RHOBTB2-Related Developmental and Epileptic Encephalopathy

Mendelian MONDO:0033373 Pathograph 10 Show in embeddings browser Epilepsy Neurological Disease

RHOBTB2-related developmental and epileptic encephalopathy (DEE64) is caused by heterozygous de novo missense variants clustering in the BTB-domain-encoding region of RHOBTB2, an atypical Rho GTPase that serves as a substrate-specific adaptor for a CUL3-based ubiquitin ligase complex - and that is itself a substrate of that complex. The pathogenic variants impair RHOBTB2's own proteasomal turnover, so the mutant protein accumulates. The disorder is therefore not a loss of function: complete loss of RHOBTB2 does not reproduce the electrophysiological phenotype, and neither do missense variants in the GTPase domain. Affected individuals have early-onset epilepsy, severe intellectual disability, postnatal microcephaly and movement disorders.

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1
Inheritance
9
Pathophys.
14
Phenotypes
2
Hypotheses
3
Gaps
10
Pathograph
1
Genes
1
Medical Actions
2
Models
1
Deep Research
👪

Inheritance

1
Autosomal dominant HP:0000006
Heterozygous and de novo, with several recurrent variants.
Autosomal dominant inheritance
Show evidence (1 reference)
PMID:29276004 SUPPORT Human Clinical
"We have now identified de novo missense variants clustering in the BTB-domain-encoding region of RHOBTB2 in ten individuals with a similar phenotype, including early-onset epilepsy, severe intellectual disability, postnatal microcephaly, and movement disorders"
Establishes the de novo heterozygous architecture, the BTB-domain clustering, and the core phenotype in the founding ten-patient cohort.
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Mechanistic Hypotheses

2
transcriptional_deregulation_model
transcriptional_deregulation_model CANONICAL
Evidence balance 1 support
Accumulated RHOBTB2 indirectly dysregulates transcription of ion channel and receptor genes, and the resulting change in channel complement alters excitability. This is the account the transcriptomic data most directly support, in both the fly overexpression model and the inducible human cell model.
Pathograph links
Increased RHOBTB2 Protein Abundance -> Deregulated Ion Channel Gene Expression INDIRECT UNKNOWN INTERMEDIATES The route from accumulated RHOBTB2 to channel deregulation is not established - see the competing-hypotheses discussion.
Show evidence (1 reference)
PMID:39849855 SUPPORT Model Organism
"We now found enrichment for ion channels among the differentially expressed genes from RNA-Seq on fly heads overexpressing RhoBTB"
Transcriptomic evidence for channel-gene deregulation downstream of excess RhoBTB.
direct_substrate_ubiquitination_model
direct_substrate_ubiquitination_model ALTERNATIVE
Evidence balance 1 support
RHOBTB2, or the RHOBTB2-CUL3 complex, ubiquitinates ion channels or their regulators directly, so impaired turnover or mistargeting of the channel proteins themselves drives the excitability change without requiring a transcriptional step. RHOBTB2 is a substrate adaptor by function, so this is the mechanism its known biology would predict. It is currently the less directly evidenced of the two: no source available to this entry identifies an ion channel as a validated RHOBTB2-CUL3 substrate.
Pathograph links
Increased RHOBTB2 Protein Abundance -> Deregulated Ion Channel Gene Expression INDIRECT UNKNOWN INTERMEDIATES The route from accumulated RHOBTB2 to channel deregulation is not established - see the competing-hypotheses discussion.
Show evidence (1 reference)
PMID:15107402 SUPPORT In Vitro
"RhoBTB2 binds to the ubiquitin ligase scaffold, Cul3, via its first BTB domain"
Supports the premise that RHOBTB2 operates as a CUL3 adaptor, which is what makes direct substrate ubiquitination a live hypothesis. Curated PARTIAL because it establishes the capability, not that any channel is such a substrate.
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Discussions and Knowledge Gaps

3
Does accumulated RHOBTB2 deregulate ion channels by changing their transcription, or by ubiquitinating the channel proteins directly?
CONTROVERSY OPEN controversy_transcriptional_versus_direct_ubiquitination_route
Attached to
pathophysiology#Increased RHOBTB2 Protein Abundance pathophysiology#Deregulated Ion Channel Gene Expression
Both accounts explain the same endpoint and neither is excluded. The transcriptional account has the more direct evidence - channel genes are enriched among differentially expressed genes in two independent systems, a fly overexpression model and an inducible human cell line. The direct-substrate account is what RHOBTB2's known biology predicts: it is a substrate adaptor for a CUL3 ubiquitin ligase, so acting on channel proteins themselves is its native mode of action, and a transcriptional effect would be the indirect one for such a protein. What is missing is an identified channel substrate; no source available to this entry validates an ion channel as a RHOBTB2-CUL3 target. The entry therefore marks the edge from accumulation to channel deregulation INDIRECT_UNKNOWN_INTERMEDIATES and tags it to both hypothesis groups rather than committing to a route. The distinction is not academic: a transcriptional mechanism predicts a delayed, cumulative phenotype amenable to transcriptional intervention, while direct ubiquitination predicts a faster, protein-level effect with different therapeutic handles.
Proposed experiments
Ubiquitinome and channel-protein turnover under RHOBTB2 accumulation
exp_ubiquitinome_of_accumulated_rhobtb2
In neurons expressing a BTB-domain hotspot variant, measure ion channel protein half-lives and ubiquitination state alongside their transcript levels. If channel protein turnover changes without a matching transcript change, the direct-substrate account is supported; if protein changes track transcript changes, the transcriptional account is.
GTPase-domain variants do not alter excitability yet do reduce Na+/K+-ATPase most strongly. What phenotype does that combination produce?
KNOWLEDGE GAP OPEN gap_what_the_gtpase_domain_variants_do
Attached to
pathophysiology#Domain-Specific Divergence of Cellular Consequence pathophysiology#Reduced Sodium-Potassium ATPase Abundance
The two lines of evidence sit awkwardly together and the entry does not smooth them. In the iPSC system, GTPase-domain missense variants produced no excitability phenotype, which is why this entry scopes itself to the BTB-domain disorder. In the inducible cell system, the same domain class showed the most prominent loss of Na+/K+-ATPase, an effect that would ordinarily be expected to disturb ion homeostasis and hence excitability. Either the Na+/K+-ATPase reduction is insufficient on its own to change firing in that preparation, or the two systems differ in a way that matters, or the GTPase-domain variants cause a different disorder whose phenotype is not the one being measured. The founding electrophysiology paper favours the last reading, concluding that other RHOBTB2 variant classes act by different pathomechanisms. Resolving this determines whether GTPase-domain variants belong in a separate entry.
Proposed experiments
Ion homeostasis and excitability in GTPase-domain variant neurons
exp_gtpase_variant_ion_homeostasis
Measure Na+/K+-ATPase abundance, intracellular sodium, and firing properties in the same GTPase-domain-variant iPSC neurons, rather than in separate systems. If the pump loss is reproduced in neurons without an excitability change, the two findings are genuinely dissociable and the GTPase arm needs its own mechanistic account.
If accumulation causes encephalopathy and loss is reported to permit tumour formation, what is the tolerated range of RHOBTB2 abundance, and does it differ by tissue?
KNOWLEDGE GAP OPEN gap_dosage_duality_too_little_and_too_much
Attached to
pathophysiology#Increased RHOBTB2 Protein Abundance
RHOBTB2 is unusual in being reported as pathogenic in both directions - accumulation in this disorder, loss of function in the tumour-suppressor literature. The neuronal data make the asymmetry concrete: complete loss produced no excitability phenotype in iPSC neurons, so neurons appear to tolerate absence while not tolerating excess. That is the opposite of the tissue sensitivity a simple dosage model would predict if one threshold governed both. Any therapeutic strategy aimed at lowering mutant RHOBTB2 needs this range, because the floor is set by a different tissue than the ceiling.
Proposed experiments
Graded RHOBTB2 abundance series in neurons
exp_graded_rhobtb2_dosage_series
Titrate RHOBTB2 abundance across a range spanning null to several-fold overexpression in the same neuronal preparation and map excitability against level, to establish where the neuronal phenotype begins and whether it is continuous or thresholded.
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Pathophysiology

9
RHOBTB2 BTB-Domain Missense Variant
The initiating lesion. Variants cluster in the BTB-domain-encoding region, and three were already recurrent in the founding cohort. Domain location is not incidental detail here - it is what separates this disorder from the other RHOBTB2-related phenotypes, because GTPase-domain variants and biallelic truncating variants do not produce the same cellular consequence.
Downstream
Impaired Proteasomal Degradation of RHOBTB2 The variant acts first on the protein's own turnover.
Show evidence (1 reference)
PMID:29276004 SUPPORT Human Clinical
"de novo missense variants clustering in the BTB-domain-encoding region of RHOBTB2 in ten individuals with a similar phenotype"
Locates the pathogenic variants to the BTB-domain-encoding region.
Impaired Proteasomal Degradation of RHOBTB2
RHOBTB2 binds the CUL3 ubiquitin ligase scaffold through its first BTB domain and is itself a substrate of that complex, so a BTB-domain variant disrupts the protein's own destruction rather than only its adaptor function. This node is the turnover defect; the resulting abundance change is curated separately below because they are measured separately and, in the GTPase-domain variants, they come apart.
proteasome-mediated ubiquitin-dependent protein catabolic process GO:0043161 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased proteasome-mediated ubiquitin-dependent protein catabolic process (GO:0043161). GO:0043161 is a biological process from the Gene Ontology. ↓ DECREASED
cullin-RING ubiquitin ligase complex GO:0031461 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves cullin-RING ubiquitin ligase complex (GO:0031461). GO:0031461 is a cellular component from the Gene Ontology.
Downstream
Increased RHOBTB2 Protein Abundance Reduced turnover raises the steady-state pool.
Show evidence (2 references)
PMID:15107402 SUPPORT In Vitro
"we demonstrate that RhoBTB2 binds to the ubiquitin ligase scaffold, Cul3, via its first BTB domain and show in vitro and in vivo that RhoBTB2 is a substrate for a Cul3-based ubiquitin ligase complex"
Establishes the baseline biology this disorder subverts - RHOBTB2 is both adaptor and substrate, and the BTB domain is the CUL3-binding interface.
PMID:15107402 SUPPORT In Vitro
"we show that a RhoBTB2 missense mutant identified in a lung cancer cell line is neither able to bind Cul3 nor is it regulated by the ubiquitin/proteasome system, resulting in increased RhoBTB2 protein levels in vivo"
Prior demonstration, in a cancer-derived allele, that a missense change can uncouple RHOBTB2 from its own degradation and raise its abundance - the same logic the DEE64 variants follow.
Increased RHOBTB2 Protein Abundance
Mutant RHOBTB2 accumulates above wild-type levels. This is the node that makes the disorder a gain rather than a loss, and it is the reason a knockout is not a model of it. Later work adds subcellular detail: hotspot mutants accumulate specifically in the nucleus and mitochondria, and GTPase-domain mutants do not accumulate at all.
None None
Downstream
Deregulated Ion Channel Gene Expression The route from accumulated RHOBTB2 to channel deregulation is not established - see the competing-hypotheses discussion. None None
Show evidence (2 references)
PMID:29276004 SUPPORT In Vitro
"Upon transfection of HEK293 cells, we found that mutant RHOBTB2 was more abundant than the wild-type, most likely because of impaired degradation in the proteasome"
The abundance measurement and its proposed cause, in the founding study.
PMID:41478322 SUPPORT In Vitro
"GTPase-domain mutants such as D92H and W217C showed no significant difference in RHOBTB2 protein levels compared with WT, while hotspot mutants (R461H, R485C, R489Q) exhibited increased RHOBTB2 protein levels with nuclear and mitochondrial accumulation"
Separates the two variant classes by abundance and adds the subcellular localisation of the accumulated protein. Residue numbering follows the cited publication.
Deregulated Ion Channel Gene Expression
Transcriptomic work in flies overexpressing RhoBTB found ion channel genes enriched among the differentially expressed set, and the enriched molecular functions among downregulated genes are receptor, channel and transporter activities. An independent inducible cell model found the R489Q hotspot mutant robustly downregulates ion-channel-related genes.
regulation of ion channel gene expression GO:0010468 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves dysregulated regulation of ion channel gene expression, annotated with regulation of gene expression (GO:0010468). GO:0010468 is a biological process from the Gene Ontology. ↕ DYSREGULATED
Downstream
Altered Neuronal Excitability Changed channel complement alters the firing properties of the neuron.
Show evidence (3 references)
PMID:39849855 SUPPORT Model Organism
"We now found enrichment for ion channels among the differentially expressed genes from RNA-Seq on fly heads overexpressing RhoBTB"
The transcriptomic finding that first implicated channel deregulation.
PMID:39849855 SUPPORT Model Organism
"All significantly enriched molecular functions among the downregulated genes are linked to neurotransmitter receptor activity, ion channel activity or transmembrane transporter activity"
Records that the deregulation is directional and concentrated in exactly the gene classes that set excitability.
PMID:41478322 SUPPORT In Vitro
"induction of the R489Q mutant caused a robust downregulation of ion channel-related genes, supporting its potential role in disrupting neuronal excitability"
Independent replication of channel-gene downregulation in a human cell model with an inducible hotspot mutant.
Altered Neuronal Excitability
Patch-clamp recordings from human iPSC-derived neurons show increased action potential firing frequency at all current injections, increased AP half width, and decreased depolarization speed. The direction is curated as measured rather than summarised as "hyperexcitability", because the three parameters do not all point the same way - the cell fires more often but each spike is broader and rises more slowly.
neuron CL:0000540 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology.
Experimental models
Patient-variant human iPSC-derived neurons IPSC DERIVED MODEL Patch-clamp recordings across three genotype classes.
Downstream
Seizures and Developmental Encephalopathy Altered excitability is the proposed cellular substrate for the clinical phenotype.
Show evidence (2 references)
PMID:39849855 SUPPORT In Vitro
"Neurons with variants in the BTB domain region show increased AP firing frequency compared to the wildtype (WT)"
The firing-rate measurement in patient-variant human neurons.
PMID:39849855 SUPPORT In Vitro
"neurons with variants in the BTB domain region present with decreased depolarization speed (G) and increased AP half width (F)"
The two waveform parameters, which move in the opposite direction to what a simple hyperexcitability account would predict and are therefore recorded explicitly.
Domain-Specific Divergence of Cellular Consequence
A negative-result node, curated because it carries more weight than most positive ones here. In the same iPSC system, GTPase-domain missense variants and complete loss of RHOBTB2 produced no excitability phenotype, while BTB-domain variants did. This excludes haploinsufficiency as the mechanism of DEE64 and is what makes the accumulation account the operative one.
Show evidence (2 references)
PMID:39849855 SUPPORT In Vitro
"This revealed significantly altered neuronal activity and excitability resulting from BTB domain variants but not from GTPase domain variants or upon complete loss of RHOBTB2"
The three-way dissociation in a single experimental system. The "not upon complete loss" clause is the part that rules out haploinsufficiency.
PMID:39849855 SUPPORT In Vitro
"suggests different pathomechanisms for other RHOBTB2-related neurological and neurodevelopmental phenotypes associated with missense variants in the GTPase domain or bi-allelic truncating variants"
The authors' own conclusion that the other RHOBTB2 variant classes act by different mechanisms, which is why this entry scopes itself to the BTB-domain disorder.
Reduced Sodium-Potassium ATPase Abundance
A separate molecular arm, and the one that complicates the tidy BTB-versus-GTPase story. Mutant RHOBTB2 lowers Na+/K+-ATPase protein through a lysosome-dependent route, and the effect is most prominent in the GTPase-domain mutants - the same class that shows no excitability phenotype. Curated as its own node rather than folded into the excitability chain, because it is a distinct measurement in a different variant class.
Show evidence (2 references)
PMID:41478322 SUPPORT In Vitro
"expression of mutant RHOBTB2 led to a reduction in Na+/K+-ATPase protein levels via a lysosome-dependent degradation pathway"
Establishes the effect and the degradation route, which is lysosomal rather than proteasomal - a different pathway from the one that handles RHOBTB2 itself.
PMID:41478322 SUPPORT In Vitro
"This effect was particularly prominent in GTPase-domain mutants (D92H and W217C), suggesting a mechanistic link between mutant RHOBTB2 and impaired ion homeostasis"
Locates the effect predominantly in the variant class that does not alter excitability, which is why this arm is not drawn into the BTB excitability chain.
Impaired Mitochondrial Respiration
Mitochondrial respiration is impaired by some mutants and not others, cutting across the domain boundary: one hotspot mutant and one GTPase-domain mutant, but not the rest. Curated because the accumulated hotspot protein localises to mitochondria, which makes a mitochondrial consequence mechanistically plausible rather than incidental.
oxidative phosphorylation GO:0006119 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased oxidative phosphorylation (GO:0006119). GO:0006119 is a biological process from the Gene Ontology. ↓ DECREASED
Show evidence (1 reference)
PMID:41478322 SUPPORT In Vitro
"the R489Q and W217C mutants impaired mitochondrial respiration, whereas other mutants did not show detectable mitochondrial dysfunction"
Curated PARTIAL because the finding holds for two of the mutants tested and explicitly not for the others, so it is a variant-specific rather than a disease-general mechanism.
Seizures and Developmental Encephalopathy
The clinical syndrome - early-onset epilepsy with severe intellectual disability, postnatal microcephaly and movement disorders.
Animal models
Drosophila RhoBTB overexpression and dendritic-arborization knockdown Fruit fly recapitulates Elevated RhoBTB produces seizure susceptibility and locomotor impairment.
Show evidence (1 reference)
PMID:29276004 SUPPORT Human Clinical
"ten individuals with a similar phenotype, including early-onset epilepsy, severe intellectual disability, postnatal microcephaly, and movement disorders"
The clinical phenotype as defined in the founding cohort.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for RHOBTB2-Related Developmental and Epileptic Encephalopathy Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

