MBD5 haploinsufficiency syndrome, historically 2q23.1 microdeletion syndrome, is a neurodevelopmental disorder caused by loss of one functional copy of MBD5, which encodes a methyl-CpG-binding domain protein. It was defined the way few syndromes are: a consortium assembled 65 subjects with 2q23.1 microdeletions or translocations, aligned the deletion breakpoints to narrow the critical region, and found MBD5 as the only gene the region contained. Patients whose alteration disrupts MBD5 alone are largely indistinguishable, clinically and transcriptionally, from those missing the whole 2q23.1 interval, which is what makes this a single-gene disorder rather than a contiguous gene syndrome. The hedge in "largely" is deliberate and matters: the same series that mapped the critical region also reported that patients whose deletion additionally removed EPC2 had a broader phenotype. MBD5 is the critical locus; larger deletions can add features on top. The clinical picture is intellectual disability with disproportionate speech impairment, seizures, autistic features, a characteristic disturbed sleep pattern, stereotypies, and coarse facial features - a combination that led to initial clinical impressions of Angelman, Rett or Smith-Magenis syndrome in several patients before the deletion was found. MBD5 is dosage-sensitive in both directions: reciprocal 2q23.1 duplication produces a related, somewhat milder syndrome, so this entry describes the deletion side of a dosage disorder rather than a simple loss-of-function disease.
Ask a research question about MBD5 Haploinsufficiency Syndrome. OpenScientist will conduct autonomous deep research using the Disorder Mechanisms Knowledge Base and PubMed literature (typically 10-30 minutes).
Do not include personal health information in your question. Questions and results are cached in your browser's local storage.
name: MBD5 Haploinsufficiency Syndrome
creation_date: "2026-08-27T23:55:00Z"
category: Mendelian
description: >-
MBD5 haploinsufficiency syndrome, historically 2q23.1 microdeletion syndrome,
is a neurodevelopmental disorder caused by loss of one functional copy of
MBD5, which encodes a methyl-CpG-binding domain protein. It was defined the
way few syndromes are: a consortium assembled 65 subjects with 2q23.1
microdeletions or translocations, aligned the deletion breakpoints to narrow
the critical region, and found MBD5 as the only gene the region contained.
Patients whose alteration disrupts MBD5 alone are largely indistinguishable,
clinically and transcriptionally, from those missing the whole 2q23.1
interval, which is what makes this a single-gene disorder rather than a
contiguous gene syndrome. The hedge in "largely" is deliberate and matters:
the same series that mapped the critical region also reported that patients
whose deletion additionally removed EPC2 had a broader phenotype. MBD5 is the
critical locus; larger deletions can add features on top. The clinical picture is intellectual disability with
disproportionate speech impairment, seizures, autistic features, a
characteristic disturbed sleep pattern, stereotypies, and coarse facial
features - a combination that led to initial clinical impressions of Angelman,
Rett or Smith-Magenis syndrome in several patients before the deletion was
found. MBD5 is dosage-sensitive in both directions: reciprocal 2q23.1
duplication produces a related, somewhat milder syndrome, so this entry
describes the deletion side of a dosage disorder rather than a simple
loss-of-function disease.
parents:
- Neurodevelopmental Disorder
- Chromatin Disorder
synonyms:
- 2q23.1 microdeletion syndrome
- MRD1
- intellectual disability, autosomal dominant 1
- MBD5-associated neurodevelopmental disorder
- MAND
disease_term:
preferred_term: intellectual disability, autosomal dominant 1
term:
id: MONDO:0007974
label: intellectual disability, autosomal dominant 1
references:
- reference: PMID:27786435
title: "MBD5 Haploinsufficiency."
tags:
- GeneReviews
notes: >-
On the entry name and the MONDO label. MONDO:0007974 and its OMIM source label
this concept "intellectual disability, autosomal dominant 1", and OMIM's
phenotypic series places it among the non-syndromic intellectual disabilities.
That label misdescribes the disease. Every clinical series of 2q23.1 deletion
reports short stature, microcephaly, seizures, a distinctive disturbed sleep
pattern, stereotypic repetitive behaviour and coarse facies alongside the
intellectual disability - the phenotype is recognisably syndromic, and was
mistaken for Angelman, Rett and Smith-Magenis syndrome precisely because it
has a syndromic gestalt. The entry is therefore named for the gene and
mechanism rather than adopting the ontology label as its name, while
disease_term remains bound to MONDO:0007974 so the mapping is not lost. This
is a case where the best available ontology term carries a clinically
misleading label; the binding is correct and the label is not, and the entry
records the discrepancy rather than propagating it.
Relationship to Autosomal_Dominant_Non-Syndromic_Intellectual_Disability.
That entry names MBD5 only as one example gene within a chromatin-regulator
module and does not carry MONDO:0007974. Given that MBD5 haploinsufficiency is
syndromic, it is arguably a poor fit for that entry's scope, but this PR does
not modify it.
environmental:
- name: Fever, viral illness and hot weather as seizure provocateurs
description: >-
Reported as provoking seizures in the MAND seizure cohort. Not causes of
the disease - the lesion is genetic - but recorded because they are
actionable: a family that knows heat and febrile illness lower the seizure
threshold can plan around them.
evidence:
- reference: PMID:33912662
reference_title: "Phenotypic Spectrum of Seizure Disorders in MBD5-Associated Neurodevelopmental Disorder."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Fever, viral illnesses, and hot weather provoked seizures.
explanation: >-
The direct observation. No exposure_term is bound: ECTO has no term
covering this trio, and binding one of the three would misrepresent
the observation as being about a single exposure.
influences_mechanisms:
- target: Seizures
environmental_effect: EXACERBATES
causal_link_type: DIRECT
description: >-
Lowers the seizure threshold in an already-epileptic patient rather
than causing epilepsy.
evidence:
- reference: PMID:33912662
reference_title: "Phenotypic Spectrum of Seizure Disorders in MBD5-Associated Neurodevelopmental Disorder."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Fever, viral illnesses, and hot weather provoked seizures.
explanation: >-
Supports the exacerbating link to the seizure phenotype
specifically.
prevalence:
- population: Individuals referred for clinical chromosomal microarray testing
measure_type: POINT_PREVALENCE
prevalence_class: BAND_1_5_PER_10000
rate_per_100000: 50.0
notes: >-
1 in 2,000 of 17,477 clinical microarray samples. This is a
diagnostic-yield figure in an already-ascertained population, not a
general-population prevalence, and it should not be read as one - the
denominator is people referred for microarray testing because something
was already wrong. It is recorded in preference to an uncited
ultra-rare class because it has a stated denominator. A general-population
estimate is not curated here: Orphanet classifies the disorder below
1/1,000,000, but ORPHA:228402 did not resolve through the reference
fetcher, and an uncited class assertion is worse than an honestly scoped
cited one.
evidence:
- reference: PMID:33912662
reference_title: "Phenotypic Spectrum of Seizure Disorders in MBD5-Associated Neurodevelopmental Disorder."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MBD5 deletions are not especially rare, found in 0.05% (1 in 2,000) of
17,477 samples that underwent clinical microarray testing.
explanation: >-
Gives both the rate and its denominator, which is what makes the
figure interpretable as a diagnostic yield rather than a population
prevalence.
inheritance:
- name: Autosomal dominant inheritance
inheritance_term:
preferred_term: Autosomal dominant inheritance
term:
id: HP:0000006
label: Autosomal dominant inheritance
description: >-
Almost always de novo, but the transmission behaviour differs by lesion
class in a way worth stating rather than flattening: parent-to-child
transmission of a 2q23.1 deletion encompassing MBD5 has not been reported,
whereas transmission of intragenic MBD5 deletions and pathogenic sequence
variants has. Penetrance appears high: no copy-number alteration of MBD5
was found in 7,878 controls.
evidence:
- reference: PMID:21981781
reference_title: >-
Assessment of 2q23.1 microdeletion syndrome implicates MBD5 as a
single causal locus of intellectual disability, epilepsy, and autism
spectrum disorder.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
No copy-number alterations of MBD5 were observed in 7878 controls,
suggesting MBD5 alterations are highly penetrant.
explanation: >-
The control-cohort observation on which the high-penetrance claim
rests. Note this establishes rarity in controls, from which the
authors infer penetrance; it is not a direct penetrance measurement.
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
To date, parent-to-child transmission of a 2q23.1 deletion that
encompasses all or part of MBD5 has not been reported. Parent-to-child
transmissions of MBD5 intragenic deletions and pathogenic sequence
variants have been reported.
explanation: >-
The lesion-class asymmetry in transmission, which a bare "almost
always de novo" statement would obscure. Relevant to recurrence-risk
counselling.
pathophysiology:
- name: MBD5 Haploinsufficiency
biological_scale: MOLECULAR
description: >-
Deletion of, or a loss-of-function alteration within, one MBD5 allele
halves MBD5 mRNA. The critical-region mapping is what makes this node a
single-gene claim rather than an inference about a deleted interval: MBD5
was the only locus defining the region shared by all deletions, and
alterations disrupting MBD5 alone reproduce the full phenotype.
genes:
- preferred_term: MBD5
term:
id: hgnc:20444
label: MBD5
notes: >-
No methyl-CpG-binding molecular function is annotated on this node, and
the absence is deliberate. MBD5 localises to non-heterochromatic active
regions and its binding to methylated DNA has been questioned, so binding
GO:0008327 here would assert the methyl-DNA-reading mechanism that the
next node's description explicitly declines to claim. No term beats a term
the cited evidence does not support.
downstream:
- target: Disrupted Chromatin-Mediated Transcriptional Regulation in Neurons
evidence:
- reference: PMID:21981781
reference_title: >-
Assessment of 2q23.1 microdeletion syndrome implicates MBD5 as a
single causal locus of intellectual disability, epilepsy, and autism
spectrum disorder.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We identified a single gene, methyl-CpG-binding domain 5 (MBD5), as
the only locus that defined the critical region. Partial or complete
deletion of MBD5 was associated with haploinsufficiency of mRNA
expression, intellectual disability, epilepsy, and autistic features.
explanation: >-
Establishes MBD5 as the sole critical-region gene and links its
deletion to reduced mRNA and to the core clinical triad.
