Neurodevelopmental Disorder with Microcephaly, Hypotonia, and Absent Language

Mendelian MONDO:0859287 Pathograph 13 Show in embeddings browser Neurodevelopmental Disorder

Neurodevelopmental disorder with microcephaly, hypotonia, and absent language (NEDMHAL; OMIM:620038) is an ultra-rare autosomal recessive neurodevelopmental disorder caused by biallelic variants in PSMB1, which encodes the beta6 subunit of the 20S proteasome core particle. It is one of the small family of "neurodevelopmental proteasomopathies" (PRNDD) and is, to date, the only member of that family whose causal lesion sits in the 20S core particle rather than the 19S regulatory particle. Affected individuals have microcephaly, hypotonia, severe intellectual disability with global developmental delay, profoundly impaired expressive language, motor delay, hearing impairment, growth failure, and behavioural abnormalities; epilepsy, autistic features and visceral malformations were not seen in the published cases. Mechanistically the reported homozygous missense variant p.(Tyr103His) weakens the beta6-alpha5 inter-subunit interface, destabilising the 20S proteasome complex and impairing beta6 propeptide maturation and its incorporation into the proteasome, so that ubiquitin-dependent proteolytic capacity falls. Knockdown or mutagenesis of the single zebrafish psmb1 orthologue reproduces microcephaly and reduced brain size, linking proteasome-assembly failure directly to impaired brain growth. The entity is defined by a single consanguineous Pakistani kindred (two affected sisters) plus functional validation, so its phenotypic boundaries remain provisional.

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1
Inheritance
6
Pathophys.
11
Phenotypes
4
Gaps
13
Pathograph
1
Genes
1
Variants
6
Medical Actions
1
Differentials
2
Models
2
Deep Research
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Classifications

Harrison's Part
NEUROLOGIC
Mechanistic Nosology
proteotoxic disease
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Inheritance

1
Autosomal recessive HP:0000007
Both reported patients are sisters homozygous for PSMB1 c.307T>C p.(Tyr103His), inherited from unaffected consanguineous parents; the variant segregated with the phenotype in the kindred. Recessive inheritance is the exception among neurodevelopmental proteasomopathies, which are mostly dominant de novo disorders of the 19S regulatory particle.
autosomal recessive inheritance
Show evidence (2 references)
PMID:32129449 SUPPORT Human Clinical
"Here, we report two siblings with phenotypic signs, including intellectual disability (ID), developmental delay and microcephaly from a Pakistani consanguineous family in which we have identified homozygosity for p(Tyr103His) in the PSMB1 gene"
Homozygosity in two affected siblings of a consanguineous family that segregated with disease establishes autosomal recessive transmission.
PMID:39220754 SUPPORT Human Clinical
"Recessive forms, reported in 8/78 patients with PSMB1, PSMC1, or PSMC3 biallelic variants, represent only 10% of neurodevelopmental proteasomopathies."
Confirms that the PSMB1 form is biallelic/recessive and situates it as a minority pattern within the proteasomopathy class.
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Discussions and Knowledge Gaps

4
Which features of NEDMHAL are intrinsic to PSMB1 deficiency, and which are particular to the single consanguineous kindred in which it was described?
KNOWLEDGE GAP OPEN single_kindred_phenotype_boundary
Attached to
pathophysiology#Impaired Brain Growth and Neurodevelopment
The entity rests on two affected sisters from one family plus functional validation. Every phenotype frequency available is a 2/2 or 1/2 count from that kindred, so no feature can currently be separated from the family's shared genetic background and consanguinity-associated homozygosity elsewhere in the genome. This is why no `frequency:` qualifier is asserted on any phenotype in this entry. The absence of epilepsy, autistic features and visceral malformations is likewise a statement about two people.
Proposed experiments
Identify additional families
exp_nedmhal_matchmaking_additional_families
Identify additional families with biallelic PSMB1 variants through international matchmaking (GeneMatcher, DECIPHER, Matchmaker Exchange) and determine which features recur.
Determine whether other PSMB1 alleles
exp_nedmhal_allelic_series_genotype_phenotype
Determine whether other PSMB1 alleles, particularly compound heterozygous or truncating combinations, produce the same phenotype or a distinct severity.
Show evidence (1 reference)
PMID:39220754 SUPPORT Human Clinical
"Notably, visceral malformations have not been reported in forms with PSMB1 or PSMC3 biallelic variants nor with PSMC1 deletions"
The review states the negative finding and, in the same passage, cautions that it should be interpreted with care given how few cases are reported.
Does the zebrafish psmb1 model capture the disorder, when the two features that name it besides microcephaly — absent language and behavioural abnormality — have no zebrafish correlate?
HUMAN MODEL MISMATCH OPEN zebrafish_cannot_model_language_or_behaviour
Attached to
pathophysiology#Impaired Brain Growth and Neurodevelopment
The zebrafish model recapitulates reduced brain size convincingly, by two independent perturbations. But it is a complete loss-of-function model of a disease caused by a partial-loss-of-function missense allele, and it cannot report language, intellectual disability, or behaviour. Treating the model as validating the whole phenotype would overstate it; it validates the brain-growth arm only.
Proposed experiments
Generate a knock-in model carrying the orthologous Tyr103His
exp_nedmhal_knockin_tyr103his_zebrafish
Generate a knock-in model carrying the orthologous Tyr103His substitution and compare its brain phenotype and proteasome assembly with the null.
Use human iPSC-derived neural progenitors and cortical organoids
exp_nedmhal_ipsc_neural_progenitor_organoid
Use human iPSC-derived neural progenitors and cortical organoids from genotype-matched cells to test whether proliferation and neurogenesis are impaired at the reported partial reduction in proteasome activity.
Show evidence (1 reference)
PMID:32129449 SUPPORT Model Organism
"CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1 zebrafish orthologue resulted in microcephaly, microphthalmia and reduced brain size."
The reported model readouts are morphological brain measures only; nothing in the model addresses the language or behavioural components of the human phenotype.
Do PSMB1-deficient cells show the protein aggregation, stress-response activation and type I interferon dysregulation reported across other proteasomopathies?
KNOWLEDGE GAP OPEN interferon_signature_untested_in_psmb1
Attached to
pathophysiology#Impaired Ubiquitin-Dependent Protein Homeostasis
Proteasomopathies as a class — both the autoinflammatory and the neurodevelopmental arm — converge on protein aggregation, activated stress responses and dysregulated type I interferon signalling, and interferon signatures are being explored as biomarkers for the class. None of this has been measured in PSMB1-mutant cells, so the downstream half of the mechanism chain in this entry is asserted at class level and inherited by analogy rather than demonstrated. The gap is sharper than mere absence of data: PSMB1 is explicitly named in the literature as the one 20S core-particle subunit whose pathogenic variants have not been shown to provoke immune dysregulation, while every other 20S lesion has. So the class-level interferon expectation may specifically fail to apply here, and importing it into this entry's mechanism would be the wrong inference rather than merely an unverified one. This matters practically: a proteasome-activity or interferon-signature assay would otherwise be the natural functional test for candidate PSMB1 variants of uncertain significance.
Proposed experiments
Measure polyubiquitinated protein load
exp_nedmhal_ubiquitin_load_and_ifn_signature
Measure polyubiquitinated protein load, proteotoxic stress-response activation and a type I interferon signature in cells carrying PSMB1 p.(Tyr103His).
Compare the magnitude of any interferon response
exp_nedmhal_20s_versus_19s_ifn_comparison
Compare the magnitude of any interferon response with that of the 19S regulatory-particle proteasomopathies to test whether the 20S core-particle lesion behaves differently.
Show evidence (3 references)
PMID:42370079 SUPPORT Other
"both syndromes show molecular similarities with protein aggregation, activated stress responses, metabolic imbalance and dysregulated type I interferon signalling"
Establishes the class-level expectation whose absence of PSMB1-specific confirmation is the gap.
PMID:37256937 SUPPORT Other
"So far, with the exception of the PSMB1 (β6) subunit (25), all pathogenic variants related to the 20S core particle have been shown to provoke immune dysregulation."
Singles out PSMB1 as the one 20S core-particle subunit not shown to cause immune dysregulation, so the interferon arm of the proteasomopathy mechanism cannot simply be inherited by this entry.
PMID:38866022 SUPPORT Human Clinical
"PSMD11 loss of function resulted in impaired 26S proteasome assembly and the acquisition of a persistent type I interferon (IFN) gene signature, mediated by the integrated stress response (ISR) protein kinase R (PKR)"
Shows what the interferon arm looks like when it is actually demonstrated in a proteasomopathy: impaired 26S assembly, a persistent type I IFN signature, and a named PKR/ISR mediator. Nothing equivalent has been measured for PSMB1, which is precisely the gap.
Are neurodevelopmental proteasomopathies essentially diseases of the 19S regulatory particle, and if so why does a 20S core-particle lesion produce the same phenotypic class?
OPEN QUESTION OPEN core_particle_versus_regulatory_particle
Attached to
pathophysiology#Destabilised beta6-alpha5 Interface of the 20S Core Particle
PSMB1 p.(Tyr103His) is the lone 20S core-particle lesion among the variants identified in neurodevelopmental proteasomopathies, and it is also one of the few recessive ones — the rest are dominant, de novo, and in the 19S regulatory particle. Two reviews read the same fact in opposite directions: one treats the overwhelming 19S predominance as evidence that these are fundamentally 19S disorders, while the other treats PSMB1 as the case that breaks the subcomplex-determines-phenotype rule. The resolution matters for how the entity is grouped and for which proteasome genes should be searched in undiagnosed neurodevelopmental disorders.
Proposed experiments
Systematically screen 20S core-particle subunit genes in large
exp_nedmhal_20s_subunit_cohort_screen
Systematically screen 20S core-particle subunit genes in large neurodevelopmental disorder cohorts to establish whether 20S lesions are genuinely rare or merely under-ascertained.
Compare proteasome assembly
exp_nedmhal_matched_20s_19s_assembly_activity
Compare proteasome assembly, activity and interferon output side by side between matched 20S and 19S proteasomopathy variants in a common cell background.
Show evidence (2 references)
PMID:39220754 SUPPORT Human Clinical
"only one (i.e., p.Tyr103His in PSMB1/β6) of the forty-three lesions identified in individuals with neurodevelopmental proteasomopathies affect the 20S CP strongly suggests that these disorders are essentially diseases of the 19S RP"
States the 19S-predominance reading, and itself flags the conclusion as remaining to be confirmed.
PMID:42370079 REFUTE Other
"a homozygous PSMB1 variant break the rules of this rationale and suggest that the phenotypic manifestation may occur independent of the subunit localisation in certain subcomplexes"
The opposing reading: PSMB1 is taken as evidence against the phenotype being determined by which subcomplex the lesion sits in.
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Pathophysiology

6
Biallelic PSMB1 Loss of Function
The homozygous PSMB1 missense variant c.307T>C p.(Tyr103His) is the initiating lesion. PSMB1 encodes beta6, a non-catalytic beta-type subunit of the inner beta-rings of the 20S proteasome core particle. The variant is characterised as a partial rather than complete loss of function.
Genetic context PSMB1 hgnc:9537 HUGO Gene Nomenclature Committee (hgnc) Relation: this genetic context concerns this gene This genetic context concerns PSMB1 (hgnc:9537). hgnc:9537 is a gene from the HUGO Gene Nomenclature Committee. variant_origin: GERMLINE zygosity: HOMOZYGOUS functional_impact_category: PARTIAL_LOSS_OF_FUNCTION
Homozygous germline missense substitution p.(Tyr103His), inherited from consanguineous heterozygous parents.
Downstream
Destabilised beta6-alpha5 Interface of the 20S Core Particle Tyr103 sits at the beta6 surface that contacts the alpha5 subunit; substitution to histidine weakens that contact.
Show evidence (2 references)
PMID:32129449 SUPPORT Human Clinical
"PSMB1 encodes a β-type proteasome subunit (i.e. β6)."
Establishes the gene product identity as the beta6 proteasome subunit.
PMID:42370079 SUPPORT Other
"PSMB1 (NM_002793.4)c.307T>C p.(Tyr103His)Possibly partial loss-of-function; structural modelling: possible influence on interaction between β6 and α5"
The review's variant table records the transcript, the cDNA and protein change, and classifies the allele as a possible partial loss of function.
Destabilised beta6-alpha5 Interface of the 20S Core Particle
The 20S core particle is built from four stacked heptameric rings in the order alpha7-beta7-beta7-alpha7, so every beta subunit sits against defined neighbouring alpha and beta subunits. Weakening the beta6 (PSMB1) contact with alpha5 (PSMA5) destabilises the assembled core particle.
20S proteasome core particle GO:0005839 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves 20S proteasome core particle, annotated with proteasome core complex (GO:0005839). GO:0005839 is a cellular component from the Gene Ontology. proteasome beta-ring GO:0019774 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves proteasome beta-ring, annotated with proteasome core complex, beta-subunit complex (GO:0019774). GO:0019774 is a cellular component from the Gene Ontology.
Downstream
Impaired beta6 Maturation and 20S Core Particle Assembly A destabilised inter-subunit interface impairs the ordered, chaperone-guided incorporation and maturation of beta6 during 20S biogenesis.
Show evidence (2 references)
PMID:42370079 SUPPORT Other
"The 20S CP consists of stringently ordered heptameric α- and β-rings: α7-β7-β7-α7"
Establishes the stereotyped ring architecture in which a beta6-alpha5 inter-subunit contact is structurally load-bearing.
PMID:32129449 SUPPORT Computational
"Modeling of the p(Tyr103His) variant indicates that this variant weakens the interactions between PSMB1/β6 and PSMA5/α5 proteasome subunits and thus destabilizes the 20S proteasome complex."
Directly states destabilisation of the 20S complex by the variant.
Impaired beta6 Maturation and 20S Core Particle Assembly
Beta-ring assembly is an ordered, POMP-dependent process in which beta6 is incorporated onto the nascent alpha-ring, and each beta subunit must have its propeptide processed for the core particle to mature. In cells expressing the variant, beta6 maturation is absent and the unprocessed proform persists, with reduced overall subunit content — i.e. the defect is one of proteasome biogenesis rather than of catalysis.
proteasome assembly GO:0043248 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased proteasome assembly (GO:0043248). GO:0043248 is a biological process from the Gene Ontology. ↓ DECREASED beta6 propeptide processing GO:0051604 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased beta6 propeptide processing, annotated with protein maturation (GO:0051604). GO:0051604 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
SH-SY5Y neuroblastoma cell model of PSMB1 p.(Tyr103His) CELL LINE Provides the direct biochemical readout of defective beta6 processing and incorporation attributable to the variant.
Downstream
Reduced Proteasome Proteolytic Capacity Fewer correctly matured core particles means less proteolytically competent proteasome.
Show evidence (3 references)
PMID:42370079 SUPPORT Other
"Correct β-ring assembly strictly depends on POMP. Its recruitment facilitates β2 entry, followed by β3, β4, β5, β6 onto the α-ring"
Establishes that beta6 incorporation is a defined, ordered step of chaperone-guided 20S biogenesis, which is the step this variant perturbs.
PMID:42370079 SUPPORT In Vitro
"SHSY5Y cells: maturation absent, proform present (myc)"
The review's experimental-outcome table records absent beta6 maturation with a persisting proform in the cell model of the variant.
PMID:32129449 SUPPORT Human Clinical
"PSMB1/β6 pathogenic variants are the cause of a recessive disease with ID, microcephaly and developmental delay due to abnormal proteasome assembly"
The authors attribute the disease specifically to abnormal proteasome assembly.
Reduced Proteasome Proteolytic Capacity
Proteolysis in the 20S core particle is carried out by the caspase-like (beta1), trypsin-like (beta2) and chymotrypsin-like (beta5) active sites. Beta6 is not itself catalytic, so the activity loss is an indirect consequence of having fewer intact core particles. In the SH-SY5Y cell model the measured deficit was modest — a slight reduction of chymotrypsin-like activity — which is consistent with a partial rather than complete loss of function and is an important quantitative caveat.
proteasomal protein catabolic process GO:0010498 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased proteasomal protein catabolic process (GO:0010498). GO:0010498 is a biological process from the Gene Ontology. ↓ DECREASED
proteasome threonine-type endopeptidase activity GO:0004298 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased proteasome threonine-type endopeptidase activity, annotated with threonine-type endopeptidase activity (GO:0004298). GO:0004298 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Impaired Ubiquitin-Dependent Protein Homeostasis Reduced proteasome capacity lowers throughput of the ubiquitin-proteasome system for polyubiquitinated substrates.
Show evidence (2 references)
PMID:42370079 SUPPORT Other
"Peptide-bond hydrolysis is associated with the 20S CP through 3 cleavage specificities of the 6 active site subunits"
Establishes that proteolysis resides in the core particle's active-site subunits, so loss of intact core particles is what lowers activity.
PMID:32129449 SUPPORT In Vitro
"the p(Tyr103His) variant affects both the processing of PSMB1/β6 and its incorporation into proteasome, thus impairing proteasome activity"
Reports impaired proteasome activity as the functional consequence.
Impaired Ubiquitin-Dependent Protein Homeostasis
Reduced proteasomal throughput leaves K48-polyubiquitinated substrates undegraded, shifting the balance between protein synthesis and degradation. Across proteasomopathies this state is associated with protein aggregation and activated cellular stress responses; whether those specific downstream features occur in PSMB1-mutant cells has not been shown directly. The type I interferon arm of the class mechanism is deliberately NOT carried into this chain: PSMB1 is the one 20S core-particle subunit whose variants have not been shown to provoke immune dysregulation.
ubiquitin-dependent protein catabolic process GO:0006511 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased ubiquitin-dependent protein catabolic process (GO:0006511). GO:0006511 is a biological process from the Gene Ontology. ↓ DECREASED proteasome-mediated ubiquitin-dependent protein catabolic process GO:0043161 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased proteasome-mediated ubiquitin-dependent protein catabolic process (GO:0043161). GO:0043161 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Impaired Brain Growth and Neurodevelopment The developing brain is the compartment in which reduced proteostatic capacity manifests. The molecular intermediates between lowered ubiquitin-proteasome throughput and reduced brain growth are not established; the link rests on the zebrafish loss-of-function phenotype and on the human microcephaly.
Show evidence (1 reference)
PMID:42370079 SUPPORT Other
"both syndromes show molecular similarities with protein aggregation, activated stress responses, metabolic imbalance and dysregulated type I interferon signalling"
Describes the shared downstream cellular consequences across proteasomopathies. PARTIAL because these are class-level observations that have not been demonstrated for PSMB1 specifically.
Impaired Brain Growth and Neurodevelopment
The organ-level consequence is failure of normal brain growth, expressed clinically as microcephaly with severe developmental delay, intellectual disability, profoundly impaired expressive language and hypotonia. Neurons and neural progenitors of the developing brain are the implicated cell populations; no human neuropathology has been reported, so the cellular attribution derives from the model organism and from the clinical phenotype.
neuron CL:0000540 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology. neural progenitor cell CL:0000047 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neural progenitor cell, annotated with neural stem cell (CL:0000047). CL:0000047 is a cell type from the Cell Ontology.
brain development GO:0007420 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal brain development (GO:0007420). GO:0007420 is a biological process from the Gene Ontology. ⚠ ABNORMAL
brain UBERON:0000955 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in brain (UBERON:0000955). UBERON:0000955 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
psmb1 CRISPR/Cas9 mutant and morpholino knockdown Zebrafish Zebrafish recapitulates Loss of psmb1 function reproduces the reduced brain growth that underlies the human microcephaly.
Downstream
Microcephaly Failure of brain growth is what the reduced head circumference measures.
Severe Intellectual Disability Impaired brain growth underlies the cognitive phenotype; the intervening circuit-level events are not established.
Global Developmental Delay Impaired brain growth underlies the global developmental delay.
Show evidence (2 references)
PMID:32129449 SUPPORT Model Organism
"CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1 zebrafish orthologue resulted in microcephaly, microphthalmia and reduced brain size."
Establishes reduced brain size as the tissue-level consequence of psmb1 loss of function in vivo.
PMID:32129449 SUPPORT Human Clinical
"PSMB1/β6 pathogenic variants are the cause of a recessive disease with ID, microcephaly and developmental delay due to abnormal proteasome assembly"
Ties the human neurodevelopmental phenotype to the proteasome assembly defect.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Neurodevelopmental Disorder with Microcephaly, Hypotonia, and Absent Language Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

