👪

Inheritance

1

Autosomal dominant inheritance HP:0000006

Heterozygous LMNB2 missense variants, de novo in most reported cases. In one family the variant was transmitted from a clinically unaffected mother who was mosaic for it, so parental mosaicism is a recurrence-risk consideration; this is parental mosaicism and is not bound to HP:0001442.

Autosomal dominant inheritance

Show evidence (1 reference)

PMID:33033404 SUPPORT Human Clinical

"For cases P4, P5, and P12, the variant was established to be de novo, while in P7, it had been inherited from the proband's mosaic, clinically unaffected, mother"

De novo heterozygous LMNB2 p.Glu398Lys in three probands and transmission from a mosaic parent in a fourth support dominant inheritance with parental mosaicism as a recurrence route.

◈

Mechanistic Hypotheses

2

Lamin B Spindle-Orientation Defect in Neural Progenitors

lamin_b_progenitor_spindle_orientation EMERGING

B-type lamins associate with the mitotic spindle, and mice lacking B-type lamins show spindle-orientation defects in neural progenitors. The hypothesis is that dominant LMNB2 variants perturb progenitor division in the same way, depleting the progenitor pool and reducing neuron output. It has not been tested with the human variants.

Pathograph links

Nuclear Lamina Assembly Defect with Lamin Aggregates -> Neural Progenitor Spindle Misorientation Hypothesized: a defective B-type lamina perturbs spindle orientation in dividing neural progenitors.

Neural Progenitor Spindle Misorientation -> Reduced Cortical Neuron Output Hypothesized: misoriented progenitor divisions deplete the progenitor pool and reduce the number of cortical neurons generated.

Nuclear Fragility of Neural Progenitors

lamin_b_progenitor_nuclear_fragility EMERGING

A lamina built partly from assembly-defective lamin B2 may leave progenitor and migrating-neuron nuclei mechanically fragile, so that the stresses of interkinetic nuclear migration and neuronal migration increase cell death during cortical development. Proposed by analogy to LMNA variants; not tested with LMNB2 variants.

Pathograph links

Nuclear Lamina Assembly Defect with Lamin Aggregates -> Neural Progenitor Nuclear Fragility and Cell Death Hypothesized: a defective lamina leaves progenitor nuclei fragile under the mechanical stresses of interkinetic nuclear migration and neuronal migration.

Neural Progenitor Nuclear Fragility and Cell Death -> Reduced Cortical Neuron Output Hypothesized: loss of fragile progenitors and young neurons reduces the number of cortical neurons.

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Discussions and Knowledge Gaps

1

Do the brain phenotypes of lamin B2-null mice, which center on neuronal migration, tell us anything about how heterozygous dominant LMNB2 missense variants cause microcephaly without a migration defect?

HUMAN MODEL MISMATCH OPEN mcph27_null_mouse_versus_dominant_missense

Attached to

pathophysiology#Neural Progenitor Spindle Misorientation pathophysiology#Neural Progenitor Nuclear Fragility and Cell Death pathophysiology#Reduced Cortical Neuron Output

Every mechanistic step below the lamina defect is supported only by null or double-null mice. Those mice show cortical layering and migration defects, and the constitutive Lmnb2 null has a nearly normal brain size, while patients with MCPH27 have severe congenital microcephaly with no migration defect. The reporting authors attribute the difference to the human variants acting dominantly rather than through loss of lamin B2. No heterozygous knock-in of a patient variant and no patient-derived neural cell or organoid model has been reported, so which of the proposed progenitor mechanisms operates in MCPH27 is unknown.

Show evidence (1 reference)

PMID:33033404 SUPPORT BACKGROUND Model Organism

"there were neuronal migration defects resulting in abnormal layering of the cerebral cortex,18 suggesting potential discordance with the human phenotype and neuroimaging findings"

The reporting authors identify the discordance between the knockout mouse brain phenotype and the human disease.

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Pathophysiology

5

LMNB2 Rod-Domain Missense Variant Disrupting Lamin B2 Dimer Assembly

Heterozygous missense variants alter conserved residues in coiled-coil segments of the lamin B2 alpha-helical rod: Asn54 at the coil 1A intradimer interface and Glu398 at the coil 2B intradimer interface. Glu398 normally repels the Glu398 of the partner chain; the p.Glu398Lys substitution is predicted by structural modeling on lamin A/C structures to aberrantly stabilize mixed mutant/wild-type dimers. The variants are proposed to act dominantly on assembly of the lamin B2 filament that forms part of the nuclear lamina, rather than by haploinsufficiency.

LMNB2 hgnc:6638

Genetic context allele_type: missense variant_origin: DE_NOVO zygosity: HETEROZYGOUS functional_impact_category: DOMINANT_NEGATIVE

Recurrent de novo missense variants at specific residues and the absence of truncating variants led the reporting authors to favor a dominant negative mechanism (with gain of function not excluded) over haploinsufficiency. This is an inference from the variant spectrum and structural modeling, not a measured effect on endogenous lamin B2.

structural constituent of nuclear lamina GO:0160123 ↕ DYSREGULATED

nuclear lamina GO:0005652 lamin filament GO:0005638

Downstream

Nuclear Lamina Assembly Defect with Lamin Aggregates Assembly-defective lamin B2 is incorporated into the lamina and disrupts its higher-order organization.

Show evidence (3 references)

PMID:33033404 SUPPORT Human Clinical

"We identified four microcephalic individuals from the DDD cohort (P4, P5, P6, P7) and one individual from the 100kGP study (P12) with the same variant in LMNB2"

Identifies the recurrent LMNB2 p.Glu398Lys variant in five microcephalic individuals, the human genetic basis of the upstream lesion.

PMID:33033404 SUPPORT INDIRECT Computational

"Therefore the heterozygous LMNB2 p.Glu398Lys substitution would result in a subset of mismatched dimers in which, instead, interaction of the two chains would be aberrantly stabilized"

Structural modeling on homologous lamin A/C structures predicts that the recurrent variant aberrantly stabilizes mutant/wild-type dimers, the basis for a dominant effect on filament assembly.

PMID:33033404 SUPPORT INDIRECT Human Clinical

"The pathogenic variants reported here are most likely dominant negative rather than haploinsufficient given that microcephaly is not present in the Lmnb1+/- mouse."

The reporting authors' interpretation of the variant spectrum favors a dominant negative rather than haploinsufficient mechanism.

Nuclear Lamina Assembly Defect with Lamin Aggregates

Cells expressing GFP-tagged lamin B2 carrying the microcephaly variants frequently contain nuclear lamin aggregates and show altered nuclear morphology, consistent with disrupted lamin assembly in cells. The experiment used overexpression above endogenous levels, and the effect has not been shown in patient neural cells.

Lamin B Spindle-Orientation Defect in Neural Progenitors Nuclear Fragility of Neural Progenitors

LMNB2 hgnc:6638

nuclear envelope organization GO:0006998 ↕ DYSREGULATED

nuclear lamina GO:0005652

Downstream

Neural Progenitor Spindle Misorientation Hypothesized: a defective B-type lamina perturbs spindle orientation in dividing neural progenitors.

Neural Progenitor Nuclear Fragility and Cell Death Hypothesized: a defective lamina leaves progenitor nuclei fragile under the mechanical stresses of interkinetic nuclear migration and neuronal migration.

Show evidence (1 reference)

PMID:33033404 SUPPORT In Vitro

"Cells expressing the LMNB1/B2 variants frequently contained nuclear aggregates and/or significantly altered nuclear morphology in comparison to cells expressing wild-type GFP-LMNB1/2"

Transfected variant lamin B2 forms nuclear aggregates and distorts nuclear shape, the cellular readout of the assembly defect.

Neural Progenitor Spindle Misorientation

B-type lamins associate with the mitotic spindle, and mice lacking B-type lamins show defects in spindle orientation in neural progenitor cells. The reporting authors propose this as the mechanism of LMNB1/LMNB2 microcephaly, in line with the spindle defects of other primary microcephaly genes. The evidence comes from null mice, not from the heterozygous human missense variants.

Lamin B Spindle-Orientation Defect in Neural Progenitors

neural progenitor cell CL:0011020 radial glial cell CL:0000681

establishment of mitotic spindle orientation GO:0000132 ↕ DYSREGULATED

Downstream

Reduced Cortical Neuron Output Hypothesized: misoriented progenitor divisions deplete the progenitor pool and reduce the number of cortical neurons generated.

