      quivering and gene-trap lines, controlling for their motor and auditory
      impairment, to establish whether a cognitive phenotype exists in the
      model at all.
  - experiment_id: sptbn4-neuropathology-registry
    name: Neuropathological examination through a patient registry
    description: >-
      Establish consent for post-mortem CNS examination within a rare-disease
      registry, since mortality in early childhood is unfortunately common in
      this disorder and no neuropathology has ever been reported.
- discussion_id: sptbn4-deafness-in-the-disease-name
  kind: CURATION_TODO
  status: OPEN
  prompt: >-
    Should the OMIM/MONDO label for this disorder continue to name deafness as
    a cardinal feature when it is present in a minority of patients?
  rationale: >-
    Both counted series put hearing impairment well below half - 2/5 in the HPO
    annotation set for OMIM:617519 and 21% in the 38-patient review - while
    hypotonia, developmental delay, absent speech and poor head control
    approach 100%. The name derives from the founding single-case report, in
    which central deafness was one of three presenting features and was the
    observation that connected the patient to the quivering mouse. The
    practical harm is real: a clinician using the disease name as a
    phenotype checklist will under-consider SPTBN4 in the much larger group of
    hypotonic, areflexic infants with normal hearing. Recorded here rather than
    acted on, because renaming is an OMIM/MONDO decision and outside the scope
    of a dismech entry; the correct dismech response is the explicit caveat in
    the entry-level notes and in the hearing-impairment phenotype.
  attaches_to:
  - "phenotypes#Sensorineural hearing impairment (auditory neuropathy)"
- discussion_id: sptbn4-late-onset-outliers
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    What are the two reported individuals with SPTBN4 variants whose disease
    onset was at 48 and 60 years of age?
  rationale: >-
    A congenital-onset neurodevelopmental disorder with two cases of
    mid-to-late-adult onset is either two different diseases or a
    misattribution. The 2025 systematic review records the observation in a
    single clause with no clinical, molecular or ascertainment detail, and the
    primary source is not identifiable from the review text alone. The
    possibilities are distinguishable and consequential: these could be
    genuinely hypomorphic alleles defining an adult-onset SPTBN4 neuropathy;
    they could be individuals ascertained through a neuropathy cohort in whom
    an SPTBN4 variant is incidental; or the ages could be errors of
    transcription in the review's supplementary table. Until this is resolved,
    the entry treats congenital-to-early-childhood onset as the disorder's
    natural history and flags the outliers rather than widening the onset
    range.
  attaches_to:
  - "pathophysiology#Residual-Function Alleles and the Mild End of the Spectrum"
  proposed_experiments:
  - experiment_id: sptbn4-late-onset-source-tracing
    name: Trace and re-phenotype the reported late-onset individuals
    description: >-
      Identify the primary publications behind the two late-onset entries in
      the pooled review, obtain their genotypes and phenotypes, and determine
      whether they represent a distinct adult-onset SPTBN4 phenotype or an
      artefact of pooling.
references:
- reference: PMID:29861105
  title: "βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy."
- reference: PMID:28540413
  title: "A recessive mutation in beta-IV-spectrin (SPTBN4) associates with congenital myopathy, neuropathy, and central deafness."
- reference: PMID:33772159
  title: "Novel bi-allelic variants expand the SPTBN4-related genetic and phenotypic spectrum."
- reference: PMID:31857255
  title: "A novel homozygous splice-site mutation in the SPTBN4 gene causes axonal neuropathy without intellectual disability."
- reference: PMID:33986717
  title: "Severe Form of ßIV-Spectrin Deficiency With Mitochondrial Dysfunction and Cardiomyopathy-A Case Report."
- reference: PMID:40781329
  title: "Natural history of SPTBN4-related neurodevelopmental disorder with hypotonia, neuropathy, and deafness."
- reference: PMID:42068471
  title: "Severe SPTBN4-Related Neurodevelopmental Disorder: Case Report of Two Siblings with Lethal Outcomes."
- reference: PMID:32672909
  title: "SPTBN4 Disorder."
  tags:
  - GeneReviews
- reference: PMID:11086001
  title: "betaIV spectrin, a new spectrin localized at axon initial segments and nodes of ranvier in the central and peripheral nervous system."
- reference: PMID:11807096
  title: "[Beta]IV-spectrin regulates sodium channel clustering through ankyrin-G at axon initial segments and nodes of Ranvier."
- reference: PMID:15381686
  title: "BetaIVSigma1 spectrin stabilizes the nodes of Ranvier and axon initial segments."
- reference: PMID:15317849
  title: "BetaIV spectrins are essential for membrane stability and the molecular organization of nodes of Ranvier."
- reference: PMID:17283186
  title: "betaIV spectrin is recruited to axon initial segments and nodes of Ranvier by ankyrinG."
- reference: PMID:17197442
  title: "Specific role of the truncated betaIV-spectrin Sigma6 in sodium channel clustering at axon initial segments and nodes of ranvier."
- reference: PMID:20962009
  title: "The C-terminal domain of ßIV-spectrin is crucial for KCNQ2 aggregation and excitability at nodes of Ranvier."
- reference: PMID:11528393
  title: "Mutant beta-spectrin 4 causes auditory and motor neuropathies in quivering mice."
- reference: PMID:19156852
  title: "Reduced excitability in the dentate gyrus network of betaIV-spectrin mutant mice in vivo."
- reference: PMID:29907663
  title: "Reorganization of Destabilized Nodes of Ranvier in βIV Spectrin Mutants Uncovers Critical Timelines for Nodal Restoration and Prevention of Motor Paresis."
- reference: PMID:35393465
  title: "Loss of β4-spectrin impairs Na(v) channel clustering at the heminode and temporal fidelity of presynaptic spikes in developing auditory brain."
- reference: PMID:23239625
  title: "Actin, spectrin, and associated proteins form a periodic cytoskeletal structure in axons."
- reference: PMID:38441922
  title: "Postsynaptic β1 spectrin maintains Na(+) channels at the neuromuscular junction."
- reference: PMID:36697767
  title: "Spectrins: molecular organizers and targets of neurological disorders."

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References & Deep Research

References

PMID:29861105

βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy.