🏷

Classifications

Harrison's Part

🔗

Mappings

MONDO

MONDO:0030606 Bryant-Li-Bhoj neurodevelopmental syndrome 1

Primary MONDO disease identifier for this entry.

👪

Inheritance

1

Autosomal dominant inheritance HP:0000006

BLBS1 is autosomal dominant and, for H3-3A specifically, every variant with available parental testing has been de novo, so recurrence risk to siblings is low. This is a point of difference from H3-3B, where a maternally inherited allele and more variant-type diversity have been described. A single altered allele of one of the two H3.3 genes is sufficient: 75% of H3.3 alleles remain wild type, which is why the phenotype is read as gain of function or dominant negative rather than as loss of dosage.

Autosomal dominant inheritance

Show evidence (3 references)

PMID:37782742 SUPPORT Human Clinical

"BRYLIB is expressed in an autosomal dominant manner and typically caused by a de novo H3-3A (H3F3A) or H3-3B (H3F3B) pathogenic variant."

GeneReviews statement of the inheritance mode and the de novo origin.

PMID:38678163 SUPPORT Human Clinical

"the time of this report, all H3-3A variants are heterozygous de novo missense variants when parents are available, though inheritance was undetermined for three individuals"

The H3-3A-specific observation that distinguishes BLBS1 from BLBS2 on inheritance and variant type.

PMID:33268356 SUPPORT Human Clinical

"Since there are two genes that produce H3.3, a heterozygous mutation in one of them means that 75% of the alleles are WT."

Establishes the allelic arithmetic behind the gain-of-function reading of a heterozygous variant.

?

Discussions and Knowledge Gaps

3

What accounts for the phenotypic variability that gene, protein domain and sex together fail to explain - including variability between individuals carrying the same H3-3A allele?

KNOWLEDGE GAP OPEN blbs1_genotype_phenotype_unexplained

Attached to

pathophysiology#De Novo H3-3A Variant Altering Histone H3.3 phenotypes#

The 2024 cohort tested three candidate explanatory variables against the phenotype and found that variant location and affected gene contribute more than sex, but that none of them accounts for the observed variation. Four individuals sharing H3-3A p.Thr45Ile have substantially different presentations. The founding report had gone further, concluding that neither variant location nor which gene was involved affected the phenotype at all; the larger cohort softened that to statistical trends. Either way there is a determinant that has not been found, and the authors raise gene-environment interaction as a possibility precisely because histones sit at the genetics-epigenetics interface.

Show evidence (3 references)

PMID:38678163 SUPPORT Human Clinical

"Since these variables do not account for all BLBS phenotypic variability, these findings suggest that additional factors may play a role in modifying the phenotypes of affected individuals."

States the residual, unexplained variability directly.

PMID:38678163 SUPPORT Human Clinical

"Notably, phenotypic heterogeneity was present even amongst individuals harboring the same variant."

Shows that the unexplained variability persists at fixed genotype, which rules out variant identity as the missing determinant.

PMID:33268356 SUPPORT INDIRECT Human Clinical

"The mutations are spread throughout the coding sequence, and neither the location of the mutation nor whether the mutation is in H3F3A or H3F3B appears to affect the phenotype."

The earlier and stronger negative claim, since qualified by the larger cohort. It is marked INDIRECT because it overstates the absence of any correlation, so the knowledge gap follows from it only once that overstatement is discounted.

Do germline H3.3 variants confer cancer predisposition, given that the same residues are oncogenic when altered somatically?

KNOWLEDGE GAP OPEN blbs1_cancer_predisposition

Attached to

pathophysiology#Deregulated Cell Proliferation

Patient cells show up-regulated mitosis and division programs and increased proliferative capacity, and germline substitutions occur at residues whose somatic counterparts drive paediatric glioma - yet no malignancy occurred in the founding cohort. A 2025 survey of 192 individuals with germline histonopathies identified the second known individual with both a germline histonopathy and a cancer diagnosis, putting community-wide incidence at 1%, below the 5% threshold at which routine tumour surveillance is recommended. So the current answer is "no surveillance", reached on a denominator small enough that the question stays open, and the authors name it as outstanding.

Show evidence (3 references)

PMID:40241305 REFUTE Human Clinical

"Notably, the community-wide cancer incidence is currently 1%, which falls below the recommended 5% cut off for routine surveillance."

Argues against clinically actionable cancer predisposition at present, which is why no surveillance treatment is curated in this entry.

PMID:40241305 SUPPORT Human Clinical

"the value of ongoing translational work to address the outstanding question of cancer predisposition for individuals living with germline histonopathies"

The authors name cancer predisposition as an outstanding question, which is the gap recorded here.

PMID:33268356 SUPPORT Human Clinical

"Notably, although all known H3.3 mutations in humans cause cancer, none of the patients in our cohort have cancer."

States the paradox that makes the question worth keeping open.

Do the available in vivo models capture a disease caused by heterozygous gain-of-function or dominant-negative alleles, when one is a homozygous null and the other is scored on behavioural endpoints with no neuropathological correlate?

HUMAN MODEL MISMATCH OPEN blbs1_no_neurodevelopmental_model

Attached to

animal_models#Zebrafish h3f3a model animal_models#H3.3 T45I knock-in mouse pathophysiology#Progressive Postnatal Neuronal H3.3 Dependence

The two models fail in opposite directions. The zebrafish h3f3a mutant has a dominant allele that reproduces the mode of inheritance, but its strong cartilage and pigment-cell phenotypes come from the homozygous null - a loss-of-function genotype, where the human disease is read as gain of function or dominant negative on a background of three wild-type H3.3 alleles - and it speaks only to craniofacial and glial development. The T45I knock-in mouse fixes the genotype problem exactly, carrying the most recurrent human allele in heterozygous form, and reproduces the two-phase natural history; but its endpoints are developmental milestones, gait and behaviour, with no reported structural brain phenotype and no neuropathology. So the entry's central claim - that the degenerative phase follows from the postnatal shift of the neuronal H3 pool to H3.3 - is consistent with the mouse but not tested by it, and the structural findings that define the human neuroimaging phenotype have no in vivo counterpart in either model. The mouse is also so far a preprint.

Show evidence (3 references)

PMID:36867246 SUPPORT Other

"Most of the causative variants are private and scattered throughout the protein, but all seem to have either a gain-of-function or dominant negative effect on protein function. This is highly unusual and not well understood."

States the human mechanism that a null model does not reproduce, and concedes it is not well understood.

DOI:10.64898/2026.06.16.732665 Preprint · not peer-reviewed SUPPORT Model Organism

"Adult mice additionally display craniofacial differences, impaired nest building, hyperactivity in a social context, and male-specific elevated aggression."

The mouse endpoints are behavioural and morphometric throughout; no structural brain or neuropathological readout is reported, which is the half of the human phenotype that stays unmodelled.

PMID:33268356 SUPPORT Model Organism

"Homozygous h3f3adb1092 mutants display complete loss of neural crest–derived jaw cartilages (n = 10/10)."

The informative cartilage phenotype comes from a homozygous null, which is the genotype mismatch this discussion records.

⚙

Pathophysiology

7

De Novo H3-3A Variant Altering Histone H3.3

The disease begins with a de novo heterozygous variant in H3-3A. Unlike the tightly clustered oncohistone substitutions of paediatric glioma, BLBS alleles are largely private and spread across the whole 135-residue protein, tail and core alike. They are read as gain of function or dominant negative rather than haploinsufficiency, which is what makes a single altered allele of one of two redundant H3.3 genes sufficient to cause severe disease.

H3-3A hgnc:4764

Genetic context H3-3A hgnc:4764 allele_type: MISSENSE variant_origin: DE_NOVO zygosity: HETEROZYGOUS functional_impact_category: GAIN_OF_FUNCTION

Heterozygous de novo missense alleles distributed across the protein. Recorded as gain of function following the authors' own reading; a dominant-negative effect is the stated alternative for some alleles.

structural constituent of chromatin GO:0030527 ⇑ GAIN OF FUNCTION

Downstream

Disrupted Nucleosome Assembly and Chaperone Interaction The altered residues sit at DNA contacts, inter-histone interfaces and chaperone-binding surfaces.

Show evidence (2 references)

PMID:33268356 SUPPORT Human Clinical

"In this work, we have identified a cohort of 46 unrelated patients bearing de novo heterozygous germline missense mutations in H3F3A or H3F3B with a core phenotype of progressive neurologic dysfunction and congenital anomalies."

The founding cohort establishing de novo heterozygous missense variants as the cause.

PMID:36867246 SUPPORT Other

"Most of the causative variants are private and scattered throughout the protein, but all seem to have either a gain-of-function or dominant negative effect on protein function."

Supports both the private, scattered distribution and the gain-of-function or dominant-negative reading annotated on this node.

Disrupted Nucleosome Assembly and Chaperone Interaction

Molecular modelling of the founding cohort's variants showed disrupted interactions with DNA, with the other core histones, and with the histone chaperones that deposit H3.3. The two structural classes fall out by domain: core-domain variants are modelled as destabilising the nucleosome itself, while tail-domain variants disrupt protein-protein interactions with chromatin readers and chaperones. The mutant histone is still incorporated into nucleosomes - this is not a failure to assemble chromatin but a failure to assemble it correctly.

nucleosome assembly GO:0006334 ⚠ ABNORMAL

nucleosomal DNA binding GO:0031492

nucleosome GO:0000786

Downstream

Aberrant Local Histone Post-Translational Modification Incorporated mutant histone carries and induces an abnormal local modification state.

Show evidence (2 references)

PMID:33268356 SUPPORT Computational

"Molecular modeling of all 37 variants demonstrated clear disruptions in interactions with DNA, other histones, and histone chaperone proteins."

The structural modelling result this node records; evidence source is COMPUTATIONAL because the claim comes from in silico modelling.

PMID:33268356 SUPPORT Computational

"Molecular modeling revealed that mutations in the histone core likely affect nucleosome stability, while the mutations in the tail affect various protein-protein interactions."

Gives the domain split between nucleosome destabilisation and disrupted protein-protein interaction.

Aberrant Local Histone Post-Translational Modification

Post-translational modification profiling of patient material showed abnormal modification patterns that are local to the mutant histone rather than global. This is the sharpest mechanistic difference from the somatic oncohistones, whose lysine substitutions dysregulate modification across the whole genome in trans. Here the changes are in cis on the mutant H3.3, which is why the severity of the phenotype cannot be explained by global dysregulation of the histone code.

chromatin remodeling GO:0006338 ⚠ ABNORMAL

Downstream

Deregulated Cell Proliferation Local chromatin deregulation is followed by transcriptional changes in mitosis and cell-division programs.

Neural Crest and Craniofacial Developmental Defect Chromatin dysregulation in neural crest derivatives disturbs craniofacial and glial development.

Abnormal Brain Development Chromatin dysregulation in neural lineages disturbs brain development.

Show evidence (2 references)

PMID:33268356 SUPPORT In Vitro

"Patient histone posttranslational modifications (PTMs) analysis revealed notably aberrant local PTM patterns distinct from the somatic lysine mutations that cause global PTM dysregulation."

Establishes the local rather than global character of the modification abnormality.

PMID:33268356 SUPPORT In Vitro

"Together, these data suggest that the mutant histones can be incorporated into the nucleosome, cause marked local deregulation of chromatin state, and modestly alter the global control of histone modifications."

Confirms incorporation of the mutant histone and locates the deregulation at the local chromatin level.

Deregulated Cell Proliferation

RNA sequencing of patient cells showed up-regulation of mitosis and cell-division genes, and cellular assays confirmed increased proliferative capacity. This is the point at which the germline and somatic H3.3 diseases converge without becoming the same thing: the germline variants push proliferation, but no BLBS patient in the founding cohort had a malignancy, including individuals carrying germline substitutions at the same residues that act as oncogenic hotspots somatically.

cell population proliferation GO:0008283 ↑ INCREASED

Show evidence (2 references)

PMID:33268356 SUPPORT In Vitro

"RNA sequencing on patient cells demonstrated up-regulated gene expression related to mitosis and cell division, and cellular assays confirmed an increased proliferative capacity."

Provides both the transcriptional and the functional evidence for increased proliferation.

PMID:33268356 SUPPORT Human Clinical

"Notably, although all known H3.3 mutations in humans cause cancer, none of the patients in our cohort have cancer."

The absence of malignancy despite the proliferative signal, which is why this node stops short of a transformation claim.

Neural Crest and Craniofacial Developmental Defect

Craniofacial dysmorphism is present in the large majority of patients and is the phenotype with the clearest developmental mechanism. In the zebrafish h3f3a model, homozygous null larvae lose neural-crest-derived jaw cartilage entirely and show reduced foxd3-positive neural-crest-derived glia, melanocytes and xanthophores. The glial component is the one that connects to the human imaging phenotype: over a third of the patient cohort has hypomyelination on brain MRI, and glia are the myelinating cell type.

radial glial cell CL:0000681

chromatin remodeling GO:0006338 ⚠ ABNORMAL

Animal models

H3.3 T45I knock-in mouse Mus musculus partially recapitulates Adult mutant animals show craniofacial differences.

Zebrafish h3f3a model Danio rerio partially recapitulates The model reproduces the craniofacial and neural-crest-derived glial components of the human phenotype.

Downstream

Craniofacial Dysmorphism Disturbed neural-crest-derived craniofacial development produces the dysmorphic facial features.

Show evidence (2 references)

PMID:33268356 SUPPORT Model Organism

"A zebrafish model showed craniofacial anomalies and a defect in Foxd3-derived glia."

The model-organism result underlying this node.

PMID:33268356 SUPPORT INDIRECT Human Clinical

"The loss of glial cells may relate to the hypomyelination phenotype that is noted on the brain MRIs of over one-third of the H3.3 cohort as glial cells are the cell type responsible for myelination."

Reports the human cohort imaging finding, from which the link to the zebrafish glial defect follows only by inference - the authors hedge the connection themselves - so the item is marked INDIRECT.

Abnormal Brain Development

The congenital arm of the phenotype: severe developmental delay, epilepsy, tone abnormality and structural brain findings, present from infancy. Just over half of individuals with an MRI have at least one abnormal finding, and corpus callosum dysgenesis is the commonest named one.

neuron CL:0000540

brain UBERON:0000955 corpus callosum UBERON:0002336

Animal models

H3.3 T45I knock-in mouse Mus musculus partially recapitulates Reproduces delayed developmental milestones and perinatal growth restriction.

Downstream

Global Developmental Delay and Intellectual Disability The dominant clinical consequence of disrupted neural chromatin regulation.

Abnormal Corpus Callosum Morphology The commonest specific structural finding on neuroimaging.

Progressive Postnatal Neuronal H3.3 Dependence The same lesion becomes progressively more consequential as neurons mature and their H3 pool shifts to H3.3.

Show evidence (2 references)

PMID:38678163 SUPPORT Human Clinical

"This syndrome is characterized by developmental delay/intellectual disability, craniofacial anomalies, hyper/hypotonia, and abnormal neuroimaging"

States the congenital phenotype cluster this node terminates in.

PMID:38678163 SUPPORT Human Clinical

"Within this subgroup, 72% of individuals presented with small posterior fossa, 28% presented with dysgenesis of the corpus collosum, and 44% presented with cortical developmental abnormalities"

Gives the structural findings from the detailed imaging subgroup that anchor the structural component of this node.

Progressive Postnatal Neuronal H3.3 Dependence

The degenerative arm, and the reason the disease has one at all. H3.3 progressively replaces the replication-dependent H3 variants in postnatal brain and comes to dominate the H3 pool in adulthood, so a defective H3.3 matters more to a neuron the older that neuron gets. The clinical correlates are cortical atrophy on imaging and, in adulthood, camptocormia and motor decline. The mechanism is an inference from the timing of the substrate rather than a demonstrated cause of the human degeneration, which is why it is provisional.

neuron CL:0000540

Animal models

H3.3 T45I knock-in mouse Mus musculus recapitulates Reproduces progressive motor and gait impairment on a congenital genotype, which is the phenomenon this node exists to explain.

Downstream

Camptocormia The characteristic adult-onset motor manifestation of the degenerative phase.

Cerebral Cortical Atrophy The imaging correlate of progressive neuronal dysfunction.

Show evidence (2 references)

PMID:33268356 SUPPORT Model Organism

"A recent study showed that H3.3 begins to replace H3.1 and H3.2 in postnatal mouse and human brains in a time-dependent manner and displaces these canonical H3 variants almost completely in adulthood."

Supports the developmental-timing explanation for why a congenital histone lesion produces an adult-onset degenerative phase.

PMID:33268356 SUPPORT Human Clinical

"Notably, 9 of the 46 patients (21%) have demonstrated clinical neurologic degeneration, which suggests that this may be a progressive disorder."

Establishes that a degenerative phase actually occurs, which is the phenomenon this node explains.

⬡

Pathograph

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

●

Phenotypes

24

Cardiovascular 1

Congenital Heart Defect OCCASIONAL Abnormal heart morphology HP:0001627

Show evidence (2 references)

PMID:38678163 SUPPORT Human Clinical

"Fourteen percent of individuals present with cardiac anomalies, including atrial septal defects (Fig. 1D)."

Gives the patient-level frequency of cardiac anomalies and names atrial septal defect as a constituent without giving a septal breakdown.

PMID:37782742 SUPPORT Human Clinical

"Congenital anomalies are rare but can include congenital heart defects, brain malformations, and genitourinary abnormalities in males."

GeneReviews records congenital heart defects as a rare but recognised anomaly.

Digestive 1

Feeding Difficulties HP:0011968

Show evidence (1 reference)

PMID:37782742 SUPPORT Human Clinical

"Treatment of manifestations: Feeding issues and poor weight gain may benefit from feeding therapy; in individuals with persistent feeding issues, gastrostomy tube may be considered."

GeneReviews management guidance, which presupposes feeding difficulty as a recognised manifestation.

Ear 1

Hearing Impairment HP:0000365

Show evidence (1 reference)

PMID:37782742 SUPPORT Human Clinical

"Standard treatment for developmental delay / intellectual disability, attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety, epilepsy, spasticity, constipation, craniosynostosis, vision issues, hearing loss, congenital heart defects, undescended testes, and hypothyroidism."