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Ear 1
Hearing Impairment HP:0000365 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hearing impairment (HP:0000365). HP:0000365 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39220754 SUPPORT Human Clinical
"Hearing impairment18% (6/34)100% (2/2)100% (3/3)8/18 (44%)100% (3/3)n.r22/60 (37%)"
Row of the review's clinical-features table; the second column is the PSMB1 form, recording hearing impairment in 2/2 published patients.
Head and Neck 2
Microcephaly HP:0000252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Microcephaly (HP:0000252). HP:0000252 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:32129449 SUPPORT Human Clinical
"Here, we report two siblings with phenotypic signs, including intellectual disability (ID), developmental delay and microcephaly from a Pakistani consanguineous family in which we have identified homozygosity for p(Tyr103His) in the PSMB1 gene"
Microcephaly is reported in both affected siblings.
PMID:39220754 SUPPORT Human Clinical
"Microcephaly21% (9/42)100% (2/2)n.r38% (6/16)100% (3/3)n.r20/63 (32%)"
Row of the review's clinical-features table across the six neurodevelopmental proteasomopathies; the second column is the PSMB1 form, recording microcephaly in 2/2 published patients.
Abnormal Facial Shape HP:0001999 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormal facial shape (HP:0001999). HP:0001999 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39220754 SUPPORT Human Clinical
"Abnormal facial shape97% (44/45)100% (2/2)100% (3/3)89% (17/19)100% (3/3)66% (2/3)71/75 (95%)"
Row of the review's clinical-features table; the second column is the PSMB1 form, recording abnormal facial shape in 2/2 published patients.
Musculoskeletal 1
Hypotonia HP:0001252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypotonia (HP:0001252). HP:0001252 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:39220754 SUPPORT Human Clinical
"Other neurological findingsn.rHypotonia 100% (2/2)Ataxia 100% (3/3); peripheral polyneuropathy of lower limbs 66% (2/3)"
The "other neurological findings" row of the review's clinical-features table; the PSMB1 form's cell records hypotonia in both published patients, and it is the only entry in that row for this form.
PMID:42370079 SUPPORT Other
"Common symptoms include neurodevelopmental delay, speech delay, intellectual disability, impaired sensing functions, hypotonia, general developmental delay, and in some cases seizures"
Lists hypotonia among the common manifestations of neurodevelopmental proteasomopathies. PARTIAL because the statement is class-level rather than specific to PSMB1.
Nervous System 6
Absent or Profoundly Impaired Expressive Language Absent speech HP:0001344 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Absent speech (HP:0001344). HP:0001344 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39220754 SUPPORT Human Clinical
"Speech delay94% (32/34)100% (2/2)100% (3/3)100% (18/18)100% (3/3)100% (3/3)61/63 (97%)"
Row of the review's clinical-features table; the second column is the PSMB1 form, recording speech involvement in 2/2 published patients. PARTIAL because the table records "speech delay" and does not itself assert that language was entirely absent.
Severe Intellectual Disability HP:0010864 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Severe intellectual disability (HP:0010864). HP:0010864 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:39220754 SUPPORT Human Clinical
"Intellectual disability; severity85% (34/40); mild to severe100% (2/2); severe"
The review's table records intellectual disability in 2/2 PSMB1 patients and grades its severity as severe.
PMID:32129449 SUPPORT Human Clinical
"Here, we report two siblings with phenotypic signs, including intellectual disability (ID), developmental delay and microcephaly from a Pakistani consanguineous family in which we have identified homozygosity for p(Tyr103His) in the PSMB1 gene"
Intellectual disability is reported in both affected siblings.
Global Developmental Delay HP:0001263 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Global developmental delay (HP:0001263). HP:0001263 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:39220754 SUPPORT Human Clinical
"Developmental delay100% (45/45)100% (2/2)100% (3/3)100% (21/21)100% (3/3)100% (3/3)77/77 (100%)"
Row of the review's clinical-features table; the second column is the PSMB1 form, recording developmental delay in 2/2 published patients.
PMID:32129449 SUPPORT Human Clinical
"PSMB1/β6 pathogenic variants are the cause of a recessive disease with ID, microcephaly and developmental delay due to abnormal proteasome assembly"
Developmental delay is named as a defining feature of the disease.
Motor Delay HP:0001270 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Motor delay (HP:0001270). HP:0001270 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39220754 SUPPORT Human Clinical
"Motor delay50% (17/34)100% (2/2)n.r78% (14/18)100% (3/3)0% (0/3)36/60 (60%)"
Row of the review's clinical-features table; the second column is the PSMB1 form, recording motor delay in 2/2 published patients.
Behavioural Abnormalities Atypical behavior HP:0000708 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Atypical behavior (HP:0000708). HP:0000708 is a phenotype from the Human Phenotype Ontology.
Bound at the non-specific level that the published evidence actually supports. The OMIM/MedGen clinical synopsis for this entity additionally records aggressive behaviour (HP:0000718), but no citable publication states it: the only quotable source is the review's "abnormal behaviors" row. A separate aggression phenotype should be split out if and when a second family is reported with a quotable description.
Show evidence (1 reference)
PMID:39220754 SUPPORT Human Clinical
"Abnormal behaviors67% (25/37)100% (2/2)66% (2/3)53% (9/17)n.a100% (3/3)41/62 (66%)"
Row of the review's clinical-features table; the second column is the PSMB1 form, recording abnormal behaviour in 2/2 published patients. The row is an exact match for the non-specific term this phenotype binds. The adjacent autistic-features cell reads 0% (0/2) for this form.
Attention Deficit Hyperactivity Features Attention deficit hyperactivity disorder HP:0007018 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Attention deficit hyperactivity disorder (HP:0007018). HP:0007018 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39220754 SUPPORT Human Clinical
"ADHD features12% (5/42)50% (1/2)0% (0/3)n.an.a33% (1/3)7/50 (14%)"
Row of the review's clinical-features table; the second column is the PSMB1 form, recording ADHD features in 1 of the 2 published patients.
Growth 1
Growth Failure Growth delay HP:0001510 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Growth delay (HP:0001510). HP:0001510 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39220754 SUPPORT Human Clinical
"Growth failure40% (4/10)100% (2/2)n.r50% (9/18)n.rn.r15/30 (50%)"
Row of the review's clinical-features table; the second column is the PSMB1 form, recording growth failure in 2/2 published patients.
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Genetic Associations

1
PSMB1
Gene: PSMB1 hgnc:9537 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PSMB1 (hgnc:9537). hgnc:9537 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (3 references)
PMID:32129449 SUPPORT Human Clinical
"PSMB1/β6 pathogenic variants are the cause of a recessive disease with ID, microcephaly and developmental delay due to abnormal proteasome assembly"
States the gene-disease relationship and its mode of inheritance.
PMID:39220754 SUPPORT Human Clinical
"a total of six neurodevelopmental proteasomopathies have been described, involving the four subunits PSMB1/β6, PSMC1/Rpt2, PSMC3/Rpt5, and PSMD12/Rpn5"
Confirms PSMB1/beta6 as one of the four proteasome subunits implicated in neurodevelopmental proteasomopathies.
PMID:38866022 SUPPORT Human Clinical
"Primary proteasomopathies have recently emerged as a new class of rare early-onset neurodevelopmental disorders (NDDs) caused by pathogenic variants in the PSMB1, PSMC1, PSMC3, or PSMD12 proteasome genes."
Names PSMB1 among the genes defining the primary-proteasomopathy disease class, independently of the two review sources.
Variants (1)
PSMB1 c.307T>C p.(Tyr103His) Pathogenic
Homozygous missense substitution in PSMB1 (NM_002793.4), the only NEDMHAL-causing allele reported to date. Structural modelling places it at the beta6-alpha5 inter-subunit interface; in a cell model it abolishes beta6 maturation, leaving the proform present, and reduces overall subunit content with a slight fall in chymotrypsin-like activity.
Show evidence (1 reference)
PMID:42370079 SUPPORT Other
"PSMB1 (NM_002793.4)c.307T>C p.(Tyr103His)Possibly partial loss-of-function; structural modelling: possible influence on interaction between β6 and α5"
The review's variant table gives the transcript, cDNA and protein change, the predicted partial loss of function, and the structural interpretation.
💊

Medical Actions

6
Supportive and Symptomatic Care
Category: Therapeutic Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
No disease-modifying or mechanism-targeted therapy exists. Management is entirely supportive: developmental and rehabilitative therapies, audiological follow-up for hearing impairment, and behavioural management. Note that proteasome inhibitors used in oncology act in the direction opposite to what this disease mechanism would require and have no role here.
Physical Therapy
Category: Therapeutic Action: physical therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is physical therapy (NCIT:C15302). NCIT:C15302 is a clinical intervention from the NCI Thesaurus. Ontology label: Physical Therapy NCIT:C15302
Physiotherapy for hypotonia and delayed motor development, following general practice for severe neurodevelopmental disorders rather than any NEDMHAL-specific protocol.
Speech and Language Therapy
Category: Therapeutic Action: speech and language therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is speech and language therapy, annotated with Speech Language Therapy (NCIT:C159273). NCIT:C159273 is a clinical intervention from the NCI Thesaurus. Ontology label: Speech Language Therapy NCIT:C159273
Speech-language therapy including augmentative and alternative communication, given the absent or profoundly impaired expressive language.
Occupational Therapy
Category: Therapeutic Action: occupational therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is occupational therapy (NCIT:C121351). NCIT:C121351 is a clinical intervention from the NCI Thesaurus. Ontology label: Occupational Therapy NCIT:C121351
Occupational therapy to support adaptive functioning and activities of daily living, given the severe global developmental impairment.
Audiological Assessment and Hearing Management
Category: Therapeutic Action: aural rehabilitation and hearing managementNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is aural rehabilitation and hearing management, annotated with Rehabilitation (NCIT:C15315). NCIT:C15315 is a clinical intervention from the NCI Thesaurus. Ontology label: Rehabilitation NCIT:C15315
Audiological follow-up with amplification where indicated. Hearing impairment was present in both published patients and is a modifiable contributor to the communication phenotype. NCIT has no clinical-action term for hearing-device use, so the generic rehabilitation action is used.
Genetic Counseling
Category: Counseling / Informational Action: genetic counselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is genetic counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. Ontology label: Genetic Counseling NCIT:C15240
Counselling for the family on autosomal recessive inheritance, with a 25% recurrence risk per pregnancy for carrier couples, and on the availability of targeted prenatal or preimplantation testing once the familial variant is known. Particularly relevant in the consanguineous setting in which this disorder was ascertained.
🔬

Diagnosis

1
Exome or genome sequencing
Diagnosis is molecular and genotype-first: identification of biallelic PSMB1 variants. In the founding kindred the variant was found by sequencing in a consanguineous family and shown to segregate with the phenotype. No consensus clinical diagnostic criteria exist, and the clinical presentation (microcephaly, hypotonia, developmental delay, absent language) is shared with many genetically distinct neurodevelopmental disorders.
Show evidence (1 reference)
PMID:32129449 SUPPORT Human Clinical
"Consanguinity due to extensive homozygosity unravels many recessive phenotypes and facilitates the detection of novel gene-disease links."
Describes the homozygosity-based sequencing approach by which the diagnosis was established in the index family.
📊

Prevalence

1
Worldwide
Cases In Literature Not yet documented
Two published patients, both female siblings from a single consanguineous Pakistani family. No population-based prevalence or incidence estimate exists, and no numeric rate is asserted here.
Show evidence (1 reference)
PMID:39220754 SUPPORT Human Clinical
"Recessive forms, reported in 8/78 patients with PSMB1, PSMC1, or PSMC3 biallelic variants, represent only 10% of neurodevelopmental proteasomopathies."
A 2024 review of the whole disease class counts only a handful of biallelic patients across three genes, consistent with a literature-case-count-only occurrence measure.
🔀

Differential Diagnoses

1

Conditions with similar clinical presentations that must be differentiated from Neurodevelopmental Disorder with Microcephaly, Hypotonia, and Absent Language:

Other neurodevelopmental proteasomopathies
Overlapping Features PSMD12-related Stankiewicz-Isidor syndrome, and the PSMC1-, PSMC3- and PSMD11-related neurodevelopmental disorders, share developmental delay, speech delay and intellectual disability. Most are dominant, de novo, and caused by 19S regulatory-particle lesions, and several have distinguishing features absent in NEDMHAL — cataract and deafness in the PSMC3 neurosensory form, thumb and visceral anomalies in Stankiewicz-Isidor syndrome. Molecular testing is required to separate them.
Show evidence (2 references)
PMID:39220754 SUPPORT Human Clinical
"a total of six neurodevelopmental proteasomopathies have been described, involving the four subunits PSMB1/β6, PSMC1/Rpt2, PSMC3/Rpt5, and PSMD12/Rpn5"
Enumerates the sibling entities from which NEDMHAL must be distinguished.
PMID:39220754 SUPPORT Human Clinical
"neurodevelopmental proteasomopathies are mostly monogenic dominant disorders arising from de novo mutations in proteasome genes"
The dominant, de novo inheritance of most sibling entities is a practical discriminator from recessive NEDMHAL.
🧫

Experimental Models

1
SH-SY5Y neuroblastoma cell model of PSMB1 p.(Tyr103His) CELL_LINE
Human SH-SY5Y neuroblastoma cells were used to assay the biochemical consequences of the p.(Tyr103His) substitution on beta6 processing, its incorporation into the proteasome, and proteasome activity. This is a heterologous cell line expressing the variant, not a patient-derived culture; no patient fibroblast or iPSC model of NEDMHAL has been reported.
Publication
PMID:32129449
Pathograph links
Impaired beta6 Maturation and 20S Core Particle Assembly measures fidelity: moderate Provides the direct biochemical readout of defective beta6 processing and incorporation attributable to the variant.
Limitations: A neuroblastoma cell line rather than patient-derived neural tissue, so results speak to the variant's molecular consequence rather than to the cellular state of the patients. The reported activity deficit is slight, leaving the quantitative link to the severe clinical phenotype unexplained.
Show evidence (1 reference)
PMID:32129449 SUPPORT In Vitro
"the p(Tyr103His) variant affects both the processing of PSMB1/β6 and its incorporation into proteasome, thus impairing proteasome activity"
States exactly what the cell model measured and what it showed for this mechanism node.
Show evidence (1 reference)
PMID:32129449 SUPPORT In Vitro
"the p(Tyr103His) variant affects both the processing of PSMB1/β6 and its incorporation into proteasome, thus impairing proteasome activity"
Names the cell system used and establishes it as the source of the biochemical evidence for this variant's molecular consequence.
🐁

Animal Models

1
psmb1 CRISPR/Cas9 mutant and morpholino knockdown Zebrafish Loss-of-function model of the single psmb1 orthologue
Zebrafish carry a single psmb1 orthologue. Two independent loss-of-function approaches — CRISPR/Cas9 mutagenesis and morpholino knockdown — were applied, and both produced microcephaly, microphthalmia and reduced brain size. The concordance of the two approaches partially mitigates the well-known off-target concerns with morpholino knockdown.
Species
Zebrafish
Genotype
psmb1 CRISPR/Cas9 mutant and morpholino knockdown
Publication
PMID:32129449
Pathograph links
Impaired Brain Growth and Neurodevelopment recapitulates fidelity: moderate Loss of psmb1 function reproduces the reduced brain growth that underlies the human microcephaly.
Limitations: The model uses complete loss of function, whereas the human allele is a partial-loss-of-function missense variant, so the model is not genotype-matched. Zebrafish cannot report the human phenotypes of language and behaviour, and no zebrafish proteasome-assembly or activity measurement is described in the abstract.
Show evidence (1 reference)
PMID:32129449 SUPPORT Model Organism
"CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1 zebrafish orthologue resulted in microcephaly, microphthalmia and reduced brain size."
Two independent loss-of-function approaches converge on reduced brain size, supporting the model as informative for the brain-growth node.
Show evidence (1 reference)
PMID:32129449 SUPPORT Model Organism
"CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1 zebrafish orthologue resulted in microcephaly, microphthalmia and reduced brain size."
Establishes the model system, the two perturbation methods, and its phenotypic output.
{ }

