🏷

Classifications

Harrison's Chapter

👪

Inheritance

1

Autosomal Dominant HP:0000006

MED13L syndrome is autosomal dominant with variable expressivity: variant class stratifies severity, and missense carriers, especially at the exon 15-17 hotspot, have more epilepsy, more cardiac defects and more severe global developmental delay than carriers of premature-truncating variants. Most probands carry a de novo variant; recurrence in siblings of unaffected parents is explained by parental gonadal or germinal mosaicism, documented directly at ~30-50% of sperm cells in one family. Recurrence risk counselling therefore cannot simply quote a de novo population baseline.

Autosomal dominant inheritance Expressivity: VARIABLE

Show evidence (2 references)

PMID:40228085 SUPPORT Human Clinical

"MED13L syndrome is an autosomal dominant disorder."

Confirms the inheritance mode.

PMID:40389839 SUPPORT Human Clinical

"A comprehensive review of published cases showed that patients with missense variants have more severe impairments, including increased cardiac defects, global developmental delay, and a higher incidence of epilepsy, than patients with premature truncated variants."

Supports the variable-expressivity statement with a variant-class axis.

◈

Mechanistic Hypotheses

5

MED13L haploinsufficiency (dosage loss) as the primary disease mechanism

med13l_haploinsufficiency CANONICAL Loss-of-function (deletion / truncating / splice)

Evidence balance 3 support 1 partial

Heterozygous deletion, frameshift, nonsense, and canonical-splice variants reduce functional MED13L dosage below a developmental threshold, reducing the pool of intact CKM available to dock on core Mediator and dysregulating CKM-gated RNA polymerase II transcription during development. Supported by the predominance of loss-of-function alleles among patients, a recognisable shared phenotype across deletion and truncating cases, and recapitulation in heterozygous Med13l mice with embryonic/neonatal lethality of the homozygous null.

Show evidence (4 references)

PMID:23403903 SUPPORT Human Clinical

"Using high resolution molecular karyotyping, we identified two intragenic de novo frameshift deletions, likely resulting in haploinsufficiency, in two patients with a similar phenotype of hypotonia, moderate ID, conotruncal heart defect and facial anomalies."

De novo intragenic dosage-loss alleles produce a shared recognisable phenotype, the founding argument for haploinsufficiency.

PMID:24781760 SUPPORT Human Clinical

"Both patients show features of the MED13L haploinsufficiency syndrome, except for the heart defects, thus further confirming the existence of the MED13L haploinsufficiency syndrome."

Independent splice and multi-exon deletion alleles reproduce the syndrome, confirming dosage loss as the mechanism.

PMID:40775066 SUPPORT Model Organism

"While homozygous Med13l knockout exhibit neonatal lethality accompanied by reduced brain volume and cortical thickness, heterozygous mice are viable and display hallmarks of MED13L syndrome, including impaired learning and memory, reduced motor coordination, and heightened anxiety."

Mouse dosage series shows the heterozygous state is sufficient to produce the syndrome phenotype while complete loss is lethal.

+ 1 more reference

A subset of recurrent missense variants act through a mechanism other than simple dosage loss

med13l_missense_non_haploinsufficient EMERGING Missense (exon 15-17 and 25-31 hotspots)

Evidence balance 3 support 1 partial

Most pathogenic MED13L missense variants destabilise the protein and mislocalise it to the cytoplasm, behaving as loss-of-function. At least one recurrent exon-15 allele, p.Pro869Ser, retains comparatively stable expression and partial nuclear localisation while associating with a more severe, epilepsy-enriched phenotype than truncating alleles — a pattern more consistent with a dominant-negative or neomorphic effect on the assembled CKM than with haploinsufficiency. This remains an inference from cell-based localisation and stability assays plus genotype-phenotype correlation; no direct demonstration of dominant-negative action on Mediator function has been published.

Treat the severity stratification as preliminary. The same study that reports p.Pro869Ser as stable and nuclear reports four other missense alleles behaving as classic loss-of-function, so this hypothesis applies to specific alleles rather than to missense variants as a class.

Show evidence (4 references)

PMID:40500968 SUPPORT In Vitro

"We identified significant reductions in protein stability across these variants, with some exhibiting aberrant cytoplasmic localization, suggesting disruptions in structural integrity and function."

Functional characterisation of five recurrent missense alleles showing heterogeneous, not uniformly loss-of-function, behaviour.

PMID:40500968 SUPPORT In Vitro

"In particular, exon 15 variants (p.Pro866Leu and p.Pro869Ser) correlated with severe phenotypes, including epilepsy and severe motor impairment, whereas p.Gly1899Arg and p.Thr2162Met were associated with milder manifestations."

Ties variant position to clinical severity, the genotype-phenotype anchor for the non-haploinsufficiency hypothesis.

PMID:32646507 SUPPORT Human Clinical

"Our case further demonstrates that Pro869Ser is a hotspot mutation of the MED13L gene."

Establishes p.Pro869Ser as a recurrent allele, a prerequisite for the allele-specific mechanism claim.

+ 1 more reference

MED13L missense variants as a cause of isolated dextro-transposition of the great arteries

med13l_isolated_dtga ⚠ DEPRECATED Isolated d-transposition of the great arteries

⚠ Overturned model — shown for reference, not as current mechanism

DisMech records superseded hypotheses explicitly rather than deleting them, so that claims still circulating in reviews, textbooks and older diagnostic criteria can be checked against an assessment. This model is not part of the disease mechanism DisMech asserts.

Citation volume does not decide standing here. A hypothesis may retain more supporting than refuting citations simply because the supporting literature accumulated for decades before the refutation landed; where the two conflict, DisMech follows the more recent and more direct evidence. Supporting citations below are retained for the historical record.