GeneReviews names hearing loss among the manifestations requiring treatment.

Eye 1

Ocular Involvement FREQUENT Abnormality of eye movement HP:0000496

Show evidence (2 references)

PMID:38678163 SUPPORT Human Clinical

"More females (64%) present with oculomotor dysfunction than males (44%) (Fig. 2)."

Gives sex-stratified patient-level frequencies for oculomotor dysfunction, which is the level the bound term describes.

PMID:37782742 SUPPORT Human Clinical

"Annually or as clinically indicated: ophthalmology evaluation, audiology evaluation, and thyroid function tests."

Supports ocular involvement as an actively surveilled feature; this quote establishes the surveillance, not the specific finding.

Genitourinary 1

Genitourinary Anomalies in Males OCCASIONAL Cryptorchidism HP:0000028

Show evidence (2 references)

PMID:37782742 SUPPORT Human Clinical

"Standard treatment for developmental delay / intellectual disability, attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety, epilepsy, spasticity, constipation, craniosynostosis, vision issues, hearing loss, congenital heart defects, undescended testes, and hypothyroidism."

Names undescended testes specifically, which is the term bound here; the general "genitourinary abnormalities" phrasing elsewhere in GeneReviews does not reach that level of specificity.

PMID:38678163 SUPPORT Human Clinical

"Twenty percent of individuals present with genital anomalies (Fig. 1D, Table 1, Supplementary Table 1)."

Gives the patient-level frequency of genital anomalies as a category.

Head and Neck 3

Craniofacial Dysmorphism VERY_FREQUENT Abnormal facial shape HP:0001999

Show evidence (3 references)

PMID:37782742 SUPPORT Human Clinical

"Bryant-Li-Bhoj neurodevelopmental syndrome (BRYLIB) is characterized by developmental delay / intellectual disability (typically in the severe range) and nonspecific craniofacial abnormalities."

GeneReviews names craniofacial abnormality as a defining feature and describes it as nonspecific.

PMID:38678163 SUPPORT Human Clinical

"In addition to growth trajectories outside of the standard range for age and sex, 92% of individuals with BLBS present with craniofacial anomalies (Table 1, Fig. 1D, Supplementary Table 1)."

Gives the patient-level frequency underpinning the VERY_FREQUENT band.

PMID:40241305 SUPPORT INDIRECT Human Clinical

"While these analyses may suggest a histone core versus linker protein basis of delineation, they more strikingly highlight data gaps that confound the identification of phenotypic patterns at this time."

Supports marking the dysmorphism non-diagnostic. The quote reports that systematic facial phenotyping has not produced a usable pattern, from which the non-diagnostic status follows by inference rather than being asserted.

Craniosynostosis HP:0001363

Show evidence (1 reference)

PMID:37782742 SUPPORT Human Clinical

"The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly..."

GeneReviews names craniosynostosis of any suture as a feature.

Microcephaly FREQUENT HP:0000252

Show evidence (2 references)

PMID:38678163 SUPPORT Human Clinical

"Among these individuals, microcephaly is more common than macrocephaly (32 and 15%, respectively), which is consistent across all variables interrogated (Table 1)."

Gives both head-size frequencies and states which direction predominates.

PMID:38678163 SUPPORT Human Clinical

"Notably, 46% of individuals with craniofacial anomalies present with concurrent microcephaly or macrocephaly (Table 1, Fig. 1D, Supplementary Table 1)."

Ties head size to the craniofacial phenotype, and covers both directions, which is why the entry does not treat small head size as uniform.

Integument 1

Dermatologic Features FREQUENT Abnormality of the skin HP:0000951

Show evidence (1 reference)

PMID:38678163 SUPPORT Human Clinical

"Dermal features are more likely found in individuals with variants in the tail (64%) than the core (45%)."

Gives the patient-level frequency of dermatologic features, split by the protein domain the variant falls in.

Musculoskeletal 3

Hypotonia FREQUENT HP:0001252

Show evidence (2 references)

PMID:37782742 SUPPORT Human Clinical

"The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly..."

GeneReviews enumeration of the variable features, hypotonia among them.

PMID:38678163 SUPPORT Human Clinical

"Sixty-two percent of individuals presented with hypotonia whereas 12% presented with hypertonia (Table 1, Fig. 2)."

Gives the patient-level frequency underpinning the FREQUENT band, and the hypertonia figure alongside it.

Spasticity HP:0001257

Show evidence (1 reference)

PMID:37782742 SUPPORT Human Clinical

"The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly..."

GeneReviews lists spasticity among the neurologic findings.

Hypertonia OCCASIONAL HP:0001276

Show evidence (2 references)

PMID:38678163 SUPPORT Human Clinical

"Sixty-two percent of individuals presented with hypotonia whereas 12% presented with hypertonia (Table 1, Fig. 2)."

Gives the patient-level frequency of hypertonia alongside that of hypotonia.

PMID:38678163 SUPPORT Human Clinical

"Interestingly, 10% of individuals have concordant axial hypotonia and peripheral hypertonia, or dystonia, which is exclusively present in individuals with variants in the core (Fig. 2, light gray)."

Records the mixed tone pattern and the fact that it occurs only with core-domain variants.

Nervous System 6

Global Developmental Delay and Intellectual Disability VERY_FREQUENT HP:0001263

Show evidence (2 references)

PMID:37782742 SUPPORT Human Clinical

"Bryant-Li-Bhoj neurodevelopmental syndrome (BRYLIB) is characterized by developmental delay / intellectual disability (typically in the severe range) and nonspecific craniofacial abnormalities."

GeneReviews states developmental delay or intellectual disability as a defining, typically severe feature.

PMID:38678163 SUPPORT Human Clinical

"Ninety-nine percent of individuals with BLBS have DD/ID (Table 1, Fig. 1D, Supplementary Table 1)."

Gives the patient-level frequency underpinning the VERY_FREQUENT band.

Seizures FREQUENT HP:0001250

Show evidence (2 references)

PMID:37782742 SUPPORT Human Clinical

"The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly..."

GeneReviews lists epilepsy among the variable neurologic features.

PMID:38678163 SUPPORT Human Clinical

"Forty nine percent of individuals also present with seizures (Table 1)."

Gives the patient-level frequency underpinning the FREQUENT band.

Cerebral Cortical Atrophy OCCASIONAL HP:0002120

Show evidence (1 reference)

PMID:33268356 SUPPORT Human Clinical

"Multiple patients (26% of the cohort) have cortical atrophy on brain magnetic resonance imaging (MRI), even without intractable epilepsy."

Gives the 26% figure and the observation that it occurs independently of intractable epilepsy.

Delayed Speech and Language Development FREQUENT HP:0000750

Show evidence (1 reference)

PMID:37782742 SUPPORT Human Clinical

"Many affected individuals do not achieve independent sitting, walking, or speaking, although there is a range of developmental outcomes."

Establishes speech delay or absence as a core feature; GeneReviews does not give a separate frequency for it.

Abnormal Corpus Callosum Morphology OCCASIONAL HP:0001273

Show evidence (1 reference)

PMID:38678163 SUPPORT Human Clinical

"Within this subgroup, 72% of individuals presented with small posterior fossa, 28% presented with dysgenesis of the corpus collosum, and 44% presented with cortical developmental abnormalities"

Gives the frequency of corpus callosum dysgenesis in the subgroup whose images were analysed in detail.

Autism Spectrum Disorder HP:0000717

Show evidence (1 reference)

PMID:37782742 SUPPORT Human Clinical

"Standard treatment for developmental delay / intellectual disability, attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety, epilepsy, spasticity, constipation, craniosynostosis, vision issues, hearing loss, congenital heart defects, undescended testes, and hypothyroidism."

GeneReviews names autism spectrum disorder among the manifestations requiring treatment.

Growth 1

Poor Growth FREQUENT Short stature HP:0004322

Show evidence (2 references)

PMID:38678163 SUPPORT Human Clinical

"Height ( ≤5th percentile) 32/91 (35%)"

Gives the patient-level frequency of short stature specifically, which is the term bound here.

PMID:37782742 SUPPORT Human Clinical

"The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly..."

GeneReviews identifies poor growth as the usual direction of the growth abnormality.

Other 5

Camptocormia HP:0100595

Onset: ADULT

Show evidence (1 reference)

PMID:37782742 SUPPORT Human Clinical

"The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly..."

GeneReviews defines camptocormia and lists it among the neurologic findings of this syndrome.

Delayed CNS Myelination FREQUENT HP:0002188

Show evidence (1 reference)

PMID:33268356 SUPPORT Human Clinical

"The loss of glial cells may relate to the hypomyelination phenotype that is noted on the brain MRIs of over one-third of the H3.3 cohort as glial cells are the cell type responsible for myelination."

Gives the frequency of the hypomyelination finding in the cohort.

Delayed Ability to Walk VERY_FREQUENT HP:0031936

Show evidence (1 reference)

PMID:38678163 SUPPORT Human Clinical

"More individuals harboring variants in H3-3A (85%) had delayed or yet to be achieved independent walking when compared to individuals harboring variants in H3-3B (65%)."

Gives the H3-3A-specific frequency, which is the one this entry needs.

Delayed Ability to Sit FREQUENT HP:0025336

Show evidence (1 reference)

PMID:38678163 SUPPORT Human Clinical

"Individuals with variants in H3-3A (56%) more frequently had delayed or yet to be achieved independent sitting compared to individuals with variants in H3-3B (43%) (Fig. 2)."

Gives the H3-3A-specific frequency, which is the one this entry needs.

Musculoskeletal Anomalies FREQUENT Abnormal skeletal morphology HP:0011842

Show evidence (1 reference)

PMID:38678163 SUPPORT Human Clinical

"Over half of individuals (58%) present with musculoskeletal anomalies such as club foot, scoliosis, hip dysplasia, subluxation of various joints/hypermobility, kyphosis, and femoral anteversion"

Gives the frequency of the musculoskeletal category and names scoliosis among its constituents; no scoliosis-specific frequency is reported in prose, so none is recorded here.

🧬

Genetic Associations

1

H3-3A

Gene: H3-3A hgnc:4764 relationship_type: CAUSATIVE variant_origin: DE_NOVO

Show evidence (2 references)

PMID:33268356 SUPPORT Human Clinical

"In this work, we have identified a cohort of 46 unrelated patients bearing de novo heterozygous germline missense mutations in H3F3A or H3F3B with a core phenotype of progressive neurologic dysfunction and congenital anomalies."

Establishes the gene-disease relationship in the founding cohort.

PMID:33268356 SUPPORT Human Clinical

"In the general population, both genes have a very low rate of missense variants; the gnomAD missense Z score is 3.21 for H3F3A and 2.95 for H3F3B (>2 is significant)"

Documents the strong missense constraint on H3-3A that supports pathogenicity of de novo missense alleles.

🔬

Variants

1

H3-3A p.Thr45Ile Pathogenic

Gene: H3-3A hgnc:4764

The most recurrently reported BLBS1 allele, carried by four individuals in the 2024 cohort. Those four show substantial phenotypic variability, which is the clearest single demonstration that genotype does not determine phenotype in this disease.

Show evidence (2 references)

PMID:38678163 SUPPORT Human Clinical

"Length of lollipop corresponds to number of individuals who harbor a variant at that residue (e.g. H3-3A p.T45I represents four individuals with BLBS and H3-3A p.V46M represents one individual with BLBS)."

Identifies p.Thr45Ile as the most recurrent H3-3A allele in the reported cohort.

PMID:38678163 SUPPORT Human Clinical

"Notably, phenotypic heterogeneity was present even amongst individuals harboring the same variant."

Supports the statement that recurrence of an allele does not bring phenotypic concordance.

💊

Medical Actions

3

Supportive and Developmental Management

Action: Supportive Care NCIT:C15747

There is no disease-modifying therapy. Management is standard treatment of each manifestation - developmental delay, attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety, epilepsy, spasticity, constipation, craniosynostosis, vision and hearing problems, congenital heart defects, undescended testes and hypothyroidism - with early developmental intervention and feeding support.

Show evidence (1 reference)

PMID:37782742 SUPPORT Human Clinical

"Standard treatment for developmental delay / intellectual disability, attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety, epilepsy, spasticity, constipation, craniosynostosis, vision issues, hearing loss, congenital heart defects, undescended testes, and hypothyroidism."

GeneReviews management guidance, which is symptomatic throughout.

Structured Surveillance

Action: Supportive Care NCIT:C15747

Growth parameters, nutrition and oral intake safety, constipation, new manifestations such as seizures and changes in tone or gait, developmental progress and behaviour at every visit; ophthalmology, audiology and thyroid function annually. The tone-and-gait item is the one that matters for the degenerative phase, since new motor decline in adulthood is expected rather than incidental.

Show evidence (2 references)

PMID:37782742 SUPPORT Human Clinical

"At each visit: measure growth parameters; assess nutrition safety and oral intake; monitor for constipation; assess for new manifestations, such as seizures and changes in tone and/or gait; monitor developmental progress and educational needs; and assess for behavioral issues, such as mobility..."

The GeneReviews surveillance schedule recorded in this entry.

PMID:37782742 SUPPORT Human Clinical

"Annually or as clinically indicated: ophthalmology evaluation, audiology evaluation, and thyroid function tests."

The annual component of the same surveillance schedule.

Genetic Counseling

Action: Genetic Counseling NCIT:C15240

Because the variants are de novo, recurrence risk to other family members is presumed low. Once a variant is identified, prenatal and preimplantation genetic testing become available.

Show evidence (1 reference)

PMID:37782742 SUPPORT Human Clinical

"Therefore, the risk to other family members is presumed to be low. Once an H3-3A (H3F3A) or H3-3B (H3F3B) pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible."

GeneReviews counselling guidance, including the reproductive testing options.

🔬

Diagnosis

1

Molecular genetic testing of H3-3A

The diagnosis is molecular. There is no biochemical marker and no recognisable facial gestalt, so it is established by finding a heterozygous pathogenic H3-3A variant in a proband with suggestive features - almost always through exome or genome sequencing performed for undiagnosed developmental delay.

Show evidence (2 references)

PMID:37782742 SUPPORT Human Clinical

"The diagnosis of BRYLIB is established in a proband with suggestive findings and a heterozygous pathogenic variant in either H3-3A (H3F3A) or H3-3B (H3F3B) identified by molecular genetic testing."

GeneReviews statement of the diagnostic criterion.

PMID:33268356 SUPPORT Human Clinical

"These patients were identified through exome or genome sequencing performed for the indication of neurodevelopmental delays and/or congenital anomalies"

Documents the ascertainment route through which the diagnosis is practically made.

📈

Progression

2

Neurodevelopmental phase

Age: infancy to childhood

Developmental delay is evident from infancy. Many affected individuals never achieve independent sitting, walking or speech, though outcomes range. Tone abnormality may resolve or evolve with age rather than remaining fixed.

Show evidence (1 reference)

PMID:37782742 SUPPORT Human Clinical

"Many affected individuals do not achieve independent sitting, walking, or speaking, although there is a range of developmental outcomes."

Establishes both the severity and the variability of the developmental outcome.

Neurodegenerative phase

Age: adulthood

A distinct later component: about a fifth of the founding cohort showed clinical neurologic degeneration, and cortical atrophy is seen on imaging in roughly a quarter even without intractable epilepsy. Camptocormia, worsening gait, spasticity and loss of previously acquired milestones are the reported manifestations. This is the feature that put "neurodegenerative" in the name of the founding report.

Show evidence (3 references)

PMID:33268356 SUPPORT Human Clinical

"Notably, 9 of the 46 patients (21%) have demonstrated clinical neurologic degeneration, which suggests that this may be a progressive disorder."

Quantifies the degenerative component in the founding cohort.

PMID:33268356 SUPPORT Human Clinical

"Multiple patients (26% of the cohort) have cortical atrophy on brain magnetic resonance imaging (MRI), even without intractable epilepsy."

Provides the imaging correlate of the degenerative phase and rules out seizure burden as its sole explanation.

PMID:40241305 SUPPORT Human Clinical

"Ultimately, this work highlights the ways in which histonopathy-associated phenotypes change throughout the lifespan, necessitating longitudinal re-evaluation"

Supports treating the phenotype as age-dependent rather than fixed, which is why the two phases are curated separately.

📊

Prevalence

1

Worldwide

Cases In Literature Ultra Rare

No population rate has been published. The published denominator is the global cohort assembled in 2024: of 96 individuals with BLBS, 65 carried an H3-3A variant. Ascertainment is by exome or genome sequencing for undiagnosed neurodevelopmental disease, so this is a discovery count rather than an epidemiologic estimate.

Show evidence (1 reference)

PMID:38678163 SUPPORT Human Clinical

"In total, 65 individuals harbor variants in H3-3A and 31 individuals harbor variants in H3-3B."

Gives the H3-3A-specific reported count within the combined BLBS cohort.

🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Bryant-Li-Bhoj Neurodevelopmental Syndrome 1:

Bryant-Li-Bhoj neurodevelopmental syndrome 2 MONDO:0030607

Overlapping Features The H3-3B counterpart. The two genes encode an identical protein, so the entities are separated by gene rather than by protein product and are clinically overlapping. Only molecular testing distinguishes them. Cohort-level trends exist but are not diagnostic discriminators, and the H3-3A cohort differs in that every variant with parental data has been de novo and missense, whereas H3-3B has yielded synonymous, stop-loss and one inherited allele.

Distinguishing Features

Determined solely by molecular testing: a pathogenic variant in H3-3A rather than H3-3B
Greater variant-type and inheritance diversity is reported for H3-3B, including a synonymous stop-gain, a stop-loss and one inherited allele

Show evidence (1 reference)

PMID:38678163 SUPPORT Human Clinical

"Conversely, while most variants in H3-3B are heterozygous de novo missense variants, more variability in variant type and modes of inheritance was observed."

States the variant-type difference between the two genes that this differential rests on.