Source YAML

click to show 
name: Neurodevelopmental Disorder with Microcephaly, Hypotonia, and Absent Language
creation_date: '2026-08-18T00:00:00Z'
category: Mendelian
synonyms:
- NEDMHAL
- PSMB1-related neurodevelopmental disorder
- PSMB1-related neurodevelopmental proteasomopathy
description: >-
  Neurodevelopmental disorder with microcephaly, hypotonia, and absent language
  (NEDMHAL; OMIM:620038) is an ultra-rare autosomal recessive neurodevelopmental
  disorder caused by biallelic variants in PSMB1, which encodes the beta6
  subunit of the 20S proteasome core particle. It is one of the small family of
  "neurodevelopmental proteasomopathies" (PRNDD) and is, to date, the only
  member of that family whose causal lesion sits in the 20S core particle rather
  than the 19S regulatory particle. Affected individuals have microcephaly,
  hypotonia, severe intellectual disability with global developmental delay,
  profoundly impaired expressive language, motor delay, hearing impairment,
  growth failure, and behavioural abnormalities; epilepsy, autistic features and
  visceral malformations were not seen in the published cases. Mechanistically
  the reported homozygous missense variant p.(Tyr103His) weakens the beta6-alpha5
  inter-subunit interface, destabilising the 20S proteasome complex and impairing
  beta6 propeptide maturation and its incorporation into the proteasome, so that
  ubiquitin-dependent proteolytic capacity falls. Knockdown or mutagenesis of the
  single zebrafish psmb1 orthologue reproduces microcephaly and reduced brain
  size, linking proteasome-assembly failure directly to impaired brain growth.
  The entity is defined by a single consanguineous Pakistani kindred (two
  affected sisters) plus functional validation, so its phenotypic boundaries
  remain provisional.
disease_term:
  preferred_term: neurodevelopmental disorder with microcephaly, hypotonia, and absent language
  term:
    id: MONDO:0859287
    label: neurodevelopmental disorder with microcephaly, hypotonia, and absent language
parents:
- Neurodevelopmental Disorder
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    evidence:
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Here, we report two siblings with phenotypic signs, including
        intellectual disability (ID), developmental delay and microcephaly from a
        Pakistani consanguineous family in which we have identified homozygosity
        for p(Tyr103His) in the PSMB1 gene
      explanation: >-
        The defining manifestations are neurological (microcephaly, intellectual
        disability, developmental delay), placing the entry in the neurologic
        chapter.
  mechanistic_category:
  - classification_value: proteotoxic disease
    notes: >-
      Assigned on the degradation side of proteostasis: the primary lesion is in
      the proteasome itself rather than in an aggregation-prone client protein,
      so this is proteostasis failure by loss of degradative capacity. No
      PSMB1-specific aggregation or interferon-signature data exist yet (see the
      knowledge-gap discussion), and the classification rests on the
      class-level characterisation of proteasomopathies.
    evidence:
    - reference: PMID:42370079
      reference_title: >-
        Molecular mechanisms in rare proteasomopathies.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        The concomitant proteasome impairment leads to imbalanced protein
        homeostasis by dysfunctional ubiquitin-mediated protein degradation.
      explanation: >-
        Establishes that proteasomopathies as a class act through failure of
        ubiquitin-mediated protein homeostasis; PARTIAL because the statement is
        class-level rather than specific to PSMB1.
inheritance:
- name: Autosomal recessive
  description: >-
    Both reported patients are sisters homozygous for PSMB1 c.307T>C
    p.(Tyr103His), inherited from unaffected consanguineous parents; the variant
    segregated with the phenotype in the kindred. Recessive inheritance is the
    exception among neurodevelopmental proteasomopathies, which are mostly
    dominant de novo disorders of the 19S regulatory particle.
  inheritance_term:
    preferred_term: autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we report two siblings with phenotypic signs, including intellectual
      disability (ID), developmental delay and microcephaly from a Pakistani
      consanguineous family in which we have identified homozygosity for
      p(Tyr103His) in the PSMB1 gene
    explanation: >-
      Homozygosity in two affected siblings of a consanguineous family that
      segregated with disease establishes autosomal recessive transmission.
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recessive forms, reported in 8/78 patients with PSMB1, PSMC1, or PSMC3
      biallelic variants, represent only 10% of neurodevelopmental
      proteasomopathies.
    explanation: >-
      Confirms that the PSMB1 form is biallelic/recessive and situates it as a
      minority pattern within the proteasomopathy class.

prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: NOT_YET_DOCUMENTED
  notes: >-
    Two published patients, both female siblings from a single consanguineous
    Pakistani family. No population-based prevalence or incidence estimate
    exists, and no numeric rate is asserted here.
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recessive forms, reported in 8/78 patients with PSMB1, PSMC1, or PSMC3
      biallelic variants, represent only 10% of neurodevelopmental
      proteasomopathies.
    explanation: >-
      A 2024 review of the whole disease class counts only a handful of biallelic
      patients across three genes, consistent with a literature-case-count-only
      occurrence measure.

pathophysiology:
- name: Biallelic PSMB1 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    The homozygous PSMB1 missense variant c.307T>C p.(Tyr103His) is the
    initiating lesion. PSMB1 encodes beta6, a non-catalytic beta-type subunit of
    the inner beta-rings of the 20S proteasome core particle. The variant is
    characterised as a partial rather than complete loss of function.
  genetic_context:
    gene:
      preferred_term: PSMB1
      term:
        id: hgnc:9537
        label: PSMB1
    zygosity: HOMOZYGOUS
    variant_origin: GERMLINE
    functional_impact_category: PARTIAL_LOSS_OF_FUNCTION
    description: >-
      Homozygous germline missense substitution p.(Tyr103His), inherited from
      consanguineous heterozygous parents.
  evidence:
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: PSMB1 encodes a β-type proteasome subunit (i.e. β6).
    explanation: Establishes the gene product identity as the beta6 proteasome subunit.
  - reference: PMID:42370079
    reference_title: >-
      Molecular mechanisms in rare proteasomopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      PSMB1 (NM_002793.4)c.307T>C p.(Tyr103His)Possibly partial loss-of-function;
      structural modelling: possible influence on interaction between β6 and α5
    explanation: >-
      The review's variant table records the transcript, the cDNA and protein
      change, and classifies the allele as a possible partial loss of function.
  downstream:
  - target: Destabilised beta6-alpha5 Interface of the 20S Core Particle
    causal_link_type: DIRECT
    description: >-
      Tyr103 sits at the beta6 surface that contacts the alpha5 subunit;
      substitution to histidine weakens that contact.
    evidence:
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: COMPUTATIONAL
      snippet: >-
        Modeling of the p(Tyr103His) variant indicates that this variant weakens
        the interactions between PSMB1/β6 and PSMA5/α5 proteasome subunits and
        thus destabilizes the 20S proteasome complex.
      explanation: >-
        Structural modelling links the specific substitution to loss of the
        beta6-alpha5 contact.

- name: Destabilised beta6-alpha5 Interface of the 20S Core Particle
  biological_scale: MOLECULAR
  description: >-
    The 20S core particle is built from four stacked heptameric rings in the
    order alpha7-beta7-beta7-alpha7, so every beta subunit sits against defined
    neighbouring alpha and beta subunits. Weakening the beta6 (PSMB1) contact
    with alpha5 (PSMA5) destabilises the assembled core particle.
  cellular_components:
  - preferred_term: 20S proteasome core particle
    term:
      id: GO:0005839
      label: proteasome core complex
  - preferred_term: proteasome beta-ring
    term:
      id: GO:0019774
      label: proteasome core complex, beta-subunit complex
  evidence:
  - reference: PMID:42370079
    reference_title: >-
      Molecular mechanisms in rare proteasomopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: 'The 20S CP consists of stringently ordered heptameric α- and β-rings: α7-β7-β7-α7'
    explanation: >-
      Establishes the stereotyped ring architecture in which a beta6-alpha5
      inter-subunit contact is structurally load-bearing.
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      Modeling of the p(Tyr103His) variant indicates that this variant weakens
      the interactions between PSMB1/β6 and PSMA5/α5 proteasome subunits and thus
      destabilizes the 20S proteasome complex.
    explanation: Directly states destabilisation of the 20S complex by the variant.
  downstream:
  - target: Impaired beta6 Maturation and 20S Core Particle Assembly
    causal_link_type: DIRECT
    description: >-
      A destabilised inter-subunit interface impairs the ordered, chaperone-guided
      incorporation and maturation of beta6 during 20S biogenesis.
    evidence:
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        the p(Tyr103His) variant affects both the processing of PSMB1/β6 and its
        incorporation into proteasome, thus impairing proteasome activity
      explanation: >-
        Biochemical work in human SH-SY5Y cells ties the variant to defective
        beta6 processing and incorporation.

- name: Impaired beta6 Maturation and 20S Core Particle Assembly
  biological_scale: MOLECULAR
  description: >-
    Beta-ring assembly is an ordered, POMP-dependent process in which beta6 is
    incorporated onto the nascent alpha-ring, and each beta subunit must have its
    propeptide processed for the core particle to mature. In cells expressing the
    variant, beta6 maturation is absent and the unprocessed proform persists,
    with reduced overall subunit content — i.e. the defect is one of proteasome
    biogenesis rather than of catalysis.
  biological_processes:
  - preferred_term: proteasome assembly
    modifier: DECREASED
    term:
      id: GO:0043248
      label: proteasome assembly
  - preferred_term: beta6 propeptide processing
    modifier: DECREASED
    term:
      id: GO:0051604
      label: protein maturation
  evidence:
  - reference: PMID:42370079
    reference_title: >-
      Molecular mechanisms in rare proteasomopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Correct β-ring assembly strictly depends on POMP. Its recruitment
      facilitates β2 entry, followed by β3, β4, β5, β6 onto the α-ring
    explanation: >-
      Establishes that beta6 incorporation is a defined, ordered step of
      chaperone-guided 20S biogenesis, which is the step this variant perturbs.
  - reference: PMID:42370079
    reference_title: >-
      Molecular mechanisms in rare proteasomopathies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: 'SHSY5Y cells: maturation absent, proform present (myc)'
    explanation: >-
      The review's experimental-outcome table records absent beta6 maturation with
      a persisting proform in the cell model of the variant.
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PSMB1/β6 pathogenic variants are the cause of a recessive disease with ID,
      microcephaly and developmental delay due to abnormal proteasome assembly
    explanation: >-
      The authors attribute the disease specifically to abnormal proteasome
      assembly.
  downstream:
  - target: Reduced Proteasome Proteolytic Capacity
    causal_link_type: DIRECT
    description: >-
      Fewer correctly matured core particles means less proteolytically competent
      proteasome.
    evidence:
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        the p(Tyr103His) variant affects both the processing of PSMB1/β6 and its
        incorporation into proteasome, thus impairing proteasome activity
      explanation: Links the assembly/maturation defect directly to impaired proteasome activity.

- name: Reduced Proteasome Proteolytic Capacity
  biological_scale: MOLECULAR
  description: >-
    Proteolysis in the 20S core particle is carried out by the caspase-like
    (beta1), trypsin-like (beta2) and chymotrypsin-like (beta5) active sites.
    Beta6 is not itself catalytic, so the activity loss is an indirect
    consequence of having fewer intact core particles. In the SH-SY5Y cell model
    the measured deficit was modest — a slight reduction of chymotrypsin-like
    activity — which is consistent with a partial rather than complete loss of
    function and is an important quantitative caveat.
  molecular_functions:
  - preferred_term: proteasome threonine-type endopeptidase activity
    modifier: DECREASED
    term:
      id: GO:0004298
      label: threonine-type endopeptidase activity
  biological_processes:
  - preferred_term: proteasomal protein catabolic process
    modifier: DECREASED
    term:
      id: GO:0010498
      label: proteasomal protein catabolic process
  evidence:
  - reference: PMID:42370079
    reference_title: >-
      Molecular mechanisms in rare proteasomopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Peptide-bond hydrolysis is associated with the 20S CP through 3 cleavage
      specificities of the 6 active site subunits
    explanation: >-
      Establishes that proteolysis resides in the core particle's active-site
      subunits, so loss of intact core particles is what lowers activity.
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      the p(Tyr103His) variant affects both the processing of PSMB1/β6 and its
      incorporation into proteasome, thus impairing proteasome activity
    explanation: Reports impaired proteasome activity as the functional consequence.
  downstream:
  - target: Impaired Ubiquitin-Dependent Protein Homeostasis
    causal_link_type: DIRECT
    description: >-
      Reduced proteasome capacity lowers throughput of the ubiquitin-proteasome
      system for polyubiquitinated substrates.
    evidence:
    - reference: PMID:42370079
      reference_title: >-
        Molecular mechanisms in rare proteasomopathies.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        The concomitant proteasome impairment leads to imbalanced protein
        homeostasis by dysfunctional ubiquitin-mediated protein degradation.
      explanation: >-
        States the class-level step from proteasome impairment to imbalanced
        protein homeostasis.

- name: Impaired Ubiquitin-Dependent Protein Homeostasis
  biological_scale: CELLULAR
  description: >-
    Reduced proteasomal throughput leaves K48-polyubiquitinated substrates
    undegraded, shifting the balance between protein synthesis and degradation.
    Across proteasomopathies this state is associated with protein aggregation
    and activated cellular stress responses; whether those specific downstream
    features occur in PSMB1-mutant cells has not been shown directly. The type I
    interferon arm of the class mechanism is deliberately NOT carried into this
    chain: PSMB1 is the one 20S core-particle subunit whose variants have not
    been shown to provoke immune dysregulation.
  biological_processes:
  - preferred_term: ubiquitin-dependent protein catabolic process
    modifier: DECREASED
    term:
      id: GO:0006511
      label: ubiquitin-dependent protein catabolic process
  - preferred_term: proteasome-mediated ubiquitin-dependent protein catabolic process
    modifier: DECREASED
    term:
      id: GO:0043161
      label: proteasome-mediated ubiquitin-dependent protein catabolic process
  evidence:
  - reference: PMID:42370079
    reference_title: >-
      Molecular mechanisms in rare proteasomopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      both syndromes show molecular similarities with protein aggregation,
      activated stress responses, metabolic imbalance and dysregulated type I
      interferon signalling
    explanation: >-
      Describes the shared downstream cellular consequences across
      proteasomopathies. PARTIAL because these are class-level observations that
      have not been demonstrated for PSMB1 specifically.
  downstream:
  - target: Impaired Brain Growth and Neurodevelopment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The developing brain is the compartment in which reduced proteostatic
      capacity manifests. The molecular intermediates between lowered
      ubiquitin-proteasome throughput and reduced brain growth are not
      established; the link rests on the zebrafish loss-of-function phenotype and
      on the human microcephaly.
    evidence:
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1
        zebrafish orthologue resulted in microcephaly, microphthalmia and reduced
        brain size.
      explanation: >-
        Two independent loss-of-function approaches in zebrafish converge on
        reduced brain size, supporting a causal link from psmb1 deficiency to
        impaired brain growth.

- name: Impaired Brain Growth and Neurodevelopment
  biological_scale: TISSUE
  description: >-
    The organ-level consequence is failure of normal brain growth, expressed
    clinically as microcephaly with severe developmental delay, intellectual
    disability, profoundly impaired expressive language and hypotonia. Neurons
    and neural progenitors of the developing brain are the implicated cell
    populations; no human neuropathology has been reported, so the cellular
    attribution derives from the model organism and from the clinical phenotype.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: neural progenitor cell
    term:
      id: CL:0000047
      label: neural stem cell
  biological_processes:
  - preferred_term: brain development
    modifier: ABNORMAL
    term:
      id: GO:0007420
      label: brain development
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1
      zebrafish orthologue resulted in microcephaly, microphthalmia and reduced
      brain size.
    explanation: >-
      Establishes reduced brain size as the tissue-level consequence of psmb1
      loss of function in vivo.
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PSMB1/β6 pathogenic variants are the cause of a recessive disease with ID,
      microcephaly and developmental delay due to abnormal proteasome assembly
    explanation: >-
      Ties the human neurodevelopmental phenotype to the proteasome assembly
      defect.

  downstream:
  - target: Microcephaly
    causal_link_type: DIRECT
    description: >-
      Failure of brain growth is what the reduced head circumference measures.
    evidence:
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1
        zebrafish orthologue resulted in microcephaly, microphthalmia and
        reduced brain size.
      explanation: >-
        Reduced brain size and microcephaly are the co-occurring output of psmb1
        loss of function in the model.
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        PSMB1/β6 pathogenic variants are the cause of a recessive disease with
        ID, microcephaly and developmental delay due to abnormal proteasome
        assembly
      explanation: >-
        Human counterpart to the model-organism readout, so this edge does not
        rest on the zebrafish result alone.
  - target: Severe Intellectual Disability
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Impaired brain growth underlies the cognitive phenotype; the intervening
      circuit-level events are not established.
    evidence:
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        PSMB1/β6 pathogenic variants are the cause of a recessive disease with
        ID, microcephaly and developmental delay due to abnormal proteasome
        assembly
      explanation: >-
        Intellectual disability is reported as a core consequence of the
        proteasome-assembly defect alongside microcephaly.
  - target: Global Developmental Delay
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Impaired brain growth underlies the global developmental delay.
    evidence:
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        PSMB1/β6 pathogenic variants are the cause of a recessive disease with
        ID, microcephaly and developmental delay due to abnormal proteasome
        assembly
      explanation: >-
        Developmental delay is reported as a core consequence of the
        proteasome-assembly defect.

phenotypes:
- category: Neurologic
  name: Microcephaly
  description: >-
    Reduced occipitofrontal head circumference, present in both published
    patients and one of the three features named in the disorder's designation.
    Microcephaly is also the phenotype reproduced by psmb1 loss of function in
    zebrafish.
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we report two siblings with phenotypic signs, including intellectual
      disability (ID), developmental delay and microcephaly from a Pakistani
      consanguineous family in which we have identified homozygosity for
      p(Tyr103His) in the PSMB1 gene
    explanation: Microcephaly is reported in both affected siblings.
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Microcephaly21% (9/42)100% (2/2)n.r38% (6/16)100% (3/3)n.r20/63 (32%)
    explanation: >-
      Row of the review's clinical-features table across the six
      neurodevelopmental proteasomopathies; the second column is the PSMB1 form,
      recording microcephaly in 2/2 published patients.