Evidence balance 1 support 3 refute

The gene entered the literature in 2003-2004 as a candidate for isolated d-transposition of the great arteries, and that framing persisted for a decade. Subsequent syndromic cohorts redefined the entity as a neurodevelopmental haploinsufficiency disorder in which congenital heart defects are a minority, variably penetrant feature, and the original missense alleles are now largely classified as variants of uncertain significance. The isolated-d-TGA association is retained here as the historical entry point to the gene, not as a supported current mechanism.

Show evidence (4 references)

PMID:15175163 SUPPORT In Vitro

"In addition, we identify as Mediator-associated proteins the CDK8-like cyclin-dependent kinase CDK11 and the TRAP240-like KIAA1025 protein (MED13L), which is mutated in patients with the congenital heart defect transposition of the great arteries (TGA)."

Records the original framing of MED13L (then KIAA1025/TRAP240-like) as a transposition-of-the-great-arteries gene.

PMID:25758992 REFUTE Human Clinical

"Here, we report eight patients with predominantly novel MED13L variants who lack such complex congenital heart malformations."

Directly refutes obligate cardiac involvement and reframes MED13L as a syndromic neurodevelopmental disorder.

PMID:23403903 REFUTE Human Clinical

"Our findings show that MED13L haploinsufficiency in contrast to the previously observed missense mutations cause a distinct syndromic phenotype."

Separates the syndromic dosage-loss entity from the earlier isolated-d-TGA missense reports.

+ 1 more reference

MED13/MED13L paralog compensation modulates expressivity

med13l_med13_paralog_compensation EMERGING

Evidence balance 2 support 1 partial

MED13 and MED13L are mutually exclusive occupants of the same structural position in the CKM and are partially redundant: combined cardiomyocyte deletion of both is lethal where either single deletion is tolerated. Incomplete, tissue-dependent compensation by the intact paralog is a candidate explanation for the variable expressivity of MED13L syndrome — in particular for why cardiac involvement is penetrant in only a minority — and, if druggable, a candidate therapeutic axis. No direct human evidence links paralog expression level to phenotype severity.

The available redundancy evidence is cardiac and murine. Whether the same buffering operates in developing human cortex, where the dominant MED13L phenotype arises, is untested.

Show evidence (3 references)

PMID:40989238 SUPPORT Model Organism

"Med13 and Med13L are mutually exclusive paralogs within the kinase submodule of the Mediator complex that have been shown to have partially redundant functions in embryonic development and transcription, but their combined roles have not been investigated in the adult heart."

States the mutual exclusivity and partial redundancy that the compensation hypothesis rests on.

PMID:40989238 SUPPORT Model Organism

"Med13/13L knockout resulted in decreased cardiac function leading to lethal heart failure in a median timeframe of 6 weeks from the start of tamoxifen."

Combined loss is lethal where single-paralog loss is tolerated, the functional signature of redundancy.

PMID:40919805 PARTIAL Model Organism

"Med13l HET mice recapitulate MED13L syndrome phenotypes including a developmental growth delay and craniofacial anomalies."

Heterozygous Med13l loss produces growth and craniofacial phenotypes but not a cardiac functional defect, consistent with — though not proof of — cardiac compensation by Med13.

Cyclin C nuclear release and mitochondrial fragmentation as a secondary disease mechanism

med13l_cyclin_c_mitochondrial EMERGING Loss-of-function (deletion / truncating / splice)

Evidence balance 2 support

MED13L tethers the cyclin C-CDK8 kinase module to Mediator; cyclin C also has a CKM-independent cytoplasmic role driving stress-induced mitochondrial fission and regulated cell death. In patient fibroblasts carrying a MED13L frameshift allele, cyclin C is aberrantly cytoplasmic even without stress, with mitochondrial fragmentation and markedly reduced respiration; blocking cyclin C mitochondrial localisation partially rescues organelle function. If this operates in neurons it would add a bioenergetic component to the intellectual disability phenotype and would be pharmacologically approachable independently of transcription. Currently demonstrated only in fibroblasts from a single patient allele.

Evidence is from one patient fibroblast line carrying a single frameshift allele. Whether the same cyclin C release occurs in MED13L-haploinsufficient neurons, and whether it contributes measurably to the neurodevelopmental phenotype, is untested.

Show evidence (2 references)

PMID:35198885 SUPPORT In Vitro

"Unstressed MED13L S1497 F/fs patient fibroblasts exhibited aberrant cytoplasmic cyclin C localization, mitochondrial fragmentation, and a 6-fold reduction in respiration."

Primary observation linking a MED13L patient allele to cyclin C mislocalisation and a measurable bioenergetic deficit.

PMID:35198885 SUPPORT In Vitro

"Pharmacological or genetic approaches preventing cyclin C-mitochondrial localization corrected the fragmented mitochondrial phenotype and partially restored organelle function."

Rescue experiment establishes cyclin C mislocalisation as causal for the mitochondrial phenotype rather than a bystander effect, and defines the candidate therapeutic handle.

⚙

Pathophysiology

7

CKM hinge anchoring by MED13L

MED13L, like its paralog MED13, is the physical hinge of the Mediator CDK8 kinase module (CKM, comprising MED13/MED13L, MED12/MED12L, CDK8/CDK19 and cyclin C). The subunit adopts an Argonaute-like bi-lobal fold, and a large intrinsically disordered region within it forms the principal CKM contact with core Mediator. That same disordered region sterically occludes the RNA polymerase II and MED26 binding surfaces, so MED13L abundance and structural integrity gate reversible CKM-core docking and thereby the switch between Mediator's repressive and permissive states.