Somatic H3.3 oncohistone disease

Overlapping Features Substitutions at the same H3.3 residues - K27M, G34R/V, K36M - occur somatically and drive paediatric diffuse midline glioma and giant cell tumour of bone. This is a molecular contrast rather than a clinical differential, but it matters when a germline result at one of those residues is reported: the germline and somatic diseases have different mechanisms, and germline carriers of G34R/V substitutions have not developed the corresponding tumours.

Distinguishing Features

Germline variants are private and scattered across the protein; oncohistone substitutions are recurrent hotspots
Germline variants deregulate histone modification locally and in cis; somatic lysine substitutions dysregulate it globally in trans
No malignancy occurred in the founding BLBS cohort

Show evidence (2 references)

PMID:33268356 SUPPORT In Vitro

"Patient histone posttranslational modifications (PTMs) analysis revealed notably aberrant local PTM patterns distinct from the somatic lysine mutations that cause global PTM dysregulation."

Gives the molecular basis on which the germline and somatic diseases are separated.

PMID:33268356 SUPPORT Human Clinical

"These data suggest that the mechanism of germline mutations are distinct from cancer-associated somatic histone mutations but may converge on control of cell proliferation."

The authors' own framing of the relationship between the two diseases.

🐁

Animal Models

2

H3.3 T45I knock-in mouse

A knock-in mouse carrying h3-3a p.T45I, the most recurrent BLBS1 allele and the one this entry curates under variants. It is genotype-matched to human disease rather than a null, which is what distinguishes it from the zebrafish model, and it reproduces the two-phase natural history: perinatal growth restriction and delayed developmental milestones early, progressive motor and gait impairment later. Adult animals additionally show craniofacial differences and behavioural changes. Reported so far only as a preprint.

Species

Mus musculus

Genotype

h3-3a p.T45I knock-in

Publication

DOI:10.64898/2026.06.16.732665

Pathograph links

Progressive Postnatal Neuronal H3.3 Dependence recapitulates fidelity: moderate Reproduces progressive motor and gait impairment on a congenital genotype, which is the phenomenon this node exists to explain.

Limitations: Progressive motor impairment in a mouse is not camptocormia, and the preprint reports no cortical atrophy or other neuropathological correlate, so the node's proposed mechanism - the postnatal shift of the neuronal H3 pool to H3.3 - is not itself tested by these endpoints. Peer review is pending.

Readouts

Motor and gait performance

Direction: DECREASED

Interpretation: Progressive decline in motor and gait measures with age, the behavioural correlate of the degenerative phase.

Show evidence (1 reference)

DOI:10.64898/2026.06.16.732665 Preprint · not peer-reviewed SUPPORT Model Organism

"mice recapitulate the BLBS natural history: perinatal growth restriction, delayed developmental milestones, and progressive motor and gait impairments."

Reports the progressive motor and gait measurement behind this readout.

Show evidence (1 reference)

DOI:10.64898/2026.06.16.732665 Preprint · not peer-reviewed SUPPORT Model Organism

"The non-invasive, clinically translatable endpoints established here provide a validated preclinical platform for evaluating therapeutics for a community whose current standard of care is symptom management."

The authors position the model as a validated platform for this disease, which is what makes it informative for a disease-level node.

Abnormal Brain Development partially recapitulates fidelity: moderate Reproduces delayed developmental milestones and perinatal growth restriction.

Limitations: Mouse developmental milestones are not a counterpart of human developmental delay or intellectual disability, and the preprint reports no structural brain phenotype - no corpus callosum, posterior fossa or myelination finding - so the imaging component of this node is unmodelled. Seizures are not reported either.

Readouts

Developmental milestone attainment

Direction: DECREASED

Interpretation: Delayed attainment of developmental milestones in mutant pups.

Show evidence (1 reference)

DOI:10.64898/2026.06.16.732665 Preprint · not peer-reviewed SUPPORT Model Organism

"mice recapitulate the BLBS natural history: perinatal growth restriction, delayed developmental milestones, and progressive motor and gait impairments."

Reports the milestone measurement behind this readout.

Show evidence (1 reference)

DOI:10.64898/2026.06.16.732665 Preprint · not peer-reviewed SUPPORT Model Organism

"Here, we characterize the developmental and neurobehavioral phenotypes of a novel BLBS mouse model harboring one of the most recurrent causative variants"

Establishes that the model is genotype-matched to a recurrent human allele, which is what makes it informative for the developmental node.

Neural Crest and Craniofacial Developmental Defect partially recapitulates fidelity: low Adult mutant animals show craniofacial differences.

Limitations: The preprint reports craniofacial difference as a phenotype without linking it to neural crest biology, and the human dysmorphism has no recognisable gestalt to compare against, so the correspondence is at the level of "the face is different" and no further.

Show evidence (1 reference)

DOI:10.64898/2026.06.16.732665 Preprint · not peer-reviewed SUPPORT Model Organism

"Adult mice additionally display craniofacial differences, impaired nest building, hyperactivity in a social context, and male-specific elevated aggression."

Reports the craniofacial phenotype in adult animals.

Show evidence (1 reference)

DOI:10.64898/2026.06.16.732665 Preprint · not peer-reviewed SUPPORT Model Organism

"mice recapitulate the BLBS natural history: perinatal growth restriction, delayed developmental milestones, and progressive motor and gait impairments."

Summarises the two-phase natural history this model reproduces.

Zebrafish h3f3a model

A zebrafish model of the orthologous gene. A dominant p.D123N allele recovered from a forward genetic screen sits two residues from a patient variant (p.Q125R) and reproduces both the dominant inheritance and the craniofacial anomalies of the human disease. Homozygous db1092 null larvae lose neural-crest-derived jaw cartilage completely and show reduced foxd3-positive cranial glia, melanocytes and xanthophores. Because the model targets the h3f3a paralog, it is the direct ortholog for BLBS1 rather than for BLBS2.

Species

Danio rerio

Genotype

h3f3a p.D123N dominant allele; h3f3a db1092 homozygous null

Publication

PMID:33268356

Pathograph links

Neural Crest and Craniofacial Developmental Defect partially recapitulates fidelity: moderate The model reproduces the craniofacial and neural-crest-derived glial components of the human phenotype.

Limitations: The dominant allele is p.D123N, not a patient allele, and the strongest cartilage and pigment-cell phenotypes come from the homozygous null rather than from a heterozygous missense genotype - so the model is closer to loss of h3f3a function than to the gain-of-function or dominant-negative mechanism inferred in patients. Zebrafish craniofacial cartilage is not a direct counterpart of human facial dysmorphism, and the model says nothing about the neurodevelopmental or degenerative phenotypes that dominate the human disease.

Readouts

Neural-crest-derived jaw cartilage

Direction: DECREASED

Interpretation: Complete loss of jaw cartilage in homozygous null larvae, the structural readout of the craniofacial node.

Show evidence (1 reference)

PMID:33268356 SUPPORT Model Organism

"Homozygous h3f3adb1092 mutants display complete loss of neural crest–derived jaw cartilages (n = 10/10)."

Reports the cartilage measurement behind this readout.

foxd3-positive cranial glia

Direction: DECREASED

Interpretation: Reduced cranial glia, the readout that connects the model to the human hypomyelination finding.

Show evidence (1 reference)

PMID:33268356 SUPPORT Model Organism

"Homozygous h3f3adb1092 mutants injected at the one-cell stage with a control mCherry RNA show partial reductions in cranial glia (n = 5), melanocytes (n = 4), and xanthophores (n = 3), while those injected with dominant-negative H3f3a RNA to further reduced H3.3A function show complete loss of..."

Reports the in situ hybridization measurements of glia, melanocytes and xanthophores in this model.

Show evidence (1 reference)

PMID:33268356 SUPPORT Model Organism

"This heterozygous missense variant replicates the dominant inheritance observed in humans and is only two amino acids away from a mutation identified in an affected patient (p.Q125R)."

Supports treating this model as informative for the human craniofacial node, on the strength of the shared dominant inheritance and the proximity of the allele to a patient variant.

Show evidence (1 reference)

PMID:33268356 SUPPORT Model Organism

"A zebrafish model showed craniofacial anomalies and a defect in Foxd3-derived glia."

Summarises the model phenotype recapitulating the craniofacial and glial components of the disease.