- category: Neurologic
  name: Hypotonia
  description: >-
    Low muscle tone, reported in both published patients and named in the
    disorder's designation. Hypotonia is listed as the distinguishing "other
    neurological finding" of the PSMB1 form in the class review.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Other neurological findingsn.rHypotonia 100% (2/2)Ataxia 100% (3/3);
      peripheral polyneuropathy of lower limbs 66% (2/3)
    explanation: >-
      The "other neurological findings" row of the review's clinical-features
      table; the PSMB1 form's cell records hypotonia in both published patients,
      and it is the only entry in that row for this form.
  - reference: PMID:42370079
    reference_title: >-
      Molecular mechanisms in rare proteasomopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Common symptoms include neurodevelopmental delay, speech delay,
      intellectual disability, impaired sensing functions, hypotonia, general
      developmental delay, and in some cases seizures
    explanation: >-
      Lists hypotonia among the common manifestations of neurodevelopmental
      proteasomopathies. PARTIAL because the statement is class-level rather than
      specific to PSMB1.

- category: Neurologic
  name: Absent or Profoundly Impaired Expressive Language
  description: >-
    Failure to acquire spoken language, named in the disorder's designation
    ("absent language"). The published cohort description records speech delay in
    both patients; the stronger "absent language" characterisation comes from the
    OMIM entity definition rather than from a quotable statement in the primary
    report, so the evidence here is graded PARTIAL and the phenotype name is
    deliberately hedged.
  phenotype_term:
    preferred_term: Absent speech
    term:
      id: HP:0001344
      label: Absent speech
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Speech delay94% (32/34)100% (2/2)100% (3/3)100% (18/18)100% (3/3)100%
      (3/3)61/63 (97%)
    explanation: >-
      Row of the review's clinical-features table; the second column is the PSMB1
      form, recording speech involvement in 2/2 published patients. PARTIAL
      because the table records "speech delay" and does not itself assert that
      language was entirely absent.

- category: Neurologic
  name: Severe Intellectual Disability
  description: >-
    Intellectual disability, graded severe in both published patients — the most
    severe grading among the neurodevelopmental proteasomopathies, which
    otherwise range from mild to severe.
  phenotype_term:
    preferred_term: Severe intellectual disability
    term:
      id: HP:0010864
      label: Severe intellectual disability
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Intellectual disability; severity85% (34/40); mild to severe100% (2/2); severe'
    explanation: >-
      The review's table records intellectual disability in 2/2 PSMB1 patients
      and grades its severity as severe.
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we report two siblings with phenotypic signs, including intellectual
      disability (ID), developmental delay and microcephaly from a Pakistani
      consanguineous family in which we have identified homozygosity for
      p(Tyr103His) in the PSMB1 gene
    explanation: Intellectual disability is reported in both affected siblings.

- category: Neurologic
  name: Global Developmental Delay
  description: >-
    Delay across developmental domains from infancy, reported in both published
    patients. Developmental delay is the universal feature of the
    neurodevelopmental proteasomopathies as a class.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Developmental delay100% (45/45)100% (2/2)100% (3/3)100% (21/21)100%
      (3/3)100% (3/3)77/77 (100%)
    explanation: >-
      Row of the review's clinical-features table; the second column is the
      PSMB1 form, recording developmental delay in 2/2 published patients.
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PSMB1/β6 pathogenic variants are the cause of a recessive disease with ID,
      microcephaly and developmental delay due to abnormal proteasome assembly
    explanation: Developmental delay is named as a defining feature of the disease.

- category: Neurologic
  name: Motor Delay
  description: >-
    Delayed acquisition of motor milestones, reported in both published patients
    — a higher proportion than in the dominant 19S forms of the disease class.
  phenotype_term:
    preferred_term: Motor delay
    term:
      id: HP:0001270
      label: Motor delay
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Motor delay50% (17/34)100% (2/2)n.r78% (14/18)100% (3/3)0%
      (0/3)36/60 (60%)
    explanation: >-
      Row of the review's clinical-features table; the second column is the
      PSMB1 form, recording motor delay in 2/2 published patients.

- category: Neurosensory
  name: Hearing Impairment
  description: >-
    Hearing loss, reported in both published patients. Impaired sensory function
    is a recurring feature across the neurodevelopmental proteasomopathies.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hearing impairment18% (6/34)100% (2/2)100% (3/3)8/18 (44%)100% (3/3)n.r22/60
      (37%)
    explanation: >-
      Row of the review's clinical-features table; the second column is the PSMB1
      form, recording hearing impairment in 2/2 published patients.

- category: Behavioral
  name: Behavioural Abnormalities
  description: >-
    Non-specific abnormal behaviour was recorded in both published patients.
    Attention deficit hyperactivity features were present in one of the two;
    autistic features were not observed in either, distinguishing this form from
    the dominant PSMD12 and PSMC3 forms in which autism is common.
  phenotype_term:
    preferred_term: Atypical behavior
    term:
      id: HP:0000708
      label: Atypical behavior
  notes: >-
    Bound at the non-specific level that the published evidence actually
    supports. The OMIM/MedGen clinical synopsis for this entity additionally
    records aggressive behaviour (HP:0000718), but no citable publication states
    it: the only quotable source is the review's "abnormal behaviors" row. A
    separate aggression phenotype should be split out if and when a second
    family is reported with a quotable description.
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Abnormal behaviors67% (25/37)100% (2/2)66% (2/3)53% (9/17)n.a100%
      (3/3)41/62 (66%)
    explanation: >-
      Row of the review's clinical-features table; the second column is the
      PSMB1 form, recording abnormal behaviour in 2/2 published patients. The
      row is an exact match for the non-specific term this phenotype binds. The
      adjacent autistic-features cell reads 0% (0/2) for this form.

- category: Behavioral
  name: Attention Deficit Hyperactivity Features
  description: >-
    Attention deficit hyperactivity features were recorded in one of the two
    published patients.
  phenotype_term:
    preferred_term: Attention deficit hyperactivity disorder
    term:
      id: HP:0007018
      label: Attention deficit hyperactivity disorder
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ADHD features12% (5/42)50% (1/2)0% (0/3)n.an.a33% (1/3)7/50 (14%)
    explanation: >-
      Row of the review's clinical-features table; the second column is the
      PSMB1 form, recording ADHD features in 1 of the 2 published patients.

- category: Growth
  name: Growth Failure
  description: >-
    Impaired growth with short stature, reported in both published patients and
    named among the defining features of the founding report.
  phenotype_term:
    preferred_term: Growth delay
    term:
      id: HP:0001510
      label: Growth delay
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Growth failure40% (4/10)100% (2/2)n.r50% (9/18)n.rn.r15/30 (50%)
    explanation: >-
      Row of the review's clinical-features table; the second column is the
      PSMB1 form, recording growth failure in 2/2 published patients.

- category: Craniofacial
  name: Abnormal Facial Shape
  description: >-
    Dysmorphic facial features were present in both published patients. As across
    this disease class, the dysmorphism is not reported as a recognisable
    gestalt.
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Abnormal facial shape97% (44/45)100% (2/2)100% (3/3)89% (17/19)100%
      (3/3)66% (2/3)71/75 (95%)
    explanation: >-
      Row of the review's clinical-features table; the second column is the
      PSMB1 form, recording abnormal facial shape in 2/2 published patients.

genetic:
- name: PSMB1
  gene_term:
    preferred_term: PSMB1
    term:
      id: hgnc:9537
      label: PSMB1
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >-
    PSMB1 (6q27) encodes beta6, a non-catalytic beta-type subunit of the 20S
    proteasome core particle. A single pathogenic allele, the homozygous missense
    c.307T>C p.(Tyr103His), has been reported. PSMB1 is the only 20S core-particle
    gene implicated in a neurodevelopmental proteasomopathy; every other gene in
    the class encodes a 19S regulatory-particle subunit.
  evidence:
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PSMB1/β6 pathogenic variants are the cause of a recessive disease with ID,
      microcephaly and developmental delay due to abnormal proteasome assembly
    explanation: States the gene-disease relationship and its mode of inheritance.
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a total of six neurodevelopmental proteasomopathies have been described,
      involving the four subunits PSMB1/β6, PSMC1/Rpt2, PSMC3/Rpt5, and
      PSMD12/Rpn5
    explanation: >-
      Confirms PSMB1/beta6 as one of the four proteasome subunits implicated in
      neurodevelopmental proteasomopathies.
  - reference: PMID:38866022
    reference_title: >-
      PSMD11 loss-of-function variants correlate with a neurobehavioral
      phenotype, obesity, and increased interferon response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Primary proteasomopathies have recently emerged as a new class of rare
      early-onset neurodevelopmental disorders (NDDs) caused by pathogenic
      variants in the PSMB1, PSMC1, PSMC3, or PSMD12 proteasome genes.
    explanation: >-
      Names PSMB1 among the genes defining the primary-proteasomopathy disease
      class, independently of the two review sources.
  variants:
  - name: PSMB1 c.307T>C p.(Tyr103His)
    description: >-
      Homozygous missense substitution in PSMB1 (NM_002793.4), the only
      NEDMHAL-causing allele reported to date. Structural modelling places it at
      the beta6-alpha5 inter-subunit interface; in a cell model it abolishes beta6
      maturation, leaving the proform present, and reduces overall subunit content
      with a slight fall in chymotrypsin-like activity.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:42370079
      reference_title: >-
        Molecular mechanisms in rare proteasomopathies.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        PSMB1 (NM_002793.4)c.307T>C p.(Tyr103His)Possibly partial
        loss-of-function; structural modelling: possible influence on interaction
        between β6 and α5
      explanation: >-
        The review's variant table gives the transcript, cDNA and protein change,
        the predicted partial loss of function, and the structural interpretation.

animal_models:
- species: Zebrafish
  genotype: psmb1 CRISPR/Cas9 mutant and morpholino knockdown
  category: Loss-of-function model of the single psmb1 orthologue
  publication: PMID:32129449
  description: >-
    Zebrafish carry a single psmb1 orthologue. Two independent loss-of-function
    approaches — CRISPR/Cas9 mutagenesis and morpholino knockdown — were applied,
    and both produced microcephaly, microphthalmia and reduced brain size. The
    concordance of the two approaches partially mitigates the well-known
    off-target concerns with morpholino knockdown.
  modeled_mechanisms:
  - target: Impaired Brain Growth and Neurodevelopment
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Loss of psmb1 function reproduces the reduced brain growth that underlies
      the human microcephaly.
    limitations: >-
      The model uses complete loss of function, whereas the human allele is a
      partial-loss-of-function missense variant, so the model is not
      genotype-matched. Zebrafish cannot report the human phenotypes of language
      and behaviour, and no zebrafish proteasome-assembly or activity measurement
      is described in the abstract.
    evidence:
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1
        zebrafish orthologue resulted in microcephaly, microphthalmia and reduced
        brain size.
      explanation: >-
        Two independent loss-of-function approaches converge on reduced brain
        size, supporting the model as informative for the brain-growth node.
  evidence:
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1
      zebrafish orthologue resulted in microcephaly, microphthalmia and reduced
      brain size.
    explanation: >-
      Establishes the model system, the two perturbation methods, and its
      phenotypic output.

experimental_models:
- name: SH-SY5Y neuroblastoma cell model of PSMB1 p.(Tyr103His)
  experimental_model_type: CELL_LINE
  publication: PMID:32129449
  description: >-
    Human SH-SY5Y neuroblastoma cells were used to assay the biochemical
    consequences of the p.(Tyr103His) substitution on beta6 processing, its
    incorporation into the proteasome, and proteasome activity. This is a
    heterologous cell line expressing the variant, not a patient-derived culture;
    no patient fibroblast or iPSC model of NEDMHAL has been reported.
  modeled_mechanisms:
  - target: Impaired beta6 Maturation and 20S Core Particle Assembly
    relationship: MEASURES
    fidelity: MODERATE
    description: >-
      Provides the direct biochemical readout of defective beta6 processing and
      incorporation attributable to the variant.
    limitations: >-
      A neuroblastoma cell line rather than patient-derived neural tissue, so
      results speak to the variant's molecular consequence rather than to the
      cellular state of the patients. The reported activity deficit is slight,
      leaving the quantitative link to the severe clinical phenotype unexplained.
    evidence:
    - reference: PMID:32129449
      reference_title: >-
        Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
        impairment of proteasome function, microcephaly, intellectual
        disability, developmental delay and short stature.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        the p(Tyr103His) variant affects both the processing of PSMB1/β6 and its
        incorporation into proteasome, thus impairing proteasome activity
      explanation: >-
        States exactly what the cell model measured and what it showed for this
        mechanism node.
  evidence:
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual disability,
      developmental delay and short stature.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      the p(Tyr103His) variant affects both the processing of PSMB1/β6 and its
      incorporation into proteasome, thus impairing proteasome activity
    explanation: >-
      Names the cell system used and establishes it as the source of the
      biochemical evidence for this variant's molecular consequence.

diagnosis:
- name: Exome or genome sequencing
  description: >-
    Diagnosis is molecular and genotype-first: identification of biallelic PSMB1
    variants. In the founding kindred the variant was found by sequencing in a
    consanguineous family and shown to segregate with the phenotype. No consensus
    clinical diagnostic criteria exist, and the clinical presentation
    (microcephaly, hypotonia, developmental delay, absent language) is shared with
    many genetically distinct neurodevelopmental disorders.
  evidence:
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Consanguinity due to extensive homozygosity unravels many recessive
      phenotypes and facilitates the detection of novel gene-disease links.
    explanation: >-
      Describes the homozygosity-based sequencing approach by which the diagnosis
      was established in the index family.

treatments:
- name: Supportive and Symptomatic Care
  description: >-
    No disease-modifying or mechanism-targeted therapy exists. Management is
    entirely supportive: developmental and rehabilitative therapies, audiological
    follow-up for hearing impairment, and behavioural management. Note that
    proteasome inhibitors used in oncology act in the direction opposite to what
    this disease mechanism would require and have no role here.
  action_category: THERAPEUTIC
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  notes: >-
    Recorded without an evidence item: no publication describes management of
    NEDMHAL, and the founding report is a gene-discovery paper. Asserting a
    treatment claim with a quoted snippet would overstate the literature.
- name: Physical Therapy
  description: >-
    Physiotherapy for hypotonia and delayed motor development, following general
    practice for severe neurodevelopmental disorders rather than any
    NEDMHAL-specific protocol.
  action_category: THERAPEUTIC
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
- name: Speech and Language Therapy
  description: >-
    Speech-language therapy including augmentative and alternative communication,
    given the absent or profoundly impaired expressive language.
  action_category: THERAPEUTIC
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: speech and language therapy
    term:
      id: NCIT:C159273
      label: Speech Language Therapy
- name: Occupational Therapy
  description: >-
    Occupational therapy to support adaptive functioning and activities of daily
    living, given the severe global developmental impairment.
  action_category: THERAPEUTIC
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: occupational therapy
    term:
      id: NCIT:C121351
      label: Occupational Therapy
- name: Audiological Assessment and Hearing Management
  description: >-
    Audiological follow-up with amplification where indicated. Hearing
    impairment was present in both published patients and is a modifiable
    contributor to the communication phenotype. NCIT has no clinical-action term
    for hearing-device use, so the generic rehabilitation action is used.
  action_category: THERAPEUTIC
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: aural rehabilitation and hearing management
    term:
      id: NCIT:C15315
      label: Rehabilitation
- name: Genetic Counseling
  description: >-
    Counselling for the family on autosomal recessive inheritance, with a 25%
    recurrence risk per pregnancy for carrier couples, and on the availability of
    targeted prenatal or preimplantation testing once the familial variant is
    known. Particularly relevant in the consanguineous setting in which this
    disorder was ascertained.
  action_category: COUNSELING_INFORMATIONAL
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling

discussions:
- discussion_id: single_kindred_phenotype_boundary
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Which features of NEDMHAL are intrinsic to PSMB1 deficiency, and which are
    particular to the single consanguineous kindred in which it was described?
  attaches_to:
  - pathophysiology#Impaired Brain Growth and Neurodevelopment
  rationale: >-
    The entity rests on two affected sisters from one family plus functional
    validation. Every phenotype frequency available is a 2/2 or 1/2 count from
    that kindred, so no feature can currently be separated from the family's
    shared genetic background and consanguinity-associated homozygosity
    elsewhere in the genome. This is why no `frequency:` qualifier is asserted on
    any phenotype in this entry. The absence of epilepsy, autistic features and
    visceral malformations is likewise a statement about two people.
  proposed_experiments:
  - experiment_id: exp_nedmhal_matchmaking_additional_families
    name: Identify additional families
    description: >-
      Identify additional families with biallelic PSMB1 variants through
      international matchmaking (GeneMatcher, DECIPHER, Matchmaker Exchange)
      and determine which features recur.
  - experiment_id: exp_nedmhal_allelic_series_genotype_phenotype
    name: Determine whether other PSMB1 alleles
    description: >-
      Determine whether other PSMB1 alleles, particularly compound
      heterozygous or truncating combinations, produce the same phenotype or
      a distinct severity.
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notably, visceral malformations have not been reported in forms with PSMB1
      or PSMC3 biallelic variants nor with PSMC1 deletions
    explanation: >-
      The review states the negative finding and, in the same passage, cautions
      that it should be interpreted with care given how few cases are reported.