14
Nervous System 9
Early-Onset Epilepsy Seizure HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:29276004 SUPPORT Human Clinical
"ten individuals with a similar phenotype, including early-onset epilepsy"
Names early-onset epilepsy as part of the shared phenotype in the founding cohort.
Severe Intellectual Disability HP:0010864 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Severe intellectual disability (HP:0010864). HP:0010864 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:29276004 SUPPORT Human Clinical
"including early-onset epilepsy, severe intellectual disability, postnatal microcephaly, and movement disorders"
Names severe intellectual disability among the shared features.
Complex Motor Phenotype OBLIGATE Abnormality of movement HP:0100022 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormality of movement (HP:0100022). HP:0100022 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33504645 SUPPORT Human Clinical
"All had a complex motor phenotype, including at least 2 different kinds of movement disorder, e.g., ataxia and dystonia"
11/11 is 100 percent, the OBLIGATE band, and the source states the count as "all".
Ataxia HP:0001251 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ataxia (HP:0001251). HP:0001251 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35315256 SUPPORT Human Clinical
"The movement disorder appears characteristic, associating ataxia, dystonia"
Names ataxia as part of the characteristic movement-disorder composite. No cohort-wide count is given for ataxia alone, so no frequency band is asserted.
Dystonia HP:0001332 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dystonia (HP:0001332). HP:0001332 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35315256 SUPPORT Human Clinical
"The movement disorder appears characteristic, associating ataxia, dystonia"
Names dystonia as part of the characteristic composite. No cohort-wide count is given for dystonia alone, so no frequency band is asserted.
Chorea HP:0002072 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Chorea (HP:0002072). HP:0002072 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35315256 SUPPORT Human Clinical
"The movement disorder appears characteristic, associating ataxia, dystonia and paroxysmal chorea"
Curated PARTIAL because the source describes the movements as chorea-like rather than as chorea, so the HP term is a close but not exact fit for the reported observation.
Intellectual Disability OBLIGATE HP:0001249 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Intellectual disability (HP:0001249). HP:0001249 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33504645 SUPPORT Human Clinical
"All patients had intellectual disability, usually moderate to severe"
11/11 is 100 percent, the OBLIGATE band, stated as "all" by the source.
Focal and Generalized Tonic-Clonic Seizures Bilateral tonic-clonic seizure HP:0002069 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bilateral tonic-clonic seizure (HP:0002069). HP:0002069 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35315256 SUPPORT Human Clinical
"The severity of the seizure types varied, from early‐onset epilepsy to focal, complex partial, and generalized tonic–clonic seizures"
The reported semiology range, quoted in full. The source renders its hyphens as U+2010 and its dash as U+2013 and those codepoints are reproduced here rather than the quote being cut short of them. No cohort-wide count is given per seizure type, so no frequency band is asserted.
Developmental Regression HP:0002376 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Developmental regression (HP:0002376). HP:0002376 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35315256 SUPPORT Human Clinical
"moderate to severe intellectual disability that was sometimes associated with developmental regression or plateauing"
Records regression as a reported course. The source's "sometimes" gives no count, so no frequency band is asserted.
Other 5
Postnatal Microcephaly Progressive microcephaly HP:0000253 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Progressive microcephaly (HP:0000253). HP:0000253 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:29276004 SUPPORT Human Clinical
"severe intellectual disability, postnatal microcephaly, and movement disorders"
Records the microcephaly as postnatal, which is what the progressive term captures.
Paroxysmal Movement Disorder VERY_FREQUENT Paroxysmal dyskinesia HP:0007166 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Paroxysmal dyskinesia (HP:0007166). HP:0007166 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33504645 SUPPORT Human Clinical
"10 patients had a movement disorder including paroxysmal elements, and 8 experienced hemiplegic episodes"
10/11 is 91 percent, in the VERY_FREQUENT band (80-99 percent).
Episodic Hemiplegia FREQUENT HP:0012194 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Episodic hemiplegia (HP:0012194). HP:0012194 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:33504645 SUPPORT Human Clinical
"10 patients had a movement disorder including paroxysmal elements, and 8 experienced hemiplegic episodes"
8/11 is 73 percent, in the FREQUENT band (30-79 percent). The full sentence is quoted rather than the hemiplegia clause alone, since the clause on its own carries no subject.
PMID:33504645 SUPPORT Human Clinical
"In contrast to classic AHC, commonly caused by mutations in ATP1A3, these events were reported later only in RHOBTB2 mutation-positive patients from 20 months of age"
Records the later onset that distinguishes RHOBTB2-related AHC from the ATP1A3 form.
Drug-Resistant Epilepsy Refractory drug response HP:0020174 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Refractory drug response (HP:0020174). HP:0020174 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:35315256 SUPPORT Human Clinical
"with approximately 4-5 seizures/month despite having started an antiepileptic tritherapy with the optimal posologies"
Quantifies the residual seizure burden on optimally dosed triple therapy in a genotype-confirmed patient, which is stronger than a general statement of drug resistance.
PMID:35315256 SUPPORT Human Clinical
"she is under a triple antiepileptic medication with partial control of her epileptic seizures"
Records partial rather than absent response, which is the accurate characterisation.
Variable Brain MRI Findings
Show evidence (2 references)
PMID:35315256 SUPPORT Human Clinical
"here the reported individual presented with late postnatal onset of microcephaly and the absence of cortical atrophy on MRI"
Documents a genotype-confirmed patient without the cortical atrophy reported in others, establishing that imaging findings are variable rather than defining.
PMID:39831600 SUPPORT Human Clinical
"Cranial MRI revealed bilateral frontotemporal and falx cerebri-adjacent extracerebral space widening"
An independent case with a different imaging abnormality, supporting the variability rather than a single characteristic pattern.
🧬

Genetic Associations

1
RHOBTB2 (Heterozygous de novo missense variants in the BTB-domain-encoding region of RHOBTB2 cause DEE64 by impairing the protein's own proteasomal degradation, so that mutant RHOBTB2 accumulates. The variant spectrum is dominated by two arginine hotspots within the BTB domain, Arg483 and Arg511, which together account for roughly half of the ~30 reported variants across ~60 reported cases; p.Arg511Gln, p.Arg483His and p.Arg511Trp each individually exceed a 10 percent incidence rate. Both hotspot residues are non-conserved across species, which is one reason the mechanism could not be read off conservation alone.)
Gene: RHOBTB2 hgnc:18756 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is RHOBTB2 (hgnc:18756). hgnc:18756 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (4 references)
PMID:29276004 SUPPORT Human Clinical
"We have established missense variants in the BTB-domain-encoding region of RHOBTB2 as causative for a developmental and epileptic encephalopathy"
The gene-disease assertion, scoped to the BTB-domain-encoding region.
PMID:39831600 SUPPORT Human Clinical
"More than half of the variants are located at Arg483 and Arg511 within the BTB domain; however, the underlying mechanism of action of these hotspot variants remains unexplored"
Locates the two hotspot residues and quantifies their share of the variant spectrum. The second clause is quoted deliberately: the source itself records that the hotspot mechanism is unexplained, which is the same gap this entry's discussions describe.
PMID:39831600 SUPPORT Human Clinical
"To date, 60 cases of DEE patients with RHOBTB2 variants have been reported, with approximately 50% of variants located at Arg483 and Arg511"
Gives the reported case count alongside the hotspot share.
+ 1 more reference
💊

Medical Actions

1
Antiseizure Medication
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: valproic acid CHEBI:39867 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses valproic acid (CHEBI:39867). CHEBI:39867 is a therapeutic agent from Chemical Entities of Biological Interest. carbamazepine CHEBI:3387 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses carbamazepine (CHEBI:3387). CHEBI:3387 is a therapeutic agent from Chemical Entities of Biological Interest. pyridoxine CHEBI:16709 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses pyridoxine (CHEBI:16709). CHEBI:16709 is a therapeutic agent from Chemical Entities of Biological Interest.
Management is symptomatic, with antiseizure drugs the mainstay. Response is genuinely variable rather than uniformly poor: 4 of the 7 patients with epilepsy in the movement-disorder series achieved seizure freedom, one infant remained seizure-free on oral sodium valproate over three months of follow-up, and valproate, carbamazepine and pyridoxine are each reported to work well in some patients - while another patient retained only partial control on triple therapy. No agent has disease-specific efficacy evidence, and no trial exists, so the agents named here are those reported to have helped rather than a recommended sequence.
Show evidence (5 references)
PMID:39831600 SUPPORT Human Clinical
"The treatment of epilepsy-related encephalopathy associated with RHOBTB2 variants primarily relies on symptomatic treatment, with antiepileptic drugs (AEDs) being the mainstay"
Establishes that management is symptomatic and drug-based.
PMID:39831600 SUPPORT Human Clinical
"Some patients respond well to valproate, carbamazepine, and pyridoxine"
Names the three agents bound as therapeutic_agent, and is the basis for describing the response as variable rather than uniformly partial.
PMID:39831600 SUPPORT Human Clinical
"Treatment with oral sodium valproate was initiated, and the patient remained seizure‐free during follow‐up"
A single-patient success on valproate monotherapy, quoted through the operative word. The source's hyphens are U+2010 and are reproduced here. The quote stops before "over 3 months" only because the source separates the numeral from the unit with a thin space (U+2009), which does not survive transcription.
+ 2 more references
🌍

Environmental Factors

2
Hyperthermia
Deliberately left without an exposure_term. ECTO was searched: its temperature terms (e.g. ECTO:1000007 exposure to high temperature environment) describe exposure to a hot environment, whereas the source says only "hyperthermia" without specifying whether the raised temperature was febrile or environmental. Binding an environmental-heat term would assert a route the source does not report, and no term is better than a wrong one.
Hyperthermia is reported as a trigger for acute encephalopathy and epileptic seizures in at least five patients. It does not cause the disorder - that is entirely genetic - but it precipitates acute decompensation on top of it, which is what makes it worth recording as an exposure acting on a mechanism rather than as a phenotype.
Show evidence (1 reference)
PMID:35315256 SUPPORT Human Clinical
"epileptic seizures triggered by hyperthermia or head trauma"
The exposure as reported.
Mechanism Target:
TRIGGERS Seizures and Developmental Encephalopathy — Precipitates acute encephalopathy and seizures in an already-susceptible brain. How raised temperature interacts with the accumulated-protein mechanism is not established by any source available to this entry, hence the unknown intermediates.
Show evidence (1 reference)
PMID:35315256 SUPPORT Human Clinical
"At least five patients were reported to have acute encephalopathy and epileptic seizures triggered by hyperthermia or head trauma"
Names hyperthermia as a reported trigger for acute encephalopathy and seizures.
Head trauma
Deliberately left without an exposure_term. ECTO was searched for mechanical, physical, force, impact and trauma exposures and has no term for head trauma or physical injury.
Head trauma is the second reported precipitant of acute encephalopathy and seizures in the same patient group.
Show evidence (1 reference)
PMID:35315256 SUPPORT Human Clinical
"triggered by hyperthermia or head trauma"
The exposure as reported.
Mechanism Target:
TRIGGERS Seizures and Developmental Encephalopathy — Precipitates acute encephalopathy and seizures. As with hyperthermia, the interaction with the underlying accumulation mechanism is unestablished.
Show evidence (1 reference)
PMID:35315256 SUPPORT Human Clinical
"acute encephalopathy and epileptic seizures triggered by hyperthermia or head trauma"
Names head trauma as a reported trigger.
🔬

Diagnosis

2
Trio Whole-Exome Sequencing
The primary diagnostic modality. Every reported case has been ascertained molecularly, and the trio design is what establishes the de novo status that the variant interpretation depends on - a heterozygous missense variant in RHOBTB2 is only interpretable as causative once both parents are shown not to carry it.
Whole Exome Sequencing NCIT:C101295 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:39831600 SUPPORT Human Clinical
"We performed whole-exome and Sanger sequencing on the patient and his parents"
The trio design - proband plus both parents - stated as the method used to reach the diagnosis.
PMID:29276004 SUPPORT Human Clinical
"We have now identified de novo missense variants clustering in the BTB-domain-encoding region of RHOBTB2"
The de novo determination that trio sequencing exists to make.
Electroencephalography
EEG typically shows focal epileptic discharges during seizures. It supports the epilepsy diagnosis but does not distinguish this disorder from other developmental and epileptic encephalopathies, so the diagnosis remains genotype-driven.
Electroencephalography NCIT:C38054 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:39831600 SUPPORT Human Clinical
"EEG typically reveals focal epileptic discharges during seizures"
States the characteristic EEG finding for RHOBTB2-related encephalopathy.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
60 reported DEE64 cases as of the 2025 hotspot analysis. No population prevalence estimate exists for this disorder.
Show evidence (1 reference)
PMID:39831600 SUPPORT Human Clinical
"To date, 60 cases of DEE patients with RHOBTB2 variants have been reported"
The reported case count, which is the only occurrence measure available.
🧫