MED13L hgnc:22962 MED13 hgnc:22474

regulation of transcription by RNA polymerase II GO:0006357

transcription coregulator activity GO:0003712

Downstream

MED13L haploinsufficiency Reduced MED13L protein reduces the pool of intact CKM competent to dock on core Mediator.

SCF-FBW7 control of MED13L abundance Because the hinge is the rate-limiting CKM-core contact, ubiquitin-mediated turnover of MED13L sets CKM-core stoichiometry.

Show evidence (5 references)

PMID:39321804 SUPPORT In Vitro

"The CKM binds to multiple regions on cMED through both MED12 and MED13, including a large intrinsically disordered region (IDR) in the latter."

Cryo-EM of the complete human Mediator identifies the MED13 intrinsically disordered region as the CKM-core interface.

PMID:39321804 SUPPORT In Vitro

"Notably, the MED13 IDR obstructs the recruitment of RNA Pol II/MED26 onto cMED by direct occlusion of their respective binding sites, leading to functional repression of cMED-dependent transcription."

Defines the structural mechanism by which the hinge subunit represses Mediator-dependent transcription, the function lost on MED13L dosage reduction.

PMID:33523904 SUPPORT In Vitro

"Unexpectedly, Med13 has a characteristic Argonaute-like bi-lobal architecture."

Establishes the structural fold of the MED13/MED13L hinge subunit.

+ 2 more references

SCF-FBW7 control of MED13L abundance

The SCF-Fbw7 ubiquitin ligase binds CDK8-Mediator and targets both MED13 and MED13L for proteasomal degradation. This is the only characterised E3-ligase control of MED13L abundance, and because MED13/MED13L physically link the CKM to Mediator, Fbw7-dependent turnover sets the kinetics of CKM dissociation from the core complex. Loss of Fbw7 increases CKM-Mediator association, the reciprocal of the dosage reduction seen in MED13L syndrome.

MED13L hgnc:22962 FBXW7 hgnc:16712

protein ubiquitination GO:0016567 proteasome-mediated ubiquitin-dependent protein catabolic process GO:0043161

Downstream

MED13L haploinsufficiency Turnover of the remaining wild-type allele's product further lowers functional MED13L in a haploinsufficient cell, making degradation kinetics a candidate modifier and therapeutic target.

Show evidence (2 references)

PMID:23322298 SUPPORT In Vitro

"We show that Fbw7, a tumor suppressor and ubiquitin ligase, binds to CDK8-Mediator and targets MED13/13L for degradation."

Establishes SCF-Fbw7 as the E3 ligase controlling MED13L protein abundance.

PMID:23322298 SUPPORT In Vitro

"MED13/13L physically link the CDK8 module to Mediator, and Fbw7 loss increases CDK8 module-Mediator association."

Shows MED13L abundance is directly coupled to CKM-core occupancy, the dosage axis perturbed in MED13L syndrome.

MED13L haploinsufficiency

Heterozygous loss-of-function alleles — whole-gene and intragenic deletions, frameshift, nonsense, and canonical splice variants — halve functional MED13L dosage. The reduced pool of intact CKM dysregulates RNA polymerase II-dependent transcriptional programs during development. Dosage loss is sufficient to produce the syndrome: heterozygous Med13l mice reproduce growth, craniofacial, learning and motor phenotypes, while homozygous loss is embryonic/neonatal lethal.

MED13L hgnc:22962

transcription by RNA polymerase II GO:0006366 ↓ DECREASED regulation of transcription by RNA polymerase II GO:0006357 ↕ DYSREGULATED

Downstream

Neurodevelopmental transcriptional dysregulation Reduced CKM-gated transcriptional control perturbs the neurodevelopmental gene programs that underlie intellectual disability, speech impairment and hypotonia.

Neural-crest and cardiac outflow-tract developmental dysregulation Dosage loss perturbs neural-crest-dependent craniofacial and cardiac outflow-tract morphogenesis.

Cyclin C nuclear release and mitochondrial dysfunction Loss of the MED13L nuclear anchor permits cyclin C to accumulate in the cytoplasm, where it drives mitochondrial fission.

Show evidence (3 references)

PMID:23403903 SUPPORT Human Clinical

"Here, we describe for the first time, three patients with copy number changes affecting MED13L and delineate a recognizable MED13L haploinsufficiency syndrome."

Founding delineation of the dosage-loss syndrome.

PMID:37512036 SUPPORT Human Clinical

"Based on these findings, heterozygous intragenic 12q24.21 deletion in the affected individual resulted in MED13L haploinsufficiency due to the premature termination of protein translation, therefore leading to MED13L haploinsufficiency syndrome."

Traces an intragenic deletion through premature translation termination to haploinsufficiency at the protein level.

PMID:40775066 SUPPORT Model Organism

"While homozygous Med13l knockout exhibit neonatal lethality accompanied by reduced brain volume and cortical thickness, heterozygous mice are viable and display hallmarks of MED13L syndrome, including impaired learning and memory, reduced motor coordination, and heightened anxiety."

Establishes the mouse dosage series and shows heterozygous loss is sufficient for the syndrome phenotype.

MED13L missense destabilisation and mislocalisation

Pathogenic missense variants cluster in two hotspots (exons 15-17 and 25-31). Functional characterisation shows they reduce MED13L protein stability, several mislocalise the protein to the cytoplasm, and 3D modelling predicts disrupted contact with the CDK8 kinase module. Most therefore behave as loss-of-function. The exon-15 alleles p.Pro866Leu and p.Pro869Ser stand out clinically, correlating with epilepsy and severe motor impairment, and p.Pro869Ser retains relatively stable, partly nuclear expression — the basis for the contested non-dosage mechanism captured in `med13l_missense_non_haploinsufficient`.

neuron CL:0000540

MED13L hgnc:22962

dendrite morphogenesis GO:0048813 ↓ DECREASED

Downstream

Neurodevelopmental transcriptional dysregulation Destabilised or mislocalised MED13L fails to support CKM-gated neurodevelopmental transcription.

