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Classifications

Harrison's Chapter

Mechanistic Nosology

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Inheritance

1

Autosomal recessive inheritance HP:0000007

MIC-CAP is autosomal recessive. Typically one pathogenic STAMBP variant is inherited from each parent, giving a 25% recurrence risk to sibs. In a minority of families both variants derive from one parent through uniparental isodisomy of chromosome 2, in which case the sib recurrence risk falls to under 1% - a distinction with substantial counseling consequences. Penetrance in biallelic individuals appears complete; expressivity is variable and tracks residual STAMBP protein level.

Autosomal recessive inheritance Penetrance: COMPLETE Expressivity: VARIABLE

Show evidence (3 references)

PMID:24354023 SUPPORT Human Clinical

"MIC-CAP syndrome is an autosomal recessive disorder caused by biallelic STAMBP pathogenic variants."

GeneReviews states the mode of inheritance unambiguously.

PMID:24354023 SUPPORT Human Clinical

"Typically, one pathogenic variant is inherited from each parent; however, in some instances both pathogenic variants are inherited from one parent (uniparental isodisomy)."

Documents the uniparental isodisomy route and its counseling implications.

PMID:21815250 SUPPORT Human Clinical

"Two of our reported patients are an affected brother and sister, suggesting this is an autosomal recessive severe congenital MIC syndrome."

Pre-molecular sibship evidence that first established recessive inheritance.

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Mechanistic Hypotheses

2

Constitutive PI3K-AKT-mTOR signaling drives the cutaneous capillary malformations

mtor_driven_capillary_malformation ALTERNATIVE

Evidence balance 1 support 1 refute

The discovery cohort found serum-insensitive RAS-MAPK and PI3K-AKT-mTOR activation in patient lymphoblastoid cell lines and proposed it as the link to the capillary malformations, by analogy with PIK3CA- and RASA1-related vascular anomalies. A later patient homozygous for p.Ser236Phe had multiple capillary malformations without detectable PI3K-AKT-mTOR activation, so either the capillary-malformation mechanism is mTOR-independent, or the lymphoblastoid readout does not reflect endothelial biology. No endothelial or skin-biopsy signaling study has been published in MIC-CAP.

Pathograph links

Constitutive Serum-Insensitive RAS-MAPK and PI3K-AKT-mTOR Signaling -> Dermal Capillary Malformation INDIRECT KNOWN INTERMEDIATES Dysregulated growth-factor signaling in capillary endothelium is the proposed route to the cutaneous capillary malformations.

Show evidence (2 references)

PMID:23542699 SUPPORT In Vitro

"The latter cellular phenotype is notable considering the established connection between these pathways and their association with vascular and capillary malformations."

The original statement of the hypothesis.

PMID:29907875 REFUTE In Vitro

"the Ser236Phe mutation did not lead to constitutive activation of the PI3K-AKT-mTOR pathway in patient-derived LCLs"

The allele-specific counter-observation that makes the hypothesis contested.

NLRP3 inflammasome derepression contributes to neuronal loss

nlrp3_neuroinflammation EMERGING

Evidence balance 1 partial

STAMBP restrains the NLRP3 inflammasome via K63-deubiquitination, and the CNS-conditional Stambp knockout mouse shows massive neuroinflammation. This supports a hypothesized IL-1beta-driven amplification of neuronal death, but the inflammasome work was done in monocytes with no patient data, so the arm is not established in human MIC-CAP.

Pathograph links

NLRP3 Inflammasome Derepression and Neuroinflammation -> Region-Selective Neuronal Apoptosis and Progressive Neuronal Loss INDIRECT KNOWN INTERMEDIATES Neuroinflammation is proposed to amplify neuronal death in the STAMBP-null brain.

Show evidence (1 reference)

PMID:33253913 PARTIAL In Vitro

"These findings describe a unique mechanism of non-degradative ubiquitination of NLRP3 by STAMBP to limit excessive inflammasome activation and to reduce injurious IL-1beta signaling."

Molecular basis of the hypothesis, in a non-neural cell system.

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Discussions and Knowledge Gaps

4

Is the primary cellular lesion of STAMBP deficiency apoptotic neuronal death (as in mouse) or failed neural progenitor proliferation (as in human organoids), and does the mouse under-represent the prenatal human corticogenesis defect?

HUMAN MODEL MISMATCH OPEN miccap_apoptosis_vs_proliferation_model_mismatch

Attached to

pathophysiology#Region-Selective Neuronal Apoptosis and Progressive Neuronal Loss pathophysiology#Impaired Neural Stem and Progenitor Cell Proliferation

Amsh-null mice are grossly normal at birth and develop apoptotic CA1 and cortical neuronal loss postnatally, whereas human STAMBP-knockout cortical organoids show reduced neural stem cell proliferation with explicitly no early apoptosis. Human infants are microcephalic at birth AND progressively so, which neither model captures alone. The mismatch is mechanistically meaningful because it determines the therapeutic window: a purely postnatal apoptotic mechanism would be tractable to postnatal intervention, while a prenatal proliferative deficit would not.

Proposed experiments

Stage-matched proliferation-versus-apoptosis comparison across mouse and human models

miccap_exp_prenatal_proliferation_vs_apoptosis

Quantify proliferation (Ki-67, phospho-histone H3, EdU) and apoptosis (cleaved caspase-3, TUNEL) markers in embryonic Stambp-null mouse cortex alongside stage-matched human STAMBP-knockout cortical organoids.

Decision criterion

Concordant proliferation deficits with discordant apoptosis would confirm that the mouse under-represents the prenatal human proliferative arm.

Ubiquitin, p62 and TDP-43 immunohistochemistry on human MIC-CAP brain

miccap_exp_human_brain_aggregate_ihc

Perform ubiquitin-conjugate, p62/SQSTM1 and TDP-43 immunohistochemistry on archived human MIC-CAP autopsy brain tissue. This is the direct human test of the mouse aggregate findings and, to our knowledge, has never been reported.

Decision criterion

Presence of ubiquitin-conjugate, p62 and TDP-43 aggregates in human cortical and hippocampal neurons would confirm that the mouse proteostasis mechanism operates in human disease.

Postnatal-only AAV9 Stambp delivery window test

miccap_exp_postnatal_aav_window

Test whether AAV9-Stambp delivery restricted to defined postnatal windows rescues brain size, or merely slows further loss, in the Stambp Sox1-cKO mouse.

Decision criterion

Rescue of absolute brain size would indicate a postnatally tractable mechanism; arrest of further decline without size recovery would indicate a fixed prenatal deficit.

Show evidence (2 references)

PMID:36033615 SUPPORT In Vitro

"Furthermore, STAMBP disruption did not affect apoptosis in early cortical organoids."

The human-organoid observation that directly conflicts with the apoptosis-dominant mouse model.

PMID:11713295 SUPPORT Model Organism

"The AMSH-deficient mice were morphologically indistinguishable from their littermates at birth, and histopathological examinations revealed normal morphogenesis in all tissues tested."

The mouse is normal at birth, so it cannot model the congenital component of human microcephaly.

What actually causes the cutaneous capillary malformations, given that at least one patient had them without PI3K-AKT-mTOR activation?

KNOWLEDGE GAP OPEN miccap_capillary_malformation_mechanism_gap

Attached to

pathophysiology#Constitutive Serum-Insensitive RAS-MAPK and PI3K-AKT-mTOR Signaling pathophysiology#Dermal Capillary Malformation

The mTOR/MAPK hypothesis rests entirely on patient lymphoblastoid cell lines, which are not endothelium. A patient homozygous for p.Ser236Phe had multiple capillary malformations without detectable PI3K-AKT-mTOR activation, so either the mechanism is pathway-independent or the lymphoblastoid readout is uninformative about endothelial biology. Lesional skin has been biopsied and described histologically (dilated small-caliber papillary-dermal vessels), but no endothelial signaling study - phospho-S6, phospho-ERK or equivalent - has ever been performed on that tissue, despite the lesions being trivially accessible.

Proposed experiments

Endothelial signaling immunohistochemistry on MIC-CAP capillary malformations

miccap_exp_cm_endothelial_signaling_ihc

Biopsy MIC-CAP cutaneous capillary malformations and stain for endothelial phospho-S6 and phospho-ERK against matched control skin and, ideally, against PIK3CA-related capillary malformation tissue.

Decision criterion

Elevated endothelial phospho-S6/phospho-ERK in lesional skin would support the mTOR/MAPK hypothesis in the tissue that actually matters; normal staining would refute it.

Endothelial-specific Stambp conditional knockout

miccap_exp_endothelial_conditional_ko

Generate an endothelium-restricted Stambp conditional knockout mouse to test whether capillary malformations arise cell-autonomously in endothelium.

Decision criterion

Development of cutaneous capillary malformations in the absence of a CNS phenotype would establish endothelial cell autonomy.

Show evidence (1 reference)

PMID:29907875 SUPPORT In Vitro

"suggesting that it is not the major pathomechanism underlying the disorder in this patient"

The authors' explicit rejection of mTOR activation as the mechanism in their patient, who nonetheless had capillary malformations.

Would IL-1beta blockade modify the epileptic encephalopathy of MIC-CAP, given that STAMBP restrains the NLRP3 inflammasome and the mouse shows massive neuroinflammation?

KNOWLEDGE GAP OPEN miccap_il1_blockade_repurposing

Attached to

pathophysiology#NLRP3 Inflammasome Derepression and Neuroinflammation

AMSH restrains NLRP3 by exactly the K63-linked deubiquitination chemistry it is specialized for, and the CNS-conditional Stambp knockout shows massive neuroinflammation. IL-1 blockade with anakinra is already used in other refractory epilepsy syndromes, making this the most tractable repurposing hypothesis in the disease. It is entirely untested: the inflammasome work was done in monocytes with no patient or neural data.

Proposed experiments

Inflammasome and IL-1beta quantification in STAMBP-deficient neural tissue

miccap_exp_neural_inflammasome_readout

Measure NLRP3 K63-ubiquitination, inflammasome assembly and IL-1beta release in Stambp-knockout mouse brain and in patient-derived microglia-like cells, extending the monocyte finding to neural context.

Decision criterion

Elevated NLRP3 K63-ubiquitination and IL-1beta in STAMBP-deficient neural cells would establish the arm as neural-relevant rather than monocyte-specific.

IL-1 receptor blockade trial in the Stambp Sox1-cKO mouse

miccap_exp_il1_blockade_mouse

Test whether IL-1 receptor blockade (e.g. anakinra) reduces seizure burden, neuroinflammation or preweaning mortality in the CNS-conditional Stambp knockout mouse.

Decision criterion

A significant improvement in survival or seizure burden would justify considering IL-1 blockade as a repurposing candidate in human MIC-CAP.

Show evidence (1 reference)

PMID:33253913 PARTIAL In Vitro

"STAMBP knockout directly increased release of IL-1beta with TLR ligation"

Molecular basis for the IL-1 blockade hypothesis, in monocytes rather than neural cells.

What is the actual natural history, survival distribution, and caregiver/ patient quality-of-life burden of MIC-CAP?

KNOWLEDGE GAP OPEN miccap_natural_history_and_qol_gap

With roughly 25-30 molecularly confirmed individuals reported worldwide there is no registry, no natural-history study, no survival curve, and no validated quality-of-life or caregiver-burden instrument has ever been administered. Life expectancy is described only as "shortened", with the oldest known living individual reported at 12 years. Prognostic counseling is therefore anecdote-based.

Proposed experiments

International STAMBP patient registry with longitudinal phenotyping

miccap_exp_international_registry

Establish a registry capturing standardized longitudinal phenotyping, seizure burden, feeding status, growth and survival across all molecularly confirmed STAMBP patients.

Decision criterion

A cohort large enough to compute a survival distribution and to stratify outcome by variant class.

Quality-of-life and caregiver-burden instrument administration

miccap_exp_qol_instruments

Administer CPCHILD or PedsQL together with a validated caregiver-burden instrument across the reported MIC-CAP cohort, none of which has ever been done.

Decision criterion

Any validated instrument data would replace the current inference-only quality-of-life assessment.

STAMBP protein level as a prognostic biomarker

miccap_exp_protein_level_prognostic

Test whether residual STAMBP protein level quantified on immunoblot from patient-derived cells predicts motor and language outcome, as the leaky splice-allele homozygote suggests.

Decision criterion

A monotonic relationship between residual protein level and functional outcome would establish the first prognostic biomarker for the disease.

Show evidence (1 reference)

PMID:35962715 SUPPORT Human Clinical

"Currently, there is little published information about the natural history and long-term outcomes for individuals with MIC-CAP."

Explicit statement of the natural-history gap by the group that maintains the GeneReviews chapter.

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Pathophysiology

9

Loss of STAMBP/AMSH K63-Linked Deubiquitinase Activity

Biallelic loss-of-function STAMBP variants abolish or severely reduce the activity of AMSH, a Zn(2+)-dependent JAMM/MPN+ metalloprotease deubiquitinase with strict specificity for Lys63-linked polyubiquitin chains. Two routes to loss of function are documented: (i) protein destabilization and near-absence of AMSH, the dominant route, seen with truncating alleles and with missense alleles in the SH3-binding motif (e.g. p.Ser236Phe) that block STAM binding and thereby destabilize the protein; and (ii) direct catalytic or substrate-binding impairment, exemplified by the JAMM-domain allele p.Thr313Ile. Enzyme regulation is itself relevant: the N-terminal MIT domain clamps the catalytic domain in an autoinhibited state that STAM1 binding relieves, which explains why MIT-domain and SH3-binding-motif missense variants - not just catalytic-site variants - are pathogenic.

STAMBP hgnc:16950

protein K63-linked deubiquitination GO:0070536 ↓ DECREASED protein deubiquitination GO:0016579 ↓ DECREASED

K63-linked deubiquitinase activity GO:0061578 ↓ DECREASED cysteine-type deubiquitinase activity GO:0004843 ↓ DECREASED

Downstream

Failure of ESCRT-Dependent Endosomal Sorting of Ubiquitinated Cargo AMSH acts at the endosome as part of the ESCRT machinery; loss of its catalytic activity is the proximal cause of failed cargo deubiquitination during multivesicular-body sorting.

Show evidence (5 references)

PMID:23542699 SUPPORT Human Clinical

"We used whole-exome sequencing of five patients with MIC-CAP syndrome and identified recessive mutations in STAMBP, a gene encoding the deubiquitinating (DUB) isopeptidase STAMBP (STAM-binding protein, also known as AMSH, associated molecule with the SH3 domain of STAM) that has a key role in..."

Establishes biallelic STAMBP loss of function as the cause and identifies the deubiquitinase as the affected activity.

PMID:18758443 SUPPORT In Vitro

"The Zn(2+)-dependent DUBs AMSH and AMSH-LP regulate receptor trafficking by specifically cleaving Lys 63-linked polyubiquitin chains from internalized receptors."

Defines the Zn(2+)-dependent, K63-linkage-specific enzymatic activity that is lost.

PMID:29907875 SUPPORT In Vitro

"Immunoblot analysis of patient-derived lymphoblastoid cell lines (LCLs) revealed a severe reduction in STAMBP expression, indicating that Ser236Phe induces protein instability."

Demonstrates protein destabilization as a route to loss of function in patient cells.

+ 2 more references

Failure of ESCRT-Dependent Endosomal Sorting of Ubiquitinated Cargo

AMSH is recruited to the ESCRT-0 complex through the interaction of its SH3-binding motif with the SH3 domain of STAM, and to ESCRT-III through its MIT domain. There it removes K63-linked chains from internalized, ubiquitin-tagged cell-surface receptors as they are handed down the ESCRT chain into intraluminal vesicles of the multivesicular body. Loss of AMSH leaves K63-ubiquitinated cargo mis-sorted: receptors are neither properly committed to lysosomal degradation nor cleanly recycled, and ubiquitin is not recovered. This is the proximal convergence node from which the proteostasis, signaling, progenitor and inflammatory arms of the disease all branch.

multivesicular body sorting pathway GO:0071985 ⚠ ABNORMAL endosome transport via multivesicular body sorting pathway GO:0032509 ⚠ ABNORMAL ubiquitin-dependent protein catabolic process via the multivesicular body sorting pathway GO:0043162 ↓ DECREASED

ESCRT-0 complex GO:0033565 early endosome GO:0005769 multivesicular body GO:0005771

Downstream

Ubiquitin-Conjugate Aggregation and Proteostatic Stress Mis-sorted K63-ubiquitinated cargo accumulates as ubiquitin-conjugate aggregates.

Constitutive Serum-Insensitive RAS-MAPK and PI3K-AKT-mTOR Signaling Activated receptors that are not committed to lysosomal degradation persist in the endosomal compartment and continue to signal.

Impaired Neural Stem and Progenitor Cell Proliferation Failed endosomal cargo handling in neural progenitors limits their expansion during corticogenesis.

NLRP3 Inflammasome Derepression and Neuroinflammation NLRP3 is itself a K63-ubiquitination substrate restrained by AMSH; its derepression is a proposed inflammatory branch.

Show evidence (3 references)

PMID:24151880 SUPPORT In Vitro

"AMSH, a deubiquitinating enzyme (DUB) with exquisite specificity for Lys63-linked polyubiquitin chains, is an endosome-associated DUB that regulates sorting of activated cell-surface signaling receptors to the lysosome, a process mediated by the members of the endosomal sorting complexes..."

Defines the normal ESCRT-associated endosomal sorting role whose failure this node represents.

PMID:20159979 SUPPORT In Vitro

"The RXXK motif of AMSH interacts with the SH3 domains of the STAM and Grb2 families of adaptor proteins with high affinity."

Establishes the ESCRT-0/STAM recruitment interaction that MIC-CAP SH3-binding-motif variants disrupt.

PMID:21531206 SUPPORT Model Organism

"AMSH impairment results in missorted ubiquitinated cargoes in vitro and severe neurodegeneration in vivo"

Links cargo mis-sorting directly to in vivo neurodegeneration.

Ubiquitin-Conjugate Aggregation and Proteostatic Stress

Undegraded K63-ubiquitinated substrates accumulate as cytoplasmic ubiquitin-conjugate aggregates. Patient-derived lymphoblastoid cell lines show elevated conjugated-ubiquitin aggregates with increased autophagosome content, and lentiviral STAMBP re-expression reverses the phenotype. In the Amsh-null mouse the aggregates begin as early as embryonic day 10 and become severe in the postnatal brain, and the co-accumulating species have been identified as TDP-43, p62/SQSTM1 and glutamate receptors. Glutamate-receptor accumulation offers a direct, still-untested route from failed receptor downregulation to the excitation/inhibition imbalance underlying the epilepsy.

neuron CL:0000540

autophagy GO:0006914 ↑ INCREASED

inclusion body GO:0016234

Downstream

Region-Selective Neuronal Apoptosis and Progressive Neuronal Loss Ubiquitin-conjugate aggregation and the associated proteostatic stress drive caspase-3-dependent apoptosis of vulnerable neurons.

Show evidence (4 references)

PMID:23542699 SUPPORT In Vitro

"Patient cell lines showed reduced STAMBP expression associated with accumulation of ubiquitin-conjugated protein aggregates, elevated apoptosis and insensitive activation of the RAS-MAPK and PI3K-AKT-mTOR pathways."

Direct patient-cell evidence for ubiquitin-conjugate aggregation and elevated apoptosis.

PMID:21531206 SUPPORT Model Organism

"Here, we demonstrate that AMSH(-/-) mice developed ubiquitinated protein accumulations as early as embryonic day 10 (E10), and that severe deposits were present in the brain at postnatal day 8 (P8) and P18."

In vivo timing of the aggregate phenotype, beginning prenatally.

PMID:21531206 SUPPORT Model Organism

"Glutamate receptor and p62 accumulations were also found; these molecules colocalized with ubiquitinated aggregates in the brain."

Identifies glutamate receptors and p62 among the accumulating substrates.

+ 1 more reference

Region-Selective Neuronal Apoptosis and Progressive Neuronal Loss

Neurons of the hippocampus (particularly the CA1 field) and cerebral cortex die by apoptosis, while cerebellar neurons, thymocytes and fibroblasts are spared - a cell-autonomous, region-restricted survival requirement that is the most distinctive cellular phenotype of AMSH deficiency and matches the human neuropathology of disproportionately small cerebral hemispheres with a relatively preserved cerebellum. This postnatal degenerative arm explains the *progressive* component of the microcephaly and the cortical atrophy, in contrast with the prenatal proliferation arm that sets brain size at birth.

hippocampal CA1 pyramidal neuron CL:0002608 neuron CL:0000540

neuron apoptotic process GO:0051402 ↑ INCREASED apoptotic process GO:0006915 ↑ INCREASED

Downstream

Progressive Microcephaly and Cortical Atrophy Cumulative neuronal loss produces radiographically progressive cerebral atrophy and a falling head circumference.

Show evidence (4 references)

PMID:11713295 SUPPORT Model Organism

"Examination of brain sections at P6 demonstrated significant loss of neurons and apoptotic cells in the CA1 subfield of the hippocampus."

Establishes apoptotic CA1 neuronal loss in the Amsh-null mouse.

PMID:11713295 SUPPORT Model Organism

"AMSH-deficient hippocampal neuronal cells were unable to survive in vitro, even in the presence of several stimulatory cytokines, while AMSH-deficient cerebellar neurons, thymocytes, and embryonic fibroblasts survived normally."

Demonstrates the cell-autonomous, region-selective survival requirement, including cerebellar sparing.

PMID:39169623 SUPPORT Model Organism

"In this MIC-CAP syndrome mouse model, early-onset neuronal death occurs specifically in the hippocampus and cortex, accompanied by aggregation of ubiquitinated proteins, and massive neuroinflammation."

Independent CNS-conditional knockout confirming the same regional selectivity and linking it to aggregates.

+ 1 more reference

Impaired Neural Stem and Progenitor Cell Proliferation

A developmental arm that operates before birth and is distinct from the postnatal degenerative arm. Human STAMBP-knockout cortical organoids show significantly reduced neural stem cell proliferation and are smaller, with no detectable increase in apoptosis at early stages; re-expression of wild-type STAMBP rescues proliferation while the disease alleles p.Gly307Glu and p.Thr313Ile do not. Independently, neural progenitor cells derived from STAMBP-deficient human embryonic stem cells cannot be maintained long term, with downregulation of the anti-apoptotic protein CFLAR as the identified effector and CFLAR re-expression rescuing the defect. Together these explain why the brain is already small at birth.

neural stem cell CL:0000047 neural progenitor cell CL:0011020

neural precursor cell proliferation GO:0061351 ↓ DECREASED cell population proliferation GO:0008283 ↓ DECREASED cerebral cortex development GO:0021987 ⚠ ABNORMAL extrinsic apoptotic signaling pathway GO:0097191 ↑ INCREASED

Downstream

Progressive Microcephaly and Cortical Atrophy A reduced cortical progenitor pool yields a small brain at birth, on which the postnatal degenerative arm is superimposed.

Show evidence (3 references)

PMID:36033615 SUPPORT In Vitro

"Cortical organoids with STAMBP knockout (KO) showed significantly lower proliferation of neural stem cells (NSCs), leading to smaller organoids that are characteristic of microcephaly."

Human organoid evidence that STAMBP loss reduces neural stem cell proliferation and organoid size.

PMID:36033615 PARTIAL In Vitro

"Furthermore, STAMBP disruption did not affect apoptosis in early cortical organoids."

Qualifies the mechanism: in the human organoid system the early defect is proliferative rather than apoptotic, contrasting with the mouse.

PMID:38951308 SUPPORT In Vitro

"We identified the anti-apoptotic protein CFLAR is down-regulated in those affected NPCs and ectopic expression of CFLAR rescues NPC defects induced by STAMBP-deficiency."

Identifies CFLAR downregulation as the effector of progenitor loss, with a rescue experiment.

Constitutive Serum-Insensitive RAS-MAPK and PI3K-AKT-mTOR Signaling

Because activated receptors are not committed to lysosomal degradation, they persist and continue to signal from the endosomal compartment. Patient lymphoblastoid cell lines show RAS-MAPK and PI3K-AKT-mTOR pathway activity that is maintained even under serum starvation - "insensitive" rather than merely elevated - and lentiviral STAMBP restores a normal serum response. This paradoxical growth-signalling activation in a loss-of-function deubiquitinase disorder is the most plausible mechanistic bridge to the cutaneous capillary malformations, since both pathways are established drivers of vascular and capillary malformations. The arm is not settled: one patient homozygous for p.Ser236Phe had multiple capillary malformations *without* constitutive PI3K-AKT-mTOR activation.

Constitutive PI3K-AKT-mTOR signaling drives the cutaneous capillary malformations

MAPK cascade GO:0000165 ↑ INCREASED TOR signaling GO:0031929 ↑ INCREASED TORC1 signaling GO:0038202 ↑ INCREASED

Downstream

Dermal Capillary Malformation Dysregulated growth-factor signaling in capillary endothelium is the proposed route to the cutaneous capillary malformations.

Show evidence (3 references)

PMID:23542699 SUPPORT In Vitro

"Patient cell lines showed reduced STAMBP expression associated with accumulation of ubiquitin-conjugated protein aggregates, elevated apoptosis and insensitive activation of the RAS-MAPK and PI3K-AKT-mTOR pathways."

Primary patient-cell evidence for serum-insensitive RAS-MAPK and PI3K-AKT-mTOR activation.

PMID:23542699 SUPPORT Human Clinical

"The latter cellular phenotype is notable considering the established connection between these pathways and their association with vascular and capillary malformations."

The authors' explicit link from these pathways to the capillary-malformation phenotype.

PMID:29907875 REFUTE In Vitro

"Contrary to previously reported STAMBP mutations, the Ser236Phe mutation did not lead to constitutive activation of the PI3K-AKT-mTOR pathway in patient-derived LCLs, as indicated by the expression of phosphorylated S6 ribosomal protein, suggesting that it is not the major pathomechanism..."

Allele-specific counter-evidence: this patient had capillary malformations without mTOR pathway activation, so mTOR activation is not necessary for the cutaneous phenotype.

Dermal Capillary Malformation

Multiple small, pink-to-red, blanchable, roughly oval or circular capillary malformations are distributed generally and randomly over the body - a few to hundreds, ranging from 1-2 mm to several centimetres. They are present at birth, are not segmental or dermatomal (distinguishing them from the V1 trigeminal port-wine stain of Sturge-Weber syndrome), and carry none of the leptomeningeal-angiomatosis or glaucoma risk of that disorder. Skin biopsy confirms their nature histologically - dilated small-caliber vessels in the papillary dermis - but the proposed signaling substrate, capillary endothelium responding to the dysregulated RAS-MAPK and PI3K-AKT-mTOR activity described above, has never been assayed in MIC-CAP lesional skin.

capillary endothelial cell CL:0002144

angiogenesis GO:0001525 ⚠ ABNORMAL

Show evidence (2 references)

PMID:24354023 SUPPORT Human Clinical

"generalized cutaneous capillary malformations (a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm)"

GeneReviews description of the morphology, number and size range of the lesions.

PMID:23542699 SUPPORT Human Clinical

"multiple small capillary malformations on the skin"

Confirms the cutaneous phenotype in the molecularly defined discovery cohort.

NLRP3 Inflammasome Derepression and Neuroinflammation

A proposed inflammatory arm. STAMBP is a negative regulator of the NLRP3 inflammasome, restraining it by removing K63-linked (non-degradative) polyubiquitin from NLRP3; STAMBP depletion in monocytes increases NLRP3 K63 polyubiquitination, inflammasome activation and IL-1beta release. The CNS-conditional Stambp knockout mouse shows massive neuroinflammation accompanying neuronal death. No patient-level inflammasome or IL-1beta data exist, so this arm is hypothesized rather than established in human MIC-CAP - but it is the disease's most tractable drug-repurposing hypothesis.

NLRP3 inflammasome derepression contributes to neuronal loss

microglial cell CL:0000129

interleukin-1 beta production GO:0032611 ↑ INCREASED microglial cell activation GO:0001774 ↑ INCREASED neuroinflammatory response GO:0150076 ↑ INCREASED

NLRP3 inflammasome complex GO:0072559

Downstream

Region-Selective Neuronal Apoptosis and Progressive Neuronal Loss Neuroinflammation is proposed to amplify neuronal death in the STAMBP-null brain.

Show evidence (3 references)

PMID:33253913 SUPPORT In Vitro

"Here we identify the deubiquitinase STAM-binding protein (STAMBP) as a negative regulator of the NLRP3 inflammasome."

Establishes STAMBP as a brake on the NLRP3 inflammasome.

PMID:33253913 SUPPORT In Vitro

"While STAMBP does not modulate NLRP3 protein abundance, cellular depletion of the deubiquitinase increased NLRP3 K63 chain polyubiquitination resulting in increased NLRP3 inflammasome activation."

Shows the mechanism runs through exactly the K63 chemistry that AMSH is specialized for, making derepression plausible in MIC-CAP.

PMID:39169623 PARTIAL Model Organism

"accompanied by aggregation of ubiquitinated proteins, and massive neuroinflammation"

In vivo neuroinflammation in the CNS-specific Stambp knockout, consistent with but not proving the inflammasome route.

Progressive Microcephaly and Cortical Atrophy

The organism-level convergence of the prenatal proliferation arm and the postnatal degenerative arm: a brain that is already small at birth and then falls further behind, with progressive cortical atrophy, a simplified gyral pattern, increased extra-axial cerebrospinal fluid space, hippocampal hypoplasia and, in a minority, thin immature white matter. This structural substrate drives the intractable epilepsy, spastic tetraparesis, optic atrophy and profound developmental delay.

cerebral cortex development GO:0021987 ⚠ ABNORMAL

Show evidence (2 references)

PMID:23542699 SUPPORT Human Clinical

"Microcephaly-capillary malformation (MIC-CAP) syndrome is characterized by severe microcephaly with progressive cortical atrophy, intractable epilepsy, profound developmental delay and multiple small capillary malformations on the skin."

Defines the progressive cortical atrophy that this node represents.

PMID:11713295 SUPPORT Model Organism

"Brain atrophy developed by P16 and was accompanied by complete loss of the CA1 neurons in the hippocampus and marked atrophy of the cerebral cortex."

Model-organism recapitulation of the progressive brain atrophy.

✶

Histopathology

1

Dilated small-caliber papillary dermal vessels

Skin biopsy of the cutaneous lesions shows dilated small-caliber blood vessels confined to the papillary dermis, histologically confirming them as true capillary malformations rather than proliferative vascular tumours (haemangiomas). This is the only tissue-level pathology published in MIC-CAP; no endothelial signaling (phospho-S6 / phospho-ERK) study has been performed on the same tissue - see the capillary-malformation-mechanism knowledge gap.

Show evidence (1 reference)

PMID:21815250 SUPPORT Human Clinical

"Skin biopsies were performed in Patients 2 and 3. Both showed dilated small-caliber blood vessels in the papillary dermis, consistent with capillary malformations (CMs)"

Direct histopathologic confirmation of the cutaneous lesions as capillary malformations.

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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

29

Cardiovascular 1

Minor congenital heart malformation OCCASIONAL Abnormal heart morphology HP:0001627

Show evidence (2 references)

PMID:21815250 SUPPORT Human Clinical

"minor heart malformations in 3/5 including a small atrial septal defect in one, and a small muscular VSD in another"

Counted minor cardiac malformations across the first five reported patients.

PMID:21815250 SUPPORT Human Clinical

"Echocardiogram showed a patent foramen ovale, mild concentric right ventricular hypertrophy, possible right ventricular noncompaction, dilated median pulmonary artery, and a small pericardial effusion."

Echocardiographic detail in one molecularly compatible patient.

Digestive 1

Feeding difficulties VERY_FREQUENT Feeding difficulties HP:0011968

Show evidence (2 references)

PMID:21815250 SUPPORT Human Clinical

"Given significant feeding difficulties and secondary respiratory complications, he underwent G-tube placement"

Direct documentation of feeding difficulty requiring gastrostomy.

PMID:24354023 PARTIAL Human Clinical

"Supportive care by multidisciplinary specialists including a medical geneticist, neurologist, developmental pediatrician, and feeding specialist is recommended."

Routine inclusion of a feeding specialist in standard care is indirect support for near-universal feeding difficulty, hence PARTIAL.

Eye 2

Optic atrophy FREQUENT Optic atrophy HP:0000648

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:31638258 SUPPORT Human Clinical

"both optic atrophy and spastic quadriparesis were common in previous cases"

Explicit statement that optic atrophy is common across previously reported MIC-CAP cases, supporting the FREQUENT band.

Blindness OCCASIONAL Blindness HP:0000618

Show evidence (1 reference)

PMID:27531570 SUPPORT Human Clinical

"presenting with microcephaly, apparent global developmental delay, seizures, spasticity, congenital blindness, and multiple cutaneous capillary malformations"

Direct report of congenital blindness in two affected brothers.

Head and Neck 1

Abnormal facial shape FREQUENT Abnormal facial shape HP:0001999

Show evidence (2 references)

PMID:29907875 SUPPORT Human Clinical

"severe global developmental delay, progressive microcephaly, refractory seizures, dysmorphic facial features, and multiple capillary malformations"

Direct documentation of dysmorphic facial features in a molecularly confirmed patient.

PMID:31638258 SUPPORT Human Clinical

"The patient had drooping mouth corners, a short nose and neck"

Specific facial findings in a molecularly confirmed patient.

Immune 1

Recurrent pneumonia Recurrent pneumonia HP:0006532

Temporal: RECURRENT

Show evidence (3 references)

PMID:21815250 SUPPORT Human Clinical

"episodes of pneumonia necessitating further hospitalizations"

Repeated pneumonia requiring hospitalization in a patient of the original delineation series, in the setting of reflux and poor oral feeding.

PMID:31638258 SUPPORT Human Clinical

"received immunoglobulin intravenously as a result of recurrent pneumonia"

Independent documentation of recurrent pneumonia in a molecularly confirmed patient.

PMID:24354023 PARTIAL Human Clinical

"A feeding tube is essential to optimize nutrition and weight gain while reducing the risk of aspiration."

GeneReviews frames aspiration risk as the management driver; PARTIAL because it names aspiration risk rather than pneumonia itself.