Show evidence (2 references)

PMID:22116031 SUPPORT INDIRECT Model Organism

"Defects in spindle orientation in neural progenitor cells and migration of neurons probably cause brain disorganizations found in lamin-B null mice."

Spindle-orientation defects in neural progenitors of lamin B-null mice; indirect because the mice lack both B-type lamins rather than carrying a dominant LMNB2 missense variant.

PMID:33033404 SUPPORT INDIRECT BACKGROUND Model Organism

"with defects in spindle orientation in neuronal precursor cells reported in Lmnb1 and Lmnb2 knockout mice,17 suggesting this could be the mechanism underlying microcephaly"

The human case report proposes the mouse spindle-orientation defect as the mechanism of LMNB1/LMNB2 microcephaly; the observation it cites is from knockout mice, not from this study.

Neural Progenitor Nuclear Fragility and Cell Death

The reporting authors propose that LMNB2 variants alter the physical properties of lamin filaments, making the nuclei of neural progenitors fragile under the mechanical stresses of interkinetic nuclear migration and neuronal migration and increasing cell death during brain development. The proposal rests on the analogous LMNA variant producing fragile nuclei; increased apoptosis in the cortex has been observed in lamin B2-null mouse embryos, but not with the human variants.

Nuclear Fragility of Neural Progenitors

neural progenitor cell CL:0011020 neuron CL:0000540

interkinetic nuclear migration GO:0022027 ↕ DYSREGULATED

Downstream

Reduced Cortical Neuron Output Hypothesized: loss of fragile progenitors and young neurons reduces the number of cortical neurons.

Show evidence (2 references)

PMID:33033404 SUPPORT INDIRECT Other

"Such fragility in neuronal precursors would enhance susceptibility to mechanical stresses of interkinetic nuclear migration and neuronal migration and lead to increased cell death during brain development."

States the nuclear-fragility hypothesis; it is a proposal in the discussion, not an observation in LMNB2 variant cells.

PMID:21976703 SUPPORT INDIRECT Model Organism

"In contrast, lamin B2 deficiency led to increased numbers of neurons with elongated nuclei."

Lamin B2-deficient mouse neurons have abnormally elongated nuclei, supporting a role for lamin B2 in resisting nuclear deformation; indirect because the model is a null rather than a dominant missense allele.

Reduced Cortical Neuron Output

Fewer cortical neurons are produced during fetal neurogenesis, giving a small but structurally normal cerebral cortex. In mice, forebrain-specific loss of lamin B2 reduces cortical neuron number and forebrain size.

cortical neuron CL:0000540

cerebral cortex development GO:0021987 ↕ DYSREGULATED

Animal models

Lmnb2 knockout mouse Mouse fails to recapitulate The constitutive null does not reproduce congenital microcephaly; its dominant brain phenotype is a neuronal migration defect that human MCPH27 imaging does not show.

Forebrain-specific Lmnb2 knockout mouse (Emx1-Cre Lmnb2fl/fl) Mouse partially recapitulates Reproduces reduced cortical neuron number and small forebrain, the tissue-level outcome of MCPH27.

Downstream

Primary microcephaly Reduced cortical neuron output gives a small brain and head from birth.

Simplified gyral pattern A smaller cortical sheet forms fewer and simpler gyri in some patients.

Reduced cerebral white matter volume Fewer cortical neurons project fewer axons, consistent with the global reduction in white matter seen on imaging.

Ventriculomegaly Ventricular enlargement accompanies the global reduction in white matter volume rather than reflecting obstruction.

Global developmental delay Reduced cortical neuron number underlies the neurodevelopmental impairment.

Seizure Seizures occur in a minority of patients on the background of the small cortex.

Show evidence (2 references)

PMID:21976703 SUPPORT INDIRECT Model Organism

"Emx1-Cre Lmnb2fl/fl mice had fewer cortical neurons than did WT mice"

Forebrain-specific loss of lamin B2 reduces cortical neuron number; indirect because it is a conditional null rather than the human dominant missense genotype.

PMID:33033404 SUPPORT Human Clinical

"In keeping with primary microcephaly, all but one case had a reduced OFC evident at birth, and neuroimaging demonstrated a structurally normal small brain with/without a simplified gyral pattern."

A congenitally small but structurally normal brain is the human expression of reduced prenatal cortical neuron output.

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Pathograph

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

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Phenotypes

8

Head and Neck 2

Primary microcephaly VERY_FREQUENT HP:0011451

Onset: CONGENITAL

Show evidence (2 references)

PMID:33033404 SUPPORT Human Clinical

"A severe nonsyndromic microcephaly without other malformations was consistently present."

Severe nonsyndromic microcephaly was present in every reported LMNB1/LMNB2 case.

PMID:33033404 SUPPORT Human Clinical

"In keeping with primary microcephaly, all but one case had a reduced OFC evident at birth"

The reduced head circumference is congenital in all but one case.

Sloping forehead HP:0000340

Show evidence (1 reference)

PMID:33033404 SUPPORT Human Clinical

"Facially, aside from a sloping forehead in some individuals, a syndromic diagnosis was not evident, nor was a consistent facial gestalt observed"

A sloping forehead was the only recurrent facial feature, seen in some individuals.

Nervous System 6

Global developmental delay HP:0001263

Show evidence (1 reference)

PMID:33033404 SUPPORT Human Clinical

"global developmental delay varied substantially between cases, classified as severe in four of eight DDD cases"

Developmental delay is present with variable severity.

Absent speech OCCASIONAL HP:0001344

Show evidence (1 reference)

PMID:33033404 SUPPORT Human Clinical

"with speech not attained in three older children"

Three older children in the pooled LMNB1/LMNB2 cohort had not acquired speech.

Seizure OCCASIONAL HP:0001250

Show evidence (1 reference)

PMID:33033404 SUPPORT Human Clinical

"Global developmental delay of varying severity was evident and seizures present in four cases"

Seizures occurred in four of the thirteen pooled LMNB1/LMNB2 cases.

Simplified gyral pattern OCCASIONAL HP:0009879

Show evidence (1 reference)

PMID:33033404 SUPPORT Human Clinical

"In two cases gyral simplification was noted accompanied by global reduction in white matter volume alongside increased extra-axial spaces and enlarged ventricles."

Gyral simplification was seen on imaging in two cases.

Reduced cerebral white matter volume OCCASIONAL HP:0034295

Show evidence (1 reference)

PMID:33033404 SUPPORT Human Clinical

"In two cases gyral simplification was noted accompanied by global reduction in white matter volume alongside increased extra-axial spaces and enlarged ventricles."

Global white matter reduction accompanied gyral simplification in two cases.

Ventriculomegaly OCCASIONAL HP:0002119

Show evidence (1 reference)

PMID:33033404 SUPPORT Human Clinical

"Ventricular dilatation reflects accompanying global reduction in white matter."

Enlarged ventricles accompany the reduced white matter rather than indicating obstruction.

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Genetic Associations

1

LMNB2 (Causative)

Gene: LMNB2 hgnc:6638

Show evidence (1 reference)

PMID:33033404 SUPPORT Human Clinical

"We identify dominant pathogenic variants in LMNB1 and LMNB2 as a genetic cause of primary microcephaly"

Establishes heterozygous LMNB2 variants as a cause of primary microcephaly.

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Medical Actions

3

Supportive and Developmental Care

Action: Supportive Care NCIT:C15747

No disease-specific therapy exists. Management is supportive, with developmental, physical, occupational and speech therapy according to need.

Anti-Seizure Medication

Action: Pharmacotherapy NCIT:C15986

Standard anti-seizure medication for the minority of patients with seizures.

Genetic Counseling

Action: Genetic Counseling NCIT:C15240

Counseling on de novo dominant inheritance, the 50% transmission risk from an affected individual, and residual recurrence risk from parental mosaicism, which has been documented in one family.

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Animal Models

2

Lmnb2 knockout mouse

Lamin B2-null mice die shortly after birth with a lissencephaly-like neuronal layering defect in the cerebral cortex and cerebellum caused by defective neuronal migration, while brain size at birth is nearly normal.

Species

Mouse

Genotype

Lmnb2 -/- (lacZ insertion in exon 1)

Publication

PMID:20145110

Pathograph links

Reduced Cortical Neuron Output fails to recapitulate fidelity: low The constitutive null does not reproduce congenital microcephaly; its dominant brain phenotype is a neuronal migration defect that human MCPH27 imaging does not show.

Limitations: A homozygous null allele, whereas MCPH27 is caused by heterozygous missense variants proposed to act dominantly on lamin assembly; heterozygous Lmnb2+/- mice are phenotypically normal. The model is closer to the biallelic loss-of-function human phenotype (PMID:40011009).