Experimental Models

1
Patient-variant human iPSC-derived neurons IPSC_DERIVED_MODEL
Mature neurons differentiated from human iPSCs carrying either patient-specific heterozygous missense variants in the GTPase or BTB domains, or homozygous frameshifts. The comparison across all three genotypes in one system is what produces the dissociation this entry is built around.
Publication
PMID:39849855
Pathograph links
Altered Neuronal Excitability recapitulates fidelity: high Patch-clamp recordings across three genotype classes.
Limitations: iPSC-derived neurons model cell-intrinsic excitability and cannot report network-level seizure activity or the clinical course.
Readouts
Action potential firing frequency
Direction: INCREASED
Interpretation: Increased at all current injections for BTB-domain variants.
Show evidence (1 reference)
PMID:39849855 SUPPORT In Vitro
"missense variants in the BTB domain region resulted in a different pattern with increased firing frequency at all current injections"
The firing-rate measurement behind this readout.
Action potential firing in complete RHOBTB2 loss
Direction: UNCHANGED
Interpretation: A real negative result. Homozygous knockout neurons fire no differently from wild-type, which is what excludes haploinsufficiency as the DEE64 mechanism and makes the accumulation account operative.
Show evidence (1 reference)
PMID:39849855 SUPPORT In Vitro
"we observed no significantly altered pattern for the homozygous knockout cells compared to the wildtype"
The negative measurement, stated directly by the source.
Show evidence (1 reference)
PMID:39849855 SUPPORT In Vitro
"We then performed patch-clamp recordings on mature neurons differentiated from human induced pluripotent stem cells with either homozygous frameshifts or patient-specific heterozygous missense variants in the GTPase or the BTB domains"
Establishes the model as human, patient-variant, and covering all three genotype classes in one comparison.
🐁

Animal Models

1
Drosophila RhoBTB overexpression and dendritic-arborization knockdown
Two complementary manipulations in one organism - raising RhoBTB to model the human accumulation, and lowering it to test the developmental role. The pairing is what makes the model informative about dosage rather than about direction alone.
Species
Fruit fly
Genotype
pan-neuronal RhoBTB overexpression; RhoBTB knockdown in da neurons
Publication
PMID:29276004
Pathograph links
Seizures and Developmental Encephalopathy recapitulates fidelity: moderate Elevated RhoBTB produces seizure susceptibility and locomotor impairment.
Limitations: The model raises wild-type RhoBTB levels rather than expressing a patient variant, so it tests the consequence of excess protein rather than of the specific human allele. Bang sensitivity is a seizure-like paralysis after mechanical shock, not spontaneous epilepsy.
Readouts
Seizure susceptibility and locomotor function
Direction: ALTERED
Interpretation: Elevated RhoBTB is associated with seizure susceptibility and severe locomotor defects.
Show evidence (1 reference)
PMID:29276004 SUPPORT Model Organism
"elevated amounts of the Drosophila ortholog RhoBTB in vivo were associated with seizure susceptibility and severe locomotor defects"
The behavioural measurements behind this readout.
Show evidence (1 reference)
PMID:29276004 SUPPORT Model Organism
"elevated amounts of the Drosophila ortholog RhoBTB in vivo were associated with seizure susceptibility and severe locomotor defects"
Supports treating raised RhoBTB dosage as informative for the human accumulation mechanism.
{ }

Source YAML

click to show 
name: RHOBTB2-Related Developmental and Epileptic Encephalopathy
creation_date: "2026-08-20T06:45:00Z"
category: Mendelian
synonyms:
- Developmental and epileptic encephalopathy 64
- DEE64
- EIEE64
- RHOBTB2-related neurodevelopmental disorder
description: >-
  RHOBTB2-related developmental and epileptic encephalopathy (DEE64) is caused by
  heterozygous de novo missense variants clustering in the BTB-domain-encoding region of
  RHOBTB2, an atypical Rho GTPase that serves as a substrate-specific adaptor for a
  CUL3-based ubiquitin ligase complex - and that is itself a substrate of that complex.
  The pathogenic variants impair RHOBTB2's own proteasomal turnover, so the mutant protein
  accumulates. The disorder is therefore not a loss of function: complete loss of RHOBTB2
  does not reproduce the electrophysiological phenotype, and neither do missense variants
  in the GTPase domain. Affected individuals have early-onset epilepsy, severe
  intellectual disability, postnatal microcephaly and movement disorders.
disease_term:
  preferred_term: developmental and epileptic encephalopathy, 64
  term:
    id: MONDO:0033373
    label: developmental and epileptic encephalopathy, 64
parents:
- Epilepsy
- Neurological Disease
inheritance:
- name: Autosomal dominant
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    Heterozygous and de novo, with several recurrent variants.
  evidence:
  - reference: PMID:29276004
    reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We have now identified de novo missense variants clustering in the
      BTB-domain-encoding region of RHOBTB2 in ten individuals with a similar phenotype,
      including early-onset epilepsy, severe intellectual disability, postnatal
      microcephaly, and movement disorders"
    explanation: >-
      Establishes the de novo heterozygous architecture, the BTB-domain clustering, and the
      core phenotype in the founding ten-patient cohort.

pathophysiology:

- name: RHOBTB2 BTB-Domain Missense Variant
  biological_scale: MOLECULAR
  description: >-
    The initiating lesion. Variants cluster in the BTB-domain-encoding region, and three
    were already recurrent in the founding cohort. Domain location is not incidental
    detail here - it is what separates this disorder from the other RHOBTB2-related
    phenotypes, because GTPase-domain variants and biallelic truncating variants do not
    produce the same cellular consequence.
  evidence:
  - reference: PMID:29276004
    reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "de novo missense variants clustering in the BTB-domain-encoding region of
      RHOBTB2 in ten individuals with a similar phenotype"
    explanation: >-
      Locates the pathogenic variants to the BTB-domain-encoding region.
  downstream:
  - target: Impaired Proteasomal Degradation of RHOBTB2
    causal_link_type: DIRECT
    description: >-
      The variant acts first on the protein's own turnover.

- name: Impaired Proteasomal Degradation of RHOBTB2
  biological_scale: MOLECULAR
  description: >-
    RHOBTB2 binds the CUL3 ubiquitin ligase scaffold through its first BTB domain and is
    itself a substrate of that complex, so a BTB-domain variant disrupts the protein's own
    destruction rather than only its adaptor function. This node is the turnover defect;
    the resulting abundance change is curated separately below because they are measured
    separately and, in the GTPase-domain variants, they come apart.
  biological_processes:
  - preferred_term: proteasome-mediated ubiquitin-dependent protein catabolic process
    modifier: DECREASED
    term:
      id: GO:0043161
      label: proteasome-mediated ubiquitin-dependent protein catabolic process
  cellular_components:
  - preferred_term: cullin-RING ubiquitin ligase complex
    term:
      id: GO:0031461
      label: cullin-RING ubiquitin ligase complex
  evidence:
  - reference: PMID:15107402
    reference_title: "RhoBTB2 is a substrate of the mammalian Cul3 ubiquitin ligase complex."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "we demonstrate that RhoBTB2 binds to the ubiquitin ligase scaffold, Cul3, via
      its first BTB domain and show in vitro and in vivo that RhoBTB2 is a substrate for a
      Cul3-based ubiquitin ligase complex"
    explanation: >-
      Establishes the baseline biology this disorder subverts - RHOBTB2 is both adaptor and
      substrate, and the BTB domain is the CUL3-binding interface.
  - reference: PMID:15107402
    reference_title: "RhoBTB2 is a substrate of the mammalian Cul3 ubiquitin ligase complex."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "we show that a RhoBTB2 missense mutant identified in a lung cancer cell line
      is neither able to bind Cul3 nor is it regulated by the ubiquitin/proteasome system,
      resulting in increased RhoBTB2 protein levels in vivo"
    explanation: >-
      Prior demonstration, in a cancer-derived allele, that a missense change can uncouple
      RHOBTB2 from its own degradation and raise its abundance - the same logic the DEE64
      variants follow.
  downstream:
  - target: Increased RHOBTB2 Protein Abundance
    causal_link_type: DIRECT
    description: >-
      Reduced turnover raises the steady-state pool.

- name: Increased RHOBTB2 Protein Abundance
  biological_scale: MOLECULAR
  description: >-
    Mutant RHOBTB2 accumulates above wild-type levels. This is the node that makes the
    disorder a gain rather than a loss, and it is the reason a knockout is not a model of
    it. Later work adds subcellular detail: hotspot mutants accumulate specifically in the
    nucleus and mitochondria, and GTPase-domain mutants do not accumulate at all.
  evidence:
  - reference: PMID:29276004
    reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Upon transfection of HEK293 cells, we found that mutant RHOBTB2 was more
      abundant than the wild-type, most likely because of impaired degradation in the
      proteasome"
    explanation: >-
      The abundance measurement and its proposed cause, in the founding study.
  - reference: PMID:41478322
    reference_title: "Mutant-specific dysfunction of RHOBTB2 impairs mitochondrial function and Na(+)/K(+)-ATPase levels in a cell model."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "GTPase-domain mutants such as D92H and W217C showed no significant difference
      in RHOBTB2 protein levels compared with WT, while hotspot mutants (R461H, R485C,
      R489Q) exhibited increased RHOBTB2 protein levels with nuclear and mitochondrial
      accumulation"
    explanation: >-
      Separates the two variant classes by abundance and adds the subcellular localisation
      of the accumulated protein. Residue numbering follows the cited publication.
  downstream:
  - target: Deregulated Ion Channel Gene Expression
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The route from accumulated RHOBTB2 to channel deregulation is not established - see
      the competing-hypotheses discussion.
    hypothesis_groups:
    - transcriptional_deregulation_model
    - direct_substrate_ubiquitination_model

- name: Deregulated Ion Channel Gene Expression
  biological_scale: CELLULAR
  description: >-
    Transcriptomic work in flies overexpressing RhoBTB found ion channel genes enriched
    among the differentially expressed set, and the enriched molecular functions among
    downregulated genes are receptor, channel and transporter activities. An independent
    inducible cell model found the R489Q hotspot mutant robustly downregulates
    ion-channel-related genes.
  notes: >-
    Term binding: the measurement here is on ion-channel gene EXPRESSION, not on transporter
    activity, so the node binds GO:0010468 regulation of gene expression with a more specific
    free-text preferred_term. The obvious ion-channel-flavoured alternatives do not work.
    GO:0032413 is negative regulation of ion transmembrane transporter activity, whose baked-in
    direction contradicts a DYSREGULATED modifier and whose subject is activity rather than
    expression; its non-directional parent GO:0032412 is obsolete. There is no GO term for
    regulation of ion-channel gene expression specifically, so the specificity is carried by
    preferred_term rather than by a worse-fitting bound term.
  biological_processes:
  - preferred_term: regulation of ion channel gene expression
    modifier: DYSREGULATED
    term:
      id: GO:0010468
      label: regulation of gene expression
  evidence:
  - reference: PMID:39849855
    reference_title: "Deregulated ion channels contribute to RHOBTB2-associated developmental and epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We now found enrichment for ion channels among the differentially expressed
      genes from RNA-Seq on fly heads overexpressing RhoBTB"
    explanation: >-
      The transcriptomic finding that first implicated channel deregulation.
  - reference: PMID:39849855
    reference_title: "Deregulated ion channels contribute to RHOBTB2-associated developmental and epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "All significantly enriched molecular functions among the downregulated genes
      are linked to neurotransmitter receptor activity, ion channel activity or
      transmembrane transporter activity"
    explanation: >-
      Records that the deregulation is directional and concentrated in exactly the gene
      classes that set excitability.
  - reference: PMID:41478322
    reference_title: "Mutant-specific dysfunction of RHOBTB2 impairs mitochondrial function and Na(+)/K(+)-ATPase levels in a cell model."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "induction of the R489Q mutant caused a robust downregulation of ion
      channel-related genes, supporting its potential role in disrupting neuronal
      excitability"
    explanation: >-
      Independent replication of channel-gene downregulation in a human cell model with an
      inducible hotspot mutant.
  downstream:
  - target: Altered Neuronal Excitability
    causal_link_type: DIRECT
    description: >-
      Changed channel complement alters the firing properties of the neuron.

- name: Altered Neuronal Excitability
  biological_scale: CELLULAR
  description: >-
    Patch-clamp recordings from human iPSC-derived neurons show increased action potential
    firing frequency at all current injections, increased AP half width, and decreased
    depolarization speed. The direction is curated as measured rather than summarised as
    "hyperexcitability", because the three parameters do not all point the same way - the
    cell fires more often but each spike is broader and rises more slowly.
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Neuronal Hyperexcitability and Hypersynchrony"
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  evidence:
  - reference: PMID:39849855
    reference_title: "Deregulated ion channels contribute to RHOBTB2-associated developmental and epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Neurons with variants in the BTB domain region show increased AP firing
      frequency compared to the wildtype (WT)"
    explanation: >-
      The firing-rate measurement in patient-variant human neurons.
  - reference: PMID:39849855
    reference_title: "Deregulated ion channels contribute to RHOBTB2-associated developmental and epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "neurons with variants in the BTB domain region present with decreased
      depolarization speed (G) and increased AP half width (F)"
    explanation: >-
      The two waveform parameters, which move in the opposite direction to what a simple
      hyperexcitability account would predict and are therefore recorded explicitly.
  downstream:
  - target: Seizures and Developmental Encephalopathy
    causal_link_type: DIRECT
    description: >-
      Altered excitability is the proposed cellular substrate for the clinical phenotype.

- name: Domain-Specific Divergence of Cellular Consequence
  biological_scale: MOLECULAR
  description: >-
    A negative-result node, curated because it carries more weight than most positive ones
    here. In the same iPSC system, GTPase-domain missense variants and complete loss of
    RHOBTB2 produced no excitability phenotype, while BTB-domain variants did. This
    excludes haploinsufficiency as the mechanism of DEE64 and is what makes the
    accumulation account the operative one.
  evidence:
  - reference: PMID:39849855
    reference_title: "Deregulated ion channels contribute to RHOBTB2-associated developmental and epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "This revealed significantly altered neuronal activity and excitability
      resulting from BTB domain variants but not from GTPase domain variants or upon
      complete loss of RHOBTB2"
    explanation: >-
      The three-way dissociation in a single experimental system. The "not upon complete
      loss" clause is the part that rules out haploinsufficiency.
  - reference: PMID:39849855
    reference_title: "Deregulated ion channels contribute to RHOBTB2-associated developmental and epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "suggests different pathomechanisms for other RHOBTB2-related neurological and
      neurodevelopmental phenotypes associated with missense variants in the GTPase domain
      or bi-allelic truncating variants"
    explanation: >-
      The authors' own conclusion that the other RHOBTB2 variant classes act by different
      mechanisms, which is why this entry scopes itself to the BTB-domain disorder.