- reference: PMID:21981781
reference_title: >-
Assessment of 2q23.1 microdeletion syndrome implicates MBD5 as a
single causal locus of intellectual disability, epilepsy, and autism
spectrum disorder.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Expression profiles and clinical characteristics were largely
indistinguishable between MBD5-specific alteration and deletion of the
entire 2q23.1 interval.
explanation: >-
The observation that justifies modelling this as a single-gene
disorder. Note the authors' own qualifier is "largely", not
"indistinguishable", and the entry description carries that hedge.
- reference: PMID:19809484
reference_title: "The 2q23.1 microdeletion syndrome: clinical and behavioural phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Another gene in the 2q23.1 region, EPC2, was deleted in 12 patients
who had a broader phenotype than those with a deletion of MBD5 only.
explanation: >-
Graded PARTIAL because it qualifies rather than supports the
single-locus claim: MBD5 alone reproduces the core phenotype, but
co-deletion of EPC2 broadens it. Included so the entry does not
present only the half of its own cited literature that makes the
cleaner story.
- name: Disrupted Chromatin-Mediated Transcriptional Regulation in Neurons
biological_scale: CELLULAR
description: >-
MBD5 carries a methyl-CpG-binding domain and a PWWP domain and acts as an
epigenetic regulator with transactivational activity. Halving its dose
dysregulates the transcriptional programmes that chromatin readers
coordinate during neuronal development. The mechanism here is less
completely characterised than the genetics: MBD5's own binding to
methylated DNA has been questioned, so the node is stated at the level the
evidence supports - a chromatin-associated transcriptional regulator whose
dose matters - rather than as a specific methyl-DNA-reading mechanism.
biological_processes:
- preferred_term: chromatin organization
term:
id: GO:0006325
label: chromatin organization
modifier: DECREASED
- preferred_term: regulation of transcription by RNA polymerase II
term:
id: GO:0006357
label: regulation of transcription by RNA polymerase II
downstream:
- target: Impaired Neurite Outgrowth and Neuronal Maturation
- target: Dysregulated Circadian Gene Expression
evidence:
- reference: PMID:23632792
reference_title: >-
Reciprocal deletion and duplication at 2q23.1 indicates a role for
MBD5 in autism spectrum disorder.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
a region that includes MBD5, an important factor in methylation
patterning and epigenetic regulation
explanation: >-
Characterises MBD5's molecular role as epigenetic regulation, which is
the level at which this node is stated.
- reference: PMID:25001218
reference_title: >-
Disruption of Mbd5 in mice causes neuronal functional deficits and
neurobehavioral abnormalities consistent with 2q23.1 microdeletion
syndrome.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
we found that MBD5 has transactivational activity and plays a role in
neuritogenesis
explanation: >-
Supports the transactivational function attributed to MBD5 here.
Graded MODEL_ORGANISM because the finding comes from the gene-trap
mouse study.
- name: Dysregulated Circadian Gene Expression
biological_scale: CELLULAR
description: >-
MBD5 haploinsufficiency alters expression of the core circadian genes
NR1D2, PER1, PER2 and PER3 in patient lymphoblastoid lines, and siRNA
knockdown perturbs further circadian pathway genes. This node is what
connects the disease's most clinically useful phenotype to its molecular
lesion. It also converts the Angelman/Rett/Smith-Magenis resemblance the
entry narrates elsewhere from a diagnostic anecdote into a mechanistic
claim: MBD5 and RAI1, the Smith-Magenis gene, carry conserved putative E
boxes and their knockdowns perturb overlapping circadian and mTOR
pathways.
biological_processes:
- preferred_term: circadian rhythm
term:
id: GO:0007623
label: circadian rhythm
modifier: DYSREGULATED
downstream:
- target: Disturbed Sleep Pattern
evidence:
- reference: PMID:25271084
reference_title: >-
MBD5 haploinsufficiency is associated with sleep disturbance and
disrupts circadian pathways common to Smith-Magenis and fragile X
syndromes.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
circadian gene mRNA levels of NR1D2, PER1, PER2, and PER3 were altered
in del 2q23.1 lymphoblastoid cell lines (LCLs), signifying that
haploinsufficiency of MBD5 can result in dysregulation of circadian
rhythm gene expression
explanation: >-
The measurement this node models, in patient-derived cells. Graded
IN_VITRO because the assay is on lymphoblastoid lines, though note the
cells are the patients' own rather than a heterologous system.
- reference: PMID:25271084
reference_title: >-
MBD5 haploinsufficiency is associated with sleep disturbance and
disrupts circadian pathways common to Smith-Magenis and fragile X
syndromes.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Bioinformatic analysis identified conserved putative E boxes in MBD5
and RAI1, and expression levels of NR1D2 and CRY2 were significantly
reduced in patient LCLs.
explanation: >-
Supports the shared-pathway claim with Smith-Magenis, which is what
makes the clinical resemblance mechanistic rather than coincidental.
- name: Impaired Neurite Outgrowth and Neuronal Maturation
biological_scale: CELLULAR
description: >-
Neuronal cultures from the Mbd5 gene-trap mouse show a deficiency in
neurite outgrowth, giving a cellular correlate for the cognitive and
behavioural phenotype. This is the one node in the chain whose direct
evidence is entirely from a model system, which is recorded rather than
smoothed over.
biological_processes:
- preferred_term: neuron projection development
term:
id: GO:0031175
label: neuron projection development
modifier: DECREASED
downstream:
- target: Neurodevelopmental Impairment with Disproportionate Speech Deficit
evidence:
- reference: PMID:25001218
reference_title: >-
Disruption of Mbd5 in mice causes neuronal functional deficits and
neurobehavioral abnormalities consistent with 2q23.1 microdeletion
syndrome.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
In addition, neuronal cultures uncovered a deficiency in neurite
outgrowth.
explanation: >-
The direct observation this node models, in cultures from the mouse
model.
- name: Neurodevelopmental Impairment with Disproportionate Speech Deficit
biological_scale: ORGANISM
description: >-
The clinical endpoint: intellectual disability in which speech delay is
pronounced relative to overall cognitive level, accompanied by seizures,
autistic features, disturbed sleep, stereotypies and a broad-based gait.
The mouse model recapitulates abnormal social behaviour, cognitive
impairment, and motor and craniofacial abnormalities, which is the
strongest available argument that the gene dose rather than the deletion
per se produces the phenotype.
downstream:
- target: Intellectual Disability
- target: Absent or Minimal Speech
- target: Seizures
- target: Autistic Features
- target: Global Developmental Delay
evidence:
- reference: PMID:19809484
reference_title: "The 2q23.1 microdeletion syndrome: clinical and behavioural phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All patients were mentally retarded with pronounced speech delay and
additional abnormalities including short stature, seizures,
microcephaly and coarse facies. The majority of cases presented with
stereotypic repetitive behaviour, a disturbed sleep pattern and a
broad-based gait.
explanation: >-
The clinical description this node summarises, including the
disproportionate speech delay and the syndromic features that make the
non-syndromic ontology label inapt. The node points at the individual
phenotypes rather than absorbing them into this sentence.
- reference: PMID:25001218
reference_title: >-
Disruption of Mbd5 in mice causes neuronal functional deficits and
neurobehavioral abnormalities consistent with 2q23.1 microdeletion
syndrome.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Our study indicates that the Mbd5(+/) (GT) mouse model recapitulates
most of the hallmark phenotypes observed in 2q23.1 deletion carriers
including abnormal social behavior, cognitive impairment, and motor
and craniofacial abnormalities.
explanation: >-
Establishes that the mouse model reproduces most hallmark phenotypes,
supporting a causal role for MBD5 dose. Graded MODEL_ORGANISM.
phenotypes:
- name: Intellectual Disability
category: Neurologic
description: >-
Present in all reported patients, generally moderate to severe.
phenotype_term:
preferred_term: Intellectual disability
term:
id: HP:0001249
label: Intellectual disability
frequency: VERY_FREQUENT
evidence:
- reference: PMID:19809484
reference_title: "The 2q23.1 microdeletion syndrome: clinical and behavioural phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All patients were mentally retarded with pronounced speech delay
explanation: >-
Reports intellectual disability in all patients of the series, which
is the basis for VERY_FREQUENT.
- name: Pronounced Speech Delay
category: Neurologic
description: >-
Speech and language impairment is disproportionately severe relative to
overall cognitive level, and is one of the features that most consistently
distinguishes this syndrome clinically.
phenotype_term:
preferred_term: Delayed speech and language development
term:
id: HP:0000750
label: Delayed speech and language development
severity: SEVERE
frequency: VERY_FREQUENT
evidence:
- reference: PMID:19809484
reference_title: "The 2q23.1 microdeletion syndrome: clinical and behavioural phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All patients were mentally retarded with pronounced speech delay
explanation: >-
Reports pronounced speech delay in every patient in the series.
- name: Seizures
category: Neurologic
description: >-
Onset usually around age two years.
phenotype_term:
preferred_term: Seizure
term:
id: HP:0001250
label: Seizure
frequency: VERY_FREQUENT
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Seizures are present in more than 80% of children; onset is usually
around age two years.
explanation: >-
GeneReviews gives the frequency figure that licenses VERY_FREQUENT
(>80% maps to the 80-99% band) and the onset age. The Talkowski
sentence cited alongside establishes that epilepsy is associated, not
how often, so it cannot on its own license a frequency band.
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
MBD5 haploinsufficiency is a neurodevelopmental disorder characterized
by developmental delay, intellectual disability, severe speech
impairment, seizures, sleep disturbances, and abnormal behaviors.
explanation: >-
The GeneReviews clinical characterisation naming seizures among the
core features.