Show evidence (1 reference)

PMID:20145110 SUPPORT Model Organism

"The brain was nearly normal in size"

Lamin B2-null embryos have a nearly normal brain size, unlike the severe congenital microcephaly of MCPH27.

Forebrain-specific Lmnb2 knockout mouse (Emx1-Cre Lmnb2fl/fl)

Conditional deletion of Lmnb2 in the forebrain gives a small forebrain with fewer cortical neurons and disorganized neuronal layering in adult mice.

Species

Mouse

Genotype

Emx1-Cre Lmnb2 fl/fl

Publication

PMID:21976703

Pathograph links

Reduced Cortical Neuron Output partially recapitulates fidelity: low Reproduces reduced cortical neuron number and small forebrain, the tissue-level outcome of MCPH27.

Limitations: A conditional null rather than a dominant missense allele, and the mice also have disorganized neuronal layering, which MCPH27 patients do not show on imaging.

Show evidence (1 reference)

PMID:21976703 SUPPORT Model Organism

"The forebrain-specific Lmnb1- and Lmnb2-knockout models had a small forebrain with disorganized layering of neurons and nuclear shape abnormalities"

Forebrain loss of lamin B2 reduces forebrain size, the outcome modeled by this link.

{ }

Source YAML

click to show

name: Microcephaly 27, Primary, Autosomal Dominant
creation_date: "2026-10-15T15:45:00Z"
category: Mendelian
disease_term:
  preferred_term: microcephaly 27, primary, autosomal dominant
  term:
    id: MONDO:0030929
    label: microcephaly 27, primary, autosomal dominant
synonyms:
- MCPH27
- LMNB2-related primary microcephaly
description: >-
  Microcephaly 27, primary, autosomal dominant (MCPH27) is a severe congenital
  primary microcephaly caused by heterozygous, usually de novo, missense
  variants in LMNB2, which encodes the B-type nuclear lamin lamin B2. It was
  defined together with the LMNB1 form (MCPH26) as a lamin B-associated
  laminopathy. Affected individuals have severe microcephaly present from birth
  without intrauterine growth restriction or major malformations, global
  developmental delay of variable severity, and, in a minority, seizures;
  neuroimaging shows a small, structurally normal brain, sometimes with a
  simplified gyral pattern and reduced white matter, and no neuronal migration
  defect. The reported variants (recurrent p.Glu398Lys and p.Asn54His) alter
  conserved residues at dimer interfaces of the lamin coiled-coil rod and are
  proposed to act dominantly on lamin filament assembly; transfected variant
  lamin B2 forms nuclear aggregates and distorts nuclear shape. How a defective
  nuclear lamina reduces cortical neuron output is not established: disrupted
  spindle orientation in neural progenitors and mechanical fragility of
  progenitor nuclei are the two hypotheses proposed.
parents:
- autosomal dominant primary microcephaly
references:
- reference: PMID:33033404
  title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
- reference: PMID:20145110
  title: Abnormal development of the cerebral cortex and cerebellum in the setting of lamin B2 deficiency.
- reference: PMID:21976703
  title: Deficiencies in lamin B1 and lamin B2 cause neurodevelopmental defects and distinct nuclear shape abnormalities in neurons.
- reference: PMID:22116031
  title: Mouse B-type lamins are required for proper organogenesis but not by embryonic stem cells.
- reference: PMID:40011009
  title: Homozygous loss of function variant in LMNB2 gene causes major brain malformation and perinatal death.
inheritance:
- name: Autosomal dominant inheritance
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    Heterozygous LMNB2 missense variants, de novo in most reported cases. In
    one family the variant was transmitted from a clinically unaffected mother
    who was mosaic for it, so parental mosaicism is a recurrence-risk
    consideration; this is parental mosaicism and is not bound to HP:0001442.
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      For cases P4, P5, and P12, the variant was established to be de novo,
      while in P7, it had been inherited from the proband's mosaic, clinically
      unaffected, mother
    explanation: >-
      De novo heterozygous LMNB2 p.Glu398Lys in three probands and transmission
      from a mosaic parent in a fourth support dominant inheritance with
      parental mosaicism as a recurrence route.
mechanistic_hypotheses:
- hypothesis_group_id: lamin_b_progenitor_spindle_orientation
  hypothesis_label: Lamin B Spindle-Orientation Defect in Neural Progenitors
  status: EMERGING
  description: >-
    B-type lamins associate with the mitotic spindle, and mice lacking B-type
    lamins show spindle-orientation defects in neural progenitors. The
    hypothesis is that dominant LMNB2 variants perturb progenitor division in
    the same way, depleting the progenitor pool and reducing neuron output. It
    has not been tested with the human variants.
- hypothesis_group_id: lamin_b_progenitor_nuclear_fragility
  hypothesis_label: Nuclear Fragility of Neural Progenitors
  status: EMERGING
  description: >-
    A lamina built partly from assembly-defective lamin B2 may leave progenitor
    and migrating-neuron nuclei mechanically fragile, so that the stresses of
    interkinetic nuclear migration and neuronal migration increase cell death
    during cortical development. Proposed by analogy to LMNA variants; not
    tested with LMNB2 variants.
pathophysiology:
- name: LMNB2 Rod-Domain Missense Variant Disrupting Lamin B2 Dimer Assembly
  description: >-
    Heterozygous missense variants alter conserved residues in coiled-coil
    segments of the lamin B2 alpha-helical rod: Asn54 at the coil 1A intradimer
    interface and Glu398 at the coil 2B intradimer interface. Glu398 normally
    repels the Glu398 of the partner chain; the p.Glu398Lys substitution is
    predicted by structural modeling on lamin A/C structures to aberrantly
    stabilize mixed mutant/wild-type dimers. The variants are proposed to act
    dominantly on assembly of the lamin B2 filament that forms part of the
    nuclear lamina, rather than by haploinsufficiency.
  biological_scale: MOLECULAR
  genetic_context:
    functional_impact_category: DOMINANT_NEGATIVE
    variant_origin: DE_NOVO
    zygosity: HETEROZYGOUS
    allele_type: missense
    description: >-
      Recurrent de novo missense variants at specific residues and the absence
      of truncating variants led the reporting authors to favor a dominant
      negative mechanism (with gain of function not excluded) over
      haploinsufficiency. This is an inference from the variant spectrum and
      structural modeling, not a measured effect on endogenous lamin B2.
  genes:
  - preferred_term: LMNB2
    term:
      id: hgnc:6638
      label: LMNB2
  molecular_functions:
  - preferred_term: structural constituent of nuclear lamina
    term:
      id: GO:0160123
      label: structural constituent of nuclear lamina
    modifier: DYSREGULATED
  cellular_components:
  - preferred_term: nuclear lamina
    term:
      id: GO:0005652
      label: nuclear lamina
  - preferred_term: lamin filament
    term:
      id: GO:0005638
      label: lamin filament
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We identified four microcephalic individuals from the DDD cohort (P4, P5,
      P6, P7) and one individual from the 100kGP study (P12) with the same
      variant in LMNB2
    explanation: >-
      Identifies the recurrent LMNB2 p.Glu398Lys variant in five microcephalic
      individuals, the human genetic basis of the upstream lesion.
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      Therefore the heterozygous LMNB2 p.Glu398Lys substitution would result in
      a subset of mismatched dimers in which, instead, interaction of the two
      chains would be aberrantly stabilized
    explanation: >-
      Structural modeling on homologous lamin A/C structures predicts that the
      recurrent variant aberrantly stabilizes mutant/wild-type dimers, the
      basis for a dominant effect on filament assembly.
    directness: INDIRECT
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The pathogenic variants reported here are most likely dominant negative
      rather than haploinsufficient given that microcephaly is not present in
      the Lmnb1+/- mouse.
    explanation: >-
      The reporting authors' interpretation of the variant spectrum favors a
      dominant negative rather than haploinsufficient mechanism.
    directness: INDIRECT
  downstream:
  - target: Nuclear Lamina Assembly Defect with Lamin Aggregates
    description: >-
      Assembly-defective lamin B2 is incorporated into the lamina and disrupts
      its higher-order organization.
- name: Nuclear Lamina Assembly Defect with Lamin Aggregates
  description: >-
    Cells expressing GFP-tagged lamin B2 carrying the microcephaly variants
    frequently contain nuclear lamin aggregates and show altered nuclear
    morphology, consistent with disrupted lamin assembly in cells. The
    experiment used overexpression above endogenous levels, and the effect has
    not been shown in patient neural cells.
  biological_scale: CELLULAR
  genes:
  - preferred_term: LMNB2
    term:
      id: hgnc:6638
      label: LMNB2
  biological_processes:
  - preferred_term: nuclear envelope organization
    term:
      id: GO:0006998
      label: nuclear envelope organization