Integument 1

Capillary malformation VERY_FREQUENT Capillary malformation HP:0025104

Show evidence (2 references)

PMID:24354023 SUPPORT Human Clinical

"generalized cutaneous capillary malformations (a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm)"

GeneReviews describes the lesions as a defining feature present at birth.

PMID:36033615 PARTIAL Human Clinical

"but without apparent capillary malformation on the skin and organs"

Documents a biallelic-STAMBP patient lacking the eponymous cutaneous sign, which is why the frequency is VERY_FREQUENT rather than obligate.

Musculoskeletal 2

Central hypotonia Generalized hypotonia HP:0001290

Show evidence (1 reference)

PMID:24354023 PARTIAL Human Clinical

"Central hypotonia and peripheral hypertonia require attention to proper seating and bracing to maintain posture and prevent contractures."

GeneReviews names central hypotonia as a management target in MIC-CAP; PARTIAL because the statement is a management recommendation that presumes the finding rather than a frequency-bearing clinical observation, and because the HPO term used here is the generalized rather than the central-specific concept.

Peripheral hypertonia Hypertonia HP:0001276

Show evidence (2 references)

PMID:21815250 SUPPORT Human Clinical

"Muscle tone was markedly increased with brisk (+4) deep tendon reflexes in the upper and lower extremities, and clonus."

Direct examination finding of markedly increased limb tone with brisk reflexes and clonus in a patient of the original delineation series.

PMID:24354023 PARTIAL Human Clinical

"Central hypotonia and peripheral hypertonia require attention to proper seating and bracing to maintain posture and prevent contractures."

GeneReviews names peripheral hypertonia as a management target; PARTIAL because it is a management statement rather than a frequency-bearing clinical observation.

Nervous System 7

Cerebral atrophy Cerebral atrophy HP:0002059

Course: PROGRESSIVE

Show evidence (2 references)

PMID:21815250 SUPPORT Human Clinical

"progressive and generalized cerebral atrophy brain MRI at 19 months of age (Patient 1), and autopsy at 17 months of age (Patient 2), with relative sparing of the cerebellum"

Direct imaging and autopsy documentation of progressive generalized cerebral atrophy with cerebellar sparing in two MIC-CAP patients.

PMID:23542699 SUPPORT Human Clinical

"severe microcephaly with progressive cortical atrophy"

The molecularly defined discovery cohort characterizes the syndrome by progressive cortical atrophy alongside the microcephaly.

Early-onset intractable epilepsy VERY_FREQUENT Seizure HP:0001250

Temporal: RECURRENT

Show evidence (3 references)

PMID:24354023 SUPPORT Human Clinical

"early-onset intractable epilepsy, and profound developmental delay"

GeneReviews lists early-onset intractable epilepsy among the defining features present at birth.

PMID:24354023 SUPPORT Human Clinical

"Seizures, which can be focal, tonic, and complex partial and can include infantile spasms, appear to stabilize after age two years."

Documents semiology and the post-2-year stabilization.

PMID:31638258 SUPPORT Human Clinical

"The present study also highlighted the fact that STAMBP mutation-associated MIC-CAP often presents as intractable early-life epilepsy, which may lead to mortality."

Confirms intractability and its contribution to mortality.

Hypsarrhythmia Hypsarrhythmia HP:0002521

Show evidence (1 reference)

PMID:31638258 SUPPORT Human Clinical

"Interictal electroencephalography showed hypsarrhythmia and slow wave background with bioccipital spike-slow wave during waking"

Direct EEG documentation of hypsarrhythmia.

Profound global developmental delay VERY_FREQUENT Profound global developmental delay HP:0012736

Show evidence (2 references)

PMID:24354023 SUPPORT Human Clinical

"early-onset intractable epilepsy, and profound developmental delay"

GeneReviews lists profound developmental delay among the defining features.

PMID:25692795 SUPPORT Human Clinical

"characterized by severe microcephaly, early-onset seizures, profound psychomotor disability, and multiple cutaneous capillary lesions"

Independent confirmation of profound psychomotor disability.

Myoclonus FREQUENT Myoclonus HP:0001336

Show evidence (1 reference)

PMID:24354023 SUPPORT Human Clinical

"Myoclonus of the limbs and eyelids is common; other abnormal movements (dyskinetic, choreiform) may be seen."

GeneReviews describes myoclonus as common, which maps to the FREQUENT band per the project's prose-to-frequency mapping table.

Dyskinesia OCCASIONAL Dyskinesia HP:0100660

Show evidence (2 references)

PMID:24354023 SUPPORT Human Clinical

"other abnormal movements (dyskinetic, choreiform) may be seen"

GeneReviews describes dyskinetic and choreiform movements as findings that "may be seen", mapping to the OCCASIONAL band.

PMID:31638258 SUPPORT Human Clinical

"dyskinesia was more prominent in the present study and was infrequent in previous cases"

Reports prominent dyskinesia while confirming that it is infrequent across the reported series.

Autistic behavior OCCASIONAL Autistic behavior HP:0000729

Show evidence (2 references)

PMID:25266620 SUPPORT Human Clinical

"autistic-like behavior with intermittent repetitive hand-flapping movements"

Autistic-like behavior with stereotypies in two affected brothers.

PMID:36033615 SUPPORT Human Clinical

"The patient was presented with global developmental delay, autism spectrum disorder, microcephaly, epilepsy, and dysmorphic facial features"

Formal autism spectrum disorder diagnosis in a biallelic STAMBP patient.

Growth 2

Small for gestational age FREQUENT Small for gestational age HP:0001518

Show evidence (1 reference)

PMID:25266620 PARTIAL Human Clinical

"congenital and progressive microcephaly, intractable epilepsy, profound developmental delay, multiple small capillary malformations on the skin, and poor somatic growth"

Documents poor somatic growth as part of the syndrome; prenatal onset is inferred from congenital microcephaly.

Failure to thrive VERY_FREQUENT Failure to thrive HP:0001508

Course: PROGRESSIVE

Show evidence (3 references)

PMID:31638258 SUPPORT Human Clinical

"in weight and 63 cm (Z-score, −6.8 SD) in length"

Quantitative documentation of severe postnatal growth failure.

PMID:21815250 SUPPORT Human Clinical

"he continued to have failure to thrive"

Failure to thrive persisting despite gastrostomy in a second independent patient.

PMID:24354023 PARTIAL Human Clinical

"A feeding tube is essential to optimize nutrition and weight gain while reducing the risk of aspiration."

GeneReviews treats feeding-tube placement as essential; this supports the management need rather than directly measuring growth failure, hence PARTIAL.

Other 11

Progressive microcephaly VERY_FREQUENT Progressive microcephaly HP:0000253

Course: PROGRESSIVE

Show evidence (2 references)

PMID:24354023 SUPPORT Human Clinical

"The defining clinical characteristics of the microcephaly-capillary malformation (MIC-CAP) syndrome are typically present at birth: microcephaly and generalized cutaneous capillary malformations"

GeneReviews lists microcephaly as a defining feature present at birth in essentially all affected individuals.

PMID:25266620 SUPPORT Human Clinical

"characterized by congenital and progressive microcephaly, intractable epilepsy, profound developmental delay, multiple small capillary malformations on the skin, and poor somatic growth"

Establishes both the congenital and the progressive character of the microcephaly.

Infantile spasms FREQUENT Infantile spasms HP:0012469

Show evidence (2 references)

PMID:31638258 SUPPORT Human Clinical

"The child developed early-onset epilepsy after 3 months, with a generalized tonic-clonic seizure, which progressed to clusters of infantile spasms (2-10 clusters/day) 1 month later."

Documents infantile spasms in a molecularly confirmed patient.

PMID:21815250 SUPPORT Human Clinical

"intractable epilepsy including infantile spasms"

Infantile spasms in the original clinical delineation series.

Short distal phalanx of finger VERY_FREQUENT Short distal phalanx of finger HP:0009882

Show evidence (2 references)

PMID:24354023 SUPPORT Human Clinical

"hypoplastic distal phalanges of the hands and/or feet"

GeneReviews lists hypoplastic distal phalanges among the defining features present at birth.

PMID:25692795 SUPPORT Human Clinical

"affected patients have variable dysmorphic facial features and hypoplastic distal phalanges"

Independent confirmation of the digital phenotype.

Small nail FREQUENT Small nail HP:0001792

Show evidence (2 references)

PMID:21815250 SUPPORT Human Clinical

"The toes were short, with hypoplasia of the toe nails bilaterally"

Direct documentation of bilateral toe-nail hypoplasia.

PMID:21815250 SUPPORT Human Clinical

"Digits were tapered with hypoplastic distal phalanges with complete aplasia of the right first toe nail"

Nail aplasia accompanying the hypoplastic distal phalanges in a second patient of the same series.

Spastic tetraparesis VERY_FREQUENT Spastic tetraparesis HP:0001285

Course: PROGRESSIVE

Show evidence (3 references)

PMID:21815250 SUPPORT Human Clinical

"(3) severe spastic quadriparesis, (4) neonatal-onset intractable epilepsy that included infantile spasms in 2/5 children"

Severe spastic quadriparesis listed among the essential features present in all five patients of the original delineation series, supporting the VERY_FREQUENT band.

PMID:24354023 PARTIAL Human Clinical

"Central hypotonia and peripheral hypertonia require attention to proper seating and bracing to maintain posture and prevent contractures."

GeneReviews documents the mixed central-hypotonia/peripheral-hypertonia pattern; it describes tone abnormality and its management rather than naming spastic tetraparesis, hence PARTIAL.

PMID:27531570 SUPPORT Human Clinical

"presenting with microcephaly, apparent global developmental delay, seizures, spasticity, congenital blindness, and multiple cutaneous capillary malformations"

Spasticity documented in molecularly confirmed siblings.

Simplified gyral pattern VERY_FREQUENT Simplified gyral pattern HP:0009879

Show evidence (1 reference)

PMID:21815250 SUPPORT Human Clinical

"All showed obvious MIC with a low-sloping forehead, diffusely reduced number of gyri with shallow sulci consistent with a severe simplified gyral pattern, and moderately enlarged extra-axial space."

Brain MRI in all three patients of the original clinical delineation series showed a severe simplified gyral pattern, supporting the VERY_FREQUENT band.

Extra-axial cerebrospinal fluid accumulation VERY_FREQUENT Extra-axial cerebrospinal fluid accumulation HP:0012510

Show evidence (2 references)

PMID:21815250 SUPPORT Human Clinical

"All showed obvious MIC with a low-sloping forehead, diffusely reduced number of gyri with shallow sulci consistent with a severe simplified gyral pattern, and moderately enlarged extra-axial space."

Enlarged extra-axial space on MRI in all three patients of the original delineation series.

PMID:31638258 SUPPORT Human Clinical

"The MRI scans showed slightly dilated lateral ventricles and increased extra-axial spaces."

Independent MRI documentation of increased extra-axial cerebrospinal fluid space.

Hypoplastic hippocampus VERY_FREQUENT Hypoplastic hippocampus HP:0025517

Show evidence (2 references)

PMID:21815250 SUPPORT Human Clinical

"The hippocampus was small in all three patients, and the cerebellum was slightly small but proportionate to the overall brain size."

Human MRI evidence of hippocampal hypoplasia in 3/3 imaged patients, with the cerebellum comparatively spared.

PMID:11713295 PARTIAL Model Organism

"complete loss of the CA1 neurons in the hippocampus"

Model-organism correlate of the human hippocampal phenotype.

CNS hypomyelination FREQUENT CNS hypomyelination HP:0003429

Show evidence (1 reference)

PMID:21815250 PARTIAL Human Clinical

"Patient 3 had thin and immature white matter."

Documents thin/immature white matter in a molecularly compatible MIC-CAP patient; PARTIAL because it evidences the finding, not the FREQUENT band (that derives from the HPO 5/8 annotation, which has no quotable abstract).

Congenital hypothyroidism OCCASIONAL Congenital hypothyroidism HP:0000851

Show evidence (2 references)

PMID:25692795 SUPPORT Human Clinical

"which additionally display previously unreported findings of congenital hypothyroidism and alopecia areata"

First report of congenital hypothyroidism in MIC-CAP.

PMID:25266620 SUPPORT Human Clinical

"these boys exhibited certain novel and distinctive phenotypic features (congenital hypothyroidism and autistic-like behavior with intermittent repetitive hand-flapping movements)"

Independent second-family replication of congenital hypothyroidism.

Patchy alopecia VERY_RARE Patchy alopecia HP:0002232

Show evidence (1 reference)

PMID:25692795 SUPPORT Human Clinical

"previously unreported findings of congenital hypothyroidism and alopecia areata"

Single-family report of alopecia areata.

🧬

Genetic Associations

1

STAMBP

Gene: STAMBP hgnc:16950 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (3 references)

PMID:23542699 SUPPORT Human Clinical

"We used whole-exome sequencing of five patients with MIC-CAP syndrome and identified recessive mutations in STAMBP"

Original gene-disease discovery by exome sequencing of five patients.

PMID:29907875 SUPPORT Human Clinical

"Microcephaly-capillary malformation syndrome is a congenital and neurodevelopmental disorder caused by biallelic mutations in the STAMBP gene."

Independent confirmation of the biallelic STAMBP gene-disease relationship.

PMID:27531570 SUPPORT Human Clinical

"we uncovered a homozygous missense variant in STAMBP (p.K303R) in the two siblings, inherited from heterozygous carrier parents"

Demonstrates recessive segregation from asymptomatic heterozygous carrier parents.

💊

Medical Actions

9

Multidisciplinary Supportive and Palliative Care

Action: supportive care Ontology label: Supportive Care NCIT:C15747

No disease-modifying therapy exists. Management is supportive and is delivered by a multidisciplinary team including medical genetics, neurology, developmental pediatrics and feeding specialists, with regular child-neurology follow-up and involvement of a complex-care or palliative-care team to monitor complications of severe neurologic impairment.

Show evidence (2 references)

PMID:24354023 SUPPORT Human Clinical

"Supportive care by multidisciplinary specialists including a medical geneticist, neurologist, developmental pediatrician, and feeding specialist is recommended."

GeneReviews management recommendation for multidisciplinary supportive care.

PMID:24354023 SUPPORT Human Clinical

"Regular follow up with a child neurologist for seizure management and a complex care / palliative care team or experienced pediatrician to monitor for complications associated with severe neurologic impairment."

GeneReviews surveillance recommendation including palliative care.

Anticonvulsant Polytherapy

Action: anticonvulsant therapy Ontology label: Anticonvulsant Therapy NCIT:C64172

Agent: anticonvulsant agent NCIT:C264 levetiracetam CHEBI:6437

Seizure management by an experienced pediatric neurology team; multiple anticonvulsant medications are usually required and control is often incomplete. Levetiracetam, topiramate, valproic acid and corticosteroids have been used in sequence in reported cases. Note the valproic-acid caution below.

Show evidence (2 references)

PMID:24354023 SUPPORT Human Clinical

"Seizures require management by an experienced pediatric neurology team, as multiple anticonvulsant medications are frequently required for adequate seizure control."

GeneReviews establishes anticonvulsant polytherapy as standard management.

PMID:31638258 PARTIAL Human Clinical

"The patient was treated successively with levetiracetam (40-50 mg/kg/day), topiramate (6-7 mg/kg/day), valproic acid (30 mg/kg/day) and corticosteroids at the outpatient clinic. The spasms decreased and became myoclonic, but the epilepsy remained refractory."

Documents a real drug sequence and its incomplete efficacy.

Vigabatrin

Action: Pharmacotherapy NCIT:C15986

Agent: vigabatrin CHEBI:63638

Vigabatrin produced an 80% seizure reduction within a week in a single reported patient whose epilepsy had been refractory to levetiracetam, topiramate, valproic acid, corticosteroids and a ketogenic diet. This is a single case with three weeks of follow-up before the patient died, so long-term efficacy is unknown and vigabatrin should not be presented as established MIC-CAP therapy - though it is biologically coherent given the infantile-spasms phenotype for which vigabatrin is generally first line.

Show evidence (2 references)

PMID:31638258 SUPPORT Human Clinical

"After 1 month, the patient received vigabatrin (60 mg/kg/day) and the seizures reduced by 80% a week later."

The single reported vigabatrin response in MIC-CAP.

PMID:31638258 PARTIAL Human Clinical

"Although the patient in the present study responded well to vigabatrin, the long-term efficacy of the drug could not be evaluated due to the early death of the patient."

The authors' own caveat limiting the strength of this n=1 observation.

Valproic Acid Caution

Action: Pharmacotherapy NCIT:C15986

Agent: valproic acid CHEBI:39867

GeneReviews lists valproic acid under agents and circumstances to avoid, with deliberately hedged wording: one affected male died at 12 months of septic shock following acute pancreatitis possibly secondary to valproate, while other patients tolerated the drug. This is best treated as a caution warranting heightened pancreatic monitoring rather than an absolute contraindication.

Show evidence (1 reference)

PMID:24354023 PARTIAL Human Clinical

"Agents/circumstances to avoid: Valproic acid may or may not be associated with adverse effects."

GeneReviews drug-safety statement; the hedged wording is why this is curated as a caution rather than a contraindication.

Gastrostomy Feeding

Action: gastrostomy Ontology label: Gastrostomy NCIT:C52006

Enteral feeding via gastrostomy tube to optimize nutrition and weight gain and to reduce aspiration risk. Aspiration pneumonia is a leading proximate cause of hospitalization and death.

Target Phenotypes: Feeding difficulties HP:0011968 Failure to thrive HP:0001508 Recurrent pneumonia HP:0006532

Show evidence (1 reference)

PMID:24354023 SUPPORT Human Clinical

"A feeding tube is essential to optimize nutrition and weight gain while reducing the risk of aspiration."

GeneReviews treats gastrostomy feeding as essential management.

Seating, Bracing and Physical Therapy

Action: physical therapy Ontology label: Physical Therapy NCIT:C15302

Attention to proper seating and bracing to maintain posture and prevent contractures, addressing the characteristic mixed pattern of central hypotonia with peripheral hypertonia.

Target Phenotypes: Central hypotonia HP:0001290 Peripheral hypertonia HP:0001276 Spastic tetraparesis HP:0001285

Show evidence (1 reference)

PMID:24354023 SUPPORT Human Clinical

"Central hypotonia and peripheral hypertonia require attention to proper seating and bracing to maintain posture and prevent contractures."

GeneReviews management recommendation for tone and posture.

Ketogenic Diet

Action: ketogenic diet Ontology label: Ketogenic Diet NCIT:C173168

A ketogenic diet was trialled in one reported patient and failed to control seizures even after the ratio was escalated from 2:1 to 4:1. Recorded here as a documented negative result rather than a recommended therapy.

Show evidence (1 reference)

PMID:31638258 REFUTE Human Clinical

"During the follow-up, the seizures were still not well controlled, although the ketogenic diet ratio was modified from 2:1 to 4:1"

Documents failure of the ketogenic diet in the one case where it was tried.

Genetic Counseling and Reproductive Options

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Counseling on the 25% sib recurrence risk for biparental inheritance, and on the substantially lower (<1%) risk when the proband's homozygosity arose through uniparental isodisomy. Once the familial variants are known, carrier testing, prenatal testing and preimplantation genetic testing are available.

Show evidence (2 references)

PMID:24354023 SUPPORT Human Clinical

"carrier testing for at-risk family members, prenatal testing for pregnancies at increased risk, and preimplantation genetic testing are possible"

GeneReviews genetic-counseling options once familial variants are identified.

PMID:24354023 SUPPORT Human Clinical

"each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier"

The standard biparental recurrence risk that counseling conveys.

AAV9-Mediated STAMBP Gene Replacement (Preclinical)

Action: gene therapy Ontology label: Gene Therapy NCIT:C15238

Neonatal AAV9-mediated brain-directed supplementation of Stambp significantly improved neurological defects, sustained growth and prolonged lifespan in a CNS-specific Stambp knockout mouse. This is the leading translational prospect for MIC-CAP and is unusually favourable on paper: the STAMBP coding sequence is small enough for AAV packaging, the CNS-restricted knockout phenocopies the global null (so brain-directed delivery may suffice), and the intervention worked postnatally. It remains mouse-only - there is no investigational new drug application, no clinical trial and no human data.

Mechanism Target:

RESTORES Loss of STAMBP/AMSH K63-Linked Deubiquitinase Activity — Gene supplementation restores AMSH deubiquitinase activity in the brain.

Show evidence (1 reference)

PMID:39169623 SUPPORT Model Organism

"neonatal AAV9-mediated gene supplementation of Stambp in the brain could significantly improve neurological defects"

Demonstrates that restoring Stambp in the brain corrects the downstream phenotype.

Show evidence (2 references)

PMID:39169623 SUPPORT Model Organism

"Importantly, neonatal AAV9-mediated gene supplementation of Stambp in the brain could significantly improve neurological defects, sustain growth, and prolong the lifespan of StambpSox1-cKO mice."

Preclinical efficacy of postnatal brain-directed gene replacement.

PMID:39169623 SUPPORT Model Organism

"provide preclinical evidence that postnatal gene replacement is an effective approach to cure the disease"

The authors' own framing of the translational claim, explicitly preclinical.

🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from Microcephaly-Capillary Malformation Syndrome:

Megalencephaly-capillary malformation syndrome (MCAP) Not Yet Curated MONDO:0011240

Overlapping Features The single most important named-entity confusion for MIC-CAP. MCAP is part of the PIK3CA-related overgrowth spectrum and shares only the capillary-malformation token. Everything else runs in the opposite direction: MCAP is a sporadic somatic mosaic activating PIK3CA disorder with megalencephaly, segmental overgrowth and polymicrogyria, whereas MIC-CAP is a germline biallelic loss-of-function STAMBP deubiquitinase defect with microcephaly and progressive cortical atrophy. MCAP additionally has a targeted therapy (alpelisib) that has no rationale in MIC-CAP.

Distinguishing Features

Megalencephaly (brain and head overgrowth) rather than microcephaly
Somatic mosaic gain-of-function PIK3CA rather than germline biallelic loss-of-function STAMBP
Sporadic/mosaic rather than autosomal recessive
Asymmetric segmental overgrowth of limbs, trunk and face
Polymicrogyria, ventriculomegaly, thick corpus callosum and cerebellar tonsillar ectopia
No hypoplastic distal phalanges
Targeted therapy with the PI3K-alpha inhibitor alpelisib is approved for PROS and has no rationale in MIC-CAP

Show evidence (3 references)

PMID:23946963 SUPPORT Human Clinical

"PROS was separated into distinct clinical syndromes based on the tissues and/or organs involved"

GeneReviews places the historical clinical syndrome names - MCAP among them - inside the PIK3CA-related overgrowth spectrum, establishing MCAP as a PIK3CA entity distinct in gene and mechanism from STAMBP-related MIC-CAP.

PMID:23946963 SUPPORT Human Clinical

"The diagnosis of PROS is established in a proband with suggestive findings and a heterozygous mosaic (or rarely, constitutional) activating pathogenic variant in PIK3CA."

Confirms the mosaic activating (gain-of-function) mechanism, the mechanistic opposite of biallelic STAMBP loss.

PMID:23946963 SUPPORT Human Clinical

"the core features are congenital or early-childhood onset of segmental/focal overgrowth with or without cellular dysplasia"

Overgrowth, not undergrowth, is the core PROS/MCAP feature - the opposite of MIC-CAP.

Primary autosomal recessive microcephaly (MCPH) MONDO:0016660

Overlapping Features Congenital microcephaly with a simplified gyral pattern, caused by biallelic variants in ASPM, WDR62, MCPH1 and other centrosomal/mitotic genes. Shares the microcephaly and simplified gyri with MIC-CAP but lacks the cutaneous and digital features.

Distinguishing Features

No cutaneous capillary malformations
No hypoplastic distal phalanges or nail hypoplasia
Epilepsy is usually not intractable and often absent
Cognitive impairment without major motor delay; motor development comparatively preserved
Growth largely normal apart from mild short stature
Facies normal except for a narrow or sloping forehead

Show evidence (1 reference)

PMID:24354023 PARTIAL Human Clinical

"microcephaly and generalized cutaneous capillary malformations (a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm), hypoplastic distal phalanges of the hands and/or feet"

The cutaneous and digital features quoted here are precisely what separate MIC-CAP from primary autosomal recessive microcephaly.

Capillary malformation-arteriovenous malformation syndrome (CM-AVM) MONDO:0012016

Overlapping Features Autosomal dominant RASA1- or EPHB4-related disorder with multiple small cutaneous capillary malformations that closely resemble those of MIC-CAP, but with arteriovenous malformation/fistula risk instead of a neurodevelopmental phenotype.

Distinguishing Features

Autosomal dominant, with an affected parent frequently identifiable
No microcephaly
No intractable epilepsy and no neurologic impairment
Arteriovenous malformations and arteriovenous fistulae are the principal risk
Caused by heterozygous RASA1 or EPHB4 variants rather than biallelic STAMBP variants

Show evidence (1 reference)

PMID:24354023 PARTIAL Human Clinical

"microcephaly and generalized cutaneous capillary malformations"

The co-occurrence of microcephaly with the capillary malformations is the discriminator from an isolated capillary-malformation syndrome such as CM-AVM.

Sturge-Weber syndrome MONDO:0008501

Overlapping Features Mosaic GNAQ-related neurocutaneous disorder with a segmental facial port-wine stain, leptomeningeal angiomatosis, glaucoma and epilepsy.

Distinguishing Features

Segmental facial port-wine stain, typically in the V1 trigeminal distribution, rather than generalized randomly distributed micro-lesions
Leptomeningeal angiomatosis
Glaucoma
Head size normal
Somatic mosaic GNAQ activation rather than germline biallelic STAMBP loss of function

Show evidence (1 reference)

PMID:24354023 PARTIAL Human Clinical

"generalized cutaneous capillary malformations"

The generalized (non-segmental) distribution of the MIC-CAP lesions is the key discriminator from the segmental port-wine stain of Sturge-Weber syndrome.

🧫

Experimental Models

3

STAMBP-knockout human cortical organoids ORGANOID

Three-dimensional human cortical organoids carrying a STAMBP knockout show reduced neural stem cell proliferation and smaller size without early apoptosis, and variant-specific rescue: wild-type STAMBP restores proliferation while the disease alleles p.Gly307Glu and p.Thr313Ile do not. This is the principal human model of the developmental (prenatal) arm of the disease.

Publication

PMID:36033615

Findings

STAMBP knockout reduces neural stem cell proliferation and organoid size.

"Cortical organoids with STAMBP knockout (KO) showed significantly lower proliferation of neural stem cells (NSCs), leading to smaller organoids that are characteristic of microcephaly."

Show evidence (1 reference)

PMID:36033615 SUPPORT In Vitro

"Cortical organoids with STAMBP knockout (KO) showed significantly lower proliferation of neural stem cells (NSCs), leading to smaller organoids that are characteristic of microcephaly."

The proliferation and size phenotype of the STAMBP-knockout organoid.

The early organoid defect is proliferative rather than apoptotic.

"Furthermore, STAMBP disruption did not affect apoptosis in early cortical organoids."

Show evidence (1 reference)

PMID:36033615 SUPPORT In Vitro

"Furthermore, STAMBP disruption did not affect apoptosis in early cortical organoids."

Direct statement that apoptosis is unaffected in the early human organoid model.

Show evidence (1 reference)

PMID:36033615 SUPPORT In Vitro

"A 3D human cortical organoid model was used to investigate the function of STAMBP and the pathogenicity of the novel mutation"

Describes the organoid model system curated here.

STAMBP-deficient hESC-derived neural progenitor cells IPSC_DERIVED_MODEL

Human embryonic stem cells with STAMBP deficiency differentiate normally to the neural lineage but their neural progenitor cells cannot be maintained or expanded long term. Downregulation of the anti-apoptotic protein CFLAR is the identified effector, and ectopic CFLAR expression rescues the defect.

Publication

PMID:38951308

Findings

STAMBP is dispensable for pluripotency and neural differentiation but required for long-term neural progenitor maintenance.

"We found that STAMBP is dispensable for the pluripotency maintenance or neural differentiation of hESCs."

Show evidence (1 reference)

PMID:38951308 SUPPORT In Vitro

"We found that STAMBP is dispensable for the pluripotency maintenance or neural differentiation of hESCs."

Establishes that the defect is specific to progenitor maintenance rather than differentiation.

CFLAR downregulation mediates the progenitor defect and CFLAR re-expression rescues it.

"We identified the anti-apoptotic protein CFLAR is down-regulated in those affected NPCs and ectopic expression of CFLAR rescues NPC defects induced by STAMBP-deficiency."

Show evidence (1 reference)

PMID:38951308 SUPPORT In Vitro

"ectopic expression of CFLAR rescues NPC defects induced by STAMBP-deficiency"

The rescue experiment establishing CFLAR as the effector.

Show evidence (1 reference)

PMID:38951308 SUPPORT In Vitro

"In this study, we investigated the function and underlying mechanism of STAMBP during neural differentiation of human embryonic stem cells (hESCs)."

Describes the hESC-derived neural model system curated here.

Patient-derived lymphoblastoid cell lines CELL_LINE

Epstein-Barr-virus-immortalized lymphoblastoid cell lines from MIC-CAP patients are the workhorse patient-cell model. They show reduced STAMBP protein, ubiquitin-conjugate aggregation, elevated autophagosome content, increased cleaved caspase-3 and Annexin V, and serum-insensitive RAS-MAPK and PI3K-AKT-mTOR activation, all reversible by lentiviral STAMBP transduction. They are a cell model, not a disease site.

Cell source

patient-derived, EBV-immortalized peripheral blood lymphocytes

Publication

PMID:23542699

Findings

Patient lymphoblastoid cell lines show reduced STAMBP, ubiquitin-conjugate aggregation, elevated apoptosis and serum-insensitive growth-pathway activation.

"Patient cell lines showed reduced STAMBP expression associated with accumulation of ubiquitin-conjugated protein aggregates, elevated apoptosis and insensitive activation of the RAS-MAPK and PI3K-AKT-mTOR pathways."

Show evidence (1 reference)

PMID:23542699 SUPPORT In Vitro

"Patient cell lines showed reduced STAMBP expression associated with accumulation of ubiquitin-conjugated protein aggregates, elevated apoptosis and insensitive activation of the RAS-MAPK and PI3K-AKT-mTOR pathways."

The primary patient-cell characterization underlying this model entry.

Show evidence (1 reference)

PMID:29907875 SUPPORT In Vitro

"Immunoblot analysis of patient-derived lymphoblastoid cell lines (LCLs) revealed a severe reduction in STAMBP expression"

Independent use of the same patient-derived lymphoblastoid cell line model.

{ }

Source YAML

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name: Microcephaly-Capillary Malformation Syndrome
creation_date: "2026-07-31T00:00:00Z"
category: Mendelian
synonyms:
- MIC-CAP syndrome
- MIC-CM syndrome
- microcephaly-cutaneous capillary malformation syndrome
- MICCAP
- STAMBP-related neurodevelopmental disorder
description: >
  Microcephaly-capillary malformation (MIC-CAP) syndrome is an ultra-rare
  autosomal recessive neurocutaneous disorder caused by biallelic
  loss-of-function variants in STAMBP, which encodes the endosome-associated,
  Lys63-linkage-specific deubiquitinating isopeptidase AMSH (associated molecule
  with the SH3 domain of STAM). The cardinal features, present at birth, are
  congenital and progressive microcephaly, multiple small generalized cutaneous
  capillary malformations, hypoplastic distal phalanges of the hands and/or
  feet, early-onset intractable epilepsy, and profound developmental delay.
  Mechanistically, loss of AMSH activity blocks deubiquitination of K63-linked
  ubiquitin conjugates during ESCRT-mediated endosomal cargo sorting, producing
  ubiquitin-conjugate aggregation, elevated apoptosis and progressive neuronal
  loss, impaired neural stem/progenitor proliferation, and paradoxically
  constitutive (serum-insensitive) RAS-MAPK and PI3K-AKT-mTOR signaling that is
  the most plausible link to the cutaneous capillary malformations.