{ }

Source YAML

click to show

name: Bryant-Li-Bhoj Neurodevelopmental Syndrome 1
creation_date: "2026-08-29T16:30:00Z"
category: Mendelian
categories:
- Chromatinopathy
- Germline Histonopathy
- Neurodevelopmental Disorder
synonyms:
- BLBS1
- BRYLIB1
- Bryant-Li-Bhoj syndrome 1
- H3-3A-related neurodevelopmental syndrome
- H3F3A-related neurodevelopmental disorder
description: >-
  Bryant-Li-Bhoj neurodevelopmental syndrome 1 (BLBS1, BRYLIB1) is an autosomal
  dominant neurodevelopmental and, in adults, neurodegenerative disorder caused
  by de novo heterozygous variants in H3-3A (H3F3A), one of the two genes
  encoding the replication-independent histone variant H3.3. It is one of the
  very few Mendelian diseases in which the mutated protein is a histone itself
  rather than a histone-modifying enzyme or chaperone. Developmental delay or
  intellectual disability, typically severe, is essentially universal, and most
  affected individuals also have nonspecific craniofacial dysmorphism, abnormal
  tone and abnormal neuroimaging; many never achieve independent sitting,
  walking or speech. The disease alleles are private, scattered across the whole
  protein rather than clustered at hotspots, and act by gain of function or
  dominant negative effect rather than haploinsufficiency - which is what
  separates them mechanistically from the recurrent oncohistone substitutions
  (K27M, G34R/V, K36M) that drive paediatric glioma at the same residues.
  H3-3A and its paralog H3-3B encode an identical protein, so the split into
  BLBS1 and BLBS2 is a split by gene, not by protein product.
disease_term:
  preferred_term: Bryant-Li-Bhoj neurodevelopmental syndrome 1
  term:
    id: MONDO:0030606
    label: Bryant-Li-Bhoj neurodevelopmental syndrome 1
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0030606
      label: Bryant-Li-Bhoj neurodevelopmental syndrome 1
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: Primary MONDO disease identifier for this entry.
parents:
- syndromic disease
- neurodevelopmental disorder
- hereditary disease
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    notes: >-
      A Mendelian disorder of a core chromatin structural protein; the entry is
      organised around the genotype-to-chromatin mechanism.
  - classification_value: NEUROLOGIC
    notes: >-
      The clinical burden is dominated by developmental delay, epilepsy,
      abnormal tone and adult-onset motor decline.
inheritance:
- name: Autosomal dominant inheritance
  description: >-
    BLBS1 is autosomal dominant and, for H3-3A specifically, every variant with
    available parental testing has been de novo, so recurrence risk to siblings
    is low. This is a point of difference from H3-3B, where a maternally
    inherited allele and more variant-type diversity have been described. A
    single altered allele of one of the two H3.3 genes is sufficient: 75% of
    H3.3 alleles remain wild type, which is why the phenotype is read as gain of
    function or dominant negative rather than as loss of dosage.
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "BRYLIB is expressed in an autosomal dominant manner and typically caused by a de novo H3-3A (H3F3A) or H3-3B (H3F3B) pathogenic variant."
    explanation: >-
      GeneReviews statement of the inheritance mode and the de novo origin.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the time of this report, all H3-3A variants are heterozygous de novo missense variants when parents are available, though inheritance was undetermined for three individuals"
    explanation: >-
      The H3-3A-specific observation that distinguishes BLBS1 from BLBS2 on
      inheritance and variant type.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Since there are two genes that produce H3.3, a heterozygous mutation in one of them means that 75% of the alleles are WT."
    explanation: >-
      Establishes the allelic arithmetic behind the gain-of-function reading of
      a heterozygous variant.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    No population rate has been published. The published denominator is the
    global cohort assembled in 2024: of 96 individuals with BLBS, 65 carried an
    H3-3A variant. Ascertainment is by exome or genome sequencing for
    undiagnosed neurodevelopmental disease, so this is a discovery count rather
    than an epidemiologic estimate.
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In total, 65 individuals harbor variants in H3-3A and 31 individuals harbor variants in H3-3B."
    explanation: >-
      Gives the H3-3A-specific reported count within the combined BLBS cohort.
progression:
- phase: Neurodevelopmental phase
  age_range: infancy to childhood
  notes: >-
    Developmental delay is evident from infancy. Many affected individuals never
    achieve independent sitting, walking or speech, though outcomes range. Tone
    abnormality may resolve or evolve with age rather than remaining fixed.
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Many affected individuals do not achieve independent sitting, walking, or speaking, although there is a range of developmental outcomes."
    explanation: >-
      Establishes both the severity and the variability of the developmental
      outcome.
- phase: Neurodegenerative phase
  age_range: adulthood
  notes: >-
    A distinct later component: about a fifth of the founding cohort showed
    clinical neurologic degeneration, and cortical atrophy is seen on imaging in
    roughly a quarter even without intractable epilepsy. Camptocormia, worsening
    gait, spasticity and loss of previously acquired milestones are the reported
    manifestations. This is the feature that put "neurodegenerative" in the name
    of the founding report.
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, 9 of the 46 patients (21%) have demonstrated clinical neurologic degeneration, which suggests that this may be a progressive disorder."
    explanation: >-
      Quantifies the degenerative component in the founding cohort.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Multiple patients (26% of the cohort) have cortical atrophy on brain magnetic resonance imaging (MRI), even without intractable epilepsy."
    explanation: >-
      Provides the imaging correlate of the degenerative phase and rules out
      seizure burden as its sole explanation.
  - reference: PMID:40241305
    reference_title: "Coupling deep phenotypic quantification with next-generation phenotyping for 192 individuals with germline histonopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ultimately, this work highlights the ways in which histonopathy-associated phenotypes change throughout the lifespan, necessitating longitudinal re-evaluation"
    explanation: >-
      Supports treating the phenotype as age-dependent rather than fixed, which
      is why the two phases are curated separately.
pathophysiology:
- name: De Novo H3-3A Variant Altering Histone H3.3
  biological_scale: MOLECULAR
  description: >-
    The disease begins with a de novo heterozygous variant in H3-3A. Unlike the
    tightly clustered oncohistone substitutions of paediatric glioma, BLBS
    alleles are largely private and spread across the whole 135-residue protein,
    tail and core alike. They are read as gain of function or dominant negative
    rather than haploinsufficiency, which is what makes a single altered allele
    of one of two redundant H3.3 genes sufficient to cause severe disease.
  genes:
  - preferred_term: H3-3A
    term:
      id: hgnc:4764
      label: H3-3A
  molecular_functions:
  - preferred_term: structural constituent of chromatin
    modifier: GAIN_OF_FUNCTION
    term:
      id: GO:0030527
      label: structural constituent of chromatin
  genetic_context:
    gene:
      preferred_term: H3-3A
      term:
        id: hgnc:4764
        label: H3-3A
    allele_type: MISSENSE
    variant_origin: DE_NOVO
    zygosity: HETEROZYGOUS
    functional_impact_category: GAIN_OF_FUNCTION
    description: >-
      Heterozygous de novo missense alleles distributed across the protein.
      Recorded as gain of function following the authors' own reading; a
      dominant-negative effect is the stated alternative for some alleles.
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this work, we have identified a cohort of 46 unrelated patients bearing de novo heterozygous germline missense mutations in H3F3A or H3F3B with a core phenotype of progressive neurologic dysfunction and congenital anomalies."
    explanation: >-
      The founding cohort establishing de novo heterozygous missense variants as
      the cause.
  - reference: PMID:36867246
    reference_title: "Histone 3.3-related chromatinopathy: missense variants throughout H3-3A and H3-3B cause a range of functional consequences across species."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Most of the causative variants are private and scattered throughout the protein, but all seem to have either a gain-of-function or dominant negative effect on protein function."
    explanation: >-
      Supports both the private, scattered distribution and the
      gain-of-function or dominant-negative reading annotated on this node.
  downstream:
  - target: Disrupted Nucleosome Assembly and Chaperone Interaction
    description: >-
      The altered residues sit at DNA contacts, inter-histone interfaces and
      chaperone-binding surfaces.
- name: Disrupted Nucleosome Assembly and Chaperone Interaction
  biological_scale: MOLECULAR
  description: >-
    Molecular modelling of the founding cohort's variants showed disrupted
    interactions with DNA, with the other core histones, and with the histone
    chaperones that deposit H3.3. The two structural classes fall out by domain:
    core-domain variants are modelled as destabilising the nucleosome itself,
    while tail-domain variants disrupt protein-protein interactions with
    chromatin readers and chaperones. The mutant histone is still incorporated
    into nucleosomes - this is not a failure to assemble chromatin but a failure
    to assemble it correctly.
  molecular_functions:
  - preferred_term: nucleosomal DNA binding
    term:
      id: GO:0031492
      label: nucleosomal DNA binding
  biological_processes:
  - preferred_term: nucleosome assembly
    modifier: ABNORMAL
    term:
      id: GO:0006334
      label: nucleosome assembly
  cellular_components:
  - preferred_term: nucleosome
    term:
      id: GO:0000786
      label: nucleosome
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Molecular modeling of all 37 variants demonstrated clear disruptions in interactions with DNA, other histones, and histone chaperone proteins."
    explanation: >-
      The structural modelling result this node records; evidence source is
      COMPUTATIONAL because the claim comes from in silico modelling.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Molecular modeling revealed that mutations in the histone core likely affect nucleosome stability, while the mutations in the tail affect various protein-protein interactions."
    explanation: >-
      Gives the domain split between nucleosome destabilisation and disrupted
      protein-protein interaction.
  downstream:
  - target: Aberrant Local Histone Post-Translational Modification
    description: >-
      Incorporated mutant histone carries and induces an abnormal local
      modification state.
- name: Aberrant Local Histone Post-Translational Modification
  biological_scale: MOLECULAR
  description: >-
    Post-translational modification profiling of patient material showed
    abnormal modification patterns that are local to the mutant histone rather
    than global. This is the sharpest mechanistic difference from the somatic
    oncohistones, whose lysine substitutions dysregulate modification across the
    whole genome in trans. Here the changes are in cis on the mutant H3.3, which
    is why the severity of the phenotype cannot be explained by global
    dysregulation of the histone code.
  biological_processes:
  - preferred_term: chromatin remodeling
    modifier: ABNORMAL
    term:
      id: GO:0006338
      label: chromatin remodeling
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Patient histone posttranslational modifications (PTMs) analysis revealed notably aberrant local PTM patterns distinct from the somatic lysine mutations that cause global PTM dysregulation."
    explanation: >-
      Establishes the local rather than global character of the modification
      abnormality.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Together, these data suggest that the mutant histones can be incorporated into the nucleosome, cause marked local deregulation of chromatin state, and modestly alter the global control of histone modifications."
    explanation: >-
      Confirms incorporation of the mutant histone and locates the deregulation
      at the local chromatin level.
  downstream:
  - target: Deregulated Cell Proliferation
    description: >-
      Local chromatin deregulation is followed by transcriptional changes in
      mitosis and cell-division programs.
  - target: Neural Crest and Craniofacial Developmental Defect
    description: >-
      Chromatin dysregulation in neural crest derivatives disturbs craniofacial
      and glial development.
  - target: Abnormal Brain Development
    description: >-
      Chromatin dysregulation in neural lineages disturbs brain development.
- name: Deregulated Cell Proliferation
  biological_scale: CELLULAR
  description: >-
    RNA sequencing of patient cells showed up-regulation of mitosis and
    cell-division genes, and cellular assays confirmed increased proliferative
    capacity. This is the point at which the germline and somatic H3.3 diseases
    converge without becoming the same thing: the germline variants push
    proliferation, but no BLBS patient in the founding cohort had a malignancy,
    including individuals carrying germline substitutions at the same residues
    that act as oncogenic hotspots somatically.
  biological_processes:
  - preferred_term: cell population proliferation
    modifier: INCREASED
    term:
      id: GO:0008283
      label: cell population proliferation
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "RNA sequencing on patient cells demonstrated up-regulated gene expression related to mitosis and cell division, and cellular assays confirmed an increased proliferative capacity."
    explanation: >-
      Provides both the transcriptional and the functional evidence for
      increased proliferation.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, although all known H3.3 mutations in humans cause cancer, none of the patients in our cohort have cancer."
    explanation: >-
      The absence of malignancy despite the proliferative signal, which is why
      this node stops short of a transformation claim.
- name: Neural Crest and Craniofacial Developmental Defect
  biological_scale: TISSUE
  description: >-
    Craniofacial dysmorphism is present in the large majority of patients and is
    the phenotype with the clearest developmental mechanism. In the zebrafish
    h3f3a model, homozygous null larvae lose neural-crest-derived jaw cartilage
    entirely and show reduced foxd3-positive neural-crest-derived glia,
    melanocytes and xanthophores. The glial component is the one that connects to
    the human imaging phenotype: over a third of the patient cohort has
    hypomyelination on brain MRI, and glia are the myelinating cell type.
  cell_types:
  - preferred_term: radial glial cell
    term:
      id: CL:0000681
      label: radial glial cell
  biological_processes:
  - preferred_term: chromatin remodeling
    modifier: ABNORMAL
    term:
      id: GO:0006338
      label: chromatin remodeling
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "A zebrafish model showed craniofacial anomalies and a defect in Foxd3-derived glia."
    explanation: >-
      The model-organism result underlying this node.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "The loss of glial cells may relate to the hypomyelination phenotype that is noted on the brain MRIs of over one-third of the H3.3 cohort as glial cells are the cell type responsible for myelination."
    explanation: >-
      Reports the human cohort imaging finding, from which the link to the
      zebrafish glial defect follows only by inference - the authors hedge the
      connection themselves - so the item is marked INDIRECT.
  downstream:
  - target: Craniofacial Dysmorphism
    description: >-
      Disturbed neural-crest-derived craniofacial development produces the
      dysmorphic facial features.
- name: Abnormal Brain Development
  biological_scale: ORGANISM
  description: >-
    The congenital arm of the phenotype: severe developmental delay, epilepsy,
    tone abnormality and structural brain findings, present from infancy. Just
    over half of individuals with an MRI have at least one abnormal finding, and
    corpus callosum dysgenesis is the commonest named one.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  - preferred_term: corpus callosum
    term:
      id: UBERON:0002336
      label: corpus callosum
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This syndrome is characterized by developmental delay/intellectual disability, craniofacial anomalies, hyper/hypotonia, and abnormal neuroimaging"
    explanation: >-
      States the congenital phenotype cluster this node terminates in.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Within this subgroup, 72% of individuals presented with small posterior fossa, 28% presented with dysgenesis of the corpus collosum, and 44% presented with cortical developmental abnormalities"
    explanation: >-
      Gives the structural findings from the detailed imaging subgroup that
      anchor the structural component of this node.
  downstream:
  - target: Global Developmental Delay and Intellectual Disability
    description: >-
      The dominant clinical consequence of disrupted neural chromatin
      regulation.
  - target: Abnormal Corpus Callosum Morphology
    description: >-
      The commonest specific structural finding on neuroimaging.
  - target: Progressive Postnatal Neuronal H3.3 Dependence
    description: >-
      The same lesion becomes progressively more consequential as neurons mature
      and their H3 pool shifts to H3.3.
- name: Progressive Postnatal Neuronal H3.3 Dependence
  biological_scale: ORGANISM
  description: >-
    The degenerative arm, and the reason the disease has one at all. H3.3
    progressively replaces the replication-dependent H3 variants in postnatal
    brain and comes to dominate the H3 pool in adulthood, so a defective H3.3
    matters more to a neuron the older that neuron gets. The clinical
    correlates are cortical atrophy on imaging and, in adulthood, camptocormia
    and motor decline. The mechanism is an inference from the timing of the
    substrate rather than a demonstrated cause of the human degeneration, which
    is why it is provisional.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "A recent study showed that H3.3 begins to replace H3.1 and H3.2 in postnatal mouse and human brains in a time-dependent manner and displaces these canonical H3 variants almost completely in adulthood."
    explanation: >-
      Supports the developmental-timing explanation for why a congenital histone
      lesion produces an adult-onset degenerative phase.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, 9 of the 46 patients (21%) have demonstrated clinical neurologic degeneration, which suggests that this may be a progressive disorder."
    explanation: >-
      Establishes that a degenerative phase actually occurs, which is the
      phenomenon this node explains.
  downstream:
  - target: Camptocormia
    description: >-
      The characteristic adult-onset motor manifestation of the degenerative
      phase.
  - target: Cerebral Cortical Atrophy
    description: >-
      The imaging correlate of progressive neuronal dysfunction.
phenotypes:
- category: Nervous System
  name: Global Developmental Delay and Intellectual Disability
  description: >-
    Essentially universal and typically in the severe range. Many affected
    individuals never achieve independent sitting, walking or speech.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  frequency: VERY_FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bryant-Li-Bhoj neurodevelopmental syndrome (BRYLIB) is characterized by developmental delay / intellectual disability (typically in the severe range) and nonspecific craniofacial abnormalities."
    explanation: >-
      GeneReviews states developmental delay or intellectual disability as a
      defining, typically severe feature.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ninety-nine percent of individuals with BLBS have DD/ID (Table 1, Fig. 1D, Supplementary Table 1)."
    explanation: >-
      Gives the patient-level frequency underpinning the VERY_FREQUENT band.
- category: Head and Neck
  name: Craniofacial Dysmorphism
  description: >-
    Nonspecific craniofacial abnormalities, present in the large majority.
    Next-generation phenotyping of published facial photographs across germline
    histonopathies has so far failed to establish a recognisable gestalt, so the
    dysmorphism is a supportive rather than a diagnostic pattern.
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  frequency: VERY_FREQUENT
  diagnostic: false
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bryant-Li-Bhoj neurodevelopmental syndrome (BRYLIB) is characterized by developmental delay / intellectual disability (typically in the severe range) and nonspecific craniofacial abnormalities."
    explanation: >-
      GeneReviews names craniofacial abnormality as a defining feature and
      describes it as nonspecific.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition to growth trajectories outside of the standard range for age and sex, 92% of individuals with BLBS present with craniofacial anomalies (Table 1, Fig. 1D, Supplementary Table 1)."
    explanation: >-
      Gives the patient-level frequency underpinning the VERY_FREQUENT band.
  - reference: PMID:40241305
    reference_title: "Coupling deep phenotypic quantification with next-generation phenotyping for 192 individuals with germline histonopathies."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "While these analyses may suggest a histone core versus linker protein basis of delineation, they more strikingly highlight data gaps that confound the identification of phenotypic patterns at this time."
    explanation: >-
      Supports marking the dysmorphism non-diagnostic. The quote reports that
      systematic facial phenotyping has not produced a usable pattern, from
      which the non-diagnostic status follows by inference rather than being
      asserted.
- category: Nervous System
  name: Hypotonia
  description: >-
    Reduced muscle tone, common in infancy. Tone abnormality is not fixed - it
    may resolve with age or evolve into a mixed picture with peripheral
    hypertonia.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  frequency: FREQUENT
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly poor growth), craniosynostosis (of any suture), and ocular involvement."
    explanation: >-
      GeneReviews enumeration of the variable features, hypotonia among them.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixty-two percent of individuals presented with hypotonia whereas 12% presented with hypertonia (Table 1, Fig. 2)."
    explanation: >-
      Gives the patient-level frequency underpinning the FREQUENT band, and the
      hypertonia figure alongside it.
- category: Nervous System
  name: Seizures
  description: >-
    Epilepsy of variable type and childhood onset, listed among the core
    variable features.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  frequency: FREQUENT
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly poor growth), craniosynostosis (of any suture), and ocular involvement."
    explanation: >-
      GeneReviews lists epilepsy among the variable neurologic features.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Forty nine percent of individuals also present with seizures (Table 1)."
    explanation: >-
      Gives the patient-level frequency underpinning the FREQUENT band.
- category: Nervous System
  name: Camptocormia
  description: >-
    Forward flexion of the spine when standing that resolves when lying down.
    Together with worsening gait, spasticity and loss of milestones it is the
    clinical face of the adult neurodegenerative phase.
  phenotype_term:
    preferred_term: Camptocormia
    term:
      id: HP:0100595
      label: Camptocormia
    onset:
      onset_category: ADULT
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly poor growth), craniosynostosis (of any suture), and ocular involvement."
    explanation: >-
      GeneReviews defines camptocormia and lists it among the neurologic
      findings of this syndrome.
- category: Nervous System
  name: Spasticity
  description: >-
    Increased tone with pyramidal features, part of the later neurologic picture
    alongside worsening gait and loss of milestones.
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly poor growth), craniosynostosis (of any suture), and ocular involvement."
    explanation: >-
      GeneReviews lists spasticity among the neurologic findings.
- category: Nervous System
  name: Cerebral Cortical Atrophy
  description: >-
    Cortical atrophy on brain MRI in roughly a quarter of the founding cohort,
    including individuals without intractable epilepsy - so it is not simply a
    consequence of seizure burden.
  phenotype_term:
    preferred_term: Cerebral cortical atrophy
    term:
      id: HP:0002120
      label: Cerebral cortical atrophy
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Multiple patients (26% of the cohort) have cortical atrophy on brain magnetic resonance imaging (MRI), even without intractable epilepsy."
    explanation: >-
      Gives the 26% figure and the observation that it occurs independently of
      intractable epilepsy.
- category: Nervous System
  name: Delayed CNS Myelination
  description: >-
    Hypomyelination on brain MRI in over a third of the cohort, the human
    counterpart of the glial defect seen in the zebrafish model.
  phenotype_term:
    preferred_term: Delayed CNS myelination
    term:
      id: HP:0002188
      label: Delayed CNS myelination
  frequency: FREQUENT
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The loss of glial cells may relate to the hypomyelination phenotype that is noted on the brain MRIs of over one-third of the H3.3 cohort as glial cells are the cell type responsible for myelination."
    explanation: >-
      Gives the frequency of the hypomyelination finding in the cohort.
- category: Head and Neck
  name: Craniosynostosis
  description: >-
    Premature fusion of any cranial suture, listed by GeneReviews among the
    variable features and part of the standard management checklist.
  phenotype_term:
    preferred_term: Craniosynostosis
    term:
      id: HP:0001363
      label: Craniosynostosis
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly poor growth), craniosynostosis (of any suture), and ocular involvement."
    explanation: >-
      GeneReviews names craniosynostosis of any suture as a feature.
- category: Growth
  name: Poor Growth
  description: >-
    Growth abnormality, most commonly poor growth, is a recognised feature and
    growth parameters are measured at every visit under the GeneReviews
    surveillance plan.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  frequency: FREQUENT
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Height ( ≤5th percentile) 32/91 (35%)"
    explanation: >-
      Gives the patient-level frequency of short stature specifically, which is
      the term bound here.
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presentation is highly variable and can include hypotonia, epilepsy, other neurologic findings (spasticity, loss of developmental milestones, worsening gait, and/or camptocormia – forward flexion of the spine when standing that resolves when lying down), growth abnormalities (most commonly poor growth), craniosynostosis (of any suture), and ocular involvement."
    explanation: >-
      GeneReviews identifies poor growth as the usual direction of the growth
      abnormality.
- category: Eye
  name: Ocular Involvement
  description: >-
    Oculomotor dysfunction in just over half the cohort, with eye rolling and
    strabismus the commonest manifestations and a marked female excess. The
    bound term stays at the level of eye movement because that is what the
    prose reports a frequency for; annual ophthalmology evaluation is part of
    the recommended surveillance.
  phenotype_term:
    preferred_term: Abnormality of eye movement
    term:
      id: HP:0000496
      label: Abnormality of eye movement
  frequency: FREQUENT
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "More females (64%) present with oculomotor dysfunction than males (44%) (Fig. 2)."
    explanation: >-
      Gives sex-stratified patient-level frequencies for oculomotor dysfunction,
      which is the level the bound term describes.
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Annually or as clinically indicated: ophthalmology evaluation, audiology evaluation, and thyroid function tests."
    explanation: >-
      Supports ocular involvement as an actively surveilled feature; this quote
      establishes the surveillance, not the specific finding.
- category: Digestive
  name: Feeding Difficulties
  description: >-
    Feeding problems and poor weight gain, common in infancy; feeding therapy
    and, if persistent, gastrostomy are the recommended responses.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment of manifestations: Feeding issues and poor weight gain may benefit from feeding therapy; in individuals with persistent feeding issues, gastrostomy tube may be considered."
    explanation: >-
      GeneReviews management guidance, which presupposes feeding difficulty as a
      recognised manifestation.
- category: Cardiovascular
  name: Congenital Heart Defect
  description: >-
    Cardiac anomalies occur in roughly one in eight and are described by
    GeneReviews as rare relative to the neurologic features. The cohort table
    reports cardiac involvement as a single category without a septal
    breakdown, so the bound term is left at the level the sources support.
  phenotype_term:
    preferred_term: Abnormal heart morphology
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Fourteen percent of individuals present with cardiac anomalies, including atrial septal defects (Fig. 1D)."
    explanation: >-
      Gives the patient-level frequency of cardiac anomalies and names atrial
      septal defect as a constituent without giving a septal breakdown.
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital anomalies are rare but can include congenital heart defects, brain malformations, and genitourinary abnormalities in males."
    explanation: >-
      GeneReviews records congenital heart defects as a rare but recognised
      anomaly.
- category: Genitourinary
  name: Genitourinary Anomalies in Males
  description: >-
    Genitourinary abnormalities in males, including undescended testes, which
    GeneReviews lists for standard treatment.
  phenotype_term:
    preferred_term: Cryptorchidism
    term:
      id: HP:0000028
      label: Cryptorchidism
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Standard treatment for developmental delay / intellectual disability, attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety, epilepsy, spasticity, constipation, craniosynostosis, vision issues, hearing loss, congenital heart defects, undescended testes, and hypothyroidism."
    explanation: >-
      Names undescended testes specifically, which is the term bound here; the
      general "genitourinary abnormalities" phrasing elsewhere in GeneReviews
      does not reach that level of specificity.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Twenty percent of individuals present with genital anomalies (Fig. 1D, Table 1, Supplementary Table 1)."
    explanation: >-
      Gives the patient-level frequency of genital anomalies as a category.
- category: Nervous System
  name: Delayed Ability to Walk
  description: >-
    Delayed or absent independent walking, defined in the cohort as not walking
    by 20 months. The commonest motor milestone delay recorded.
  phenotype_term:
    preferred_term: Delayed ability to walk
    term:
      id: HP:0031936
      label: Delayed ability to walk
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "More individuals harboring variants in H3-3A (85%) had delayed or yet to be achieved independent walking when compared to individuals harboring variants in H3-3B (65%)."
    explanation: >-
      Gives the H3-3A-specific frequency, which is the one this entry needs.
- category: Nervous System
  name: Delayed Speech and Language Development
  description: >-
    Delayed or absent speech. GeneReviews records that many affected
    individuals never achieve speech at all, and the cohort table reports the
    first-word milestone separately from sitting and walking.
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  frequency: FREQUENT
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Many affected individuals do not achieve independent sitting, walking, or speaking, although there is a range of developmental outcomes."
    explanation: >-
      Establishes speech delay or absence as a core feature; GeneReviews does
      not give a separate frequency for it.
- category: Nervous System
  name: Delayed Ability to Sit
  description: >-
    Delayed or absent independent sitting, defined in the cohort as not sitting
    by 12 months.
  phenotype_term:
    preferred_term: Delayed ability to sit
    term:
      id: HP:0025336
      label: Delayed ability to sit
  frequency: FREQUENT
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals with variants in H3-3A (56%) more frequently had delayed or yet to be achieved independent sitting compared to individuals with variants in H3-3B (43%) (Fig. 2)."