- discussion_id: zebrafish_cannot_model_language_or_behaviour
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Does the zebrafish psmb1 model capture the disorder, when the two features
    that name it besides microcephaly — absent language and behavioural
    abnormality — have no zebrafish correlate?
  attaches_to:
  - pathophysiology#Impaired Brain Growth and Neurodevelopment
  rationale: >-
    The zebrafish model recapitulates reduced brain size convincingly, by two
    independent perturbations. But it is a complete loss-of-function model of a
    disease caused by a partial-loss-of-function missense allele, and it cannot
    report language, intellectual disability, or behaviour. Treating the model as
    validating the whole phenotype would overstate it; it validates the
    brain-growth arm only.
  proposed_experiments:
  - experiment_id: exp_nedmhal_knockin_tyr103his_zebrafish
    name: Generate a knock-in model carrying the orthologous Tyr103His
    description: >-
      Generate a knock-in model carrying the orthologous Tyr103His
      substitution and compare its brain phenotype and proteasome assembly
      with the null.
  - experiment_id: exp_nedmhal_ipsc_neural_progenitor_organoid
    name: Use human iPSC-derived neural progenitors and cortical organoids
    description: >-
      Use human iPSC-derived neural progenitors and cortical organoids from
      genotype-matched cells to test whether proliferation and neurogenesis
      are impaired at the reported partial reduction in proteasome activity.
  evidence:
  - reference: PMID:32129449
    reference_title: >-
      Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause
      impairment of proteasome function, microcephaly, intellectual
      disability, developmental delay and short stature.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1
      zebrafish orthologue resulted in microcephaly, microphthalmia and reduced
      brain size.
    explanation: >-
      The reported model readouts are morphological brain measures only; nothing
      in the model addresses the language or behavioural components of the human
      phenotype.

- discussion_id: interferon_signature_untested_in_psmb1
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Do PSMB1-deficient cells show the protein aggregation, stress-response
    activation and type I interferon dysregulation reported across other
    proteasomopathies?
  attaches_to:
  - pathophysiology#Impaired Ubiquitin-Dependent Protein Homeostasis
  rationale: >-
    Proteasomopathies as a class — both the autoinflammatory and the
    neurodevelopmental arm — converge on protein aggregation, activated stress
    responses and dysregulated type I interferon signalling, and interferon
    signatures are being explored as biomarkers for the class. None of this has
    been measured in PSMB1-mutant cells, so the downstream half of the mechanism
    chain in this entry is asserted at class level and inherited by analogy
    rather than demonstrated. The gap is sharper than mere absence of data:
    PSMB1 is explicitly named in the literature as the one 20S core-particle
    subunit whose pathogenic variants have not been shown to provoke immune
    dysregulation, while every other 20S lesion has. So the class-level
    interferon expectation may specifically fail to apply here, and importing it
    into this entry's mechanism would be the wrong inference rather than merely
    an unverified one. This matters practically: a proteasome-activity or
    interferon-signature assay would otherwise be the natural functional test
    for candidate PSMB1 variants of uncertain significance.
  proposed_experiments:
  - experiment_id: exp_nedmhal_ubiquitin_load_and_ifn_signature
    name: Measure polyubiquitinated protein load
    description: >-
      Measure polyubiquitinated protein load, proteotoxic stress-response
      activation and a type I interferon signature in cells carrying PSMB1
      p.(Tyr103His).
  - experiment_id: exp_nedmhal_20s_versus_19s_ifn_comparison
    name: Compare the magnitude of any interferon response
    description: >-
      Compare the magnitude of any interferon response with that of the 19S
      regulatory-particle proteasomopathies to test whether the
      20S core-particle lesion behaves differently.
  evidence:
  - reference: PMID:42370079
    reference_title: >-
      Molecular mechanisms in rare proteasomopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      both syndromes show molecular similarities with protein aggregation,
      activated stress responses, metabolic imbalance and dysregulated type I
      interferon signalling
    explanation: >-
      Establishes the class-level expectation whose absence of PSMB1-specific
      confirmation is the gap.
  - reference: PMID:37256937
    reference_title: >-
      PSMC3 proteasome subunit variants are associated with neurodevelopmental
      delay and type I interferon production.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      So far, with the exception of the PSMB1 (β6) subunit (25), all pathogenic
      variants related to the 20S core particle have been shown to provoke
      immune dysregulation.
    explanation: >-
      Singles out PSMB1 as the one 20S core-particle subunit not shown to cause
      immune dysregulation, so the interferon arm of the proteasomopathy
      mechanism cannot simply be inherited by this entry.
  - reference: PMID:38866022
    reference_title: >-
      PSMD11 loss-of-function variants correlate with a neurobehavioral
      phenotype, obesity, and increased interferon response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PSMD11 loss of function resulted in impaired 26S proteasome assembly and
      the acquisition of a persistent type I interferon (IFN) gene signature,
      mediated by the integrated stress response (ISR) protein kinase R (PKR)
    explanation: >-
      Shows what the interferon arm looks like when it is actually demonstrated
      in a proteasomopathy: impaired 26S assembly, a persistent type I IFN
      signature, and a named PKR/ISR mediator. Nothing equivalent has been
      measured for PSMB1, which is precisely the gap.

- discussion_id: core_particle_versus_regulatory_particle
  kind: OPEN_QUESTION
  status: OPEN
  prompt: >-
    Are neurodevelopmental proteasomopathies essentially diseases of the 19S
    regulatory particle, and if so why does a 20S core-particle lesion produce
    the same phenotypic class?
  attaches_to:
  - pathophysiology#Destabilised beta6-alpha5 Interface of the 20S Core Particle
  rationale: >-
    PSMB1 p.(Tyr103His) is the lone 20S core-particle lesion among the variants
    identified in neurodevelopmental proteasomopathies, and it is also one of the
    few recessive ones — the rest are dominant, de novo, and in the 19S
    regulatory particle. Two reviews read the same fact in opposite directions:
    one treats the overwhelming 19S predominance as evidence that these are
    fundamentally 19S disorders, while the other treats PSMB1 as the case that
    breaks the subcomplex-determines-phenotype rule. The resolution matters for
    how the entity is grouped and for which proteasome genes should be searched
    in undiagnosed neurodevelopmental disorders.
  proposed_experiments:
  - experiment_id: exp_nedmhal_20s_subunit_cohort_screen
    name: Systematically screen 20S core-particle subunit genes in large
    description: >-
      Systematically screen 20S core-particle subunit genes in large
      neurodevelopmental disorder cohorts to establish whether 20S lesions
      are genuinely rare or merely under-ascertained.
  - experiment_id: exp_nedmhal_matched_20s_19s_assembly_activity
    name: Compare proteasome assembly
    description: >-
      Compare proteasome assembly, activity and interferon output side by
      side between matched 20S and 19S proteasomopathy variants in a common
      cell background.
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      only one (i.e., p.Tyr103His in PSMB1/β6) of the forty-three lesions
      identified in individuals with neurodevelopmental proteasomopathies affect
      the 20S CP strongly suggests that these disorders are essentially diseases
      of the 19S RP
    explanation: >-
      States the 19S-predominance reading, and itself flags the conclusion as
      remaining to be confirmed.
  - reference: PMID:42370079
    reference_title: >-
      Molecular mechanisms in rare proteasomopathies.
    supports: REFUTE
    evidence_source: OTHER
    snippet: >-
      a homozygous PSMB1 variant break the rules of this rationale and suggest
      that the phenotypic manifestation may occur independent of the subunit
      localisation in certain subcomplexes
    explanation: >-
      The opposing reading: PSMB1 is taken as evidence against the phenotype
      being determined by which subcomplex the lesion sits in.

differential_diagnoses:
- name: Other neurodevelopmental proteasomopathies
  description: >-
    PSMD12-related Stankiewicz-Isidor syndrome, and the PSMC1-, PSMC3- and
    PSMD11-related neurodevelopmental disorders, share developmental delay,
    speech delay and intellectual disability. Most are dominant, de novo, and
    caused by 19S regulatory-particle lesions, and several have distinguishing
    features absent in NEDMHAL — cataract and deafness in the PSMC3 neurosensory
    form, thumb and visceral anomalies in Stankiewicz-Isidor syndrome. Molecular
    testing is required to separate them.
  evidence:
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a total of six neurodevelopmental proteasomopathies have been described,
      involving the four subunits PSMB1/β6, PSMC1/Rpt2, PSMC3/Rpt5, and
      PSMD12/Rpn5
    explanation: >-
      Enumerates the sibling entities from which NEDMHAL must be distinguished.
  - reference: PMID:39220754
    reference_title: >-
      Understanding neurodevelopmental proteasomopathies as new rare
      disease entities: A review of current concepts, molecular
      biomarkers, and perspectives.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      neurodevelopmental proteasomopathies are mostly monogenic dominant
      disorders arising from de novo mutations in proteasome genes
    explanation: >-
      The dominant, de novo inheritance of most sibling entities is a practical
      discriminator from recessive NEDMHAL.

notes: >-
  Curation caveats. (1) No `frequency:` qualifier is asserted on any phenotype.
  Every available proportion is a 2/2 or 1/2 count from a single sibship, which
  is not a population frequency; the counts are stated in the phenotype
  descriptions and evidenced instead. (2) The biochemical work behind the
  mechanism chain was done in human SH-SY5Y neuroblastoma cells expressing the
  variant, not in patient-derived fibroblasts — a deep-research draft asserted
  patient fibroblasts and was not followed. (3) The measured functional deficit
  is modest (a slight reduction in chymotrypsin-like activity), which sits
  uneasily with the severity of the clinical phenotype and is recorded as such
  rather than smoothed over. (4) No GeneReviews chapter exists for PSMB1 or
  NEDMHAL; a PubMed search for one returned nothing, so the GeneReviews phenotype
  baseline step was not applicable. (5) An `Inability to walk` phenotype
  (HP:0002540) was drafted from the OMIM/MedGen clinical synopsis and then
  removed: its only available evidence was the motor-delay table row already
  cited elsewhere, and motor delay does not support non-ambulation. The synopsis
  records it, but no citable publication states it, and OMIM is not a
  snippet-validatable reference source here. (6) The deep-research datum that
  the variant is absent from gnomAD and from 300 in-house control chromosomes is
  NOT curated: it appears only in the deep-research report, not in any cached
  abstract, so adding it would be exactly the treat-a-DR-lead-as-truth failure
  the evidence SOP warns about. (7) Named-entity-confusion watch: this entity
  must not be conflated with the similarly named MONDO:0100348
  (neurodevelopmental disorder with microcephaly, impaired language, and gait
  abnormalities) or MONDO:0971172 (RNU4-2-related, with hypotonia and absent
  language), nor with CDK19-related DEE87 (OMIM:618916), which surfaced during
  literature search on description similarity alone.
📚

References & Deep Research

Deep Research

2
Claude Code ▸
1. Disease Information
claude-haiku-4-5-20251001, claude-sonnet-5 11 citations 2026-08-18T15:12:53.288859

1. Disease Information

Overview: Neurodevelopmental disorder with microcephaly, hypotonia, and absent language (NEDMHAL) is an ultra-rare, autosomal recessive proteasome-assembly disorder ("neurodevelopmental proteasomopathy") first described in 2020 in two affected sisters from a consanguineous Pakistani family. It is caused by biallelic pathogenic variants in PSMB1, which encodes the β6 subunit of the 20S core proteasome. Affected individuals present with severe global developmental delay, postnatal microcephaly, axial hypotonia, absent expressive language, short stature, aggressive/behavioral abnormalities, and sensorineural hearing loss. Functional work in patient fibroblasts and a zebrafish model showed that the causal variant destabilizes 20S/26S proteasome assembly, directly linking impaired proteostasis to a human neurodevelopmental phenotype (Ansar et al., 2020, PMID:32129449).

Key identifiers: - OMIM (phenotype): #620038 — NEURODEVELOPMENTAL DISORDER WITH MICROCEPHALY, HYPOTONIA, AND ABSENT LANGUAGE; NEDMHAL - OMIM (gene): 602017 — PROTEASOME SUBUNIT, BETA-TYPE, 1; PSMB1 - Gene location: Chromosome 6q27 - HGNC: PSMB1 (HGNC:9537) - Inheritance: Autosomal recessive - Suggested MONDO:* a MONDO term for this OMIM-derived entity is expected to exist as a cross-reference to OMIM:620038 (mapping should be confirmed directly against the MONDO release rather than assumed, since it was not independently verified in this search pass). - Orphanet does not appear to carry a dedicated, separately numbered entry distinct from the OMIM phenotype as of this search; the PSMB1 gene page on Orphanet cross-references the associated disorder.

Synonyms: NEDMHAL (OMIM abbreviation); "PSMB1-related neurodevelopmental disorder"; "PSMB1-related proteasomopathy." It is one of a small family of related but molecularly distinct "neurodevelopmental proteasomopathies" (also including disorders caused by PSMC1, PSMC3, PSMD12, and PSMD11) (Cuinat et al., 2024, PMID:39220754).

Data provenance: The disease-defining data derive from a single aggregated case report of an index consanguineous family (two affected sisters, family "F200") combined with functional/mechanistic validation studies (patient-derived cells, in silico protein modeling, and a zebrafish model) — not from large-scale registries or EHR-based aggregation. As of this research pass, no independently published second family was identified; the entity remains defined by this single kindred plus experimental validation.

Sources: - OMIM #620038 — NEDMHAL - OMIM *602017 — PSMB1 - Biallelic variants in PSMB1... — PubMed - Understanding neurodevelopmental proteasomopathies... — PubMed

2. Etiology

Disease causal factors: NEDMHAL is a monogenic, purely genetic disorder — no environmental, infectious, or acquired etiology has been implicated. It is caused by biallelic (homozygous, in the reported family) loss-of-function/destabilizing missense variation in PSMB1.

Genetic risk factors: - Causal variant: A homozygous PSMB1 c.307T>C transition, predicting p.(Tyr103His) (Y103H), was identified in both affected sisters by whole-exome/genome sequencing in the index consanguineous Pakistani family (Ansar et al. 2020, PMID:32129449). The variant affects a highly conserved tyrosine residue. - Molecular consequence: Structural modeling indicated the Y103H substitution "weakens the interactions between PSMB1/β6 and PSMA5/α5 proteasome subunits and thus destabilizes the 20S proteasome complex" — i.e., it is not a simple catalytic-site loss-of-function but an assembly-interface–disrupting variant. - Population frequency: The Y103H variant was absent from gnomAD and from 300 in-house control chromosomes, consistent with a rare, highly penetrant recessive allele (GeneCards/PubMed). - Consanguinity: The proband family was consanguineous, and autosomal recessive transmission with homozygosity was the observed inheritance mechanism — consistent with the broader pattern that recessive, biallelic proteasome-subunit disease alleles are strongly enriched by consanguinity, since core proteasome subunits are highly constrained and most heterozygous loss-of-function variants would be expected to be selected against or, in other proteasome genes (e.g., PSMD12), to instead cause a dominant de novo disorder.

Risk-factor caveat for curation: No independent GWAS, epidemiological, or environmental-exposure risk-factor literature exists for this ultra-rare Mendelian condition; population-level risk-factor databases (GWAS Catalog, PheGenI, CTD) were not found to carry entries for this specific disorder.

Protective factors: None reported. No protective variants or modifier alleles have been described.

Gene-environment interactions: None described; this is not currently modeled as a gene-environment interaction disease.

Sources: - Biallelic variants in PSMB1 — PubMed - PSMB1 gene — GeneCards

3. Phenotypes

Based on the OMIM clinical synopsis and the founding case report, the core phenotype set is:

Phenotype Type Onset/Course Suggested HPO term (verify before curation)
Microcephaly (postnatal) Physical/clinical sign Present from early childhood, non-progressive but persistent HP:0000252 Microcephaly
Global developmental delay Behavioral/developmental Infancy onset HP:0001263 Global developmental delay
Severe intellectual disability Cognitive Persistent, non-regressive HP:0010864 Severe intellectual disability (or HP:0001249 Intellectual disability, if severity unconfirmed)
Absent speech / absent language Behavioral/developmental Lifelong, never acquired HP:0001344 Absent speech
Axial/truncal hypotonia Clinical sign Infantile onset HP:0001252 Hypotonia
Short stature Physical Postnatal HP:0004322 Short stature
Sensorineural hearing loss Clinical sign/lab Reported in affected sibs HP:0000365 Hearing impairment (or HP:0000407 Sensorineural hearing impairment, if specified)
Aggressive behavior Behavioral Reported HP:0000718 Aggressive behavior

Severity/progression: The disorder is described as severe and non-progressive/static in its core neurodevelopmental features (developmental delay is profound from infancy rather than regressive), consistent with a primary neurodevelopmental (rather than neurodegenerative) proteasomopathy. Because the condition is known from only two affected siblings, formal frequency percentages (e.g., "80% of patients have X") cannot be computed — features should be curated as present/absent in the reported cases rather than as population frequencies. This is an important curation caveat: standard HPO frequency modifiers (FREQUENT/OCCASIONAL) are not statistically meaningful for an n=2 cohort and should be omitted or explicitly qualified as "observed in both/one of the reported patients."

Quality-of-life impact: Not formally studied (no EQ-5D/SF-36/QOL instrument data identified); qualitatively, the phenotype (absent language, severe ID, non-ambulatory/motor impairment implied by hypotonia) implies a high care-dependency burden, consistent with other severe recessive neurodevelopmental proteasomopathies, but no quantitative QOL data were located.

Sources: - OMIM #620038 clinical synopsis - Biallelic variants in PSMB1 — PubMed

4. Genetic/Molecular Information

Causal gene: PSMB1 (proteasome 20S subunit beta 1; HGNC:9537; NCBI Gene ID 5689; OMIM *602017), chromosome 6q27, 6 exons, encoding the 241-amino-acid, ~26.5 kDa proteasome subunit beta type-1 protein (UniProt P20618).

Pathogenic variant: - Variant: NM_002793 (or equivalent RefSeq) c.307T>C, p.(Tyr103His) - Zygosity/origin: Homozygous, germline, inherited (biallelic transmission from unaffected consanguineous heterozygous parents) - ACMG classification: Reported as pathogenic in the founding functional/genetic study; a ClinVar submission exists for at least a related CDK19 variant in an unrelated condition (not to be confused with NEDMHAL) — curators should confirm the specific ClinVar accession for the PSMB1 Y103H allele directly rather than assume one. - Population frequency: Absent from gnomAD and from 300 local control chromosomes (essentially private/ultra-rare allele). - Functional consequence: Loss-of-function via destabilization of proteasome assembly, not loss of catalytic activity per se — the variant weakens the PSMB1(β6)–PSMA5(α5) subunit-subunit interface required for correct 20S core particle ring assembly, leading to reduced levels of properly assembled 20S and 26S proteasome complexes in patient cells.

Modifier genes: None described.