Show evidence (4 references)

PMID:40500968 SUPPORT In Vitro

"In this study, we investigated five pathogenic missense variants in MED13L-c.2597C>T p.Pro866Leu, c.2605C>T p.Pro869Ser, c.3392G>A p.Cys1131Tyr, c.5695G>A p.Gly1899Arg, and c.6485C>T p.Thr2162Met-associated with different clinical severities."

Defines the characterised missense allele series.

PMID:40500968 SUPPORT Computational

"3D protein modeling suggested that these missense variants may disrupt MED13L's interaction with the CDK8 kinase module, leading to functional deficits."

Provides the structural rationale linking missense position to impaired CKM assembly.

PMID:29511999 SUPPORT Human Clinical

"Missense variants clustered in two mutation hot-spots, i.e., exons 15-17 and 25-31."

Establishes the positional clustering of pathogenic missense alleles.

+ 1 more reference

Neurodevelopmental transcriptional dysregulation

Reduced or dysfunctional MED13L dysregulates RNA polymerase II-dependent neurodevelopmental gene programs. Mechanistically, MED13L acts by priming transcriptional activation of key cortical developmental genes (including Neurod2, Sox5, Auts2 and Nfib), a priming step mediated by MED13L binding to core Mediator that licenses the complex to associate with RNA Pol II. Loss impairs neural progenitor differentiation and cortical neurogenesis, and reduces dendritic number and length in cortical pyramidal neurons — the cellular substrate for intellectual disability, motor speech impairment, and hypotonia.

neural progenitor cell CL:0011020 neuron CL:0000540

cerebral cortex development GO:0021987 ↕ DYSREGULATED dendrite morphogenesis GO:0048813 ↓ DECREASED

Downstream

Intellectual disability Disrupted cortical neurogenesis and dendritic development underlie the core cognitive impairment.

Motor speech disorder Impaired corticogenesis in motor-speech networks produces the apraxia/dysarthria that dominates the MED13L communication phenotype.

Global developmental delay Early milestone acquisition is impaired across domains.

Generalized hypotonia Disrupted neurodevelopmental programs contribute to the near-universal hypotonia.

Motor delay Delayed acquisition of motor milestones, with mean walking age near 2 years.

Seizure Disrupted cortical network formation predisposes to seizures, disproportionately in missense carriers.

Gastrointestinal problems Hypotonia and impaired oromotor and gut motor control contribute to the gastrointestinal and feeding difficulties affecting over half of individuals.

Abnormality of the musculoskeletal system Distal limb, digit and foot deformities arise partly secondary to the central hypotonia and reduced motor loading.

Scoliosis Secondary to long-standing axial hypotonia, which is why spinal assessment is recommended at every visit.

Autistic behavior Neurobehavioral manifestations including autistic features.

Abnormal brain morphology Disturbed corticogenesis and myelination contribute to the MRI abnormalities (ventriculomegaly, thin or absent corpus callosum, white matter change).

Global developmental delay Impaired cortical neurogenesis delays milestone acquisition across all domains.

Absent speech At the severe end of the motor-speech phenotype, children remain minimally verbal or nonverbal beyond age four.

Delayed speech and language development Near-universal expressive language delay, disproportionate to the degree of intellectual disability.

Ataxia Disrupted cerebellar and corticospinal output contributes to ataxia and coordination problems.

Show evidence (3 references)

PMID:40775066 SUPPORT Model Organism

"Single-cell transcriptomics and immunofluorescence reveal severe cortical neurogenesis deficits in Med13l knockout embryos, driven by impaired neural progenitor differentiation."

Locates the primary cellular defect at neural progenitor differentiation during corticogenesis.

PMID:40775066 SUPPORT Model Organism

"Integrative multi-omics analyses reveal that MED13L orchestrates cortical neurogenesis by priming the transcriptional activation of key developmental genes, including Neurod2, Sox5, Auts2, and Nfib."

Identifies the specific transcriptional-priming mechanism and its downstream target genes.

PMID:36798993 SUPPORT Model Organism

"Taken together, our results demonstrate that MED13L expression is relevant to corticogenesis and influences the dendritic branching characteristics of cortical excitatory neurons."

Establishes a MED13L requirement for dendritic development in cortical excitatory neurons.

Neural-crest and cardiac outflow-tract developmental dysregulation

MED13L dosage reduction perturbs cranial neural crest cell migration and neural-crest-dependent morphogenesis, producing the craniofacial gestalt and the variable conotruncal and septal congenital heart defects seen in a minority of patients. Knockdown of the MED13L zebrafish orthologue med13b causes defective cranial neural crest migration and cartilage deformities that phenocopy the human craniofacial anomalies, and heterozygous Med13l mice show midfacial hypoplasia. The clinical impression of a neurocristopathy predates and motivated this mechanistic work.

neural crest cell CL:0000333

cardiac neural crest cell development involved in heart development GO:0061308 ↕ DYSREGULATED heart development GO:0007507 ↕ DYSREGULATED

Downstream

Abnormal heart morphology Perturbed outflow-tract morphogenesis contributes to the conotruncal and septal defects seen in a minority of patients.

Abnormal facial shape Disrupted cranial neural crest patterning produces the recognisable facial gestalt.

Bulbous nose Component of the neural-crest-derived facial gestalt.

Depressed nasal bridge Component of the neural-crest-derived facial gestalt.