- reference: PMID:21981781
reference_title: >-
Assessment of 2q23.1 microdeletion syndrome implicates MBD5 as a
single causal locus of intellectual disability, epilepsy, and autism
spectrum disorder.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Partial or complete deletion of MBD5 was associated with
haploinsufficiency of mRNA expression, intellectual disability,
epilepsy, and autistic features.
explanation: >-
Names epilepsy among the three core features associated with MBD5
deletion.
- name: Autistic Features
category: Behavioral
phenotype_term:
preferred_term: Autistic behavior
term:
id: HP:0000729
label: Autistic behavior
frequency: VERY_FREQUENT
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Abnormal behaviors can include autistic-like behaviors (80%) and
self-injury and aggression (>60%).
explanation: >-
GeneReviews puts autistic-like behaviours at 80%, the VERY_FREQUENT
floor.
- reference: PMID:21981781
reference_title: >-
Assessment of 2q23.1 microdeletion syndrome implicates MBD5 as a
single causal locus of intellectual disability, epilepsy, and autism
spectrum disorder.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Partial or complete deletion of MBD5 was associated with
haploinsufficiency of mRNA expression, intellectual disability,
epilepsy, and autistic features.
explanation: >-
Names autistic features among the core associated phenotypes.
- name: Disturbed Sleep Pattern
category: Behavioral
description: >-
A distinctive and clinically useful feature; its combination with
stereotypies and coarse facies is what prompted initial diagnoses of
Angelman, Rett or Smith-Magenis syndrome before the deletion was found.
phenotype_term:
preferred_term: Sleep disturbance
term:
id: HP:0002360
label: Sleep disturbance
frequency: VERY_FREQUENT
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Sleep disturbances, present in about 90%, can result in excessive
daytime drowsiness.
explanation: >-
GeneReviews gives ~90%, which is VERY_FREQUENT, and adds the daytime
consequence.
- reference: PMID:19809484
reference_title: "The 2q23.1 microdeletion syndrome: clinical and behavioural phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The majority of cases presented with stereotypic repetitive
behaviour, a disturbed sleep pattern and a broad-based gait.
explanation: >-
Reports the disturbed sleep pattern in the majority of cases, which
maps to FREQUENT.
- name: Stereotypic Repetitive Behaviour
category: Behavioral
phenotype_term:
preferred_term: Motor stereotypy
term:
id: HP:0000733
label: Motor stereotypy
frequency: FREQUENT
evidence:
- reference: PMID:19809484
reference_title: "The 2q23.1 microdeletion syndrome: clinical and behavioural phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The majority of cases presented with stereotypic repetitive
behaviour, a disturbed sleep pattern and a broad-based gait.
explanation: >-
Reports stereotypic repetitive behaviour in the majority of cases.
- name: Coarse Facial Features
category: Craniofacial
phenotype_term:
preferred_term: Coarse facial features
term:
id: HP:0000280
label: Coarse facial features
frequency: VERY_FREQUENT
evidence:
- reference: PMID:19809484
reference_title: "The 2q23.1 microdeletion syndrome: clinical and behavioural phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All patients were mentally retarded with pronounced speech delay and
additional abnormalities including short stature, seizures,
microcephaly and coarse facies.
explanation: >-
Lists coarse facies among the additional abnormalities present across
the series.
- name: Microcephaly
category: Craniofacial
frequency: FREQUENT
phenotype_term:
preferred_term: Microcephaly
term:
id: HP:0000252
label: Microcephaly
evidence:
- reference: PMID:19809484
reference_title: "The 2q23.1 microdeletion syndrome: clinical and behavioural phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
additional abnormalities including short stature, seizures,
microcephaly and coarse facies
explanation: >-
Names microcephaly among the additional abnormalities.
- reference: PMID:33912662
reference_title: "Phenotypic Spectrum of Seizure Disorders in MBD5-Associated Neurodevelopmental Disorder."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Sleep disturbance during childhood was reported in 17 patients and
involved frequent nocturnal awakenings. Nine patients had
microcephaly.
explanation: >-
Nine of the cohort's 23 patients, which is what places the frequency
in the FREQUENT band rather than leaving it unquantified. Quoted with
the preceding sentence because the microcephaly count alone is a
four-word fragment. The cohort included two duplication patients, so
the fraction is approximate for the deletion side specifically.
- name: Short Stature
category: Growth
phenotype_term:
preferred_term: Short stature
term:
id: HP:0004322
label: Short stature
evidence:
- reference: PMID:19809484
reference_title: "The 2q23.1 microdeletion syndrome: clinical and behavioural phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
additional abnormalities including short stature, seizures,
microcephaly and coarse facies
explanation: >-
Names short stature among the additional abnormalities.
- name: Broad-Based Gait
category: Neurologic
phenotype_term:
preferred_term: Broad-based gait
term:
id: HP:0002136
label: Broad-based gait
frequency: FREQUENT
evidence:
- reference: PMID:19809484
reference_title: "The 2q23.1 microdeletion syndrome: clinical and behavioural phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The majority of cases presented with stereotypic repetitive
behaviour, a disturbed sleep pattern and a broad-based gait.
explanation: >-
Reports broad-based gait in the majority of cases.
- name: Self-Injury and Aggression
category: Behavioral
description: >-
The behavioural feature most often driving psychiatric referral, and the
one families report as hardest to manage.
phenotype_term:
preferred_term: Self-injurious behavior
term:
id: HP:0100716
label: Self-injurious behavior
frequency: FREQUENT
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Abnormal behaviors can include autistic-like behaviors (80%) and
self-injury and aggression (>60%).
explanation: >-
GeneReviews reports self-injury and aggression in more than 60%,
which maps to FREQUENT.
- name: Global Developmental Delay
category: Neurologic
phenotype_term:
preferred_term: Global developmental delay
term:
id: HP:0001263
label: Global developmental delay
frequency: VERY_FREQUENT
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
MBD5 haploinsufficiency is a neurodevelopmental disorder characterized
by developmental delay, intellectual disability, severe speech
impairment, seizures, sleep disturbances, and abnormal behaviors.
explanation: >-
Developmental delay is the first-named core feature in the
GeneReviews characterisation.
- name: Absent or Minimal Speech
category: Neurologic
description: >-
More specific than the delayed-speech phenotype above: most affected
children never progress beyond single words or short phrases.
phenotype_term:
preferred_term: Absent speech
term:
id: HP:0001344
label: Absent speech
frequency: VERY_FREQUENT
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Most children lack speech entirely or have single words, short
phrases, or short sentences.
explanation: >-
Quantifies how severe the speech impairment is, rather than only
that it is delayed.
- name: Constipation
category: Gastrointestinal
description: >-
Common enough that GeneReviews puts it on the list of things to assess at
every visit.
phenotype_term:
preferred_term: Constipation
term:
id: HP:0002019
label: Constipation
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Assess for seizures, feeding issues, constipation, and family support
needs at each visit.
explanation: >-
Constipation is named in the GeneReviews surveillance schedule. No
frequency is recorded because the abstract gives none.
- name: Feeding Difficulties
category: Gastrointestinal
frequency: VERY_FREQUENT
phenotype_term:
preferred_term: Feeding difficulties
term:
id: HP:0011968
label: Feeding difficulties
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Feeding therapy with gastrostomy tube feeding as needed
explanation: >-
The management entry implies the phenotype; gastrostomy is not offered
for a problem that does not occur.
- reference: PMID:27222293
reference_title: "Clinical and Molecular Aspects of MBD5-Associated Neurodevelopmental Disorder (MAND)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In infancy, hypotonia contributes to feeding dif ficulties for over 90%
of the 2q23.1 population
explanation: >-
Supplies the frequency, which belongs to the feeding difficulty rather
than to the hypotonia that causes it. The broken word is the cached
PDF extraction, quoted as it stands rather than silently repaired.
- name: Scoliosis
category: Skeletal
description: >-
Named in the GeneReviews management section as requiring orthopaedic
referral and in the surveillance schedule as needing annual assessment.
The same reasoning applied to feeding difficulties applies here: an annual
screening recommendation is not made for a finding that does not occur.
phenotype_term:
preferred_term: Scoliosis
term:
id: HP:0002650
label: Scoliosis
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Clinical assessment for scoliosis annually.
explanation: >-
The surveillance recommendation, which is the strongest statement the
abstract makes about scoliosis. No frequency is recorded because none
is given.
- name: Hip Dysplasia
category: Skeletal
phenotype_term:
preferred_term: Hip dysplasia
term:
id: HP:0001385
label: Hip dysplasia
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
treatment of hip dysplasia and scoliosis per orthopedist; treatment of
cardiovascular anomalies per cardiologist
explanation: >-
Named in the GeneReviews management section. An orthopaedic referral
for hip dysplasia implies the finding occurs.
- name: Cardiovascular Anomalies
category: Cardiovascular
description: >-
Congenital heart defects requiring cardiology referral.
phenotype_term:
preferred_term: Abnormal heart morphology
term:
id: HP:0001627
label: Abnormal heart morphology
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
treatment of hip dysplasia and scoliosis per orthopedist; treatment of
cardiovascular anomalies per cardiologist
explanation: >-
Named in the GeneReviews management section. The bound term is the
general heart-morphology parent rather than a specific defect, because
the abstract says "cardiovascular anomalies" without naming which.
- name: Hyperactivity
category: Behavioral
frequency: OCCASIONAL
description: >-
Named among the psychiatric features of MAND alongside aggression, but
uncommon in the deletion cohort specifically - reported in about 9% of
patients. This is worth separating from short attention span, which is a
distinct and far more common feature curated separately below; conflating
the two is what produces the frequently quoted "hyperactivity, short
attention span, >60%".
phenotype_term:
preferred_term: Hyperactivity
term:
id: HP:0000752
label: Hyperactivity
evidence:
- reference: PMID:33912662
reference_title: "Phenotypic Spectrum of Seizure Disorders in MBD5-Associated Neurodevelopmental Disorder."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
features of MAND include intellectual disability, epilepsy,
psychiatric features of aggression and hyperactivity, and dysmorphic
features including short stature and microcephaly, sleep disturbance,
and ataxia
explanation: >-
Names hyperactivity among the MAND features. Note the cited cohort
included duplication as well as deletion and point-mutation patients,
so this quote is used for the MAND feature list it states rather than
for any cohort frequency.