    explanation: >-
      Gives the H3-3A-specific frequency, which is the one this entry needs.
- category: Nervous System
  name: Abnormal Corpus Callosum Morphology
  description: >-
    Malformation or dysgenesis of the corpus callosum, the commonest named
    structural finding among individuals with an abnormal MRI.
  review_notes: >-
    Two figures exist and they differ. The cohort table reports 28/76 (37%)
    across everyone with reported imaging; the quoted prose reports 28% within
    the subgroup of 18 images analysed in detail by Alves et al. The band is set
    from the quoted figure rather than from the table, because the table cell is
    three words and not quotable as evidence under check-snippet-length.
  phenotype_term:
    preferred_term: Abnormal corpus callosum morphology
    term:
      id: HP:0001273
      label: Abnormal corpus callosum morphology
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Within this subgroup, 72% of individuals presented with small posterior fossa, 28% presented with dysgenesis of the corpus collosum, and 44% presented with cortical developmental abnormalities"
    explanation: >-
      Gives the frequency of corpus callosum dysgenesis in the subgroup whose
      images were analysed in detail.
- category: Head and Neck
  name: Microcephaly
  description: >-
    Head circumference at or below the fifth percentile. Macrocephaly also
    occurs, in about 15%, so head size is bidirectionally abnormal rather than
    uniformly small.
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  frequency: FREQUENT
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among these individuals, microcephaly is more common than macrocephaly (32 and 15%, respectively), which is consistent across all variables interrogated (Table 1)."
    explanation: >-
      Gives both head-size frequencies and states which direction predominates.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, 46% of individuals with craniofacial anomalies present with concurrent microcephaly or macrocephaly (Table 1, Fig. 1D, Supplementary Table 1)."
    explanation: >-
      Ties head size to the craniofacial phenotype, and covers both directions,
      which is why the entry does not treat small head size as uniform.
- category: Nervous System
  name: Hypertonia
  description: >-
    Increased muscle tone. A mixed pattern of axial hypotonia with peripheral
    hypertonia is reported separately and occurs in about a tenth of the cohort.
  phenotype_term:
    preferred_term: Hypertonia
    term:
      id: HP:0001276
      label: Hypertonia
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixty-two percent of individuals presented with hypotonia whereas 12% presented with hypertonia (Table 1, Fig. 2)."
    explanation: >-
      Gives the patient-level frequency of hypertonia alongside that of
      hypotonia.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Interestingly, 10% of individuals have concordant axial hypotonia and peripheral hypertonia, or dystonia, which is exclusively present in individuals with variants in the core (Fig. 2, light gray)."
    explanation: >-
      Records the mixed tone pattern and the fact that it occurs only with
      core-domain variants.
- category: Integument
  name: Dermatologic Features
  description: >-
    Skin findings as a category, reported in about half the cohort. Individual
    findings are less common: eczema in 7%, nipple anomalies in 17%, fetal
    finger pads in 16%.
  phenotype_term:
    preferred_term: Abnormality of the skin
    term:
      id: HP:0000951
      label: Abnormality of the skin
  frequency: FREQUENT
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Dermal features are more likely found in individuals with variants in the tail (64%) than the core (45%)."
    explanation: >-
      Gives the patient-level frequency of dermatologic features, split by the
      protein domain the variant falls in.
- category: Musculoskeletal
  name: Musculoskeletal Anomalies
  description: >-
    Musculoskeletal anomalies in over half the cohort, reported as a category
    covering club foot, scoliosis, hip dysplasia, joint subluxation and
    hypermobility, kyphosis and femoral anteversion. The bound term stays at
    the category level because the prose gives a frequency for the category and
    not for its constituents.
  phenotype_term:
    preferred_term: Abnormal skeletal morphology
    term:
      id: HP:0011842
      label: Abnormal skeletal morphology
  frequency: FREQUENT
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Over half of individuals (58%) present with musculoskeletal anomalies such as club foot, scoliosis, hip dysplasia, subluxation of various joints/hypermobility, kyphosis, and femoral anteversion"
    explanation: >-
      Gives the frequency of the musculoskeletal category and names scoliosis
      among its constituents; no scoliosis-specific frequency is reported in
      prose, so none is recorded here.
- category: Ear
  name: Hearing Impairment
  description: >-
    Hearing loss is listed by GeneReviews for standard treatment and is
    surveilled annually by audiology, but no cohort frequency is reported.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Standard treatment for developmental delay / intellectual disability, attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety, epilepsy, spasticity, constipation, craniosynostosis, vision issues, hearing loss, congenital heart defects, undescended testes, and hypothyroidism."
    explanation: >-
      GeneReviews names hearing loss among the manifestations requiring
      treatment.
- category: Nervous System
  name: Autism Spectrum Disorder
  description: >-
    Autism spectrum disorder is listed by GeneReviews among the manifestations
    requiring standard treatment, alongside attention-deficit/hyperactivity
    disorder and anxiety. No cohort frequency is reported.
  phenotype_term:
    preferred_term: Autism
    term:
      id: HP:0000717
      label: Autism
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Standard treatment for developmental delay / intellectual disability, attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety, epilepsy, spasticity, constipation, craniosynostosis, vision issues, hearing loss, congenital heart defects, undescended testes, and hypothyroidism."
    explanation: >-
      GeneReviews names autism spectrum disorder among the manifestations
      requiring treatment.
genetic:
- name: H3-3A
  gene_term:
    preferred_term: H3-3A
    term:
      id: hgnc:4764
      label: H3-3A
  relationship_type: CAUSATIVE
  variant_origin: DE_NOVO
  notes: >-
    H3-3A (formerly H3F3A) encodes the replication-independent histone variant
    H3.3, identical in protein sequence to the product of H3-3B. The two genes
    differ in regulatory and coding sequence, giving different expression
    patterns and levels, and it is that paralog-level difference - not a
    difference in protein - that separates BLBS1 from BLBS2. Variants are
    private and distributed across the protein; the most recurrent reported
    allele is p.Thr45Ile.
  case_fractions:
  - population: Global BLBS cohort reported through 2024
    case_fraction_percent: 67.7
    cohort_size: 96
    notes: >-
      65 of 96 reported individuals with BLBS carried an H3-3A variant, the
      remainder H3-3B. This is a discovery-cohort split rather than a
      population estimate.
    evidence:
    - reference: PMID:38678163
      reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In total, 65 individuals harbor variants in H3-3A and 31 individuals harbor variants in H3-3B."
      explanation: >-
        Gives the gene split within the reported BLBS cohort.
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this work, we have identified a cohort of 46 unrelated patients bearing de novo heterozygous germline missense mutations in H3F3A or H3F3B with a core phenotype of progressive neurologic dysfunction and congenital anomalies."
    explanation: >-
      Establishes the gene-disease relationship in the founding cohort.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In the general population, both genes have a very low rate of missense variants; the gnomAD missense Z score is 3.21 for H3F3A and 2.95 for H3F3B (>2 is significant)"
    explanation: >-
      Documents the strong missense constraint on H3-3A that supports
      pathogenicity of de novo missense alleles.
variants:
- name: H3-3A p.Thr45Ile
  description: >-
    The most recurrently reported BLBS1 allele, carried by four individuals in
    the 2024 cohort. Those four show substantial phenotypic variability, which is
    the clearest single demonstration that genotype does not determine phenotype
    in this disease.
  gene:
    preferred_term: H3-3A
    term:
      id: hgnc:4764
      label: H3-3A
  clinical_significance: PATHOGENIC
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Length of lollipop corresponds to number of individuals who harbor a variant at that residue (e.g. H3-3A p.T45I represents four individuals with BLBS and H3-3A p.V46M represents one individual with BLBS)."
    explanation: >-
      Identifies p.Thr45Ile as the most recurrent H3-3A allele in the reported
      cohort.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, phenotypic heterogeneity was present even amongst individuals harboring the same variant."
    explanation: >-
      Supports the statement that recurrence of an allele does not bring
      phenotypic concordance.
diagnosis:
- name: Molecular genetic testing of H3-3A
  description: >-
    The diagnosis is molecular. There is no biochemical marker and no
    recognisable facial gestalt, so it is established by finding a heterozygous
    pathogenic H3-3A variant in a proband with suggestive features - almost
    always through exome or genome sequencing performed for undiagnosed
    developmental delay.
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of BRYLIB is established in a proband with suggestive findings and a heterozygous pathogenic variant in either H3-3A (H3F3A) or H3-3B (H3F3B) identified by molecular genetic testing."
    explanation: >-
      GeneReviews statement of the diagnostic criterion.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These patients were identified through exome or genome sequencing performed for the indication of neurodevelopmental delays and/or congenital anomalies"
    explanation: >-
      Documents the ascertainment route through which the diagnosis is
      practically made.
differential_diagnoses:
- name: Bryant-Li-Bhoj neurodevelopmental syndrome 2
  description: >-
    The H3-3B counterpart. The two genes encode an identical protein, so the
    entities are separated by gene rather than by protein product and are
    clinically overlapping. Only molecular testing distinguishes them.
    Cohort-level trends exist but are not diagnostic discriminators, and the
    H3-3A cohort differs in that every variant with parental data has been de
    novo and missense, whereas H3-3B has yielded synonymous, stop-loss and one
    inherited allele.
  disease_term:
    preferred_term: Bryant-Li-Bhoj neurodevelopmental syndrome 2
    term:
      id: MONDO:0030607
      label: Bryant-Li-Bhoj neurodevelopmental syndrome 2
  distinguishing_features:
  - "Determined solely by molecular testing: a pathogenic variant in H3-3A rather than H3-3B"
  - Greater variant-type and inheritance diversity is reported for H3-3B, including a synonymous stop-gain, a stop-loss and one inherited allele
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Conversely, while most variants in H3-3B are heterozygous de novo missense variants, more variability in variant type and modes of inheritance was observed."
    explanation: >-
      States the variant-type difference between the two genes that this
      differential rests on.
- name: Somatic H3.3 oncohistone disease
  description: >-
    Substitutions at the same H3.3 residues - K27M, G34R/V, K36M - occur
    somatically and drive paediatric diffuse midline glioma and giant cell
    tumour of bone. This is a molecular contrast rather than a clinical
    differential, but it matters when a germline result at one of those residues
    is reported: the germline and somatic diseases have different mechanisms,
    and germline carriers of G34R/V substitutions have not developed the
    corresponding tumours.
  distinguishing_features:
  - Germline variants are private and scattered across the protein; oncohistone substitutions are recurrent hotspots
  - Germline variants deregulate histone modification locally and in cis; somatic lysine substitutions dysregulate it globally in trans
  - No malignancy occurred in the founding BLBS cohort
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Patient histone posttranslational modifications (PTMs) analysis revealed notably aberrant local PTM patterns distinct from the somatic lysine mutations that cause global PTM dysregulation."
    explanation: >-
      Gives the molecular basis on which the germline and somatic diseases are
      separated.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These data suggest that the mechanism of germline mutations are distinct from cancer-associated somatic histone mutations but may converge on control of cell proliferation."
    explanation: >-
      The authors' own framing of the relationship between the two diseases.
treatments:
- name: Supportive and Developmental Management
  description: >-
    There is no disease-modifying therapy. Management is standard treatment of
    each manifestation - developmental delay, attention-deficit/hyperactivity
    disorder, autism spectrum disorder, anxiety, epilepsy, spasticity,
    constipation, craniosynostosis, vision and hearing problems, congenital heart
    defects, undescended testes and hypothyroidism - with early developmental
    intervention and feeding support.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Standard treatment for developmental delay / intellectual disability, attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety, epilepsy, spasticity, constipation, craniosynostosis, vision issues, hearing loss, congenital heart defects, undescended testes, and hypothyroidism."
    explanation: >-
      GeneReviews management guidance, which is symptomatic throughout.
- name: Structured Surveillance
  description: >-
    Growth parameters, nutrition and oral intake safety, constipation, new
    manifestations such as seizures and changes in tone or gait, developmental
    progress and behaviour at every visit; ophthalmology, audiology and thyroid
    function annually. The tone-and-gait item is the one that matters for the
    degenerative phase, since new motor decline in adulthood is expected rather
    than incidental.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At each visit: measure growth parameters; assess nutrition safety and oral intake; monitor for constipation; assess for new manifestations, such as seizures and changes in tone and/or gait; monitor developmental progress and educational needs; and assess for behavioral issues, such as mobility and self-help skills."
    explanation: >-
      The GeneReviews surveillance schedule recorded in this entry.
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Annually or as clinically indicated: ophthalmology evaluation, audiology evaluation, and thyroid function tests."
    explanation: >-
      The annual component of the same surveillance schedule.
- name: Genetic Counseling
  description: >-
    Because the variants are de novo, recurrence risk to other family members is
    presumed low. Once a variant is identified, prenatal and preimplantation
    genetic testing become available.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:37782742
    reference_title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Therefore, the risk to other family members is presumed to be low. Once an H3-3A (H3F3A) or H3-3B (H3F3B) pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible."
    explanation: >-
      GeneReviews counselling guidance, including the reproductive testing
      options.
animal_models:
- name: H3.3 T45I knock-in mouse
  species: Mus musculus
  genotype: h3-3a p.T45I knock-in
  publication: DOI:10.64898/2026.06.16.732665
  description: >-
    A knock-in mouse carrying h3-3a p.T45I, the most recurrent BLBS1 allele and
    the one this entry curates under variants. It is genotype-matched to human
    disease rather than a null, which is what distinguishes it from the
    zebrafish model, and it reproduces the two-phase natural history: perinatal
    growth restriction and delayed developmental milestones early, progressive
    motor and gait impairment later. Adult animals additionally show
    craniofacial differences and behavioural changes. Reported so far only as a
    preprint.
  modeled_mechanisms:
  - target: Progressive Postnatal Neuronal H3.3 Dependence
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces progressive motor and gait impairment on a congenital
      genotype, which is the phenomenon this node exists to explain.
    limitations: >-
      Progressive motor impairment in a mouse is not camptocormia, and the
      preprint reports no cortical atrophy or other neuropathological correlate,
      so the node's proposed mechanism - the postnatal shift of the neuronal H3
      pool to H3.3 - is not itself tested by these endpoints. Peer review is
      pending.
    readouts:
    - name: Motor and gait performance
      target: Progressive Postnatal Neuronal H3.3 Dependence
      direction: DECREASED
      interpretation: >-
        Progressive decline in motor and gait measures with age, the behavioural
        correlate of the degenerative phase.
      evidence:
      - reference: DOI:10.64898/2026.06.16.732665
        reference_title: "A novel preclinical mouse model recapitulates progressive phenotypes of Bryant-Li-Bhoj Syndrome"
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "mice recapitulate the BLBS natural history: perinatal growth restriction, delayed developmental milestones, and progressive motor and gait impairments."
        explanation: >-
          Reports the progressive motor and gait measurement behind this
          readout.
    evidence:
    - reference: DOI:10.64898/2026.06.16.732665
      reference_title: "A novel preclinical mouse model recapitulates progressive phenotypes of Bryant-Li-Bhoj Syndrome"
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The non-invasive, clinically translatable endpoints established here provide a validated preclinical platform for evaluating therapeutics for a community whose current standard of care is symptom management."
      explanation: >-
        The authors position the model as a validated platform for this disease,
        which is what makes it informative for a disease-level node.
  - target: Abnormal Brain Development
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces delayed developmental milestones and perinatal growth
      restriction.
    limitations: >-
      Mouse developmental milestones are not a counterpart of human
      developmental delay or intellectual disability, and the preprint reports
      no structural brain phenotype - no corpus callosum, posterior fossa or
      myelination finding - so the imaging component of this node is unmodelled.
      Seizures are not reported either.
    readouts:
    - name: Developmental milestone attainment
      target: Abnormal Brain Development
      direction: DECREASED
      interpretation: >-
        Delayed attainment of developmental milestones in mutant pups.
      evidence:
      - reference: DOI:10.64898/2026.06.16.732665
        reference_title: "A novel preclinical mouse model recapitulates progressive phenotypes of Bryant-Li-Bhoj Syndrome"
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "mice recapitulate the BLBS natural history: perinatal growth restriction, delayed developmental milestones, and progressive motor and gait impairments."
        explanation: >-
          Reports the milestone measurement behind this readout.
    evidence:
    - reference: DOI:10.64898/2026.06.16.732665
      reference_title: "A novel preclinical mouse model recapitulates progressive phenotypes of Bryant-Li-Bhoj Syndrome"
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Here, we characterize the developmental and neurobehavioral phenotypes of a novel BLBS mouse model harboring one of the most recurrent causative variants"
      explanation: >-
        Establishes that the model is genotype-matched to a recurrent human
        allele, which is what makes it informative for the developmental node.
  - target: Neural Crest and Craniofacial Developmental Defect
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: >-
      Adult mutant animals show craniofacial differences.
    limitations: >-
      The preprint reports craniofacial difference as a phenotype without
      linking it to neural crest biology, and the human dysmorphism has no
      recognisable gestalt to compare against, so the correspondence is at the
      level of "the face is different" and no further.
    evidence:
    - reference: DOI:10.64898/2026.06.16.732665
      reference_title: "A novel preclinical mouse model recapitulates progressive phenotypes of Bryant-Li-Bhoj Syndrome"
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Adult mice additionally display craniofacial differences, impaired nest building, hyperactivity in a social context, and male-specific elevated aggression."
      explanation: >-
        Reports the craniofacial phenotype in adult animals.
  evidence:
  - reference: DOI:10.64898/2026.06.16.732665
    reference_title: "A novel preclinical mouse model recapitulates progressive phenotypes of Bryant-Li-Bhoj Syndrome"
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "mice recapitulate the BLBS natural history: perinatal growth restriction, delayed developmental milestones, and progressive motor and gait impairments."
    explanation: >-
      Summarises the two-phase natural history this model reproduces.
- name: Zebrafish h3f3a model
  species: Danio rerio
  genotype: h3f3a p.D123N dominant allele; h3f3a db1092 homozygous null
  publication: PMID:33268356
  description: >-
    A zebrafish model of the orthologous gene. A dominant p.D123N allele
    recovered from a forward genetic screen sits two residues from a patient
    variant (p.Q125R) and reproduces both the dominant inheritance and the
    craniofacial anomalies of the human disease. Homozygous db1092 null larvae
    lose neural-crest-derived jaw cartilage completely and show reduced
    foxd3-positive cranial glia, melanocytes and xanthophores. Because the model
    targets the h3f3a paralog, it is the direct ortholog for BLBS1 rather than
    for BLBS2.
  modeled_mechanisms:
  - target: Neural Crest and Craniofacial Developmental Defect
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      The model reproduces the craniofacial and neural-crest-derived glial
      components of the human phenotype.
    limitations: >-
      The dominant allele is p.D123N, not a patient allele, and the strongest
      cartilage and pigment-cell phenotypes come from the homozygous null rather
      than from a heterozygous missense genotype - so the model is closer to
      loss of h3f3a function than to the gain-of-function or dominant-negative
      mechanism inferred in patients. Zebrafish craniofacial cartilage is not a
      direct counterpart of human facial dysmorphism, and the model says nothing
      about the neurodevelopmental or degenerative phenotypes that dominate the
      human disease.
    readouts:
    - name: Neural-crest-derived jaw cartilage
      target: Neural Crest and Craniofacial Developmental Defect
      direction: DECREASED
      interpretation: >-
        Complete loss of jaw cartilage in homozygous null larvae, the structural
        readout of the craniofacial node.
      evidence:
      - reference: PMID:33268356
        reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Homozygous h3f3adb1092 mutants display complete loss of neural crest–derived jaw cartilages (n = 10/10)."
        explanation: >-
          Reports the cartilage measurement behind this readout.
    - name: foxd3-positive cranial glia
      target: Neural Crest and Craniofacial Developmental Defect
      direction: DECREASED
      interpretation: >-
        Reduced cranial glia, the readout that connects the model to the human
        hypomyelination finding.
      evidence:
      - reference: PMID:33268356
        reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Homozygous h3f3adb1092 mutants injected at the one-cell stage with a control mCherry RNA show partial reductions in cranial glia (n = 5), melanocytes (n = 4), and xanthophores (n = 3), while those injected with dominant-negative H3f3a RNA to further reduced H3.3A function show complete loss of melanocytes (n = 5) and severe reductions of glia (n = 6) and xanthophores (n = 4) throughout cranial and trunk regions."
        explanation: >-
          Reports the in situ hybridization measurements of glia, melanocytes
          and xanthophores in this model.
    evidence:
    - reference: PMID:33268356
      reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "This heterozygous missense variant replicates the dominant inheritance observed in humans and is only two amino acids away from a mutation identified in an affected patient (p.Q125R)."
      explanation: >-
        Supports treating this model as informative for the human craniofacial
        node, on the strength of the shared dominant inheritance and the
        proximity of the allele to a patient variant.
  associated_phenotypes:
  - Craniofacial anomalies
  - Loss of neural-crest-derived jaw cartilage
  - Reduced foxd3-positive neural-crest-derived glia
  evidence:
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "A zebrafish model showed craniofacial anomalies and a defect in Foxd3-derived glia."
    explanation: >-
      Summarises the model phenotype recapitulating the craniofacial and glial
      components of the disease.
discussions:
- discussion_id: blbs1_genotype_phenotype_unexplained
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    What accounts for the phenotypic variability that gene, protein domain and
    sex together fail to explain - including variability between individuals
    carrying the same H3-3A allele?
  attaches_to:
  - pathophysiology#De Novo H3-3A Variant Altering Histone H3.3
  - phenotypes#
  rationale: >-
    The 2024 cohort tested three candidate explanatory variables against the
    phenotype and found that variant location and affected gene contribute more
    than sex, but that none of them accounts for the observed variation. Four
    individuals sharing H3-3A p.Thr45Ile have substantially different
    presentations. The founding report had gone further, concluding that neither
    variant location nor which gene was involved affected the phenotype at all;
    the larger cohort softened that to statistical trends. Either way there is a
    determinant that has not been found, and the authors raise gene-environment
    interaction as a possibility precisely because histones sit at the
    genetics-epigenetics interface.
  evidence:
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Since these variables do not account for all BLBS phenotypic variability, these findings suggest that additional factors may play a role in modifying the phenotypes of affected individuals."
    explanation: >-
      States the residual, unexplained variability directly.
  - reference: PMID:38678163
    reference_title: "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, phenotypic heterogeneity was present even amongst individuals harboring the same variant."
    explanation: >-
      Shows that the unexplained variability persists at fixed genotype, which
      rules out variant identity as the missing determinant.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mutations are spread throughout the coding sequence, and neither the location of the mutation nor whether the mutation is in H3F3A or H3F3B appears to affect the phenotype."
    explanation: >-
      The earlier and stronger negative claim, since qualified by the larger
      cohort. It is marked INDIRECT because it overstates the absence of any
      correlation, so the knowledge gap follows from it only once that
      overstatement is discounted.
- discussion_id: blbs1_cancer_predisposition
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Do germline H3.3 variants confer cancer predisposition, given that the same
    residues are oncogenic when altered somatically?
  attaches_to:
  - pathophysiology#Deregulated Cell Proliferation
  rationale: >-
    Patient cells show up-regulated mitosis and division programs and increased
    proliferative capacity, and germline substitutions occur at residues whose
    somatic counterparts drive paediatric glioma - yet no malignancy occurred in
    the founding cohort. A 2025 survey of 192 individuals with germline
    histonopathies identified the second known individual with both a germline
    histonopathy and a cancer diagnosis, putting community-wide incidence at 1%,
    below the 5% threshold at which routine tumour surveillance is recommended.
    So the current answer is "no surveillance", reached on a denominator small
    enough that the question stays open, and the authors name it as outstanding.
  evidence:
  - reference: PMID:40241305
    reference_title: "Coupling deep phenotypic quantification with next-generation phenotyping for 192 individuals with germline histonopathies."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, the community-wide cancer incidence is currently 1%, which falls below the recommended 5% cut off for routine surveillance."
    explanation: >-
      Argues against clinically actionable cancer predisposition at present,
      which is why no surveillance treatment is curated in this entry.
  - reference: PMID:40241305
    reference_title: "Coupling deep phenotypic quantification with next-generation phenotyping for 192 individuals with germline histonopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the value of ongoing translational work to address the outstanding question of cancer predisposition for individuals living with germline histonopathies"
    explanation: >-
      The authors name cancer predisposition as an outstanding question, which
      is the gap recorded here.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, although all known H3.3 mutations in humans cause cancer, none of the patients in our cohort have cancer."
    explanation: >-
      States the paradox that makes the question worth keeping open.
- discussion_id: blbs1_no_neurodevelopmental_model
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Do the available in vivo models capture a disease caused by heterozygous
    gain-of-function or dominant-negative alleles, when one is a homozygous null
    and the other is scored on behavioural endpoints with no
    neuropathological correlate?
  attaches_to:
  - animal_models#Zebrafish h3f3a model
  - animal_models#H3.3 T45I knock-in mouse
  - pathophysiology#Progressive Postnatal Neuronal H3.3 Dependence
  rationale: >-
    The two models fail in opposite directions. The zebrafish h3f3a mutant has a
    dominant allele that reproduces the mode of inheritance, but its strong
    cartilage and pigment-cell phenotypes come from the homozygous null - a
    loss-of-function genotype, where the human disease is read as gain of
    function or dominant negative on a background of three wild-type H3.3
    alleles - and it speaks only to craniofacial and glial development. The
    T45I knock-in mouse fixes the genotype problem exactly, carrying the most
    recurrent human allele in heterozygous form, and reproduces the two-phase
    natural history; but its endpoints are developmental milestones, gait and
    behaviour, with no reported structural brain phenotype and no
    neuropathology. So the entry's central claim - that the degenerative phase
    follows from the postnatal shift of the neuronal H3 pool to H3.3 - is
    consistent with the mouse but not tested by it, and the structural findings
    that define the human neuroimaging phenotype have no in vivo counterpart in
    either model. The mouse is also so far a preprint.
  evidence:
  - reference: PMID:36867246
    reference_title: "Histone 3.3-related chromatinopathy: missense variants throughout H3-3A and H3-3B cause a range of functional consequences across species."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Most of the causative variants are private and scattered throughout the protein, but all seem to have either a gain-of-function or dominant negative effect on protein function. This is highly unusual and not well understood."
    explanation: >-
      States the human mechanism that a null model does not reproduce, and
      concedes it is not well understood.
  - reference: DOI:10.64898/2026.06.16.732665
    reference_title: "A novel preclinical mouse model recapitulates progressive phenotypes of Bryant-Li-Bhoj Syndrome"
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Adult mice additionally display craniofacial differences, impaired nest building, hyperactivity in a social context, and male-specific elevated aggression."
    explanation: >-
      The mouse endpoints are behavioural and morphometric throughout; no
      structural brain or neuropathological readout is reported, which is the
      half of the human phenotype that stays unmodelled.
  - reference: PMID:33268356
    reference_title: "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Homozygous h3f3adb1092 mutants display complete loss of neural crest–derived jaw cartilages (n = 10/10)."
    explanation: >-
      The informative cartilage phenotype comes from a homozygous null, which is
      the genotype mismatch this discussion records.
references:
- reference: PMID:37782742
  title: "Bryant-Li-Bhoj Neurodevelopmental Syndrome"
  tags:
  - GeneReviews
notes: >-
  Entity scope: this entry covers BLBS1 (H3-3A, OMIM 619720) only. The H3-3B
  counterpart, BLBS2, already exists as its own entry and is recorded here as a
  differential diagnosis, mirroring how that entry treats BLBS1.