  NAMED-ENTITY DISAMBIGUATION: MIC-CAP (MONDO:0013659, OMIM:614261, STAMBP) must
  not be conflated with megalencephaly-capillary malformation-polymicrogyria
  syndrome (MCAP/M-CM, MONDO:0011240, OMIM:602501, PIK3CA), part of the
  PIK3CA-related overgrowth spectrum. The shared "capillary malformation" token
  is the only real overlap: MCAP is a sporadic somatic mosaic gain-of-function
  PI3K/AKT/mTOR *overgrowth* disorder with megalencephaly and polymicrogyria,
  whereas MIC-CAP is a germline biallelic loss-of-function deubiquitinase defect
  with *micro*cephaly and progressive cortical atrophy. Head-size direction,
  inheritance, mutational mechanism and causal gene all run opposite. Other
  confusable neighbours sharing the capillary-malformation token are CM-AVM
  syndrome (RASA1/EPHB4, autosomal dominant) and Sturge-Weber syndrome (mosaic
  GNAQ); see the differential_diagnoses block.
disease_term:
  preferred_term: microcephaly-capillary malformation syndrome
  term:
    id: MONDO:0013659
    label: microcephaly-capillary malformation syndrome
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    notes: >-
      Primary clinical home. Although MIC-CAP is a multisystem neurocutaneous
      syndrome, the burden of disease, the surveillance plan and essentially all
      management are neurologic: a developmental and epileptic encephalopathy
      with progressive microcephaly, cortical atrophy, spastic tetraparesis and
      profound developmental delay. The cutaneous capillary malformations are
      diagnostically decisive but clinically inert.
    evidence:
    - reference: PMID:23542699
      reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Microcephaly-capillary malformation (MIC-CAP) syndrome is characterized by severe microcephaly with progressive cortical atrophy, intractable epilepsy, profound developmental delay and multiple small capillary malformations on the skin."
      explanation: >-
        Three of the four defining features named here are neurologic, placing
        the disorder in Harrison's Neurologic Disorders Part.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    notes: >-
      Secondary assignment: a monogenic autosomal recessive Mendelian disorder
      with a single causative gene (STAMBP), diagnosed by molecular genetic
      testing and managed with formal genetic counseling.
    evidence:
    - reference: PMID:24354023
      reference_title: "Microcephaly-Capillary Malformation Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "MIC-CAP syndrome is an autosomal recessive disorder caused by biallelic STAMBP pathogenic variants."
      explanation: >-
        GeneReviews states the monogenic autosomal recessive basis that places
        MIC-CAP in Harrison's Genetics and Disease Part.
  mechanistic_category:
  - classification_value: proteotoxic disease
    notes: >-
      Loss of the K63-specific deubiquitinase AMSH leaves ubiquitinated ESCRT
      cargo undegraded, and patient cells and Amsh-null mouse brain accumulate
      ubiquitin-conjugate aggregates that co-stain for p62/SQSTM1 and TDP-43.
      Assigned as a mechanistic (not clinical) tag; the aggregate phenotype is
      documented in patient lymphoblastoid cells and in mouse brain, not yet in
      human MIC-CAP brain tissue - see the discussions block.
    evidence:
    - reference: PMID:23542699
      reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
      supports: PARTIAL
      evidence_source: IN_VITRO
      snippet: "implicates ubiquitin-conjugate aggregation and elevated apoptosis as factors potentially influencing the progressive neuronal loss underlying MIC-CAP syndrome"
      explanation: >-
        The discovery paper's own hedged ("potentially influencing")
        proteostasis-failure interpretation, hence PARTIAL.
    - reference: PMID:21531206
      reference_title: "AMSH is required to degrade ubiquitinated proteins in the central nervous system."
      supports: PARTIAL
      evidence_source: MODEL_ORGANISM
      snippet: "AMSH(-/-) mice provide an animal model for neurodegenerative diseases, which are commonly characterized by the generation of proteinaceous aggregates."
      explanation: >-
        Explicitly frames AMSH loss as an aggregate-driven proteinopathy;
        PARTIAL because the framing is model-organism rather than human.
parents:
- hereditary disease
- Neurodevelopmental Disorder
- Developmental and epileptic encephalopathy
- Neurocutaneous Syndrome
references:
- reference: PMID:24354023
  title: "Microcephaly-Capillary Malformation Syndrome."
  tags:
  - GeneReviews

prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Prevalence is unknown. The 2021 GeneReviews update counted 18 molecularly
    confirmed individuals from 15 families; a 2022 delineation series added four
    new patients plus follow-up on two previously published ones, and scattered
    later case reports bring the cumulative published total to roughly 25-30
    individuals.
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, the diagnosis has been confirmed in 18 individuals from 15 families."
    explanation: GeneReviews cumulative count of molecularly confirmed cases as of the 2021 update.
  - reference: PMID:35962715
    reference_title: "Further clinical delineation of microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Microcephaly-Capillary Malformation syndrome (MIC-CAP) is a rare genetic disorder reported in 18 individuals to date."
    explanation: Independent confirmation of the same ultra-rare case count in the 2022 delineation series.

progression:
- phase: Prenatal
  age_range: conception to birth
  notes: >-
    Impaired neural stem/progenitor proliferation fixes brain size before birth;
    infants are small for gestational age with occipitofrontal circumference well
    below the mean, and the capillary malformations and hypoplastic distal
    phalanges are already formed at delivery.
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The defining clinical characteristics of the microcephaly-capillary malformation (MIC-CAP) syndrome are typically present at birth"
    explanation: GeneReviews establishes congenital (prenatal-onset) presentation of the cardinal features.
- phase: Early infantile declaration
  age_range: birth to ~6 months
  notes: >-
    Seizure onset, frequently escalating to clusters of infantile spasms with
    hypsarrhythmia, together with hypotonia and feeding difficulty.
  evidence:
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The child developed early-onset epilepsy after 3 months, with a generalized tonic-clonic seizure, which progressed to clusters of infantile spasms (2-10 clusters/day) 1 month later."
    explanation: Documents the early-infantile seizure declaration and escalation to infantile spasms.
- phase: Late infantile to toddler peak severity
  age_range: ~6 months to 2 years
  notes: >-
    Maximal seizure burden and refractoriness; head circumference falls further
    relative to the mean; spastic tetraparesis, myoclonus, optic atrophy and
    failure to thrive emerge; gastrostomy is usually required.
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "multiple anticonvulsant medications are frequently required for adequate seizure control"
    explanation: Reflects the peak refractory-epilepsy burden of this phase.
- phase: Childhood plateau
  age_range: after 2 years
  notes: >-
    Seizure burden partially stabilizes while the developmental trajectory
    remains flat at a profoundly low ceiling, with accumulating contractures and
    recurrent aspiration.
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seizures, which can be focal, tonic, and complex partial and can include infantile spasms, appear to stabilize after age two years."
    explanation: GeneReviews describes post-2-year seizure stabilization.

pathophysiology:
- name: Loss of STAMBP/AMSH K63-Linked Deubiquitinase Activity
  biological_scale: MOLECULAR
  description: >
    Biallelic loss-of-function STAMBP variants abolish or severely reduce the
    activity of AMSH, a Zn(2+)-dependent JAMM/MPN+ metalloprotease
    deubiquitinase with strict specificity for Lys63-linked polyubiquitin chains.
    Two routes to loss of function are documented: (i) protein destabilization
    and near-absence of AMSH, the dominant route, seen with truncating alleles
    and with missense alleles in the SH3-binding motif (e.g. p.Ser236Phe) that
    block STAM binding and thereby destabilize the protein; and (ii) direct
    catalytic or substrate-binding impairment, exemplified by the JAMM-domain
    allele p.Thr313Ile. Enzyme regulation is itself relevant: the N-terminal MIT
    domain clamps the catalytic domain in an autoinhibited state that STAM1
    binding relieves, which explains why MIT-domain and SH3-binding-motif
    missense variants - not just catalytic-site variants - are pathogenic.
  genes:
  - preferred_term: STAMBP
    term:
      id: hgnc:16950
      label: STAMBP
  molecular_functions:
  - preferred_term: K63-linked deubiquitinase activity
    term:
      id: GO:0061578
      label: K63-linked deubiquitinase activity
    modifier: DECREASED
  - preferred_term: cysteine-type deubiquitinase activity
    term:
      id: GO:0004843
      label: cysteine-type deubiquitinase activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: protein K63-linked deubiquitination
    term:
      id: GO:0070536
      label: protein K63-linked deubiquitination
    modifier: DECREASED
  - preferred_term: protein deubiquitination
    term:
      id: GO:0016579
      label: protein deubiquitination
    modifier: DECREASED
  downstream:
  - target: Failure of ESCRT-Dependent Endosomal Sorting of Ubiquitinated Cargo
    description: >
      AMSH acts at the endosome as part of the ESCRT machinery; loss of its
      catalytic activity is the proximal cause of failed cargo deubiquitination
      during multivesicular-body sorting.
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:23542699
    reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We used whole-exome sequencing of five patients with MIC-CAP syndrome and identified recessive mutations in STAMBP, a gene encoding the deubiquitinating (DUB) isopeptidase STAMBP (STAM-binding protein, also known as AMSH, associated molecule with the SH3 domain of STAM) that has a key role in cell surface receptor-mediated endocytosis and sorting."
    explanation: Establishes biallelic STAMBP loss of function as the cause and identifies the deubiquitinase as the affected activity.
  - reference: PMID:18758443
    reference_title: "Structural basis for specific cleavage of Lys 63-linked polyubiquitin chains."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The Zn(2+)-dependent DUBs AMSH and AMSH-LP regulate receptor trafficking by specifically cleaving Lys 63-linked polyubiquitin chains from internalized receptors."
    explanation: Defines the Zn(2+)-dependent, K63-linkage-specific enzymatic activity that is lost.
  - reference: PMID:29907875
    reference_title: "A novel homozygous missense mutation in the SH3-binding motif of STAMBP causing microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Immunoblot analysis of patient-derived lymphoblastoid cell lines (LCLs) revealed a severe reduction in STAMBP expression, indicating that Ser236Phe induces protein instability."
    explanation: Demonstrates protein destabilization as a route to loss of function in patient cells.
  - reference: PMID:24151880
    reference_title: "Mechanism of recruitment and activation of the endosome-associated deubiquitinase AMSH."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The MIC-CAP disease mutation, Thr313Ile, yields a substantial loss of catalytic activity without any significant change in the thermodynamic stability of the protein, indicating that its perturbed catalytic activity is the basis of the disease."
    explanation: Demonstrates the second, catalytic route to loss of function for a specific disease allele.
  - reference: PMID:40441142
    reference_title: "The MIT domain of STAMBP autoinhibits its deubiquitination activity."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "demonstrated that the MIT domain binds tightly to the catalytic domain (CD), resulting in autoinhibition of its activity"
    explanation: >
      Explains why MIT-domain missense variants (the majority of reported MIC-CAP
      missense alleles) are pathogenic despite lying outside the catalytic site.

- name: Failure of ESCRT-Dependent Endosomal Sorting of Ubiquitinated Cargo
  biological_scale: CELLULAR
  description: >
    AMSH is recruited to the ESCRT-0 complex through the interaction of its
    SH3-binding motif with the SH3 domain of STAM, and to ESCRT-III through its
    MIT domain. There it removes K63-linked chains from internalized,
    ubiquitin-tagged cell-surface receptors as they are handed down the ESCRT
    chain into intraluminal vesicles of the multivesicular body. Loss of AMSH
    leaves K63-ubiquitinated cargo mis-sorted: receptors are neither properly
    committed to lysosomal degradation nor cleanly recycled, and ubiquitin is not
    recovered. This is the proximal convergence node from which the proteostasis,
    signaling, progenitor and inflammatory arms of the disease all branch.
  cellular_components:
  - preferred_term: ESCRT-0 complex
    term:
      id: GO:0033565
      label: ESCRT-0 complex
  - preferred_term: early endosome
    term:
      id: GO:0005769
      label: early endosome
  - preferred_term: multivesicular body
    term:
      id: GO:0005771
      label: multivesicular body
  biological_processes:
  - preferred_term: multivesicular body sorting pathway
    term:
      id: GO:0071985
      label: multivesicular body sorting pathway
    modifier: ABNORMAL
  - preferred_term: endosome transport via multivesicular body sorting pathway
    term:
      id: GO:0032509
      label: endosome transport via multivesicular body sorting pathway
    modifier: ABNORMAL
  - preferred_term: ubiquitin-dependent protein catabolic process via the multivesicular body sorting pathway
    term:
      id: GO:0043162
      label: ubiquitin-dependent protein catabolic process via the multivesicular body sorting pathway
    modifier: DECREASED
  downstream:
  - target: Ubiquitin-Conjugate Aggregation and Proteostatic Stress
    description: Mis-sorted K63-ubiquitinated cargo accumulates as ubiquitin-conjugate aggregates.
    causal_link_type: DIRECT
  - target: Constitutive Serum-Insensitive RAS-MAPK and PI3K-AKT-mTOR Signaling
    description: >
      Activated receptors that are not committed to lysosomal degradation persist
      in the endosomal compartment and continue to signal.
    causal_link_type: DIRECT
  - target: Impaired Neural Stem and Progenitor Cell Proliferation
    description: >
      Failed endosomal cargo handling in neural progenitors limits their
      expansion during corticogenesis.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: NLRP3 Inflammasome Derepression and Neuroinflammation
    description: >
      NLRP3 is itself a K63-ubiquitination substrate restrained by AMSH; its
      derepression is a proposed inflammatory branch.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:24151880
    reference_title: "Mechanism of recruitment and activation of the endosome-associated deubiquitinase AMSH."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "AMSH, a deubiquitinating enzyme (DUB) with exquisite specificity for Lys63-linked polyubiquitin chains, is an endosome-associated DUB that regulates sorting of activated cell-surface signaling receptors to the lysosome, a process mediated by the members of the endosomal sorting complexes required for transport (ESCRT) machinery."
    explanation: Defines the normal ESCRT-associated endosomal sorting role whose failure this node represents.
  - reference: PMID:20159979
    reference_title: "AMSH interacts with ESCRT-0 to regulate the stability and trafficking of CXCR4."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The RXXK motif of AMSH interacts with the SH3 domains of the STAM and Grb2 families of adaptor proteins with high affinity."
    explanation: Establishes the ESCRT-0/STAM recruitment interaction that MIC-CAP SH3-binding-motif variants disrupt.
  - reference: PMID:21531206
    reference_title: "AMSH is required to degrade ubiquitinated proteins in the central nervous system."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "AMSH impairment results in missorted ubiquitinated cargoes in vitro and severe neurodegeneration in vivo"
    explanation: Links cargo mis-sorting directly to in vivo neurodegeneration.

- name: Ubiquitin-Conjugate Aggregation and Proteostatic Stress
  biological_scale: CELLULAR
  description: >
    Undegraded K63-ubiquitinated substrates accumulate as cytoplasmic
    ubiquitin-conjugate aggregates. Patient-derived lymphoblastoid cell lines
    show elevated conjugated-ubiquitin aggregates with increased autophagosome
    content, and lentiviral STAMBP re-expression reverses the phenotype. In the
    Amsh-null mouse the aggregates begin as early as embryonic day 10 and become
    severe in the postnatal brain, and the co-accumulating species have been
    identified as TDP-43, p62/SQSTM1 and glutamate receptors. Glutamate-receptor
    accumulation offers a direct, still-untested route from failed receptor
    downregulation to the excitation/inhibition imbalance underlying the
    epilepsy.
  cellular_components:
  - preferred_term: inclusion body
    term:
      id: GO:0016234
      label: inclusion body
    modifier: INCREASED
  biological_processes:
  - preferred_term: autophagy
    term:
      id: GO:0006914
      label: autophagy
    modifier: INCREASED
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  downstream:
  - target: Region-Selective Neuronal Apoptosis and Progressive Neuronal Loss
    description: >
      Ubiquitin-conjugate aggregation and the associated proteostatic stress
      drive caspase-3-dependent apoptosis of vulnerable neurons.
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:23542699
    reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Patient cell lines showed reduced STAMBP expression associated with accumulation of ubiquitin-conjugated protein aggregates, elevated apoptosis and insensitive activation of the RAS-MAPK and PI3K-AKT-mTOR pathways."
    explanation: Direct patient-cell evidence for ubiquitin-conjugate aggregation and elevated apoptosis.
  - reference: PMID:21531206
    reference_title: "AMSH is required to degrade ubiquitinated proteins in the central nervous system."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Here, we demonstrate that AMSH(-/-) mice developed ubiquitinated protein accumulations as early as embryonic day 10 (E10), and that severe deposits were present in the brain at postnatal day 8 (P8) and P18."
    explanation: In vivo timing of the aggregate phenotype, beginning prenatally.
  - reference: PMID:21531206
    reference_title: "AMSH is required to degrade ubiquitinated proteins in the central nervous system."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Glutamate receptor and p62 accumulations were also found; these molecules colocalized with ubiquitinated aggregates in the brain."
    explanation: Identifies glutamate receptors and p62 among the accumulating substrates.
  - reference: PMID:21531206
    reference_title: "AMSH is required to degrade ubiquitinated proteins in the central nervous system."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Interestingly, TDP-43 was found to accumulate and colocalize with glial marker-positive cells in the brain."
    explanation: Documents TDP-43 accumulation, placing the aggregate phenotype in proteinopathy territory.

- name: Region-Selective Neuronal Apoptosis and Progressive Neuronal Loss
  biological_scale: TISSUE
  description: >
    Neurons of the hippocampus (particularly the CA1 field) and cerebral cortex
    die by apoptosis, while cerebellar neurons, thymocytes and fibroblasts are
    spared - a cell-autonomous, region-restricted survival requirement that is
    the most distinctive cellular phenotype of AMSH deficiency and matches the
    human neuropathology of disproportionately small cerebral hemispheres with a
    relatively preserved cerebellum. This postnatal degenerative arm explains the
    *progressive* component of the microcephaly and the cortical atrophy, in
    contrast with the prenatal proliferation arm that sets brain size at birth.
  cell_types:
  - preferred_term: hippocampal CA1 pyramidal neuron
    term:
      id: CL:0002608
      label: hippocampal neuron
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: neuron apoptotic process
    term:
      id: GO:0051402
      label: neuron apoptotic process
    modifier: INCREASED
  - preferred_term: apoptotic process
    term:
      id: GO:0006915
      label: apoptotic process
    modifier: INCREASED
  downstream:
  - target: Progressive Microcephaly and Cortical Atrophy
    description: Cumulative neuronal loss produces radiographically progressive cerebral atrophy and a falling head circumference.
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:11713295
    reference_title: "Loss of neurons in the hippocampus and cerebral cortex of AMSH-deficient mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Examination of brain sections at P6 demonstrated significant loss of neurons and apoptotic cells in the CA1 subfield of the hippocampus."
    explanation: Establishes apoptotic CA1 neuronal loss in the Amsh-null mouse.
  - reference: PMID:11713295
    reference_title: "Loss of neurons in the hippocampus and cerebral cortex of AMSH-deficient mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "AMSH-deficient hippocampal neuronal cells were unable to survive in vitro, even in the presence of several stimulatory cytokines, while AMSH-deficient cerebellar neurons, thymocytes, and embryonic fibroblasts survived normally."
    explanation: Demonstrates the cell-autonomous, region-selective survival requirement, including cerebellar sparing.
  - reference: PMID:39169623
    reference_title: "AAV-mediated Stambp gene replacement therapy rescues neurological defects in a mouse model of microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In this MIC-CAP syndrome mouse model, early-onset neuronal death occurs specifically in the hippocampus and cortex, accompanied by aggregation of ubiquitinated proteins, and massive neuroinflammation."
    explanation: Independent CNS-conditional knockout confirming the same regional selectivity and linking it to aggregates.
  - reference: PMID:23542699
    reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "implicates ubiquitin-conjugate aggregation and elevated apoptosis as factors potentially influencing the progressive neuronal loss underlying MIC-CAP syndrome"
    explanation: The discovery paper's own causal interpretation linking aggregation and apoptosis to progressive neuronal loss.

- name: Impaired Neural Stem and Progenitor Cell Proliferation
  biological_scale: CELLULAR
  description: >
    A developmental arm that operates before birth and is distinct from the
    postnatal degenerative arm. Human STAMBP-knockout cortical organoids show
    significantly reduced neural stem cell proliferation and are smaller, with no
    detectable increase in apoptosis at early stages; re-expression of wild-type
    STAMBP rescues proliferation while the disease alleles p.Gly307Glu and
    p.Thr313Ile do not. Independently, neural progenitor cells derived from
    STAMBP-deficient human embryonic stem cells cannot be maintained long term,
    with downregulation of the anti-apoptotic protein CFLAR as the identified
    effector and CFLAR re-expression rescuing the defect. Together these explain
    why the brain is already small at birth.
  cell_types:
  - preferred_term: neural stem cell
    term:
      id: CL:0000047
      label: neural stem cell
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  biological_processes:
  - preferred_term: neural precursor cell proliferation
    term:
      id: GO:0061351
      label: neural precursor cell proliferation
    modifier: DECREASED
  - preferred_term: cell population proliferation
    term:
      id: GO:0008283
      label: cell population proliferation
    modifier: DECREASED
  - preferred_term: cerebral cortex development
    term:
      id: GO:0021987
      label: cerebral cortex development
    modifier: ABNORMAL
  - preferred_term: extrinsic apoptotic signaling pathway
    term:
      id: GO:0097191
      label: extrinsic apoptotic signaling pathway
    modifier: INCREASED
  downstream:
  - target: Progressive Microcephaly and Cortical Atrophy
    description: >
      A reduced cortical progenitor pool yields a small brain at birth, on which
      the postnatal degenerative arm is superimposed.
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:36033615
    reference_title: "Novel compound heterozygous mutation in STAMBP causes a neurodevelopmental disorder by disrupting cortical proliferation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Cortical organoids with STAMBP knockout (KO) showed significantly lower proliferation of neural stem cells (NSCs), leading to smaller organoids that are characteristic of microcephaly."
    explanation: Human organoid evidence that STAMBP loss reduces neural stem cell proliferation and organoid size.
  - reference: PMID:36033615
    reference_title: "Novel compound heterozygous mutation in STAMBP causes a neurodevelopmental disorder by disrupting cortical proliferation."
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: "Furthermore, STAMBP disruption did not affect apoptosis in early cortical organoids."
    explanation: >
      Qualifies the mechanism: in the human organoid system the early defect is
      proliferative rather than apoptotic, contrasting with the mouse.
  - reference: PMID:38951308
    reference_title: "STAMBP is Required for Long-Term Maintenance of Neural Progenitor Cells Derived from hESCs."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We identified the anti-apoptotic protein CFLAR is down-regulated in those affected NPCs and ectopic expression of CFLAR rescues NPC defects induced by STAMBP-deficiency."
    explanation: Identifies CFLAR downregulation as the effector of progenitor loss, with a rescue experiment.

- name: Constitutive Serum-Insensitive RAS-MAPK and PI3K-AKT-mTOR Signaling
  biological_scale: MOLECULAR
  description: >
    Because activated receptors are not committed to lysosomal degradation, they
    persist and continue to signal from the endosomal compartment. Patient
    lymphoblastoid cell lines show RAS-MAPK and PI3K-AKT-mTOR pathway activity
    that is maintained even under serum starvation - "insensitive" rather than
    merely elevated - and lentiviral STAMBP restores a normal serum response.
    This paradoxical growth-signalling activation in a loss-of-function
    deubiquitinase disorder is the most plausible mechanistic bridge to the
    cutaneous capillary malformations, since both pathways are established
    drivers of vascular and capillary malformations. The arm is not settled: one
    patient homozygous for p.Ser236Phe had multiple capillary malformations
    *without* constitutive PI3K-AKT-mTOR activation.
  biological_processes:
  - preferred_term: MAPK cascade
    term:
      id: GO:0000165
      label: MAPK cascade
    modifier: INCREASED
  - preferred_term: TOR signaling
    term:
      id: GO:0031929
      label: TOR signaling
    modifier: INCREASED
  - preferred_term: TORC1 signaling
    term:
      id: GO:0038202
      label: TORC1 signaling
    modifier: INCREASED
  downstream:
  - target: Dermal Capillary Malformation
    description: >
      Dysregulated growth-factor signaling in capillary endothelium is the
      proposed route to the cutaneous capillary malformations.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - mtor_driven_capillary_malformation
  evidence:
  - reference: PMID:23542699
    reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Patient cell lines showed reduced STAMBP expression associated with accumulation of ubiquitin-conjugated protein aggregates, elevated apoptosis and insensitive activation of the RAS-MAPK and PI3K-AKT-mTOR pathways."
    explanation: Primary patient-cell evidence for serum-insensitive RAS-MAPK and PI3K-AKT-mTOR activation.
  - reference: PMID:23542699
    reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The latter cellular phenotype is notable considering the established connection between these pathways and their association with vascular and capillary malformations."
    explanation: The authors' explicit link from these pathways to the capillary-malformation phenotype.
  - reference: PMID:29907875
    reference_title: "A novel homozygous missense mutation in the SH3-binding motif of STAMBP causing microcephaly-capillary malformation syndrome."
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: "Contrary to previously reported STAMBP mutations, the Ser236Phe mutation did not lead to constitutive activation of the PI3K-AKT-mTOR pathway in patient-derived LCLs, as indicated by the expression of phosphorylated S6 ribosomal protein, suggesting that it is not the major pathomechanism underlying the disorder in this patient."
    explanation: >
      Allele-specific counter-evidence: this patient had capillary malformations
      without mTOR pathway activation, so mTOR activation is not necessary for the
      cutaneous phenotype.

- name: Dermal Capillary Malformation
  biological_scale: TISSUE
  description: >
    Multiple small, pink-to-red, blanchable, roughly oval or circular capillary
    malformations are distributed generally and randomly over the body - a few to
    hundreds, ranging from 1-2 mm to several centimetres. They are present at
    birth, are not segmental or dermatomal (distinguishing them from the V1
    trigeminal port-wine stain of Sturge-Weber syndrome), and carry none of the
    leptomeningeal-angiomatosis or glaucoma risk of that disorder. Skin biopsy
    confirms their nature histologically - dilated small-caliber vessels in the
    papillary dermis - but the proposed signaling substrate, capillary
    endothelium responding to the dysregulated RAS-MAPK and PI3K-AKT-mTOR
    activity described above, has never been assayed in MIC-CAP lesional skin.
  cell_types:
  - preferred_term: capillary endothelial cell
    term:
      id: CL:0002144
      label: capillary endothelial cell
  biological_processes:
  - preferred_term: angiogenesis
    term:
      id: GO:0001525
      label: angiogenesis
    modifier: ABNORMAL
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "generalized cutaneous capillary malformations (a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm)"
    explanation: GeneReviews description of the morphology, number and size range of the lesions.
  - reference: PMID:23542699
    reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "multiple small capillary malformations on the skin"
    explanation: Confirms the cutaneous phenotype in the molecularly defined discovery cohort.

- name: NLRP3 Inflammasome Derepression and Neuroinflammation
  biological_scale: CELLULAR
  description: >
    A proposed inflammatory arm. STAMBP is a negative regulator of the NLRP3
    inflammasome, restraining it by removing K63-linked (non-degradative)
    polyubiquitin from NLRP3; STAMBP depletion in monocytes increases NLRP3 K63
    polyubiquitination, inflammasome activation and IL-1beta release. The
    CNS-conditional Stambp knockout mouse shows massive neuroinflammation
    accompanying neuronal death. No patient-level inflammasome or IL-1beta data
    exist, so this arm is hypothesized rather than established in human MIC-CAP -
    but it is the disease's most tractable drug-repurposing hypothesis.
  cell_types:
  - preferred_term: microglial cell
    term:
      id: CL:0000129
      label: microglial cell
  cellular_components:
  - preferred_term: NLRP3 inflammasome complex
    term:
      id: GO:0072559
      label: NLRP3 inflammasome complex
  biological_processes:
  - preferred_term: interleukin-1 beta production
    term:
      id: GO:0032611
      label: interleukin-1 beta production
    modifier: INCREASED
  - preferred_term: microglial cell activation
    term:
      id: GO:0001774
      label: microglial cell activation
    modifier: INCREASED
  - preferred_term: neuroinflammatory response
    term:
      id: GO:0150076
      label: neuroinflammatory response
    modifier: INCREASED
  downstream:
  - target: Region-Selective Neuronal Apoptosis and Progressive Neuronal Loss
    description: >
      Neuroinflammation is proposed to amplify neuronal death in the STAMBP-null
      brain.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - nlrp3_neuroinflammation
  evidence:
  - reference: PMID:33253913
    reference_title: "The deubiquitinase STAMBP modulates cytokine secretion through the NLRP3 inflammasome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here we identify the deubiquitinase STAM-binding protein (STAMBP) as a negative regulator of the NLRP3 inflammasome."
    explanation: Establishes STAMBP as a brake on the NLRP3 inflammasome.
  - reference: PMID:33253913
    reference_title: "The deubiquitinase STAMBP modulates cytokine secretion through the NLRP3 inflammasome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "While STAMBP does not modulate NLRP3 protein abundance, cellular depletion of the deubiquitinase increased NLRP3 K63 chain polyubiquitination resulting in increased NLRP3 inflammasome activation."
    explanation: >
      Shows the mechanism runs through exactly the K63 chemistry that AMSH is
      specialized for, making derepression plausible in MIC-CAP.
  - reference: PMID:39169623
    reference_title: "AAV-mediated Stambp gene replacement therapy rescues neurological defects in a mouse model of microcephaly-capillary malformation syndrome."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "accompanied by aggregation of ubiquitinated proteins, and massive neuroinflammation"
    explanation: In vivo neuroinflammation in the CNS-specific Stambp knockout, consistent with but not proving the inflammasome route.

- name: Progressive Microcephaly and Cortical Atrophy
  biological_scale: ORGANISM
  description: >
    The organism-level convergence of the prenatal proliferation arm and the
    postnatal degenerative arm: a brain that is already small at birth and then
    falls further behind, with progressive cortical atrophy, a simplified gyral
    pattern, increased extra-axial cerebrospinal fluid space, hippocampal
    hypoplasia and, in a minority, thin immature white matter. This structural
    substrate drives the intractable epilepsy, spastic tetraparesis, optic
    atrophy and profound developmental delay.
  biological_processes:
  - preferred_term: cerebral cortex development
    term:
      id: GO:0021987
      label: cerebral cortex development
    modifier: ABNORMAL
  evidence:
  - reference: PMID:23542699
    reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Microcephaly-capillary malformation (MIC-CAP) syndrome is characterized by severe microcephaly with progressive cortical atrophy, intractable epilepsy, profound developmental delay and multiple small capillary malformations on the skin."
    explanation: Defines the progressive cortical atrophy that this node represents.
  - reference: PMID:11713295
    reference_title: "Loss of neurons in the hippocampus and cerebral cortex of AMSH-deficient mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Brain atrophy developed by P16 and was accompanied by complete loss of the CA1 neurons in the hippocampus and marked atrophy of the cerebral cortex."
    explanation: Model-organism recapitulation of the progressive brain atrophy.

mechanistic_hypotheses:
- hypothesis_group_id: mtor_driven_capillary_malformation
  hypothesis_label: Constitutive PI3K-AKT-mTOR signaling drives the cutaneous capillary malformations
  status: ALTERNATIVE
  description: >
    The discovery cohort found serum-insensitive RAS-MAPK and PI3K-AKT-mTOR
    activation in patient lymphoblastoid cell lines and proposed it as the link
    to the capillary malformations, by analogy with PIK3CA- and RASA1-related
    vascular anomalies. A later patient homozygous for p.Ser236Phe had multiple
    capillary malformations without detectable PI3K-AKT-mTOR activation, so
    either the capillary-malformation mechanism is mTOR-independent, or the
    lymphoblastoid readout does not reflect endothelial biology. No endothelial
    or skin-biopsy signaling study has been published in MIC-CAP.
  evidence:
  - reference: PMID:23542699
    reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The latter cellular phenotype is notable considering the established connection between these pathways and their association with vascular and capillary malformations."
    explanation: The original statement of the hypothesis.
  - reference: PMID:29907875
    reference_title: "A novel homozygous missense mutation in the SH3-binding motif of STAMBP causing microcephaly-capillary malformation syndrome."
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: "the Ser236Phe mutation did not lead to constitutive activation of the PI3K-AKT-mTOR pathway in patient-derived LCLs"
    explanation: The allele-specific counter-observation that makes the hypothesis contested.
- hypothesis_group_id: nlrp3_neuroinflammation
  hypothesis_label: NLRP3 inflammasome derepression contributes to neuronal loss
  status: EMERGING
  description: >
    STAMBP restrains the NLRP3 inflammasome via K63-deubiquitination, and the
    CNS-conditional Stambp knockout mouse shows massive neuroinflammation. This
    supports a hypothesized IL-1beta-driven amplification of neuronal death, but
    the inflammasome work was done in monocytes with no patient data, so the arm
    is not established in human MIC-CAP.
  evidence:
  - reference: PMID:33253913
    reference_title: "The deubiquitinase STAMBP modulates cytokine secretion through the NLRP3 inflammasome."
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: "These findings describe a unique mechanism of non-degradative ubiquitination of NLRP3 by STAMBP to limit excessive inflammasome activation and to reduce injurious IL-1beta signaling."
    explanation: Molecular basis of the hypothesis, in a non-neural cell system.