- reference: PMID:27222293
reference_title: "Clinical and Molecular Aspects of MBD5-Associated Neurodevelopmental Disorder (MAND)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Other behaviors mentioned in ~ 9% of reported patients are anxiety,
hyperactivity, inappropriate happy demeanor, and social withdrawal
explanation: >-
Supplies the deletion-cohort frequency and places hyperactivity among
the occasional rather than the consistent features.
- name: Short Attention Span
category: Behavioral
frequency: VERY_FREQUENT
description: >-
Distractibility and a short attention span are among the consistent
features of the deletion syndrome, reported alongside the autistic-like
behaviours in more than 80% of individuals. Curated separately from
hyperactivity because the deletion literature separates them and gives
them frequencies an order of magnitude apart.
phenotype_term:
preferred_term: Short attention span
term:
id: HP:0000736
label: Short attention span
evidence:
- reference: PMID:27222293
reference_title: "Clinical and Molecular Aspects of MBD5-Associated Neurodevelopmental Disorder (MAND)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
repetitive behaviors, are reported in more than 80% of individuals
explanation: >-
Carries the frequency figure for the sentence that opens "Short
attention span and autistic-like behaviors" - the clause is quoted
from after the hyphenated line break in the cached full text, which
falls inside "includ-ing" and not inside the figure.
- name: Hypotonia
category: Neurological
description: >-
Infantile hypotonia is among the consistent features of the deletion
syndrome and is the proximate reason for the feeding difficulties curated
above.
No frequency is recorded, deliberately. The only prose figure in the
sentence below - over 90% - belongs to the feeding difficulty, not to the
hypotonia that contributes to it, and the deletion review's frequency
table lists hypotonia under its consistent band only in a row whose
PDF-extracted column layout is not quotable as prose. A band taken from
the neighbouring figure would be a number this source does not state.
phenotype_term:
preferred_term: Hypotonia
term:
id: HP:0001252
label: Hypotonia
evidence:
- reference: PMID:27222293
reference_title: "Clinical and Molecular Aspects of MBD5-Associated Neurodevelopmental Disorder (MAND)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In infancy, hypotonia contributes to feeding dif ficulties for over 90%
of the 2q23.1 population
explanation: >-
Establishes infantile hypotonia in the deletion cohort and its causal
relation to feeding difficulty. The over-90% figure attaches to the
feeding difficulty, not to the hypotonia, and is used there rather
than here.
- name: Fifth-Finger Clinodactyly
category: Skeletal
frequency: FREQUENT
description: >-
Reported in about 70% of the deletion cohort, in the same sentence that
reports small hands and feet and with the same caveat that hand and foot
anomalies are not uniform across patients.
phenotype_term:
preferred_term: Fifth finger clinodactyly
term:
id: HP:0004209
label: Clinodactyly of the 5th finger
evidence:
- reference: PMID:27222293
reference_title: "Clinical and Molecular Aspects of MBD5-Associated Neurodevelopmental Disorder (MAND)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
small hands and feet
(~75.0%), fifth finger clinodactyly (~70%)
explanation: >-
Gives the frequency directly. The two broken words are the cached PDF
extraction's ligature handling, quoted as they stand - the same
treatment the hypotonia item above gives "dif ficulties".
- name: Small Hands and Feet
category: Skeletal
frequency: FREQUENT
description: >-
Hand and foot anomalies are not uniform across the population, but small
hands and feet are the most consistently reported of them at about 75%.
The source quantifies hands and feet together; HPO has no combined term,
so the node binds HP:0200055 for the hands and the feet are carried in
this description rather than split into a second node with a frequency
the source does not separately state.
phenotype_term:
preferred_term: Small hand
term:
id: HP:0200055
label: Small hand
evidence:
- reference: PMID:27222293
reference_title: "Clinical and Molecular Aspects of MBD5-Associated Neurodevelopmental Disorder (MAND)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
the type of anomalies are wide ranging and not uniform and include
small hands and feet (~75.0%)
explanation: >-
Gives the frequency and states the heterogeneity, which is why the
node is scoped to the one anomaly the source quantifies.
- reference: PMID:27222293
reference_title: "Clinical and Molecular Aspects of MBD5-Associated Neurodevelopmental Disorder (MAND)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
phenotypes present in 2q23.1 deletion cases: postnatal growth
retardation, microcephaly, open mouth, small hands and feet,
cardiovascular abnormalities, and constipation, were not noted in
2q23.1 duplication cases
explanation: >-
Attributes small hands and feet to the deletion cohort specifically
and excludes the reciprocal duplication syndrome, which is the
distinction that makes this quotable in a haploinsufficiency entry.
genetic:
- name: MBD5
relationship_type: CAUSATIVE
variant_origin: DE_NOVO
gene_term:
preferred_term: MBD5
term:
id: hgnc:20444
label: MBD5
notes: >-
Both whole-gene deletion and intragenic alterations cause the disease,
including partial deletions of non-coding regions that routine diagnostic
screening does not typically capture or call pathogenic. That detection
gap is clinically material: a patient can be MBD5-haploinsufficient and
test negative on a standard array.
Origin is almost always de novo, which is what `variant_origin` records,
but not invariably - transmission from a mildly affected parent is
reported, and germline mosaicism in a clinically normal parent has now
been demonstrated directly by deep-coverage sequencing. That is the case
that makes "de novo" and "no recurrence risk" different statements: the
family below had three affected siblings and two phenotypically normal
parents, and only deep sequencing found the mosaic mother.
Recurrence risk is not hypothetical here: mosaicism was found in 14% of
families in the seizure cohort, identified through their having had two
affected pregnancies. That is the number the counselling caveat is about.
Not curated here, and the reasons differ. The variant-class breakdown
across deletions, intragenic CNVs and sequence variants is in the
deep-research report but is not quotable: the report attributes the ~5%
sequence-variant figure to the Mullegama and Elsea MAND review, and that
review's full text - now fetched and cached - does not state the
breakdown. So this is a genuine sourcing gap, not an unfetched reference.
The ClinGen dosage-sensitivity assertion is not a research gap at all but a
tooling one: `just clingen-dosage-refresh` fails on a checksum mismatch
against the pinned manifest, so no `CGDS:` record can be built for any gene
until that pin is updated. `just refresh-orphadata` fails the same way,
which is why this entry's prevalence record is a diagnostic yield rather
than the Orphanet population class.
inheritance:
- name: Autosomal dominant inheritance
inheritance_term:
preferred_term: Autosomal dominant inheritance
term:
id: HP:0000006
label: Autosomal dominant inheritance
evidence:
- reference: PMID:33912662
reference_title: "Phenotypic Spectrum of Seizure Disorders in MBD5-Associated Neurodevelopmental Disorder."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Deletions or mutations are almost always de novo although inheritance
from mildly affected or mosaic parents has been reported.
explanation: >-
Sources the de novo predominance and, more usefully for counselling,
the documented exceptions to it.
- reference: PMID:36396431
reference_title: >-
Germline mosaicism in a family with MBD5 haploinsufficiency.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Both parents were phenotypically normal but deep coverage sequencing
of the parents showed germline mosaicism in the mother
explanation: >-
Demonstrates germline mosaicism directly rather than inferring it from
recurrence, and shows it can be invisible to standard parental
testing - which is what turns the counselling caveat above into a
concrete testing recommendation.
- reference: PMID:33912662
reference_title: "Phenotypic Spectrum of Seizure Disorders in MBD5-Associated Neurodevelopmental Disorder."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Our molecular data highlight the importance of mosaicism, both in
patient 12 and, even more critically, in 3/22 (14%) families who had 2
affected pregnancies
explanation: >-
Quantifies how often mosaicism is actually in play, which is the
difference between a caveat worth mentioning and one worth acting on
in a recurrence-risk discussion.
- reference: PMID:21981781
reference_title: >-
Assessment of 2q23.1 microdeletion syndrome implicates MBD5 as a
single causal locus of intellectual disability, epilepsy, and autism
spectrum disorder.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Fourteen alterations, including partial deletions of noncoding regions
not typically captured or considered pathogenic by current diagnostic
screening, disrupted MBD5 alone.
explanation: >-
Supports both that MBD5-only alterations are sufficient and that some
of them evade standard diagnostic screening.
discussions:
- discussion_id: mbd5_dosage_sensitivity_both_directions
kind: KNOWLEDGE_GAP
prompt: >-
By what mechanism does MBD5 overexpression, in reciprocal 2q23.1
duplication, produce a phenotype overlapping the one caused by MBD5
haploinsufficiency?
attaches_to:
- pathophysiology#Disrupted Chromatin-Mediated Transcriptional Regulation in Neurons
rationale: >-
MBD5 is dosage-sensitive in both directions: deletion and duplication both
cause neurodevelopmental disease with overlapping features, the
duplication phenotype being somewhat milder. A model in which
haploinsufficiency simply reduces a required activity does not explain why
doubling that activity is also harmful. This entry curates the deletion
side only; the shared mechanism that would account for both is not
established, and this discussion marks that as a gap rather than leaving
the asymmetry unremarked.
evidence:
- reference: PMID:23632792
reference_title: >-
Reciprocal deletion and duplication at 2q23.1 indicates a role for
MBD5 in autism spectrum disorder.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The features associated with a deletion, mutation or duplication of
MBD5 and the gene expression changes observed support MBD5 as a
dosage-sensitive gene critical for normal development.
explanation: >-
States the bidirectional dosage sensitivity that motivates this gap.