    modifier: DYSREGULATED
  cellular_components:
  - preferred_term: nuclear lamina
    term:
      id: GO:0005652
      label: nuclear lamina
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Cells expressing the LMNB1/B2 variants frequently contained nuclear
      aggregates and/or significantly altered nuclear morphology in comparison
      to cells expressing wild-type GFP-LMNB1/2
    explanation: >-
      Transfected variant lamin B2 forms nuclear aggregates and distorts nuclear
      shape, the cellular readout of the assembly defect.
  downstream:
  - target: Neural Progenitor Spindle Misorientation
    description: >-
      Hypothesized: a defective B-type lamina perturbs spindle orientation in
      dividing neural progenitors.
    hypothesis_groups:
    - lamin_b_progenitor_spindle_orientation
  - target: Neural Progenitor Nuclear Fragility and Cell Death
    description: >-
      Hypothesized: a defective lamina leaves progenitor nuclei fragile under
      the mechanical stresses of interkinetic nuclear migration and neuronal
      migration.
    hypothesis_groups:
    - lamin_b_progenitor_nuclear_fragility
- name: Neural Progenitor Spindle Misorientation
  conforms_to: neural_progenitor_centrosome_spindle_dysfunction#Abnormal Progenitor Division and Fate Choice
  description: >-
    B-type lamins associate with the mitotic spindle, and mice lacking B-type
    lamins show defects in spindle orientation in neural progenitor cells. The
    reporting authors propose this as the mechanism of LMNB1/LMNB2
    microcephaly, in line with the spindle defects of other primary
    microcephaly genes. The evidence comes from null mice, not from the
    heterozygous human missense variants.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  - preferred_term: radial glial cell
    term:
      id: CL:0000681
      label: radial glial cell
  biological_processes:
  - preferred_term: establishment of mitotic spindle orientation
    term:
      id: GO:0000132
      label: establishment of mitotic spindle orientation
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:22116031
    reference_title: Mouse B-type lamins are required for proper organogenesis but not by embryonic stem cells.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: INDIRECT
    snippet: >-
      Defects in spindle orientation in neural progenitor cells and migration of
      neurons probably cause brain disorganizations found in lamin-B null mice.
    explanation: >-
      Spindle-orientation defects in neural progenitors of lamin B-null mice;
      indirect because the mice lack both B-type lamins rather than carrying a
      dominant LMNB2 missense variant.
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: BACKGROUND
    directness: INDIRECT
    snippet: >-
      with defects in spindle orientation in neuronal precursor cells reported
      in Lmnb1 and Lmnb2 knockout mice,17 suggesting this could be the mechanism
      underlying microcephaly
    explanation: >-
      The human case report proposes the mouse spindle-orientation defect as
      the mechanism of LMNB1/LMNB2 microcephaly; the observation it cites is
      from knockout mice, not from this study.
  downstream:
  - target: Reduced Cortical Neuron Output
    description: >-
      Hypothesized: misoriented progenitor divisions deplete the progenitor
      pool and reduce the number of cortical neurons generated.
    hypothesis_groups:
    - lamin_b_progenitor_spindle_orientation
- name: Neural Progenitor Nuclear Fragility and Cell Death
  description: >-
    The reporting authors propose that LMNB2 variants alter the physical
    properties of lamin filaments, making the nuclei of neural progenitors
    fragile under the mechanical stresses of interkinetic nuclear migration
    and neuronal migration and increasing cell death during brain development.
    The proposal rests on the analogous LMNA variant producing fragile nuclei;
    increased apoptosis in the cortex has been observed in lamin B2-null mouse
    embryos, but not with the human variants.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: interkinetic nuclear migration
    term:
      id: GO:0022027
      label: interkinetic nuclear migration
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: OTHER
    directness: INDIRECT
    snippet: >-
      Such fragility in neuronal precursors would enhance susceptibility to
      mechanical stresses of interkinetic nuclear migration and neuronal
      migration and lead to increased cell death during brain development.
    explanation: >-
      States the nuclear-fragility hypothesis; it is a proposal in the
      discussion, not an observation in LMNB2 variant cells.
  - reference: PMID:21976703
    reference_title: Deficiencies in lamin B1 and lamin B2 cause neurodevelopmental defects and distinct nuclear shape abnormalities in neurons.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: INDIRECT
    snippet: >-
      In contrast, lamin B2 deficiency led to increased numbers of neurons with
      elongated nuclei.
    explanation: >-
      Lamin B2-deficient mouse neurons have abnormally elongated nuclei,
      supporting a role for lamin B2 in resisting nuclear deformation; indirect
      because the model is a null rather than a dominant missense allele.
  downstream:
  - target: Reduced Cortical Neuron Output
    description: >-
      Hypothesized: loss of fragile progenitors and young neurons reduces the
      number of cortical neurons.
    hypothesis_groups:
    - lamin_b_progenitor_nuclear_fragility
- name: Reduced Cortical Neuron Output
  conforms_to: neural_progenitor_centrosome_spindle_dysfunction#Abnormal Cortical Neuron Output and Gyration
  description: >-
    Fewer cortical neurons are produced during fetal neurogenesis, giving a
    small but structurally normal cerebral cortex. In mice, forebrain-specific
    loss of lamin B2 reduces cortical neuron number and forebrain size.
  biological_scale: TISSUE
  cell_types:
  - preferred_term: cortical neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: cerebral cortex development
    term:
      id: GO:0021987
      label: cerebral cortex development
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:21976703
    reference_title: Deficiencies in lamin B1 and lamin B2 cause neurodevelopmental defects and distinct nuclear shape abnormalities in neurons.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: INDIRECT
    snippet: >-
      Emx1-Cre Lmnb2fl/fl mice had fewer cortical neurons than did WT mice
    explanation: >-
      Forebrain-specific loss of lamin B2 reduces cortical neuron number;
      indirect because it is a conditional null rather than the human dominant
      missense genotype.
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In keeping with primary microcephaly, all but one case had a reduced OFC
      evident at birth, and neuroimaging demonstrated a structurally normal
      small brain with/without a simplified gyral pattern.
    explanation: >-
      A congenitally small but structurally normal brain is the human
      expression of reduced prenatal cortical neuron output.
  downstream:
  - target: Primary microcephaly
    description: Reduced cortical neuron output gives a small brain and head from birth.
  - target: Simplified gyral pattern
    description: A smaller cortical sheet forms fewer and simpler gyri in some patients.
  - target: Reduced cerebral white matter volume
    description: >-
      Fewer cortical neurons project fewer axons, consistent with the global
      reduction in white matter seen on imaging.
  - target: Ventriculomegaly
    description: >-
      Ventricular enlargement accompanies the global reduction in white matter
      volume rather than reflecting obstruction.
  - target: Global developmental delay
    description: Reduced cortical neuron number underlies the neurodevelopmental impairment.
  - target: Seizure
    description: Seizures occur in a minority of patients on the background of the small cortex.
phenotypes:
- name: Primary microcephaly
  category: Neurological
  frequency: VERY_FREQUENT
  description: >-
    Severe microcephaly present from birth in nearly all reported individuals,
    without intrauterine growth restriction or other major malformations. The
    published frequencies pool LMNB1 and LMNB2 cases.
  phenotype_term:
    preferred_term: Severe congenital primary microcephaly
    term:
      id: HP:0011451
      label: Primary microcephaly
    onset:
      onset_category: CONGENITAL
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A severe nonsyndromic microcephaly without other malformations was
      consistently present.
    explanation: Severe nonsyndromic microcephaly was present in every reported LMNB1/LMNB2 case.
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In keeping with primary microcephaly, all but one case had a reduced OFC
      evident at birth
    explanation: The reduced head circumference is congenital in all but one case.
- name: Global developmental delay
  category: Neurological
  description: >-
    Global developmental delay of variable severity, severe in about half of
    the DDD-ascertained cases.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      global developmental delay varied substantially between cases, classified