- name: Reduced Sodium-Potassium ATPase Abundance
  biological_scale: MOLECULAR
  description: >-
    A separate molecular arm, and the one that complicates the tidy BTB-versus-GTPase
    story. Mutant RHOBTB2 lowers Na+/K+-ATPase protein through a lysosome-dependent route,
    and the effect is most prominent in the GTPase-domain mutants - the same class that
    shows no excitability phenotype. Curated as its own node rather than folded into the
    excitability chain, because it is a distinct measurement in a different variant class.
  evidence:
  - reference: PMID:41478322
    reference_title: "Mutant-specific dysfunction of RHOBTB2 impairs mitochondrial function and Na(+)/K(+)-ATPase levels in a cell model."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "expression of mutant RHOBTB2 led to a reduction in Na+/K+-ATPase protein
      levels via a lysosome-dependent degradation pathway"
    explanation: >-
      Establishes the effect and the degradation route, which is lysosomal rather than
      proteasomal - a different pathway from the one that handles RHOBTB2 itself.
  - reference: PMID:41478322
    reference_title: "Mutant-specific dysfunction of RHOBTB2 impairs mitochondrial function and Na(+)/K(+)-ATPase levels in a cell model."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "This effect was particularly prominent in GTPase-domain mutants (D92H and
      W217C), suggesting a mechanistic link between mutant RHOBTB2 and impaired ion
      homeostasis"
    explanation: >-
      Locates the effect predominantly in the variant class that does not alter
      excitability, which is why this arm is not drawn into the BTB excitability chain.

- name: Impaired Mitochondrial Respiration
  biological_scale: CELLULAR
  description: >-
    Mitochondrial respiration is impaired by some mutants and not others, cutting across
    the domain boundary: one hotspot mutant and one GTPase-domain mutant, but not the rest.
    Curated because the accumulated hotspot protein localises to mitochondria, which makes
    a mitochondrial consequence mechanistically plausible rather than incidental.
  biological_processes:
  - preferred_term: oxidative phosphorylation
    modifier: DECREASED
    term:
      id: GO:0006119
      label: oxidative phosphorylation
  evidence:
  - reference: PMID:41478322
    reference_title: "Mutant-specific dysfunction of RHOBTB2 impairs mitochondrial function and Na(+)/K(+)-ATPase levels in a cell model."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "the R489Q and W217C mutants impaired mitochondrial respiration, whereas other
      mutants did not show detectable mitochondrial dysfunction"
    explanation: >-
      Curated PARTIAL because the finding holds for two of the mutants tested and
      explicitly not for the others, so it is a variant-specific rather than a
      disease-general mechanism.

- name: Seizures and Developmental Encephalopathy
  biological_scale: ORGANISM
  description: >-
    The clinical syndrome - early-onset epilepsy with severe intellectual disability,
    postnatal microcephaly and movement disorders.
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Recurrent Unprovoked Seizures"
  evidence:
  - reference: PMID:29276004
    reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ten individuals with a similar phenotype, including early-onset epilepsy,
      severe intellectual disability, postnatal microcephaly, and movement disorders"
    explanation: >-
      The clinical phenotype as defined in the founding cohort.

mechanistic_hypotheses:
- hypothesis_group_id: transcriptional_deregulation_model
  status: CANONICAL
  description: >-
    Accumulated RHOBTB2 indirectly dysregulates transcription of ion channel and receptor
    genes, and the resulting change in channel complement alters excitability. This is the
    account the transcriptomic data most directly support, in both the fly overexpression
    model and the inducible human cell model.
  evidence:
  - reference: PMID:39849855
    reference_title: "Deregulated ion channels contribute to RHOBTB2-associated developmental and epileptic encephalopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We now found enrichment for ion channels among the differentially expressed
      genes from RNA-Seq on fly heads overexpressing RhoBTB"
    explanation: >-
      Transcriptomic evidence for channel-gene deregulation downstream of excess RhoBTB.

- hypothesis_group_id: direct_substrate_ubiquitination_model
  status: ALTERNATIVE
  description: >-
    RHOBTB2, or the RHOBTB2-CUL3 complex, ubiquitinates ion channels or their regulators
    directly, so impaired turnover or mistargeting of the channel proteins themselves
    drives the excitability change without requiring a transcriptional step. RHOBTB2 is a
    substrate adaptor by function, so this is the mechanism its known biology would
    predict. It is currently the less directly evidenced of the two: no source available to
    this entry identifies an ion channel as a validated RHOBTB2-CUL3 substrate.
  evidence:
  - reference: PMID:15107402
    reference_title: "RhoBTB2 is a substrate of the mammalian Cul3 ubiquitin ligase complex."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "RhoBTB2 binds to the ubiquitin ligase scaffold, Cul3, via its first BTB
      domain"
    explanation: >-
      Supports the premise that RHOBTB2 operates as a CUL3 adaptor, which is what makes
      direct substrate ubiquitination a live hypothesis. Curated PARTIAL because it
      establishes the capability, not that any channel is such a substrate.

phenotypes:

- category: Neurological
  name: Early-Onset Epilepsy
  description: >-
    Seizures beginning early in life are a defining feature of the disorder.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:29276004
    reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ten individuals with a similar phenotype, including early-onset epilepsy"
    explanation: >-
      Names early-onset epilepsy as part of the shared phenotype in the founding cohort.

- category: Neurological
  name: Severe Intellectual Disability
  description: >-
    Severe intellectual impairment across the reported cohort.
  phenotype_term:
    preferred_term: Severe intellectual disability
    term:
      id: HP:0010864
      label: Severe intellectual disability
  evidence:
  - reference: PMID:29276004
    reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "including early-onset epilepsy, severe intellectual disability, postnatal
      microcephaly, and movement disorders"
    explanation: >-
      Names severe intellectual disability among the shared features.

- category: Neurological
  name: Postnatal Microcephaly
  description: >-
    Microcephaly is acquired after birth rather than congenital.
  phenotype_term:
    preferred_term: Progressive microcephaly
    term:
      id: HP:0000253
      label: Progressive microcephaly
  evidence:
  - reference: PMID:29276004
    reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "severe intellectual disability, postnatal microcephaly, and movement
      disorders"
    explanation: >-
      Records the microcephaly as postnatal, which is what the progressive term captures.

- category: Neurological
  name: Complex Motor Phenotype
  description: >-
    Every patient in the dedicated movement-disorder series had at least two distinct kinds
    of movement disorder. The composite is what is characteristic - ataxia, dystonia and
    paroxysmal chorea-like movements together - rather than any single element, which is why
    the specific components are curated separately below rather than collapsed into one
    general movement abnormality.
  frequency: OBLIGATE
  phenotype_term:
    preferred_term: Abnormality of movement
    term:
      id: HP:0100022
      label: Abnormality of movement
  evidence:
  - reference: PMID:33504645
    reference_title: "RHOBTB2 Mutations Expand the Phenotypic Spectrum of Alternating Hemiplegia of Childhood."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All had a complex motor phenotype, including at least 2 different kinds of
      movement disorder, e.g., ataxia and dystonia"
    explanation: >-
      11/11 is 100 percent, the OBLIGATE band, and the source states the count as "all".

- category: Neurological
  name: Paroxysmal Movement Disorder
  description: >-
    Episodic rather than continuous movement abnormality, present in 10 of 11 patients in
    the movement-disorder series. The paroxysmal quality is part of what makes the phenotype
    meet criteria for alternating hemiplegia of childhood.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Paroxysmal dyskinesia
    term:
      id: HP:0007166
      label: Paroxysmal dyskinesia
  evidence:
  - reference: PMID:33504645
    reference_title: "RHOBTB2 Mutations Expand the Phenotypic Spectrum of Alternating Hemiplegia of Childhood."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "10 patients had a movement disorder including paroxysmal elements, and 8
      experienced hemiplegic episodes"
    explanation: >-
      10/11 is 91 percent, in the VERY_FREQUENT band (80-99 percent).

- category: Neurological
  name: Episodic Hemiplegia
  description: >-
    Hemiplegic episodes in 8 of 11 patients - the finding that placed RHOBTB2 within the
    alternating hemiplegia of childhood spectrum. The onset is later than in classic
    ATP1A3-related AHC, from 20 months of age, which is the discriminating feature between
    the two.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Episodic hemiplegia
    term:
      id: HP:0012194
      label: Episodic hemiplegia
  evidence:
  - reference: PMID:33504645
    reference_title: "RHOBTB2 Mutations Expand the Phenotypic Spectrum of Alternating Hemiplegia of Childhood."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "10 patients had a movement disorder including paroxysmal elements, and 8
      experienced hemiplegic episodes"
    explanation: >-
      8/11 is 73 percent, in the FREQUENT band (30-79 percent). The full sentence is quoted
      rather than the hemiplegia clause alone, since the clause on its own carries no
      subject.
  - reference: PMID:33504645
    reference_title: "RHOBTB2 Mutations Expand the Phenotypic Spectrum of Alternating Hemiplegia of Childhood."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In contrast to classic AHC, commonly caused by mutations in ATP1A3, these
      events were reported later only in RHOBTB2 mutation-positive patients from 20 months
      of age"
    explanation: >-
      Records the later onset that distinguishes RHOBTB2-related AHC from the ATP1A3 form.

- category: Neurological
  name: Ataxia
  description: >-
    One of the two movement-disorder elements named as typical of the complex motor
    phenotype.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The movement disorder appears characteristic, associating ataxia, dystonia"
    explanation: >-
      Names ataxia as part of the characteristic movement-disorder composite. No
      cohort-wide count is given for ataxia alone, so no frequency band is asserted.

- category: Neurological
  name: Dystonia
  description: >-
    The second named element of the characteristic movement-disorder composite.
  phenotype_term:
    preferred_term: Dystonia
    term:
      id: HP:0001332
      label: Dystonia
  evidence:
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The movement disorder appears characteristic, associating ataxia, dystonia"
    explanation: >-
      Names dystonia as part of the characteristic composite. No cohort-wide count is given
      for dystonia alone, so no frequency band is asserted.

- category: Neurological
  name: Chorea
  description: >-
    Paroxysmal chorea-like movements, reported as part of the characteristic movement
    disorder. The source qualifies these as chorea-like rather than as chorea outright, and
    that hedge is preserved here rather than upgraded.
  phenotype_term:
    preferred_term: Chorea
    term:
      id: HP:0002072
      label: Chorea
  evidence:
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The movement disorder appears characteristic, associating ataxia, dystonia and
      paroxysmal chorea"
    explanation: >-
      Curated PARTIAL because the source describes the movements as chorea-like rather than
      as chorea, so the HP term is a close but not exact fit for the reported observation.

- category: Neurological
  name: Intellectual Disability
  description: >-
    Present in every patient in the movement-disorder series, usually moderate to severe.
    Curated alongside the severe-intellectual-disability entry above because this source
    reports the range rather than a single severity.
  frequency: OBLIGATE
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:33504645
    reference_title: "RHOBTB2 Mutations Expand the Phenotypic Spectrum of Alternating Hemiplegia of Childhood."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients had intellectual disability, usually moderate to severe"
    explanation: >-
      11/11 is 100 percent, the OBLIGATE band, stated as "all" by the source.

- category: Neurological
  name: Focal and Generalized Tonic-Clonic Seizures
  description: >-
    Seizure semiology spans the range rather than settling on one type: early-onset
    epilepsy, focal, complex partial and generalized tonic-clonic seizures all occur, and
    some patients have only late-onset febrile seizures. The breadth is itself the finding -
    there is no semiology that identifies this disorder.
  phenotype_term:
    preferred_term: Bilateral tonic-clonic seizure
    term:
      id: HP:0002069
      label: Bilateral tonic-clonic seizure
  evidence:
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The severity of the seizure types varied, from early‐onset epilepsy
      to focal, complex partial, and generalized tonic–clonic seizures"
    explanation: >-
      The reported semiology range, quoted in full. The source renders its hyphens as
      U+2010 and its dash as U+2013 and those codepoints are reproduced here rather than
      the quote being cut short of them. No cohort-wide count is given per seizure type, so
      no frequency band is asserted.

- category: Neurological
  name: Developmental Regression
  description: >-
    Intellectual disability is sometimes accompanied by regression or plateauing rather than
    by static delay alone.
  phenotype_term:
    preferred_term: Developmental regression
    term:
      id: HP:0002376
      label: Developmental regression
  evidence:
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "moderate to severe intellectual disability that was sometimes associated with
      developmental regression or plateauing"
    explanation: >-
      Records regression as a reported course. The source's "sometimes" gives no count, so
      no frequency band is asserted.

- category: Neurological
  name: Drug-Resistant Epilepsy
  description: >-
    Seizures frequently resist multiple antiseizure agents. One reported patient continued
    to have four to five seizures a month on optimally dosed triple therapy.
  phenotype_term:
    preferred_term: Refractory drug response
    term:
      id: HP:0020174
      label: Refractory drug response
  evidence:
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "with approximately 4-5 seizures/month despite having started an antiepileptic
      tritherapy with the optimal posologies"
    explanation: >-
      Quantifies the residual seizure burden on optimally dosed triple therapy in a
      genotype-confirmed patient, which is stronger than a general statement of drug
      resistance.
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "she is under a triple antiepileptic medication with partial control of her
      epileptic seizures"
    explanation: >-
      Records partial rather than absent response, which is the accurate characterisation.