- reference: PMID:23632792
reference_title: >-
Reciprocal deletion and duplication at 2q23.1 indicates a role for
MBD5 in autism spectrum disorder.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Phenotypic analyses suggest that 2q23.1 duplication results in a
slightly less severe phenotype than the reciprocal deletion.
explanation: >-
Records the severity asymmetry between the two dosage directions,
which any candidate mechanism would have to account for.
treatments:
- name: Multidisciplinary Symptomatic Management
description: >-
There is no disease-modifying therapy. Management is symptomatic and
multidisciplinary. GeneReviews names clinical genetics, neurology, child
development, behavioural therapy, nutrition and feeding, speech and
language therapy, and occupational and physical therapy.
therapeutic_modality: BEHAVIORAL
treatment_term:
preferred_term: supportive care
term:
id: NCIT:C15747
label: Supportive Care
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
A multidisciplinary approach that typically includes specialists in
clinical genetics, neurology, child development, behavioral therapy,
nutrition/feeding, speech and language therapy, and occupational and
physical therapy is recommended.
explanation: >-
The GeneReviews management recommendation.
- name: Early Speech Therapy with Nonverbal Communication
description: >-
Introduced early and explicitly including nonverbal methods, because most
affected children never acquire more than single words. This is the
intervention that follows directly from the entry's most distinctive
phenotype.
therapeutic_modality: BEHAVIORAL
treatment_term:
preferred_term: speech therapy
term:
id: NCIT:C159273
label: Speech Language Therapy
target_mechanisms:
- target: Neurodevelopmental Impairment with Disproportionate Speech Deficit
description: >-
Addresses the communication consequence. It does not act on the
chromatin lesion.
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Speech therapy (including nonverbal methods of communication) should
be introduced early.
explanation: >-
Names the intervention and the timing, and the parenthesis is what
makes it appropriate for children who will not become verbal.
- name: Early Intervention and Individualized Education
description: >-
Enrollment in an early-intervention programme in infancy and an
individualized educational programme at school age.
therapeutic_modality: BEHAVIORAL
treatment_term:
preferred_term: supportive care
term:
id: NCIT:C15747
label: Supportive Care
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Infants benefit from enrollment in an early-intervention program, and
school-age children benefit from an individualized educational
program.
explanation: >-
The GeneReviews developmental-support recommendation.
- name: Routine Management of Seizures, Behaviour, Sleep and Constipation
description: >-
GeneReviews is explicit that these are treated in a routine manner - there
is no MBD5-specific protocol. Recorded because the absence of a
disease-specific approach is itself the clinically useful fact, and
because the sleep disturbance in particular has a curated mechanism in
this entry without a curated targeted therapy.
"Routine" is not the same as "no agent preference", and the cohort
literature supplies one that GeneReviews does not: valproate was the most
consistently effective anti-seizure medication, while carbamazepine made
seizures worse in one patient. A single patient is not a contraindication,
but it is the only agent-specific caution available for this disorder and
is recorded for that reason. The same cohort's ketogenic-diet response in
that patient is reported alongside it in the source.
therapeutic_modality: OTHER
treatment_term:
preferred_term: supportive care
term:
id: NCIT:C15747
label: Supportive Care
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Seizures, behavior problems, sleep disturbances, and constipation are
treated in a routine manner.
explanation: >-
States that management of these features is not disease-specific.
- reference: PMID:33912662
reference_title: "Phenotypic Spectrum of Seizure Disorders in MBD5-Associated Neurodevelopmental Disorder."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Although no drug was clearly superior, valproate showed the most
consistent beneficial effect (12/14 cases), while carbamazepine
exacerbated seizures in patient 2
explanation: >-
Graded PARTIAL because it qualifies rather than supports the routine
claim: the source states plainly that no drug was clearly superior,
which is consistent with routine management, while still identifying
a preferred agent and one that worsened seizures in a single patient.
- name: Orthopedic Management of Scoliosis and Hip Dysplasia
therapeutic_modality: SURGERY
treatment_term:
preferred_term: orthopedic surgical procedure
term:
id: NCIT:C16186
label: Orthopedic Surgical Procedure
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
treatment of hip dysplasia and scoliosis per orthopedist; treatment of
cardiovascular anomalies per cardiologist
explanation: >-
Names the orthopaedic and cardiac referrals in the GeneReviews
management section.
diagnosis:
- name: Molecular Genetic Testing for 2q23.1 Deletion or Intragenic MBD5 Variant
description: >-
The diagnosis is molecular. This section exists because the genetic block
warns that a patient can be MBD5-haploinsufficient and test negative on
routine screening, and a warning without a remedy is incomplete: the
answer is testing that detects both a heterozygous 2q23.1 deletion
encompassing all or part of MBD5 and an intragenic MBD5 variant, since
either is sufficient.
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
The diagnosis of MBD5 haploinsufficiency is established in a proband
by identification on molecular genetic testing of a heterozygous
deletion of 2q23.1 encompassing all or part of MBD5, or of an
intragenic MBD5 pathogenic variant.
explanation: >-
The diagnostic criteria, covering both lesion classes.
- name: Annual Scoliosis Assessment and Periodic Neurodevelopmental Review
description: >-
Surveillance rather than diagnosis, recorded here because the entry has no
other home for it.
evidence:
- reference: PMID:27786435
reference_title: "MBD5 Haploinsufficiency."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Periodic neurodevelopmental and behavioral evaluations to assist in
the management of cognitive issues, behavior issues, and sleep
disturbance. Assess for seizures, feeding issues, constipation, and
family support needs at each visit. Clinical assessment for scoliosis
annually.
explanation: >-
The GeneReviews surveillance schedule.
animal_models:
- name: Mbd5 gene-trap heterozygous mouse
species: Mouse
genotype: Mbd5 heterozygous gene-trap insertion
publication: PMID:25001218
description: >-
Insertional gene-trap mutagenesis producing a heterozygous hypomorph.
Curated as a structured model because two of this entry's four
pathophysiology nodes rest on it, and that dependency should be visible in
the data rather than only in the node descriptions.
modeled_mechanisms:
- target: Neurodevelopmental Impairment with Disproportionate Speech Deficit
relationship: PARTIALLY_RECAPITULATES
fidelity: MODERATE
description: >-
Reproduces abnormal social behaviour, cognitive impairment, and motor
and craniofacial abnormalities.
limitations: >-
The defining human feature cannot be modelled. Disproportionate speech
impairment - most affected children never progress beyond single words
- has no murine analogue, so the model is silent on the phenotype that
most distinguishes this disorder clinically. Homozygotes are not
available for comparison, and this is a hypomorph rather than a clean
heterozygous null, so the dose it models is not exactly the human one.
readouts:
- name: Social behaviour and cognitive performance
target: Neurodevelopmental Impairment with Disproportionate Speech Deficit
direction: DECREASED
interpretation: >-
Behavioural correlate of the human neurodevelopmental phenotype.
evidence:
- reference: PMID:25001218
reference_title: >-
Disruption of Mbd5 in mice causes neuronal functional deficits
and neurobehavioral abnormalities consistent with 2q23.1
microdeletion syndrome.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Our study indicates that the Mbd5(+/) (GT) mouse model
recapitulates most of the hallmark phenotypes observed in
2q23.1 deletion carriers including abnormal social behavior,
cognitive impairment, and motor and craniofacial
abnormalities.
explanation: >-
The behavioural and craniofacial phenotypes reproduced.
evidence:
- reference: PMID:25001218
reference_title: >-
Disruption of Mbd5 in mice causes neuronal functional deficits and
neurobehavioral abnormalities consistent with 2q23.1 microdeletion
syndrome.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
These findings support a causal role of MBD5 in 2q23.1
microdeletion syndrome and suggest a role for MBD5 in neuronal
processes.
explanation: >-
The authors' conclusion that the model supports a causal role for
MBD5, which is what makes it informative for this node.
- target: Impaired Neurite Outgrowth and Neuronal Maturation
relationship: RECAPITULATES
fidelity: MODERATE
description: >-
Neuronal cultures from the model show a neurite outgrowth deficiency.
This is the sole source of evidence for that node, which the node
description states.
readouts:
- name: Neurite outgrowth in neuronal culture
target: Impaired Neurite Outgrowth and Neuronal Maturation
direction: DECREASED
interpretation: >-
The cellular measurement the node models.
evidence:
- reference: PMID:25001218
reference_title: >-
Disruption of Mbd5 in mice causes neuronal functional deficits
and neurobehavioral abnormalities consistent with 2q23.1
microdeletion syndrome.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
In addition, neuronal cultures uncovered a deficiency in
neurite outgrowth.
explanation: >-
The measurement itself.
evidence:
- reference: PMID:25001218
reference_title: >-
Disruption of Mbd5 in mice causes neuronal functional deficits and
neurobehavioral abnormalities consistent with 2q23.1 microdeletion
syndrome.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
we found that MBD5 has transactivational activity and plays a role
in neuritogenesis
explanation: >-
Supports treating this model as informative for neuritogenesis
specifically.
Overview. MBD5 haploinsufficiency — increasingly referred to under the umbrella term MBD5-Associated Neurodevelopmental Disorder (MAND) — is a genetic neurodevelopmental syndrome caused by reduced dosage of the MBD5 gene at chromosome 2q23.1. It was originally described as "2q23.1 microdeletion syndrome" following identification of overlapping deletions in affected individuals; systematic mapping of the smallest region of overlap (SRO) across cases subsequently showed that MBD5 itself, not neighboring genes, is the critical locus, and that point mutations/intragenic deletions of MBD5 alone reproduce the full syndrome (Talkowski et al., PMID 21981781; GeneReviews, NBK390803). The condition is characterized by developmental delay, intellectual disability (usually moderate–severe), severe expressive speech impairment, epilepsy, sleep disturbance, and behavioral/autistic features, often with mild dysmorphism, microcephaly, and skeletal anomalies.