Open mouth Hypotonic open-mouth appearance, combining the craniofacial and hypotonia arms.

Low-set ears Component of the neural-crest-derived facial gestalt.

Upslanted palpebral fissure Component of the neural-crest-derived facial gestalt.

Visual impairment Disrupted ocular and periocular development contributes to the high burden of visual impairment.

Strabismus Disrupted development of ocular alignment contributes to strabismus.

Hearing impairment Otic and inner-ear structural involvement, including the vestibular abnormality documented on imaging, arises from the same neural-crest and placodal programs.

Recurrent otitis media Craniofacial and eustachian-tube anatomy predisposes to recurrent middle-ear infection, which compounds the hearing and speech phenotype.

Show evidence (3 references)

PMID:25137640 SUPPORT Model Organism

"Knockdown of MED13L orthologue in zebrafish, med13b, showed early defective migration of cranial neural crest cells (NCCs) that contributed to cartilage structure deformities in the later stage, recapitulating craniofacial anomalies seen in human patients."

Direct model-organism evidence that MED13L loss impairs cranial neural crest migration and produces the craniofacial phenotype.

PMID:23403903 SUPPORT Human Clinical

"The clinical features suggesting a neurocristopathy may be explained by animal model studies indicating involvement of the Mediator complex subunit 13 in neural crest induction."

Records the clinical inference of a neurocristopathy that the zebrafish work subsequently supported.

PMID:40919805 SUPPORT Model Organism

"We observed Med13l HET mice are smaller than wildtype (WT) littermates, and over 60% of them exhibited one of two craniofacial anomalies: a pug snout with midface hypoplasia or a crooked snout."

Quantifies the craniofacial penetrance of heterozygous Med13l loss in a mammalian model.

Cyclin C nuclear release and mitochondrial dysfunction

Cyclin C is retained in the nucleus by the MED13L-anchored CKM. When MED13L is lost, cyclin C is aberrantly released to the cytoplasm even in unstressed cells, where its CKM-independent activity drives mitochondrial fission. Patient fibroblasts carrying a MED13L frameshift allele show mitochondrial fragmentation, a six-fold reduction in respiration, reduced mtDNA copy number and hypersensitivity to oxidative stress. This is a candidate secondary, bioenergetic arm of the disease; it has been demonstrated in fibroblasts, not neurons.

fibroblast CL:0000057

mitochondrial fission GO:0000266 ↑ INCREASED response to oxidative stress GO:0006979 ↕ DYSREGULATED

Downstream

Intellectual disability A bioenergetic contribution to the cognitive phenotype, predicted if the cyclin C release demonstrated in patient fibroblasts also occurs in neurons. Flagged as inference: no neuronal data exist.

Generalized hypotonia Reduced oxidative capacity is a plausible contributor to the near-universal hypotonia, on the same fibroblast-to-muscle inference as above.

Show evidence (2 references)

PMID:35198885 SUPPORT In Vitro

"In addition, the fibroblasts exhibited reduced mtDNA copy number, reduction in mitochondrial membrane integrity, and hypersensitivity to oxidative stress."

Characterises the mitochondrial phenotype of MED13L-mutant patient cells beyond morphology alone.

PMID:35198885 SUPPORT In Vitro

"In conclusion, this study found that mitochondrial dysfunction is an underlying defect in cells harboring the MED13L S1497 F/fs allele and identified cyclin C mis-localization as the likely cause."

Attributes the mitochondrial defect specifically to cyclin C mislocalisation.

⬡

Pathograph

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

●

Phenotypes

25

Cardiovascular 1

Abnormal heart morphology OCCASIONAL Abnormal heart morphology HP:0001627

Show evidence (4 references)

PMID:29511999 SUPPORT Human Clinical

"Hypotonia, ataxia, and recognizable facial gestalt were frequent findings, but not congenital heart defects."

Explicitly excludes congenital heart defects from the frequent findings in a 36-patient cohort, the key evidence for the OCCASIONAL band.

PMID:28645799 SUPPORT Human Clinical

"Subsequent reports of 22 further patients diagnosed by genome-wide testing further delineated the syndrome with expansion of the phenotypic spectrum and showed reduced penetrance for congenital heart defects."

Documents reduced penetrance of the cardiac phenotype.

PMID:25712080 SUPPORT Human Clinical

"Congenital heart diseases are found in some subjects with various degree of severity."

Confirms cardiac involvement as a variable, subset finding.

+ 1 more reference

Digestive 1

Gastrointestinal problems FREQUENT Abnormality of the gastrointestinal tract HP:0011024

Show evidence (1 reference)

PMID:40993520 SUPPORT Human Clinical

"Notable medical features included hypotonia (83%), vision problems (72%), recurrent otitis media (58%), gastrointestinal problems (57%), and seizures (31%)."

Quantifies gastrointestinal problems at 57%, supporting the FREQUENT band.

Ear 3

Low-set ears FREQUENT Low-set ears HP:0000369

Show evidence (1 reference)

PMID:28645799 SUPPORT Human Clinical

"With reference to facial anomalies, the majority of patients were reported to show broad/prominent forehead, low set ears, bitemporal narrowing, upslanting palpebral fissures, depressed/flat nasal bridge, bulbous nose, and abnormal chin, but macroglossia and horizontal eyebrows were also..."

Low-set ears listed among features reported in the majority of patients.

Hearing impairment OCCASIONAL Hearing impairment HP:0000365

Show evidence (3 references)

PMID:40228085 SUPPORT Human Clinical

"Other reported features include seizures and/or hearing impairment."

GeneReviews lists hearing impairment among the reported minority features.