- category: Neuroimaging
  name: Variable Brain MRI Findings
  description: >-
    MRI is not a consistent discriminator. Reported findings range from a normal scan
    through extracerebral space widening to brain atrophy, corpus callosum hypoplasia and
    delayed myelination, and at least one genotype-confirmed patient had normal imaging
    with no cortical atrophy despite the full clinical syndrome.
  evidence:
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "here the reported individual presented with late postnatal onset of
      microcephaly and the absence of cortical atrophy on MRI"
    explanation: >-
      Documents a genotype-confirmed patient without the cortical atrophy reported in
      others, establishing that imaging findings are variable rather than defining.
  - reference: PMID:39831600
    reference_title: "RHOBTB2 Variant p.Arg511Gln Causes Developmental and Epileptic Encephalopathy Type 64 in an Infant: A Case Report and Hotspot Variant Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cranial MRI revealed bilateral frontotemporal and falx cerebri-adjacent
      extracerebral space widening"
    explanation: >-
      An independent case with a different imaging abnormality, supporting the variability
      rather than a single characteristic pattern.

prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    60 reported DEE64 cases as of the 2025 hotspot analysis. No population prevalence
    estimate exists for this disorder.
  evidence:
  - reference: PMID:39831600
    reference_title: "RHOBTB2 Variant p.Arg511Gln Causes Developmental and Epileptic Encephalopathy Type 64 in an Infant: A Case Report and Hotspot Variant Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, 60 cases of DEE patients with RHOBTB2 variants have been reported"
    explanation: >-
      The reported case count, which is the only occurrence measure available.

environmental:
- name: Hyperthermia
  description: >-
    Hyperthermia is reported as a trigger for acute encephalopathy and epileptic seizures in
    at least five patients. It does not cause the disorder - that is entirely genetic - but
    it precipitates acute decompensation on top of it, which is what makes it worth
    recording as an exposure acting on a mechanism rather than as a phenotype.
  influences_mechanisms:
  - target: Seizures and Developmental Encephalopathy
    environmental_effect: TRIGGERS
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Precipitates acute encephalopathy and seizures in an already-susceptible brain. How
      raised temperature interacts with the accumulated-protein mechanism is not established
      by any source available to this entry, hence the unknown intermediates.
    evidence:
    - reference: PMID:35315256
      reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "At least five patients were reported to have acute encephalopathy and
        epileptic seizures triggered by hyperthermia or head trauma"
      explanation: >-
        Names hyperthermia as a reported trigger for acute encephalopathy and seizures.
  evidence:
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "epileptic seizures triggered by hyperthermia or head trauma"
    explanation: >-
      The exposure as reported.
  notes: >-
    Deliberately left without an exposure_term. ECTO was searched: its temperature terms
    (e.g. ECTO:1000007 exposure to high temperature environment) describe exposure to a hot
    environment, whereas the source says only "hyperthermia" without specifying whether the
    raised temperature was febrile or environmental. Binding an environmental-heat term
    would assert a route the source does not report, and no term is better than a wrong one.

- name: Head trauma
  description: >-
    Head trauma is the second reported precipitant of acute encephalopathy and seizures in
    the same patient group.
  influences_mechanisms:
  - target: Seizures and Developmental Encephalopathy
    environmental_effect: TRIGGERS
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Precipitates acute encephalopathy and seizures. As with hyperthermia, the interaction
      with the underlying accumulation mechanism is unestablished.
    evidence:
    - reference: PMID:35315256
      reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "acute encephalopathy and epileptic seizures triggered by hyperthermia or
        head trauma"
      explanation: >-
        Names head trauma as a reported trigger.
  evidence:
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "triggered by hyperthermia or head trauma"
    explanation: >-
      The exposure as reported.
  notes: >-
    Deliberately left without an exposure_term. ECTO was searched for mechanical, physical,
    force, impact and trauma exposures and has no term for head trauma or physical injury.

genetic:
- name: RHOBTB2
  gene_term:
    preferred_term: RHOBTB2
    term:
      id: hgnc:18756
      label: RHOBTB2
  relationship_type: CAUSATIVE
  association: >-
    Heterozygous de novo missense variants in the BTB-domain-encoding region of RHOBTB2
    cause DEE64 by impairing the protein's own proteasomal degradation, so that mutant
    RHOBTB2 accumulates. The variant spectrum is dominated by two arginine hotspots within
    the BTB domain, Arg483 and Arg511, which together account for roughly half of the ~30
    reported variants across ~60 reported cases; p.Arg511Gln, p.Arg483His and p.Arg511Trp
    each individually exceed a 10 percent incidence rate. Both hotspot residues are
    non-conserved across species, which is one reason the mechanism could not be read off
    conservation alone.
  evidence:
  - reference: PMID:29276004
    reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We have established missense variants in the BTB-domain-encoding region of
      RHOBTB2 as causative for a developmental and epileptic encephalopathy"
    explanation: >-
      The gene-disease assertion, scoped to the BTB-domain-encoding region.
  - reference: PMID:39831600
    reference_title: "RHOBTB2 Variant p.Arg511Gln Causes Developmental and Epileptic Encephalopathy Type 64 in an Infant: A Case Report and Hotspot Variant Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "More than half of the variants are located at Arg483 and Arg511 within the BTB
      domain; however, the underlying mechanism of action of these hotspot variants remains
      unexplored"
    explanation: >-
      Locates the two hotspot residues and quantifies their share of the variant spectrum.
      The second clause is quoted deliberately: the source itself records that the hotspot
      mechanism is unexplained, which is the same gap this entry's discussions describe.
  - reference: PMID:39831600
    reference_title: "RHOBTB2 Variant p.Arg511Gln Causes Developmental and Epileptic Encephalopathy Type 64 in an Infant: A Case Report and Hotspot Variant Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, 60 cases of DEE patients with RHOBTB2 variants have been reported,
      with approximately 50% of variants located at Arg483 and Arg511"
    explanation: >-
      Gives the reported case count alongside the hotspot share.
  - reference: PMID:39831600
    reference_title: "RHOBTB2 Variant p.Arg511Gln Causes Developmental and Epileptic Encephalopathy Type 64 in an Infant: A Case Report and Hotspot Variant Analysis."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "We screened 10 recurrent RHOBTB2 variants, and homology analysis revealed
      that Arg483, Arg507, and Arg511 are non‐conserved residues"
    explanation: >-
      Curated COMPUTATIONAL because this is a sequence homology analysis. The source's
      hyphen is U+2010 and is reproduced here rather than the quote being cut short of it.
  notes: >-
    Variant residue numbering differs between publications - the founding cohort and the
    2026 inducible-cell study use different numbering for the hotspot residues - and each
    is quoted here as published rather than reconciled to one convention, since no source
    available to this entry states the mapping.
    RHOBTB2 has a separate identity as a candidate tumour suppressor, where loss of
    function rather than accumulation is the disease-relevant direction. That literature is
    not curated here, but it is the reason the dosage argument in the discussions matters:
    the same gene is reported to be pathogenic when there is too little of it and when
    there is too much.

diagnosis:
- name: Trio Whole-Exome Sequencing
  description: >-
    The primary diagnostic modality. Every reported case has been ascertained molecularly,
    and the trio design is what establishes the de novo status that the variant
    interpretation depends on - a heterozygous missense variant in RHOBTB2 is only
    interpretable as causative once both parents are shown not to carry it.
  diagnosis_term:
    preferred_term: Whole Exome Sequencing
    term:
      id: NCIT:C101295
      label: Whole Exome Sequencing
  evidence:
  - reference: PMID:39831600
    reference_title: "RHOBTB2 Variant p.Arg511Gln Causes Developmental and Epileptic Encephalopathy Type 64 in an Infant: A Case Report and Hotspot Variant Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We performed whole-exome and Sanger sequencing on the patient and his
      parents"
    explanation: >-
      The trio design - proband plus both parents - stated as the method used to reach the
      diagnosis.
  - reference: PMID:29276004
    reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We have now identified de novo missense variants clustering in the
      BTB-domain-encoding region of RHOBTB2"
    explanation: >-
      The de novo determination that trio sequencing exists to make.

- name: Electroencephalography
  description: >-
    EEG typically shows focal epileptic discharges during seizures. It supports the
    epilepsy diagnosis but does not distinguish this disorder from other developmental and
    epileptic encephalopathies, so the diagnosis remains genotype-driven.
  diagnosis_term:
    preferred_term: Electroencephalography
    term:
      id: NCIT:C38054
      label: Electroencephalography
  evidence:
  - reference: PMID:39831600
    reference_title: "RHOBTB2 Variant p.Arg511Gln Causes Developmental and Epileptic Encephalopathy Type 64 in an Infant: A Case Report and Hotspot Variant Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "EEG typically reveals focal epileptic discharges during seizures"
    explanation: >-
      States the characteristic EEG finding for RHOBTB2-related encephalopathy.

treatments:
- name: Antiseizure Medication
  description: >-
    Management is symptomatic, with antiseizure drugs the mainstay. Response is genuinely
    variable rather than uniformly poor: 4 of the 7 patients with epilepsy in the
    movement-disorder series achieved seizure freedom, one infant remained seizure-free on
    oral sodium valproate over three months of follow-up, and valproate, carbamazepine and
    pyridoxine are each reported to work well in some patients - while another patient
    retained only partial control on triple therapy. No agent has disease-specific efficacy
    evidence, and no trial exists, so the agents named here are those reported to have
    helped rather than a recommended sequence.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: valproic acid
      term:
        id: CHEBI:39867
        label: valproic acid
    - preferred_term: carbamazepine
      term:
        id: CHEBI:3387
        label: carbamazepine
    - preferred_term: pyridoxine
      term:
        id: CHEBI:16709
        label: pyridoxine
  evidence:
  - reference: PMID:39831600
    reference_title: "RHOBTB2 Variant p.Arg511Gln Causes Developmental and Epileptic Encephalopathy Type 64 in an Infant: A Case Report and Hotspot Variant Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The treatment of epilepsy-related encephalopathy associated with RHOBTB2
      variants primarily relies on symptomatic treatment, with antiepileptic drugs (AEDs)
      being the mainstay"
    explanation: >-
      Establishes that management is symptomatic and drug-based.
  - reference: PMID:39831600
    reference_title: "RHOBTB2 Variant p.Arg511Gln Causes Developmental and Epileptic Encephalopathy Type 64 in an Infant: A Case Report and Hotspot Variant Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Some patients respond well to valproate, carbamazepine, and pyridoxine"
    explanation: >-
      Names the three agents bound as therapeutic_agent, and is the basis for describing the
      response as variable rather than uniformly partial.
  - reference: PMID:39831600
    reference_title: "RHOBTB2 Variant p.Arg511Gln Causes Developmental and Epileptic Encephalopathy Type 64 in an Infant: A Case Report and Hotspot Variant Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment with oral sodium valproate was initiated, and the patient
      remained seizure‐free during follow‐up"
    explanation: >-
      A single-patient success on valproate monotherapy, quoted through the operative word.
      The source's hyphens are U+2010 and are reproduced here. The quote stops before "over
      3 months" only because the source separates the numeral from the unit with a thin
      space (U+2009), which does not survive transcription.
  - reference: PMID:33504645
    reference_title: "RHOBTB2 Mutations Expand the Phenotypic Spectrum of Alternating Hemiplegia of Childhood."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seven patients had epilepsy, but of these, 4 patients achieved seizure
      freedom"
    explanation: >-
      The cohort-level counterexample to a uniformly drug-resistant reading: a majority of
      the patients with epilepsy in this series became seizure-free.
  - reference: PMID:35315256
    reference_title: "Developmental and epileptic encephalopathy related to a heterozygous variant of the RHOBTB2 gene: A case report from French Guiana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "she is under a triple antiepileptic medication with partial control of her
      epileptic seizures"
    explanation: >-
      Curated PARTIAL: the other side of the variability, a patient retaining only partial
      control on triple therapy.
  notes: >-
    An earlier draft of this entry described patients as achieving "at best partial control
    on multi-drug regimens". That was contradicted by the entry's own cited sources and has
    been corrected: seizure freedom is reported both at cohort level (4 of 7) and in a
    single-patient report on valproate monotherapy. The drug-resistant-epilepsy phenotype
    curated above remains accurate for the patients in whom it is reported; the two coexist
    because response varies across the reported population, and neither generalizes.
    The accumulation mechanism suggests lowering mutant protein abundance as a rational
    target, but no such approach has been tested, and the dosage discussion records why the
    therapeutic window is not yet defined.

animal_models:
- name: Drosophila RhoBTB overexpression and dendritic-arborization knockdown
  species: Fruit fly
  genotype: pan-neuronal RhoBTB overexpression; RhoBTB knockdown in da neurons
  publication: PMID:29276004
  description: >-
    Two complementary manipulations in one organism - raising RhoBTB to model the human
    accumulation, and lowering it to test the developmental role. The pairing is what makes
    the model informative about dosage rather than about direction alone.
  modeled_mechanisms:
  - target: Seizures and Developmental Encephalopathy
    relationship: RECAPITULATES
    fidelity: MODERATE
    limitations: >-
      The model raises wild-type RhoBTB levels rather than expressing a patient variant, so
      it tests the consequence of excess protein rather than of the specific human allele.
      Bang sensitivity is a seizure-like paralysis after mechanical shock, not spontaneous
      epilepsy.
    description: >-
      Elevated RhoBTB produces seizure susceptibility and locomotor impairment.
    readouts:
    - name: Seizure susceptibility and locomotor function
      target: Seizures and Developmental Encephalopathy
      direction: ALTERED
      interpretation: >-
        Elevated RhoBTB is associated with seizure susceptibility and severe locomotor
        defects.
      evidence:
      - reference: PMID:29276004
        reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "elevated amounts of the Drosophila ortholog RhoBTB in vivo were
          associated with seizure susceptibility and severe locomotor defects"
        explanation: >-
          The behavioural measurements behind this readout.
    evidence:
    - reference: PMID:29276004
      reference_title: "Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "elevated amounts of the Drosophila ortholog RhoBTB in vivo were associated
        with seizure susceptibility and severe locomotor defects"
      explanation: >-
        Supports treating raised RhoBTB dosage as informative for the human accumulation
        mechanism.

experimental_models:
- name: Patient-variant human iPSC-derived neurons
  experimental_model_type: IPSC_DERIVED_MODEL
  description: >-
    Mature neurons differentiated from human iPSCs carrying either patient-specific
    heterozygous missense variants in the GTPase or BTB domains, or homozygous frameshifts.
    The comparison across all three genotypes in one system is what produces the
    dissociation this entry is built around.
  publication: PMID:39849855
  modeled_mechanisms:
  - target: Altered Neuronal Excitability
    relationship: RECAPITULATES
    fidelity: HIGH
    limitations: >-
      iPSC-derived neurons model cell-intrinsic excitability and cannot report network-level
      seizure activity or the clinical course.
    description: >-
      Patch-clamp recordings across three genotype classes.
    readouts:
    - name: Action potential firing frequency
      target: Altered Neuronal Excitability
      direction: INCREASED
      interpretation: >-
        Increased at all current injections for BTB-domain variants.
      evidence:
      - reference: PMID:39849855
        reference_title: "Deregulated ion channels contribute to RHOBTB2-associated developmental and epileptic encephalopathy."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "missense variants in the BTB domain region resulted in a different pattern
          with increased firing frequency at all current injections"
        explanation: >-
          The firing-rate measurement behind this readout.
    - name: Action potential firing in complete RHOBTB2 loss
      target: Altered Neuronal Excitability
      direction: UNCHANGED
      interpretation: >-
        A real negative result. Homozygous knockout neurons fire no differently from
        wild-type, which is what excludes haploinsufficiency as the DEE64 mechanism and
        makes the accumulation account operative.
      evidence:
      - reference: PMID:39849855
        reference_title: "Deregulated ion channels contribute to RHOBTB2-associated developmental and epileptic encephalopathy."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "we observed no significantly altered pattern for the homozygous knockout
          cells compared to the wildtype"
        explanation: >-
          The negative measurement, stated directly by the source.
    evidence:
    - reference: PMID:39849855
      reference_title: "Deregulated ion channels contribute to RHOBTB2-associated developmental and epileptic encephalopathy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "We then performed patch-clamp recordings on mature neurons differentiated
        from human induced pluripotent stem cells with either homozygous frameshifts or
        patient-specific heterozygous missense variants in the GTPase or the BTB domains"
      explanation: >-
        Establishes the model as human, patient-variant, and covering all three genotype
        classes in one comparison.

discussions:

- discussion_id: controversy_transcriptional_versus_direct_ubiquitination_route
  kind: CONTROVERSY
  status: OPEN
  attaches_to:
  - pathophysiology#Increased RHOBTB2 Protein Abundance
  - pathophysiology#Deregulated Ion Channel Gene Expression
  prompt: >-
    Does accumulated RHOBTB2 deregulate ion channels by changing their transcription, or by
    ubiquitinating the channel proteins directly?
  rationale: >-
    Both accounts explain the same endpoint and neither is excluded. The transcriptional
    account has the more direct evidence - channel genes are enriched among differentially
    expressed genes in two independent systems, a fly overexpression model and an inducible
    human cell line. The direct-substrate account is what RHOBTB2's known biology predicts:
    it is a substrate adaptor for a CUL3 ubiquitin ligase, so acting on channel proteins
    themselves is its native mode of action, and a transcriptional effect would be the
    indirect one for such a protein. What is missing is an identified channel substrate; no
    source available to this entry validates an ion channel as a RHOBTB2-CUL3 target. The
    entry therefore marks the edge from accumulation to channel deregulation
    INDIRECT_UNKNOWN_INTERMEDIATES and tags it to both hypothesis groups rather than
    committing to a route. The distinction is not academic: a transcriptional mechanism
    predicts a delayed, cumulative phenotype amenable to transcriptional intervention, while
    direct ubiquitination predicts a faster, protein-level effect with different therapeutic
    handles.
  proposed_experiments:
  - experiment_id: exp_ubiquitinome_of_accumulated_rhobtb2
    name: Ubiquitinome and channel-protein turnover under RHOBTB2 accumulation
    description: >-
      In neurons expressing a BTB-domain hotspot variant, measure ion channel protein
      half-lives and ubiquitination state alongside their transcript levels. If channel
      protein turnover changes without a matching transcript change, the direct-substrate
      account is supported; if protein changes track transcript changes, the
      transcriptional account is.