Key identifiers: - OMIM (gene): MBD5, MIM 611472 ("METHYL-CpG-BINDING DOMAIN PROTEIN 5") - Orphanet: ORPHA228402 (2q23.1 microdeletion syndrome / MBD5 haploinsufficiency) - HGNC: HGNC:20444 (approved symbol MBD5; former aliases KIAA1461, FLJ11113) - NCBI Gene: Entrez Gene ID 55777 - Ensembl: ENSG00000204406 (chr2:148,021,011–148,516,971, cytoband 2q23.1) - GeneReviews: NBK390803 (Mullegama, Mendoza-Londono, Elsea; initial 2016, updated 2026) - MalaCards / MONDO: cross-referenced as "MBD5 haploinsufficiency" / 2q23.1 deletion syndrome
Common synonyms: 2q23.1 microdeletion syndrome; 2q23.1 deletion syndrome; MBD5-associated neurodevelopmental disorder (MAND); intellectual developmental disorder, autosomal dominant 1 (MRD1/IDDAD1 in some nosologies).
Source of information: Predominantly aggregated, disease-level clinical genetics literature (case series, GeneReviews systematic reviews, cohort studies of 5–78+ patients pooled across publications) rather than large-scale EHR data, reflecting its status as an ultra-rare Mendelian disorder.
Primary cause — genetic haploinsufficiency. Three molecular mechanisms converge on reduced MBD5 dosage: 1. Heterozygous deletion of 2q23.1 encompassing all or part of MBD5 (~80% of diagnosed cases) — ranging from small 38 kb intragenic deletions up to >19 Mb multigene deletions (Talkowski et al. 2011, PMID 21981781, cohort of 65 subjects). 2. Intragenic deletions/duplications of one or more MBD5 exons, including noncoding exons 1–5 (~15% of cases). 3. Heterozygous pathogenic/likely pathogenic sequence variants (nonsense, frameshift, canonical splice-site, and some missense) in MBD5 (~5% of cases) (Mullegama et al. 2016, PMID 27514998 / PMC4989212; Talkowski et al. 2011).
MBD5 is explicitly established as a dosage-sensitive gene: MBD5 mRNA in lymphocytes from deletion carriers is reduced to ~0.22–0.59-fold of normal (22.5–55.4% expression, P<0.0001), while individuals with 2q23.1 microduplications show elevated MBD5 mRNA (1.5–1.83-fold, P<0.0001) and a phenotypically overlapping but generally milder syndrome — both over- and under-expression produce convergent neurodevelopmental phenotypes (PMC4989212).
ClinGen Dosage Sensitivity curation (CCID:007440, last evaluated 08/29/2025): - Haploinsufficiency score: 3 — Sufficient Evidence for Haploinsufficiency. Rationale cites at least six independent reports of de novo nonsense/frameshift variants plus segregation data. - Triplosensitivity score: 0 — No Evidence for Triplosensitivity at the single-gene level (regional 2q23.1 duplications spanning multiple genes exist, but no isolated whole-gene MBD5 duplication case has been reported to establish gene-specific triplosensitivity).
Genetic risk factors. No population susceptibility loci are described (this is a fully penetrant monogenic disorder, not polygenic). MBD5 shows strong evolutionary constraint against loss-of-function variation in gnomAD (high pLI / low LOEUF, consistent with the broader observation that monogenic neurodevelopmental disorder genes cluster among genes with o/e LoF confidence-interval upper bound <0.35, equivalent to pLI>0.9), consistent with dosage sensitivity.
Environmental/infectious risk factors: None identified as causal. However, fever, viral illness, and hot weather are reported seizure triggers/exacerbating factors in MAND patients with epilepsy (Smith-Hicks et al. 2021, PMID 33912662), representing a gene-environment interaction relevant to symptom exacerbation rather than causation.
Protective factors: None specifically described in the literature; this reflects the rarity and recency of syndrome delineation rather than an established absence.
Phenotype frequency data are drawn primarily from GeneReviews (NBK390803) and the Mullegama/Elsea 2016 review (PMC4989212), synthesizing Talkowski et al. (2011) and subsequent cohorts.
| Phenotype | Frequency | Notes | Suggested HPO |
|---|---|---|---|
| Developmental delay | 100% | Global | HP:0001263 |
| Intellectual disability | ~100% | Usually moderate–severe | HP:0001249 |
| Severe speech impairment | >80% | Many nonverbal or limited to single words/short phrases | HP:0002167 (Severe speech delay) / HP:0002376 |
| Motor delay, ataxic/poorly coordinated gait | >70% | Independent walking often delayed to 2–3 yrs | HP:0002194, HP:0002066 |
| Hypotonia | ~80% | Contributes to feeding difficulty | HP:0001252 |
| Phenotype | Frequency | Onset/course | HPO |
|---|---|---|---|
| Seizures/epilepsy | >80–90% | Median onset 2.9 yrs (range 3 days–13 yrs); generalized tonic-clonic most common; focal, atypical absence, tonic, drop attacks, myoclonic also seen; 7/23 had convulsive and 3/23 nonconvulsive status epilepticus in one cohort (Smith-Hicks 2021, PMID 33912662) | HP:0001250 |
| Microcephaly | ~80% | Postnatal/progressive in many | HP:0000252 |
| Phenotype | Frequency | Character | HPO |
|---|---|---|---|
| Sleep disturbance | ~90% | Frequent night waking, short sleep duration, early-morning waking, apparent night terrors, snoring, daytime sleepiness | HP:0002360 |
Mechanistically linked to disrupted circadian gene expression (see Mechanism, below) — molecularly overlapping with Smith-Magenis syndrome and fragile X syndrome sleep pathophysiology (Mullegama et al. 2014, PMID 25271084).
| Phenotype | Frequency | HPO |
|---|---|---|
| Autistic-like behaviors (gaze avoidance, stereotypies) | ~80% | HP:0000729 |
| Self-injurious behavior and/or aggression | >60% | HP:0100716 / HP:0000718 |
| Hyperactivity, short attention span | Frequent (>60%) | HP:0000752 |
No disease-specific QOL instrument has been validated; caregiver-reported burden centers on nonverbal communication, seizure management, disrupted sleep (affecting the whole family), and self-injurious/aggressive behavior requiring behavioral or psychiatric support.
Causal gene: MBD5 (HGNC:20444; OMIM *611472; chr2q23.1; Entrez 55777).
Protein/gene structure: MBD5 has two principal isoforms. Isoform 1 (1,448 aa, encoded across exons 6–15) contains both a methyl-CpG-binding domain (MBD) (~70 residues) and a PWWP domain (Pro-Trp-Trp-Pro motif, ~100–150 aa, associated with cell division/growth/differentiation proteins). Isoform 2 (851 aa, exons 6–9 with retained intron 9) lacks the PWWP domain. Isoform 1 is broadly expressed but enriched in brain and testis; isoform 2 is broadly expressed but enriched in brain and ovary (PMC4989212).
Variant spectrum (Mullegama 2016; Talkowski 2011; Hodge et al. 2014, PMID 24173355/PMC3831065): - Large deletions: 38 kb to >19 Mb (2q23.1 deletion syndrome) - Intragenic deletions/duplications: e.g., 19–68 kb deletions; a 34 kb duplication spanning exons 5–10 - Nonsense: c.440C>G, p.(Ser147) (de novo) - Frameshift: c.340_347del, p.(Lys114Glyfs35) - Missense variants in protein-coding exons (multiple, including inherited variants identified in ASD cohorts — 6 of 747 ASD subjects vs. 2,043 controls; 32 MBD5 changes across a 287-patient ASD cohort) - Duplications (whole 2q23.1 region, ~40 documented cases, 68 kb–53.7 Mb), producing a milder but overlapping phenotype
Variant classification: ACMG/AMP-classified pathogenic/likely pathogenic variants are predominantly protein-truncating (nonsense, frameshift, canonical splice-site) or gene-disrupting CNVs; missense VUS are more common in ASD-ascertained cohorts and require careful curation (ClinVar, ClinGen).
Allele frequency: Essentially absent from gnomAD/population databases for pathogenic truncating alleles, consistent with strong LoF constraint and full penetrance of a severe pediatric-onset phenotype.
Origin: Predominantly de novo (both deletions and point variants). Rare parent-to-child transmission has been documented for intragenic deletions and sequence variants (not for whole-MBD5-encompassing large deletions, which have not been reported to transmit). Germline mosaicism has been documented in at least one family (Bagchi et al., Molecular Case Studies, PMC/CSHL, "Germline mosaicism in a family with MBD5 haploinsufficiency"), supporting counseling for a nonzero sibling recurrence risk even when parental blood testing is negative.
Functional consequence: Loss of function via haploinsufficiency (reduced transcriptional activator dosage). No dominant-negative or gain-of-function mechanism is described; the disease model is straightforward dosage insufficiency of a chromatin-associated transcriptional regulator, with dosage in the opposite direction (duplication) also pathogenic — a "two-hit dosage" model unusual for classic haploinsufficiency syndromes.
Modifier genes: Three genes adjacent to MBD5 in the 2q23.1 region — ORC4, KIF5C, and EPC2 — are proposed to contribute to phenotypic variability (e.g., microcephaly severity, additional neurobehavioral features) in individuals with larger deletions spanning multiple genes, though core MAND features map to MBD5 alone (PMC4989212).
Epigenetic information: MBD5 itself is a chromatin-associated, methyl-CpG-domain-containing protein and functions in epigenetic regulation rather than being regulated epigenetically as a downstream target; it interacts with the PR-DUB (Polycomb repressive deubiquitinase) complex to remove monoubiquitin from histone H2A-K119 (H2AK119ub1), a repressive chromatin mark (Guo et al. 2024, Nucleic Acids Research, PMID 38366571/PMC11077058 — zebrafish model). Its target loci show enrichment for both RNA m5C modification and H2A-K119ub1 signal, positioning MBD5 as a novel RNA m5C reader linking RNA modification to chromatin state.
Chromosomal abnormalities: Contiguous gene deletions/duplications of 2q23.1 are themselves the chromosomal abnormality class most associated with this disorder (see Etiology); also reported: "apparently balanced complex chromosome rearrangements" of 2q23.1 disrupting MBD5 (GeneReviews).