      as severe in four of eight DDD cases
    explanation: Developmental delay is present with variable severity.
- name: Absent speech
  category: Neurological
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Absent speech
    term:
      id: HP:0001344
      label: Absent speech
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: with speech not attained in three older children
    explanation: Three older children in the pooled LMNB1/LMNB2 cohort had not acquired speech.
- name: Seizure
  category: Neurological
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Global developmental delay of varying severity was evident and seizures
      present in four cases
    explanation: Seizures occurred in four of the thirteen pooled LMNB1/LMNB2 cases.
- name: Simplified gyral pattern
  category: Neurological
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Simplified gyral pattern
    term:
      id: HP:0009879
      label: Simplified gyral pattern
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In two cases gyral simplification was noted accompanied by global
      reduction in white matter volume alongside increased extra-axial spaces
      and enlarged ventricles.
    explanation: Gyral simplification was seen on imaging in two cases.
- name: Reduced cerebral white matter volume
  category: Neurological
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Reduced cerebral white matter volume
    term:
      id: HP:0034295
      label: Reduced cerebral white matter volume
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In two cases gyral simplification was noted accompanied by global
      reduction in white matter volume alongside increased extra-axial spaces
      and enlarged ventricles.
    explanation: Global white matter reduction accompanied gyral simplification in two cases.
- name: Ventriculomegaly
  category: Neurological
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Ventriculomegaly
    term:
      id: HP:0002119
      label: Ventriculomegaly
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Ventricular dilatation reflects accompanying global reduction in white
      matter.
    explanation: Enlarged ventricles accompany the reduced white matter rather than indicating obstruction.
- name: Sloping forehead
  category: Craniofacial
  phenotype_term:
    preferred_term: Sloping forehead
    term:
      id: HP:0000340
      label: Sloping forehead
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Facially, aside from a sloping forehead in some individuals, a syndromic
      diagnosis was not evident, nor was a consistent facial gestalt observed
    explanation: A sloping forehead was the only recurrent facial feature, seen in some individuals.
genetic:
- name: LMNB2
  association: Causative
  gene_term:
    preferred_term: LMNB2
    term:
      id: hgnc:6638
      label: LMNB2
  notes: >-
    No ClinGen gene-disease validity assertion for LMNB2 and this disease was
    found in the committed ClinGen export (cache/clingen/gene_validity.csv), so
    gene_disease_validity is left absent. Biallelic LMNB2 loss of function
    (PMID:40011009, a perinatal-lethal brain malformation), homozygous
    p.His157Tyr in progressive myoclonus epilepsy, and LMNB2 variants reported
    in acquired partial lipodystrophy are different allelic conditions and are
    not part of this entry.
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We identify dominant pathogenic variants in LMNB1 and LMNB2 as a genetic
      cause of primary microcephaly
    explanation: Establishes heterozygous LMNB2 variants as a cause of primary microcephaly.
treatments:
- name: Supportive and Developmental Care
  description: >-
    No disease-specific therapy exists. Management is supportive, with
    developmental, physical, occupational and speech therapy according to need.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
- name: Anti-Seizure Medication
  description: Standard anti-seizure medication for the minority of patients with seizures.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
- name: Genetic Counseling
  description: >-
    Counseling on de novo dominant inheritance, the 50% transmission risk from
    an affected individual, and residual recurrence risk from parental
    mosaicism, which has been documented in one family.
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
animal_models:
- name: Lmnb2 knockout mouse
  species: Mouse
  genotype: Lmnb2 -/- (lacZ insertion in exon 1)
  publication: PMID:20145110
  description: >-
    Lamin B2-null mice die shortly after birth with a lissencephaly-like
    neuronal layering defect in the cerebral cortex and cerebellum caused by
    defective neuronal migration, while brain size at birth is nearly normal.
  modeled_mechanisms:
  - target: Reduced Cortical Neuron Output
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: >-
      The constitutive null does not reproduce congenital microcephaly; its
      dominant brain phenotype is a neuronal migration defect that human
      MCPH27 imaging does not show.
    limitations: >-
      A homozygous null allele, whereas MCPH27 is caused by heterozygous
      missense variants proposed to act dominantly on lamin assembly;
      heterozygous Lmnb2+/- mice are phenotypically normal. The model is closer
      to the biallelic loss-of-function human phenotype (PMID:40011009).
    evidence:
    - reference: PMID:20145110
      reference_title: Abnormal development of the cerebral cortex and cerebellum in the setting of lamin B2 deficiency.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: The brain was nearly normal in size
      explanation: Lamin B2-null embryos have a nearly normal brain size, unlike the severe congenital microcephaly of MCPH27.
- name: Forebrain-specific Lmnb2 knockout mouse (Emx1-Cre Lmnb2fl/fl)
  species: Mouse
  genotype: Emx1-Cre Lmnb2 fl/fl
  publication: PMID:21976703
  description: >-
    Conditional deletion of Lmnb2 in the forebrain gives a small forebrain
    with fewer cortical neurons and disorganized neuronal layering in adult
    mice.
  modeled_mechanisms:
  - target: Reduced Cortical Neuron Output
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: >-
      Reproduces reduced cortical neuron number and small forebrain, the
      tissue-level outcome of MCPH27.
    limitations: >-
      A conditional null rather than a dominant missense allele, and the mice
      also have disorganized neuronal layering, which MCPH27 patients do not
      show on imaging.
    evidence:
    - reference: PMID:21976703
      reference_title: Deficiencies in lamin B1 and lamin B2 cause neurodevelopmental defects and distinct nuclear shape abnormalities in neurons.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        The forebrain-specific Lmnb1- and Lmnb2-knockout models had a small
        forebrain with disorganized layering of neurons and nuclear shape
        abnormalities
      explanation: Forebrain loss of lamin B2 reduces forebrain size, the outcome modeled by this link.
discussions:
- discussion_id: mcph27_null_mouse_versus_dominant_missense
  prompt: >-
    Do the brain phenotypes of lamin B2-null mice, which center on neuronal
    migration, tell us anything about how heterozygous dominant LMNB2 missense
    variants cause microcephaly without a migration defect?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Neural Progenitor Spindle Misorientation
  - pathophysiology#Neural Progenitor Nuclear Fragility and Cell Death
  - pathophysiology#Reduced Cortical Neuron Output
  rationale: >-
    Every mechanistic step below the lamina defect is supported only by null
    or double-null mice. Those mice show cortical layering and migration
    defects, and the constitutive Lmnb2 null has a nearly normal brain size,
    while patients with MCPH27 have severe congenital microcephaly with no
    migration defect. The reporting authors attribute the difference to the
    human variants acting dominantly rather than through loss of lamin B2.
    No heterozygous knock-in of a patient variant and no patient-derived
    neural cell or organoid model has been reported, so which of the proposed
    progenitor mechanisms operates in MCPH27 is unknown.
  evidence:
  - reference: PMID:33033404
    reference_title: Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: BACKGROUND
    snippet: >-
      there were neuronal migration defects resulting in abnormal layering of
      the cerebral cortex,18 suggesting potential discordance with the human
      phenotype and neuroimaging findings
    explanation: The reporting authors identify the discordance between the knockout mouse brain phenotype and the human disease.
notes: >-
  Phenotype frequencies come from the founding report, which pools six LMNB2
  and seven LMNB1 individuals; per-gene detail is in its supplementary tables.
  LMNB1-related microcephaly (MCPH26) has the same clinical picture but is a
  separate MONDO disease and is not covered here. The molecular function
  binding GO:0160123 (structural constituent of nuclear lamina) is the GO
  term for the activity of a lamina structural protein; current QuickGO
  annotation of human LMNB2 (UniProt Q03252) carries the broader
  phylogenetically inferred GO:0005200 (structural constituent of
  cytoskeleton).