PMID:38454295 SUPPORT Human Clinical

"The child showed bilateral sloping sensorineural hearing loss, a bilateral vestibular weakness, and an inner ear vestibular structural abnormality on imaging."

First objective vestibulometry in MED13L syndrome, extending the otologic phenotype beyond hearing loss to vestibular dysfunction.

PMID:38454295 SUPPORT Human Clinical

"Hearing loss has been reported very rarely, and vestibular weakness has never been reported in the condition."

States the prior rarity of otologic reporting, justifying the OCCASIONAL band and the novelty of the vestibular finding.

Recurrent otitis media FREQUENT Recurrent otitis media HP:0000403

Show evidence (1 reference)

PMID:40993520 SUPPORT Human Clinical

"Notable medical features included hypotonia (83%), vision problems (72%), recurrent otitis media (58%), gastrointestinal problems (57%), and seizures (31%)."

Quantifies recurrent otitis media at 58%, supporting the FREQUENT band.

Eye 2

Visual impairment FREQUENT Visual impairment HP:0000505

Show evidence (2 references)

PMID:40389839 SUPPORT Human Clinical

"The GenIDA series identified a higher prevalence of visual impairment (76%) and highlighted under-recognized musculoskeletal issues, such as foot deformities, which had previously received little attention."

Family-reported registry data quantify visual impairment at 76% and explicitly flag it as previously under-recognised.

PMID:40993520 SUPPORT Human Clinical

"Notable medical features included hypotonia (83%), vision problems (72%), recurrent otitis media (58%), gastrointestinal problems (57%), and seizures (31%)."

Independent cohort corroborates the high frequency of vision problems (72%).

Strabismus Strabismus HP:0000486

`frequency` omitted deliberately: strabismus is repeatedly named in case reports and in the GeneReviews surveillance guidance, but no source reports a numerator and denominator for it separately from the grouped visual-impairment figure.

Show evidence (2 references)

PMID:33930262 SUPPORT Human Clinical

"Uncommon findings like lack of speech, strabismus and self-destructive behaviour present in our patient allowed us to further define the phenotypic spectrum of mental retardation and distinctive facial features with or without cardiac defects syndrome."

Case-level documentation of strabismus.

PMID:37512036 SUPPORT Human Clinical

"This complex neurodevelopmental disorder is characterised by various phenotypic features, including plagiocephaly, strabismus, clubfoot, poor speech, and developmental delay."

Lists strabismus among the characteristic features of the disorder.

Head and Neck 4

Abnormal facial shape VERY_FREQUENT Abnormal facial shape HP:0001999

Show evidence (2 references)

PMID:28645799 SUPPORT Human Clinical

"With reference to facial anomalies, the majority of patients were reported to show broad/prominent forehead, low set ears, bitemporal narrowing, upslanting palpebral fissures, depressed/flat nasal bridge, bulbous nose, and abnormal chin, but macroglossia and horizontal eyebrows were also..."

Enumerates the component features of the gestalt and their approximate frequencies.

PMID:28645799 SUPPORT Human Clinical

"Review of the reported patients with MED13L haploinsufficiency indicates moderate to severe ID and facial anomalies in all patients, as well as severe speech delay and muscular hypotonia in the majority."

Facial anomalies present in all reviewed haploinsufficiency patients, supporting the VERY_FREQUENT band.

Bulbous nose FREQUENT Bulbous nose HP:0000414

Show evidence (2 references)

PMID:29959045 SUPPORT Human Clinical

"the syndrome may be suspected in some individuals based on the association of developmental delay, speech impairment, bulbous nasal tip, and macroglossia, macrostomia, or open mouth appearance."

Bulbous nasal tip named as one of four features that raise clinical suspicion of the syndrome.

PMID:40228085 SUPPORT Human Clinical

"Dysmorphic facial features, including depressed nasal bridge, bulbous nose, and hypotonic open mouth, are present in most individuals."

GeneReviews places bulbous nose among the features present in most individuals.

Depressed nasal bridge FREQUENT Depressed nasal bridge HP:0005280

Show evidence (1 reference)

PMID:40228085 SUPPORT Human Clinical

"Dysmorphic facial features, including depressed nasal bridge, bulbous nose, and hypotonic open mouth, are present in most individuals."

Lists depressed nasal bridge among features present in most individuals.

Upslanted palpebral fissure FREQUENT Upslanted palpebral fissure HP:0000582

Show evidence (1 reference)

PMID:28645799 SUPPORT Human Clinical

"With reference to facial anomalies, the majority of patients were reported to show broad/prominent forehead, low set ears, bitemporal narrowing, upslanting palpebral fissures, depressed/flat nasal bridge, bulbous nose, and abnormal chin, but macroglossia and horizontal eyebrows were also..."

Upslanting palpebral fissures listed among majority facial features.

Musculoskeletal 2

Generalized hypotonia VERY_FREQUENT Generalized hypotonia HP:0001290

Show evidence (2 references)

PMID:40993520 SUPPORT Human Clinical

"Notable medical features included hypotonia (83%), vision problems (72%), recurrent otitis media (58%), gastrointestinal problems (57%), and seizures (31%)."

Quantifies hypotonia at 83%, supporting the VERY_FREQUENT band (80-99%).

PMID:28645799 SUPPORT Human Clinical

"Review of the reported patients with MED13L haploinsufficiency indicates moderate to severe ID and facial anomalies in all patients, as well as severe speech delay and muscular hypotonia in the majority."

Independent literature review places hypotonia in the majority of patients.

Scoliosis OCCASIONAL Scoliosis HP:0002650

Show evidence (2 references)

PMID:29046205 SUPPORT Human Clinical

"The anteroposterior and lateral films of the spine showed scoliosis"

Radiographically confirmed scoliosis in a MED13L syndrome proband.