No causal environmental, infectious, or toxin exposure is implicated in disease etiology — this is a monogenic disorder. The only established environmental interaction is symptom modulation: fever, intercurrent viral illness, and hot ambient temperature are reported precipitants of seizures (including status epilepticus) in individuals with MAND-associated epilepsy (PMID 33912662). No lifestyle/behavioral risk-factor literature exists specific to this ultra-rare disorder. No infectious agent is causally or triggeringly implicated beyond the generic "febrile illness lowers seizure threshold" mechanism common to many pediatric epilepsies.
Causal chain overview: 1. Initiating event: Heterozygous deletion, intragenic CNV, or truncating/missense variant reduces functional MBD5 protein to ~50% (or, for duplications, increases it ~1.5–1.8×). 2. Molecular consequence: MBD5, unlike its paralog MeCP2, localizes to non-heterochromatic, transcriptionally active nuclear regions and functions as a transcriptional activator rather than a classical methyl-DNA-mediated repressor (Camarena et al. 2014, PMID 25001217/PMC4154127). It interacts with histone acetyltransferase KAT2A (linked to memory formation and glucose metabolism) and, per the 2024 zebrafish work, with the PR-DUB complex, promoting H2A-K119 deubiquitylation at loci enriched for RNA m5C modification (PMC11077058) — an unanticipated RNA-modification/chromatin-crosstalk mechanism, since zebrafish Mbd5 was found not to bind methylated DNA directly but instead to bind m5C-modified mRNA. 3. Transcriptional dysregulation: Haploinsufficiency dysregulates a network of other autism/neurodevelopmental disease genes, including UBE3A (Angelman syndrome), RAI1 (Smith-Magenis syndrome), TCF4 (Pitt-Hopkins syndrome), MEF2C, and FMR1 (GeneReviews NBK390803; Mullegama 2014 PMID 25271084). iPSC-derived neural progenitor cell (NPC) transcriptome studies from three MAND patients found 468 differentially expressed genes (q<0.05), including 20 SFARI autism genes (upregulated: FOXG1, GABRA3, SLC30A3; downregulated: MBD5, SLC1A1, GPR37, OXTR), with enrichment for TGFβ signaling, Hippo signaling, DNA replication/cell cycle, spliceosome, and MAPK signaling pathways, and striking overlap with autism gene sets in "forebrain and telencephalon regionalization, neuron fate commitment" (PMC8163803). 4. Circadian pathway disruption: Patient lymphoblastoid lines show altered circadian gene expression (NR1D2, PER1, PER2, PER3), and circadian/mTOR pathway alterations overlap between MBD5 and RAI1 knockdown models and FMR1-related data — mechanistically linking MBD5 haploinsufficiency to the syndrome's prominent sleep phenotype and drawing a direct molecular parallel to Smith-Magenis syndrome (RAI1) and fragile X syndrome (FMR1) (PMID 25271084). 5. Neuronal/circuit consequence: Cortical neurons cultured from Mbd5+/GT mouse embryos show significantly reduced neurite length and branching within the first 2 days in culture (PMC4154129), consistent with impaired activity-dependent neuronal maturation. 6. Mouse-brain regional transcriptomics: In the Mbd5+/GT hypomorph, cortex shows the most widespread transcriptional changes of three brain regions examined, and gene co-expression network analysis reveals clusters enriched for ciliary function terms associated with reduced Mbd5 (Vegas et al. 2020, Molecular Autism, PMID 32503625/PMC7275313) — a novel and still poorly understood link, especially compared to CRISPR-edited human iPSC-neuron models, underscoring context-dependence of the transcriptional signature. 7. Clinical manifestation: The cumulative effect of dysregulated chromatin/transcriptional networks (autism genes), circadian genes, and neurite outgrowth deficits during brain development produces the clinical triad of intellectual disability/developmental delay, epilepsy, and autistic/behavioral features, plus the syndrome's characteristic sleep disturbance.
Cell types/processes implicated: cortical excitatory neurons (neurite outgrowth/branching deficits); suprachiasmatic/peripheral circadian oscillator cells (via PER1/2/3, NR1D2); neural progenitor cells (differentiation/fate commitment pathways).
Suggested GO terms: GO:0006357 (regulation of transcription by RNA polymerase II); GO:0006325 (chromatin organization); GO:0035522 (monoubiquitinated histone H2A deubiquitination); GO:0007623 (circadian rhythm); GO:0031175 (neuron projection development).
Suggested CL terms: CL:0000679 (glutamatergic neuron) / CL:0000540 (neuron); CL:0002608 (embryonic stem cell / iPSC-derived NPC context — CL:0011020 neural progenitor cell).
Molecular profiling data available: transcriptomics (mouse brain RNA-seq across 3 regions; human iPSC-NPC RNA-seq, 468 DEGs); no proteomics, metabolomics, or lipidomics datasets specific to MBD5 identified in the literature searched. Single-cell/spatial transcriptomic and multi-omic integration studies for MAND were not found — a notable gap.
Organ level: - Primary: Central nervous system (cerebral cortex, and by extension cognitive/behavioral circuitry); the disorder is fundamentally a neurodevelopmental/encephalopathic condition. - Secondary: Skeletal system (hands, feet, digits — clinodactyly, brachydactyly); cardiovascular system (~10% septal defects, pulmonic stenosis); gastrointestinal system (constipation, feeding dysfunction secondary to hypotonia); craniofacial structures (mild dysmorphism, microcephaly). - Body systems involved: Nervous, musculoskeletal, digestive, cardiovascular, and (via sleep/circadian dysregulation) the endocrine/circadian system.
Tissue/cell level: Cerebral cortical neurons (reduced neurite length/branching in model systems); neural progenitor cells (dysregulated fate/regionalization programs).
Subcellular level: Nucleus — specifically non-heterochromatic, transcriptionally active chromatin regions (GO:0000785 chromatin; the MBD5 protein is notably excluded from classical heterochromatin, distinguishing it from MeCP2). Involvement of the PR-DUB histone-deubiquitination complex implicates chromatin/nucleosome subcompartments (H2A-K119ub1 sites).
Localization/UBERON suggestions: UBERON:0000955 (brain); UBERON:0001851 (cortex); UBERON:0002037 (cerebellum, less prominently implicated); UBERON:0002542 (chromatophore/skeletal structures for digit anomalies, e.g., UBERON:0002389 hand); UBERON:0000948 (heart) for the cardiac subset.
Lateralization: Not applicable — a symmetric, bilateral neurodevelopmental syndrome.
Onset: Congenital/early-infantile in terms of underlying genetic lesion, but clinical recognition typically follows in infancy through early childhood as developmental delay becomes apparent; hypotonia and feeding difficulty may be evident from infancy (>90%). Seizure onset has a median of 2.9 years (range 3 days–13 years) (PMID 33912662); GeneReviews notes seizure onset "typically around age two."
Onset pattern: Insidious/progressive developmental delay rather than acute onset; epilepsy onset can be abrupt (including presentation with status epilepticus in some patients).
Progression: The neurodevelopmental phenotype is generally static-to-slowly evolving rather than degenerative — this is a developmental encephalopathy, not a neurodegenerative disorder. Seizures may show a relapsing/fluctuating course with fever/illness-provoked exacerbations. Behavioral features (self-injury, aggression) and sleep disturbance often persist chronically through childhood and adulthood; disease duration is lifelong.
Disease course pattern: Chronic, non-remitting core neurodevelopmental impairment; episodic component from seizure recurrence; some reports of germline-mosaic parents being "apparently asymptomatic" while transmitting to affected offspring, suggesting a spectrum of expressivity rather than true adult-onset remission.
Critical periods: Early childhood (0–5 years) is the key intervention window per GeneReviews management guidance (early intervention services, developmental preschool, early augmentative/alternative communication), reflecting the general neurodevelopmental-disorder principle that early therapeutic engagement optimizes outcomes even though no disease-modifying therapy exists.
Epidemiology: True population prevalence and incidence are unknown; the disorder is likely underdiagnosed. Orphanet classifies point prevalence as <1/1,000,000 worldwide. One notable yield estimate: approximately 1% of 4,808 individuals ascertained for autism spectrum disorder carried MBD5 haploinsufficiency (GeneReviews), suggesting enrichment within syndromic-ASD/ID cohorts far above general-population prevalence. The condition has been identified across diverse populations worldwide, with no reported geographic or ethnic clustering or founder effect.
Inheritance pattern: Autosomal dominant, overwhelmingly via de novo mutation/deletion. Rare parent-to-child transmission occurs for intragenic deletions and point variants (not for large 2q23.1-spanning deletions, which have not been observed to transmit, presumably due to more severe reproductive-fitness effects or ascertainment).
Penetrance: Predicted complete, though "an apparently asymptomatic mother" has transmitted a pathogenic variant to an affected child, which the GeneReviews authors interpret as more consistent with variable expressivity than incomplete penetrance.
Expressivity: Variable — genotype-phenotype correlation is generally poor between deletion vs. sequence-variant mechanisms, though larger multigene deletions may correlate with more severe/additional features (contribution from ORC4, KIF5C, EPC2). One reported patient with a de novo nonsense mutation (p.Ser147*) showed a notably more severe phenotype (nonambulatory, nonverbal at age 10) than typical deletion carriers, illustrating variant-specific severity variation (PMC3831065).
Genetic anticipation: Not described/applicable (not a repeat-expansion disorder).
Germline mosaicism: Documented in at least one family (Bagchi et al., Molecular Case Studies), with direct implications for recurrence-risk counseling of ostensibly "de novo" cases.
Founder effects / consanguinity: None reported; consistent with autosomal dominant de novo mechanism rather than recessive/founder biology.
Carrier frequency: Not applicable in the classic sense (dominant, not carrier-based); population allele frequency of pathogenic LoF variants is essentially zero in gnomAD, consistent with strong purifying selection against a severe pediatric neurodevelopmental phenotype.
Demographics: No sex-ratio skew reported (autosomal, dominant); age distribution reflects lifelong persistence with diagnosis typically in early-to-mid childhood following developmental/epilepsy workup.