📚

References & Deep Research

References

5

PMID:33033404

Heterozygous lamin B1 and lamin B2 variants cause primary microcephaly and define a novel laminopathy.

No top-level findings curated for this source.

PMID:20145110

Abnormal development of the cerebral cortex and cerebellum in the setting of lamin B2 deficiency.

No top-level findings curated for this source.

PMID:21976703

Deficiencies in lamin B1 and lamin B2 cause neurodevelopmental defects and distinct nuclear shape abnormalities in neurons.

No top-level findings curated for this source.

PMID:22116031

Mouse B-type lamins are required for proper organogenesis but not by embryonic stem cells.

No top-level findings curated for this source.

PMID:40011009

Homozygous loss of function variant in LMNB2 gene causes major brain malformation and perinatal death.

No top-level findings curated for this source.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Create: Microcephaly 27, Primary, Autosomal Dominant · 2026-10-15T15:43:56Z · View source

New standalone entry for MCPH27 (MONDO:0030929), caused by heterozygous, mostly de novo LMNB2 missense variants. Kept separate from Autosomal_Recessive_Primary_Microcephaly (whose MONDO descendants exclude MCPH26/MCPH27), from the LMNB1 form (MCPH26, no entry yet), and from LMNB2 allelic conditions (biallelic LoF perinatal brain malformation, PME, acquired partial lipodystrophy). Deep-research report: research/Microcephaly_27_Primary_Autosomal_Dominant-deep-research-claude_code.md (falcon returned 503, claude_code used). All snippets quoted from cached PMIDs 33033404, 20145110, 21976703, 22116031; the two progenitor-mechanism branches are recorded as EMERGING hypotheses because only null mice support them, with a HUMAN_MODEL_MISMATCH discussion. LMNB2 bound to GO:0160123 structural constituent of nuclear lamina. Validated with validate-disorders, validate-terms and count-verified-snippets.

Claude Code ▸

Research report: Microcephaly 27, Primary, Autosomal Dominant (MCPH27, *LMNB2*)

claude-haiku-5-5, claude-opus-5-5 15 citations 2026-10-15T15:34:12.339742

I'm checking a few more mouse-model and mechanism citations before writing the MCPH27 report.

Research report: Microcephaly 27, Primary, Autosomal Dominant (MCPH27, LMNB2)

Scope and access. PubMed MCP search was not permitted in this session. The report rests on two sources:

Full text read: Parry et al. 2021 (PMID:33033404) and the abstract of Desgrouas et al. 2025 (PMID:40011009). Both are already in this worktree's references_cache/.
Web search only: OMIM/LOVD, PanelApp, ClinVar Miner and the mouse-model papers. I confirmed their titles and PMIDs, but I did not read their abstracts here.

Quotes marked [cached] are exact text from the cache files. Everything else is paraphrased. Fetch those references with just fetch-reference before taking a snippet from them.

The literature is very small. One primary case series reports six LMNB2 individuals. I found no follow-up case reports for 2022–2024 by web search. Several template sections therefore come back "no data".

1. Disease information

Overview. MCPH27 is a dominant, mostly de novo form of severe primary microcephaly. It is caused by heterozygous missense variants in LMNB2, which encodes lamin B2, a component of the nuclear lamina. Parry et al. described it as a new kind of laminopathy, together with the LMNB1 form (MCPH26).

"We identify dominant pathogenic variants in LMNB1 and LMNB2 as a genetic cause of primary microcephaly, implicating a major structural component of the nuclear envelope in its etiology and defining a new form of laminopathy." — PMID:33033404 [cached]

Identifier	Value	Source
MONDO	MONDO:0030929	template; ClinVar Miner condition 30929
OMIM (phenotype)	619180	LOVD #07163, PanelApp AUS
OMIM (gene)	*150341 LMNB2 (not verified this session)	—
Disease Ontology	DOID:0051038	DO
Orphanet / ICD	No specific code found. Probably falls under a general primary microcephaly code.	—

Synonyms: MCPH27; LMNB2-related primary microcephaly; lamin B2-associated microcephaly. The broader term "lamin B-associated laminopathy" also covers MCPH26 (LMNB1).
Data type: The phenotype comes from a research cohort analysis of individual patients (DDD exomes and 100,000 Genomes Project genomes, with HPO terms extracted per patient). It is not drawn from a disease-level aggregate.

2. Etiology

Cause: Monoallelic LMNB2 missense variants in the coiled-coil α-helical rod domain. Most arise de novo.
Genetic risk factors: Only the causal variants (Section 4). No susceptibility loci or modifier genes have been described.
Environmental risk, protective factors, gene–environment interactions: None reported. This is a monogenic developmental disorder.
Parental mosaicism is a real recurrence risk. In one family the variant came from a mosaic mother who was clinically unaffected:

"in P7, it had been inherited from the proband's mosaic, clinically unaffected, mother" — PMID:33033404 [cached]

3. Phenotypes

The data come from 13 LMNB1/LMNB2 patients analysed together. The paper gives pooled figures, so per-gene frequencies for the six LMNB2 individuals are only in its supplementary tables (S1–S3, S5), which I did not access.

Phenotype	Type	Onset / course	Frequency (pooled)	Candidate HPO (verify every ID)
Severe microcephaly, OFC −5.85 ± 1.14 SD	sign	congenital, nonprogressive	13/13	Primary microcephaly HP:0011451 (now labelled "Congenital microcephaly"?); Severe microcephaly
Microcephaly present at birth	sign	neonatal	12/13 ("all but one")	as above
Global developmental delay, mild to severe	neurodevelopmental	infancy	all; severe in 4/8 DDD cases	Global developmental delay HP:0001263
Speech not attained	neurodevelopmental	childhood	3 older children	Absent speech HP:0001344
Intellectual disability	neurodevelopmental	childhood	implied (OMIM: "impaired intellectual development")	Intellectual disability HP:0001249
Seizures	neurological	variable	4/13	Seizure HP:0001250
Simplified gyral pattern	imaging	congenital, nonprogressive	2/13	Simplified gyral pattern HP:0009879
Reduced white-matter volume, ventriculomegaly, wide extra-axial spaces	imaging	congenital	2/13	Ventriculomegaly HP:0002119; Reduced cerebral white matter volume (look up)
Sloping forehead	dysmorphic	congenital	"some"	Sloping forehead HP:0000340
Normal birth weight and stature	negative finding	—	most	(state as absent IUGR / short stature)

Key quotes [cached, PMID:33033404]:

"All LMNB1/2 cases had severe microcephaly (OFC −5.85 ± 1.14 SD, Fig. 2a, Table S5), evident from birth in all but one case."

"Global developmental delay of varying severity was evident and seizures present in four cases"

"Neuroimaging demonstrated a structurally normal brain, without evidence of abnormal neuronal migration"

"In P8, where serial scans were available, this was nonprogressive."

"global developmental delay varied substantially between cases, classified as severe in four of eight DDD cases, with speech not attained in three older children."

Notable negatives. There was no IUGR, no major malformations, no consistent facial gestalt and no migration defect on imaging.

Quality of life. No validated QoL data exist. The disability burden is set by the severity of developmental delay and intellectual disability and by the seizures.

4. Genetic / molecular information

Gene: LMNB2 (lamin B2), on 19p13.3. HGNC id is probably hgnc:6638; look it up before binding.

Pathogenic variants (NM_032737.4) [cached]:

Variant	Domain	Recurrence	De novo	gnomAD v2.1
c.1192G>A p.(Glu398Lys)	coil 2B, intradimer interface	5 individuals (P4, P5, P6, P7, P12)	P4, P5, P12; P7 inherited from mosaic mother	absent
c.160A>C p.(Asn54His)	coil 1A, intradimer interface	1	yes	absent

"We identified four microcephalic individuals from the DDD cohort (P4, P5, P6, P7) and one individual from the 100kGP study (P12) with the same variant in LMNB2 (NM_032737.4: c.1192G>A, p.Glu398Lys)" [cached]

Variant class: Missense only. No truncating variants have been seen in dominant cases.
Functional consequence: Proposed to be dominant-negative or gain of function, not haploinsufficiency:

"The pathogenic variants reported here are most likely dominant negative rather than haploinsufficient given that microcephaly is not present in the Lmnb1+/− mouse. The recurrent nature of the pathogenic variants at specific residues and absence of truncating variants favors gain of function or dominant negative mechanisms." [cached]

The "Lmnb1+/−" argument is drawn from the paralog. No Lmnb2+/− brain-size data were cited. - Origin: Germline; de novo or inherited from a mosaic parent. - Classification: - ClinVar Miner for MONDO condition 30929: 3 Pathogenic, 3 VUS and 1 Likely benign submissions (ClinVar Miner). - PanelApp Green (high evidence) for severe microcephaly in both Genomics England and Australia (GE PanelApp, PanelApp AUS). - I found no ClinGen gene-disease validity curation and no GenCC tier. Leave gene_disease_validity absent unless a source tier is found.

Allelic disorders of LMNB2 (keep these separate, see Section 9 on the lump/split question):

Autosomal recessive progressive myoclonus epilepsy with early ataxia. Homozygous p.His157Tyr in a consanguineous Palestinian Arab family; the mutant protein was defective at forming assembly arrays. Damiano et al., Hum Mol Genet 2015, PMID:25954030 (source).
Susceptibility to acquired partial lipodystrophy (OMIM 608709). Hegele et al., AJHG 2006, PMID:16826530. The reported variants are common in gnomAD, and PanelApp AUS rates the gene Amber with GenCC at "Limited" (PanelApp AUS lipodystrophy).
Biallelic loss of function with lethal brain malformation. A homozygous LoF variant in two related newborns (PMID:40011009, [cached]):

"Both newborns died in the perinatal period and exhibited a similar phenotype at birth, including severe brain development abnormalities, which closely mirror findings observed in several Lmnb2-deficient mouse models."