PMID:40228085 SUPPORT Human Clinical

"clinical assessment for scoliosis at each visit with radiographs as needed"

Scoliosis is prominent enough in the phenotype to warrant dedicated surveillance in the GeneReviews management guidance.

Nervous System 9

Intellectual disability VERY_FREQUENT Intellectual disability HP:0001249

Show evidence (3 references)

PMID:29511999 SUPPORT Human Clinical

"All patients presented with intellectual disability and severe language impairment."

All 36 patients in the largest genotype-phenotype cohort had intellectual disability, supporting a VERY_FREQUENT band.

PMID:28645799 SUPPORT Human Clinical

"Review of the reported patients with MED13L haploinsufficiency indicates moderate to severe ID and facial anomalies in all patients, as well as severe speech delay and muscular hypotonia in the majority."

Literature review confirms intellectual disability in all reported haploinsufficiency patients and places the modal severity at moderate-to-severe.

PMID:40993520 SUPPORT Human Clinical

"Full scale IQs fell in the borderline to intellectual disability range, consistent with reported cognitive impairment in 97% of the virtual cohort."

Direct standardized cognitive testing quantifies the impairment and its near-universal frequency.

Global developmental delay VERY_FREQUENT Global developmental delay HP:0001263

Show evidence (2 references)

PMID:40228085 SUPPORT Human Clinical

"MED13L syndrome is characterized by mild-to-profound developmental delay, intellectual disability, and hypotonia."

GeneReviews places developmental delay among the defining features.

PMID:29959045 SUPPORT Human Clinical

"Phenotypically, they all had intellectual disability, speech and motor delay, and features of the mouth (open mouth appearance, macroglossia, and/or macrostomia)."

All eight patients in this series had combined speech and motor delay.

Motor speech disorder VERY_FREQUENT Speech apraxia HP:0011098

Show evidence (2 references)

PMID:40993520 SUPPORT Human Clinical

"All individuals who completed in-person articulation testing met diagnostic criteria for speech apraxia, dysarthria, or both."

Deep-phenotyping study establishing motor speech disorder, not generic speech delay, as the MED13L communication phenotype.

PMID:40993520 SUPPORT Human Clinical

"MED13L-related disorder is characterized by a high rate of motor speech disorders that occur in the context of globally impaired motor, language, and cognitive skills."

States the conclusion directly and situates the speech phenotype within global motor impairment.

Delayed speech and language development VERY_FREQUENT Delayed speech and language development HP:0000750

Show evidence (2 references)

PMID:40993520 SUPPORT Human Clinical

"Language impairment was present in all of the in-person cohort and reported for almost all (97%) of the virtual cohort."

Quantifies language impairment at essentially 100%, supporting VERY_FREQUENT.

PMID:25758992 SUPPORT Human Clinical

"A prominent feature of the MED13L neurocognitive presentation is profound language impairment, often in combination with articulatory deficits."

Identifies profound language impairment with articulatory involvement as the signature neurocognitive feature.

Absent speech OCCASIONAL Absent speech HP:0001344

Show evidence (1 reference)

PMID:33930262 SUPPORT Human Clinical

"Uncommon findings like lack of speech, strabismus and self-destructive behaviour present in our patient allowed us to further define the phenotypic spectrum of mental retardation and distinctive facial features with or without cardiac defects syndrome."

Documents complete absence of speech as a recognised but uncommon end of the MED13L communication spectrum.

Motor delay VERY_FREQUENT Motor delay HP:0001270

Show evidence (2 references)

PMID:34654706 SUPPORT Human Clinical

"Affected individuals share overlapping features comprising intellectual disability, hypotonia, motor delay, remarkable speech delay, and a recognizable facial gestalt."

Lists motor delay among the shared core features of the syndrome.

PMID:29959045 SUPPORT Human Clinical

"Phenotypically, they all had intellectual disability, speech and motor delay, and features of the mouth (open mouth appearance, macroglossia, and/or macrostomia)."

Motor delay present in all patients of this series.

Autistic behavior FREQUENT Autistic behavior HP:0000729

Show evidence (2 references)

PMID:40228085 SUPPORT Human Clinical

"Neurobehavioral manifestations (autistic features, agitation/aggression, restlessness, self-harm, tantrums, frustration, overfriendliness, and/or hyperactivity) are also reported."

GeneReviews records autistic features within the recognised neurobehavioral profile.

PMID:32646507 SUPPORT Human Clinical

"Behavioral difficulties and autistic features were observed in 55.6% of the patients."

Quantifies behavioural/autistic features at 55.6% in the missense-variant literature subset, supporting the FREQUENT band.

Seizure FREQUENT Seizure HP:0001250

Show evidence (3 references)

PMID:40993520 SUPPORT Human Clinical

"Notable medical features included hypotonia (83%), vision problems (72%), recurrent otitis media (58%), gastrointestinal problems (57%), and seizures (31%)."

Quantifies seizures at 31% of a 67-individual cohort, which falls in the FREQUENT band (30-79%).

PMID:29511999 SUPPORT Human Clinical

"We found that patients carrying missense mutations had more frequently epilepsy and showed a more severe phenotype."

Establishes the genotype dependence of the seizure risk, which is what makes the overall frequency band an average across two different risk groups.

PMID:32646507 SUPPORT Human Clinical

"Of these patients, 44.4% had epileptic seizures."

Quantifies the higher seizure frequency specifically within the missense-variant subset.

Ataxia FREQUENT Ataxia HP:0001251

Show evidence (2 references)

PMID:29511999 SUPPORT Human Clinical

"Hypotonia, ataxia, and recognizable facial gestalt were frequent findings, but not congenital heart defects."