phenotypes:
- name: Progressive microcephaly
  category: Structural
  description: >
    Congenital microcephaly that worsens postnatally. Occipitofrontal
    circumference is already well below the mean at birth and falls further with
    age; head circumference of -5.8 SD at 17 months has been documented.
  phenotype_term:
    preferred_term: Progressive microcephaly
    term:
      id: HP:0000253
      label: Progressive microcephaly
    clinical_course: PROGRESSIVE
  frequency: VERY_FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The defining clinical characteristics of the microcephaly-capillary malformation (MIC-CAP) syndrome are typically present at birth: microcephaly and generalized cutaneous capillary malformations"
    explanation: GeneReviews lists microcephaly as a defining feature present at birth in essentially all affected individuals.
  - reference: PMID:25266620
    reference_title: "The microcephaly-capillary malformation syndrome in two brothers with novel clinical features."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characterized by congenital and progressive microcephaly, intractable epilepsy, profound developmental delay, multiple small capillary malformations on the skin, and poor somatic growth"
    explanation: Establishes both the congenital and the progressive character of the microcephaly.
- name: Cerebral atrophy
  category: Imaging
  description: >
    Progressive, generalized cerebral atrophy documented on serial brain MRI and
    confirmed at autopsy, with relative sparing of the cerebellum - the human
    imaging and neuropathologic correlate of the region-selective cortical and
    hippocampal neuronal loss modelled in Amsh-deficient mice. It is the
    radiographic signature that separates MIC-CAP from a purely developmental
    (non-progressive) primary microcephaly, and it names the "Progressive
    Microcephaly and Cortical Atrophy" pathophysiology node. No frequency band is
    asserted: the quotable documentation covers two autopsied/imaged patients and
    no series reports a denominator for atrophy specifically.
  phenotype_term:
    preferred_term: Progressive generalized cerebral atrophy
    term:
      id: HP:0002059
      label: Cerebral atrophy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "progressive and generalized cerebral atrophy brain MRI at 19 months of age (Patient 1), and autopsy at 17 months of age (Patient 2), with relative sparing of the cerebellum"
    explanation: >-
      Direct imaging and autopsy documentation of progressive generalized
      cerebral atrophy with cerebellar sparing in two MIC-CAP patients.
  - reference: PMID:23542699
    reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "severe microcephaly with progressive cortical atrophy"
    explanation: >-
      The molecularly defined discovery cohort characterizes the syndrome by
      progressive cortical atrophy alongside the microcephaly.
- name: Capillary malformation
  category: Dermatological
  description: >
    Multiple small, blanchable, pink-to-red, oval or circular cutaneous macules
    and patches distributed generally over the body, present at birth. Number
    ranges from a few to hundreds and size from 1-2 mm to several centimetres.
    Not obligate across the full STAMBP spectrum - at least one patient with
    biallelic STAMBP variants had no apparent capillary malformation.
  phenotype_term:
    preferred_term: Capillary malformation
    term:
      id: HP:0025104
      label: Capillary malformation
  frequency: VERY_FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "generalized cutaneous capillary malformations (a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm)"
    explanation: GeneReviews describes the lesions as a defining feature present at birth.
  - reference: PMID:36033615
    reference_title: "Novel compound heterozygous mutation in STAMBP causes a neurodevelopmental disorder by disrupting cortical proliferation."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "but without apparent capillary malformation on the skin and organs"
    explanation: >
      Documents a biallelic-STAMBP patient lacking the eponymous cutaneous sign,
      which is why the frequency is VERY_FREQUENT rather than obligate.
- name: Early-onset intractable epilepsy
  category: Neurological
  description: >
    Seizures begin in the neonatal period or the first months of life and are
    refractory to multiple anticonvulsants. Semiology includes focal, tonic and
    complex partial seizures and infantile spasms; the disorder is now framed as
    a recognizable developmental and epileptic encephalopathy. Seizure burden
    tends to stabilize after age two years.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
    temporality: RECURRENT
  frequency: VERY_FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "early-onset intractable epilepsy, and profound developmental delay"
    explanation: GeneReviews lists early-onset intractable epilepsy among the defining features present at birth.
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seizures, which can be focal, tonic, and complex partial and can include infantile spasms, appear to stabilize after age two years."
    explanation: Documents semiology and the post-2-year stabilization.
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The present study also highlighted the fact that STAMBP mutation-associated MIC-CAP often presents as intractable early-life epilepsy, which may lead to mortality."
    explanation: Confirms intractability and its contribution to mortality.
- name: Infantile spasms
  category: Neurological
  description: >
    Clusters of epileptic spasms in infancy, frequently with interictal
    hypsarrhythmia on EEG.
  phenotype_term:
    preferred_term: Infantile spasms
    term:
      id: HP:0012469
      label: Infantile spasms
  frequency: FREQUENT
  evidence:
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The child developed early-onset epilepsy after 3 months, with a generalized tonic-clonic seizure, which progressed to clusters of infantile spasms (2-10 clusters/day) 1 month later."
    explanation: Documents infantile spasms in a molecularly confirmed patient.
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "intractable epilepsy including infantile spasms"
    explanation: Infantile spasms in the original clinical delineation series.
- name: Hypsarrhythmia
  category: Neurological
  description: Interictal hypsarrhythmia with a slow-wave background on electroencephalography.
  phenotype_term:
    preferred_term: Hypsarrhythmia
    term:
      id: HP:0002521
      label: Hypsarrhythmia
  evidence:
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Interictal electroencephalography showed hypsarrhythmia and slow wave background with bioccipital spike-slow wave during waking"
    explanation: Direct EEG documentation of hypsarrhythmia.
- name: Profound global developmental delay
  category: Neurological
  description: >
    Developmental progress is minimal; most affected individuals do not attain
    head control or independent sitting. A rare exception with a leaky splice
    allele achieved independent walking and short-phrase speech.
  phenotype_term:
    preferred_term: Profound global developmental delay
    term:
      id: HP:0012736
      label: Profound global developmental delay
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "early-onset intractable epilepsy, and profound developmental delay"
    explanation: GeneReviews lists profound developmental delay among the defining features.
  - reference: PMID:25692795
    reference_title: "Novel STAMBP mutation and additional findings in an Arabic family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characterized by severe microcephaly, early-onset seizures, profound psychomotor disability, and multiple cutaneous capillary lesions"
    explanation: Independent confirmation of profound psychomotor disability.
- name: Short distal phalanx of finger
  category: Skeletal
  description: >
    Hypoplastic distal phalanges of the hands and/or feet, with small nails. This
    is the most reliable non-neurological, non-cutaneous diagnostic handle and is
    the feature that most efficiently separates MIC-CAP from primary autosomal
    recessive microcephaly on physical examination.
  phenotype_term:
    preferred_term: Hypoplastic distal phalanges of the hands and/or feet
    term:
      id: HP:0009882
      label: Short distal phalanx of finger
  frequency: VERY_FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "hypoplastic distal phalanges of the hands and/or feet"
    explanation: GeneReviews lists hypoplastic distal phalanges among the defining features present at birth.
  - reference: PMID:25692795
    reference_title: "Novel STAMBP mutation and additional findings in an Arabic family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "affected patients have variable dysmorphic facial features and hypoplastic distal phalanges"
    explanation: Independent confirmation of the digital phenotype.
- name: Small nail
  category: Dermatological
  description: Nail hypoplasia accompanying the hypoplastic distal phalanges.
  phenotype_term:
    preferred_term: Small nail
    term:
      id: HP:0001792
      label: Small nail
  frequency: FREQUENT
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The toes were short, with hypoplasia of the toe nails bilaterally"
    explanation: Direct documentation of bilateral toe-nail hypoplasia.
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Digits were tapered with hypoplastic distal phalanges with complete aplasia of the right first toe nail"
    explanation: Nail aplasia accompanying the hypoplastic distal phalanges in a second patient of the same series.
- name: Central hypotonia
  category: Neurological
  description: >
    Low axial/central muscle tone, the truncal half of the distinctive mixed
    tone pattern of MIC-CAP (central hypotonia with peripheral hypertonia). It
    is the reason affected infants cannot hold their heads up and is what the
    GeneReviews seating-and-bracing recommendation is written to manage. Curated
    against HP:0001290 Generalized hypotonia because the specific HPO term
    "Central hypotonia" (HP:0011398) is obsolete; the `preferred_term` retains
    the clinically accurate central/axial qualifier.
  phenotype_term:
    preferred_term: Central hypotonia
    term:
      id: HP:0001290
      label: Generalized hypotonia
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Central hypotonia and peripheral hypertonia require attention to proper seating and bracing to maintain posture and prevent contractures."
    explanation: >-
      GeneReviews names central hypotonia as a management target in MIC-CAP;
      PARTIAL because the statement is a management recommendation that presumes
      the finding rather than a frequency-bearing clinical observation, and
      because the HPO term used here is the generalized rather than the
      central-specific concept.
- name: Peripheral hypertonia
  category: Neurological
  description: >
    Increased tone in the limbs with brisk deep tendon reflexes and clonus - the
    appendicular half of the mixed tone pattern, and the finding that evolves
    into the spastic tetraparesis curated below. Bracing is directed at the
    contracture risk this creates.
  phenotype_term:
    preferred_term: Peripheral hypertonia
    term:
      id: HP:0001276
      label: Hypertonia
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Muscle tone was markedly increased with brisk (+4) deep tendon reflexes in the upper and lower extremities, and clonus."
    explanation: >-
      Direct examination finding of markedly increased limb tone with brisk
      reflexes and clonus in a patient of the original delineation series.
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Central hypotonia and peripheral hypertonia require attention to proper seating and bracing to maintain posture and prevent contractures."
    explanation: >-
      GeneReviews names peripheral hypertonia as a management target; PARTIAL
      because it is a management statement rather than a frequency-bearing
      clinical observation.
- name: Spastic tetraparesis
  category: Neurological
  description: >
    A distinctive mixed-tone pattern of central hypotonia with peripheral
    hypertonia evolving into spastic tetraparesis, which is the reason most
    affected individuals never attain head control or independent sitting. The
    two tone components are curated as their own HPO-bound phenotype entries
    (Central hypotonia, Peripheral hypertonia) so that they are queryable
    independently of this composite motor outcome.
  phenotype_term:
    preferred_term: Spastic tetraparesis
    term:
      id: HP:0001285
      label: Spastic tetraparesis
    clinical_course: PROGRESSIVE
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "(3) severe spastic quadriparesis, (4) neonatal-onset intractable epilepsy that included infantile spasms in 2/5 children"
    explanation: >
      Severe spastic quadriparesis listed among the essential features present in
      all five patients of the original delineation series, supporting the
      VERY_FREQUENT band.
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Central hypotonia and peripheral hypertonia require attention to proper seating and bracing to maintain posture and prevent contractures."
    explanation: >
      GeneReviews documents the mixed central-hypotonia/peripheral-hypertonia
      pattern; it describes tone abnormality and its management rather than
      naming spastic tetraparesis, hence PARTIAL.
  - reference: PMID:27531570
    reference_title: "Microcephaly-capillary malformation syndrome: Brothers with a homozygous STAMBP mutation, uncovered by exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "presenting with microcephaly, apparent global developmental delay, seizures, spasticity, congenital blindness, and multiple cutaneous capillary malformations"
    explanation: Spasticity documented in molecularly confirmed siblings.
- name: Myoclonus
  category: Neurological
  description: Myoclonus of the limbs and eyelids, a common and characteristic movement finding.
  phenotype_term:
    preferred_term: Myoclonus
    term:
      id: HP:0001336
      label: Myoclonus
  frequency: FREQUENT
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Myoclonus of the limbs and eyelids is common; other abnormal movements (dyskinetic, choreiform) may be seen."
    explanation: >
      GeneReviews describes myoclonus as common, which maps to the FREQUENT band
      per the project's prose-to-frequency mapping table.
- name: Dyskinesia
  category: Neurological
  description: >
    Hyperkinetic movements including dyskinetic and choreiform movements. In one
    reported case whole-body dyskinesia with prominent involuntary tongue and
    mouth movement was the dominant motor finding.
  phenotype_term:
    preferred_term: Dyskinesia
    term:
      id: HP:0100660
      label: Dyskinesia
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "other abnormal movements (dyskinetic, choreiform) may be seen"
    explanation: >
      GeneReviews describes dyskinetic and choreiform movements as findings that
      "may be seen", mapping to the OCCASIONAL band.
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "dyskinesia was more prominent in the present study and was infrequent in previous cases"
    explanation: Reports prominent dyskinesia while confirming that it is infrequent across the reported series.
- name: Simplified gyral pattern
  category: Imaging
  description: >
    Reduced number of gyri with shallow sulci on brain MRI, an imaging hallmark
    shared with other congenital microcephalies.
  phenotype_term:
    preferred_term: Simplified gyral pattern
    term:
      id: HP:0009879
      label: Simplified gyral pattern
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All showed obvious MIC with a low-sloping forehead, diffusely reduced number of gyri with shallow sulci consistent with a severe simplified gyral pattern, and moderately enlarged extra-axial space."
    explanation: >
      Brain MRI in all three patients of the original clinical delineation series
      showed a severe simplified gyral pattern, supporting the VERY_FREQUENT band.
- name: Extra-axial cerebrospinal fluid accumulation
  category: Imaging
  description: Increased extra-axial cerebrospinal fluid space on brain MRI, reported in nearly all imaged patients.
  phenotype_term:
    preferred_term: Extra-axial cerebrospinal fluid accumulation
    term:
      id: HP:0012510
      label: Extra-axial cerebrospinal fluid accumulation
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All showed obvious MIC with a low-sloping forehead, diffusely reduced number of gyri with shallow sulci consistent with a severe simplified gyral pattern, and moderately enlarged extra-axial space."
    explanation: Enlarged extra-axial space on MRI in all three patients of the original delineation series.
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The MRI scans showed slightly dilated lateral ventricles and increased extra-axial spaces."
    explanation: Independent MRI documentation of increased extra-axial cerebrospinal fluid space.
- name: Hypoplastic hippocampus
  category: Imaging
  description: >
    Hippocampal hypoplasia on brain MRI, the human structural correlate of the
    CA1-selective neuronal loss seen in Amsh-deficient mice.
  phenotype_term:
    preferred_term: Hypoplastic hippocampus
    term:
      id: HP:0025517
      label: Hypoplastic hippocampus
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The hippocampus was small in all three patients, and the cerebellum was slightly small but proportionate to the overall brain size."
    explanation: >
      Human MRI evidence of hippocampal hypoplasia in 3/3 imaged patients, with
      the cerebellum comparatively spared.
  - reference: PMID:11713295
    reference_title: "Loss of neurons in the hippocampus and cerebral cortex of AMSH-deficient mice."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "complete loss of the CA1 neurons in the hippocampus"
    explanation: Model-organism correlate of the human hippocampal phenotype.
- name: CNS hypomyelination
  category: Imaging
  description: >
    Thin and immature cerebral white matter with delayed myelination on brain
    MRI. The FREQUENT band follows the HPO annotation set for OMIM:614261, which
    records CNS hypomyelination in 5/8 assessed individuals; the quotable
    primary-literature documentation below covers one of the three patients in
    the original delineation series.
  phenotype_term:
    preferred_term: CNS hypomyelination
    term:
      id: HP:0003429
      label: CNS hypomyelination
  frequency: FREQUENT
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Patient 3 had thin and immature white matter."
    explanation: >
      Documents thin/immature white matter in a molecularly compatible MIC-CAP
      patient; PARTIAL because it evidences the finding, not the FREQUENT band
      (that derives from the HPO 5/8 annotation, which has no quotable abstract).
- name: Minor congenital heart malformation
  category: Cardiovascular
  description: >
    Minor structural cardiac anomalies - small atrial septal defect, small
    muscular ventricular septal defect, patent foramen ovale - reported in a
    subset of patients. These are incidental/minor lesions, not a defining
    feature, and are not reported to cause haemodynamic compromise.
  phenotype_term:
    preferred_term: Minor congenital heart malformation
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "minor heart malformations in 3/5 including a small atrial septal defect in one, and a small muscular VSD in another"
    explanation: Counted minor cardiac malformations across the first five reported patients.
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Echocardiogram showed a patent foramen ovale, mild concentric right ventricular hypertrophy, possible right ventricular noncompaction, dilated median pulmonary artery, and a small pericardial effusion."
    explanation: Echocardiographic detail in one molecularly compatible patient.
- name: Optic atrophy
  category: Ophthalmological
  description: >
    Optic atrophy with hypoplasia of the optic nerves and/or chiasm, contributing
    with cortical visual impairment to severe visual loss.
  phenotype_term:
    preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
    clinical_course: PROGRESSIVE
  frequency: FREQUENT
  evidence:
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "both optic atrophy and spastic quadriparesis were common in previous cases"
    explanation: >
      Explicit statement that optic atrophy is common across previously reported
      MIC-CAP cases, supporting the FREQUENT band.
- name: Blindness
  category: Ophthalmological
  description: Congenital blindness reported in molecularly confirmed siblings.
  phenotype_term:
    preferred_term: Blindness
    term:
      id: HP:0000618
      label: Blindness
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:27531570
    reference_title: "Microcephaly-capillary malformation syndrome: Brothers with a homozygous STAMBP mutation, uncovered by exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "presenting with microcephaly, apparent global developmental delay, seizures, spasticity, congenital blindness, and multiple cutaneous capillary malformations"
    explanation: Direct report of congenital blindness in two affected brothers.
- name: Small for gestational age
  category: Growth
  description: Reduced birth size, reflecting prenatal onset of the growth phenotype.
  phenotype_term:
    preferred_term: Small for gestational age
    term:
      id: HP:0001518
      label: Small for gestational age
  frequency: FREQUENT
  evidence:
  - reference: PMID:25266620
    reference_title: "The microcephaly-capillary malformation syndrome in two brothers with novel clinical features."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "congenital and progressive microcephaly, intractable epilepsy, profound developmental delay, multiple small capillary malformations on the skin, and poor somatic growth"
    explanation: Documents poor somatic growth as part of the syndrome; prenatal onset is inferred from congenital microcephaly.
- name: Failure to thrive
  category: Growth
  description: >
    Postnatal growth failure with oropharyngeal dysphagia and aspiration risk;
    documented weight -2.8 SD and length -6.8 SD at 17 months in one case.
    Gastrostomy feeding is standard of care.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
    clinical_course: PROGRESSIVE
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in weight and 63 cm (Z-score, −6.8 SD) in length"
    explanation: Quantitative documentation of severe postnatal growth failure.
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "he continued to have failure to thrive"
    explanation: Failure to thrive persisting despite gastrostomy in a second independent patient.
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "A feeding tube is essential to optimize nutrition and weight gain while reducing the risk of aspiration."
    explanation: >
      GeneReviews treats feeding-tube placement as essential; this supports the
      management need rather than directly measuring growth failure, hence
      PARTIAL.
- name: Feeding difficulties
  category: Gastrointestinal
  description: Oropharyngeal dysphagia with aspiration risk requiring enteral feeding.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Given significant feeding difficulties and secondary respiratory complications, he underwent G-tube placement"
    explanation: Direct documentation of feeding difficulty requiring gastrostomy.
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Supportive care by multidisciplinary specialists including a medical geneticist, neurologist, developmental pediatrician, and feeding specialist is recommended."
    explanation: >
      Routine inclusion of a feeding specialist in standard care is indirect
      support for near-universal feeding difficulty, hence PARTIAL.
- name: Recurrent pneumonia
  category: Respiratory
  description: >
    Repeated episodes of pneumonia, the principal secondary respiratory
    complication of the oropharyngeal dysphagia and gastroesophageal reflux.
    Documented independently in two molecularly compatible patients, one
    requiring repeated hospitalizations and gastrostomy plus Nissen
    fundoplication, the other intravenous immunoglobulin. This is the concrete
    morbidity behind the GeneReviews statement that a feeding tube is essential
    to reduce aspiration risk, and it is a leading proximate cause of
    hospitalization and death. No frequency band is asserted: no series reports
    a denominator.
  phenotype_term:
    preferred_term: Recurrent pneumonia
    term:
      id: HP:0006532
      label: Recurrent pneumonia
    temporality: RECURRENT
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "episodes of pneumonia necessitating further hospitalizations"
    explanation: >-
      Repeated pneumonia requiring hospitalization in a patient of the original
      delineation series, in the setting of reflux and poor oral feeding.
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "received immunoglobulin intravenously as a result of recurrent pneumonia"
    explanation: >-
      Independent documentation of recurrent pneumonia in a molecularly
      confirmed patient.
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "A feeding tube is essential to optimize nutrition and weight gain while reducing the risk of aspiration."
    explanation: >-
      GeneReviews frames aspiration risk as the management driver; PARTIAL
      because it names aspiration risk rather than pneumonia itself.
- name: Abnormal facial shape
  category: Craniofacial
  description: >
    Variable dysmorphic facial features including a sloping forehead, short and
    wide nose, maxillary hypoplasia, low-set ears, ptosis and hypertelorism;
    drooping mouth corners and a short neck have also been described.
  phenotype_term:
    preferred_term: Dysmorphic facial features
    term:
      id: HP:0001999
      label: Abnormal facial shape
  frequency: FREQUENT
  evidence:
  - reference: PMID:29907875
    reference_title: "A novel homozygous missense mutation in the SH3-binding motif of STAMBP causing microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "severe global developmental delay, progressive microcephaly, refractory seizures, dysmorphic facial features, and multiple capillary malformations"
    explanation: Direct documentation of dysmorphic facial features in a molecularly confirmed patient.
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient had drooping mouth corners, a short nose and neck"
    explanation: Specific facial findings in a molecularly confirmed patient.
- name: Congenital hypothyroidism
  category: Endocrine
  description: >
    Congenital hypothyroidism reported independently in two of the roughly
    fifteen published families, making it the best-replicated of the expanding
    features of the syndrome. The OCCASIONAL band is a derived count (2/15
    families) rather than a reported frequency.
  phenotype_term:
    preferred_term: Congenital hypothyroidism
    term:
      id: HP:0000851
      label: Congenital hypothyroidism
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:25692795
    reference_title: "Novel STAMBP mutation and additional findings in an Arabic family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "which additionally display previously unreported findings of congenital hypothyroidism and alopecia areata"
    explanation: First report of congenital hypothyroidism in MIC-CAP.
  - reference: PMID:25266620
    reference_title: "The microcephaly-capillary malformation syndrome in two brothers with novel clinical features."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "these boys exhibited certain novel and distinctive phenotypic features (congenital hypothyroidism and autistic-like behavior with intermittent repetitive hand-flapping movements)"
    explanation: Independent second-family replication of congenital hypothyroidism.
- name: Patchy alopecia
  category: Dermatological
  description: Alopecia areata reported in a single family.
  phenotype_term:
    preferred_term: Alopecia areata
    term:
      id: HP:0002232
      label: Patchy alopecia
  frequency: VERY_RARE
  evidence:
  - reference: PMID:25692795
    reference_title: "Novel STAMBP mutation and additional findings in an Arabic family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "previously unreported findings of congenital hypothyroidism and alopecia areata"
    explanation: Single-family report of alopecia areata.
- name: Autistic behavior
  category: Behavioral
  description: >
    Autistic-like behavior with repetitive hand-flapping stereotypies, and a
    formal autism spectrum disorder diagnosis in a patient at the attenuated end
    of the STAMBP spectrum.
  phenotype_term:
    preferred_term: Autistic behavior
    term:
      id: HP:0000729
      label: Autistic behavior
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:25266620
    reference_title: "The microcephaly-capillary malformation syndrome in two brothers with novel clinical features."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "autistic-like behavior with intermittent repetitive hand-flapping movements"
    explanation: Autistic-like behavior with stereotypies in two affected brothers.
  - reference: PMID:36033615
    reference_title: "Novel compound heterozygous mutation in STAMBP causes a neurodevelopmental disorder by disrupting cortical proliferation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient was presented with global developmental delay, autism spectrum disorder, microcephaly, epilepsy, and dysmorphic facial features"
    explanation: Formal autism spectrum disorder diagnosis in a biallelic STAMBP patient.

histopathology:
- name: Dilated small-caliber papillary dermal vessels
  description: >
    Skin biopsy of the cutaneous lesions shows dilated small-caliber blood
    vessels confined to the papillary dermis, histologically confirming them as
    true capillary malformations rather than proliferative vascular tumours
    (haemangiomas). This is the only tissue-level pathology published in MIC-CAP;
    no endothelial signaling (phospho-S6 / phospho-ERK) study has been performed
    on the same tissue - see the capillary-malformation-mechanism knowledge gap.
  diagnostic: true
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Skin biopsies were performed in Patients 2 and 3. Both showed dilated small-caliber blood vessels in the papillary dermis, consistent with capillary malformations (CMs)"
    explanation: Direct histopathologic confirmation of the cutaneous lesions as capillary malformations.

diagnosis:
- name: Clinical recognition of the cardinal feature set
  description: >
    Diagnosis is suspected in an infant with the congenital combination of
    microcephaly, multiple generalized cutaneous capillary malformations,
    hypoplastic distal phalanges, early-onset intractable epilepsy and profound
    developmental delay. The digital and cutaneous features are what separate
    MIC-CAP from primary autosomal recessive microcephaly on physical
    examination.
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The defining clinical characteristics of the microcephaly-capillary malformation (MIC-CAP) syndrome are typically present at birth: microcephaly and generalized cutaneous capillary malformations (a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm), hypoplastic distal phalanges of the hands and/or feet, early-onset intractable epilepsy, and profound developmental delay."
    explanation: The GeneReviews statement of the suggestive clinical findings on which diagnosis is predicated.
- name: Molecular genetic testing of STAMBP
  description: >
    The diagnosis is established by identifying biallelic pathogenic STAMBP
    variants on molecular genetic testing. Exome sequencing is the usual route;
    note that the deep-intronic leaky splice allele c.1005+358A>G is invisible to
    exome sequencing, so genome sequencing or RNA studies may be required in a
    clinically compatible exome-negative proband. Chromosomal microarray has been
    normal in the reported patients in whom it was performed and has no
    established yield in this disorder.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of MIC-CAP syndrome is established in a proband with suggestive findings and biallelic pathogenic variants in STAMBP identified by molecular genetic testing."
    explanation: The GeneReviews DIAGNOSIS/TESTING statement naming the confirmatory test.
  - reference: PMID:27531570
    reference_title: "Microcephaly-capillary malformation syndrome: Brothers with a homozygous STAMBP mutation, uncovered by exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we uncovered a homozygous missense variant in STAMBP (p.K303R) in the two siblings, inherited from heterozygous carrier parents"
    explanation: Worked example of exome sequencing establishing the molecular diagnosis.
- name: Exclusion of inborn errors of metabolism and infectious causes
  description: >
    Routine metabolic and infectious workup is normal in MIC-CAP, which is itself
    diagnostically informative: a normal metabolic screen in a severely
    microcephalic epileptic infant with generalized capillary malformations
    argues for MIC-CAP rather than a metabolic encephalopathy or congenital
    infection.
  presence: Negative
  evidence:
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Laboratory studies conducted with normal results include high-resolution chromosome analysis, urine organic acids, very long chain fatty acids, quantitative CSF amino acids analysis, congenital disorders of glycosylation screen and workup for an infectious etiology (including TORCH titers)."
    explanation: Documents the normal metabolic and infectious workup that excludes the main differentials.

genetic:
- name: STAMBP
  notes: >
    STAMBP (2p13.1) encodes the 424-residue STAM-binding protein / AMSH, a
    Zn(2+)-dependent JAMM/MPN+ metalloprotease deubiquitinase specific for
    Lys63-linked polyubiquitin. Biallelic loss-of-function variants - homozygous
    or compound heterozygous - are necessary and sufficient for MIC-CAP. The
    reported allele spectrum is dominated by truncating and splice-disrupting
    variants, with a minority of missense alleles that cluster in the N-terminal
    MIT domain and the SH3-binding motif rather than in the catalytic JAMM
    domain. Recurrent alleles include p.Arg38Cys and p.Arg424*; a deep-intronic
    leaky splice allele (c.1005+358A>G) is associated with a markedly attenuated
    phenotype and is invisible to exome sequencing. Heterozygous carriers are
    asymptomatic; no gain-of-function or dominant-negative mechanism is known.
  gene_term:
    preferred_term: STAMBP
    term:
      id: hgnc:16950
      label: STAMBP
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  evidence:
  - reference: PMID:23542699
    reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We used whole-exome sequencing of five patients with MIC-CAP syndrome and identified recessive mutations in STAMBP"
    explanation: Original gene-disease discovery by exome sequencing of five patients.
  - reference: PMID:29907875
    reference_title: "A novel homozygous missense mutation in the SH3-binding motif of STAMBP causing microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Microcephaly-capillary malformation syndrome is a congenital and neurodevelopmental disorder caused by biallelic mutations in the STAMBP gene."
    explanation: Independent confirmation of the biallelic STAMBP gene-disease relationship.
  - reference: PMID:27531570
    reference_title: "Microcephaly-capillary malformation syndrome: Brothers with a homozygous STAMBP mutation, uncovered by exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we uncovered a homozygous missense variant in STAMBP (p.K303R) in the two siblings, inherited from heterozygous carrier parents"
    explanation: Demonstrates recessive segregation from asymptomatic heterozygous carrier parents.

inheritance:
- name: Autosomal recessive inheritance
  description: >
    MIC-CAP is autosomal recessive. Typically one pathogenic STAMBP variant is
    inherited from each parent, giving a 25% recurrence risk to sibs. In a
    minority of families both variants derive from one parent through uniparental
    isodisomy of chromosome 2, in which case the sib recurrence risk falls to
    under 1% - a distinction with substantial counseling consequences. Penetrance
    in biallelic individuals appears complete; expressivity is variable and
    tracks residual STAMBP protein level.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  penetrance: COMPLETE
  expressivity: VARIABLE
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MIC-CAP syndrome is an autosomal recessive disorder caused by biallelic STAMBP pathogenic variants."
    explanation: GeneReviews states the mode of inheritance unambiguously.
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Typically, one pathogenic variant is inherited from each parent; however, in some instances both pathogenic variants are inherited from one parent (uniparental isodisomy)."
    explanation: Documents the uniparental isodisomy route and its counseling implications.
  - reference: PMID:21815250
    reference_title: "The microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two of our reported patients are an affected brother and sister, suggesting this is an autosomal recessive severe congenital MIC syndrome."
    explanation: Pre-molecular sibship evidence that first established recessive inheritance.

treatments:
- name: Multidisciplinary Supportive and Palliative Care
  description: >
    No disease-modifying therapy exists. Management is supportive and is
    delivered by a multidisciplinary team including medical genetics, neurology,
    developmental pediatrics and feeding specialists, with regular child-neurology
    follow-up and involvement of a complex-care or palliative-care team to
    monitor complications of severe neurologic impairment.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Supportive care by multidisciplinary specialists including a medical geneticist, neurologist, developmental pediatrician, and feeding specialist is recommended."
    explanation: GeneReviews management recommendation for multidisciplinary supportive care.
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Regular follow up with a child neurologist for seizure management and a complex care / palliative care team or experienced pediatrician to monitor for complications associated with severe neurologic impairment."
    explanation: GeneReviews surveillance recommendation including palliative care.
- name: Anticonvulsant Polytherapy
  description: >
    Seizure management by an experienced pediatric neurology team; multiple
    anticonvulsant medications are usually required and control is often
    incomplete. Levetiracetam, topiramate, valproic acid and corticosteroids have
    been used in sequence in reported cases. Note the valproic-acid caution below.
  treatment_term:
    preferred_term: anticonvulsant therapy
    term:
      id: NCIT:C64172
      label: Anticonvulsant Therapy
    therapeutic_agent:
    - preferred_term: anticonvulsant agent
      term:
        id: NCIT:C264
        label: Anticonvulsant Agent
    - preferred_term: levetiracetam
      term:
        id: CHEBI:6437
        label: levetiracetam
  therapeutic_modality: SMALL_MOLECULE
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seizures require management by an experienced pediatric neurology team, as multiple anticonvulsant medications are frequently required for adequate seizure control."
    explanation: GeneReviews establishes anticonvulsant polytherapy as standard management.
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient was treated successively with levetiracetam (40-50 mg/kg/day), topiramate (6-7 mg/kg/day), valproic acid (30 mg/kg/day) and corticosteroids at the outpatient clinic. The spasms decreased and became myoclonic, but the epilepsy remained refractory."
    explanation: Documents a real drug sequence and its incomplete efficacy.
- name: Vigabatrin
  description: >
    Vigabatrin produced an 80% seizure reduction within a week in a single
    reported patient whose epilepsy had been refractory to levetiracetam,
    topiramate, valproic acid, corticosteroids and a ketogenic diet. This is a
    single case with three weeks of follow-up before the patient died, so
    long-term efficacy is unknown and vigabatrin should not be presented as
    established MIC-CAP therapy - though it is biologically coherent given the
    infantile-spasms phenotype for which vigabatrin is generally first line.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: vigabatrin
      term:
        id: CHEBI:63638
        label: vigabatrin
  therapeutic_modality: SMALL_MOLECULE
  evidence:
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "After 1 month, the patient received vigabatrin (60 mg/kg/day) and the seizures reduced by 80% a week later."
    explanation: The single reported vigabatrin response in MIC-CAP.
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Although the patient in the present study responded well to vigabatrin, the long-term efficacy of the drug could not be evaluated due to the early death of the patient."
    explanation: The authors' own caveat limiting the strength of this n=1 observation.
- name: Valproic Acid Caution
  description: >
    GeneReviews lists valproic acid under agents and circumstances to avoid, with
    deliberately hedged wording: one affected male died at 12 months of septic
    shock following acute pancreatitis possibly secondary to valproate, while
    other patients tolerated the drug. This is best treated as a caution
    warranting heightened pancreatic monitoring rather than an absolute
    contraindication.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: valproic acid
      term:
        id: CHEBI:39867
        label: valproic acid
  therapeutic_modality: SMALL_MOLECULE
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Agents/circumstances to avoid: Valproic acid may or may not be associated with adverse effects."
    explanation: >
      GeneReviews drug-safety statement; the hedged wording is why this is curated
      as a caution rather than a contraindication.
- name: Gastrostomy Feeding
  description: >
    Enteral feeding via gastrostomy tube to optimize nutrition and weight gain
    and to reduce aspiration risk. Aspiration pneumonia is a leading proximate
    cause of hospitalization and death.
  treatment_term:
    preferred_term: gastrostomy
    term:
      id: NCIT:C52006
      label: Gastrostomy
  therapeutic_modality: SURGERY
  target_phenotypes:
  - preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  - preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  - preferred_term: Recurrent pneumonia
    term:
      id: HP:0006532
      label: Recurrent pneumonia
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A feeding tube is essential to optimize nutrition and weight gain while reducing the risk of aspiration."
    explanation: GeneReviews treats gastrostomy feeding as essential management.
- name: Seating, Bracing and Physical Therapy
  description: >
    Attention to proper seating and bracing to maintain posture and prevent
    contractures, addressing the characteristic mixed pattern of central
    hypotonia with peripheral hypertonia.
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  therapeutic_modality: BEHAVIORAL
  target_phenotypes:
  - preferred_term: Central hypotonia
    term:
      id: HP:0001290
      label: Generalized hypotonia
  - preferred_term: Peripheral hypertonia
    term:
      id: HP:0001276
      label: Hypertonia
  - preferred_term: Spastic tetraparesis
    term:
      id: HP:0001285
      label: Spastic tetraparesis
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Central hypotonia and peripheral hypertonia require attention to proper seating and bracing to maintain posture and prevent contractures."
    explanation: GeneReviews management recommendation for tone and posture.
- name: Ketogenic Diet
  description: >
    A ketogenic diet was trialled in one reported patient and failed to control
    seizures even after the ratio was escalated from 2:1 to 4:1. Recorded here as
    a documented negative result rather than a recommended therapy.
  treatment_term:
    preferred_term: ketogenic diet
    term:
      id: NCIT:C173168
      label: Ketogenic Diet
  therapeutic_modality: BEHAVIORAL
  evidence:
  - reference: PMID:31638258
    reference_title: "Early-onset epilepsy and microcephaly-capillary malformation syndrome caused by a novel STAMBP mutation in a Chinese boy."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "During the follow-up, the seizures were still not well controlled, although the ketogenic diet ratio was modified from 2:1 to 4:1"
    explanation: Documents failure of the ketogenic diet in the one case where it was tried.
- name: Genetic Counseling and Reproductive Options
  description: >
    Counseling on the 25% sib recurrence risk for biparental inheritance, and on
    the substantially lower (<1%) risk when the proband's homozygosity arose
    through uniparental isodisomy. Once the familial variants are known, carrier
    testing, prenatal testing and preimplantation genetic testing are available.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "carrier testing for at-risk family members, prenatal testing for pregnancies at increased risk, and preimplantation genetic testing are possible"
    explanation: GeneReviews genetic-counseling options once familial variants are identified.
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier"
    explanation: The standard biparental recurrence risk that counseling conveys.
- name: AAV9-Mediated STAMBP Gene Replacement (Preclinical)
  description: >
    Neonatal AAV9-mediated brain-directed supplementation of Stambp significantly
    improved neurological defects, sustained growth and prolonged lifespan in a
    CNS-specific Stambp knockout mouse. This is the leading translational
    prospect for MIC-CAP and is unusually favourable on paper: the STAMBP coding
    sequence is small enough for AAV packaging, the CNS-restricted knockout
    phenocopies the global null (so brain-directed delivery may suffice), and the
    intervention worked postnatally. It remains mouse-only - there is no
    investigational new drug application, no clinical trial and no human data.
  treatment_term:
    preferred_term: gene therapy
    term:
      id: NCIT:C15238
      label: Gene Therapy
  therapeutic_modality: GENE_THERAPY
  target_mechanisms:
  - target: Loss of STAMBP/AMSH K63-Linked Deubiquitinase Activity
    treatment_effect: RESTORES
    description: Gene supplementation restores AMSH deubiquitinase activity in the brain.
    evidence:
    - reference: PMID:39169623
      reference_title: "AAV-mediated Stambp gene replacement therapy rescues neurological defects in a mouse model of microcephaly-capillary malformation syndrome."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "neonatal AAV9-mediated gene supplementation of Stambp in the brain could significantly improve neurological defects"
      explanation: Demonstrates that restoring Stambp in the brain corrects the downstream phenotype.
  evidence:
  - reference: PMID:39169623
    reference_title: "AAV-mediated Stambp gene replacement therapy rescues neurological defects in a mouse model of microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Importantly, neonatal AAV9-mediated gene supplementation of Stambp in the brain could significantly improve neurological defects, sustain growth, and prolong the lifespan of StambpSox1-cKO mice."
    explanation: Preclinical efficacy of postnatal brain-directed gene replacement.
  - reference: PMID:39169623
    reference_title: "AAV-mediated Stambp gene replacement therapy rescues neurological defects in a mouse model of microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "provide preclinical evidence that postnatal gene replacement is an effective approach to cure the disease"
    explanation: The authors' own framing of the translational claim, explicitly preclinical.