First-tier test: Chromosomal microarray analysis (CMA) — recommended as the initial test because ~80% of cases arise from deletions detectable by CMA but not by single-gene sequencing.
Second-tier / complementary testing: - Multigene neurodevelopmental-disorder panel including MBD5 - Exome or genome sequencing (captures point variants missed by CMA) - Single-gene sequence analysis plus gene-targeted deletion/duplication analysis (must include noncoding exon 1, which harbors some pathogenic deletions)
Laboratory/biomarker tests: No specific biochemical or enzymatic biomarker exists; MBD5 mRNA quantification (qRT-PCR in lymphocytes/lymphoblastoid lines) has been used as a research tool to confirm dosage effect (e.g., 22.5–55.4% of normal expression in deletion carriers) but is not a standard clinical diagnostic.
Imaging: No pathognomonic neuroimaging finding; brain MRI is typically part of the standard neurodevelopmental-disorder/epilepsy workup but is nonspecific in MAND (used to exclude alternative structural causes).
Electrophysiology: EEG is central to characterizing the seizure phenotype (documenting generalized tonic-clonic, focal, atypical absence, tonic, myoclonic patterns, and episodes of convulsive/nonconvulsive status epilepticus).
Histopathology/biopsy: Not applicable — no tissue-diagnostic biopsy finding is described.
Genetic testing detail: - CMA is preferred over karyotype for initial detection given resolution needed for intragenic/smaller deletions. - FISH is generally insufficiently sensitive for the smaller intragenic events but could confirm larger cytogenetically visible deletions. - Mitochondrial DNA testing and repeat-expansion testing are not relevant to this disorder's mechanism.
Omics-based diagnostics: Not part of routine clinical diagnosis; iPSC/NPC transcriptomics and mouse transcriptomics are research tools only at this time.
Clinical diagnostic criteria: No formal consensus clinical diagnostic criteria (e.g., DSM/ICD-style) exist; diagnosis is genetically confirmed (molecular finding required) rather than clinically defined, given the nonspecific overlapping phenotype.
Differential diagnosis: Broad — essentially all causes of syndromic intellectual disability/developmental delay without pathognomonic features, including the autosomal dominant, autosomal recessive, and X-linked nonsyndromic ID phenotypic series in OMIM. Specific syndromes with mechanistic/phenotypic overlap warranting consideration: Smith-Magenis syndrome (RAI1, shares sleep/circadian and behavioral phenotype), Pitt-Hopkins syndrome (TCF4), Angelman syndrome (UBE3A), fragile X syndrome (FMR1), and Rett syndrome-spectrum disorders (MECP2, same MBD protein family).
Screening: No population newborn-screening or carrier-screening program exists (ultra-rare, predominantly de novo disorder); genetic counseling and prenatal/preimplantation testing become relevant only after a pathogenic variant is identified in an affected family member (relevant chiefly in the rare inherited/mosaic-parent scenario).
Survival/mortality: No mortality data specific to MAND were identified in the literature searched; the disorder is not classically associated with reduced life expectancy from the underlying genetic lesion itself, though uncontrolled epilepsy (including reported episodes of convulsive/nonconvulsive status epilepticus in ~30–40% of one seizure cohort) represents a recognized risk for morbidity/mortality common to severe childhood epilepsies generally.
Morbidity/function: Substantial lifelong functional impairment is typical — most affected individuals have limited-to-absent expressive speech, require ongoing multidisciplinary support (speech/OT/PT), and a majority exhibit clinically significant behavioral challenges (self-injury/aggression >60%) requiring behavioral or psychiatric intervention.
Quality of life: No validated disease-specific QOL metric; qualitatively, sleep disturbance (~90%) is described as a major contributor to impaired daytime functioning/excessive daytime sleepiness for both patients and caregivers.
Complications: Epilepsy/status epilepticus; feeding difficulties sometimes requiring gastrostomy; scoliosis/hip dysplasia (musculoskeletal surveillance recommended); chronic constipation (>80%).
Recovery potential: No spontaneous "recovery" — this is a static/chronic developmental disorder; early multidisciplinary intervention is associated with better functional/communication outcomes (standard neurodevelopmental-disorder principle applied by GeneReviews management guidance), though no controlled outcome trial specific to MAND exists.
Prognostic factors: Variant type/deletion size appears to influence severity (larger multigene deletions and certain truncating variants like p.Ser147* correlate with more severe presentations), but no formal validated prognostic biomarker or scoring system exists.
There is no disease-modifying or curative therapy; management is symptomatic and multidisciplinary, per GeneReviews consensus recommendations.
Pharmacotherapy: - Anti-seizure medications: Valproate, clonazepam, zonisamide, and clobazam are reported as effective in case series (NCIT:C15986 Pharmacotherapy for the general category). - Sleep disturbance: Melatonin, clonidine, and trazodone, combined with sleep-hygiene behavioral measures. - No MBD5-specific pharmacogenomic guidance has been established.
Advanced therapeutics: No gene therapy, cell therapy, RNA-based therapy (ASO/siRNA/mRNA), targeted small-molecule therapy, or immunotherapy is in development or clinical use specific to MBD5 haploinsufficiency; this is a candidate area for future gene-dosage-correction research (e.g., ASO-based upregulation strategies analogous to those explored for other haploinsufficiency ID syndromes) but nothing is documented in the current literature.
Surgical/interventional: Orthopedic surgical management for hip dysplasia/scoliosis as clinically indicated (NCIT:C16186 Orthopedic Surgical Procedure); gastrostomy tube placement for persistent feeding difficulty (NCIT relevant to nutritional support procedures).
Supportive/rehabilitative: - Speech-language therapy with early introduction of augmentative/alternative communication (sign language, AAC devices) — NCIT:C159273 (Speech Therapy) - Occupational and physical therapy — NCIT:C15302 (Physical Therapy) - Feeding therapy — relevant to NCIT:C15447 (Dietary Intervention) / nutritional support - Applied behavior analysis (ABA) and psychiatric consultation for aggressive/self-injurious behavior — NCIT:C181743 (Behavioral Counseling) category - Early intervention services (0–3 years) and developmental preschool (3–5 years); annual IEP review in least-restrictive educational placement
Experimental treatments: No registered clinical trials specific to MBD5 haploinsufficiency were identified in this search (searches did not surface an active ClinicalTrials.gov/ICTRP entry).
Treatment strategy / algorithm: Management follows a surveillance-and-symptom-management algorithm: developmental assessment at each visit; seizure, feeding, constipation, and sleep assessment; annual scoliosis screening; family psychosocial support assessment; multidisciplinary team including clinical genetics, neurology, developmental pediatrics, behavioral health, nutrition, and speech/OT/PT.
Suggested therapeutic_modality mapping: anti-seizure medications and sleep agents → SMALL_MOLECULE; speech/OT/PT/ABA → BEHAVIORAL; orthopedic surgery/gastrostomy → SURGERY.
No primary prevention exists for this de novo genetic disorder (no modifiable environmental or lifestyle risk factor is causal). Relevant preventive/counseling measures are exclusively in the genetic-counseling and reproductive-planning domain:
No naturally occurring veterinary or companion-animal disease caused by MBD5 ortholog disruption has been reported (no OMIA entry identified in this search). The gene is evolutionarily conserved (murine Mbd5, zebrafish mbd5), enabling engineered models (see below), but no spontaneous animal disease analog is documented. No zoonotic or cross-species transmission relevance applies, as this is a purely genetic, non-infectious disorder.
Orthologs used in model systems: - Mouse: Mbd5 (chromosome 2, syntenic region) - Zebrafish: mbd5
HUMAN_MODEL_MISMATCH consideration for dismech curation).| Citation | Topic |
|---|---|
| PMID 21981781 (Talkowski et al. 2011) | SRO mapping establishing MBD5 as sole causal locus |
| NBK390803 (GeneReviews, Mullegama/Mendoza-Londono/Elsea) | Comprehensive clinical synopsis, testing, management |
| PMID 27514998 / PMC4989212 (Mullegama & Elsea 2016) | MAND clinical/molecular review, deletion/duplication dosage data |
| PMID 33912662 (Smith-Hicks et al. 2021) | Seizure phenotype spectrum, 23-patient cohort |
| PMID 25271084 (Mullegama et al. 2014) | Circadian gene dysregulation, sleep mechanism |
| PMID 25001217 / PMC4154127 (Camarena et al. 2014) | Mbd5 gene-trap mouse generation |
| PMID 25001218 / PMC4154129 (Sanders et al. 2014) | Mbd5+/GT neurobehavioral/neuronal phenotyping |
| PMID 32503625 / PMC7275313 (Vegas et al. 2020) | Mouse brain / iPSC-neuron transcriptomics |
| PMC8163803 | iPSC-NPC transcriptome, autism gene dysregulation |
| PMID 38366571 / PMC11077058 (Guo et al. 2024) | Zebrafish Mbd5, RNA m5C, PR-DUB mechanism |
| PMC3831065 (Hodge et al.) | Extended MBD5 mutation spectrum, 78-patient cohort |
| ClinGen CCID:007440 | Dosage sensitivity curation (HI=3, TS=0) |
| Orphanet ORPHA228402 | Prevalence classification |
Notable gaps for curation: no validated disease-specific QOL instrument; no proteomics/metabolomics/single-cell/spatial transcriptomic datasets; no registered clinical trials; no veterinary/natural-disease analog; mouse-vs-human transcriptomic model discordance flagged as an open translational question.
Checked with linkml-reference-validator 0.2.1.
| Outcome | Count |
|---|---|
| References checked | 16 |
| Resolved | 16 |
| Unresolved (possible confabulation) | 0 |
| Unverifiable | 0 |
| Quoted claims checked | 1 |
| Quoted claims found in source | 0 |
| Quoted claims not found in source | 1 |
| References weighed for topical relevance | 16 |
| On topic | 12 |
| Off topic | 0 |
Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:
Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.
PMC:PMC8163803 (abstract only): "forebrain and telencephalon regionalization, neuron fate commitment"