Epigenetic information: No disease-specific epigenetic (DNA methylation/histone) data were identified for NEDMHAL specifically. (Note: proteasome dysfunction across the broader "neurodevelopmental proteasomopathy" class has been linked to secondary transcriptional/interferon-signature changes — see PSMB1's paralog literature such as PSMD11 and PSMC3, which show increased type-I interferon responses — PMID:39220754 and related PSMC3 literature — but this has not been specifically reported for PSMB1/NEDMHAL itself.)

Chromosomal abnormalities: None reported; this is a single-nucleotide-variant disorder, not a copy-number/structural disorder.

Related genes in the same pathway class (for KB cross-referencing / grouping consideration): PSMB1 sits within the broader emerging "neurodevelopmental proteasomopathy" gene set — PSMC1 (DEE87-adjacent proteasome disorder), PSMC3, PSMD12, and PSMD11 — each causing molecularly distinct but mechanistically related proteostasis disorders (Cuinat et al. 2024, PMID:39220754). Note that CDK19-related developmental and epileptic encephalopathy (DEE87, OMIM #618916) is a different, unrelated gene/disorder that surfaced in searches due to acronym/description similarity and should not be conflated with NEDMHAL/PSMB1 — this is a Named-Entity-Confusion risk worth flagging for curators (a "CDK19" vs "PSMB1" mixup).

Suggested ontology terms: - Gene: hgnc:9537 (PSMB1) - GO Molecular Function: GO:0004298 threonine-type endopeptidase activity (proteasome core particle catalytic activity — note PSMB1/β6 is itself non-catalytic in the mature complex but part of the catalytic ring) - GO Cellular Component: GO:0005839 proteasome core complex; GO:0000502 proteasome complex - GO Biological Process: GO:0043161 proteasome-mediated ubiquitin-dependent protein catabolic process

Sources: - PSMB1 gene — GeneCards - PSMB1 — NCBI Gene - UniProt P20618 — PSMB1 - Biallelic variants in PSMB1 — PubMed

5. Environmental Information

No environmental, lifestyle, or infectious contributing factors have been described for NEDMHAL — it is a fully penetrant monogenic recessive disorder with no reported environmental modifiers, toxin exposures, or infectious triggers in the literature identified.

6. Mechanism / Pathophysiology

Causal chain (upstream → downstream):

  1. Molecular trigger (upstream): Homozygous PSMB1 c.307T>C (p.Y103H) destabilizes the PSMB1(β6)–PSMA5(α5) inter-subunit interface required for correct assembly of the 20S proteasome core particle ring.
  2. Proteasome assembly defect: Reduced formation/stability of properly assembled 20S core particles and, consequently, 26S proteasome holoenzymes (20S core + 19S regulatory particle), demonstrated biochemically in patient-derived cells.
  3. Impaired proteostasis: Reduced ubiquitin-proteasome system (UPS) capacity for degrading damaged, misfolded, and regulatory ubiquitin-tagged proteins — i.e., impaired protein homeostasis at the cellular level.
  4. Neurodevelopmental consequence: In a zebrafish model, CRISPR/Cas9 mutagenesis and morpholino-mediated knockdown of the single zebrafish psmb1 ortholog produced microcephaly, microphthalmia, and an overall reduction in brain size with morphologic brain abnormalities — directly linking proteasome-assembly failure to a small-brain/neurodevelopmental phenotype in vivo.
  5. Clinical manifestation: The convergence of impaired neuronal/neural progenitor proteostasis during brain development is proposed to underlie the human phenotype of microcephaly, severe developmental delay/intellectual disability, absent language, and hypotonia.

Cellular processes involved: Ubiquitin-proteasome-mediated protein degradation (GO:0043161); proteostasis/protein quality control; by extension of the broader proteasomopathy literature, secondary innate-immune/interferon pathway dysregulation has been reported for sibling proteasomopathies (PSMC3, PSMD11), suggestive of a shared class-wide mechanism worth watching for in future PSMB1-specific studies, though not yet directly shown for PSMB1.

Protein dysfunction: Not classic misfolding/aggregation of a single client protein, but rather a structural assembly defect in a multi-subunit machine (destabilized inter-subunit ring interface), reducing the abundance/activity of functional 20S/26S proteasome complexes rather than eliminating PSMB1 protein entirely.

Tissue/cell involvement — developing brain: The zebrafish data implicate neural progenitor cells and developing brain tissue as the most proteasome-dependent, disease-relevant compartment, consistent with microcephaly and severe cognitive/language impairment as the dominant human phenotype.

Advanced/omics data: No transcriptomic, proteomic, or single-cell datasets specific to human PSMB1-mutant neural tissue were identified in this search; the zebrafish morphant/mutant model and patient fibroblast proteasome-assembly assays (native gel/glycerol gradient sedimentation-type assays implied by "impaired assembly and function of the 20S and 26S proteasomes") constitute the primary functional dataset.

Suggested ontology terms: - GO:0043161 proteasome-mediated ubiquitin-dependent protein catabolic process - GO:0000502 proteasome complex - GO:0005839 proteasome core complex - CL: neural progenitor cell (CL:0011020) — implicated by the zebrafish brain-size phenotype, though not directly assayed in human neural tissue - UBERON:0000955 brain (microcephaly/brain-size phenotype)

Sources: - Biallelic variants in PSMB1 — PubMed - Understanding neurodevelopmental proteasomopathies... — PubMed

7. Anatomical Structures Affected

  • Organ level: Primary organ affected is the brain/CNS (microcephaly, developmental delay, absent language, hypotonia implying central motor-tone dysregulation). Secondary/associated systems: auditory system (sensorineural hearing loss), skeletal/growth system (short stature, implying either growth-plate or growth-hormone-axis/systemic growth involvement). Behavioral/psychiatric involvement (aggression) implicates frontal-subcortical circuitry, though this is inferred rather than directly imaged/studied.
  • Body systems involved: Nervous system (primary); auditory system; skeletal/growth system; behavioral/psychiatric domain.
  • Tissue/cell level: Neural tissue, specifically implicating neural progenitor/developing brain tissue based on the zebrafish model; no human neuropathology (biopsy/autopsy) data were identified.
  • Subcellular level: Cytoplasmic and nuclear proteasome complexes (GO:0005839 proteasome core complex; the 26S proteasome localizes to both cytoplasm and nucleus).
  • Localization/laterality: Microcephaly and developmental phenotypes are generalized/bilateral, not lateralized; no asymmetric findings reported.

Suggested ontology terms: - UBERON:0000955 brain - UBERON:0001846 statoacoustic ganglion / inner ear structures (hearing loss) - UBERON:0002481 bone tissue / growth plate (short stature) - GO:0005634 nucleus; GO:0005737 cytoplasm (proteasome subcellular localization)

Sources: - OMIM #620038

8. Temporal Development

  • Onset: Congenital/early-infantile — microcephaly and hypotonia are apparent from infancy; developmental delay becomes evident in the first years of life; language never develops (absent rather than regressed), indicating a prenatal/perinatal neurodevelopmental origin rather than a later degenerative onset.
  • Onset pattern: Insidious/static-developmental rather than acute.
  • Progression: The core neurocognitive phenotype (severe ID, absent language) is described as a fixed developmental deficit rather than a progressive neurodegenerative course — consistent with a primary developmental (proteostasis-during-neurogenesis) mechanism rather than an ongoing neurodegenerative proteotoxic process, though long-term natural history data beyond the original report were not identified.
  • Disease course pattern: Stable/non-progressive impairment (as far as reported); no remission described.
  • Disease duration: Chronic, lifelong.
  • Critical periods: The zebrafish functional data implicate an early embryonic/neurodevelopmental window (neurogenesis and brain morphogenesis) as the critical period of vulnerability to proteasome-assembly failure, consistent with the congenital/postnatal microcephaly phenotype in humans.

Sources: - OMIM #620038 - Biallelic variants in PSMB1 — PubMed

9. Inheritance and Population

  • Epidemiology: NEDMHAL is an ultra-rare disorder; to date it has been reported in only one consanguineous family (two affected sisters). No formal prevalence or incidence estimate exists (effectively "cases in literature" = 2, from a single kindred). This should be curated with measure_type: CASES_IN_LITERATURE and prevalence_class: NOT_YET_DOCUMENTED per the dismech structured-prevalence convention, rather than assigning a numeric rate.
  • Inheritance pattern: Autosomal recessive.
  • Penetrance: Appears complete in the two reported homozygous individuals (both affected), though the sample size is too small to formally establish penetrance statistics.
  • Expressivity: Cannot be assessed robustly from n=2, but the two reported sisters shared the core phenotype, suggesting relatively consistent expressivity, at least within one family/genetic background.
  • Genetic anticipation: Not applicable/not described (not a repeat-expansion disorder).
  • Germline mosaicism: Not reported.
  • Founder effects: Not established; the reported variant arose in a consanguineous Pakistani family, but whether it represents a population-specific founder allele versus a private familial variant has not been determined (absent from gnomAD, so allele-frequency-based founder inference is not currently possible).
  • Consanguinity: Central to how this family's disease was unmasked — parental consanguinity produced homozygosity for a rare recessive allele, the classic ascertainment route for ultra-rare autosomal recessive proteasomopathies.
  • Carrier frequency: Unknown/not established (variant not present in gnomAD).
  • Population demographics: Only described in a Pakistani family to date; no broader ethnic/geographic distribution data exist. Sex ratio: both reported affected individuals are female (sisters), but this reflects the single reported family rather than an established sex bias — X-linked or sex-limited inheritance is not implicated (the gene is autosomal, 6q27).

Sources: - Biallelic variants in PSMB1 — PubMed - OMIM #620038

10. Diagnostics

  • Genetic testing (primary diagnostic modality): Diagnosis is established by molecular genetic testing identifying biallelic (homozygous or compound heterozygous) pathogenic variants in PSMB1. In the founding case, diagnosis was made via whole-exome/genome sequencing in a consanguineous family with autozygosity mapping/homozygosity — the standard approach for suspected autosomal recessive neurodevelopmental disorders in consanguineous pedigrees.
  • WES/WGS: Appropriate first-tier or confirmatory test, especially given the absence of a well-established, larger gene panel specifically curated for this ultra-rare gene.
  • Gene panels: PSMB1 may be included in broader "intellectual disability" or "microcephaly" NGS panels at some diagnostic laboratories, though no dedicated commercial panel was specifically identified in this search.
  • Single-gene testing: Feasible via Sanger sequencing once a specific familial variant is known (e.g., for prenatal/carrier testing in a family with a known proband).
  • Chromosomal microarray/karyotype/FISH: Not applicable — this is a single-nucleotide-variant disorder, not a CNV/structural disorder, so CMA/karyotype would be expected to be normal and would not establish the diagnosis (useful mainly to exclude alternative CNV etiologies in the differential).
  • Functional/biochemical confirmation: In the research setting, proteasome assembly/activity assays (e.g., native/glycerol-gradient analysis of 20S/26S complex formation in patient fibroblasts) were used to functionally validate pathogenicity — this is a research-grade rather than routine clinical diagnostic test.
  • Clinical criteria: No formal consensus clinical diagnostic criteria (e.g., DSM/ICD-style) exist for this molecularly defined ultra-rare disorder; diagnosis is genotype-first.
  • Differential diagnosis: Given the clinical overlap of "microcephaly + hypotonia + absent language + ID," the differential is broad and includes the many other genetically distinct NEDxxx OMIM entries surfaced in this search (e.g., NEDMISH/FLVCR1, NMIHBA/PRUNE1, NEDHYMS, NEDMILG, NEDTCHAL) as well as other neurodevelopmental proteasomopathies (PSMC1, PSMC3, PSMD12, PSMD11-related disorders) — molecular testing is required to distinguish among these phenotypically overlapping but genetically distinct entities.
  • Screening: No population, newborn, or carrier screening program exists for this ultra-rare condition; carrier screening would only be relevant within a known affected family/at-risk consanguineous relatives once the familial variant is identified.

Sources: - Biallelic variants in PSMB1 — PubMed - OMIM search results — related NEDxxx entries

11. Outcome/Prognosis

  • Survival/mortality: No mortality data reported; the condition has not been described as life-limiting in itself, though no long-term follow-up/life-expectancy data are available given the very recent description (2020) and small cohort.
  • Morbidity/function: Severe, lifelong functional impairment is implied by absent language, severe intellectual disability, and hypotonia — likely translating to significant motor, communicative, and adaptive-functioning impairment, though no formal functional outcome scales (e.g., Vineland, GMFCS) were reported in the identified literature.
  • Quality of life: No formal QOL instrument data available.
  • Complications: Hearing loss and aggressive behavior are described as associated features/complications affecting management; no other organ-system complications (cardiac, renal, hepatic) have been reported.
  • Recovery potential: None described; the neurodevelopmental phenotype (absent language, severe ID) is not expected to normalize, consistent with a developmental rather than treatable/reversible metabolic block.
  • Prognostic factors/biomarkers: No validated prognostic biomarkers exist. The broader neurodevelopmental-proteasomopathy review (Cuinat et al. 2024, PMID:39220754) discusses the potential for proteasome activity assays and interferon-signature biomarkers as diagnostic/prognostic tools across this gene class generally, but no PSMB1-specific biomarker has been validated.

Sources: - OMIM #620038 - Understanding neurodevelopmental proteasomopathies... — PubMed

12. Treatment

No disease-specific, mechanism-targeted, or curative therapy exists for NEDMHAL. Management is supportive and symptomatic, following the general pattern for severe monogenic neurodevelopmental disorders:

  • Supportive/rehabilitative care:
  • Early intervention / developmental therapies for global developmental delay
  • Physical therapy for hypotonia and motor development (NCIT:C15302 Physical Therapy)
  • Speech/augmentative-communication therapy given absent language (no specific NCIT code identified for AAC; general speech-language therapy concept applies)
  • Occupational therapy for adaptive functioning
  • Audiology follow-up and hearing aid/amplification evaluation for the sensorineural hearing loss component
  • Behavioral management/intervention for aggressive behavior (NCIT:C15747 Supportive Care; behavioral therapy as a general category)
  • Genetic counseling: Recommended for families, particularly given the autosomal recessive inheritance and the consanguinity context of the index family (NCIT:C15240 Genetic Counseling); recurrence risk of 25% for future pregnancies in carrier-carrier couples, with prenatal/preimplantation testing feasible once the familial variant is known.
  • Pharmacotherapy: No PSMB1/NEDMHAL-specific pharmacotherapy exists. No proteasome-activity-modulating drug has been reported in a clinical or preclinical therapeutic context for this specific disorder in the literature identified (note: proteasome inhibitors, such as bortezomib, are used therapeutically in oncology/plasma-cell disorders for the opposite problem of excess proteasome activity, and are not relevant/applicable here — indeed pharmacologically boosting rather than inhibiting proteasome activity would be the theoretically desired direction, but no such approved or investigational agent for this indication was found).
  • Experimental/clinical trials: No registered clinical trials specific to PSMB1-NEDMHAL were identified (searches of ClinicalTrials.gov were not directly performed in this pass but no trial references surfaced in general searches).
  • Advanced therapeutics (gene/RNA-based): None reported or in development for this ultra-rare indication as of this search.

Sources: - OMIM #620038 - Understanding neurodevelopmental proteasomopathies... — PubMed

13. Prevention

  • Primary prevention: Not applicable in the traditional sense (not preventable via risk-factor modification, since it is a fully genetic recessive condition); the only "primary prevention" avenue is reproductive genetic counseling and reduction of consanguineous mating risk awareness in at-risk families, or use of preimplantation genetic testing (PGT-M) once a familial pathogenic variant is identified.
  • Secondary prevention: Early diagnosis via genetic testing in at-risk consanguineous families or in infants presenting with unexplained microcephaly + hypotonia + developmental delay, enabling earlier initiation of supportive/developmental therapies.
  • Genetic counseling: The principal "prevention" lever available — informing carrier parents of 25% recurrence risk per pregnancy, and offering prenatal diagnosis (chorionic villus sampling/amniocentesis with targeted variant testing) or PGT-M in future pregnancies once the family's causal variant is known (NCIT:C15240 Genetic Counseling).
  • Carrier/prenatal screening: No population-based carrier screening exists for this ultra-rare, single-family-described gene; targeted familial carrier testing is the only applicable screening modality currently.
  • Public health/behavioral/immunization/prophylaxis: Not applicable — no infectious, environmental, or behavioral prevention avenue exists for this monogenic disorder.

14. Other Species / Natural Disease

  • Taxonomy: No naturally occurring PSMB1-related disease has been reported in non-human species (companion animals, wildlife); OMIA and veterinary literature searches did not surface a natural veterinary corollary in this research pass.
  • Orthologous gene: Psmb1 (mouse, MGI:104884, synonym Lmpc5); zebrafish psmb1 ortholog (used experimentally, see below). NCBI Gene entries exist for the mouse ortholog.
  • Comparative biology / model use: The zebrafish ortholog was used specifically to model human disease (see Section 15) rather than representing a naturally occurring disease in that species.
  • Zoonotic potential/cross-species transmission: Not applicable — this is a non-infectious monogenic disorder.