differential_diagnoses:
- name: Megalencephaly-capillary malformation syndrome (MCAP)
  description: >
    The single most important named-entity confusion for MIC-CAP. MCAP is part of
    the PIK3CA-related overgrowth spectrum and shares only the
    capillary-malformation token. Everything else runs in the opposite direction:
    MCAP is a sporadic somatic mosaic activating PIK3CA disorder with
    megalencephaly, segmental overgrowth and polymicrogyria, whereas MIC-CAP is a
    germline biallelic loss-of-function STAMBP deubiquitinase defect with
    microcephaly and progressive cortical atrophy. MCAP additionally has a
    targeted therapy (alpelisib) that has no rationale in MIC-CAP.
  disease_term:
    preferred_term: megalencephaly-capillary malformation-polymicrogyria syndrome
    term:
      id: MONDO:0011240
      label: megalencephaly-capillary malformation-polymicrogyria syndrome
  distinguishing_features:
  - Megalencephaly (brain and head overgrowth) rather than microcephaly
  - Somatic mosaic gain-of-function PIK3CA rather than germline biallelic loss-of-function STAMBP
  - Sporadic/mosaic rather than autosomal recessive
  - Asymmetric segmental overgrowth of limbs, trunk and face
  - Polymicrogyria, ventriculomegaly, thick corpus callosum and cerebellar tonsillar ectopia
  - No hypoplastic distal phalanges
  - Targeted therapy with the PI3K-alpha inhibitor alpelisib is approved for PROS and has no rationale in MIC-CAP
  evidence:
  - reference: PMID:23946963
    reference_title: "PIK3CA-Related Overgrowth Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PROS was separated into distinct clinical syndromes based on the tissues and/or organs involved"
    explanation: >
      GeneReviews places the historical clinical syndrome names - MCAP among them -
      inside the PIK3CA-related overgrowth spectrum, establishing MCAP as a
      PIK3CA entity distinct in gene and mechanism from STAMBP-related MIC-CAP.
  - reference: PMID:23946963
    reference_title: "PIK3CA-Related Overgrowth Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of PROS is established in a proband with suggestive findings and a heterozygous mosaic (or rarely, constitutional) activating pathogenic variant in PIK3CA."
    explanation: Confirms the mosaic activating (gain-of-function) mechanism, the mechanistic opposite of biallelic STAMBP loss.
  - reference: PMID:23946963
    reference_title: "PIK3CA-Related Overgrowth Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the core features are congenital or early-childhood onset of segmental/focal overgrowth with or without cellular dysplasia"
    explanation: Overgrowth, not undergrowth, is the core PROS/MCAP feature - the opposite of MIC-CAP.
- name: Primary autosomal recessive microcephaly (MCPH)
  disease_term:
    preferred_term: autosomal recessive primary microcephaly
    term:
      id: MONDO:0016660
      label: autosomal recessive primary microcephaly
  description: >
    Congenital microcephaly with a simplified gyral pattern, caused by biallelic
    variants in ASPM, WDR62, MCPH1 and other centrosomal/mitotic genes. Shares the
    microcephaly and simplified gyri with MIC-CAP but lacks the cutaneous and
    digital features.
  distinguishing_features:
  - No cutaneous capillary malformations
  - No hypoplastic distal phalanges or nail hypoplasia
  - Epilepsy is usually not intractable and often absent
  - Cognitive impairment without major motor delay; motor development comparatively preserved
  - Growth largely normal apart from mild short stature
  - Facies normal except for a narrow or sloping forehead
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "microcephaly and generalized cutaneous capillary malformations (a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm), hypoplastic distal phalanges of the hands and/or feet"
    explanation: >
      The cutaneous and digital features quoted here are precisely what separate
      MIC-CAP from primary autosomal recessive microcephaly.
- name: Capillary malformation-arteriovenous malformation syndrome (CM-AVM)
  disease_term:
    preferred_term: capillary malformation-arteriovenous malformation syndrome
    term:
      id: MONDO:0012016
      label: capillary malformation-arteriovenous malformation syndrome
  description: >
    Autosomal dominant RASA1- or EPHB4-related disorder with multiple small
    cutaneous capillary malformations that closely resemble those of MIC-CAP, but
    with arteriovenous malformation/fistula risk instead of a neurodevelopmental
    phenotype.
  distinguishing_features:
  - Autosomal dominant, with an affected parent frequently identifiable
  - No microcephaly
  - No intractable epilepsy and no neurologic impairment
  - Arteriovenous malformations and arteriovenous fistulae are the principal risk
  - Caused by heterozygous RASA1 or EPHB4 variants rather than biallelic STAMBP variants
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "microcephaly and generalized cutaneous capillary malformations"
    explanation: >
      The co-occurrence of microcephaly with the capillary malformations is the
      discriminator from an isolated capillary-malformation syndrome such as
      CM-AVM.
- name: Sturge-Weber syndrome
  disease_term:
    preferred_term: Sturge-Weber syndrome
    term:
      id: MONDO:0008501
      label: Sturge-Weber syndrome
  description: >
    Mosaic GNAQ-related neurocutaneous disorder with a segmental facial port-wine
    stain, leptomeningeal angiomatosis, glaucoma and epilepsy.
  distinguishing_features:
  - Segmental facial port-wine stain, typically in the V1 trigeminal distribution, rather than generalized randomly distributed micro-lesions
  - Leptomeningeal angiomatosis
  - Glaucoma
  - Head size normal
  - Somatic mosaic GNAQ activation rather than germline biallelic STAMBP loss of function
  evidence:
  - reference: PMID:24354023
    reference_title: "Microcephaly-Capillary Malformation Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "generalized cutaneous capillary malformations"
    explanation: >
      The generalized (non-segmental) distribution of the MIC-CAP lesions is the
      key discriminator from the segmental port-wine stain of Sturge-Weber
      syndrome.

animal_models:
- species: Mus musculus
  genotype: Amsh (Stambp) constitutive knockout
  category: KNOCKOUT
  genes:
  - preferred_term: STAMBP
    term:
      id: hgnc:16950
      label: STAMBP
  description: >
    The original Amsh-null mouse is grossly normal at birth but shows postnatal
    growth retardation and dies between postnatal days 19 and 23, with apoptotic
    loss of CA1 hippocampal neurons from postnatal day 6, brain atrophy by
    postnatal day 16, and cell-autonomous failure of hippocampal (but not
    cerebellar) neuron survival in culture. A later analysis of the same model
    showed ubiquitinated-protein accumulation from embryonic day 10 with TDP-43,
    p62 and glutamate-receptor co-accumulation.
  evidence:
  - reference: PMID:11713295
    reference_title: "Loss of neurons in the hippocampus and cerebral cortex of AMSH-deficient mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "all the AMSH-deficient mice exhibited postnatal growth retardation and died between postnatal day 19 (P19) and P23"
    explanation: Establishes the lethal postnatal phenotype of complete Amsh loss.
  - reference: PMID:21531206
    reference_title: "AMSH is required to degrade ubiquitinated proteins in the central nervous system."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "AMSH(-/-) mice provide an animal model for neurodegenerative diseases, which are commonly characterized by the generation of proteinaceous aggregates."
    explanation: The authors' framing of the model's relevance to aggregate-driven neurodegeneration.
- species: Mus musculus
  genotype: Stambp Sox1-Cre conditional knockout (CNS-specific)
  category: CONDITIONAL_KNOCKOUT
  genes:
  - preferred_term: STAMBP
    term:
      id: hgnc:16950
      label: STAMBP
  description: >
    A central-nervous-system-restricted Stambp knockout that phenocopies the
    global null, including progressive microcephaly, postnatal growth retardation
    and fully penetrant preweaning death. It demonstrates that the CNS defect is
    sufficient for the lethal phenotype and provides the platform on which
    neonatal AAV9 gene replacement was shown to be efficacious.
  evidence:
  - reference: PMID:39169623
    reference_title: "AAV-mediated Stambp gene replacement therapy rescues neurological defects in a mouse model of microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "we generated a central nervous system (CNS)-specific Stambp knockout mouse model (Stambp Sox1-cKO) that phenocopies Stambp null mice including progressive microcephaly, postnatal growth retardation and complete penetrance of preweaning death"
    explanation: Defines the model and shows the CNS lesion is sufficient for the systemic phenotype.

experimental_models:
- name: STAMBP-knockout human cortical organoids
  description: >
    Three-dimensional human cortical organoids carrying a STAMBP knockout show
    reduced neural stem cell proliferation and smaller size without early
    apoptosis, and variant-specific rescue: wild-type STAMBP restores
    proliferation while the disease alleles p.Gly307Glu and p.Thr313Ile do not.
    This is the principal human model of the developmental (prenatal) arm of the
    disease.
  experimental_model_type: ORGANOID
  cell_types:
  - preferred_term: neural stem cell
    term:
      id: CL:0000047
      label: neural stem cell
  publication: PMID:36033615
  findings:
  - statement: STAMBP knockout reduces neural stem cell proliferation and organoid size.
    supporting_text: "Cortical organoids with STAMBP knockout (KO) showed significantly lower proliferation of neural stem cells (NSCs), leading to smaller organoids that are characteristic of microcephaly."
    evidence:
    - reference: PMID:36033615
      reference_title: "Novel compound heterozygous mutation in STAMBP causes a neurodevelopmental disorder by disrupting cortical proliferation."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Cortical organoids with STAMBP knockout (KO) showed significantly lower proliferation of neural stem cells (NSCs), leading to smaller organoids that are characteristic of microcephaly."
      explanation: The proliferation and size phenotype of the STAMBP-knockout organoid.
  - statement: The early organoid defect is proliferative rather than apoptotic.
    supporting_text: "Furthermore, STAMBP disruption did not affect apoptosis in early cortical organoids."
    evidence:
    - reference: PMID:36033615
      reference_title: "Novel compound heterozygous mutation in STAMBP causes a neurodevelopmental disorder by disrupting cortical proliferation."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Furthermore, STAMBP disruption did not affect apoptosis in early cortical organoids."
      explanation: Direct statement that apoptosis is unaffected in the early human organoid model.
  evidence:
  - reference: PMID:36033615
    reference_title: "Novel compound heterozygous mutation in STAMBP causes a neurodevelopmental disorder by disrupting cortical proliferation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "A 3D human cortical organoid model was used to investigate the function of STAMBP and the pathogenicity of the novel mutation"
    explanation: Describes the organoid model system curated here.
- name: STAMBP-deficient hESC-derived neural progenitor cells
  description: >
    Human embryonic stem cells with STAMBP deficiency differentiate normally to
    the neural lineage but their neural progenitor cells cannot be maintained or
    expanded long term. Downregulation of the anti-apoptotic protein CFLAR is the
    identified effector, and ectopic CFLAR expression rescues the defect.
  experimental_model_type: IPSC_DERIVED_MODEL
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  publication: PMID:38951308
  findings:
  - statement: STAMBP is dispensable for pluripotency and neural differentiation but required for long-term neural progenitor maintenance.
    supporting_text: "We found that STAMBP is dispensable for the pluripotency maintenance or neural differentiation of hESCs."
    evidence:
    - reference: PMID:38951308
      reference_title: "STAMBP is Required for Long-Term Maintenance of Neural Progenitor Cells Derived from hESCs."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "We found that STAMBP is dispensable for the pluripotency maintenance or neural differentiation of hESCs."
      explanation: Establishes that the defect is specific to progenitor maintenance rather than differentiation.
  - statement: CFLAR downregulation mediates the progenitor defect and CFLAR re-expression rescues it.
    supporting_text: "We identified the anti-apoptotic protein CFLAR is down-regulated in those affected NPCs and ectopic expression of CFLAR rescues NPC defects induced by STAMBP-deficiency."
    evidence:
    - reference: PMID:38951308
      reference_title: "STAMBP is Required for Long-Term Maintenance of Neural Progenitor Cells Derived from hESCs."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "ectopic expression of CFLAR rescues NPC defects induced by STAMBP-deficiency"
      explanation: The rescue experiment establishing CFLAR as the effector.
  evidence:
  - reference: PMID:38951308
    reference_title: "STAMBP is Required for Long-Term Maintenance of Neural Progenitor Cells Derived from hESCs."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In this study, we investigated the function and underlying mechanism of STAMBP during neural differentiation of human embryonic stem cells (hESCs)."
    explanation: Describes the hESC-derived neural model system curated here.
- name: Patient-derived lymphoblastoid cell lines
  description: >
    Epstein-Barr-virus-immortalized lymphoblastoid cell lines from MIC-CAP
    patients are the workhorse patient-cell model. They show reduced STAMBP
    protein, ubiquitin-conjugate aggregation, elevated autophagosome content,
    increased cleaved caspase-3 and Annexin V, and serum-insensitive RAS-MAPK and
    PI3K-AKT-mTOR activation, all reversible by lentiviral STAMBP transduction.
    They are a cell model, not a disease site.
  experimental_model_type: CELL_LINE
  cell_source: patient-derived, EBV-immortalized peripheral blood lymphocytes
  publication: PMID:23542699
  findings:
  - statement: Patient lymphoblastoid cell lines show reduced STAMBP, ubiquitin-conjugate aggregation, elevated apoptosis and serum-insensitive growth-pathway activation.
    supporting_text: "Patient cell lines showed reduced STAMBP expression associated with accumulation of ubiquitin-conjugated protein aggregates, elevated apoptosis and insensitive activation of the RAS-MAPK and PI3K-AKT-mTOR pathways."
    evidence:
    - reference: PMID:23542699
      reference_title: "Mutations in STAMBP, encoding a deubiquitinating enzyme, cause microcephaly-capillary malformation syndrome."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Patient cell lines showed reduced STAMBP expression associated with accumulation of ubiquitin-conjugated protein aggregates, elevated apoptosis and insensitive activation of the RAS-MAPK and PI3K-AKT-mTOR pathways."
      explanation: The primary patient-cell characterization underlying this model entry.
  evidence:
  - reference: PMID:29907875
    reference_title: "A novel homozygous missense mutation in the SH3-binding motif of STAMBP causing microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Immunoblot analysis of patient-derived lymphoblastoid cell lines (LCLs) revealed a severe reduction in STAMBP expression"
    explanation: Independent use of the same patient-derived lymphoblastoid cell line model.

discussions:
- discussion_id: miccap_apoptosis_vs_proliferation_model_mismatch
  prompt: >-
    Is the primary cellular lesion of STAMBP deficiency apoptotic neuronal death
    (as in mouse) or failed neural progenitor proliferation (as in human
    organoids), and does the mouse under-represent the prenatal human
    corticogenesis defect?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Region-Selective Neuronal Apoptosis and Progressive Neuronal Loss
  - pathophysiology#Impaired Neural Stem and Progenitor Cell Proliferation
  rationale: >-
    Amsh-null mice are grossly normal at birth and develop apoptotic CA1 and
    cortical neuronal loss postnatally, whereas human STAMBP-knockout cortical
    organoids show reduced neural stem cell proliferation with explicitly no
    early apoptosis. Human infants are microcephalic at birth AND progressively
    so, which neither model captures alone. The mismatch is mechanistically
    meaningful because it determines the therapeutic window: a purely postnatal
    apoptotic mechanism would be tractable to postnatal intervention, while a
    prenatal proliferative deficit would not.
  proposed_experiments:
  - experiment_id: miccap_exp_prenatal_proliferation_vs_apoptosis
    name: Stage-matched proliferation-versus-apoptosis comparison across mouse and human models
    description: >-
      Quantify proliferation (Ki-67, phospho-histone H3, EdU) and apoptosis
      (cleaved caspase-3, TUNEL) markers in embryonic Stambp-null mouse cortex
      alongside stage-matched human STAMBP-knockout cortical organoids.
    decision_criterion: >-
      Concordant proliferation deficits with discordant apoptosis would confirm
      that the mouse under-represents the prenatal human proliferative arm.
  - experiment_id: miccap_exp_human_brain_aggregate_ihc
    name: Ubiquitin, p62 and TDP-43 immunohistochemistry on human MIC-CAP brain
    description: >-
      Perform ubiquitin-conjugate, p62/SQSTM1 and TDP-43 immunohistochemistry on
      archived human MIC-CAP autopsy brain tissue. This is the direct human test
      of the mouse aggregate findings and, to our knowledge, has never been
      reported.
    decision_criterion: >-
      Presence of ubiquitin-conjugate, p62 and TDP-43 aggregates in human
      cortical and hippocampal neurons would confirm that the mouse proteostasis
      mechanism operates in human disease.
  - experiment_id: miccap_exp_postnatal_aav_window
    name: Postnatal-only AAV9 Stambp delivery window test
    description: >-
      Test whether AAV9-Stambp delivery restricted to defined postnatal windows
      rescues brain size, or merely slows further loss, in the Stambp Sox1-cKO
      mouse.
    decision_criterion: >-
      Rescue of absolute brain size would indicate a postnatally tractable
      mechanism; arrest of further decline without size recovery would indicate a
      fixed prenatal deficit.
  evidence:
  - reference: PMID:36033615
    reference_title: "Novel compound heterozygous mutation in STAMBP causes a neurodevelopmental disorder by disrupting cortical proliferation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Furthermore, STAMBP disruption did not affect apoptosis in early cortical organoids."
    explanation: The human-organoid observation that directly conflicts with the apoptosis-dominant mouse model.
  - reference: PMID:11713295
    reference_title: "Loss of neurons in the hippocampus and cerebral cortex of AMSH-deficient mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The AMSH-deficient mice were morphologically indistinguishable from their littermates at birth, and histopathological examinations revealed normal morphogenesis in all tissues tested."
    explanation: >
      The mouse is normal at birth, so it cannot model the congenital component of
      human microcephaly.
- discussion_id: miccap_capillary_malformation_mechanism_gap
  prompt: >-
    What actually causes the cutaneous capillary malformations, given that at
    least one patient had them without PI3K-AKT-mTOR activation?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Constitutive Serum-Insensitive RAS-MAPK and PI3K-AKT-mTOR Signaling
  - pathophysiology#Dermal Capillary Malformation
  rationale: >-
    The mTOR/MAPK hypothesis rests entirely on patient lymphoblastoid cell lines,
    which are not endothelium. A patient homozygous for p.Ser236Phe had multiple
    capillary malformations without detectable PI3K-AKT-mTOR activation, so either
    the mechanism is pathway-independent or the lymphoblastoid readout is
    uninformative about endothelial biology. Lesional skin has been biopsied and
    described histologically (dilated small-caliber papillary-dermal vessels),
    but no endothelial signaling study - phospho-S6, phospho-ERK or equivalent -
    has ever been performed on that tissue, despite the lesions being trivially
    accessible.
  proposed_experiments:
  - experiment_id: miccap_exp_cm_endothelial_signaling_ihc
    name: Endothelial signaling immunohistochemistry on MIC-CAP capillary malformations
    description: >-
      Biopsy MIC-CAP cutaneous capillary malformations and stain for endothelial
      phospho-S6 and phospho-ERK against matched control skin and, ideally,
      against PIK3CA-related capillary malformation tissue.
    decision_criterion: >-
      Elevated endothelial phospho-S6/phospho-ERK in lesional skin would support
      the mTOR/MAPK hypothesis in the tissue that actually matters; normal
      staining would refute it.
  - experiment_id: miccap_exp_endothelial_conditional_ko
    name: Endothelial-specific Stambp conditional knockout
    description: >-
      Generate an endothelium-restricted Stambp conditional knockout mouse to
      test whether capillary malformations arise cell-autonomously in
      endothelium.
    decision_criterion: >-
      Development of cutaneous capillary malformations in the absence of a CNS
      phenotype would establish endothelial cell autonomy.
  evidence:
  - reference: PMID:29907875
    reference_title: "A novel homozygous missense mutation in the SH3-binding motif of STAMBP causing microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "suggesting that it is not the major pathomechanism underlying the disorder in this patient"
    explanation: The authors' explicit rejection of mTOR activation as the mechanism in their patient, who nonetheless had capillary malformations.
- discussion_id: miccap_il1_blockade_repurposing
  prompt: >-
    Would IL-1beta blockade modify the epileptic encephalopathy of MIC-CAP, given
    that STAMBP restrains the NLRP3 inflammasome and the mouse shows massive
    neuroinflammation?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#NLRP3 Inflammasome Derepression and Neuroinflammation
  rationale: >-
    AMSH restrains NLRP3 by exactly the K63-linked deubiquitination chemistry it
    is specialized for, and the CNS-conditional Stambp knockout shows massive
    neuroinflammation. IL-1 blockade with anakinra is already used in other
    refractory epilepsy syndromes, making this the most tractable repurposing
    hypothesis in the disease. It is entirely untested: the inflammasome work was
    done in monocytes with no patient or neural data.
  proposed_experiments:
  - experiment_id: miccap_exp_neural_inflammasome_readout
    name: Inflammasome and IL-1beta quantification in STAMBP-deficient neural tissue
    description: >-
      Measure NLRP3 K63-ubiquitination, inflammasome assembly and IL-1beta
      release in Stambp-knockout mouse brain and in patient-derived
      microglia-like cells, extending the monocyte finding to neural context.
    decision_criterion: >-
      Elevated NLRP3 K63-ubiquitination and IL-1beta in STAMBP-deficient neural
      cells would establish the arm as neural-relevant rather than
      monocyte-specific.
  - experiment_id: miccap_exp_il1_blockade_mouse
    name: IL-1 receptor blockade trial in the Stambp Sox1-cKO mouse
    description: >-
      Test whether IL-1 receptor blockade (e.g. anakinra) reduces seizure burden,
      neuroinflammation or preweaning mortality in the CNS-conditional Stambp
      knockout mouse.
    decision_criterion: >-
      A significant improvement in survival or seizure burden would justify
      considering IL-1 blockade as a repurposing candidate in human MIC-CAP.
  evidence:
  - reference: PMID:33253913
    reference_title: "The deubiquitinase STAMBP modulates cytokine secretion through the NLRP3 inflammasome."
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: "STAMBP knockout directly increased release of IL-1beta with TLR ligation"
    explanation: Molecular basis for the IL-1 blockade hypothesis, in monocytes rather than neural cells.
- discussion_id: miccap_natural_history_and_qol_gap
  prompt: >-
    What is the actual natural history, survival distribution, and caregiver/
    patient quality-of-life burden of MIC-CAP?
  kind: KNOWLEDGE_GAP
  status: OPEN
  rationale: >-
    With roughly 25-30 molecularly confirmed individuals reported worldwide there
    is no registry, no natural-history study, no survival curve, and no validated
    quality-of-life or caregiver-burden instrument has ever been administered.
    Life expectancy is described only as "shortened", with the oldest known living
    individual reported at 12 years. Prognostic counseling is therefore
    anecdote-based.
  proposed_experiments:
  - experiment_id: miccap_exp_international_registry
    name: International STAMBP patient registry with longitudinal phenotyping
    description: >-
      Establish a registry capturing standardized longitudinal phenotyping,
      seizure burden, feeding status, growth and survival across all molecularly
      confirmed STAMBP patients.
    decision_criterion: >-
      A cohort large enough to compute a survival distribution and to stratify
      outcome by variant class.
  - experiment_id: miccap_exp_qol_instruments
    name: Quality-of-life and caregiver-burden instrument administration
    description: >-
      Administer CPCHILD or PedsQL together with a validated caregiver-burden
      instrument across the reported MIC-CAP cohort, none of which has ever been
      done.
    decision_criterion: >-
      Any validated instrument data would replace the current inference-only
      quality-of-life assessment.
  - experiment_id: miccap_exp_protein_level_prognostic
    name: STAMBP protein level as a prognostic biomarker
    description: >-
      Test whether residual STAMBP protein level quantified on immunoblot from
      patient-derived cells predicts motor and language outcome, as the leaky
      splice-allele homozygote suggests.
    decision_criterion: >-
      A monotonic relationship between residual protein level and functional
      outcome would establish the first prognostic biomarker for the disease.
  evidence:
  - reference: PMID:35962715
    reference_title: "Further clinical delineation of microcephaly-capillary malformation syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Currently, there is little published information about the natural history and long-term outcomes for individuals with MIC-CAP."
    explanation: Explicit statement of the natural-history gap by the group that maintains the GeneReviews chapter.

notes: >
  Scope and nosology. Recent reports show that the STAMBP phenotype is broader
  than classic MIC-CAP: at least one patient with biallelic STAMBP variants had
  global developmental delay, autism spectrum disorder, microcephaly, epilepsy
  and dysmorphism but no apparent capillary malformation, and a homozygote for a
  leaky deep-intronic splice allele achieved independent walking and short-phrase
  speech. This entry keeps the MIC-CAP name to match MONDO:0013659 but treats
  capillary malformation as very frequent rather than obligate, and should be
  read as covering the severe/complete end of a STAMBP-related neurodevelopmental
  spectrum.

  Somatic STAMBP biology is out of scope. STAMBP is recurrently dysregulated
  somatically in several cancers (melanoma, lung adenocarcinoma, pancreatic and
  colorectal carcinoma). Those are oncology findings about the same protein, not
  about MIC-CAP, and are deliberately not imported here.

  Deliberately omitted phenotypes. The HPO annotation set for OMIM:614261 also
  records hypoplasia of the corpus callosum, brachydactyly, clinodactyly,
  vesicoureteral reflux, and single-individual reports of cleft palate,
  sensorineural hearing impairment and adrenal insufficiency. None of these is
  quotable from any cached abstract or open full text, so they are not curated as
  phenotype entries rather than being propped up with topically adjacent
  citations. Note in particular that "corpus callosum" appears in none of the
  MIC-CAP references cited here - the only cited reference mentioning it is the
  PIK3CA/MCAP GeneReviews, i.e. the confusable neighbouring entity, where the
  callosum is characteristically *thick*.

  Ontology-term choices for the mixed tone pattern. The central/peripheral tone
  dissociation is curated as two entries - Central hypotonia and Peripheral
  hypertonia - because HPO has no single term for the pattern. HPO's specific
  "Central hypotonia" term, HP:0011398, is obsolete, so the axial component is
  bound to HP:0001290 Generalized hypotonia with the central qualifier carried
  in `preferred_term`. HP:0032361 was considered and rejected: it is "Decreased
  post-bronchodilator forced expiratory flow 25-75%", an unrelated spirometry
  concept.

  Frequency bands are deliberately absent on Cerebral atrophy, Central
  hypotonia, Peripheral hypertonia and Recurrent pneumonia. Each is documented
  in named individual patients or as a GeneReviews management target, but no
  published series reports a denominator for any of them, so assigning a
  FrequencyEnum band would be unsupported.

  No biochemical marker. There is no diagnostic blood, urine or cerebrospinal
  fluid analyte; blood and urinary metabolic screening is normal, which is itself
  diagnostically useful for excluding inborn errors of metabolism. The only
  abnormal biochemical readouts are research-grade immunoblots and
  immunofluorescence, so no `biochemical:` block is curated.

  Deliberate negatives. No environmental, infectious, lifestyle or teratogenic
  contribution has been implicated; no modifier or protective locus is known; no
  recurrent copy-number variant is known (chromosomal microarray was normal in
  the reported patients in whom it was performed, so it has no established
  diagnostic yield); no
  transcriptomic, proteomic, metabolomic or single-cell dataset of MIC-CAP
  patient or model tissue has been published.

📚

References & Deep Research

References

1

PMID:24354023

Microcephaly-Capillary Malformation Syndrome.

No top-level findings curated for this source.

Deep Research

1

Claude Code ▸

Microcephaly–Capillary Malformation Syndrome (MIC-CAP): Comprehensive Research Report

claude-haiku-4-5-20251001, claude-opus-5[1m] 32 citations 2026-07-31T18:45:22.923270

Microcephaly–Capillary Malformation Syndrome (MIC-CAP): Comprehensive Research Report

Prepared: 2026-07-31 · Target MONDO: MONDO:0013659 · Category: Mendelian (autosomal recessive)

Evidence-provenance note (read before curating)

Quotes below are marked with a verification status, because the dismech SOP requires evidence snippet: values to be exact substrings of a validator-generated references_cache/ file:

[CACHE-VERIFIED] — quote checked character-for-character against an existing file in references_cache/ in this worktree (PMIDs 24354023, 23542699, 39169623, 36033615, 27531570, 29907875, 25692795, 31638258, 25266620).
[TRANSCRIBED] — quote obtained by transcription of the live PubMed record via web fetch. High confidence, but run just fetch-reference PMID:<id> and just validate-references before committing (PMIDs 21815250, 35962715, 38951308, 11713295, 21531206, 18758443, 33253913, 40441142).
[SOURCE-PARAPHRASE] — factual content from GeneReviews/Orphanet/HPO/ClinVar/UniProt web records, not suitable as a verbatim snippet without re-fetch.

Ontology IDs were checked against OLS4 / the HPO API where noted; a handful are flagged [VERIFY].

1. Disease Information

Overview

Microcephaly–capillary malformation syndrome (MIC-CAP) is an ultra-rare autosomal recessive neurocutaneous disorder — formally a developmental and epileptic encephalopathy with a cutaneous vascular signature — defined by the co-occurrence of congenital and progressive microcephaly, multiple small generalized cutaneous capillary malformations, early-onset intractable epilepsy, profound global developmental delay, and hypoplastic distal phalanges. It is caused by biallelic loss-of-function variants in STAMBP, which encodes the endosome-associated K63-specific deubiquitinating isopeptidase AMSH.

The defining GeneReviews summary [CACHE-VERIFIED, PMID:24354023]:

"The defining clinical characteristics of the microcephaly-capillary malformation (MIC-CAP) syndrome are typically present at birth: microcephaly and generalized cutaneous capillary malformations (a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm), hypoplastic distal phalanges of the hands and/or feet, early-onset intractable epilepsy, and profound developmental delay."

And the molecular definition [CACHE-VERIFIED, PMID:23542699]:

"Microcephaly-capillary malformation (MIC-CAP) syndrome is characterized by severe microcephaly with progressive cortical atrophy, intractable epilepsy, profound developmental delay and multiple small capillary malformations on the skin."

MIC-CAP is conceptually the mirror image of megalencephaly–capillary malformation (MCAP/M-CM, PIK3CA-related overgrowth): both couple a capillary malformation phenotype to a PI3K-AKT-mTOR signaling abnormality, but MCAP is a mosaic gain-of-function overgrowth disorder while MIC-CAP is a germline recessive loss-of-function undergrowth disorder. This pairing is a useful curation anchor and a common source of Named Entity Confusion (NEC) — see §1.4.

Key identifiers

Resource	Identifier	Notes
MONDO	MONDO:0013659	label: `microcephaly-capillary malformation syndrome` (OLS4-verified)
OMIM (disease)	#614261	MICROCEPHALY-CAPILLARY MALFORMATION SYNDROME; MICCAP
OMIM (gene)	*606247*	STAMBP
Orphanet	ORPHA:294016	"Microcephaly-capillary malformation syndrome"
UMLS	C3280296	via NIH GTR condition page
HGNC	HGNC:16950 → dismech CURIE `hgnc:16950`	STAMBP (lowercase prefix per repo convention)
NCBI Gene	10617
Ensembl	ENSG00000124356
UniProt	O95630 (STABP_HUMAN)	STAM-binding protein
GeneReviews	NBK174452 / PMID:24354023	Carter, Mirzaa, McDonell, Boycott; posted 2013-12-12, updated 2021-03-18
ICD-10	No specific code. Coded compositionally: Q02 (microcephaly) + Q82.5 (congenital non-neoplastic nevus)	Orphanet maps ORPHA:294016 to Q02
ICD-11	No specific stem code; nearest are LD24.M0 (microcephaly) / LA90 congenital vascular malformation of skin [VERIFY against current ICD-11 release]
MeSH	No dedicated descriptor. Indexed via Microcephaly (D008831), Vascular Malformations (D054079), Ubiquitin Thiolesterase (D043422), Endosomal Sorting Complexes Required for Transport

Synonyms and alternative names

MIC-CAP syndrome (the standard abbreviation)
MICCAP (OMIM style)
Microcephaly–capillary malformation syndrome
STAMBP-related microcephaly–capillary malformation syndrome
Historical/descriptive: "A new syndrome with multiple capillary malformations, intractable seizures, and brain and limb anomalies" (Carter et al. 2011, Am J Med Genet A 155A:301–306, the original delineation)
Emerging/broader: STAMBP-related neurodevelopmental disorder — justified by PMID:36033615, which reported a STAMBP patient without cutaneous capillary malformation

Data provenance character

Essentially all human knowledge of MIC-CAP is aggregated case-level literature, not EHR- or registry-derived: a series of single-family case reports plus one multiplex exome cohort (PMID:23542699, 5 families) and one follow-up delineation series (PMID:35962715, 4 new + 2 followed patients). There is no patient registry, no natural-history study, no EHR-derived cohort, and no ICEES/COHD-type comorbidity signal for this disease. Curators should expect CASES_IN_LITERATURE to be the only defensible measure_type for prevalence.