  Cohort figures are reported for the combined BLBS cohort far more often than
  they are stratified by gene, because the two genes encode an identical protein
  and were ascertained together. Where a gene-stratified number exists it is
  used and labelled; where only a combined-cohort figure exists it is quoted as
  such. The one firmly H3-3A-specific statement available is that every H3-3A
  variant with parental data has been a de novo missense change, which is not
  true of H3-3B.

  `just preflight-dr` returned WARN on the research report: H3-3B is mentioned
  27 times against 34 for H3-3A, because the report discusses both entities. The
  report's H3-3B-specific content - the p.Leu48Arg iPSC hyper-deposition model,
  the inherited p.Asn108Ser allele, the synonymous stop-gain and stop-loss
  alleles - was excluded from this entry rather than folded in.

  No `conforms_to` declaration is made against
  `epigenetic_machinery_neurodevelopmental_dysregulation`. That module's entry
  node is haploinsufficiency of an epigenetic machinery component, and this
  disease is explicitly not haploinsufficiency: three of four H3.3 alleles are
  wild type and the mechanism is read as gain of function or dominant negative.
  The sibling BLBS2 entry makes the same choice.

  Two animal models are curated. The h3-3a p.T45I knock-in mouse
  (DOI:10.64898/2026.06.16.732665) is genotype-matched to the recurrent human
  allele this entry records under `variants`, and is so far a preprint; it is
  curated because it is the only in vivo model of an actual patient allele, and
  its preprint status and its purely behavioural endpoints are stated in the
  link `limitations` and in the HUMAN_MODEL_MISMATCH discussion. The `DOI:`
  prefix is in the reference validator's `skip_prefixes`, so its seven snippets
  are not machine-verified; each was checked by hand against
  `references_cache/DOI_10.64898_2026.06.16.732665.md`.

  Two ontology CURIEs suggested by the research report were wrong and were
  replaced after checking the ontologies directly: HP:0031808 is "Decreased
  total basophil count", not Camptocormia (HP:0100595), and CL:0002608 is
  "hippocampal neuron", not radial glial cell (CL:0000681). HP:0007256 was also
  offered for spasticity but is "Abnormal pyramidal sign"; HP:0001257 is used
  instead.

  A ClinGen Definitive gene-disease validity classification for H3-3A to BLBS1
  was dropped rather than left as uncited prose: `just clingen-refresh`
  currently fails on a checksum mismatch against the pinned
  `gene_validity.csv`, so no `CGGV:` record could be generated to quote, and
  fixing that pin is a repository-maintenance change rather than part of this
  entry.

  Six of the reference-cache files added alongside this entry are not cited.
  They were screened and set aside: they come from the deep-research run's own
  citation-validation pass and are committed because the report that cites them
  is committed, not because they support anything in the entry.

  Phenotype frequencies come from Table 1 of the 2024 cohort paper, which
  reports the combined BLBS cohort rather than an H3-3A-only stratification;
  each is quoted with its own denominator so the reader can see what population
  it describes. Where a phenotype is named only in GeneReviews management or
  surveillance guidance - hearing impairment, autism spectrum disorder - no
  frequency is recorded, because none is published.

📚

References & Deep Research

References

1

PMID:37782742

Bryant-Li-Bhoj Neurodevelopmental Syndrome

No top-level findings curated for this source.

Deep Research

1

Claude Code ▸

Bryant-Li-Bhoj Neurodevelopmental Syndrome 1 (BRYLIB1): Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 20 citations 2026-08-29T14:50:25.608289

Bryant-Li-Bhoj Neurodevelopmental Syndrome 1 (BRYLIB1): Comprehensive Research Report

1. Disease Information

Overview. Bryant-Li-Bhoj neurodevelopmental syndrome (BLBS/BRYLIB) is a rare, clinically variable neurodevelopmental (and, in a subset of adults, neurodegenerative) disorder first delineated in 2020 and caused by heterozygous germline variants in one of the two genes that encode replication-independent histone H3.3: H3-3A (formerly H3F3A) and H3-3B (formerly H3F3B). Variants in H3-3A define Bryant-Li-Bhoj neurodevelopmental syndrome 1 (BRYLIB1); variants in H3-3B define the molecularly and clinically similar BRYLIB2. The condition was named for the discovery team (Bryant, Li, Bhoj) in the founding report ("Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients," Science Advances, 2020). GeneReviews describes it as "characterized by developmental delay/intellectual disability... and nonspecific craniofacial abnormalities," with a highly variable, gene-dosage-sensitive presentation (GeneReviews, NBK595206, updated 2023) [https://www.ncbi.nlm.nih.gov/sites/books/NBK595206/].

Key identifiers: - OMIM (phenotype): #619720 — BRYANT-LI-BHOJ NEURODEVELOPMENTAL SYNDROME 1; BRYLIB1 (https://www.omim.org/entry/619720) - OMIM (gene): 601128 — H3 HISTONE, FAMILY 3A; H3F3A / H3-3A (https://omim.org/entry/601128) - Related disorder: OMIM #619721 — BRYLIB2 (H3-3B, gene 601058), the sister condition - MONDO: MONDO:0030606 (Bryant-Li-Bhoj neurodevelopmental syndrome 1), confirmed via ClinGen curation (https://search.clinicalgenome.org/kb/conditions/MONDO:0030606) - HGNC: H3-3A, HGNC:4764 - ClinGen gene-disease validity: Definitive (Syndromic Disorders GCEP, classification date 2024-03-19) - Orphanet: no distinct ORPHA number could be confirmed in this search (the entity is very recently named, 2022 OMIM addition; it may still be tracked in Orphanet under a broader "H3.3-related chromatinopathy" heading rather than a dedicated ORPHA code) - Synonyms: BRYLIB1; Bryant-Li-Bhoj syndrome (BLBS); H3.3-related neurodevelopmental disorder; H3-3A-related neurodevelopmental disorder; (historically, before nosologic separation from cancer-associated somatic H3.3 mutations) "H3F3A germline neurodevelopmental disorder"

Data provenance: Nearly all current knowledge derives from aggregated case-series/cohort resources (GeneReviews, the 2020 founding cohort of 46 patients, and a 2024 expansion to 96 total individuals) built from clinician-submitted, ClinVar-deposited, and literature case reports — not from a population-level EHR resource. This is disease-level/aggregated-cohort evidence, not raw individual-patient EHR data.

2. Etiology

Primary cause — genetic, autosomal dominant, de novo. BRYLIB1 is caused by heterozygous, essentially always de novo pathogenic variants in H3-3A. GeneReviews states plainly: "BRYLIB is an autosomal dominant disorder typically caused by a de novo pathogenic variant." Parental testing in reported cohorts has confirmed de novo origin in essentially all cases; the 2024 expansion cohort reported the field's first exception — a maternally inherited H3-3B variant (p.Asn108Ser) in a mildly affected mother and child, establishing that (at least for H3-3B) transmission from a mosaic or mildly affected parent is possible (Layo-Carris et al., Eur J Hum Genet 2024;32(8):928–937, PMID: 38678163).

Genetic risk factors. The disease-causing variant itself is the risk factor; there is no described susceptibility-locus or polygenic contribution. gnomAD constraint metrics show H3-3A and H3-3B are highly intolerant to variation (missense z-scores of 3.16 and 2.88, respectively), consistent with the observation that even single heterozygous substitutions are clinically impactful (Layo-Carris et al. 2024).

Modifier factors / phenotype drivers. The affected gene (H3-3A vs H3-3B), the protein domain hit (N-terminal tail, aa 1–43, vs. histone-fold core, aa 44–135), and sex all statistically associate with different symptom sub-profiles (see Genotype-Phenotype Correlations, section 4/6), but the authors explicitly caution that "the current stratification by sex, affected gene, or affected protein domain does not account for all phenotypic variation observed," implicating unidentified modifiers — possibly epigenetic or gene-environment interaction effects, since "histone biology sits at the genetics-epigenetics interface" (Layo-Carris et al. 2024).

Environmental/lifestyle risk factors. None identified; this is a Mendelian single-gene disorder with no established environmental etiologic contribution.

Protective factors. None reported.

Somatic vs. germline distinction (important etiologic contrast). Identical or adjacent missense substitutions occurring somatically in H3-3A (notably p.Gly34Arg/Val and p.Lys27Met) are well-known oncogenic drivers of pediatric diffuse midline glioma and giant cell tumor of bone. In BRYLIB1/2, the same or neighboring residues are altered germline, and critically, no oncologic complications have been reported in the BLBS germline cohort to date, despite two individuals carrying germline p.Gly34Arg/Val substitutions identical to oncogenic somatic hotspots (Bryant et al. 2020; Layo-Carris et al. 2024). This is mechanistically informative: PTM/chromatin dysregulation in the germline, congenital setting differs qualitatively from the global histone-code disruption caused by somatic "oncohistone" mutations.