"Western blot and immunofluorescence cell labelling performed on the patient's fibroblasts obtained at birth confirmed the complete absence of lamin B2 and revealed an increase in lamin B1, together with alterations in alpha-tubulin and vimentin organisation."

Genomics England changed LMNB2's inheritance to "BOTH monoallelic and biallelic" in March 2026, presumably because of this report.

Other categories:

Modifier genes: None known.
Epigenetics: None disease-specific. In general, B-type lamins tether lamina-associated domains, but lamin B binding is not strictly required for silencing in mouse ESCs (Kim et al. 2011, PMID:22116031).
Chromosomal abnormalities: Not part of MCPH27. Contrast LMNB1 duplication, which causes adult-onset leukodystrophy.

5. Environmental information

None reported for environmental, lifestyle or infectious factors. Not applicable.

6. Mechanism / pathophysiology

Ordered causal chain

A heterozygous germline missense variant (most often de novo p.Glu398Lys) changes a conserved residue at a dimer interface in the lamin B2 coiled-coil rod. (Human genetic evidence: demonstrated.)
This leads to abnormal dimer and filament assembly. (Inferred from modelling, so computational.)
Glu398 normally repels its partner chain's Glu398. Lys398 forms an ionic bond with wild-type Glu398 and over-stabilises mixed mutant/wild-type dimers (FoldX ΔΔG −2.0 kcal/mol).
Asn54 sits at the coil 1A intradimer interface.

"the heterozygous LMNB2 p.Glu398Lys substitution would result in a subset of mismatched dimers in which, instead, interaction of the two chains would be aberrantly stabilized" [cached] 3. This results in a dominant-negative "poisoning" of the higher-order lamina. (Inferred from recurrence, the absence of truncating variants, and the LMNA analogy.) 4. This results in nuclear lamin aggregates and abnormal nuclear shape. (In vitro, with GFP fusions overexpressed in cultured cells.)

"Cells expressing the LMNB1/B2 variants frequently contained nuclear aggregates and/or significantly altered nuclear morphology in comparison to cells expressing wild-type GFP-LMNB1/2" [cached]

The pathway then branches (hypothesised, not shown in human tissue):
5a. Mitotic defect. B-type lamins associate with the mitotic spindle. Their loss in mouse neural progenitors disturbs spindle orientation. This is proposed to shift progenitors from symmetric proliferative to asymmetric or neurogenic divisions, depleting the progenitor pool and reducing neuron output. (Mouse: Kim et al. 2011, PMID:22116031, authors' "probably"; spindle-matrix work: Tsai et al. 2006, Science, PMID:16543416, not verified this session.)
5b. Nuclear fragility. A mechanically fragile nucleus is more easily damaged during interkinetic nuclear migration and neuronal migration, which is proposed to increase progenitor and neuron death. (Analogy to the LMNA equivalent of LMNB1 p.Lys33del; speculative.)

"B-type lamins associate with the mitotic spindle21 with defects in spindle orientation in neuronal precursor cells reported in Lmnb1 and Lmnb2 knockout mice,17 suggesting this could be the mechanism underlying microcephaly." [cached]

"Such fragility in neuronal precursors would enhance susceptibility to mechanical stresses of interkinetic nuclear migration and neuronal migration and lead to increased cell death during brain development." [cached] 6. Both branches lead to fewer cortical neurons and a reduced cerebral cortex volume during fetal neurogenesis. (Inferred.) 7. This results in congenital microcephaly with a structurally normal or simplified-gyral brain and reduced white matter, followed by developmental delay, intellectual disability and, in some patients, seizures. (Human clinical: demonstrated.)

Discordance to record. Biallelic-null mice (and the 2025 biallelic-LoF human newborns) have migration defects and lissencephaly-like lamination. Heterozygous MCPH27 patients show no migration defect. This suggests the dominant missense mechanism is different from null loss. It is a good candidate for a HUMAN_MODEL_MISMATCH discussion.

Suggested ontology terms (all IDs to be looked up; none are verified)

Category	Suggested terms
GO biological process	nuclear envelope organization (GO:0006998); intermediate filament cytoskeleton organization; mitotic spindle orientation (GO:0000132); cerebral cortex development (GO:0021987); neuron migration (GO:0001764); neural precursor cell proliferation (GO:0061351)
GO cellular component	nuclear lamina (GO:0005652); nuclear envelope; spindle
GO molecular function	structural molecule activity / structural constituent of nuclear lamina? (check)
CL	neural progenitor cell (CL:0011020); radial glial cell (CL:0000681); neuron (CL:0000540)

Biological scale per node: variant, dimer and filament steps are MOLECULAR; aggregates, nuclear shape and spindle orientation are CELLULAR; cortical neuron number is TISSUE; microcephaly is ORGANISM.

Omics, single-cell and spatial data: None disease-specific. No GEO datasets were found (just discover-datasets was not run).

7. Anatomical structures

Primary: Brain, especially the cerebral cortex (UBERON:0000955 brain, UBERON:0000956 cerebral cortex) and cerebral white matter.
Secondary: Lateral ventricles (ventriculomegaly) and skull or head size as a consequence.
Body systems: Nervous system only.
Cells: Neural progenitors / radial glia and cortical neurons (inferred).
Subcellular: Nuclear lamina and nuclear envelope; possibly the spindle.
Lateralization: Bilateral and symmetric.

8. Temporal development

Onset: Prenatal or congenital (OFC reduced at birth in 12/13).
Course: Static or nonprogressive. Serial MRI in one patient showed no progression.
Critical period: Fetal cortical neurogenesis, roughly mid-gestation (inferred).
Stages and remission: None defined; not applicable.
Duration: Lifelong.

9. Inheritance and population

Inheritance. Autosomal dominant, usually de novo (HPO: Autosomal dominant inheritance HP:0000006; Sporadic HP:0003745 – verify).

Somatic mosaicism. One affected child inherited the variant from an unaffected mosaic mother. That is parental mosaicism, which the CLAUDE.md somatic-mosaicism guidance says must not be bound to HP:0001442. Record it as a recurrence-risk note instead.

Penetrance: Appears complete in heterozygotes who are not mosaic (n=6, so very limited data).
Expressivity: Variable, especially in developmental-delay severity.
Anticipation, founder effects, consanguinity: None. No population or sex bias is known; the pooled cohort contained both sexes.

Epidemiology. Ultra-rare; about 6 LMNB2 cases published.

measure_type: CASES_IN_LITERATURE
prevalence_class: ULTRA_RARE or NOT_YET_DOCUMENTED
No incidence or carrier frequency data.

Lump/split question for curation. The dominant missense microcephaly (MCPH27) and the recessive LoF perinatal-lethal brain malformation (PMID:40011009) have different inheritance, mechanism (dominant-negative vs null) and severity. Treat the 2025 recessive phenotype as a separate disease or allelic note, not as a subtype of MCPH27. The progressive myoclonus epilepsy (PME) and lipodystrophy associations are also separate.

10. Diagnostics

Clinical criteria: OFC ≤ −3 SD (here typically −5 to −6 SD) at birth, without major malformations or IUGR.
Imaging: Brain MRI shows a small, structurally normal brain, sometimes with a simplified gyral pattern, reduced white matter and ventriculomegaly. No cortical migration defect, which helps distinguish it from the biallelic LoF phenotype and from lissencephaly.
Genetic testing: Exome or genome sequencing, ideally as a trio (de novo calling), is the approach that found these cases.
Microcephaly gene panels: LMNB2 is Green on Genomics England panel 162 (severe microcephaly) and PanelApp AUS panels 138 and 250.
Consider testing for low-level parental mosaicism.
CMA, karyotype, FISH, mtDNA testing and repeat-expansion testing are not relevant except to rule out other causes.
Biomarkers and laboratory tests: None. Research fibroblast immunofluorescence can show lamin aggregates or abnormal nuclear shape, but this is not a clinical test.
Differential diagnosis:
Other MCPH genes (ASPM, WDR62, CDK5RAP2, MCPH1, etc.; mostly autosomal recessive), and LMNB1 MCPH26 (clinically indistinguishable).
Congenital infections (TORCH, Zika).
Fetal alcohol exposure.
Chromosomal syndromes.
Nuclear pore microcephalies (Galloway–Mowat syndrome, with nephrotic syndrome).
Screening: No newborn or carrier screening.