NEC preflight (mandatory before using any deep-research output)

MIC-CAP sits in two high-NEC-risk classes simultaneously:

Near-homograph collision: MIC-CAP (microcephaly, STAMBP, AR, MONDO:0013659, OMIM 614261) vs. MCAP / M-CM (megalencephaly-capillary malformation-polymicrogyria, PIK3CA, mosaic, MONDO:0013192, OMIM 602501). Identical "capillary malformation" token, opposite head-size direction, opposite mutational mechanism. A DR report that repeatedly names PIK3CA or describes overgrowth/somatic mosaicism/alpelisib is describing MCAP, not MIC-CAP — discard entirely.
Capillary-malformation family collision: CM-AVM syndrome (RASA1/EPHB4, AD), Sturge-Weber (GNAQ, mosaic), and diffuse capillary malformation with overgrowth all share the CM token.

Anchors: the causal gene must be STAMBP; OMIM xref must be 614261; inheritance must be autosomal recessive; head size must be microcephaly. If any of these four disagree with the DR report, rebuild from primary literature.

2. Etiology

Disease causal factors

MIC-CAP is monogenic and fully genetically determined: biallelic (homozygous or compound heterozygous) pathogenic variants in STAMBP (2p13.1). There is no known environmental, infectious, or multifactorial contribution. The landmark discovery [CACHE-VERIFIED, PMID:23542699]:

"We used whole-exome sequencing of five patients with MIC-CAP syndrome and identified recessive mutations in STAMBP, a gene encoding the deubiquitinating (DUB) isopeptidase STAMBP (STAM-binding protein, also known as AMSH, associated molecule with the SH3 domain of STAM) that has a key role in cell surface receptor-mediated endocytosis and sorting."

Confirmed independently [CACHE-VERIFIED, PMID:29907875]:

"Microcephaly-capillary malformation syndrome is a congenital and neurodevelopmental disorder caused by biallelic mutations in the STAMBP gene."

Risk factors

Genetic (causal): - Biallelic STAMBP pathogenic variants — necessary and sufficient. GENO relationship type: CAUSAL. - Consanguinity is the single strongest population-level risk factor, and drives homozygous presentations. Documented in an Egyptian family [CACHE-VERIFIED, PMID:27531570]: "We describe two brothers from a consanguineous family of Egyptian ancestry"; in a Saudi family [CACHE-VERIFIED, PMID:25266620]: "We describe two brothers (ages 7 and 12 years) from consanguineous parents of Saudi ancestry"; and in an Arab family (PMID:25692795, MeSH-indexed Consanguinity). - Carrier parents (obligate heterozygotes) — asymptomatic; see §9. - Uniparental isodisomy (UPD) is an unusual but documented non-Mendelian route [CACHE-VERIFIED, PMID:24354023]: "in some instances both pathogenic variants are inherited from one parent (uniparental isodisomy)." GeneReviews attributes this to 1/15 families (maternal isodisomy of chromosome 2 homozygosing p.Arg424*, patient P4.1 in PMID:23542699).

Environmental: None identified. No toxin, teratogen, radiation, occupational, dietary, maternal-age, or infectious risk factor has been implicated. This is an important negative for the KB — MIC-CAP is a mechanistically "pure" genetic microcephaly, in explicit contrast to acquired congenital microcephalies (congenital Zika, CMV, toxoplasmosis, fetal alcohol spectrum), which are the principal differential rather than co-factors.

Sex: No sex bias expected or reported (autosomal recessive). Reported patients include both sexes.

Protective factors

Genetic: No modifier or protective allele identified. However, residual protein expression is strongly protective at the phenotype level — a genotype-driven "protective" gradient rather than a separate locus. GeneReviews describes a female homozygous for the leaky intronic variant c.1005+358A>G with "threefold reduction in STAMBP transcript expression; STAMBP protein expression was markedly reduced but not absent" who "achieved independent walking and short-phrase speech at age five" [SOURCE-PARAPHRASE, GeneReviews NBK174452] — far exceeding the typical outcome of no head control and no independent sitting.
Environmental: None. No diet, supplement, or exposure is known to modify risk or course. (Ketogenic diet is a treatment for the epilepsy, not a protective factor — and in the one reported trial it failed; see §12.)

Gene–environment interactions

No established GxE interaction. Two iatrogenic gene–environment style interactions are clinically actionable and should be curated as treatment-safety items rather than etiologic factors:

Valproic acid caution. [CACHE-VERIFIED, PMID:24354023]: "Agents/circumstances to avoid: Valproic acid may or may not be associated with adverse effects." GeneReviews elaborates that one male died at 12 months of "septic shock following acute pancreatitis, possibly secondary to valproate therapy", while other patients tolerated valproate without issue [SOURCE-PARAPHRASE].
Catabolic/infectious stress precipitates decompensation via aspiration pneumonia and status epilepticus — a general severe-neurodisability interaction, not MIC-CAP-specific.

3. Phenotypes

Authoritative frequency data

The HPO annotation set for OMIM:614261 (retrieved from the HPO API, ontology.jax.org) is the best-curated frequency source and should seed the dismech phenotypes: block. Frequencies are n/N counted-cohort values, which map cleanly to dismech FrequencyEnum bands with derivable justification (see docs/frequency-evidence-guidelines.md).

HPO ID	Label (canonical)	HPO frequency	Derived band	System
HP:0000253	Progressive microcephaly	10/10 (100%)	OBLIGATE / VERY_FREQUENT	Head & neck
HP:0025104	Capillary malformation	10/10 (100%)	OBLIGATE / VERY_FREQUENT	Skin
HP:0001250	Seizure	10/10 (100%), onset in infancy	VERY_FREQUENT	Nervous
HP:0001263	Global developmental delay	10/10 (100%)	VERY_FREQUENT	Nervous
HP:0003577	Congenital onset	10/10 (100%)	— (clinical course)	Clinical course
HP:0009882	Short distal phalanx of finger	19/20 (95%)	VERY_FREQUENT	Limbs
HP:0009879	Simplified gyral pattern	9/9 (100%)	VERY_FREQUENT	Nervous (imaging)
HP:0012510	Extra-axial cerebrospinal fluid accumulation	9/9 (100%)	VERY_FREQUENT	Nervous (imaging)
HP:0001285	Spastic tetraparesis	8/10 (80%)	VERY_FREQUENT	Musculature
HP:0000648	Optic atrophy	6/8 (75%)	FREQUENT	Eye
HP:0001518	Small for gestational age	7/10 (70%)	FREQUENT	Growth
HP:0025517	Hypoplastic hippocampus	6/7 (86%)	VERY_FREQUENT	Nervous (imaging)
HP:0001336	Myoclonus	6/10 (60%)	FREQUENT	Nervous
HP:0003429	CNS hypomyelination	5/8 (63%)	FREQUENT	Nervous (imaging)
HP:0012469	Infantile spasms	4/9 (44%)	FREQUENT	Nervous
HP:0011344	Severe global developmental delay	reported	FREQUENT	Nervous
HP:0002059	Cerebral atrophy	reported	FREQUENT	Nervous
HP:0012448	Delayed myelination	reported	FREQUENT	Nervous
HP:0002079	Hypoplasia of the corpus callosum	reported	OCCASIONAL	Nervous
HP:0001252 / HP:0001290	Hypotonia / Generalized hypotonia	reported	FREQUENT	Musculature
HP:0001508	Failure to thrive	reported	FREQUENT	Growth
HP:0004322	Short stature	Occasional	OCCASIONAL	Growth
HP:0001156	Brachydactyly	reported	FREQUENT	Limbs
HP:0030084	Clinodactyly	reported	OCCASIONAL	Limbs
HP:0001792	Small nail	reported	FREQUENT	Skin/nails
HP:0010721	Abnormal hair whorl	reported	OCCASIONAL	Skin/hair
HP:0003196	Short nose	reported	FREQUENT	Head & neck
HP:0000445	Wide nose	reported	OCCASIONAL	Head & neck
HP:0000340	Sloping forehead	reported	FREQUENT	Head & neck
HP:0000327	Hypoplasia of the maxilla	reported	OCCASIONAL	Head & neck
HP:0000175	Cleft palate	1 individual	VERY_RARE	Head & neck
HP:0000508	Ptosis	reported	OCCASIONAL	Eye
HP:0000316	Hypertelorism	reported	OCCASIONAL	Eye
HP:0000365	Hearing impairment	1 individual (sensorineural)	VERY_RARE	Ear
HP:0000369	Low-set ears	reported	OCCASIONAL	Ear
HP:0000076	Vesicoureteral reflux	Occasional	OCCASIONAL	Genitourinary
HP:0001629	Ventricular septal defect	reported	OCCASIONAL	Cardiovascular
HP:0001631	Atrial septal defect	reported	OCCASIONAL	Cardiovascular
HP:0001655	Patent foramen ovale	reported	OCCASIONAL	Cardiovascular
HP:0001667	Right ventricular hypertrophy	reported	VERY_RARE	Cardiovascular
HP:0000007	Autosomal recessive inheritance	—	—	Inheritance

GeneReviews adds two counted frequencies out of its 18-individual denominator [SOURCE-PARAPHRASE, NBK174452]: "Myoclonus of limbs and eyelids is common (8/18 reported individuals)" and "Optic atrophy (10/18 reported individuals)", plus single-case reports of sensorineural hearing impairment, cleft palate, and adrenal insufficiency (1 individual — no standard HP term beyond HP:0000846 Adrenal insufficiency).

Phenotype-by-phenotype detail

1. Progressive microcephaly (HP:0000253) — congenital onset, severe, progressive The cardinal feature and the one that most sharply separates MIC-CAP from MCAP. Occipitofrontal circumference (OFC) at birth ranges −1.8 to −8 SD, worsening to −2.5 to −8 SD on later assessment (PMID:23542699 Table 1) [SOURCE-PARAPHRASE]. The Chinese case illustrates the severity at 17 months [CACHE-VERIFIED, PMID:31638258]: "The head circumference was 39.5 cm (Z-score, −5.8 SD)." Because the head is small at birth and falls further across postnatal life, both HP:0011451 (Congenital microcephaly) and HP:0000253 (Progressive microcephaly) are defensible; HP:0000253 with clinical_course: PROGRESSIVE is the better single annotation and matches the HPO disease annotation. QoL: microcephaly per se is not symptomatic, but it is the imaging/biometric proxy for the neuronal loss that drives everything else.

2. Generalized cutaneous capillary malformations (HP:0025104) — congenital, non-progressive in number, cosmetic The eponymous cutaneous sign. Morphology per GeneReviews suggestive-findings: "Pink or red, blanchable, roughly oval or circular macules or patches" distributed widely over the body [SOURCE-PARAPHRASE], numbering "a few to hundreds", sized "1-2 mm to several cm" [CACHE-VERIFIED, PMID:24354023]; McDonell reports 2–20 mm lesions visible at birth [SOURCE-PARAPHRASE, PMID:23542699]. Confirmed across ancestries [CACHE-VERIFIED, PMID:27531570]: "multiple cutaneous capillary malformations"; and [CACHE-VERIFIED, PMID:31638258]: "sporadic, multiple, small capillary malformations." Critically, they are not universal in the broadened STAMBP spectrum — see phenotype 12. QoL: the lesions are asymptomatic and blanchable; the burden is cosmetic and diagnostic rather than functional. They do not carry the Sturge-Weber risks (no leptomeningeal angiomatosis, no glaucoma reported).

3. Early-onset intractable epilepsy (HP:0001250; HP:0012469 infantile spasms; HP:0011097 epileptic spasms) — neonatal/infantile onset, severe, refractory, partially stabilizing The dominant morbidity. GeneReviews: seizures "can be focal, tonic, and complex partial and can include infantile spasms, appear to stabilize after age two years" [CACHE-VERIFIED, PMID:24354023]. The natural history in a single well-documented case [CACHE-VERIFIED, PMID:31638258]: "The child developed early-onset epilepsy after 3 months, with a generalized tonic-clonic seizure, which progressed to clusters of infantile spasms (2–10 clusters/day) 1 month later." Multi-drug refractoriness is the rule [CACHE-VERIFIED, PMID:24354023]: "multiple anticonvulsant medications are frequently required for adequate seizure control." The disorder is now framed as a recognizable developmental and epileptic encephalopathy (DEE) (PMID:35770778, Epileptic Disord 2022, title). EEG: interictal hypsarrhythmia is documented [CACHE-VERIFIED, PMID:31638258]: "Interictal electroencephalography showed hypsarrhythmia and slow wave background with bioccipital spike-slow wave during waking." Suggested terms: HP:0002521 (Hypsarrhythmia), HP:0011153 (Focal motor seizure), HP:0002069 (Bilateral tonic-clonic seizure), HP:0011098 (Speech apraxia — n/a), HP:0032794 (Refractory epilepsy) [VERIFY]. QoL: the single largest driver — status epilepticus risk, sedation from polypharmacy, sleep disruption, caregiver burden.

4. Profound global developmental delay / intellectual disability (HP:0001263, HP:0011344) — congenital, profound, static-to-slowly-regressive Universal (10/10). GeneReviews: "Developmental progress is minimal. Most individuals do not attain head control or independent sitting due to spastic quadriparesis" [SOURCE-PARAPHRASE]. Suggested: HP:0002187 (Profound global developmental delay) [VERIFY] as a more specific alternative to HP:0011344. QoL: total dependence for all activities of daily living.

5. Spastic quadriparesis with central hypotonia (HP:0001285, HP:0001290) — infantile, progressive 8/10 (HPO); 9/10 in the McDonell series. The mixed tone pattern is clinically distinctive and management-relevant [CACHE-VERIFIED, PMID:24354023]: "Central hypotonia and peripheral hypertonia require attention to proper seating and bracing to maintain posture and prevent contractures." QoL: contractures, positioning pain, scoliosis risk, inability to sit.

6. Myoclonus and hyperkinetic movement disorder (HP:0001336; HP:0002072 chorea; HP:0002072/HP:0100660 dyskinesia) — infantile, chronic [CACHE-VERIFIED, PMID:24354023]: "Myoclonus of the limbs and eyelids is common; other abnormal movements (dyskinetic, choreiform) may be seen." Prominent dyskinesia was the notable feature of the Chinese case [CACHE-VERIFIED, PMID:31638258]: "The boy could not hold his head and had prominent dyskinesia of the whole body, particularly involuntary movement of the tongue and mouth" — and the authors note "dyskinesia was more prominent in the present study and was infrequent in previous cases." Suggested: HP:0100660 (Dyskinesia) [VERIFY], HP:0002072 (Chorea) [VERIFY].

7. Hypoplastic distal phalanges and nail hypoplasia (HP:0009882, HP:0001792, HP:0001156) — congenital, static 19/20 — the most reliable non-neurological, non-cutaneous diagnostic handle, and the feature that most efficiently separates MIC-CAP from primary autosomal recessive microcephaly on physical exam. Affects hands and/or feet.

8. Ophthalmologic involvement (HP:0000648 optic atrophy; HP:0000618 blindness) — infantile, progressive 6/8 to 10/18. Congenital blindness reported in the Egyptian sibs [CACHE-VERIFIED, PMID:27531570]: "presenting with microcephaly, apparent global developmental delay, seizures, spasticity, congenital blindness, and multiple cutaneous capillary malformations." Structurally correlated with hypoplasia of the optic nerves/chiasm on MRI. QoL: compounds the sensory deprivation of profound ID.

9. Growth failure / feeding difficulty (HP:0001508, HP:0001518, HP:0004322, HP:0011968 feeding difficulties) — congenital→postnatal, progressive SGA in 7/10; postnatal failure to thrive near-universal. [CACHE-VERIFIED, PMID:31638258]: "the patient was 8 kg [Z-score, −2.8 Standard Deviation (SD)] in weight and 63 cm (Z-score, −6.8 SD) in length." Feeding-tube dependence is standard of care [CACHE-VERIFIED, PMID:24354023]: "A feeding tube is essential to optimize nutrition and weight gain while reducing the risk of aspiration." QoL: aspiration pneumonia is a leading proximate cause of hospitalization and death.

10. Dysmorphic facial features — congenital, static Sloping forehead (HP:0000340), short nose (HP:0003196), wide nose (HP:0000445), maxillary hypoplasia (HP:0000327), low-set ears (HP:0000369), ptosis (HP:0000508), hypertelorism (HP:0000316). [CACHE-VERIFIED, PMID:29907875]: "severe global developmental delay, progressive microcephaly, refractory seizures, dysmorphic facial features, and multiple capillary malformations." [CACHE-VERIFIED, PMID:31638258]: "The patient had drooping mouth corners, a short nose and neck."

11. Rare/expanding features (each 1–2 individuals; curate as VERY_RARE with the specific PMID) - Congenital hypothyroidism (HP:0000851) — two independent families. [CACHE-VERIFIED, PMID:25692795]: "previously unreported findings of congenital hypothyroidism and alopecia areata." [CACHE-VERIFIED, PMID:25266620]: "these boys exhibited certain novel and distinctive phenotypic features (congenital hypothyroidism and autistic-like behavior with intermittent repetitive hand-flapping movements)." Two-family replication makes this the strongest of the "rare" features. - Alopecia areata (HP:0002232) — PMID:25692795. - Autistic behavior / stereotypies (HP:0000729, HP:0000733) — PMID:25266620 (hand-flapping); PMID:36033615 (formal ASD diagnosis). - Adrenal insufficiency (HP:0000846) — 1 individual, GeneReviews. - Cleft palate (HP:0000175), sensorineural hearing impairment (HP:0000407) — 1 individual each. - Congenital heart defects — VSD/ASD/PFO/RVH. - Vesicoureteral reflux (HP:0000076). - Recurrent pneumonia (HP:0006532) — [CACHE-VERIFIED, PMID:31638258]: "received immunoglobulin intravenously as a result of recurrent pneumonia." - Recurrent unilateral epistaxis (HP:0000421) — PMID:38058451 (dual MIC-CAP + Mowat-Wilson diagnosis; attribute cautiously).

12. Phenotype-expansion caveat — capillary malformation is NOT obligate The most important recent nosological finding for KB scoping [CACHE-VERIFIED, PMID:36033615]:

"The patient was presented with global developmental delay, autism spectrum disorder, microcephaly, epilepsy, and dysmorphic facial features but without apparent capillary malformation on the skin and organs."

and:

"Our findings demonstrate that the clinical phenotype of STAMBP mutations is highly variable, and patients with different STAMBP mutations show differences in the severity of symptoms."

Curation implication: the disease entity should be framed as STAMBP-related neurodevelopmental disorder, of which classic MIC-CAP is the severe/complete form. The dismech entry should keep the MIC-CAP name (matching MONDO:0013659) but record this variability in notes or as a has_subtypes split (classic MIC-CAP vs. attenuated/CM-negative STAMBP-NDD), and should not encode HP:0025104 as strictly obligate.

Quality-of-life summary. No EQ-5D, SF-36, PROMIS, PedsQL, or any validated instrument has been applied to a MIC-CAP cohort — a genuine and citable evidence gap. Inferentially, affected children sit at the most severe end of the pediatric neurodisability spectrum: GMFCS-equivalent level V, no independent sitting, no speech, cortical visual impairment, gastrostomy dependence, refractory epilepsy. Caregiver burden is correspondingly extreme, and GeneReviews explicitly recommends "a complex care / palliative care team" [CACHE-VERIFIED, PMID:24354023].

4. Genetic / Molecular Information

Causal gene

STAMBP — "STAM binding protein" (HGNC:16950, hgnc:16950), 2p13.1, Entrez 10617, ENSG00000124356, OMIM 606247. Reference transcript NM_006463.4 (used by PMID:29907875). Protein: STAM-binding protein / AMSH (UniProt O95630), 424 aa*.

Protein architecture (UniProt O95630; PMID:18758443; PMID:40441142):

Region	Approx. residues	Function
MIT domain (microtubule-interacting and trafficking)	N-terminal ~1–100	Binds ESCRT-III CHMP proteins (CHMP1A/CHMP3); autoinhibits the catalytic domain
SH3-binding motif (SBM)	~residues 219–240 (includes Ser236)	Binds the SH3 domain of STAM1/STAM2; recruits AMSH to the ESCRT-0 complex; required for protein stability
Clathrin-binding region	central	endosomal/clathrin association
MPN⁺/JAMM domain (catalytic)	257–388, JAMM motif 335–348	Zn²⁺-dependent isopeptidase; K63-linkage-specific
Zn²⁺ coordination	H335, H337, D348 (+ contacts at 350, 390, 396, 398; indirect at 280)	2 Zn²⁺ per subunit

Enzymology: EC 3.4.19.- zinc metalloprotease. Strictly K63-linkage-selective — cleaves Lys63-linked polyubiquitin, does not cleave Lys48-linked chains (UniProt; PMID:18758443).

Pathogenic variant spectrum

Nine families from the discovery cohort [SOURCE-PARAPHRASE, PMID:23542699 / PMC4000253]:

Patient	cDNA	Protein	Zygosity	Ancestry
P1.1 / P1.2 (sibs)	c.125A>G ; c.532C>T	p.Glu42Gly ; p.Arg178*	comp het	African-American
P2.1	c.112C>T ; c.279+5G>T	p.Arg38Cys ; splice	comp het	European
P3.1	c.299T>A ; c.1270C>T	p.Phe100Tyr ; p.Arg424*	comp het	European
P4.1	c.1270C>T	p.Arg424*	homozygous by maternal isodisomy	European
P5.1	c.1005+358A>G	deep-intronic, leaky splicing	homozygous	European
P6.1	c.1134_1138delACTAA ; c.203+5G>A	p.Lys378Asnfs*2 ; splice	comp het	European
P7.1	c.112C>T ; c.203+5G>A	p.Arg38Cys ; splice	comp het	European
P8.1	c.112C>T ; c.938C>T	p.Arg38Cys ; p.Thr313Ile	comp het	European
P9.1	c.41G>C ; (2nd)	p.Arg14Pro ; —	comp het	Polynesian

Variants added by later reports:

Variant	Protein	Zygosity	Population	Reference
c.908A>G	p.Lys303Arg	homozygous	Egyptian (consanguineous)	[CACHE-VERIFIED, PMID:27531570]: "we uncovered a homozygous missense variant in STAMBP (p.K303R) in the two siblings, inherited from heterozygous carrier parents"
c.707C>T	p.Ser236Phe (SH3-binding motif)	homozygous	Japanese	[CACHE-VERIFIED, PMID:29907875]: "the novel homozygous mutation located in the SH3 binding motif of STAMBP (NM_006463.4) (c.707C>T: p.Ser236Phe)"
novel splice variant	—	homozygous	Arab (Saudi/Kuwaiti)	PMID:25692795 (also PMID:25266620 sibs)
c.843_844del ; c.920G>A	*p.Cys282Trpfs11 ; p.Gly307Glu**	comp het	Chinese	[CACHE-VERIFIED, PMID:36033615]
novel variant	—	—	Chinese	PMID:31638258
c.376-1G>A (intron 4 splice acceptor)	—	—	Indian	PMID:41603106 (2026)
novel variants	—	—	Chinese (co-occurring Mowat-Wilson)	PMID:38058451

Recurrent variants: p.Arg38Cys (c.112C>T) is the clearest recurrent allele — 3 of 9 discovery families. p.Arg424* (c.1270C>T) recurs in 2 families. These are the two alleles worth flagging for targeted testing.

ClinVar snapshot (STAMBP, P/LP query; 52 records) [SOURCE-PARAPHRASE] — representative classified entries:

Variant	Consequence	Germline classification	Condition
c.133C>T (p.Arg45Ter)	nonsense	Likely pathogenic (multiple submitters, no conflicts)	MIC-CAP
c.5_6dup (p.Asp3fs)	frameshift	Pathogenic	MIC-CAP
c.487dup (p.His163fs)	frameshift	Pathogenic	—
c.376-1G>A	splice acceptor	Likely pathogenic	MIC-CAP
c.1006-2A>T	splice acceptor	Likely pathogenic	MIC-CAP
c.868-1G>A	splice acceptor	Likely pathogenic	—
c.113G>A (p.Arg38His)	missense	Conflicting classifications	MIC-CAP
c.824C>G (p.Thr275Ser)	missense	VUS	MIC-CAP
c.41G>T (p.Arg14Leu), c.32C>T (p.Pro11Leu), c.692C>G (p.Pro231Arg)	missense	VUS	—

Variant-class distribution: the spectrum is dominated by truncating (nonsense/frameshift) and splice-disrupting alleles, with a minority of missense. This is a classic complete-loss-of-function architecture.

Structural clustering of missense alleles — an important and under-appreciated pattern. McDonell noted that five of six discovery missense variants (R14P, R38C, E42G, Y63C, F100Y) cluster in the N-terminal MIT domain, not the catalytic JAMM domain [SOURCE-PARAPHRASE, PMC4000253]. The single JAMM-domain missense, p.Thr313Ile, sits "in the distal ubiquitin binding site within the JAMM domain" and "eliminates a hydrogen bond between the ubiquitin carbon backbone and STAMBP, likely decreasing ubiquitin binding." Later alleles fit the same picture: S236F in the SBM, K303R and G307E flanking the JAMM domain.

The 2025 structural work explains why MIT-domain mutations are so damaging [TRANSCRIBED, PMID:40441142]:

"we conducted comprehensive biochemical analyses of full-length STAMBP and several fragments and demonstrated that the MIT domain binds tightly to the catalytic domain (CD), resulting in autoinhibition of its activity. The crystal structure of the MIT-CD complex reveals that the MIT domain occupies a large portion of the distal ubiquitin-binding site of the CD domain, thereby obstructing substrate binding. Additionally, our biochemical data show that STAM1 binding to STAMBP facilitates substrate binding and enhances its activity, whereas binding of CHMP3 does not relieve autoinhibition or enhance activity."

So the MIT domain is not a passive tether — it is a regulatory clamp whose relief requires STAM1 binding. MIT-domain and SBM missense variants therefore disrupt the regulated activation of AMSH and/or its stability, rather than the catalytic chemistry itself.

Functional consequence class: LOSS OF FUNCTION, achieved through at least two distinct routes: 1. Protein destabilization / absence — the dominant route. Directly shown for S236F [CACHE-VERIFIED, PMID:29907875]: "Immunoblot analysis of patient-derived lymphoblastoid cell lines (LCLs) revealed a severe reduction in STAMBP expression, indicating that Ser236Phe induces protein instability." The proposed mechanism is elegant: "The substitution of Ser236Phe found in the case patient was located in the SH3-binding motif, and we propose the mutation may block STAM binding and subsequently induce STAMBP degradation." Generalized in the discovery paper [CACHE-VERIFIED, PMID:23542699]: "Patient cell lines showed reduced STAMBP expression." 2. Catalytic/substrate-binding impairment — T313I.

No gain-of-function or dominant-negative mechanism is reported. Heterozygotes are unaffected, consistent with pure recessive LOF.

Allele frequencies. No MIC-CAP pathogenic allele reaches appreciable frequency in gnomAD; all reported disease alleles are rare or private. Precise gnomAD constraint metrics (pLI, LOEUF, missense Z) for STAMBP could not be retrieved — the gnomAD browser requires a GraphQL POST that the available tooling cannot issue. Action for curator: query gnomAD v4 for ENSG00000124356 directly. A priori, LOEUF is expected to be permissive (recessive genes are typically not LoF-constrained in heterozygotes).

Somatic vs. germline. MIC-CAP variants are exclusively germline biallelic. This is a sharp contrast to MCAP (mosaic somatic PIK3CA) and to Sturge-Weber (mosaic somatic GNAQ), and is worth an explicit notes statement to forestall confusion. Separately, STAMBP is recurrently dysregulated somatically in cancer — melanoma (SLUG stabilization, PMID:30454887), lung adenocarcinoma (EGFR/MAPK, PMID:34102455), pancreatic ductal adenocarcinoma (BAG3, PMID:41611844; gemcitabine resistance, PMID:39242557), colorectal cancer (YY1/c-Myc, PMID:41456274; CXCR4/MDSC, PMID:41559433). These are oncology findings about the same protein, not about MIC-CAP, and should not be imported into the disease entry except as a mechanistic cross-reference.

Modifier genes. None identified. The best candidate axis is STAM1/STAM2, given that STAM1 binding both stabilizes AMSH and relieves its autoinhibition (PMID:40441142) — a testable hypothesis, not an established modifier.

Epigenetics. No DNA methylation, histone-modification, or chromatin study of MIC-CAP exists. No episignature has been described (contrast: many NDDs now have EpiSign classifiers). Genuine gap. Note the mechanistic irony that STAMBP work is repeatedly published from the Shanghai Key Laboratory of Medical Epigenetics — this reflects lab affiliation, not an epigenetic disease mechanism.

Chromosomal abnormalities. No recurrent CNV. GeneReviews reports 0/15 families with a detectable deletion/duplication, so CMA has essentially no diagnostic yield for MIC-CAP. The one structural mechanism of note is uniparental isodisomy of chromosome 2, which homozygoses a single paternal/maternal allele (1/15 families) and has direct recurrence-risk consequences (§9).

5. Environmental Information

Not applicable — a deliberate and citable negative.

Environmental factors: none. No CTD/TOXNET chemical–disease association for MIC-CAP. No radiation, pollution, or occupational exposure implicated.
Lifestyle factors: none. No maternal smoking, alcohol, nutrition, or exercise association.
Infectious agents: none causal. Infection matters only as (a) the principal differential diagnosis for congenital microcephaly with a cutaneous sign — congenital Zika (dermatologic findings absent, but microcephaly + simplified gyri + calcifications overlap), congenital CMV (blueberry-muffin rash mimics capillary malformations in the newborn), congenital toxoplasmosis, congenital rubella; and (b) a leading complication — recurrent aspiration pneumonia [CACHE-VERIFIED, PMID:31638258]: "received immunoglobulin intravenously as a result of recurrent pneumonia."

The distinction matters clinically: in a newborn with microcephaly and scattered red macules, the TORCH/Zika workup is mandatory before attributing findings to MIC-CAP.

6. Mechanism / Pathophysiology

The causal chain, upstream → downstream

[MOLECULAR — trigger]
Biallelic STAMBP LOF variants
  → reduced or absent AMSH protein (destabilization via SBM/MIT disruption, NMD of truncating alleles,
    or catalytic/substrate-binding failure via T313I)
  → loss of Zn²⁺-dependent K63-linkage-specific deubiquitinase activity at the endosome
│
[CELLULAR — proximal convergence node]
  → failure of ESCRT-associated deubiquitination of K63-Ub cargo during MVB sorting
│
├────────────────────────────┬──────────────────────────────┬───────────────────────┐
[ARM A: proteostasis]        [ARM B: signaling]            [ARM C: progenitor]      [ARM D: inflammation]
K63-Ub conjugate             failure of receptor            impaired NSC/NPC         NLRP3 K63-Ub
aggregation (+p62,           downregulation → cargo         proliferation;           accumulation →
TDP-43, glutamate            recycling instead of           CFLAR (c-FLIP)           inflammasome
receptors)                   lysosomal degradation          downregulation           activation
   ↓                              ↓                              ↓                        ↓
↑ autophagosomes            constitutive, serum-           death-receptor          ↑ IL-1β
(LC3-II)                    INSENSITIVE RAS-MAPK           apoptosis in NPCs        (in vitro only)
   ↓                        and PI3K-AKT-mTOR                   ↓                        ↓
caspase-3 activation        activation                     reduced cortical         neuroinflammation
↑ apoptosis                      ↓                         progenitor pool          (mouse brain)
   ↓                        dysregulated capillary              ↓                        ↓
[TISSUE]                    endothelial patterning         smaller cortex           microglial activation
progressive neuronal loss        ↓
(CA1 hippocampus, cortex)   CUTANEOUS CAPILLARY
   ↓                        MALFORMATIONS
[ORGANISM]
progressive microcephaly · cortical atrophy · simplified gyri · intractable epilepsy ·
spastic quadriparesis · optic atrophy · profound DD · early death

Normal AMSH function (the baseline the disease departs from)

AMSH is the endosomal "editor" of the ubiquitin signal that consigns internalized receptors to lysosomal destruction. Activated cell-surface receptors are tagged with K63-linked polyubiquitin, recognized by ESCRT-0 (STAM/HRS), and handed down the ESCRT-I/II/III chain into intraluminal vesicles of the multivesicular body. AMSH, recruited via its SBM to the STAM SH3 domain and via its MIT domain to ESCRT-III CHMP3, removes those K63 chains — thereby rescuing cargo from degradation and recycling ubiquitin. Its linkage specificity is structurally hard-wired [TRANSCRIBED, PMID:18758443]:

"The Zn(2+)-dependent DUBs AMSH and AMSH-LP regulate receptor trafficking by specifically cleaving Lys 63-linked polyubiquitin chains from internalized receptors." "The core and Ins-1 form a catalytic groove that accommodates the Lys 63 side chain of the proximal ubiquitin and the isopeptide-linked carboxy-terminal tail of the distal ubiquitin."

GO terms for normal function: GO:0061578 K63-linked deubiquitinase activity (OLS-verified) · GO:0070536 protein K63-linked deubiquitination (OLS-verified) · GO:0016579 protein deubiquitination · GO:0071985 multivesicular body sorting pathway (OLS-verified) · GO:0032509 endosome transport via multivesicular body sorting pathway (OLS-verified) · GO:0043162 ubiquitin-dependent protein catabolic process via the multivesicular body sorting pathway (OLS-verified) · GO:0031623 receptor internalization [VERIFY] · GO:0008270 zinc ion binding [VERIFY] · GO:0008237 metallopeptidase activity [VERIFY].

GO cellular components: GO:0005769 early endosome [VERIFY] · GO:0005771 multivesicular body [VERIFY] · GO:0000813 ESCRT I complex / GO:0036452 ESCRT complex [VERIFY] · GO:0005634 nucleus · GO:0005829 cytosol. UniProt localizes AMSH to nucleus, cytoplasm, early endosomes, and peripheral membrane.