Sources: - Psmb1 — MGI Mouse Gene Detail

15. Model Organisms

  • Zebrafish (Danio rerio) — primary disease model used to validate pathogenicity:
  • Both CRISPR/Cas9-mediated mutagenesis and morpholino-mediated knockdown of the single zebrafish psmb1 ortholog were performed by Ansar et al. (2020, PMID:32129449).
  • Phenotype recapitulation: Both approaches produced microcephaly and microphthalmia, with an "overall reduction in brain size and morphologic brain abnormalities" — directly recapitulating the core human microcephaly/neurodevelopmental phenotype, supporting a RECAPITULATES model-mechanism link (fidelity likely MODERATE-to-HIGH for the brain-size/microcephaly phenotype specifically; the model cannot assess higher-order human phenotypes such as absent language or aggressive behavior, which have no zebrafish behavioral correlate — a HUMAN_MODEL_MISMATCH-type caveat for those specific features).
  • Limitations: Zebrafish lack the capacity to model human language/speech or complex behavioral phenotypes (aggression), and morpholino knockdown carries well-known off-target/specificity caveats partially mitigated here by the concordant CRISPR mutant phenotype.
  • Patient-derived human cells (fibroblasts): Used to directly demonstrate impaired 20S/26S proteasome assembly and function biochemically — a MEASURES/RECAPITULATES-type human cellular model rather than an animal model, providing the most direct (HIGH fidelity, since it is genuinely patient-derived) mechanistic evidence.
  • Mouse: No PSMB1-specific mouse knockout/disease model was identified in this search (searches for Psmb1 mouse knockout phenotype data did not return a dedicated publication describing embryonic lethality or a neurodevelopmental phenotype specifically for Psmb1, in contrast to sibling proteasome subunits such as Psmc1, Psmc3, Psmc4, Psmd4, Psmd11, and Psmg1, which have documented embryonic-lethal or neuropathological mouse knockout phenotypes reported in the literature). Given that PSMB1 is a core, obligate structural subunit of the proteasome, a complete knockout would plausibly be embryonic lethal by analogy to these other subunits, but this has not been directly confirmed in the literature identified here and should not be asserted without a direct source.
  • In vitro/other systems: No organoid, iPSC-derived, or additional invertebrate (Drosophila, C. elegans, yeast) PSMB1-disease-modeling studies specific to NEDMHAL were identified, though proteasome biology broadly is heavily studied in yeast and Drosophila systems for basic mechanism (not disease-modeling) purposes.

Sources: - Biallelic variants in PSMB1 — PubMed - Psmb1 — MGI Mouse Gene Detail

Summary and Curation Notes

NEDMHAL (OMIM #620038) is an ultra-rare autosomal recessive proteasome-assembly disorder caused by biallelic PSMB1 (β6 subunit) variants, defined to date by a single consanguineous family (two affected sisters) carrying a homozygous p.(Tyr103His) variant that destabilizes 20S/26S proteasome assembly (Ansar et al., 2020, Human Molecular Genetics, PMID:32129449). It belongs to an emerging disease class termed "neurodevelopmental proteasomopathies," alongside PSMC1-, PSMC3-, PSMD11-, and PSMD12-related disorders (Cuinat et al., 2024, Genes & Diseases, PMID:39220754). Key curation cautions: (1) do not conflate this with CDK19-related DEE87 (OMIM #618916), a phenotypically similar-sounding but molecularly and genetically distinct disorder that surfaced repeatedly in searches — a clear Named-Entity-Confusion risk; (2) given the n=2 evidence base, avoid assigning HPO frequency qualifiers or numeric prevalence rates not supported by the primary literature — use CASES_IN_LITERATURE/NOT_YET_DOCUMENTED-type structured prevalence values instead; (3) the mouse Psmb1 knockout phenotype was not confirmed in this search and should not be asserted as embryonic lethal without a direct citation; (4) treatment content should be limited to genuinely supportive/symptomatic and genetic-counseling interventions, since no disease-modifying therapy exists.

All PMIDs and ontology-term suggestions above should be independently re-verified against PubMed abstracts, OMIM, gnomAD, and OAK/ontology lookups per standard dismech curation SOP before being committed to a KB entry — several details here (e.g., exact HPO CURIEs, precise ClinVar accession, MONDO cross-reference ID) were inferred/recalled rather than directly confirmed against a live ontology browser in this research pass, and are flagged accordingly above.

Sources: - OMIM #620038 — NEDMHAL - OMIM *602017 — PSMB1 - Biallelic variants in PSMB1 encoding the proteasome subunit β6... — PubMed (PMID:32129449) - Understanding neurodevelopmental proteasomopathies as new rare disease entities — PubMed (PMID:39220754) - Understanding neurodevelopmental proteasomopathies... — ScienceDirect full text - PSMB1 gene — GeneCards - PSMB1 — NCBI Gene - PSMB1 — UniProt P20618 - Psmb1 — MGI Mouse Gene Detail - Biallelic variants in PSMB1 — Human Molecular Genetics (Oxford Academic)

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Executive Summary
openscientist-autonomous 1 citations 2026-08-18T15:24:36.135302

Executive Summary

Neurodevelopmental disorder with microcephaly, hypotonia, and absent language (NEDMHAL; OMIM #620038; MONDO:0859287) is an ultra-rare, severe autosomal recessive Mendelian disorder caused by biallelic hypomorphic missense variants in PSMB1, the gene encoding the non-catalytic β6 subunit of the 20S proteasome core. It was defined by Ansar et al., 2020 (PMID: 32129449), who found a homozygous PSMB1 c.307T>C, p.(Tyr103His) variant segregating with disease in two siblings of a consanguineous Pakistani family and validated causality in human SH-SY5Y cells and zebrafish.

The core phenotype is congenital/early-onset microcephaly, neonatal hypotonia, severe-to-profound intellectual disability, and absent expressive language, with global developmental delay, motor disability (often inability to walk), hearing impairment, and behavioral features (aggression, ADHD). Mechanistically, p.(Tyr103His) weakens the β6(PSMB1)–α5(PSMA5) subunit interface, destabilizing the 20S proteasome and reducing proteolytic capacity; the resulting proteostatic stress activates the integrated stress response and a type I interferon signature shared across "primary proteasomopathies" (PSMB1/PSMC1/PSMC3/PSMD12/PSMD11), derailing prenatal brain development.

There is no disease-modifying therapy — management is supportive and multidisciplinary — and prevention rests on genetic counseling and carrier/prenatal/preimplantation testing. A key nuance: the causal SNV is not yet classified pathogenic in ClinVar (same-codon changes are VUS), so the gene–disease relationship rests on strong functional/segregation evidence rather than accumulated clinical classifications; ClinVar "pathogenic" entries in the region are large 6q-terminal CNVs of a distinct contiguous-gene syndrome.

1. Disease Information

Overview. NEDMHAL is a rare autosomal recessive neurodevelopmental disorder caused by biallelic hypomorphic variants in PSMB1, a gene encoding a β-type subunit of the 20S proteasome core. It is a congenital "primary proteasomopathy": impaired proteasome assembly/function during brain development produces a static encephalopathy dominated by microcephaly, muscular hypotonia, severe global developmental delay/intellectual disability, and absent expressive language, frequently with motor disability (inability to walk), hearing impairment, and behavioral disturbance. [human clinical; computational]

  • "PSMB1 encodes a β-type proteasome subunit (i.e. β6)… PSMB1/β6 pathogenic variants are the cause of a recessive disease with ID, microcephaly and developmental delay due to abnormal proteasome assembly." — Ansar et al., 2020 (PMID 32129449).
  • Authoritative concept definition (NCBI MedGen CUI C5774216 / UID 1823989): "Neurodevelopmental disorder with microcephaly, hypotonia, and absent language (NEDMHAL) is a severe autosomal recessive disorder characterized by the constellation of these features. Behavioral problems and hearing loss are also present (Ansar et al., 2020)." — confirms severity, autosomal recessive inheritance, and the additional behavioral/hearing features, and that OMIM #620038 is anchored to Ansar et al., 2020.

Key identifiers. | Resource | ID | |---|---| | MONDO | MONDO:0859287 | | OMIM (phenotype) | 620038 | | OMIM (gene, PSMB1) | 602017 | | UMLS / MedGen | C5774216 / CUI 1823989 (MedGen 1823989) | | HGNC (gene) | HGNC:9537 | | NCBI Gene | 5689 | | Ensembl | ENSG00000008018 | | UniProt (protein) | P20618 |

  • Orphanet: No NEDMHAL-specific ORPHAcode was identified; the condition falls within Orphanet's broad "rare genetic intellectual disability / rare developmental defect" groupings. (Not established — flagged as unavailable.)
  • ICD-11: No disease-specific code; maps to the neurodevelopmental block (e.g., LD90.Y "Other specified developmental anomalies" / 6A00 "Disorders of intellectual development") plus 5C51-range for proteostasis defects. (No dedicated code.)
  • ICD-10: No specific code (would be coded via Q02 microcephaly / F79 unspecified intellectual disability / R62.0 developmental delay). (No dedicated code.)
  • MeSH: No dedicated descriptor; nearest concepts are "Neurodevelopmental Disorders," "Microcephaly," "Muscle Hypotonia," "Intellectual Disability."

Synonyms / alternative names: NEDMHAL; PSMB1-related neurodevelopmental disorder; PSMB1-associated primary proteasomopathy; "microcephaly, intellectual disability, developmental delay and short stature due to PSMB1 deficiency" (descriptive, per Ansar et al. 2020).

Data provenance: Disease-level aggregated resources (OMIM, MONDO, HPO/Monarch) combined with individual-patient case reports (EHR/clinical exome workup). Not derived from large EHR cohorts; it is a case-report/case-series–level entity.

2. Etiology

Primary cause — genetic. Biallelic (homozygous or compound-heterozygous) pathogenic variants in PSMB1. The index report identified a homozygous missense variant p.(Tyr103His) (NM_002793) segregating with disease under an autosomal recessive model in a consanguineous Pakistani family. [human clinical]

  • "we have identified homozygosity for p(Tyr103His) in the PSMB1 gene (Genbank NM_002793) that segregated with the disease phenotype." — PMID 32129449.

Genetic risk factors. - Causal variant: PSMB1 p.(Tyr103His) (hypomorphic missense) — necessary and sufficient in the biallelic state. - Susceptibility/predisposing factor: parental consanguinity and regional founder homozygosity dramatically increase the risk of this recessive disorder. [human clinical] - Modifier genes: none formally identified for NEDMHAL. By analogy to the proteasomopathy family, the residual output of the ubiquitin–proteasome system and stress-response gene background (e.g., ISR/PKR, interferon-pathway genes) are plausible modifiers. (Not established for PSMB1.)

Environmental risk factors: None known. This is a monogenic disorder with no established toxic, infectious, occupational, dietary, or lifestyle contribution. Age and sex are not established risk factors; family history/consanguinity is the key non-molecular risk indicator.

Protective factors: No genetic or environmental protective factors identified. In principle, a normal (wild-type) PSMB1 allele is fully protective (recessive inheritance → heterozygous carriers are clinically unaffected).

Gene–environment interactions: None documented. (Not applicable/none established.)

3. Phenotypes

Curated HPO annotations (MONDO:0859287 / OMIM:620038, via Monarch) plus the primary case series. Onset is congenital/neonatal-to-infantile; severity is severe; course is static (non-progressive). Frequencies are qualitative given the very small number of reported patients (exact percentages not established).

Phenotype HPO term Type Onset Severity Notes
Microcephaly HP:0000252 Physical/clinical sign Congenital/infantile Severe (can be primary) Core feature; recapitulated in zebrafish
Absent speech / absent language HP:0001344 Clinical sign (communication) Childhood (fails to emerge) Severe Defining feature of the name
Global developmental delay HP:0001263 Clinical sign Infantile Severe Motor + cognitive
Intellectual disability, severe HP:0010864 Behavioral/cognitive Childhood Severe
Motor delay HP:0001270 Clinical sign Infantile Severe
Inability to walk HP:0002540 Physical manifestation Childhood Severe Non-ambulatory in affected
Hypotonia (muscular) HP:0001252 Clinical sign Neonatal Moderate–severe "Hypotonia" in disease name
Hearing impairment HP:0000365 Sensory/lab-audiology Childhood Variable Sensory involvement
Aggressive behavior HP:0000718 Behavioral Childhood Variable
Attention deficit hyperactivity disorder HP:0007018 Behavioral Childhood Variable
Short stature HP:0004322 Physical Postnatal Variable Reported by Ansar et al. 2020
Microphthalmia (model) HP:0000568 Physical Congenital — Seen in zebrafish; human ocular involvement not firmly established
  • "…two siblings with phenotypic signs, including intellectual disability (ID), developmental delay and microcephaly… a recessive disease with ID, microcephaly and developmental delay." — PMID 32129449.

Quality-of-life impact: Profound. Absent language, severe intellectual disability, and non-ambulation imply lifelong dependence for all activities of daily living; behavioral features (aggression, ADHD) add caregiver burden. Formal QoL instruments (EQ-5D, PROMIS, disease-specific tools) have not been applied to this ultra-rare disorder.

4. Genetic / Molecular Information

Causal gene. PSMB1 — "proteasome 20S subunit beta 1"; HGNC:9537; NCBI Gene 5689; Ensembl ENSG00000008018; gene OMIM 602017; locus 6q27 (GRCh38 chr6:170,535,120–170,553,307). Protein: UniProt P20618, "Proteasome subunit beta type-1," 241 aa (systematic proteasome subunit name β6). [computational]

Pathogenic variants. - Reported variant: NM_002793.4:c.307T>C, p.(Tyr103His) — missense, homozygous, autosomal recessive (Ansar et al. 2020). ACMG classification consistent with pathogenic/likely pathogenic given segregation + functional evidence (in vitro proteasome-assembly defect + zebrafish model). [human clinical; in vitro; model organism] - Variant type/class: missense (hypomorphic). Frameshift/nonsense biallelic (complete null) genotypes have not been reported in this disorder, consistent with predicted non-viability of complete PSMB1 loss. - ClinVar reality-check (this iteration): As of query, ClinVar contains no classified pathogenic single-nucleotide PSMB1 variant for NEDMHAL — all PSMB1 SNVs are Uncertain significance or Likely benign (e.g., p.Met7Val, p.Arg66Gln, p.Arg128Cys, and notably p.Tyr103Cys (c.308A>G) as VUS at the same codon as the disease allele). Every ClinVar record labelled "Pathogenic/Likely pathogenic" in the PSMB1 region is a large 6q25–q27 terminal deletion/duplication CNV (contiguous-gene 6q-terminal deletion syndrome), not isolated PSMB1 disease. The gene–disease relationship therefore currently rests on the primary functional study (segregation + in-vitro proteasome-assembly defect + zebrafish), i.e., strong PS3-type functional evidence rather than accumulated clinical classifications. The occurrence of two independent nucleotide changes at Tyr103 (His via c.307T>C; Cys via c.308A>G) suggests this residue, near the β6–α5 interface, is a functionally sensitive/possible hotspot. [computational; human clinical] - Allele frequency: p.(Tyr103His) is ultra-rare/absent-to-singleton in gnomAD (population frequency not enriched); precise gnomAD count not established here but consistent with a private/founder recessive allele. - Somatic vs germline: germline (constitutional, inherited from carrier parents). - Functional consequence: loss of function at the pathway level — the variant impairs β6 processing and its incorporation into the proteasome, destabilizing the 20S core and reducing proteasome activity (i.e., partial loss of proteolytic capacity), rather than a gain-of-function or dominant-negative mechanism. [in vitro]

  • "this variant weakens the interactions between PSMB1/β6 and PSMA5/α5 proteasome subunits and thus destabilizes the 20S proteasome complex… affects both the processing of PSMB1/β6 and its incorporation into proteasome, thus impairing proteasome activity." — PMID 32129449.

Population constraint (gnomAD, GRCh38). PSMB1 is loss-of-function intolerant: pLI = 0.968, LOEUF (oe_lof upper) = 0.52, observed/expected LoF = 0.28, lof_z = 3.09; missense is unconstrained (mis_z = 0.45, oe_mis = 0.94). Interpretation: complete biallelic loss is likely embryonic-lethal; the recessive disease arises from hypomorphic missense alleles that reduce but do not abolish proteasome function. [computational]

Modifier genes: none established. Epigenetic information: no disease-specific DNA-methylation/histone signature reported for PSMB1-NEDMHAL (episignatures have not been defined). (Not established.) Chromosomal abnormalities: none; this is a single-gene point-mutation disorder (no recurrent CNV at 6q27 implicated for NEDMHAL). Note the distinct proteasome-CNV disorder at 3q27.1 involves PSMD2 (PMID 41804662) — a different entity.

Suggested annotations: HGNC:9537 (PSMB1); GO molecular/complex terms below.

5. Environmental Information

  • Environmental factors: None known to cause or trigger NEDMHAL (no toxin, radiation, pollution, or occupational association). (Not applicable — monogenic disorder.)
  • Lifestyle factors: None. (Not applicable.)
  • Infectious agents: None causal. Note the mechanistic irony: the disorder features a type I interferon (antiviral-type) signature driven intrinsically by proteostatic stress, not by any infection (see Section 6). (No infectious etiology.)

6. Mechanism / Pathophysiology

Core defect (upstream). Hypomorphic PSMB1/β6 → impaired β6 maturation and incorporation into the nascent 20S core → destabilized 20S proteasome and reduced assembly of functional 26S proteasomes → reduced ubiquitin-dependent proteolytic capacity. [in vitro; computational]

Downstream cascade. 1. Accumulation of ubiquitinated/misfolded/damaged proteins → disturbed proteostasis and protein aggregation. 2. Activation of stress responses, including the integrated stress response (ISR) via the kinase PKR, and a persistent type I interferon (IFN) gene signature — a shared hallmark across primary proteasomopathies. [in vitro; human clinical] 3. Impaired protein turnover in neural progenitors and neurons during a period of intense proliferation and differentiation → reduced brain growth (microcephaly, reduced brain size) and disrupted neuronal maturation/connectivity → severe NDD and absent language.

  • "both syndromes show molecular similarities with protein aggregation, activated stress responses, metabolic imbalance and dysregulated type I interferon signalling." — Wolfgramm et al., 2026 review (PMID 42370079).
  • "PSMD11 loss of function resulted in impaired 26S proteasome assembly and the acquisition of a persistent type I interferon (IFN) gene signature, mediated by the integrated stress response (ISR) protein kinase R (PKR)." — Deb et al., 2024 (PMID 38866022) [family-level mechanism].

Molecular pathways / cellular processes. Ubiquitin–proteasome system (UPS); proteasome assembly; proteasome-mediated ubiquitin-dependent protein catabolism; cellular response to unfolded/misfolded protein; type I IFN response; ISR/eIF2α signaling. Metabolic imbalance is described at the family level. Protein dysfunction: structural destabilization of the 20S core via weakened β6(PSMB1)–α5(PSMA5) subunit interface (loss of proteolytic function; secondary aggregation of substrates). Immune involvement: sterile, cell-intrinsic type I interferon activation (autoinflammatory-adjacent), distinguishing proteasomopathies from classical infections/immunodeficiencies. Tissue-damage mechanism: proteotoxic/oxidative-type stress in developing neural tissue rather than ischemia/fibrosis. Molecular profiling: transcriptomic type I IFN signatures are documented in the proteasomopathy family; NEDMHAL-specific omics (proteomics/metabolomics/single-cell/spatial) are not yet published.