11. Outcome / prognosis

Survival: No data on survival or mortality. Nothing suggests reduced lifespan in heterozygotes, but this is unstudied.
Morbidity: Lifelong neurodevelopmental disability ranging from mild to severe. Some patients have no speech, and some have epilepsy.
Prognostic factors: Unknown, including any genotype–phenotype correlation between Glu398Lys and Asn54His.

12. Treatment

There is no disease-specific therapy, and there are no clinical trials (none found). Management is supportive. Candidate NCIT terms below must be verified against the TreatmentTerm enum.

Intervention	Candidate NCIT term	`therapeutic_modality`
Antiseizure medication for seizures	Pharmacotherapy NCIT:C15986 (+ `therapeutic_agent` only if a source names drugs)	SMALL_MOLECULE
Early intervention: physical, occupational and speech therapy	Physical Therapy NCIT:C15302; Speech Language Therapy NCIT:C159273; Occupational therapy NCIT:C121351	BEHAVIORAL
Genetic counseling (recurrence risk, parental mosaicism)	Genetic Counseling NCIT:C15240	—
Developmental and educational support	Supportive Care NCIT:C15747	—

No primary source specific to MCPH27 supports these interventions. Cite general guidance or leave the evidence out rather than over-claim.

Pharmacogenomics, gene therapy, RNA therapies: None.

13. Prevention

Primary prevention: Not applicable.
Genetic counseling:
Recurrence risk is low for a confirmed de novo variant, but parental germline or somatic mosaicism must be considered (documented in one family).
An affected individual has a 50% transmission risk.
Reproductive options: Prenatal or preimplantation testing for a known familial variant. Fetal ultrasound OFC monitoring in later pregnancies of mosaic carriers.

14. Other species / natural disease

Animal disease: No naturally occurring animal disease found (OMIA not checked).
Orthologs: Mouse Lmnb2 and zebrafish lmnb2 (ZFIN).
Conservation: The mutated residues are conserved across all metazoan lamins, including C. elegans LMN-1 (PMID:33033404).
Zoonotic or transmission aspects: None.

15. Model organisms

Model	Phenotype	Recapitulation	Source
Lmnb2−/− mouse	Normal during development but dies soon after birth; disordered cortical layering, lissencephaly-like; neurons accumulate in the intermediate zone; hypoplastic cerebellum without sulci. Brain size not reduced at birth (per Parry).	Models biallelic LoF (the 2025 human phenotype) better than dominant MCPH27. Has a migration defect that MCPH27 lacks, so PARTIALLY / FAILS_TO_RECAPITULATE for MCPH27.	Coffinier et al., PNAS 2010, PMID:20145110 (PMC2841930)
Forebrain-specific Lmnb2 and Lmnb1/Lmnb2 double knockout	Small forebrain with disorganized layering; elongated, comet-shaped nuclei in Lmnb2-deficient neurons; double knockout gives cortical atrophy.	Small forebrain fits microcephaly; mechanism is null, not dominant-negative.	Coffinier et al., MBoC 2011, PMID:21976703 (PMC3226484)
Lmnb1/Lmnb2 knockouts (mouse ESCs and embryos)	ESCs do not need lamins; organogenesis does. Spindle-orientation defects in neural progenitors, proposed as the cause of brain disorganization.	Supports the mitotic branch (5a) of the causal chain.	Kim et al., Science 2011, PMID:22116031 (PMC3306219)
C. elegans LMN-1 with the ΔK46-equivalent change	Disrupted protofilament assembly; nuclear aggregates.	Shows the LMNB1 p.Lys33del paralog mechanism, not LMNB2 itself.	cited in PMID:33033404
Cell overexpression, GFP-LMNB2 E398K/N54H	Nuclear aggregates; abnormal nuclear shape.	IN_VITRO; overexpressed above endogenous levels (a SUPRAPHYSIOLOGICAL caveat).	PMID:33033404

Gaps. There is no heterozygous knock-in (Lmnb2 E398K) mouse, no patient-derived iPSC or cortical organoid model, and no measurement of spindle orientation with the actual dominant variants. These are the key experiments that would test chain steps 3–6.

Curation notes for the dismech entry

Evidence to quote:
PMID:33033404 (full text cached) carries nearly every clinical and mechanistic claim. Quote the abstract or results sentences above, and grade modelling as COMPUTATIONAL, GFP experiments as IN_VITRO, and patients as HUMAN_CLINICAL.
The mouse-spindle sentence is the paper's discussion of other work: use quote_role: BACKGROUND with MODEL_ORGANISM.
Mouse-paper quotes: Fetch PMIDs 20145110, 21976703 and 22116031 before quoting them.
Gene-disease validity: No ClinGen tier was found, so do not record gene_disease_validity.
Parental mosaicism: Do not bind HP:0001442.
2025 biallelic LoF report: Keep PMID:40011009 out of the MCPH27 phenotype list, or cite it only as an allelic and mechanistic contrast (HUMAN_MODEL_MISMATCH discussion).
CURIEs: Every CURIE in this report must be checked with runoak or the cache before it is written.

Sources: - LOVD MCPH27 #07163 - PanelApp AUS – ID panel LMNB2 - PanelApp AUS – microcephaly LMNB2 - Genomics England PanelApp – LMNB2 - PanelApp AUS – lipodystrophy LMNB2 - Disease Ontology DOID:0051038 - ClinVar Miner, MONDO 30929 - Parry et al. 2021, PMC7862057 - Coffinier et al. 2010, PMC2841930 - Coffinier et al. 2011, PMID 21976703 - Kim et al. 2011, PMC3306219 - Damiano et al. 2015, PMID 25954030 - Hegele et al. 2006, PMID 16826530 - ZFIN lmnb2 - Desgrouas et al. 2025, J Med Genet, PMID:40011009 (cached)

Reference Validation

Checked with linkml-reference-validator 0.3.0.

Outcome	Count
References checked	12
Resolved	12
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	12
On topic	7
Off topic	1

References that may not be about this subject

These identifiers resolve, so they are not fabrications, but the records they resolve to share almost none of this report's vocabulary. That is a clue and not a verdict - a paper can be relevant in ways its title and abstract do not spell out - so read them before deciding:

PMID:16543416 (1 mention) - Deconvolution of the factors contributing to the increase in global hurricane intensity.
shared terms: none

Weighed against this report's own most characteristic terms: lmnb2, microcephaly, mcph27, variant, phenotype, found, cached, brain, nuclear, patient, genetic, novo, lamin, lmnb1, dominant, primary, cortical, mechanism, reduced, mosaicism.

All extracted references resolved successfully. Resolving is not the same as being relevant, though - see the references listed above as possibly off topic.

Term Validation

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

Outcome	Count
Terms checked	30
Resolved	30
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	0
Terms whose name was checked	6
Terms named correctly	1
Terms named as a different term	4
Terms whose name is worth a second look	1

Terms the report names something else

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

MONDO:0030929 (1 mention) - the report calls it "MONDO"; MONDO calls it microcephaly 27, primary, autosomal dominant
DOID:0051038 (5 mentions) - the report calls it "Disease Ontology"; DOID calls it autosomal dominant primary microcephaly 27
HP:0003745 (1 mention) - the report calls it "verify"; HP calls it Sporadic
NCIT:C15986 (1 mention) - the report calls it "+ therapeutic_agent only if a source names drugs"; NCIT calls it Pharmacotherapy

Terms whose name is worth a second look

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

HP:0011451 (1 mention) - the report calls it "now labelled "Congenital microcephaly"?"; HP calls it Primary microcephaly, and lists "Congenital microcephaly" among its other names

Microcephaly 27, Primary, Autosomal Dominant

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Research report: Microcephaly 27, Primary, Autosomal Dominant (MCPH27, LMNB2)

1. Disease information

2. Etiology

3. Phenotypes

4. Genetic / molecular information

5. Environmental information

6. Mechanism / pathophysiology

Ordered causal chain

Suggested ontology terms (all IDs to be looked up; none are verified)

7. Anatomical structures

8. Temporal development

9. Inheritance and population

10. Diagnostics

11. Outcome / prognosis

12. Treatment

13. Prevention

14. Other species / natural disease

15. Model organisms

Curation notes for the dismech entry

Reference Validation

References that may not be about this subject

Term Validation

Terms the report names something else

Terms whose name is worth a second look