Arm A — Ubiquitin-conjugate aggregation, autophagy, and apoptosis

The originally proposed and best-replicated mechanism. Patient-derived LCL findings [CACHE-VERIFIED, PMID:23542699]:

"Patient cell lines showed reduced STAMBP expression associated with accumulation of ubiquitin-conjugated protein aggregates, elevated apoptosis and insensitive activation of the RAS-MAPK and PI3K-AKT-mTOR pathways."

and the authors' own causal interpretation:

"our findings of a congenital human disorder caused by a defective DUB protein that functions in endocytosis implicates ubiquitin-conjugate aggregation and elevated apoptosis as factors potentially influencing the progressive neuronal loss underlying MIC-CAP syndrome."

Supporting experimental detail [SOURCE-PARAPHRASE, PMC4000253]: STAMBP siRNA knockdown in T98G cells produced elevated conjugated-ubiquitin aggregates (anti-FK2 IF); patient LCLs (P1.1, P3.1, P7.1) showed the same after 24 h serum starvation; lentiviral STAMBP transduction reversed the phenotype (a genuine rescue, strengthening causal attribution). Apoptosis was read out by cleaved caspase-3 and Annexin V in P1.2, P3.1, P7.1. Autophagic flux was elevated (LC3-II ↑ after bafilomycin A1), consistent with increased autophagosome content.

The mouse work independently establishes the same chain in vivo, and identifies the substrates [TRANSCRIBED, PMID:21531206]:

"Here, we demonstrate that AMSH(-/-) mice developed ubiquitinated protein accumulations as early as embryonic day 10 (E10), and that severe deposits were present in the brain at postnatal day 8 (P8) and P18." "Interestingly, TDP-43 was found to accumulate and colocalize with glial marker-positive cells in the brain." "Glutamate receptor and p62 accumulations were also found; these molecules colocalized with ubiquitinated aggregates in the brain." "These data suggest that AMSH plays an important role in degrading ubiquitinated proteins and glutamate receptors in vivo."

Two mechanistically loaded observations here deserve KB capture. TDP-43 accumulation places MIC-CAP in unexpected proximity to the ALS/FTD proteinopathies (the authors state "AMSH(-/-) mice provide an animal model for neurodegenerative diseases, which are commonly characterized by the generation of proteinaceous aggregates"). Glutamate receptor accumulation offers a direct, and largely untested, explanation for the epilepsy: failure to downregulate ionotropic glutamate receptors would produce a cell-autonomous excitation/inhibition imbalance — a natural link to the epilepsy_excitation_inhibition_imbalance module.

GO terms: GO:0006914 autophagy [VERIFY] · GO:0016236 macroautophagy [VERIFY] · GO:0051402 neuron apoptotic process (OLS-verified) · GO:0097190 apoptotic signaling pathway [VERIFY] · GO:0043524 negative regulation of neuron apoptotic process [VERIFY] · GO:0043161 proteasome-mediated ubiquitin-dependent protein catabolic process [VERIFY] · GO:0016240/GO:0034389 protein aggregate/inclusion body assembly [VERIFY].

Arm B — Constitutive, serum-insensitive RAS-MAPK and PI3K-AKT-mTOR signaling → the capillary malformations

This arm is what explains the cutaneous half of the syndrome, and it is the reason MIC-CAP belongs in the RASopathy/PI3K-vascular-anomaly conceptual neighborhood despite its recessive LOF genetics. [CACHE-VERIFIED, PMID:23542699]:

"The latter cellular phenotype is notable considering the established connection between these pathways and their association with vascular and capillary malformations."

Experimental detail [SOURCE-PARAPHRASE, PMC4000253]: - RAS-MAPK: elevated RAS-GTP pulled down from patient LCLs; pS338-C-RAF maintained in the absence of serum (i.e., pathway is on when it should be off); pERK1/2 elevated even after MEK1/2 inhibition — "insensitive" rather than merely "elevated." - PI3K-AKT-mTOR: elevated phospho-PI3K; pAKT-T308, pTSC2-T1462 and pS6-S240/244 all maintained under serum starvation. - Rescue: lentiviral STAMBP restored "a normal signaling response to serum starvation."

The logic is coherent: if K63-Ub cargo cannot be deubiquitinated and committed to the MVB, activated RTKs persist in the endosomal compartment and continue to signal. Signaling from the endosome, not just the plasma membrane, is the mechanistic crux.

Important dissenting datum — do not curate this arm as settled. [CACHE-VERIFIED, PMID:29907875]:

"Contrary to previously reported STAMBP mutations, the Ser236Phe mutation did not lead to constitutive activation of the PI3K-AKT-mTOR pathway in patient-derived LCLs, as indicated by the expression of phosphorylated S6 ribosomal protein, suggesting that it is not the major pathomechanism underlying the disorder in this patient."

This is a genuine, allele-specific contradiction and an ideal mechanistic_hypotheses entry with status: EMERGING plus a discussions block of kind: KNOWLEDGE_GAP. Note that this patient nonetheless had multiple capillary malformations — so if mTOR activation were the necessary cause of the CMs, S236F should not have produced them. Either the CM mechanism is mTOR-independent, or the LCL readout does not reflect endothelial biology.

GO terms: GO:0000165 MAPK cascade [VERIFY] · GO:0007265 Ras protein signal transduction [VERIFY] · GO:0014065 phosphatidylinositol 3-kinase signaling [VERIFY] · GO:0031929 TOR signaling [VERIFY] · GO:0038095/GO:0007169 transmembrane receptor protein tyrosine kinase signaling pathway [VERIFY] · GO:0001525 angiogenesis [VERIFY] · GO:0001569 branching involved in blood vessel morphogenesis [VERIFY].

Module conformance opportunity: this arm maps onto rtk_grb2_signaling_adaptation (RTK phosphotyrosine docking → proliferation output) and, in the negative direction, is the loss-of-downregulation mirror of sustaining_proliferative_signaling.

Arm C — Neural progenitor proliferation failure (the competing microcephaly mechanism)

The apoptosis model does not fully explain a brain that is already small at birth (OFC −1.8 to −8 SD). Human cortical organoid work supplies the missing developmental arm [CACHE-VERIFIED, PMID:36033615]:

"Cortical organoids with STAMBP knockout (KO) showed significantly lower proliferation of neural stem cells (NSCs), leading to smaller organoids that are characteristic of microcephaly. Furthermore, STAMBP disruption did not affect apoptosis in early cortical organoids."

and, establishing variant-specific causality:

"After re-expressing wild-type STAMBP, STAMBP G307E , and STAMBP T313I (a known pathogenic mutation) within STAMBP KO organoids, only STAMBP WT rescued the impaired proliferation of STAMBP deficient organoids, but not STAMBP G307E and STAMBP T313I ."

The hESC-derived NPC work identifies a molecular effector and, notably, restores a death pathway — but a different one [TRANSCRIBED, PMID:38951308]:

"We found that STAMBP is dispensable for the pluripotency maintenance or neural differentiation of hESCs. However, neural progenitor cells (NPCs) derived from STAMBP-deficient hESCs fail to be long-term maintained/expanded in vitro. We identified the anti-apoptotic protein CFLAR is down-regulated in those affected NPCs and ectopic expression of CFLAR rescues NPC defects induced by STAMBP-deficiency."

Synthesis for the KB. Two-phase model, best curated as two nodes rather than one: - Prenatal phase (developmental): reduced NSC/NPC proliferation and CFLAR-dependent death-receptor apoptosis in the progenitor pool → small brain at birth. - Postnatal phase (degenerative): ubiquitin-aggregate-driven, caspase-3-mediated apoptosis of post-mitotic neurons, plus neuroinflammation → progressive atrophy, epilepsy, and regression.

This resolves the "congenital and progressive" microcephaly that a single mechanism cannot account for, and it makes the HUMAN_MODEL_MISMATCH designation appropriate for the apoptosis-vs-proliferation discrepancy between mouse (apoptosis-dominant) and human organoid (proliferation-dominant, apoptosis-negative) systems.

GO terms: GO:0021987 cerebral cortex development [VERIFY] · GO:0061351 neural precursor cell proliferation [VERIFY] · GO:0050767 regulation of neurogenesis [VERIFY] · GO:0008283 cell population proliferation [VERIFY] · GO:0097191 extrinsic apoptotic signaling pathway [VERIFY] (CFLAR/death-receptor arm).

Arm D — Neuroinflammation and the NLRP3 inflammasome

The CNS-conditional mouse adds an inflammatory component absent from the original model [CACHE-VERIFIED, PMID:39169623]:

"In this MIC-CAP syndrome mouse model, early-onset neuronal death occurs specifically in the hippocampus and cortex, accompanied by aggregation of ubiquitinated proteins, and massive neuroinflammation."

Mechanistically plausible, because AMSH restrains NLRP3 via exactly the K63 chemistry it is specialized for [TRANSCRIBED, PMID:33253913]:

"Here we identify the deubiquitinase STAM-binding protein (STAMBP) as a negative regulator of the NLRP3 inflammasome." "While STAMBP does not modulate NLRP3 protein abundance, cellular depletion of the deubiquitinase increased NLRP3 K63 chain polyubiquitination resulting in increased NLRP3 inflammasome activation." "These findings describe a unique mechanism of non-degradative ubiquitination of NLRP3 by STAMBP to limit excessive inflammasome activation and to reduce injurious IL-1β signaling."

Curation caution: PMID:33253913 is a monocyte/CRISPR study with no MIC-CAP patient data. Curate as evidence_source: IN_VITRO supporting a hypothesized IL-1β arm; do not assert clinical inflammasome-driven disease. It is, however, the most tractable repurposing hypothesis in the whole disease (IL-1 blockade, e.g. anakinra) and belongs in a discussions / proposed_experiments block.

GO terms: GO:0002376 immune system process · GO:0072559 NLRP3 inflammasome complex [VERIFY] · GO:0050702 interleukin-1 beta secretion [VERIFY] · GO:0006954 inflammatory response [VERIFY] · GO:0001774 microglial cell activation [VERIFY].

Protein dysfunction, metabolic, and biochemical layers

Protein dysfunction: loss of function by destabilization (dominant route) or substrate-binding failure. Notably, this is a disorder of failed protein clearance, so the pathologic species is not the mutant protein itself but the accumulated K63-ubiquitinated substrate pool (p62/SQSTM1, TDP-43, glutamate receptors). Conceptually adjacent to amyloidogenesis and lysosomal_substrate_accumulation in the dismech module set — the shared logic is "an enzyme that clears something is missing, so the something accumulates and is cytotoxic" — though the substrate is a ubiquitin-conjugate pool rather than a lipid or a fibril.
Metabolic changes: none identified. Blood and urine metabolic screening is normal [CACHE-VERIFIED, PMID:31638258]: "Blood and urinary metabolic screening indicated normal results." This is diagnostically useful (excludes inborn errors) and means MIC-CAP does not conform to metabolic_intoxication_decompensation.
Biochemical abnormalities: no enzyme assay, biomarker, or metabolite is abnormal in a clinically measurable way. The only "biochemical" readouts are research-grade immunoblots (STAMBP level, pS6, cleaved caspase-3, LC3-II, FK2 ubiquitin-conjugate IF).
Immune involvement: no immunodeficiency or autoimmunity. Alopecia areata in one family (PMID:25692795) is the sole autoimmune-adjacent report and is probably coincidental at n=1. Recurrent pneumonia is aspiration-related, not immunologic.
Tissue damage mechanism: apoptotic neuronal death (not necrosis, not ischemia, not fibrosis), regionally selective for hippocampal CA1 and cerebral cortex, with secondary neuroinflammation.

Molecular profiling

Transcriptomics / proteomics / metabolomics / lipidomics / single-cell / spatial: no MIC-CAP-specific dataset exists. No GEO/ArrayExpress series, no PRIDE submission, no MetaboLights study, no single-cell atlas of patient or model tissue. The closest available resources are the Stambp^Sox1-cKO mouse brain and the STAMBP-KO cortical organoid system, either of which would be an obvious substrate for such profiling. This is one of the clearest, most actionable gaps in the disease.

Functional genomics screens: STAMBP appears in DepMap and in a high-throughput DUB-autophagy screen (PMID:32453962), but no MIC-CAP-directed CRISPR screen has been published.

7. Anatomical Structures Affected

Organ level

Primary: - Brain (UBERON:0000955) — the dominant target organ and, per the mouse gene-therapy work, the sufficient one: [CACHE-VERIFIED, PMID:39169623] "our findings reveal a central role of brain defects in the pathogenesis of STAMBP deficiency." - Skin (UBERON:0002097 skin of body) — capillary malformations, generalized distribution.

Secondary / systemic: - Eye and optic pathway (UBERON:0000970 eye; UBERON:0000941 optic nerve [VERIFY]; UBERON:0000959 optic chiasma [VERIFY]) — optic atrophy, optic nerve/chiasm hypoplasia, cortical visual impairment, congenital blindness. - Musculoskeletal — distal phalanges (UBERON:0004300 distal phalanx [VERIFY]), nails (UBERON:0001705 nail [VERIFY]); secondary contractures/scoliosis from spasticity. - Gastrointestinal — oropharyngeal dysphagia, aspiration; gastrostomy dependence. - Respiratory (UBERON:0002048 lung) — recurrent aspiration pneumonia (secondary). - Endocrine — thyroid (UBERON:0002046 [VERIFY]) in congenital hypothyroidism (2 families); adrenal gland (UBERON:0002369 [VERIFY]) in 1 case. - Cardiovascular — septal defects, PFO (occasional). - Genitourinary — vesicoureteral reflux (occasional).

Body systems: nervous (primary), integumentary (primary), visual, musculoskeletal, digestive, respiratory, endocrine, cardiovascular.

Regional CNS specificity — a strikingly selective vulnerability

The regional selectivity is one of the most mechanistically interesting features of the disease and is consistent across human imaging, human neuropathology, and mouse.

Hippocampus (UBERON:0002421 hippocampal formation [VERIFY]), specifically the CA1 field (UBERON:0003881 CA1 field of hippocampus — OLS-verified). [TRANSCRIBED, PMID:11713295]: "Examination of brain sections at P6 demonstrated significant loss of neurons and apoptotic cells in the CA1 subfield of the hippocampus." Human correlate: hypoplastic hippocampus in 6/7.
Cerebral cortex (UBERON:0000956). [TRANSCRIBED, PMID:11713295]: "Brain atrophy developed by P16 and was accompanied by complete loss of the CA1 neurons in the hippocampus and marked atrophy of the cerebral cortex." [CACHE-VERIFIED, PMID:39169623]: "early-onset neuronal death occurs specifically in the hippocampus and cortex."
Cerebellum is relatively spared — a genuine dissociation. [TRANSCRIBED, PMID:11713295]: "AMSH-deficient hippocampal neuronal cells were unable to survive in vitro, even in the presence of several stimulatory cytokines, while AMSH-deficient cerebellar neurons, thymocytes, and embryonic fibroblasts survived normally." The human neuropathology matches [SOURCE-PARAPHRASE, GeneReviews]: "disproportionately small cerebral hemispheres compared to the cerebellum." This cell-autonomous, region-restricted survival requirement is the single most distinctive cellular phenotype in MIC-CAP and deserves its own pathophysiology node.
Corpus callosum (UBERON:0002336 [VERIFY]) — thinning/hypoplasia.
White matter (UBERON:0002316 white matter [VERIFY]) — hypomyelination, delayed myelination, white-matter loss.
Extra-axial CSF space (UBERON:0006330? [VERIFY]) — increased extra-axial space in 9/9.

Lateralization: bilateral and symmetric throughout (brain atrophy, optic atrophy, digital hypoplasia). Capillary malformations are generalized and randomly distributed, explicitly not dermatomal/segmental — a useful discriminator from Sturge-Weber (V1 trigeminal distribution) and from mosaic segmental vascular anomalies. The one asymmetric report is unilateral epistaxis in the dual-diagnosis case (PMID:38058451).

Tissue and cell level

Cell type	CL term	Role
Neuron	`CL:0000540` [VERIFY]	primary target of apoptotic loss
Hippocampal neuron	`CL:0002608` (OLS-verified)	CA1 pyramidal neurons — most vulnerable population
Neural progenitor cell	`CL:0011020` (OLS-verified)	reduced proliferation (organoid/hESC arm)
Neural stem cell	`CL:0000047` [VERIFY]	"NSC" in PMID:36033615
Radial glial cell	`CL:0000681` [VERIFY]	cortical progenitor; inferred, not directly assayed
Capillary endothelial cell	`CL:0002144` (OLS-verified)	substrate of the capillary malformations
Microglial cell	`CL:0000129` [VERIFY]	neuroinflammation (mouse)
Astrocyte	`CL:0000127` [VERIFY]	glial marker-positive TDP-43 accumulation (PMID:21531206)
Cerebellar neuron	`CL:0000121` Purkinje cell [VERIFY]	spared — curate as an explicit negative
Lymphoblast / EBV-LCL	`CL:0000542` lymphocyte [VERIFY]	the workhorse patient-cell model, not a disease site
Fibroblast	`CL:0000057` [VERIFY]	spared in mouse
Thymocyte	`CL:0000893` [VERIFY]	spared in mouse

Tissue types: nervous tissue (primary), vascular endothelium/connective tissue of dermis, skeletal (terminal phalangeal ossification), ectodermal appendages (nail).

Subcellular level

Compartment	GO CC term	Relevance
Early endosome	`GO:0005769` [VERIFY]	AMSH's principal site of action
Multivesicular body / late endosome	`GO:0005771`, `GO:0005770` [VERIFY]	cargo sorting failure
ESCRT complexes	`GO:0036452` [VERIFY]	ESCRT-0 (STAM) and ESCRT-III (CHMP3) partners
Lysosome	`GO:0005764` [VERIFY]	failed terminal degradation
Autophagosome	`GO:0005776` [VERIFY]	elevated LC3-II
Cytoplasmic ubiquitin-conjugate aggregates / inclusion body	`GO:0016234` inclusion body [VERIFY]	the pathologic accumulation
Plasma membrane	`GO:0005886`	receptor internalization origin
Nucleus, cytosol	`GO:0005634`, `GO:0005829`	secondary AMSH pools (UniProt)

Xogenesis note: MIC-CAP forms two candidate pathological structures — (1) intracellular ubiquitin-conjugate/p62/TDP-43 aggregates, and (2) the cutaneous capillary malformation itself. Neither has an established MPATH continuant analogous to granuloma or thrombus; a curator considering the Xogenesis anchor convention should treat both as OBO gaps and anchor with OGMS:0000078/OGMS:0000081 plus UBERON site only.

8. Temporal Development

Onset

Onset category: CONGENITAL — HPO annotates HP:0003577 (Congenital onset) at 10/10. [CACHE-VERIFIED, PMID:24354023]: "The defining clinical characteristics ... are typically present at birth."
Prenatal onset is inferable from birth OFC of −1.8 to −8 SD and SGA in 7/10, and is directly supported in the mouse, where ubiquitinated protein accumulation begins at E10 [TRANSCRIBED, PMID:21531206].
Onset pattern: insidious/chronic with a subacute epileptic inflection. Microcephaly and CMs are present at birth; seizures declare themselves in the neonatal period to the first months. In the Chinese case, seizure onset was at 3 months with escalation to infantile spasms at 4 months [CACHE-VERIFIED, PMID:31638258]. GeneReviews describes "neonatal-onset intractable epilepsy".

Progression

Stages (proposed for progression: curation):

Stage	Timing	Features
Prenatal	conception → birth	Reduced NSC proliferation; small brain and SGA at birth; CMs and digital hypoplasia already formed
Early infantile (declaration)	birth → ~6 mo	Seizure onset, often escalating to infantile spasms/hypsarrhythmia; hypotonia; feeding difficulty
Late infantile / toddler (peak severity)	~6 mo → 2 y	Maximal seizure burden and refractoriness; head circumference falls further; emergence of spastic quadriparesis and myoclonus; optic atrophy; failure to thrive; gastrostomy
Childhood (plateau)	> 2 y	Seizures "appear to stabilize after age two years" [CACHE-VERIFIED, PMID:24354023]; developmental trajectory flat; contractures; recurrent aspiration
Terminal	variable, infancy → adolescence	Death from aspiration pneumonia, status epilepticus, sepsis, or unexplained sudden death

Progression rate: the microcephaly is genuinely and relentlessly progressive (clinical_course: PROGRESSIVE) — OFC falling from −1.8/−8 SD at birth to −2.5/−8 SD later, with radiographically progressive cerebral atrophy. Development is essentially static at a profoundly low ceiling rather than frankly regressive in most patients. The two axes should be curated separately.

Course pattern: chronic-progressive with superimposed episodic seizure exacerbations. Not relapsing-remitting.

Duration: lifelong, with markedly shortened lifespan.

Patterns

Remission: none spontaneous. The one meaningful partial remission is pharmacological and specific: vigabatrin produced an 80% seizure reduction within a week where four other agents and a ketogenic diet had failed [CACHE-VERIFIED, PMID:31638258]: "the patient received vigabatrin (60 mg/kg/day) and the seizures reduced by 80% a week later." Confounded by the patient's death three weeks later, so long-term efficacy is unknown — the authors say so explicitly.
Critical periods:
Prenatal neurogenesis (roughly GW 8–20) — the window in which the proliferation defect fixes brain size. Almost certainly not rescuable postnatally.
Neonatal/early-infantile period — the therapeutic window demonstrated in mouse. [CACHE-VERIFIED, PMID:39169623]: "neonatal AAV9-mediated gene supplementation of Stambp in the brain could significantly improve neurological defects, sustain growth, and prolong the lifespan", supporting the claim that "postnatal gene replacement is an effective approach to cure the disease." This is the central translational finding for MIC-CAP and defines the intervention window that any future human trial would target.
First 2 years — maximal seizure burden; the period where aggressive AED optimization has the most to gain.

9. Inheritance and Population

Epidemiology

Prevalence: unknown; ultra-rare. GeneReviews states plainly [SOURCE-PARAPHRASE, NBK174452]: "Prevalence is unknown. To date 18 affected individuals (including 3 sets of sibs) from 15 families worldwide have molecularly confirmed MIC-CAP syndrome" (as of the 2021-03-18 update).
Orphanet: "no prevalence information available ... Not enough data available about incidence and published cases."
Current cumulative literature count (this report's tally): the 18 in GeneReviews, plus 4 new patients in PMID:35962715 (2022), plus the STAMBP-NDD patient without CMs (PMID:36033615), the dual-diagnosis patient (PMID:38058451), the 2026 Indian patient (PMID:41603106), and the Russian case (PMID:32929933) — with some overlap. A defensible statement is "approximately 25–30 molecularly confirmed individuals reported worldwide as of mid-2026." Note that PMID:31638258 (2019) independently counted "18 pathogenic mutations ... reported in 16 patients from 8 ethnic groups."
Incidence: not estimable.

Dismech Prevalence block recommendation:

prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Prevalence unknown. GeneReviews (2021 update) reported 18 molecularly confirmed
    individuals from 15 families; subsequent case reports bring the cumulative
    published total to roughly 25-30 individuals as of mid-2026.
  evidence:
  - reference: PMID:24354023
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, the diagnosis has been confirmed in 18 individuals from 15 families."
    explanation: GeneReviews cumulative count of molecularly confirmed cases.

(The snippet above is cache-verified against references_cache/PMID_24354023.md.)

Genetic transmission

Inheritance pattern: AUTOSOMAL RECESSIVE. HPO: HP:0000007. [CACHE-VERIFIED, PMID:24354023]: "MIC-CAP syndrome is an autosomal recessive disorder caused by biallelic STAMBP pathogenic variants." Note that the MedlinePlus-derived summary retrieved during this research incorrectly stated autosomal dominant inheritance — that was a retrieval artifact, not the source's content; AR is unambiguous across OMIM, Orphanet, GeneReviews, and every primary report.
Penetrance: appears complete in biallelic individuals — no unaffected homozygote has been reported. Heterozygous carriers (including all obligate-carrier parents) are entirely asymptomatic.
Expressivity: variable, and increasingly recognized as such. The range runs from death in infancy to a child who "achieved independent walking and short-phrase speech at age five" (the leaky c.1005+358A>G homozygote), and now includes a patient without the eponymous capillary malformations (PMID:36033615). The best-supported determinant is residual protein level [SOURCE-PARAPHRASE, GeneReviews]: "complete absence of protein production leading to the most severe phenotypes", with "The effect of pathogenic variant(s) on the protein STAMBP likely influences the severity."
Genetic anticipation: not applicable (no repeat expansion).
Germline mosaicism: not reported.
Uniparental isodisomy: documented in 1/15 families and carries a materially different recurrence risk — see the counseling block below.
Founder effects: none identified. Reported alleles are private or recurrent-by-chance (p.Arg38Cys in 3 European families is more plausibly a mutational hotspot at a CpG dinucleotide than a founder haplotype, though no haplotype analysis has been done — a real gap).
Consanguinity: a major contributor to homozygous cases, documented in Egyptian, Saudi, and Arab families (PMIDs 27531570, 25266620, 25692795).
Carrier frequency: not established. Given ~25–30 cases worldwide, carrier frequency is presumably far below 1/1000 in outbred populations. No newborn or carrier screening panel includes STAMBP.

Recurrence risk (essential for the `prevention`/`counseling` sections)

Two distinct scenarios, both from [CACHE-VERIFIED, PMID:24354023]:

Standard biparental inheritance — "If both parents are known to be heterozygous for a STAMBP pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier."

Uniparental isodisomy — "If the proband has MIC-CAP syndrome as the result of uniparental isodisomy, only one parent is heterozygous for a STAMBP pathogenic variant, and if neither parent has a chromosome rearrangement, each sib of an affected individual has at conception a 50% chance of being an asymptomatic carrier and an approximately 50% chance of being unaffected and not a carrier. The risk to sibs of a proband of being affected is unknown but is presumed to be less than 1%."

This UPD distinction changes counseling from 25% to <1% and is therefore one of the highest-value facts in the entire entry.

Population demographics

Affected populations: "Most reported individuals are of European descent; individuals from other ethnic backgrounds (African, Arab, Asian, and Polynesian) have also been reported" [SOURCE-PARAPHRASE, GeneReviews]. Documented ancestries across the literature: European, African-American, Polynesian, Egyptian, Saudi/Arab, Kuwaiti, Japanese, Chinese, Indian, Russian. PMID:31638258 counted "8 ethnic groups." The European predominance almost certainly reflects ascertainment through exome-sequencing-rich health systems, not true biology.
Geographic distribution: worldwide; no endemic focus. Elevated case density is expected in high-consanguinity regions (Middle East, North Africa, South Asia).
Variant geography: p.Arg38Cys and p.Arg424 in European families; p.Lys303Arg in an Egyptian family; p.Ser236Phe in a Japanese family; p.Gly307Glu/p.Cys282Trpfs11 in a Chinese family; c.376-1G>A in an Indian family. Too few families for meaningful population-genetic inference.
Sex ratio: ~1:1 expected; both sexes reported. No sex effect on severity has been described.
Age distribution of living affected individuals: heavily skewed to infancy and early childhood by early mortality. "The oldest living individual known was 12 years old at last assessment" [SOURCE-PARAPHRASE, GeneReviews]; PMID:25266620 reports the longest follow-up, two brothers aged 7 and 12.

10. Diagnostics

Diagnostic approach

Diagnosis is clinical recognition confirmed by molecular testing; there is no biochemical or functional confirmatory assay. [CACHE-VERIFIED, PMID:24354023]:

"The diagnosis of MIC-CAP syndrome is established in a proband with suggestive findings and biallelic pathogenic variants in STAMBP identified by molecular genetic testing."

Suggestive clinical findings (GeneReviews) [SOURCE-PARAPHRASE]

Head circumference "more than two standard deviations (SD) below the mean"
"Pink or red, blanchable, roughly oval or circular macules or patches" widely distributed
"Neonatal-onset intractable epilepsy"
Hypoplastic distal phalanges with abnormal nails
Characteristic facial dysmorphism and neuroimaging abnormalities

The combination of microcephaly + generalized blanchable capillary macules + hypoplastic distal phalanges is essentially pathognomonic and should trigger STAMBP testing directly.

Genetic testing

Modality	Utility in MIC-CAP	Notes
*Single-gene STAMBP* sequencing**	High — 15/15 families detected by sequence analysis (GeneReviews Table 1)	Reasonable first-line when the clinical gestalt is classic
Multigene panel (microcephaly / DEE / vascular anomaly panels)	High	STAMBP is included on most epileptic-encephalopathy and primary-microcephaly panels
WES	High — the historical discovery modality. Every major MIC-CAP report used WES: PMID:23542699 (5 patients), PMID:27531570 ("uncovered by exome sequencing"), PMID:29907875 ("through whole-exome sequencing"), PMID:36033615 ("Whole exome sequencing was performed on a patient presenting with a neurodevelopmental disorder")	Best choice for an atypical or CM-negative presentation
WGS	Superior for one specific reason: the deep-intronic c.1005+358A>G allele is invisible to WES	Consider WGS (± RNA-seq) when WES finds a single heterozygous STAMBP variant
CMA	Very low yield — 0/15 families had a detectable del/dup	Still appropriate as a general microcephaly workup step
Karyotype / FISH	Not indicated
mtDNA testing	Not indicated
Repeat-expansion testing	Not indicated
SNP array / UPD testing	Specifically indicated when a proband is homozygous for a variant carried by only one parent — identifies uniparental isodisomy (1/15 families) and changes recurrence risk from 25% to <1%	High counseling value
RNA sequencing	Emerging adjunct — would resolve leaky/deep-intronic splice alleles by quantifying transcript reduction	Not yet standard

Laboratory tests and biomarkers

No diagnostic biomarker exists. No blood, urine, or CSF analyte is specific to MIC-CAP.
Metabolic screening is normal and should be sent to exclude alternatives [CACHE-VERIFIED, PMID:31638258]: "Blood and urinary metabolic screening indicated normal results."
TORCH/Zika serology and PCR — mandatory in a newborn with microcephaly.
Thyroid function (TSH, free T4) — congenital hypothyroidism reported in 2 independent families; newborn screening will usually catch it, but explicit testing is warranted. LOINC: 3016-3 (TSH) [VERIFY], 3024-7 (free T4) [VERIFY].
Research-only assays (not clinically available): STAMBP immunoblot on patient LCLs (PMIDs 23542699, 29907875); anti-FK2 ubiquitin-conjugate immunofluorescence; phospho-S6/pERK/pAKT immunoblot; cleaved caspase-3 / Annexin V.

Imaging

Brain MRI is the key imaging study, and the findings are consistent enough to be diagnostically supportive [SOURCE-PARAPHRASE, GeneReviews]:

"Simplified gyral pattern (reduced number of gyri and shallow sulci) with increased extra-axial space and progressive cerebral atrophy" "Cortical myelination may be reduced or abnormal" "Hippocampal hypoplasia, thinning of the corpus callosum, hypoplasia of the optic nerves and/or optic chiasm and other malformations of cortical development"

Real-world example [CACHE-VERIFIED, PMID:31638258]: "The MRI scans showed slightly dilated lateral ventricles and increased extra-axial spaces."

Hand/foot radiographs — confirm distal phalangeal hypoplasia. Echocardiogram — screen for septal defects. Renal ultrasound / VCUG — if vesicoureteral reflux is suspected.

Electrophysiology

EEG — essential. Hypsarrhythmia with a slow background and multifocal epileptiform discharges [CACHE-VERIFIED, PMID:31638258]: "Interictal electroencephalography showed hypsarrhythmia and slow wave background with bioccipital spike-slow wave during waking."
VEP / ERG — assess optic atrophy and cortical visual impairment.
BAER — one case of sensorineural hearing impairment; audiologic screening is reasonable.
ECG — not specifically indicated.

Biopsy and pathology

Skin biopsy — not required for diagnosis; the CMs are clinically recognizable. No distinctive dermatopathology has been published, which is itself notable (a skin-biopsy study of MIC-CAP CMs, with endothelial pERK/pS6 staining, would be a high-value and easily-obtained experiment).
Neuropathology (autopsy, rare) [SOURCE-PARAPHRASE, GeneReviews]: "very small brain...with disproportionately small cerebral hemispheres compared to the cerebellum, diffuse cortical atrophy, thin corpus callosum, and white matter loss." Note that PMID:23542699 includes a neuropathologist (J. Woulfe) among its authors.
Ubiquitin/p62/TDP-43 immunohistochemistry on brain tissue would be the direct human test of the mouse aggregate findings — to our knowledge this has not been reported in human MIC-CAP brain, and it is arguably the single most important missing human experiment.

Clinical criteria and differential diagnosis

There are no formal consensus diagnostic criteria (no society guideline, no DSM/ICD operational definition). Diagnosis rests on GeneReviews' suggestive findings plus molecular confirmation.

Differential diagnosis (GeneReviews list, with the discriminators):

Condition	Gene(s)	Inheritance	How it differs from MIC-CAP
CM-AVM syndrome	RASA1, EPHB4	AD	Multiple small CMs are similar, but "no microcephaly, intractable epilepsy, or neurologic impairment"; AVM/AVF risk instead
Primary autosomal recessive microcephaly (MCPH)	ASPM, WDR62, MCPH1, etc.	AR	Congenital microcephaly with simplified gyri, but "normal facies (except narrow/sloping forehead), mild-to-severe cognitive impairment without major motor delay, normal growth except mild short stature"; no CMs, no distal limb anomalies, epilepsy not intractable. ASPM alone "explains 30%-50% of primary microcephaly depending on geographic origin"
MCAP / megalencephaly-capillary malformation	PIK3CA (mosaic)	sporadic/mosaic	Opposite head size (megalencephaly), overgrowth, polymicrogyria, somatic mosaicism
Sturge-Weber syndrome	GNAQ (mosaic)	sporadic/mosaic	Segmental facial port-wine stain in V1 distribution, leptomeningeal angiomatosis, glaucoma; not generalized micro-CMs
Congenital infection (Zika, CMV, toxoplasmosis, rubella)	—	acquired	Positive serology/PCR, intracranial calcifications, chorioretinitis; blueberry-muffin rash can mimic CMs
Diffuse capillary malformation with overgrowth (DCMO)	GNA11/GNAQ mosaic	mosaic	Overgrowth rather than microcephaly

The discriminating sentence [SOURCE-PARAPHRASE, GeneReviews]: "MIC-CAP syndrome is distinguished from primary autosomal recessive microcephaly by the presence of capillary malformations, intractable epilepsy, severe neurologic impairment, and distal limb anomalies."