- discussion_id: gap_what_the_gtpase_domain_variants_do
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Domain-Specific Divergence of Cellular Consequence
  - pathophysiology#Reduced Sodium-Potassium ATPase Abundance
  prompt: >-
    GTPase-domain variants do not alter excitability yet do reduce Na+/K+-ATPase most
    strongly. What phenotype does that combination produce?
  rationale: >-
    The two lines of evidence sit awkwardly together and the entry does not smooth them.
    In the iPSC system, GTPase-domain missense variants produced no excitability phenotype,
    which is why this entry scopes itself to the BTB-domain disorder. In the inducible cell
    system, the same domain class showed the most prominent loss of Na+/K+-ATPase, an effect
    that would ordinarily be expected to disturb ion homeostasis and hence excitability.
    Either the Na+/K+-ATPase reduction is insufficient on its own to change firing in that
    preparation, or the two systems differ in a way that matters, or the GTPase-domain
    variants cause a different disorder whose phenotype is not the one being measured. The
    founding electrophysiology paper favours the last reading, concluding that other RHOBTB2
    variant classes act by different pathomechanisms. Resolving this determines whether
    GTPase-domain variants belong in a separate entry.
  proposed_experiments:
  - experiment_id: exp_gtpase_variant_ion_homeostasis
    name: Ion homeostasis and excitability in GTPase-domain variant neurons
    description: >-
      Measure Na+/K+-ATPase abundance, intracellular sodium, and firing properties in the
      same GTPase-domain-variant iPSC neurons, rather than in separate systems. If the
      pump loss is reproduced in neurons without an excitability change, the two findings
      are genuinely dissociable and the GTPase arm needs its own mechanistic account.

- discussion_id: gap_dosage_duality_too_little_and_too_much
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Increased RHOBTB2 Protein Abundance
  prompt: >-
    If accumulation causes encephalopathy and loss is reported to permit tumour formation,
    what is the tolerated range of RHOBTB2 abundance, and does it differ by tissue?
  rationale: >-
    RHOBTB2 is unusual in being reported as pathogenic in both directions - accumulation in
    this disorder, loss of function in the tumour-suppressor literature. The neuronal data
    make the asymmetry concrete: complete loss produced no excitability phenotype in iPSC
    neurons, so neurons appear to tolerate absence while not tolerating excess. That is the
    opposite of the tissue sensitivity a simple dosage model would predict if one threshold
    governed both. Any therapeutic strategy aimed at lowering mutant RHOBTB2 needs this
    range, because the floor is set by a different tissue than the ceiling.
  proposed_experiments:
  - experiment_id: exp_graded_rhobtb2_dosage_series
    name: Graded RHOBTB2 abundance series in neurons
    description: >-
      Titrate RHOBTB2 abundance across a range spanning null to several-fold overexpression
      in the same neuronal preparation and map excitability against level, to establish
      where the neuronal phenotype begins and whether it is continuous or thresholded.

notes: >-
  Scope: this entry curates DEE64, the disorder caused by heterozygous missense variants in
  the BTB-domain-encoding region. RHOBTB2 GTPase-domain missense variants and biallelic
  truncating variants are associated with other neurological and neurodevelopmental
  phenotypes that the electrophysiology paper concludes act by different pathomechanisms;
  they are referenced here for contrast and are deliberately not modeled as part of DEE64.
  The deep-research report used to build this entry proposed GO:0004871 for the GTPase-domain
  function; that term is obsolete and was not used. It also advised excluding CL:0000598 on
  the ground that it is "dendritic cell" - the exclusion was right but the reason was not,
  since CL:0000598 is pyramidal neuron. No cell type narrower than neuron is bound here,
  because the iPSC recordings are from mature differentiated neurons without a stated
  cortical subtype.
📚

References & Deep Research

Deep Research

1
Claude Code ▸
RHOBTB2-Related Developmental and Epileptic Encephalopathy (DEE64) — Comprehensive Research Report
claude-haiku-4-5-20251001, claude-sonnet-5 15 citations 2026-08-20T12:13:27.390535

RHOBTB2-Related Developmental and Epileptic Encephalopathy (DEE64) — Comprehensive Research Report

1. Disease Information

Overview. RHOBTB2-related developmental and epileptic encephalopathy (also designated Developmental and Epileptic Encephalopathy 64, DEE64; formerly Early Infantile Epileptic Encephalopathy 64, EIEE64) is a rare, autosomal dominant neurodevelopmental disorder caused by heterozygous, almost always de novo, missense variants in RHOBTB2 (Rho-related BTB domain-containing protein 2). It was first delineated in 2018 and is characterized by early-onset (usually first-year-of-life) seizures, moderate-to-severe intellectual disability, postnatal microcephaly, hypotonia, and a distinctive polymorphic movement disorder with paroxysmal, alternating-hemiplegia-of-childhood (AHC)-like features (dystonia, ataxia, chorea-like movements) (Straub et al. 2018, PMC5777381; OMIM #618004). The disease spectrum has since expanded to include milder phenotypes from GTPase-domain variants and biallelic loss-of-function variants, so the field increasingly uses the umbrella term "RHOBTB2-related disorders" (RHOBTB2-RD) rather than a single DEE label (Genetics in Medicine 2023; Epilepsia 2026, epi.70286).

Key identifiers:

Database Identifier
OMIM phenotype #618004 — Developmental and Epileptic Encephalopathy 64 (DEE64)
OMIM gene *607352 — RHOBTB2
HGNC HGNC:18756 (RHOBTB2)
NCBI Gene 23221
Ensembl ENSG00000008853
UniProt Q9BYZ6
Cytogenetic location 8p21.3 (GRCh38: chr8:22,950,813–23,020,199)
GARD Developmental and epileptic encephalopathy, 64 (GARD ID 13681)
ClinVar Multiple RCVs, e.g. RCV000656374 for c.1465C>T (p.Arg489Trp)
MONDO A MONDO term unifying DEE64 is expected to exist (mapped from OMIM:618004) but could not be independently confirmed via web search in this session — verify directly at mondo.monarchinitiative.org before curating

Synonyms/alternative names: RHOBTB2-related developmental and epileptic encephalopathy; Early Infantile Epileptic Encephalopathy 64 (EIEE64) — older nomenclature; RHOBTB2-related disorders (RHOBTB2-RD, encompassing DEE64 plus the milder GTPase-domain and biallelic-variant phenotypes); the protein/gene is also known by the alias DBC2 ("Deleted in Breast Cancer 2") and p83.

Evidence basis: Nearly all published knowledge derives from aggregated case series and case reports (patient-level clinical, EEG, MRI, and genetic data), i.e., disease-level literature rather than large-scale EHR aggregation. The largest cohort to date integrates 12 Chinese patients with 79 previously published international cases (~91 total) (Epilepsia 2026); earlier landmark series include the original 10-patient description (PMC5777381), a 34-patient early series, and the 11-patient AHC-spectrum expansion (Zagaglia et al. 2021, Neurology).

2. Etiology

Disease causal factor: Monogenic — heterozygous, predominantly de novo missense variants in RHOBTB2, an atypical Rho GTPase family gene (8p21.3). No environmental or infectious causal factor is implicated; this is a purely genetic (Mendelian) disorder within dismech's "Mendelian" category classification.

Genetic risk factors: - Causal variants: De novo heterozygous missense variants clustering in the two BTB (Broad-complex, Tramtrack, Bric-à-brac) domains — hotspots at Arg483 (p.Arg483His, recurrent) and Arg511 (p.Arg511Trp, p.Arg511Gln, p.Arg511Gly, all recurrent) account for "more than half" of reported BTB-domain variants (PMC11744465; Epilepsia 2026, reporting 75% of Chinese-cohort variants in the BTB domain with p.Arg483His as a conserved hotspot). Other BTB-region variants include p.(Ala471Val), p.(Ala474Gly), p.(Arg507Cys), p.(Arg489Trp) — the latter confirmed de novo in the French Guiana case report (Defo et al. 2022, PMC9184662). - A second class of variants affects the N-terminal GTPase domain — e.g., p.(Asp114His), p.(Arg116Cys), p.(Arg154Gln), p.(Arg154Leu) — and is mechanistically and phenotypically distinct (see §6). - Biallelic (recessive) variants: Homozygous/compound-heterozygous splice-site and truncating variants (e.g., p.(Ser543Alafs52)) have been described in 9 families, showing that complete loss of RHOBTB2 function is also pathogenic, producing "variable neurodevelopmental phenotypes" distinct from the dominant gain-of-function BTB presentation (GIM 2023). - Constraint metrics (gnomAD pLI/LOEUF/missense-Z) could not be retrieved directly in this session (page was JS-rendered); prior functional work notes ExAC-era constraint data suggested RHOBTB2 tolerates loss-of-function variants, arguing against simple haploinsufficiency as the dominant-disease mechanism (PMC5777381) — consistent with the biallelic-LOF-vs-dominant-missense dichotomy above. This should be independently verified against the current gnomAD v4 browser before curation. - Modifier genes: None specifically established; CEBPA* has been proposed as an upstream transcriptional regulator of RHOBTB2 expression in a rat prenatal-malnutrition model (see §15), but this is not a human disease modifier per se.

Environmental risk/trigger factors: Not causal, but recognized precipitants of acute encephalopathic/seizure exacerbation in already-affected individuals: - Fever/hyperthermia — recurring trigger for acute encephalopathy and status epilepticus episodes. - Head trauma (including mild) — documented as a trigger for acute encephalopathy in RHOBTB2 patients (Neurology Genetics, "Acute encephalopathy after head trauma in a patient with a RHOBTB2 mutation"; Neurología English Edition, "Mild head trauma: Acute encephalopathy trigger..."). At least five patients across the literature have had acute encephalopathy/seizures triggered by hyperthermia or head trauma, with severe EEG abnormalities and abnormal MRI (hemisphere swelling, restricted diffusion) during these episodes.

Protective factors: None identified in the literature reviewed.

Gene-environment interactions: The fever/trauma-triggered encephalopathy pattern suggests a gene-environment interaction in which the already-destabilized RHOBTB2 protein/ion-channel network has reduced tolerance for physiological stress, but no formal GxE study has been published.

3. Phenotypes

Core clinical features (with suggested HPO terms; frequencies drawn from the literature reviewed — verify against the largest cohort, Epilepsia 2026, for precise percentages before final curation)

Phenotype Category Onset/Course Frequency (literature) Suggested HPO term
Seizures (multiple types: tonic-clonic, focal clonic, myoclonic, epileptic spasms) Symptom/clinical sign Onset typically <12 months, some as early as 4 days postnatal Core/near-universal feature HP:0001250 (Seizure); HP:0002069 (Bilateral tonic-clonic seizure); HP:0002123 (Generalized myoclonic seizure)
Drug-resistant/refractory epilepsy Clinical course Chronic Common — many patients remain seizure-prone despite polytherapy HP:0011722 (Drug-resistant seizures, i.e., "intractable epilepsy")
Severe intellectual disability / developmental delay Behavioral/cognitive From infancy, static-to-progressive Core feature, most patients HP:0001249 (Intellectual disability); HP:0001263 (Global developmental delay)
Postnatal microcephaly Physical/laboratory (growth) Postnatal onset (often not present at birth; e.g., French Guiana case emerged at 9 months, -2.5 SD) Frequent (e.g., 5 of a reported series had microcephaly, -3 to -4.5 SD) HP:0005484 (Postnatal microcephaly)
Hypotonia Physical sign Infancy onward Common HP:0001252 (Hypotonia)
Movement disorder — dystonia Physical sign Variable, often paroxysmal Common HP:0001332 (Dystonia)
Movement disorder — ataxia Physical sign Variable Common HP:0001251 (Ataxia)
Paroxysmal chorea-like movements / choreoathetosis Physical sign Episodic Characteristic HP:0002072 (Chorea); HP:0002119 (Ventriculomegaly — not relevant, omit)
Alternating hemiplegia of childhood (AHC)-like episodes Physical sign Paroxysmal, episodic Reported in ~84% of cases per one review; established as a distinct expanded phenotype (Zagaglia 2021) HP:0032794 (Alternating hemiplegia — check exact HPO term)
Poor/absent speech Behavioral Static Common HP:0002465 (Poor speech) or HP:0001344 (Absent speech)
Motor delay ranging to complete lack of head control / non-ambulation Physical sign Progressive spectrum Variable severity HP:0001270 (Motor delay)
Nonspecific facial dysmorphism Physical sign Congenital Common but nonspecific HP:0001999 (Abnormal facial shape)
Acute encephalopathy episodes (fever/trauma-triggered) Clinical course Episodic, triggered Documented in ≥5 reported patients HP:0006846 (Encephalopathy, episodic)
Poor postnatal growth Physical sign Postnatal Common ("many patients had poor overall postnatal growth") HP:0008897 (Postnatal growth retardation)

Genotype-linked phenotype severity (see also §6, §9): - BTB-domain variants → earlier seizure onset, more severe DEE, drug-resistant epilepsy, and the full AHC-like movement disorder. - GTPase-domain variants → broader, generally milder spectrum: mild-to-moderate intellectual disability, learning difficulties, developmental regression in some, and — per the mechanistic study below — seizures that are typically better controlled with antiseizure medication (HMG 2025, PMC/Oxford Academic; GIM 2023). - Biallelic loss-of-function variants → variable neurodevelopmental phenotypes distinct from the classic dominant BTB presentation. - A milder phenotype was also correlated with a specific variant, p.(Ala474Gly), in the original ten-patient cohort (PMC5777381).