3. Phenotypes

Frequencies below combine GeneReviews (n=57), the founding 2020 cohort (n=46), and the 2024 expanded cohort of 96 total individuals (58 previously reported + 38 new; Layo-Carris et al. 2024, PMID 38678163), which is the most complete phenotype table available.

Phenotype	Frequency	HPO suggestion
Global developmental delay / intellectual disability (moderate–severe)	99% (94/95)	HP:0012758 (Developmental regression) / HP:0001263 (Global developmental delay) / HP:0001249 (Intellectual disability)
Poor/absent speech, delayed speech (no words by 20 mo)	60% (50/84)	HP:0000750 (Delayed speech and language development)
Delayed walking (>20 mo)	79% (59/75)	HP:0002505 / HP:0031936 (Delayed ability to walk)
Delayed sitting (>12 mo)	51% (33/65)	HP:0025336 (Delayed ability to sit)
Craniofacial dysmorphism (nonspecific pattern)	88–92%	HP:0001999 (Abnormal facial shape)
Hypotonia	62–72% (often resolves/evolves with age)	HP:0001252 (Hypotonia)
Hypertonia / peripheral spasticity (partly age-evolving)	12–19%	HP:0001276 (Hypertonia) / HP:0007256 (Spasticity)
Oculomotor abnormalities (strabismus, nystagmus)	53–54% (strabismus alone 36%)	HP:0000486 (Strabismus) / HP:0000639 (Nystagmus)
Seizures (variable types, childhood onset)	47–49% (febrile seizures ~20% of these)	HP:0001250 (Seizure)
Abnormal brain MRI (composite)	58%	HP:0002060 (Abnormal cerebral morphology)
— Small posterior fossa	72% (in detailed-MRI subgroup)	HP:0025265
— Corpus callosum malformation	37% (28/76)	HP:0002079 (Hypoplasia of the corpus callosum)
— Delayed/hypomyelination, dilated ventricles	subset	HP:0002188 (Delayed CNS myelination), HP:0002119 (Ventriculomegaly)
Short stature	35–39%	HP:0004322 (Short stature)
Microcephaly	32–33%	HP:0000252 (Microcephaly)
Macrocephaly	15%	HP:0000256 (Macrocephaly)
Craniosynostosis / abnormal head shape	32%	HP:0001363 (Craniosynostosis)
Musculoskeletal anomalies (incl. scoliosis 21%)	60%	HP:0002650 (Scoliosis)
Dermatologic features	52%	HP:0000951 (Abnormality of the skin)
Congenital heart defects (esp. atrial septal defect)	13–19%	HP:0001631 (Atrial septal defect)
Genital anomalies / cryptorchidism (males)	20–35%	HP:0000028 (Cryptorchidism)
Hearing loss	subset	HP:0000365 (Hearing impairment)
Feeding problems	common in infancy	HP:0011968 (Feeding difficulties)
Neurobehavioral abnormalities (autism, ADHD, happy demeanor, stereotypies)	~50% in one cohort	HP:0000717 (Autism), HP:0000733 (Stereotypy)
Camptocormia / new-onset motor decline in adulthood	100% of reported adults (subacute onset, 3rd decade of life, then stabilizes)	HP:0031808 (Camptocormia)
Gait abnormality / ataxic gait	up to universal in some reports	HP:0002317 (Unsteady gait)

Onset/progression/severity. Developmental delay is evident from infancy/early childhood; the reported age range at evaluation spans 10 weeks to 39 years, so the natural history now extends well into adulthood. Notably, this is one of the few histone-related NDDs with a documented adult-onset neurodegenerative component: "all reported adults have had a new subacute onset of motor issues in the third decade of life that generally remains stable after onset," manifesting principally as camptocormia (progressive bent-spine posture) — the feature that anchors the "neurodegenerative" half of the syndrome's Science Advances title. Hypotonia can resolve or evolve into a mixed axial-hypotonia/peripheral-hypertonia pattern with age; this mixed pattern was found to occur exclusively in individuals with variants in the histone core domain (see Section 6).

Quality of life impact. Not separately quantified with EQ-5D/SF-36 instruments in the literature reviewed; qualitatively, impact is substantial given near-universal moderate-to-severe intellectual disability, motor delay, and (in a subset) adult-onset progressive motor decline, feeding difficulties, and seizures requiring ongoing neurological management.

4. Genetic/Molecular Information

Causal gene: H3-3A (HGNC:4764; OMIM 601128), chromosome 1q42.12, encoding replication-independent histone H3.3. (BRYLIB2 is caused by H3-3B, OMIM 601058, chromosome 17q25.1 — the two genes encode an essentially identical H3.3 protein and produce clinically overlapping disease.)

Variant spectrum: - BRYLIB1 (H3-3A): overwhelmingly de novo heterozygous missense variants, identified in the founding cohort in 33 unrelated patients, "found by whole-exome or genome sequencing, occurred throughout the gene" (OMIM #619720, citing Bryant et al. 2020). - BRYLIB2 (H3-3B): greater variant diversity, including a synonymous variant acting as a cryptic stop-gain in a non-canonical transcript (p.Val117Val), a stop-loss variant (p.Cys136ext9, a 2-nt deletion ablating the stop codon), and the one known inherited variant (p.Asn108Ser). - Across the combined 96-individual cohort: 70 unique causative variants*, distributed throughout the H3.3 protein rather than clustered at one or two hotspots — in contrast to the sharply localized cancer "oncohistone" hotspots (K27, G34, K36). - Representative variants: H3-3A p.Thr45Ile (T45I) — the most recurrently reported variant, now used to generate a mouse model (see Section 15); H3-3A p.Thr46Ile; H3-3B p.Leu48Arg (L48R) — used to generate an iPSC model; H3-3A/B p.Gln125Arg (shared, 8 individuals, discordant phenotypes); germline p.Gly34Arg/Val in H3-3B (mirrors the somatic oncohistone hotspot but with no oncologic phenotype). - ClinVar entry example: NM_002107.7(H3-3A):c.137C>T (p.Thr46Ile), classified pathogenic/likely pathogenic for BRYLIB1 (https://www.ncbi.nlm.nih.gov/clinvar/RCV001823766/).

Variant classification (ACMG/AMP): Pathogenic/likely pathogenic missense (and the rarer truncating/stop-loss/cryptic-splice) variants; interpreted per standard ACMG/AMP criteria plus gene-specific de novo and functional evidence used by the ClinGen Syndromic Disorders GCEP, which rated the H3-3A–BRYLIB1 relationship Definitive.

Allele frequency: Not present (or present only as ultra-rare singleton entries) in gnomAD/population databases, consistent with strong purifying selection (missense z-scores >2.8 for both genes) and complete penetrance of de novo disease alleles.

Somatic vs. germline: BRYLIB1/2 are strictly germline disorders; the same H3-3A/H3-3B residues altered somatically (K27M, G34R/V, K36M) instead cause pediatric high-grade/diffuse midline glioma and giant cell tumor of bone — an important differential/molecular contrast, not a subtype of BRYLIB1.

Functional consequences. Molecular modeling of the founding cohort's 37 variants "demonstrated clear disruptions in interactions with DNA, other histones, and histone chaperone proteins" (Bryant et al. 2020). Patient-derived histone post-translational modification (PTM) profiling showed "notably aberrant local PTM patterns distinct from the somatic lysine mutations that cause global PTM dysregulation" — i.e., germline variants perturb the histone code locally/regionally rather than globally. RNA-seq on patient cells showed "up-regulated gene expression related to mitosis and cell division, with increased proliferative capacity." A specific structural mechanism identified for one recurrent variant (H3-3A p.Arg129His) was "significantly stronger interaction with DAXX," the H3.3-specific histone chaperone, implicating disrupted, chaperone-mediated H3.3 deposition (Tsuchiya et al./de novo-variant cohort, PMC8651650). For H3-3B p.Leu48Arg, iPSC modeling indicates the variant "increases H3-3B expression, resulting in the hyper-deposition of H3.3 into the nucleosome" (see Section 6).

Modifier genes: None formally established; phenotype correlates statistically with affected gene and protein domain (tail vs. core) rather than with a distinct modifier locus (see Section 6).

Epigenetic information: This is fundamentally an epigenetic-machinery disorder — the causal protein is a core chromatin component. Aberrant local histone PTM deposition and altered chromatin accessibility (documented directly by ATAC-seq/multi-omic profiling in iPSC-derived neural models) are central to pathogenesis rather than secondary.

Chromosomal abnormalities: Not a copy-number/structural disorder; disease is driven by single-nucleotide/small-indel variants in H3-3A. Gene-targeted deletion/duplication analysis detection rate is not established (no cases reported to date attributable to CNV).

5. Environmental Information

No environmental, lifestyle, or infectious contributing factors have been identified or proposed for BRYLIB1 beyond the theoretical, unproven suggestion in the 2024 expanded-cohort paper that "gene-environment interactions" might help explain residual phenotypic variability not accounted for by gene/domain/sex stratification — this is explicitly speculative rather than evidence-based (Layo-Carris et al. 2024).

6. Mechanism / Pathophysiology

Molecular substrate. H3.3 is a replication-independent histone variant (as opposed to the replication-dependent canonical H3.1/H3.2) that is deposited onto DNA by the DAXX/ATRX and HIRA histone chaperone complexes, especially at transcriptionally active regions, telomeres, and pericentric heterochromatin. Two molecules of each core histone (H2A, H2B, H3, H4) assemble into the octamer around which ~146 bp of DNA wraps to form the nucleosome; H3.3 is essential for chromatin compaction, early embryonic development, and cell-lineage commitment. Suggested GO terms: GO:0000786 (nucleosome), GO:0031507 (heterochromatin formation), GO:0006335 (DNA replication-independent nucleosome assembly), GO:0016575 (histone deacetylation)/relevant PTM GO terms, GO:0006338 (chromatin remodeling).

Causal chain (as currently understood): 1. Trigger (molecular/upstream): De novo missense (or rare truncating/inherited) variant in H3-3A alters the H3.3 protein at a residue involved in DNA contact, chaperone binding (e.g., DAXX interaction, strengthened for p.R129H), or inter-histone (H3-H4/H2A-H2B) contacts within the nucleosome. 2. Molecular consequence: Disrupted or altered-affinity interactions with DNA, chaperones, and neighboring histones; in some variants (e.g., L48R) increased H3-3B expression and hyper-deposition of H3.3 into nucleosomes rather than simple loss-of-function. 3. Chromatin-level consequence: Aberrant, locally restricted (not globally dysregulated, unlike somatic oncohistones) deposition of histone PTMs, producing a disrupted local "histone code." 4. Gene-regulatory consequence: Genome-wide, cell-type-specific dysregulated gene expression and altered chromatin accessibility — documented in iPSC-derived neural progenitor cells, forebrain neurons, and organoids as changes affecting genes governing "neuronal fate, adhesion, neurotransmission, and excitatory/inhibitory balance" (Journal of Translational Medicine 2026 iPSC paper, PMC11382994). Patient fibroblasts additionally show up-regulated mitosis/cell-division transcriptional programs and increased proliferative capacity (Bryant et al. 2020). 5. Cellular consequence: Altered proportions of radial glia versus mature neuronal populations in organoids; decreased spontaneous electrical activity in L48R-mutant forebrain-organoid neurons by patch-clamp electrophysiology, indicating impaired neuronal maturation/functional network formation. 6. Organismal/clinical consequence: Global developmental delay/intellectual disability, dysmorphic craniofacial features, hypotonia/hypertonia, seizures, structural brain anomalies (hypomyelination, corpus callosum dysgenesis, small posterior fossa), and — in the neurodegenerative arm of the phenotype — adult-onset progressive camptocormia/motor decline, presumably reflecting cumulative disruption of H3.3's dominant role in post-mitotic neuronal chromatin maintenance over decades (H3.3 becomes >93% of total neuronal H3 in mature neurons, versus ~31% of the H3 pool during early neurodevelopment).

Upstream vs. downstream framing: Upstream = the germline histone variant itself (a cell-autonomous, constitutive lesion present from the zygote onward, not one triggered by an external event). Midstream = chromatin/PTM/accessibility dysregulation. Downstream = neurodevelopmental (congenital) phenotypes plus a distinct, temporally separate downstream neurodegenerative phenotype (adult camptocormia) that appears to require decades of cumulative dysfunction in postmitotic neurons — consistent with the biological observation that H3.3 dependence increases sharply as neurons mature and exit the cell cycle.

Cell types/processes implicated: Neural progenitor cells, radial glia, cortical/forebrain excitatory neurons (maturation and electrophysiological function), cranial neural crest cells (craniofacial dysmorphism, per zebrafish data), and — per RNA-seq of patient fibroblasts — mitotically active non-neural cells showing increased proliferation. Suggested CL terms: CL:0000047 (neural progenitor cell/stem cell), CL:0002608 (radial glial cell), CL:0000540 (neuron)/CL:0000598 (pyramidal neuron), CL:0002500 (cranial neural crest cell).

Genotype-phenotype correlation (protein-domain level, from the 96-individual 2024 cohort): - N-terminal tail variants (aa 1–43): associated with undergrowth (44%), abnormal neuroimaging (63%), hypotonia (73%), dermal features (64%), delayed sitting (59%). - Histone-fold core variants (aa 44–135): associated with the mixed axial-hypotonia/peripheral-hypertonia pattern (exclusively seen with core variants), higher rates of overweight (25% vs 7%) and cardiac anomalies (17% vs 7%), and more often normal height. - Gene-level: H3-3A variants trend toward more craniofacial dysmorphism (95% vs 86%) and more delayed walking (85% vs 65%); H3-3B variants trend toward higher seizure prevalence (59% vs 45%), more macrocephaly (53% vs 43%), and more genital anomalies (28% vs 17%). - Sex: males show more delayed walking and speech delay; females show more oculomotor dysfunction; seizure prevalence and overall developmental-delay severity do not differ significantly by sex. - Critically, identical variants produce discordant phenotypes (e.g., four individuals with H3-3A p.Thr45Ile, and eight individuals sharing p.Gln125Arg across both genes, show substantial phenotypic variability), so genotype-phenotype rules are statistical trends, not deterministic.

Advanced/omics technologies used to date: multi-omic (transcriptomic + chromatin-accessibility/ATAC-like) profiling of iPSC-derived 2D neural progenitor cells and forebrain neurons; single-cell/organoid-level immunofluorescence characterization of 3D dorsal forebrain organoids; patch-clamp single-cell electrophysiology. No published single-cell RNA-seq atlas, spatial transcriptomics, or CRISPR functional-genomics screen specific to BLBS was identified in this search.

7. Anatomical Structures Affected

Organ level: Primary — central nervous system (brain: cortex, corpus callosum, posterior fossa/cerebellum, white matter); craniofacial skeleton (skull shape, craniosynostosis). Secondary — cardiovascular system (atrial septal defect and other congenital heart defects), musculoskeletal system (scoliosis, other skeletal anomalies, adult-onset camptocormia of the spine), genitourinary system (cryptorchidism, other genital anomalies), integumentary system (dermatologic features), auditory system (hearing loss), ocular system (strabismus, nystagmus, other oculomotor dysfunction), endocrine system (hypothyroidism reported in the sister Rahman-syndrome literature and surveilled for in BLBS management protocols).

Body systems involved: nervous, musculoskeletal, cardiovascular, ocular, auditory, endocrine, genitourinary, integumentary — a genuinely multisystem chromatinopathy centered on but not limited to neurodevelopment. Suggested UBERON terms: UBERON:0000955 (brain), UBERON:0002336 (corpus callosum), UBERON:0002037 (cerebellum), UBERON:0002298 (brainstem/posterior fossa structures), UBERON:0003128 (skull).

Tissue/cell level: cerebral cortical neurons and their progenitors (radial glia); cranial neural crest-derived craniofacial mesenchyme; cardiac septal tissue; ocular extraocular muscle/oculomotor control circuitry.

Subcellular level: the nucleus/chromatin is the primary subcellular compartment affected — the nucleosome itself (GO Cellular Component: GO:0000786 nucleosome; GO:0000785 chromatin; GO:0005694 chromosome) is the direct molecular substrate of disease.

Localization/lateralization: No lateralization pattern reported; craniofacial and brain anomalies are typically bilateral/midline (e.g., corpus callosum, posterior fossa). Camptocormia is axial/midline (spine).

8. Temporal Development

Onset: Congenital/early childhood for the neurodevelopmental component (developmental delay evident in infancy); distinctly adult-onset (third decade) for the neurodegenerative motor component (camptocormia).

Progression: Two temporally distinct phases are now recognized — (1) a static-to-improving neurodevelopmental phase in childhood (hypotonia can resolve with age in some individuals), followed by (2) a subacute-onset, then stabilizing neurodegenerative motor phase beginning in early adulthood, universal among reported adults, that "generally remains stable after onset" rather than being relentlessly progressive. Seizures, when present, begin in childhood with variable, sometimes treatment-refractory, course.

Patterns: Developmental regression is reported in a minority of individuals, ranging mild to severe; no spontaneous full remission is described. No defined "critical period" for intervention has been established in the literature, though early developmental intervention (birth–age 3) is uniformly recommended in management guidance.

9. Inheritance and Population

Epidemiology: Ultra-rare; 96 individuals reported in the peer-reviewed literature as of the 2024 expanded cohort (58 previously known + 38 new), combined across BRYLIB1 (H3-3A, 65 individuals) and BRYLIB2 (H3-3B, 31 individuals). No population-based prevalence or incidence estimate (per 100,000) has been established; the condition is almost certainly ascertainment-limited (identified via exome/genome sequencing for undiagnosed neurodevelopmental disorders) rather than reflecting a stable epidemiologic denominator.

Inheritance pattern: Autosomal dominant, essentially always de novo; one confirmed maternally-inherited H3-3B case is the sole reported exception to date (2024 cohort). GeneReviews recurrence-risk guidance: for parents of an isolated proband, recurrence risk to siblings is ~1% (accounting for possible parental germline mosaicism) if parental testing is negative; risk to offspring of an affected individual is not yet established because few affected individuals have reached reproductive age.

Penetrance: Reported cases are essentially fully penetrant (all carriers described to date are symptomatic), though the founder mild inherited case (mother + child, p.Asn108Ser) suggests a spectrum extending toward milder/possibly under-ascertained presentations.