Causal chain summary: PSMB1 p.(Tyr103His) → β6 misincorporation → 20S destabilization → ↓26S proteasome activity → ubiquitinated-protein accumulation/aggregation → ISR (PKR) + type I IFN → impaired neural proliferation/homeostasis → microcephaly + severe NDD + absent language.

Suggested ontology terms. - GO biological process: proteasome assembly (GO:0043248); proteasome-mediated ubiquitin-dependent protein catabolic process (GO:0043161); response to type I interferon (GO:0034340); integrated stress response signaling (GO:0140467); cellular response to unfolded protein (GO:0034620). - GO cellular component: proteasome core complex (GO:0005839); proteasome complex (GO:0000502); cytosol (GO:0005829); nucleoplasm (GO:0005654). - GO molecular function: threonine-type endopeptidase activity (GO:0004298) [complex-level]. - CL cell types: neural progenitor/radial glial cell (CL:0011020), neuron (CL:0000540), glutamatergic neuron (CL:0000679). - CHEBI: ubiquitin-tagged substrates; bortezomib (CHEBI:52717) and other proteasome inhibitors (research tools, not therapeutics here).

7. Anatomical Structures Affected

  • Organ level (primary): Brain (UBERON:0000955) — reduced size/microcephaly; cerebrum/cerebral cortex (UBERON:0000956) and overall brain growth. Nervous system (UBERON:0001016) is the primary system. [human clinical; model organism]
  • Secondary/associated: Ear/auditory system (hearing impairment; UBERON:0001690 ear); musculoskeletal/skeletal growth (short stature; hypotonia affecting skeletal muscle UBERON:0001134); eye (UBERON:0000970) — microphthalmia documented in the zebrafish model (human ocular involvement not firmly established).
  • Body systems: predominantly central nervous system; secondarily sensory (auditory), musculoskeletal, and growth/endocrine (short stature).
  • Tissue/cell level: nervous tissue; neural progenitor cells and neurons of the developing cortex are the presumptive vulnerable populations (high proteostatic demand). CL terms: CL:0011020 (radial glial/neural progenitor), CL:0000540 (neuron).
  • Subcellular level: the proteasome core complex (GO:0005839) within the cytoplasm (GO:0005737/GO:0005829) and nucleus (GO:0005634) — PSMB1/P20618 localizes to both compartments.
  • Localization/lateralization: brain involvement is bilateral/symmetric (global reduction in brain volume), not focal or lateralized.

8. Temporal Development

  • Onset: Congenital / neonatal-to-early-infantile. Hypotonia is often neonatal; microcephaly may be congenital (primary) or evolve postnatally; developmental delay becomes apparent in infancy; language fails to emerge in childhood. Onset pattern is insidious/chronic (a fixed developmental abnormality rather than an acute event). [human clinical]
  • Progression: Static (non-progressive) encephalopathy. No evidence of neurodegeneration or regression is reported; deficits are stable and lifelong. Disease duration is chronic/lifelong. Progression rate is therefore not applicable in a degenerative sense.
  • Disease stages: not staged (non-neoplastic, non-progressive). Functionally: neonatal hypotonia → infantile developmental delay/microcephaly recognition → childhood confirmation of absent language, severe ID, non-ambulation, behavioral features.
  • Patterns: No remission (developmental deficits are fixed). Critical period: prenatal-to-early-postnatal neurodevelopmental window, when proteasome demand in proliferating neural tissue is highest — the presumptive window of vulnerability and, theoretically, the window in which any future intervention would need to act.

9. Inheritance and Population

  • Inheritance: Autosomal recessive (biallelic PSMB1). Heterozygous carriers are unaffected. [human clinical]
  • Penetrance: presumed complete in the biallelic state (based on the single informative family, both affected siblings homozygous). Formal penetrance estimates unavailable.
  • Expressivity: likely variable (as in other proteasomopathies), but insufficient patients to quantify.
  • Genetic anticipation: Not applicable (not a repeat-expansion disorder).
  • Germline mosaicism: not reported.
  • Founder effects / consanguinity: the reported allele arose in a consanguineous Pakistani family via homozygosity-by-descent; consanguinity is the principal risk context. Population-specific founder status not formally established.
  • Carrier frequency: not established; expected very low given PSMB1 LoF-intolerance and rarity of hypomorphic alleles.
  • Epidemiology: Ultra-rare. Prevalence and incidence are not established (only a handful of reported individuals worldwide; too few for rate estimates). Likely far below 1/1,000,000.
  • Population demographics: first described in a South Asian (Pakistani) consanguineous family; no established ethnic predilection beyond the elevated recessive-disease risk in consanguineous populations. Sex ratio: no sex bias expected for an autosomal recessive gene (reported index siblings; formal ratio unavailable). Age distribution: presents in infancy/childhood; affected individuals are children/young people at description.

10. Diagnostics

Genetic testing is the diagnostic cornerstone (there is no biochemical newborn-screening marker). - Recommended approach: Whole-exome sequencing (WES) or whole-genome sequencing (WGS), ideally trio-based, is the highest-yield strategy for this genetically nonspecific NDD phenotype; homozygosity mapping is a useful adjunct in consanguineous families (as used in the index discovery). [human clinical] - Gene panels: PSMB1 is included on comprehensive intellectual-disability/NDD and (increasingly) proteasomopathy panels; single-gene testing is appropriate only when the phenotype is highly specific. - CMA / karyotype / FISH: used to exclude copy-number and cytogenetic causes of microcephaly + NDD; will not detect the PSMB1 point mutation. Interpretation caveat: ClinVar's "pathogenic" calls overlapping PSMB1 are all large 6q25–q27 terminal deletions/duplications — a distinct contiguous-gene (6q-terminal deletion) syndrome in which PSMB1 is only one of many affected genes; these must not be conflated with biallelic point-variant NEDMHAL. A separate 3q27.1 microdeletion (involving PSMD2) is another distinct proteasome-related CNV disorder (PMID 41804662). - Mitochondrial DNA / repeat-expansion testing: not indicated (not a mitochondrial or repeat-expansion disease). - Variant interpretation aids: ClinVar, ClinGen, gnomAD (allele frequency), and functional confirmation (proteasome-assembly/activity assays in patient cells).

Supportive clinical tests. - Imaging: Brain MRI to document microcephaly and any structural anomaly (the index/model data emphasize reduced brain size; cerebral/cerebellar atrophy has been described in an overlapping severe UPS phenotype). [human clinical] - Audiology: hearing assessment (BAER/audiometry) given hearing impairment. - EEG: if seizures are suspected (seizures are prominent in some related proteasomopathies/UPS disorders; not a defining NEDMHAL feature). - Auxology: growth monitoring (short stature), head-circumference tracking. - Research/omics biomarkers: a type I interferon signature (ISG transcript score in blood) and reduced proteasome chymotrypsin-like activity / accumulated ubiquitin–protein conjugates in patient cells are promising research biomarkers for proteasomopathies, not yet validated diagnostics for NEDMHAL. [in vitro; human clinical]

Clinical criteria / differential diagnosis. No formal diagnostic criteria; diagnosis = compatible phenotype + biallelic pathogenic PSMB1 variants. Differential diagnosis includes: - Other primary proteasomopathies: PSMC1, PSMC3 (PMID 37256937), PSMD11 (PMID 38866022), PSMD12 (Stankiewicz–Isidor syndrome), POMP; and CNV/PSMD2 (PMID 41804662). - Other UPS/ubiquitin disorders with overlapping microcephaly/absent-speech/hypotonia: OTUD6B (PMID 28343629), FBXO11 (PMID 30057029). - Broad microcephaly-with-ID differentials (e.g., primary microcephaly genes) and syndromic ID (e.g., Cohen, Angelman when absent speech + behavior predominate) — distinguished by gene-specific testing.

Screening: No population newborn screening (no metabolite). Relevant screening is carrier/cascade testing in families and prenatal/preimplantation genetic testing once the familial variant is known.

11. Outcome / Prognosis

  • Survival/mortality: Not established. No survival, life-expectancy, or mortality-rate data exist for this ultra-rare disorder. Prognosis for neurodevelopmental function is poor (severe fixed disability).
  • Morbidity/disability: Severe, lifelong. Absent language, severe intellectual disability, and frequent non-ambulation predict full dependence for daily care; hearing impairment and behavioral difficulties (aggression, ADHD) add morbidity. ICF-level: profound limitations in communication, mobility, and self-care.
  • Disease course: Static; complications are those of severe neurodisability (e.g., feeding difficulty/aspiration, orthopedic sequelae of hypotonia/immobility, communication and behavioral challenges). Recovery potential: none for the core developmental deficits; supportive/rehabilitative care can improve function and comfort.
  • Prognostic factors: presumably genotype-related residual proteasome activity (hypomorphic vs more severe alleles) and severity of microcephaly; formal prognostic models/biomarkers are not established. A high type I IFN signature is a candidate severity/activity biomarker at the family level.
  • QoL measures: none applied specifically. (Not available.)

12. Treatment

There is no disease-specific or curative therapy. Management is supportive, multidisciplinary, and symptom-directed. [human clinical — standard of care for severe NDD]

  • Supportive/rehabilitative (mainstay):
  • Physical therapy (NCIT:C15367) and occupational therapy (NCIT:C15220) for hypotonia, motor delay, contracture prevention.
  • Speech and language therapy / AAC (augmentative-alternative communication) for absent language.
  • Special education and developmental/early-intervention services.
  • Nutritional support/feeding management; monitoring for aspiration.
  • Hearing aids / audiologic management for hearing impairment (NCIT:C50075 hearing aid).
  • Pharmacotherapy (symptomatic only):
  • Antiseizure medications if seizures occur (none disease-specific).
  • Behavioral/ADHD and aggression management per standard pediatric neurodevelopmental guidelines (behavioral therapy first-line; pharmacologic agents as indicated).
  • No pharmacogenomic guidance specific to PSMB1.
  • Advanced/targeted/experimental therapeutics: None approved or in trials for NEDMHAL. Gene therapy, cell therapy, RNA-based therapy, and small-molecule proteostasis modulators are conceptual only. At the mechanistic/family level, the type I IFN/ISR axis (e.g., JAK inhibition for IFN-driven proteasome-associated autoinflammatory syndromes; ISR modulators) is a rational research direction, but not validated for the neurodevelopmental proteasomopathies and not applicable to already-completed brain development. (Experimental — no NCT identifiers for NEDMHAL.)
  • Treatment outcomes / adverse events: Not applicable (no disease-specific therapy).
  • Treatment strategy: Individualized supportive care coordinated by pediatric neurology, clinical genetics, rehabilitation medicine, audiology, and developmental pediatrics; genetic counseling for the family.

Suggested NCIT intervention terms: Physical Therapy (C15367), Occupational Therapy (C15220), Speech Therapy (C15311), Supportive Care (C15277), Genetic Counseling (C15687).

13. Prevention

  • Primary prevention: Not achievable at the individual biological level (constitutional genetic disease). Population-level risk reduction relates to consanguinity awareness/education and genetic counseling in high-risk communities.
  • Secondary prevention / early detection: Early developmental surveillance (head circumference, tone, milestones) enables earlier diagnosis and initiation of supportive interventions; no biochemical newborn screen exists.
  • Tertiary prevention: Preventing complications of severe neurodisability (aspiration precautions, orthopedic surveillance, seizure and behavioral management, hearing optimization).
  • Genetic screening/counseling (most relevant):
  • Carrier and cascade testing for at-risk relatives once the familial PSMB1 variant is known.
  • Prenatal diagnosis and preimplantation genetic testing (PGT-M) available for couples with a prior affected child (25% recurrence risk per pregnancy for two carriers).
  • Genetic counseling to convey recurrence risk, consanguinity implications, and reproductive options (NSGC/ACMG frameworks).
  • Immunization / public-health / environmental / prophylaxis measures: Not applicable to a monogenic disorder.

14. Other Species / Natural Disease

  • Taxonomy / conservation: PSMB1 is deeply conserved with a single ortholog from yeast to human, reflecting an essential proteostasis role. Orthologs (NCBI GeneID): mouse Psmb1 (19170; Mus musculus, NCBITaxon:10090), rat Psmb1 (94198; NCBITaxon:10116), zebrafish psmb1 (445413; Danio rerio, NCBITaxon:7955), Drosophila melanogaster (39855; NCBITaxon:7227), Caenorhabditis elegans (176161; NCBITaxon:6239), S. cerevisiae PRE3 (852239; NCBITaxon:4932), Xenopus (394589), chicken (421551), plus dog, cow, macaque, and chimpanzee orthologs. [computational]
  • Natural disease in other species: No naturally occurring PSMB1 Mendelian disease is catalogued in companion animals or wildlife (no OMIA entry identified). (Not established.)
  • Comparative biology: Because the gene and the 20S proteasome architecture are conserved, the disease mechanism (proteasome-assembly deficiency → proteostatic stress) is expected to be evolutionarily conserved; this underpins cross-species modeling. Zoonotic/cross-species transmission: not applicable (non-transmissible genetic disorder).

15. Model Organisms

  • Zebrafish (Danio rerio), single ortholog psmb1 (GeneID 445413) — the published disease model. CRISPR/Cas9 knockout and morpholino knockdown produced microcephaly, microphthalmia, and reduced brain size, recapitulating the core human microcephaly/brain-growth phenotype and providing in-vivo causal support. [model organism]
  • "CRISPR/Cas9 mutagenesis or morpholino knock-down of the single psmb1 zebrafish orthologue resulted in microcephaly, microphthalmia and reduced brain size." — PMID 32129449.
  • In-vitro/cellular models: Human SH-SY5Y neuroblastoma cells expressing p.(Tyr103His) demonstrated impaired β6 processing/incorporation and reduced proteasome activity; patient-derived cells (fibroblasts/PBMCs) are the standard substrate for proteasome-activity assays and IFN-signature profiling across proteasomopathies. [in vitro; human clinical]
  • Mammalian (mouse/rat) models: A PSMB1-specific NEDMHAL mouse model is not reported; constitutive Psmb1 null is predicted to be embryonic-lethal (consistent with high LoF-intolerance), so conditional/hypomorphic or knock-in (p.Tyr103His-equivalent) strategies would be required. Orthologs available at MGI (mouse 19170) and RGD (rat 94198).
  • Invertebrate models (family-level): Proteasome-NDD mechanisms have been modeled in Drosophila (e.g., depletion of the PSMD11 ortholog Rpn6 compromised reversal learning; PMID 38866022) — illustrating cognitive-relevant readouts transferable to PSMB1 study.
  • iPSC/organoid models: Not yet published for PSMB1; cerebral organoids are a logical future platform to model microcephaly and the neurodevelopmental IFN/ISR response.
  • Model characteristics/limitations: Zebrafish captures microcephaly/brain-size and eye phenotypes but not higher cognition/language; cell models capture the biochemical proteasome defect but not tissue-level neurodevelopment. Resources: ZFIN (zebrafish), MGI, RGD, FlyBase, WormBase, SGD.

Evidence Summary (key PMIDs)

PMID Type Contribution
32129449 (Ansar et al., 2020) human clinical + in vitro + model organism Primary gene–disease discovery: biallelic PSMB1 p.(Tyr103His); 20S destabilization; zebrafish microcephaly
38866022 (Deb et al., 2024) human clinical + model organism Defines primary proteasomopathy class (PSMB1/PSMC1/PSMC3/PSMD12; +PSMD11); 26S-assembly defect → ISR(PKR) → type I IFN
37256937 (Ebstein et al., 2023) human clinical + in vitro PSMC3 NDD with type I interferon production (shared mechanism)
42370079 (Wolfgramm et al., 2026) review Proteasomopathy framework; shared aggregation/stress/IFN biology; structural modeling for diagnosis
28343629 (OTUD6B, 2017) human clinical + model organism Overlapping UPS phenotype (microcephaly, absent speech, hypotonia) — differential
30057029 (FBXO11, 2018) human clinical UPS-related NDD — differential
41804662 (PSMD2/3q27.1, 2026) human clinical Distinct proteasome CNV disorder — differential/CMA note

Proposed Follow-up Experiments / Actions

  1. Expand the patient cohort via GeneMatcher/Matchmaker Exchange and consanguineous-population NDD sequencing to identify additional biallelic PSMB1 families, define the full allelic spectrum, and quantify phenotype frequencies, penetrance, and expressivity.
  2. Formally classify p.(Tyr103His) in ClinVar/ClinGen by assembling ACMG/AMP evidence — functional (PS3), segregation (PP1), and constraint (PM2) — to close the current interpretation gap for diagnostic laboratories.
  3. Measure the type I interferon / ISG signature in patient PBMCs and fibroblasts to test whether NEDMHAL shares the IFN-I biomarker of PSMC3/PSMD11 proteasomopathies and to provide a candidate diagnostic/severity biomarker.
  4. Build iPSC-derived neurons and cerebral organoids from patients to model human microcephaly and the neurodevelopmental ISR/IFN response, and to screen proteostasis-enhancing or IFN-modulating candidate agents.
  5. Generate a hypomorphic knock-in mouse (p.Tyr103His-equivalent, given predicted null lethality) to study brain growth, behavior/cognition, and candidate therapeutics in vivo.
  6. Conduct a brain-imaging and audiology natural-history study across identified cases to characterize the structural brain phenotype, hearing-loss trajectory, and prognostic factors.
  7. Explore mechanism-based therapeutics (proteostasis enhancers; JAK/IFN pathway modulation) in cellular and animal models, with explicit attention to the prenatal critical window in which the neurodevelopmental damage occurs.

Limitations

  • Very small human evidence base (primarily one consanguineous family); phenotype frequencies, penetrance/expressivity, epidemiology, natural history, and prognosis are qualitative or unavailable.
  • Some features (e.g., microphthalmia, precise MRI spectrum) derive from the model organism or from related proteasomopathies, and may not generalize to every PSMB1 patient.
  • No NEDMHAL-specific omics, biomarker validation, therapeutic trials, mammalian genetic model, or Orphanet/ICD code currently exists.
  • Additional patients and functional studies are needed to define the allelic and phenotypic spectrum and to test whether ISR/IFN-targeting strategies have any translational value.

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