Screening

Newborn screening: STAMBP is not on any NBS panel and would not meet Wilson-Jungner criteria (no presymptomatic treatment currently exists). Congenital hypothyroidism is on standard NBS panels and will incidentally capture that MIC-CAP feature.
Carrier screening: STAMBP is not on standard expanded carrier screening panels. Reasonable to include in bespoke panels for high-consanguinity populations.
Cascade screening: offered to at-risk relatives once familial variants are known [CACHE-VERIFIED, PMID:24354023]: "Once the STAMBP pathogenic variants have been identified in an affected family member ... carrier testing for at-risk family members, prenatal testing for pregnancies at increased risk, and preimplantation genetic testing are possible."

11. Outcome / Prognosis

Survival and mortality

Life expectancy: markedly shortened, magnitude unquantified. GeneReviews [SOURCE-PARAPHRASE]: "Unknown but shortened because of severe neurologic impairments. The oldest living individual known was 12 years old at last assessment."
No survival curve, 5-year survival figure, or actuarial life table exists. With ~25–30 total reported patients, none can be computed — this should be stated as an explicit gap rather than estimated.
Deaths reported: "At least three children have died in infancy" (GeneReviews). The single well-characterized cause: a male aged 12 months whose "cause of death...was thought to be septic shock following acute pancreatitis, possibly secondary to valproate therapy." Additional deaths in the literature include the Chinese boy who "suddenly succumbed 3 weeks later; no definitive causes were found as no autopsy was performed" [CACHE-VERIFIED, PMID:31638258] — a presentation compatible with SUDEP.
Longest survival: 12 years (two independent reports: GeneReviews' oldest living individual, and the older of the two brothers in PMID:25266620).
The mouse model is uniformly lethal, which usefully brackets the severity of complete protein loss [CACHE-VERIFIED, PMID:39169623]: "complete penetrance of preweaning death"; and [TRANSCRIBED, PMID:11713295]: "all the AMSH-deficient mice exhibited postnatal growth retardation and died between postnatal day 19 (P19) and P23."

Morbidity and function

Functional outcome is at the floor of the pediatric disability range. [SOURCE-PARAPHRASE, GeneReviews]: "Developmental progress is minimal. Most individuals do not attain head control or independent sitting due to spastic quadriparesis." No speech, no independent mobility, no self-feeding.
The known exception — the leaky-splice-variant homozygote who walked independently and used short phrases by age 5 — demonstrates that residual protein buys substantial function and is the strongest available proof-of-concept that partial STAMBP restoration would be clinically meaningful in humans.
Disability classification: ICF-equivalent profound multiple disability; GMFCS level V; cortical visual impairment; enteral-feeding dependence.
Quality-of-life measures: none published. No EQ-5D, PedsQL, SF-36, PROMIS, CPCHILD, or caregiver-burden instrument has been administered in MIC-CAP. Explicit gap.

Complications

Complication	Mechanism	Frequency
Aspiration pneumonia	oropharyngeal dysphagia	Common; drives feeding-tube recommendation and IVIG use in one case
Status epilepticus	refractory DEE	Expected; not systematically quantified
Failure to thrive / malnutrition	feeding dysfunction + growth failure	Near-universal
Contractures, hip subluxation, scoliosis	spastic quadriparesis	Expected; drives the bracing/seating recommendation
Cortical visual impairment / blindness	optic atrophy + cortical loss	6/8–10/18
Sepsis	secondary to pneumonia, pancreatitis	at least 1 fatal
Valproate-associated pancreatitis	idiosyncratic drug reaction	1 fatal case; basis for the "agents to avoid" note
Sudden unexplained death (possible SUDEP)	refractory epilepsy	≥1

Recovery potential: none. MIC-CAP is a static-plus-degenerative encephalopathy with no reversible component. No treatment currently alters the natural history.

Prognostic factors

Residual STAMBP protein level — the dominant prognostic factor. Complete absence → most severe phenotype; hypomorphic/leaky alleles → substantially better motor and language outcome. GeneReviews: "complete absence of protein production leading to the most severe phenotypes."
Variant class as a proxy: biallelic truncating/null → severe; ≥1 leaky splice or partially functional missense → attenuated.
Seizure control — refractoriness in the first two years correlates with the worst trajectory; seizures "appear to stabilize after age two years," so surviving that window is prognostically favorable.
Feeding/respiratory status — aspiration risk is the main proximate mortality driver, so early gastrostomy is plausibly outcome-modifying (unproven).
Presence/absence of capillary malformations is not prognostic — the CM-negative patient (PMID:36033615) had a comparatively milder neurodevelopmental course, but n=1.

Prognostic biomarkers: none validated. STAMBP protein level on immunoblot is the obvious candidate and is currently research-only. Establishing a quantitative STAMBP-level → severity relationship would be a genuinely useful, low-cost study.

12. Treatment

No disease-modifying therapy exists for humans. All current management is supportive. [CACHE-VERIFIED, PMID:24354023]:

"Treatment of manifestations: Supportive care by multidisciplinary specialists including a medical geneticist, neurologist, developmental pediatrician, and feeding specialist is recommended."

Current standard of care

Intervention	Detail	NCIT term	Modality
Multidisciplinary supportive care	genetics, neurology, developmental pediatrics, feeding specialist	`NCIT:C15747` Supportive Care	—
Anticonvulsant polytherapy	"multiple anticonvulsant medications are frequently required for adequate seizure control" [CACHE-VERIFIED, PMID:24354023]	`NCIT:C64172` Anticonvulsant Therapy (OLS-verified); agent class `NCIT:C264` Anticonvulsant Agent (OLS-verified); action `NCIT:C15986` Pharmacotherapy	`SMALL_MOLECULE`
Gastrostomy feeding	"A feeding tube is essential to optimize nutrition and weight gain while reducing the risk of aspiration" [CACHE-VERIFIED, PMID:24354023]	`NCIT:C157864` Gastrostomy Tube Procedure or `NCIT:C52006` Gastrostomy (both OLS-verified)	`SURGERY`
Seating, bracing, positioning	"Central hypotonia and peripheral hypertonia require attention to proper seating and bracing to maintain posture and prevent contractures" [CACHE-VERIFIED, PMID:24354023]	`NCIT:C15302` Physical Therapy / `NCIT:C15315` Rehabilitation	`BEHAVIORAL` / `DEVICE`
Genetic counseling	recurrence risk, carrier testing, prenatal/PGT options	`NCIT:C15240` Genetic Counseling	—
Complex care / palliative care	"Regular follow up with a child neurologist for seizure management and a complex care / palliative care team" [CACHE-VERIFIED, PMID:24354023]	`NCIT:C15747` Supportive Care	—
Levothyroxine	for the congenital hypothyroidism subset (PMIDs 25692795, 25266620)	`NCIT:C15986` Pharmacotherapy + agent `CHEBI:15062`? [VERIFY levothyroxine CHEBI]	`SMALL_MOLECULE`

Specific antiseizure medications, with the one real efficacy signal

The best-documented drug sequence in the literature [CACHE-VERIFIED, PMID:31638258]:

"The patient was treated successively with levetiracetam (40–50 mg/kg/day), topiramate (6–7 mg/kg/day), valproic acid (30 mg/kg/day) and corticosteroids at the outpatient clinic. The spasms decreased and became myoclonic, but the epilepsy remained refractory."

Ketogenic diet then failed:

"During the follow-up, the seizures were still not well controlled, although the ketogenic diet ratio was modified from 2:1 to 4:1 (4 g fat/l g combined protein, carbohydrate)."

Vigabatrin then worked, strikingly:

"After 1 month, the patient received vigabatrin (60 mg/kg/day) and the seizures reduced by 80% a week later."

With the authors' own honest caveat:

"Although the patient in the present study responded well to vigabatrin, the long-term efficacy of the drug could not be evaluated due to the early death of the patient."

Curation guidance: vigabatrin (CHEBI:63638, OLS-verified) is worth curating as a treatment with an explicit n=1 caveat and evidence_source: HUMAN_CLINICAL. It is biologically coherent — vigabatrin is first-line for infantile spasms generally — but this is a single case with three weeks of follow-up. Do not present it as established MIC-CAP therapy.

Agents and CHEBI IDs: valproic acid CHEBI:39867 (OLS-verified), vigabatrin CHEBI:63638 (OLS-verified), levetiracetam CHEBI:6437 [VERIFY], topiramate CHEBI:9625 [VERIFY]. Ketogenic diet NCIT:C173168 (OLS-verified), modality BEHAVIORAL.

Agents to avoid

Valproic acid carries a specific, mortality-linked caution [CACHE-VERIFIED, PMID:24354023]: "Agents/circumstances to avoid: Valproic acid may or may not be associated with adverse effects." The underlying event was a fatal acute pancreatitis with septic shock at 12 months. The GeneReviews hedging is deliberate — other patients tolerated valproate — so this should be curated as a caution with heightened pancreatic monitoring, not an absolute contraindication.

Pharmacogenomics

No STAMBP-specific pharmacogenomic interaction is known. General pediatric-epilepsy PGx applies and should be considered: HLA-B*15:02 / HLA-A*31:01 for carbamazepine hypersensitivity, CYP2C9 for phenytoin dosing, POLG for valproate hepatotoxicity (relevant given the valproate signal — POLG testing before valproate is standard in unexplained DEE and would be prudent here). CPIC/PharmGKB guidelines apply unchanged.

Advanced therapeutics

Gene replacement therapy — the leading translational prospect, preclinical. [CACHE-VERIFIED, PMID:39169623]:

"Importantly, neonatal AAV9-mediated gene supplementation of Stambp in the brain could significantly improve neurological defects, sustain growth, and prolong the lifespan of StambpSox1-cKO mice. Together, our findings reveal a central role of brain defects in the pathogenesis of STAMBP deficiency and provide preclinical evidence that postnatal gene replacement is an effective approach to cure the disease."

Why this is unusually promising for a microcephaly gene: - STAMBP cDNA is small (424 aa, ~1.3 kb) — comfortably within AAV packaging capacity. - The rate-limiting pathology is CNS-intrinsic — the Sox1-cKO (CNS-restricted) mouse phenocopies the global null, so brain-directed delivery should be sufficient. This is a genuinely important finding: it means peripheral/endothelial correction may be unnecessary. - Postnatal intervention worked, meaning the therapeutic window is not closed at birth. - AAV9 CNS gene therapy is a clinically validated route (onasemnogene abeparvovec for SMA).

Limits to state plainly: mouse only; neonatal dosing (human equivalent window is narrow and would require prenatal or immediate-postnatal diagnosis); improvement not cure; no IND, no trial, no human data. NCIT NCIT:C15238 Gene Therapy; modality GENE_THERAPY.

Other advanced modalities: no cell therapy, no ASO, no siRNA, no mRNA therapy, no small-molecule targeted agent, no immunotherapy has been developed or trialled. aso_details is not applicable.

Rationally-derived experimental hypotheses (none tested in MIC-CAP)

These belong in discussions with kind: KNOWLEDGE_GAP and proposed_experiments, not in treatments:

mTOR inhibition (sirolimus/everolimus). Rationale: patient LCLs show constitutive PI3K-AKT-mTOR activation (PMID:23542699); sirolimus is established in PIK3CA-related vascular anomalies and everolimus in TSC-associated epilepsy. Counter-argument: the S236F patient had CMs without mTOR activation (PMID:29907875), and inhibiting a pathway in a cell already dying from failed proteostasis could plausibly worsen matters. Speculative.
MEK inhibition. Same logic via the RAS-MAPK arm; same caveats.
IL-1β blockade (anakinra/canakinumab). Rationale: AMSH restrains NLRP3 via K63-deubiquitination (PMID:33253913) and the mouse shows "massive neuroinflammation" (PMID:39169623). Attractive because anakinra is already used in refractory epilepsy syndromes (FIRES). Untested.
CFLAR/death-receptor pathway modulation. Rationale: "ectopic expression of CFLAR rescues NPC defects induced by STAMBP-deficiency" (PMID:38951308). Currently a cell-culture rescue with no druggable route.
Autophagy/proteostasis enhancement. Rationale: ubiquitin-conjugate aggregates plus elevated LC3-II. Direction of benefit unclear — flux is already up.

Treatment strategy summary

There is no published treatment algorithm for MIC-CAP. Practical sequence, synthesized from GeneReviews plus the case literature:

Confirm diagnosis molecularly; counsel family on recurrence risk (checking for UPD).
Establish seizure control with standard DEE-directed ASMs; consider vigabatrin early given the infantile-spasms phenotype and the one reported response; consider POLG status and exercise caution with valproate, monitoring lipase/amylase if used.
Assess swallowing early; place a gastrostomy before recurrent aspiration is established.
Ophthalmology (optic atrophy/CVI), audiology, thyroid function, echocardiogram at baseline.
Physiotherapy, orthotics, seating; contracture prophylaxis.
Introduce complex-care/palliative-care involvement early — this is explicitly recommended and reflects realistic prognosis.
Discuss research participation; there are no open trials, but natural-history data collection is badly needed.

Clinical trials

A ClinicalTrials.gov search returns no interventional or observational study for MIC-CAP or STAMBP. Curators should record zero trials. Note that NCT05577754 (alpelisib in MCAP) surfaces in searches for "capillary malformation" — it is for megalencephaly-CAP (PIK3CA) and is not applicable to MIC-CAP. Including it would be a Named Entity Confusion error.

13. Prevention

Primary prevention

No primary prevention of the genetic lesion is possible. The available levers are reproductive:

Preconception carrier testing in families with a known variant, and in consanguineous couples in high-prevalence settings.
Consanguinity counseling at the community/public-health level — the only population-level intervention with any plausible effect, and relevant given the Egyptian, Saudi, Arab, and Kuwaiti families reported.
Preimplantation genetic testing (PGT-M) and prenatal diagnosis (CVS/amniocentesis) — both explicitly available once familial variants are known [CACHE-VERIFIED, PMID:24354023]: "carrier testing for at-risk family members, prenatal testing for pregnancies at increased risk, and preimplantation genetic testing are possible."
Gamete/embryo donation as an alternative reproductive option.

Not applicable: vaccination, chemoprophylaxis, dietary or lifestyle modification, environmental remediation, vector control — none has any bearing on a monogenic recessive disorder with no environmental component.

Secondary prevention (early detection)

No newborn screening for STAMBP, and no near-term prospect of it — NBS requires a presymptomatic intervention, which does not yet exist. However, the AAV9 mouse result changes the calculus prospectively: if postnatal gene replacement ever reaches the clinic, STAMBP would become a rational NBS candidate, since the demonstrated therapeutic window is neonatal. Worth recording as a forward-looking note.
Prenatal ultrasound may detect microcephaly and IUGR in the third trimester in a pregnancy already known to be at risk, but is neither sensitive nor specific enough for population screening.
Cascade testing of at-risk relatives once the familial variants are known.
Risk stratification: the only meaningfully high-risk group is sibs of an affected proband — 25% with biparental inheritance, <1% with UPD.

Tertiary prevention (preventing complications in affected individuals)

This is where nearly all realizable prevention lies, and it maps directly onto the GeneReviews surveillance recommendations [CACHE-VERIFIED, PMID:24354023]: "Regular follow up with a child neurologist for seizure management and a complex care / palliative care team or experienced pediatrician to monitor for complications associated with severe neurologic impairment."

Target complication	Preventive measure
Aspiration pneumonia	Early swallowing assessment; gastrostomy — "A feeding tube is essential"; positioning; oral-secretion management
Malnutrition / growth failure	Enteral nutrition with dietitian oversight
Contractures, hip subluxation, scoliosis	"proper seating and bracing to maintain posture and prevent contractures"; PT/OT; orthopedic surveillance
Status epilepticus	Optimized ASM regimen; written rescue-medication plan for families
Valproate-associated pancreatitis	Avoid or use valproate cautiously; monitor amylase/lipase if used — this is a preventable death mode based on the one documented fatality
Respiratory infection	Routine immunizations incl. influenza/RSV prophylaxis; chest physiotherapy
Vision/hearing deprivation	Ophthalmology and audiology surveillance
Untreated hypothyroidism	Thyroid function testing (NBS plus targeted retesting)
Dental disease, pressure injury, constipation	Standard complex-care protocols for profound neurodisability

Counseling

Genetic counseling is the central preventive intervention. Content must cover: autosomal recessive inheritance; the 25% vs. <1% recurrence-risk fork depending on biparental inheritance vs. uniparental isodisomy; carrier status of sibs; prenatal and PGT options; the poor prognosis and the appropriateness of early palliative-care involvement; and the absence of disease-modifying therapy alongside the existence of promising preclinical gene-therapy data. NCIT: NCIT:C15240 Genetic Counseling.

14. Other Species / Natural Disease

Taxonomy and orthologs

Species	NCBI Taxon	Gene	Gene ID	Notes
Homo sapiens	NCBITaxon:9606	STAMBP	10617	reference
Mus musculus	NCBITaxon:10090	Stambp	14676 [VERIFY]	the principal disease model
Rattus norvegicus	NCBITaxon:10116	Stambp	— [VERIFY]	no disease model reported
Danio rerio	NCBITaxon:7955	stambp	— [VERIFY]	no published MIC-CAP model
Drosophila melanogaster	NCBITaxon:7227	AMSH (CG battery) [VERIFY]	—	ESCRT/Notch trafficking studies
C. elegans	NCBITaxon:6239	ortholog present [VERIFY]	—
Arabidopsis thaliana	NCBITaxon:3702	AMSH3	—	Plant ortholog; endosomal localization requires ALIX (PMID:26324913)
Magnaporthe oryzae	NCBITaxon:318829	MoAMSH	—	Fungal ortholog inhibits autophagy via MoAtg6 (PMID:41310665, 2025)

Human paralog: STAMBPL1 (AMSH-LP), which shares the K63-specific JAMM activity and provided the crystal structures in PMID:18758443. STAMBPL1 is not a MIC-CAP gene and evidently cannot compensate for STAMBP loss in neurons — a notable and unexplained lack of paralog redundancy.

Evolutionary conservation

The AMSH/ESCRT axis is conserved from plants and fungi to mammals, and the K63-linkage-selective JAMM chemistry is conserved across the family. The disease-relevant function — a cell-autonomous survival requirement in forebrain neurons — is, however, a vertebrate/mammalian specialization, since plant and fungal orthologs regulate autophagy and endosomal sorting without any neuronal context. This makes mouse the only species in which the disease mechanism is meaningfully modelable.

Natural disease in other species

None reported. A search of the comparative-genetics literature finds: - No OMIA entry for a naturally occurring STAMBP disorder in any domestic or wild animal species. - No canine, feline, bovine, ovine, equine, or porcine microcephaly-capillary malformation phenotype attributed to STAMBP. - No VBO breed-specific association.

All animal Stambp disease phenotypes are laboratory-engineered, not natural. This is a clean negative worth recording explicitly.

Comparative pathology

The mouse-to-human concordance is unusually good for a microcephaly gene, which is what makes the model credible:

Feature	Human MIC-CAP	Stambp/AMSH-null mouse
Microcephaly	congenital + progressive	"progressive microcephaly" [PMID:39169623]
Growth failure	SGA 7/10, postnatal FTT	"postnatal growth retardation" [PMIDs 11713295, 39169623]
Hippocampal vulnerability	hypoplastic hippocampus 6/7	"complete loss of the CA1 neurons in the hippocampus" [PMID:11713295]
Cortical atrophy	progressive, universal	"marked atrophy of the cerebral cortex" [PMID:11713295]
Cerebellar sparing	"disproportionately small cerebral hemispheres compared to the cerebellum"	"AMSH-deficient cerebellar neurons ... survived normally" [PMID:11713295]
Ubiquitin aggregates	patient LCLs	brain, from E10 [PMID:21531206]
Neuroinflammation	not assessed in human	"massive neuroinflammation" [PMID:39169623]
Early death	≥3 infant deaths; oldest 12 y	P19–P23, 100% penetrant
Capillary malformations	universal (10/10)	NOT reported
Epilepsy	universal (10/10)	NOT reported

The two mismatches are the interesting part and should be curated as kind: HUMAN_MODEL_MISMATCH (evidence exists in the model, but translational validity for these specific features is the open question): 1. No capillary malformation in the mouse. Either the vascular phenotype requires human-specific dermal vascular biology, or it is too subtle to have been looked for. Nobody appears to have examined mouse skin vasculature systematically in a Stambp null. A tractable, cheap experiment. 2. No reported seizures in the mouse. Given hippocampal CA1 destruction and glutamate-receptor accumulation, a seizure phenotype is predicted; the absence may simply reflect that no one has done video-EEG on these animals before they die at P19–P23. Also tractable.

Zoonotic potential and cross-species transmission

Not applicable. MIC-CAP is a non-transmissible germline genetic disorder.

15. Model Organisms

Mouse models — the workhorse

1. Constitutive AMSH/Stambp knockout (Ishii et al., 2001) — the original, still the most-cited [TRANSCRIBED, PMID:11713295]:

"To investigate the in vivo functional role of AMSH, we have generated AMSH-deficient mice by gene targeting." "The AMSH-deficient mice were morphologically indistinguishable from their littermates at birth, and histopathological examinations revealed normal morphogenesis in all tissues tested. However, all the AMSH-deficient mice exhibited postnatal growth retardation and died between postnatal day 19 (P19) and P23." "Taken together, these observations indicate that AMSH is an essential molecule for the survival of neuronal cells in early postnatal mice."

Note the important detail that the mice are normal at birth and degenerate postnatally — a partial mismatch with the human congenital microcephaly, and further support for the two-phase (developmental + degenerative) model in §6.

2. Same line, proteostasis characterization (2011) [TRANSCRIBED, PMID:21531206] — establishes E10 onset of ubiquitin accumulation, and TDP-43 / p62 / glutamate-receptor co-accumulation. Framed by its authors as a neurodegeneration model as much as a MIC-CAP model.

3. CNS-conditional Stambp^Sox1-cKO (Hu et al., 2024) — the current best preclinical model, and the one purpose-built for therapy testing [CACHE-VERIFIED, PMID:39169623]:

"To establish a suitable preclinical animal model for clinical therapeutic practice, we generated a central nervous system (CNS)-specific Stambp knockout mouse model (Stambp Sox1-cKO) that phenocopies Stambp null mice including progressive microcephaly, postnatal growth retardation and complete penetrance of preweaning death."

The Sox1-Cre driver deletes across neural-plate-derived CNS lineages. That this fully phenocopies the global null is the model's key scientific contribution: it localizes the lethal pathology to the CNS and justifies brain-restricted therapy. Applications: gene-therapy dosing/timing, biomarker development, neuroinflammation studies.

MGI/IMSR: the mouse gene is Stambp, chromosome 6 [VERIFY MGI accession — the MGI marker page could not be retrieved during this research; do not cite an MGI ID without confirming it]. Check MGI, IMPC, KOMP/EuMMCR, and IMSR for currently distributed alleles.

Human cellular and organoid models

4. Patient-derived EBV-transformed lymphoblastoid cell lines (LCLs) — the standard patient-material assay system. Used in PMID:23542699 (P1.1, P1.2, P3.1, P7.1: ubiquitin aggregates, cleaved caspase-3, Annexin V, RAS-GTP, pERK, pAKT, pS6, LC3-II, plus lentiviral rescue) and PMID:29907875 (STAMBP immunoblot, pS6). Strength: genuine patient genotype, easy to bank. Major limitation: a B-lymphoblast is not a neuron and not an endothelial cell — the two cell types that actually matter. The S236F pS6 discrepancy may well be an artifact of this mismatch, and the KB should say so.

5. STAMBP-knockout human cortical organoids (Hu et al., 2022) [CACHE-VERIFIED, PMID:36033615] — "A 3D human cortical organoid model was used to investigate the function of STAMBP and the pathogenicity of the novel mutation (c.920G > A, p.G307E)." Recapitulates reduced organoid size via NSC proliferation failure and supports variant-specific functional testing (WT rescues; G307E and T313I do not). This is the best available human assay for classifying STAMBP VUS — directly relevant to the several VUS sitting in ClinVar.

6. STAMBP-deficient hESC-derived NPCs (2024) [TRANSCRIBED, PMID:38951308] — establishes that STAMBP is dispensable for pluripotency and for neural differentiation per se, but required for long-term NPC maintenance via CFLAR. Also yields a methods insight the authors flag: "counteracting this cell death pathway could be beneficial to the generation of NPCs in vitro."

7. Transformed cell lines — T98G glioblastoma with STAMBP siRNA (PMID:23542699); monocyte lines with CRISPR STAMBP KO for inflammasome work (PMID:33253913). Useful for pathway dissection, not for disease modeling.

8. Biochemical/structural systems — recombinant AMSH-LP DUB domain ± K63-di-ubiquitin (PMID:18758443, 1.2 Å and 1.6 Å); full-length STAMBP and MIT-CD complex (PMID:40441142). These provide the structural basis for interpreting missense variants and are directly useful for ACMG PS3/PM1 argumentation.

Models that do NOT exist (all are real, fillable gaps)

No zebrafish stambp model — surprising, given that zebrafish is the standard rapid model for both microcephaly and vascular patterning, and would be the natural system in which to test whether AMSH loss produces a capillary phenotype.
No Drosophila or C. elegans MIC-CAP model.
No conditional endothelial-specific Stambp knockout — this is the single most important missing model, because it is the only way to test the capillary-malformation arm directly. A Cdh5-CreER;Stambp^fl/fl mouse would resolve whether the CMs are endothelial-cell-autonomous and whether they are mTOR-dependent.
No patient-derived iPSC lines reported in a public repository (check hPSCreg/Cellosaurus before asserting this definitively).
No humanized or knock-in point-mutation mouse (e.g., a Stambp^R38C/R38C or ^T313I/T313I allele that would test genotype-phenotype correlation in vivo).
No large-animal model.

Phenotype recapitulation summary

Human feature	Mouse KO	Cortical organoid	hESC-NPC	Patient LCL
Microcephaly / small brain	✅ progressive	✅ smaller organoids	—	—
Neuronal loss (CA1, cortex)	✅ strongly	❌ no apoptosis early	✅ NPC death (CFLAR)	✅ ↑caspase-3, Annexin V
Ubiquitin aggregates	✅ from E10	—	—	✅
RAS-MAPK / PI3K-mTOR activation	not assessed	—	—	✅ (except S236F)
Reduced progenitor proliferation	not assessed	✅ primary finding	✅	—
Neuroinflammation	✅	—	—	—
Growth failure / early death	✅ 100% penetrant	n/a	n/a	n/a
Capillary malformations	❌	❌ (no vasculature)	❌	❌
Epilepsy	❌ not reported	❌	❌	❌

Resources to query

MGI (informatics.jax.org), IMPC, KOMP/EuMMCR, IMSR, MMRRC, EMMA, Alliance of Genome Resources, ZFIN (no model expected), Cellosaurus / hPSCreg (iPSC lines), Addgene (STAMBP constructs), PDB (AMSH-LP DUB domain structures from PMID:18758443; MIT-CD complex from PMID:40441142).

Consolidated curation checklist for the dismech entry

Recommended dismech modeling decisions:

Entity scope: single Disease entry, disease_term: MONDO:0013659. Consider has_subtypes splitting Classic MIC-CAP vs. Attenuated / CM-negative STAMBP-NDD (PMID:36033615), since capillary malformation is no longer obligate.
biological_scale tagging: MOLECULAR (STAMBP LOF; loss of K63-DUB activity) → CELLULAR (ESCRT sorting failure; Ub-conjugate aggregation; NSC proliferation failure; apoptosis) → TISSUE (CA1/cortical neuronal loss; dermal capillary malformation) → ORGANISM (microcephaly, DEE, spastic quadriparesis).
Candidate module conformances to evaluate:
epilepsy_excitation_inhibition_imbalance#Excitation-Inhibition Imbalance — well-supported, especially via glutamate-receptor accumulation (PMID:21531206).
rtk_grb2_signaling_adaptation — the RTK-downregulation-failure arm.
peripheral_axonal_degeneration — probably not; this is a central, not peripheral, degeneration.
A "failed clearance → substrate accumulation → cytotoxicity" pattern shared with lysosomal_substrate_accumulation and amyloidogenesis, but the substrate class (K63-Ub conjugate pool) differs enough that a new module may be warranted rather than a forced conformance.
mechanistic_hypotheses to declare:
ubiquitin_aggregate_apoptosis (CANONICAL) — PMIDs 23542699, 11713295, 21531206, 39169623.
mtor_mapk_capillary_malformation (EMERGING, contested) — supported by PMID:23542699, refuted for one allele by PMID:29907875.
progenitor_proliferation_failure (EMERGING) — PMIDs 36033615, 38951308; explains congenital (vs. progressive) microcephaly.
nlrp3_il1b_neuroinflammation (EMERGING, in vitro only) — PMIDs 33253913, 39169623.
discussions blocks:
HUMAN_MODEL_MISMATCH — mouse shows apoptosis-dominant pathology; human organoids show proliferation-dominant pathology with no early apoptosis (PMID:36033615). Also: mouse lacks both capillary malformations and epilepsy, the two human features most in need of a model.
KNOWLEDGE_GAP — no human brain ubiquitin/TDP-43 IHC; no skin-biopsy endothelial signaling study; no omics of any kind; no QoL instrument; no natural-history study; no gnomAD constraint retrieved; no endothelial-conditional mouse.
Evidence hygiene: run just fetch-reference for every PMID marked [TRANSCRIBED] (21815250, 35962715, 38951308, 11713295, 21531206, 18758443, 33253913, 40441142) and re-verify snippets before commit. The nine [CACHE-VERIFIED] PMIDs are already safe to quote.
Ontology hygiene: run just validate-terms on the finished file. Terms marked [VERIFY] in this report were reasoned from convention, not confirmed against OAK/OLS in this session.
NEC guardrail: add a notes line distinguishing MIC-CAP (STAMBP, AR, microcephaly) from MCAP/M-CM (PIK3CA, mosaic, megalencephaly). The two are the most confusable disease pair in this corner of the nosology, and the alpelisib trial NCT05577754 is a live trap.

Sources

Primary literature (PubMed/PMC): - PMID:23542699 — McDonell et al. 2013, Nat Genet — STAMBP mutations cause MIC-CAP · PMC4000253 - PMID:24354023 / NBK174452 — Carter, Mirzaa, McDonell, Boycott — GeneReviews (updated 2021-03-18) - PMID:21815250 — Mirzaa et al. 2011, Am J Med Genet A · PMID:21834052 — Carter & Boycott 2011 commentary · Carter et al. 2011, Am J Med Genet A 155A:301–306 (original delineation) - PMID:35962715 — Further clinical delineation, 2022 · PMID:41603106 — Expanding the phenotype, 2026 · PMID:35770778 — MIC-CAP as recognizable DEE, 2022 - PMID:27531570 · PMID:29907875 · PMID:25692795 · PMID:25266620 · PMID:31638258 · PMID:38058451 · PMID:32929933 - PMID:36033615 — cortical organoid, proliferation defect, 2022 · PMID:38951308 — hESC-NPC/CFLAR, 2024 · PMID:39169623 — AAV9 gene therapy in Stambp^Sox1-cKO, 2024 - PMID:11713295 — AMSH-deficient mice, 2001 · PMID:21531206 — AMSH and ubiquitinated protein degradation in CNS, 2011 - PMID:18758443 — Sato et al., structural basis for K63-specific cleavage, Nature 2008 · PMID:40441142 — MIT-domain autoinhibition, Structure 2025 · PMID:33253913 — STAMBP and the NLRP3 inflammasome, 2021

Databases: - OMIM #614261 (MICCAP) · OMIM *606247 (STAMBP) - Orphanet ORPHA:294016 - HPO annotations for OMIM:614261 (ontology.jax.org API) - UniProt O95630 · HGNC:16950 - ClinVar (STAMBP P/LP query, NCBI E-utilities) · NIH GTR condition C3280296 - MONDO:0013659 via EBI OLS4 (also used for GO/CL/UBERON/CHEBI/NCIT verification) - MedlinePlus Genetics: microcephaly-capillary malformation syndrome · GARD entry

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Classifications

Inheritance

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Histopathology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Differential Diagnoses

Experimental Models

Source YAML

References & Deep Research

References

Deep Research

Microcephaly–Capillary Malformation Syndrome (MIC-CAP): Comprehensive Research Report

Evidence-provenance note (read before curating)

1. Disease Information

Overview

Key identifiers

Synonyms and alternative names

Data provenance character

NEC preflight (mandatory before using any deep-research output)

2. Etiology

Disease causal factors

Risk factors

Protective factors

Gene–environment interactions

3. Phenotypes

Authoritative frequency data

Phenotype-by-phenotype detail

4. Genetic / Molecular Information

Causal gene

Pathogenic variant spectrum

5. Environmental Information

6. Mechanism / Pathophysiology

The causal chain, upstream → downstream

Normal AMSH function (the baseline the disease departs from)

Arm A — Ubiquitin-conjugate aggregation, autophagy, and apoptosis

Arm B — Constitutive, serum-insensitive RAS-MAPK and PI3K-AKT-mTOR signaling → the capillary malformations

Arm C — Neural progenitor proliferation failure (the competing microcephaly mechanism)

Arm D — Neuroinflammation and the NLRP3 inflammasome

Protein dysfunction, metabolic, and biochemical layers

Molecular profiling

7. Anatomical Structures Affected

Organ level

Regional CNS specificity — a strikingly selective vulnerability

Tissue and cell level

Subcellular level

8. Temporal Development

Onset

Progression

Patterns

9. Inheritance and Population

Epidemiology

Genetic transmission

Recurrence risk (essential for the prevention/counseling sections)

Population demographics

10. Diagnostics

Diagnostic approach

Suggestive clinical findings (GeneReviews) [SOURCE-PARAPHRASE]

Genetic testing

Laboratory tests and biomarkers

Imaging

Electrophysiology

Biopsy and pathology

Clinical criteria and differential diagnosis

Screening

11. Outcome / Prognosis

Survival and mortality

Morbidity and function

Complications

Prognostic factors

12. Treatment

Current standard of care

Specific antiseizure medications, with the one real efficacy signal

Agents to avoid

Recurrence risk (essential for the `prevention`/`counseling` sections)