Quality of life impact: No disease-specific EQ-5D/SF-36/PROMIS data were located. Qualitatively, the combination of drug-resistant epilepsy, severe intellectual disability, and a debilitating paroxysmal movement disorder (with episodic AHC-like crises) is described as substantially disabling, with motor function ranging "from total lack of head control and inability to walk to walking with a broad-based or unsteady gait" (Frontiers Pediatrics 2024).

4. Genetic/Molecular Information

Causal gene: RHOBTB2 (HGNC:18756; NCBI Gene 23221; Ensembl ENSG00000008853; OMIM *607352). Encodes an atypical Rho GTPase with a modular architecture: N-terminal GTPase domain, proline-rich region, tandem BTB1–BTB2 domains, and a conserved C-terminal region (Wikipedia/HGNC; RhoBTB family review).

Pathogenic variant classification and type: - Predominantly de novo heterozygous missense variants, clustering in the BTB1/BTB2 domain region (dominant, gain-of-function-like mechanism) or the N-terminal GTPase domain (distinct, milder mechanism). - Recurrent/hotspot residues: Arg483 and Arg511 (BTB domain) — collectively >50% of BTB variants. - Documented BTB-domain variants: p.(Ala471Val), p.(Ala474Gly), p.(Arg483His), p.(Arg489Trp), p.(Arg507Cys), p.(Arg511Gly), p.(Arg511Trp), p.(Arg511Gln), p.(Ser543Alafs52 — homozygous/biallelic). - Documented GTPase-domain variants: p.(Asp114His), p.(Arg116Cys), p.(Arg154Gln), p.(Arg154Leu). - Biallelic (recessive) variants: splice-site and truncating variants reported in 9 families (GIM 2023), establishing complete loss-of-function as a second, distinct disease mechanism. - ACMG/ClinVar classification: individual variants (e.g., c.1465C>T p.(Arg489Trp), ClinVar RCV000656374) are classified case-by-case; consult ClinVar/ClinGen directly for current classifications before curation. - Allele frequency: Pathogenic variants are essentially absent from population databases (gnomAD) consistent with de novo, severe, dominant disease — exact gnomAD constraint values (pLI/LOEUF) should be pulled directly from the gnomAD browser (not confirmed in this session due to a fetch limitation). - Somatic vs. germline: Germline (constitutional) de novo variants for DEE64; separately, somatic* loss-of-function/deletion events in RHOBTB2 are described in cancer (see below) — these are a biologically related but clinically distinct phenomenon.

Functional consequence — the central genotype-mechanism finding:

"Mutant RHOBTB2 was more abundant than the wild-type, most likely because of impaired degradation in the proteasome" — and this effect was reversed by proteasome inhibition, "confirming proteasomal degradation impairment as the primary mechanism" for BTB-domain variants (Straub et al. 2018, PMC5777381).

This is a gain-of-function / dominant-negative-like accumulation mechanism (increased mutant protein abundance due to impaired 26S proteasomal degradation), not simple haploinsufficiency — a genuinely unusual, notable mechanism among developmental encephalopathy genes. Co-immunoprecipitation studies found no differential CUL3 binding between mutant and wild-type RHOBTB2, indicating the pathogenic effect operates downstream of/independent from simple loss of CUL3 engagement (PMC5777381).

By contrast, GTPase-domain variants do not impair proteasomal degradation — RHOBTB2 protein levels remain normal — pointing to an alternative (likely direct protein-protein-interaction or GTPase-cycle) pathogenic mechanism.

Epigenetic information: In cancer contexts (not DEE), RHOBTB2 promoter CpG-island hypermethylation causes epigenetic silencing and loss of tumor-suppressor function (see §6). No epigenetic mechanism has been specifically described for the DEE64 phenotype.

Chromosomal abnormalities: No recurrent large-scale chromosomal rearrangement (translocation, aneuploidy) is described for DEE64; disease is driven by point/small-indel variants within RHOBTB2.

5. Environmental Information

  • Environmental/toxin factors: None established as causal for RHOBTB2-RD; disease is monogenic.
  • Lifestyle factors: Not applicable as causal factors; however, avoidance of known triggers (fever control, minimizing head trauma risk) is a practical management consideration given the documented trigger relationship (§2).
  • Infectious agents: Not causal, but febrile illness (of any infectious etiology) is a recognized trigger for acute encephalopathic crises in affected individuals, not a cause of the underlying genetic disease.

6. Mechanism / Pathophysiology

Molecular function of RHOBTB2 (baseline biology)

RHOBTB2 (a.k.a. DBC2) is a substrate-specific adaptor for a Cullin-3 (CUL3)–RBX1-based E3 ubiquitin ligase complex (Wilkins et al., PMC2749729; Berthold et al., "RhoBTB2 is a substrate of the mammalian Cul3 ubiquitin ligase complex"). Mechanism: 1. RHOBTB2's BTB domains bind CUL3's N-terminal region. 2. RHOBTB2 recruits specific substrates for ubiquitination. 3. RBX1 recruits E2 ubiquitin-conjugating enzymes, transferring ubiquitin to the CUL3/RHOBTB2-bound substrate, building a polyubiquitin chain. 4. The polyubiquitinated substrate — and RHOBTB2 itself — is degraded by the 26S proteasome. 5. An autoregulatory mechanism exists: the non-GTP-binding GTPase domain can fold back and interact intramolecularly with the BTB region, keeping RHOBTB2 in an inactive, degradation-protected state — a proposed "closed" conformation model.

Suggested GO terms: GO:0004871 (signal transducer activity — for GTPase-domain function); GO:0031624 (ubiquitin conjugating enzyme binding); GO:0031461 (cullin-RING ubiquitin ligase complex); GO:0043161 (proteasome-mediated ubiquitin-dependent protein catabolic process); GO:0007015 (actin filament organization); GO:0016477 (cell migration).

Causal chain for DEE64 (BTB-domain, dominant/gain-of-function arm)

  1. Trigger: De novo missense variant at a BTB-domain hotspot (e.g., p.Arg483His, p.Arg511Trp/Gln/Gly).
  2. Molecular lesion: Variant impairs proteasomal recognition/degradation of RHOBTB2 without disrupting CUL3 binding → increased steady-state abundance of mutant RHOBTB2 protein in neurons.
  3. Downstream transcriptional/ion-channel effect: RNA-seq in a Drosophila overexpression model shows enrichment for differentially expressed ion channel genes, including orthologs of human voltage-gated sodium channels (paralytic → SCN1A/SCN2A/SCN3A/SCN8A), a potassium channel (slowpoke → KCNMA1/BK channel), and an ionotropic glutamate receptor (ir76a) (Human Molecular Genetics 2025).
  4. Cellular electrophysiology (human iPSC-derived neurons): Neurons carrying patient BTB-domain variants show significantly altered neuronal excitability — increased action-potential firing frequency, increased AP half-width, and decreased depolarization speed — compared to wild-type. Critically, this electrophysiological derangement was not seen in neurons with GTPase-domain variants or with complete RHOBTB2 knockout, mechanistically explaining the BTB-vs-GTPase genotype-phenotype divergence.
  5. Organismal phenotype (Drosophila): Pan-neuronal RhoBTB overexpression causes bang-sensitivity (seizure-like paralysis after mechanical shock) and severe locomotor impairment in negative-geotaxis assays; RhoBTB knockdown in dendritic arborization (da) neurons causes reduced dendritic branch number — implicating RHOBTB2 dosage in both neuronal excitability and dendritic morphogenesis (Straub et al. 2018, PMC5777381).
  6. Clinical manifestation: Neuronal hyperexcitability + disrupted dendritic architecture → seizures, developmental encephalopathy, movement disorder.

Two candidate mechanistic hypotheses remain open (not yet distinguished): (a) RHOBTB2 accumulation indirectly dysregulates ion-channel gene transcription; (b) RHOBTB2 (or a RHOBTB2-CUL3 complex) directly ubiquitinates ion channels as substrates, and impaired turnover/mistargeting of the channels themselves drives hyperexcitability.

Cell types/anatomical scale: Primarily central nervous system neurons (cortical/dendritic-arborization-type neurons in the fly model; iPSC-derived cortical neurons in the human model). Suggested CL terms: CL:0000540 (neuron); CL:0000598 (dendritic cell — not relevant, exclude); CL:0011020 (neural progenitor cell, if precursor-stage effects are modeled); consider CL:0000679 (glutamatergic neuron) given the ionotropic glutamate receptor link.

Cancer-associated mechanism (contrast arm — informs the "gain vs. loss" duality)

In sporadic cancers, loss of RHOBTB2 function — via deletions, loss-of-function variants (found in ~10% of breast cancer samples), or CpG-island promoter hypermethylation — removes its tumor-suppressor activity (failure to degrade oncogenic substrates such as Cyclin D1), promoting unchecked proliferation in breast, lung, bladder, gastric cancers, and osteosarcoma (Frontiers Pediatrics 2024; Oncogene 2016, DBC2/RhoBTB2-Musashi-2 axis). This is the biological converse of the DEE64 mechanism: precise RHOBTB2 dosage is essential — too little predisposes to malignancy, too much (via impaired degradation) is neurotoxic.

Additional hypothesized pathway: dysregulation of an E2F1–RHOBTB2 axis affecting apoptotic signaling has been proposed as contributing to the neurodevelopmental phenotype and was leveraged in an AI-guided drug-repurposing screen (see §12).

Metabolic/immune involvement: No specific metabolic pathway or immune-mediated mechanism has been reported for RHOBTB2-RD; this is a cell-intrinsic proteostasis/ion-channel-excitability disorder of the CNS.

Molecular profiling data: RNA-seq (Drosophila overexpression model) is the principal transcriptomic dataset reported; no human patient-derived multi-omics (proteomics, metabolomics, single-cell) datasets specific to RHOBTB2-RD were identified in this search.

7. Anatomical Structures Affected

Organ level: - Primary: Central nervous system (brain) — cerebral cortex (seizure generation, cognitive impairment), basal ganglia/extrapyramidal circuits (dystonia, chorea), cerebellum (ataxia). - Secondary: Growth (postnatal microcephaly, poor postnatal growth) reflects secondary CNS/systemic developmental effects rather than a distinct organ-level primary lesion. - Body systems: Nervous system (primary); musculoskeletal system secondarily affected via hypotonia/movement disorder.

Suggested UBERON terms: UBERON:0000955 (brain); UBERON:0001872 (cerebral hemisphere); UBERON:0002037 (cerebellum); UBERON:0002420 (basal ganglion).

Tissue/cell level: Cortical and dendritic-arborization neurons (per the Drosophila and iPSC modeling). RHOBTB2 tissue expression is reported as primarily neural, with lesser expression in fetal heart and lungs.

Subcellular level: Cytosol, plasma membrane, cytoskeleton (actin) per baseline RHOBTB2 biology (Wikipedia/UniProt); the ubiquitin-proteasome degradation machinery (26S proteasome) is a key subcellular locus of pathogenic mechanism. Suggested GO Cellular Component terms: GO:0005737 (cytoplasm); GO:0005886 (plasma membrane); GO:0015629 (actin cytoskeleton); GO:0000502 (proteasome complex).

Localization/lateralization: The characteristic AHC-like movement-disorder episodes are, by definition, often lateralized/alternating (hemiplegic episodes shifting sides), a distinguishing clinical feature from typical bilateral movement disorders.

8. Temporal Development

  • Onset: Congenital/neonatal predisposition with clinical onset typically in the first year of life; seizures have been documented as early as 4 days postnatal in the most severe cases. Microcephaly is typically postnatal in onset (normal head circumference at birth in documented cases, e.g., the French Guiana patient, with microcephaly emerging by 9 months).
  • Onset pattern: Acute-to-subacute onset of seizures; insidious emergence of developmental delay/regression.
  • Progression: Variable — ranges from static severe DEE with drug-resistant epilepsy and profound motor/cognitive impairment (BTB-domain variants) to a milder, more static-to-slowly-progressive course with learning difficulties (GTPase-domain variants); some patients show frank developmental regression.
  • Disease course pattern: Chronic, lifelong; punctuated by episodic/paroxysmal exacerbations — both the intrinsic AHC-like movement episodes and acute encephalopathic crises triggered by fever or head trauma.
  • Critical periods: Infancy/early childhood is the period of highest vulnerability for seizure onset and encephalopathic crises; avoidance of febrile illness complications and head trauma is a practically important window for intervention (see §13).

9. Inheritance and Population

Epidemiology: RHOBTB2-RD is an ultra-rare disorder. Approximately 91 cases have been aggregated in the most recent comprehensive cohort (12 Chinese + 79 international) (Epilepsia 2026); earlier series reported 19–34 patients. No formal population-based prevalence or incidence estimate (per 100,000) has been published; RHOBTB2-related AHC-spectrum disease is grouped among ultra-rare neurological disorders generally estimated at 1:100,000–1:1,000,000 by analogy to related AHC etiologies, but this figure is not RHOBTB2-specific and should be treated as a rough proxy, not a citable disease-specific statistic.

Inheritance pattern: Autosomal dominant for the classic BTB-domain and GTPase-domain missense phenotypes, essentially always occurring as de novo variants (parental testing consistently negative in reported trios). A separate autosomal recessive (biallelic loss-of-function) inheritance pattern has been described in 9 families for splice-site/truncating variants (GIM 2023), producing a distinct, variable neurodevelopmental phenotype.

Penetrance/expressivity: Appears fully penetrant for the dominant missense variants (all reported carriers are symptomatic), with highly variable expressivity — phenotype severity ranges from classic severe DEE64 to milder learning-difficulty/movement-disorder-predominant presentations, correlating with variant domain location (BTB vs. GTPase) as detailed in §6.

Genetic anticipation: Not applicable/not reported — this is not a repeat-expansion disorder.

Germline mosaicism: Not specifically documented for RHOBTB2 in the sources reviewed; general possibility exists for any de novo dominant disorder but should be discussed with families as a theoretical (low) recurrence-risk consideration, not confirmed by RHOBTB2-specific mosaicism reports found here.

Founder effects / consanguinity: No founder-population effect reported for the dominant missense variants (occur as independent de novo events across diverse populations/ethnicities, including reports from France/French Guiana, China, UK, and elsewhere). The biallelic/recessive presentation would be expected to show increased likelihood in consanguineous families, consistent with general autosomal-recessive genetics, though this was not explicitly detailed in the sources reviewed.

Carrier frequency: Not applicable in the classical sense for a dominant de novo disorder (BTB/GTPase arm); for the recessive biallelic arm, population carrier frequency of individual loss-of-function alleles is expected to be very low (ultra-rare), consistent with a rare recessive disorder, but no specific carrier-frequency data were located.