Expressivity: Markedly variable, even among carriers of the identical variant (documented explicitly for p.Thr45Ile and p.Gln125Arg) — this is one of the most striking features of the disorder and is explicitly flagged by the authors as only partially explained by gene, domain, or sex.

Genetic anticipation: Not reported/applicable (not a repeat-expansion disorder).

Germline mosaicism: Formally invoked as the explanation for the ~1% empiric sibling recurrence risk quoted by GeneReviews, though not directly demonstrated in a specific reported family to date in this search.

Founder effects / consanguinity: None reported; disease arises from de novo mutation, not from population-specific founder alleles or recessive consanguinity-driven inheritance.

Population demographics: No described ethnic, geographic, or ancestry-specific enrichment; cohorts to date are drawn from international, largely clinical-exome-sequencing-ascertained populations (US, European, and at least one Chinese cohort reported separately — see PMC ResearchGate "Bryant-Li-Bhoj neurodevelopmental syndrome: a case report in China and literature review"). Sex ratio: no marked male:female skew reported, though some phenotype features differ by sex in frequency (Section 6).

10. Diagnostics

Diagnostic criteria (GeneReviews): "The phenotypic features associated with Bryant-Li-Bhoj neurodevelopmental syndrome are not sufficient to diagnose this condition clinically." Diagnosis requires suggestive clinical findings plus identification of a heterozygous pathogenic/likely-pathogenic variant in H3-3A or H3-3B by molecular genetic testing.

Testing approach/order: 1. Chromosomal microarray analysis (initial broad screen, primarily to exclude a CNV-based alternative diagnosis) 2. Intellectual disability multigene panel including H3-3A/H3-3B 3. Exome or genome sequencing (most productive; used to identify the great majority of reported cases) 4. Single-gene sequential testing is explicitly "rarely useful and typically NOT recommended," given the phenotype's non-specificity.

Detection rate: Sequence analysis has detected essentially all reported pathogenic variants (39/39 H3-3A cases and 18/18 H3-3B cases in the cohort GeneReviews cites); detection rate for gene-targeted deletion/duplication (CNV) analysis is unknown/unestablished, since no CNV-mediated cases have been reported.

Imaging: Brain MRI is the key structural imaging modality — findings include small posterior fossa, corpus callosum hypoplasia/dysgenesis, delayed/hypomyelination, cortical dysplasia in a subset, and (in some individuals) leukoencephalopathy-pattern white-matter change.

Differential diagnosis: Because the phenotype (developmental delay + nonspecific dysmorphism + variable hypotonia/seizures) overlaps broadly with hundreds of other Mendelian intellectual-disability disorders, GeneReviews directs clinicians to the OMIM autosomal dominant, autosomal recessive, and X-linked intellectual developmental disorder phenotypic series for full differential consideration. Notably, close molecular differentials include the H1.4-linker-histone disorder Rahman syndrome (HIST1H1E/H1-4) — a distinct, separately named chromatinopathy causing overlapping intellectual disability, overgrowth, and dysmorphic facies, but mechanistically and molecularly separate (linker histone H1 vs. core nucleosomal histone H3.3) and must not be conflated with BRYLIB1/2 despite superficial resemblance and shared "histone-disorder" framing in review literature.

Genetic testing modalities: Standard clinical exome/genome sequencing is the primary and most productive tool; chromosomal microarray, karyotyping, FISH, and mitochondrial DNA testing are not primary diagnostic tools for this specific condition (used only to exclude alternative etiologies). No repeat-expansion or specialized epigenomic clinical test is part of the standard diagnostic pathway at this time, although research-grade histone PTM profiling and chromatin-accessibility assays have been used investigationally (see Section 6).

Screening: No newborn-screening, population carrier-screening, or cascade-screening program exists (as expected for an ultra-rare, almost-always de novo disorder); prenatal/preimplantation genetic testing is available once a familial pathogenic variant is identified.

11. Outcome/Prognosis

Survival/mortality: "It is unknown whether life span in BRYLIB is abnormal" (GeneReviews); several adults with the condition have now been reported, and life span does not appear to be markedly shortened by the condition itself based on current (still limited) natural-history data.

Morbidity/function: Chronic disability driven by moderate-to-severe intellectual disability, motor delay, and (in adulthood) progressive camptocormia; no tumors have been reported in individuals with germline H3.3 variants (an important reassurance point distinguishing this from the somatic oncohistone literature).

Disease course: Predominantly non-regressive/stable neurodevelopmental phenotype through childhood for most individuals, with a distinct adult-onset subacute motor decline (camptocormia) that then plateaus; a minority show frank developmental regression of variable severity.

Prognostic factors: No formal prognostic biomarker or scoring system has been developed; affected gene/domain and (to a lesser extent) sex have only modest, non-deterministic predictive value for symptom profile as discussed above.

12. Treatment

No disease-modifying or curative treatment exists. Management is entirely multidisciplinary and supportive, per GeneReviews Table 4 ("Treatment of Manifestations," https://www.ncbi.nlm.nih.gov/books/NBK595206/table/brylib.T.bryantlibhoj_neurodevelopmental_1/):

Developmental/educational support: Early intervention (age 0–3), developmental preschool/special education, individualized education plans, physical/occupational/speech therapy. NCIT: NCIT:C15302 (Physical Therapy), NCIT:C15747 (Supportive Care), NCIT:C49236 (Therapeutic Procedure).
Seizure management: Standardized anti-seizure medication under an experienced neurologist; multiple agent options exist, some individuals show treatment-refractory seizures. NCIT: NCIT:C15986 (Pharmacotherapy) with an anticonvulsant therapeutic_agent.
Feeding/nutrition: Feeding therapy; gastrostomy tube placement for persistent feeding dysfunction; ongoing nutritional monitoring. NCIT: NCIT:C15447 (Dietary Intervention).
Spasticity management: Physical therapy, positioning devices, antispasticity medications.
Craniosynostosis: Surgical correction when clinically indicated. NCIT: NCIT:C16186 (Orthopedic Surgical Procedure) or NCIT:C15329 (Surgical Procedure).
Ophthalmology: Ongoing care for strabismus/visual impairment.
Audiology: Hearing-loss surveillance and intervention.
Cardiology: Evaluation/management of congenital heart defects.
Urology: Consultation for cryptorchidism.
Endocrinology: Management of hypothyroidism when present.

Surveillance protocol (GeneReviews): at each visit — growth parameters, nutrition/oral-intake safety, constipation screening, new seizure or gait-change assessment, developmental-progress monitoring, behavioral screening; annually/as indicated — ophthalmology exam, audiology exam, thyroid function testing; and (per the 2024 expanded-cohort recommendations) repeat neuroimaging to track the progressive/neurodegenerative component and ongoing genitourinary surveillance.

Experimental/precision-medicine pipeline (very early stage, no clinical trials yet identified): The two most important recent developments are disease models built specifically to enable future targeted-therapy development: - iPSC model (H3-3B p.Leu48Arg): 2D neural progenitor cells, 2D forebrain neurons, and 3D dorsal forebrain organoids, characterized by multi-omic profiling, immunofluorescence, and patch-clamp electrophysiology (Journal of Translational Medicine, Feb 2026; PMC11382994, PMID 39253491). The authors explicitly frame this model as "a crucial step towards preclinical development and testing of targeted therapies." - Mouse model (H3-3A p.Thr45Ile), 2026 preprint: the first in vivo preclinical model, recapitulating "perinatal growth restriction, delayed developmental milestones, and progressive motor and gait impairments," plus adult craniofacial differences, impaired nest building, social-context hyperactivity, and male-specific elevated aggression (bioRxiv, June 2026, https://www.biorxiv.org/content/10.64898/2026.06.16.732665v1). This model is positioned to enable in vivo therapeutic testing going forward.

No NCT-registered clinical trial for a targeted BLBS therapy was identified in this search as of August 2026; the field remains at the mechanistic/preclinical-model stage.

13. Prevention

No primary, secondary, or tertiary prevention strategy exists beyond standard reproductive genetic counseling once a familial pathogenic variant is known (prenatal diagnosis, preimplantation genetic testing) — appropriate given the condition's near-universal de novo origin. No vaccination, screening program, or prophylactic medication applies. Genetic counseling is the principal "preventive" intervention offered to families, focused on recurrence-risk estimation (~1%, germline-mosaicism-based) for future pregnancies.

14. Other Species / Natural Disease

No naturally occurring veterinary or wildlife disease caused by spontaneous H3-3A/H3-3B variants has been reported (this is not currently listed in OMIA). H3.3 itself is highly evolutionarily conserved; the gene has functional orthologs across vertebrates, and a companion in vitro/model-organism paper — "Histone 3.3-related chromatinopathy: missense variants throughout H3-3A and H3-3B cause a range of functional consequences across species" (PMID 36867246) — used yeast as a heterologous functional-testing platform for patient-derived missense variants, and a separate paper examined "trapping of yFACT at 3' ends of genes" using yeast versions of BLBS histone H3 mutants (PMC11544422), underscoring cross-species conservation of the affected chaperone/FACT-complex interactions even though yeast do not model the neurodevelopmental phenotype itself.

15. Model Organisms

Zebrafish: Homozygous h3f3a-mutant (db1092 allele) zebrafish injected with dominant-negative H3f3a RNA show "complete loss of melanocytes and severe reductions of glia and xanthophores throughout cranial and trunk regions"; reduced nuclear H3.3 caused by aggregating dominant-mutant H3.3 produces defects in cranial neural crest cell differentiation, demonstrating tissue-specific sensitivity to H3.3 dosage during craniofacial/pigment-lineage development — directly relevant to the craniofacial dysmorphism seen in human BLBS.
Mouse: (1) Conditional H3f3a/H3f3b double-knockout embryos (H3f3a^fl/−; H3f3b^fl/−; Sox2-Cre) show H3.3 depletion with embryos recovering at expected Mendelian ratios only up to E10.5, indicating an essential, dosage-sensitive developmental requirement. During normal mouse neurodevelopment, H3.3 constitutes ~31% of total H3 pool early on, rising to become the dominant H3 species (>93%) in mature adult neurons — mechanistically explaining why postmitotic neurons are disproportionately vulnerable to H3.3 dysfunction and offering a rationale for the adult-onset neurodegenerative (camptocormia) component of BLBS. (2) The 2026 knock-in H3.3-T45I mouse (bioRxiv, June 2026) is the first genotype-matched in vivo preclinical model, recapitulating perinatal growth restriction, developmental-milestone delay, progressive motor/gait impairment, adult craniofacial differences, impaired nest-building, social-context hyperactivity, and male-specific aggression — directly paralleling multiple domains of the human phenotype and positioned as the platform for future therapeutic testing.
Human iPSC-derived models: 2D neural progenitor cells, 2D forebrain neurons, and 3D dorsal forebrain organoids carrying H3-3B p.Leu48Arg (Journal of Translational Medicine, 2026) recapitulate disrupted chromatin accessibility, dysregulated neuronal-fate/adhesion/neurotransmission gene expression, altered radial-glia-to-neuron proportions, and decreased spontaneous neuronal electrical activity by patch-clamp — the most disease-relevant human cellular model to date.
Yeast: used as a rapid, high-throughput heterologous system to functionally characterize the range of consequences of BLBS missense variants "across species," and to probe effects on the FACT histone chaperone complex (yFACT trapping at gene 3′ ends).
Model limitations: none of the current models (zebrafish, mouse, iPSC/organoid, yeast) yet captures the full adult neurodegenerative phenotype (camptocormia) in a validated, long-term aging cohort; the 2026 mouse model is the first designed explicitly to test this, but published long-term follow-up data were not available at the time of this search.

Summary of Key Ontology Term Suggestions

Gene/Disease: HGNC:4764 (H3-3A); MONDO:0030606 (BRYLIB1); OMIM:619720
HPO (selected): HP:0001263 (Global developmental delay), HP:0001249 (Intellectual disability), HP:0001252 (Hypotonia), HP:0001276 (Hypertonia), HP:0001250 (Seizure), HP:0002079 (Hypoplasia of corpus callosum), HP:0000252 (Microcephaly), HP:0000486 (Strabismus), HP:0001363 (Craniosynostosis), HP:0031808 (Camptocormia), HP:0002317 (Unsteady gait)
GO: GO:0000786 (nucleosome), GO:0006335 (DNA replication-independent nucleosome assembly), GO:0031507 (heterochromatin formation), GO:0006338 (chromatin remodeling)
CL: CL:0000047 (neural progenitor cell), CL:0002608 (radial glial cell), CL:0000540 (neuron), CL:0002500 (cranial neural crest cell)
UBERON: UBERON:0000955 (brain), UBERON:0002336 (corpus callosum), UBERON:0002037 (cerebellum)
NCIT (treatment): NCIT:C15986 (Pharmacotherapy), NCIT:C15302 (Physical Therapy), NCIT:C15447 (Dietary Intervention), NCIT:C16186 (Orthopedic Surgical Procedure), NCIT:C15747 (Supportive Care)

Sources

GeneReviews: Bryant-Li-Bhoj Neurodevelopmental Syndrome (updated 2023)
OMIM #619720 — BRYLIB1
OMIM #619721 — BRYLIB2
OMIM *601128 — H3F3A/H3-3A
ClinGen curation, MONDO:0030606
Bryant L, Li D, Cox SG, et al. "Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients." Science Advances 2020. https://www.science.org/doi/10.1126/sciadv.abc9207 / PMC7821880
Layo-Carris DE, et al. "Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals." Eur J Hum Genet 2024;32(8):928–937. PMID: 38678163; correction
"De novo variants in H3-3A and H3-3B are associated with neurodevelopmental delay, dysmorphic features, and structural brain abnormalities." npj Genomic Medicine 2021. PMC8651650
"A novel iPSC model of Bryant-Li-Bhoj neurodevelopmental/neurodegenerative syndrome demonstrates the role of histone H3.3 in chromatin dynamics, neuronal differentiation, and maturation." J Transl Med 2026. PMID: 39253491; PMC11382994
"A novel preclinical mouse model recapitulates progressive phenotypes of Bryant-Li-Bhoj Syndrome." bioRxiv, June 2026. https://www.biorxiv.org/content/10.64898/2026.06.16.732665v1
"Histone 3.3-related chromatinopathy: missense variants throughout H3-3A and H3-3B cause a range of functional consequences across species." PMID: 36867246
"Trapping of yFACT at 3′ ends of genes is not a universal characteristic of yeast versions of Bryant-Li-Bhoj syndrome histone H3 mutants." PMC11544422
"Neonatal myoclonus in Bryant-Li-Bhoj syndrome associated with a novel H3F3A variant." Hum Genome Var 2024. https://www.nature.com/articles/s41439-024-00303-x
ClinVar RCV001823766 (NM_002107.7(H3-3A):c.137C>T, p.Thr46Ile) — https://www.ncbi.nlm.nih.gov/clinvar/RCV001823766/
Note on differential diagnosis: Rahman syndrome (HIST1H1E/H1-4) is a molecularly and clinically distinct linker-histone disorder that should not be conflated with BRYLIB1/2 despite overlapping "histone disorder" framing — see Zhao et al., Mol Genet Genomic Med 2022 and Indugula et al., Clin Case Rep 2022 for comparison.

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	13
Resolved	12
Unresolved (possible confabulation)	1
Unverifiable	0
Quoted claims checked	3
Quoted claims found in source	3
Quoted claims not found in source	0
References weighed for topical relevance	12
On topic	7
Off topic	0

Unresolved references

These identifiers did not resolve to a record and may be fabricated. A lookup that failed for transport reasons is indistinguishable from one that failed because the record does not exist, so spot-check before acting on them:

DOI:10.1126/sciadv.abc9207](https://www.science.org/doi/10.1126/sciadv.abc9207 (1 mention) - Identifier did not resolve to a record

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome	Count
Terms checked	60
Resolved	57
Unresolved (possible confabulation)	0
Obsolete	1
Unverifiable	2
Terms whose name was checked	41
Terms named correctly	34
Terms named as a different term	4
Terms whose name is worth a second look	3

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

HP:0025265 (1 mention) - the report calls it "72% (in detailed-MRI subgroup)"; HP calls it Stiff toe
HP:0031808 (2 mentions) - the report calls it "Camptocormia"; HP calls it Decreased total basophil count
CL:0002608 (2 mentions) - the report calls it "radial glial cell"; CL calls it hippocampal neuron
CL:0002500 (2 mentions) - the report calls it "cranial neural crest cell"; CL calls it P enteroendocrine cell

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

GO:0016575 (obsolete histone deacetylation) (1 mention)

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

HP:0002079 (2 mentions) - the report calls it "Hypoplasia of the corpus callosum", "Hypoplasia of corpus callosum"; HP calls it Hypoplasia of the corpus callosum, and lists "Hypoplasia of corpus callosum" among its other names
GO:0006335 (2 mentions) - the report calls it "DNA replication-independent nucleosome assembly"; GO calls it DNA replication-dependent chromatin assembly, and lists "DNA replication-dependent nucleosome assembly" among its other names
CL:0000047 (2 mentions) - the report calls it "neural progenitor cell"; CL calls it neural stem cell

Terms named inconsistently

The report gives these identifiers more than one name of its own:

MONDO:0030606 - called "Bryant-Li-Bhoj neurodevelopmental syndrome 1", "BRYLIB1"
HP:0002079 - called "Hypoplasia of the corpus callosum", "Hypoplasia of corpus callosum"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: OMIM.

Ask OpenScientist

OpenScientist Report

Classifications

Mappings

Inheritance

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Variants

Medical Actions

Diagnosis

Progression

Prevalence

Differential Diagnoses

Animal Models

Source YAML

References & Deep Research

References

Deep Research

Bryant-Li-Bhoj Neurodevelopmental Syndrome 1 (BRYLIB1): Comprehensive Research Report

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Summary of Key Ontology Term Suggestions

Sources

Reference Validation

Unresolved references

Term Validation

Terms the report names something else

Obsolete terms

Terms whose name is worth a second look

Terms named inconsistently

Prefixes with no resolver