Population demographics: Cases reported across multiple continents/ethnicities (European, Chinese, South American [French Guiana]) with no described geographic clustering or strong ethnic predisposition. Sex ratio: not clearly skewed in the sources reviewed (no strong male:female bias reported); should be checked against the largest published cohort (Epilepsia 2026) directly if precise ratios are needed for curation. Age distribution: pediatric-onset disorder by definition (first year of life), tracked through childhood in the reported literature (long-term adult natural history data are limited given the disorder's recent [2018] delineation).

10. Diagnostics

Clinical/laboratory tests: No RHOBTB2-specific biochemical biomarker has been identified; diagnosis is clinical + genetic. Standard metabolic/laboratory work-up is used mainly to exclude alternative etiologies of DEE.

Imaging: - Brain MRI is frequently normal, particularly early in the disease course (e.g., normal at both 3 and 10 months in the French Guiana case) — an important diagnostic point, since normal neuroimaging does not exclude RHOBTB2-RD. - During acute encephalopathic crises (fever/trauma-triggered), MRI can show transient abnormalities: hemisphere swelling and/or reduced diffusion in various brain regions.

Electrophysiology: - EEG findings are variable; documented findings include slowed background electrogenesis for age (delta rhythm) and diffuse/focal polyspikes (e.g., right-hemisphere polyspikes in the French Guiana case). During acute encephalopathic episodes, severe EEG abnormalities have been documented. - No RHOBTB2-specific EEG signature/biomarker (e.g., a pathognomonic ictal or interictal pattern) has been established.

Genetic testing (primary diagnostic modality): - Whole exome sequencing (WES) or whole genome sequencing (WGS), typically as a trio (proband + both parents) to confirm de novo status, is the standard diagnostic approach given the phenotypic heterogeneity and lack of a pathognomonic clinical sign. - Epilepsy/DEE gene panels that include RHOBTB2 are also used in clinical practice (e.g., Genomics England PanelApp lists RHOBTB2 under both "Early onset or syndromic epilepsy" and "Paroxysmal central nervous system disorders" panels). - Single-gene Sanger confirmation follows panel/WES identification of a candidate variant. - Chromosomal microarray, karyotyping, FISH, and mitochondrial DNA testing are not primary diagnostic tools for this disorder but are commonly part of a broader DEE diagnostic work-up to exclude other etiologies before/alongside RHOBTB2 sequencing.

Clinical diagnostic criteria: No formal consensus clinical diagnostic criteria (e.g., DSM/ICD-style) exist specifically for RHOBTB2-RD; diagnosis relies on the combination of characteristic phenotype (early-onset DEE + paroxysmal movement disorder ± AHC-like features + postnatal microcephaly) plus confirmatory molecular genetic testing.

Differential diagnosis: Most importantly, ATP1A3-related alternating hemiplegia of childhood (classic AHC), given phenotypic overlap in the paroxysmal movement-disorder domain — RHOBTB2-RD is explicitly framed in the literature as an AHC-mimicking/AHC-spectrum-expanding disorder distinct from ATP1A3-AHC ("RHOBTB2-Associated Neurological Phenotypes and Underlying Mechanisms: Alternating Hemiplegia of Childhood Beyond ATP1A3," Diseases journal). Other DEE genes (SCN1A, SCN2A, SCN8A, STXBP1, CDKL5, etc.) should be considered in the broader differential given phenotypic overlap in early-onset DEE.

Screening: No population-based newborn or carrier screening program exists for this ultra-rare de novo disorder; cascade/family screening is relevant primarily for the rare biallelic/recessive presentation.

11. Outcome/Prognosis

  • Survival/mortality: No disease-specific mortality rate or life-expectancy data were located in the sources reviewed; RHOBTB2-RD is not classically described as directly life-limiting in the literature surveyed, though acute encephalopathic crises (fever/trauma-triggered, with severe EEG changes and MRI abnormalities) represent a recognized acute risk requiring urgent management.
  • Morbidity/function: Substantial chronic morbidity from the combination of drug-resistant epilepsy, severe intellectual disability, and the paroxysmal movement disorder. Motor function outcomes span a wide spectrum — from complete lack of head control and non-ambulation to walking with a broad-based/unsteady gait — reflecting the broad genotype-driven severity spectrum.
  • Complications: Acute encephalopathy episodes (fever- or trauma-triggered) with transient MRI/EEG abnormalities represent the most severe recognized complication category.
  • Prognostic factors: The clearest identified prognostic determinant is variant location — BTB-domain variants predict earlier onset, more severe DEE, and drug-resistant epilepsy; GTPase-domain variants predict a milder, more variable course with better anti-seizure medication responsiveness. This genotype-phenotype correlation is the primary prognostic biomarker currently available (no molecular/biochemical prognostic biomarker has been validated).

12. Treatment

Pharmacotherapy (seizure management — current standard of care): Antiseizure medications are the mainstay, with the most frequently used agents being: - Valproic acid (CHEBI:39867) — NCIT: Pharmacotherapy (NCIT:C15986) - Levetiracetam (CHEBI:6437) - Topiramate (CHEBI:9366) - Oxcarbazepine (CHEBI:7824)

These were used, for example, in combination (triple therapy: topiramate + valproic acid + oxcarbazepine) in the French Guiana case, achieving partial but incomplete seizure control (PMC9184662). Explicitly noted limitation: "no treatments have been identified that address the other symptoms or the underlying pathophysiological mechanisms" — i.e., current therapy is purely symptomatic for seizures and does not target the movement disorder, cognitive impairment, or the proteasomal-degradation mechanism itself.

Pharmacogenomics: No RHOBTB2-specific pharmacogenomic (drug-metabolism) data were identified.

Emerging/experimental therapeutics: - AI-guided drug repurposing: A computational screen implicated NSAIDs — celecoxib (CHEBI:41423), diclofenac (CHEBI:47381), indomethacin (CHEBI:5773) — as potential RHOBTB2 pathway modulators, acting via downregulation of E2F1 (the hypothesized apoptotic-signaling axis noted in §6). This is preclinical/in-silico and not yet in clinical use (Frontiers Pediatrics 2024). - Antisense oligonucleotide (ASO) therapy targeting RHOBTB2 mRNA is described as "in development" — consistent with a rational precision-medicine approach given the gain-of-function/protein-accumulation mechanism (an ASO-mediated knockdown strategy would directly counter the pathogenic mechanism of excess mutant protein). No clinical trial identifier (NCT) was located for this program in the sources reviewed — this should be verified against ClinicalTrials.gov directly before curation, as no active registered trial was confirmed.

Surgical/interventional: No disease-specific surgical intervention (e.g., epilepsy surgery) was described as a standard approach in the literature reviewed, though it may be considered on a case-by-case basis for focal drug-resistant epilepsy as in general DEE management.

Supportive/rehabilitative care: Physical therapy, occupational therapy, and speech/communication therapy are inferred standard supportive management for the motor and speech impairments, consistent with general DEE management, though not explicitly detailed with RHOBTB2-specific outcome data in the sources reviewed. NCIT: Physical Therapy (NCIT:C15302); Rehabilitation (NCIT:C15315).

Treatment outcomes: Explicitly drug-resistant epilepsy is common; the disorder is generally refractory to standard antiseizure polytherapy in the more severe (BTB-domain) cases, while GTPase-domain-variant patients show comparatively better seizure control.

13. Prevention

Because RHOBTB2-RD arises from de novo germline variants with no known environmental causal contribution, classic primary prevention (risk-factor modification) is not applicable to preventing disease occurrence.

  • Tertiary prevention (preventing complications in affected individuals): Given the documented fever- and head-trauma-triggered acute encephalopathy phenomenon, practical management should include prompt, aggressive fever control and head-injury precaution/avoidance counseling as a tertiary-prevention strategy to reduce acute encephalopathic crisis risk — this is directly supported by the trigger literature in §2, though no formal prospective prevention trial has validated this approach.
  • Genetic counseling: Given the essentially universal de novo occurrence for the dominant missense variants, recurrence risk for future pregnancies in a family with an affected child is low (approximating general population risk, with residual risk from theoretical parental germline mosaicism) — standard genetic counseling practice for de novo dominant disorders. For the rare biallelic/recessive presentation, standard autosomal-recessive recurrence-risk counseling (25% per pregnancy) applies once both parental carrier variants are confirmed.
  • Prenatal/preimplantation testing: Once a familial variant is known (e.g., after an affected child), prenatal diagnosis or preimplantation genetic testing could theoretically be offered for future pregnancies, per standard practice for known de novo monogenic disorders — no RHOBTB2-specific prenatal testing program was documented in the sources reviewed.
  • Screening: No population or newborn screening program exists or is anticipated for this ultra-rare disorder.

14. Other Species / Natural Disease

No naturally occurring RHOBTB2-associated disease in non-human species (companion animals, livestock, wildlife) was identified in this search — no OMIA (Online Mendelian Inheritance in Animals) entry or veterinary case report surfaced. This appears to be a human-genetics-delineated disorder without a described natural-disease veterinary correlate at this time. This gap should be explicitly noted as "not identified" rather than assumed absent, since OMIA was not directly queried in this session.

Orthology: The Drosophila melanogaster ortholog is RhoBTB (single fly gene corresponding to the mammalian RhoBTB1/2/3 subfamily), used extensively as the primary in vivo functional model (see §6, §15). No specific mouse, rat, zebrafish, or other vertebrate ortholog gene ID was independently retrieved in this session beyond the human/mouse Wikipedia infobox coordinates (mouse Rhobtb2 at chromosome 14, band 14 D2).

15. Model Organisms

Model type System Manipulation Key findings
Invertebrate (fly) Drosophila melanogaster, ortholog RhoBTB Pan-neuronal overexpression (mimicking BTB-domain gain-of-function/protein-accumulation) Bang-sensitivity (seizure-like paralysis/spasms post-mechanical-shock); severe locomotor impairment (negative geotaxis assay); RNA-seq shows ion-channel-gene enrichment among differentially expressed genes (Straub 2018, PMC5777381; HMG 2025)
Invertebrate (fly) Drosophila, dendritic arborization (da) neurons Pan-neuronal/tissue-specific RhoBTB knockdown Significantly reduced dendritic branch number and reduced total dendrite size/length, implicating RHOBTB2 in dendritic development; complete RhoBTB-null flies show seizures and motor degeneration
Cellular/patient-derived Human iPSC-derived neurons (patient-specific lines) Endogenous patient variants: BTB-domain vs. GTPase-domain vs. complete knockout, studied by whole-cell patch-clamp BTB-domain variants → significantly altered excitability (increased AP firing frequency and half-width, decreased depolarization speed); GTPase-domain variants and complete knockout → no significant electrophysiological alteration, directly explaining the clinical genotype-phenotype divergence (HMG 2025)
Cell line (biochemical) HEK293 transfection Overexpression of wild-type vs. mutant RHOBTB2, ± proteasome inhibitor Confirms impaired proteasomal degradation as the proximate mechanism of BTB-variant protein accumulation (PMC5777381)
Mammalian (indirect) Rat, prenatal-malnutrition model Not a direct patient-variant model; used to study RHOBTB2's normal role in learning/synaptic development Validated RHOBTB2's role in learning and synaptic development; identified Cebpa as a transcriptional regulator of RHOBTB2 expression

Explicit modeling gap: As of the most recent review located, "no patient-variant animal models [e.g., knock-in mouse] have been generated" to study RHOBTB2-related neurodevelopmental disease in vivo in a mammalian system — the iPSC-neuron and Drosophila systems represent the current state of the art, with the mammalian (mouse knock-in) gap flagged as an open need in the field (Frontiers Pediatrics 2024).

Model limitations: The Drosophila system captures dosage-sensitive seizure/locomotor and dendritic phenotypes but cannot recapitulate human-specific cortical architecture or the AHC-like alternating-hemiplegia clinical phenomenon. iPSC-neuron patch-clamp captures single-cell excitability changes but not network-level or whole-organism seizure semiology. No model to date recapitulates the postnatal-microcephaly or the fever/trauma-triggered acute-encephalopathy phenotypes specifically.

Summary of Key Curation-Relevant Ontology Term Suggestions

  • Gene/protein: HGNC:18756 (RHOBTB2); UniProt Q9BYZ6
  • Disease: OMIM:618004 (DEE64); OMIM:607352 (gene locus entry) — MONDO ID should be independently confirmed
  • HPO (partial): HP:0001250 (Seizure), HP:0001249 (Intellectual disability), HP:0005484 (Postnatal microcephaly), HP:0001252 (Hypotonia), HP:0001332 (Dystonia), HP:0001251 (Ataxia), HP:0002072 (Chorea), HP:0011722 (Drug-resistant seizures), HP:0001263 (Global developmental delay), HP:0006846 (episodic encephalopathy — verify exact term)
  • GO (mechanism): GO:0043161 (proteasome-mediated ubiquitin-dependent protein catabolic process), GO:0031461 (cullin-RING ubiquitin ligase complex), GO:0000502 (proteasome complex)
  • CL: CL:0000540 (neuron)
  • UBERON: UBERON:0000955 (brain), UBERON:0002420 (basal ganglion), UBERON:0002037 (cerebellum)
  • CHEBI (treatments): CHEBI:39867 (valproic acid), CHEBI:6437 (levetiracetam), CHEBI:9366 (topiramate), CHEBI:7824 (oxcarbazepine)
  • NCIT (treatment action): NCIT:C15986 (Pharmacotherapy)

Notable Evidence Gaps / Caveats for Curators

  1. gnomAD constraint metrics (pLI, LOEUF, missense-Z) could not be retrieved directly in this session — verify at gnomad.broadinstitute.org before curating population-constraint claims.
  2. MONDO ID for DEE64 was not independently confirmed — verify at mondo.monarchinitiative.org.
  3. Several full-text sources (OMIM full clinical synopsis, GIM 2023 full text, Epilepsia 2026 full text) returned HTTP 403 on direct fetch; the summaries above rely on search-engine-indexed excerpts and secondary citations (Frontiers Pediatrics 2024 review, GeneCards, Wikipedia) rather than full primary-text extraction — snippets used for KB curation should be independently re-verified against the cached/fetched primary abstract per dismech's evidence SOP before being committed as evidence.snippet values.
  4. No OMIA veterinary/natural-disease entry was directly queried — treat "no natural disease in other species identified" as an evidence gap, not a confirmed negative.
  5. Precise phenotype frequency percentages (e.g., % with each seizure type, exact sex ratio) should be pulled directly from the largest cohort study (Epilepsia 2026, 91 cases) once full-text access is available, as only fragmentary percentages were recoverable via search snippets in this session.

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 10
Resolved 10
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 1
Quoted claims found in source 0
Quoted claims not found in source 1
References weighed for topical relevance 10
On topic 7
Off topic 0

Quotes not found in the cited source

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

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

  • DOI:10.3389/fped.2024.1448793 (abstract only): "from total lack of head control and inability to walk to walking with a broad-based or unsteady gait"
  • Text part not found as substring: 'from total lack of head control and inability to walk to walking with a broad-based or unsteady gait' (note: only abstract available for DOI:10.3389/fped.2024.1448793, full text may contain this excerpt)