Ataxia explicitly described as a frequent finding in a 36-patient cohort, and in the same sentence contrasted with the non-frequency of cardiac defects.

PMID:28645799 SUPPORT Human Clinical

"Further common signs include abnormal MRI findings of myelination defects and abnormal corpus callosum, ataxia and coordination problems, autistic features, seizures/abnormal EEG, or congenital heart defects, present in about 20-50% of the patients."

Places ataxia and coordination problems in a 20-50% band across reviewed patients.

Other 3

Abnormal brain morphology FREQUENT Abnormal brain morphology HP:0012443

Show evidence (2 references)

PMID:40228085 SUPPORT Human Clinical

"Some individuals have abnormal findings on brain imaging (ventriculomegaly, delayed or lack of myelination, thin or absent corpus callosum, periventricular foci, and/or subcortical white matter abnormalities)."

Enumerates the specific neuroimaging abnormalities seen in MED13L syndrome.

PMID:28645799 SUPPORT Human Clinical

"Further common signs include abnormal MRI findings of myelination defects and abnormal corpus callosum, ataxia and coordination problems, autistic features, seizures/abnormal EEG, or congenital heart defects, present in about 20-50% of the patients."

Places MRI abnormalities in a 20-50% frequency band.

Open mouth FREQUENT Open mouth HP:0000194

Show evidence (2 references)

PMID:40228085 SUPPORT Human Clinical

"Dysmorphic facial features, including depressed nasal bridge, bulbous nose, and hypotonic open mouth, are present in most individuals."

GeneReviews lists hypotonic open mouth among the majority features.

PMID:29959045 SUPPORT Human Clinical

"Phenotypically, they all had intellectual disability, speech and motor delay, and features of the mouth (open mouth appearance, macroglossia, and/or macrostomia)."

Oral features present in all eight patients of this series.

Abnormality of the musculoskeletal system Abnormality of the musculoskeletal system HP:0033127

`frequency` deliberately omitted: the registry study establishes that musculoskeletal involvement is more common than previously appreciated but does not report a numerator/denominator for the grouped term used here.

Show evidence (2 references)

PMID:40389839 SUPPORT Human Clinical

"The GenIDA series identified a higher prevalence of visual impairment (76%) and highlighted under-recognized musculoskeletal issues, such as foot deformities, which had previously received little attention."

Identifies musculoskeletal involvement, specifically foot deformities, as an under-recognised part of the phenotype.

PMID:40228085 SUPPORT Human Clinical

"Distal limb and/or digit anomalies, ocular manifestations and vision issues, and congenital heart defects have been reported."

GeneReviews records distal limb and digit anomalies in the phenotype.

🧬

Genetic Associations

1

MED13L heterozygous pathogenic variants (Causative)

Gene: MED13L hgnc:22962 relationship_type: CAUSATIVE variant_origin: GERMLINE

Autosomal Dominant

Show evidence (5 references)

PMID:40228085 SUPPORT Human Clinical

"The majority of probands reported to date whose parents have undergone molecular genetic testing have the disorder as the result of a pathogenic variant that occurred as a de novo event in the proband."

Establishes de novo predominance.

PMID:40228085 SUPPORT Human Clinical

"Rarely, individuals diagnosed with MED13L syndrome have the disorder as the result of a pathogenic variant inherited from a mosaic, apparently unaffected parent."

Documents parental mosaicism as the recurrence mechanism, the basis for the recurrence-risk counselling below.

PMID:34654706 SUPPORT Human Clinical

"We now present the first case of paternal germinal mosaicism for a missense MED13L variant causing MRFACD syndrome in one of the father's children and being the likely cause of intellectual disability and facial dysmorphism in the other."

First direct demonstration of paternal germinal mosaicism, converting a theoretical recurrence risk into a documented one.

+ 2 more references

💊

Medical Actions

9

Speech and Language Therapy

Action: speech therapy Ontology label: Speech Language Therapy NCIT:C159273

The highest-priority developmental intervention. Because the MED13L speech phenotype is specifically a motor speech disorder (apraxia and/or dysarthria) rather than a nonspecific delay, assessment should screen explicitly for apraxia so that motor-speech techniques and, for minimally verbal or nonverbal children, augmentative and alternative communication are introduced early.

Target Phenotypes: Speech apraxia HP:0011098 Delayed speech and language development HP:0000750

Show evidence (2 references)

PMID:40993520 SUPPORT Human Clinical

"Children would benefit from early referrals to speech therapy to assess their speech, language, and support needs."

Direct recommendation from the deep-phenotyping study that established the motor speech phenotype.

PMID:40993520 SUPPORT Human Clinical

"All individuals who completed in-person articulation testing met diagnostic criteria for speech apraxia, dysarthria, or both."

Justifies apraxia/dysarthria-specific assessment rather than generic language therapy.

Physical Therapy

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

Physiotherapy from infancy for hypotonia, motor delay and the coordination and balance problems associated with ataxia and, in some children, vestibular weakness.

Target Phenotypes: Generalized hypotonia HP:0001290 Motor delay HP:0001270

Show evidence (1 reference)

PMID:40228085 SUPPORT Human Clinical

"assessment of mobility and self-help skills at each visit"

GeneReviews surveillance guidance establishes ongoing motor assessment as standard care, the trigger for physiotherapy input.

Occupational Therapy

Action: occupational therapy Ontology label: Occupational Therapy NCIT:C121351

Occupational therapy as part of the multidisciplinary developmental package, targeting self-help skills and the significant visual-motor integration deficits demonstrated on standardized testing.

Show evidence (1 reference)

PMID:40993520 SUPPORT Human Clinical

"Those who were able to complete motor testing demonstrated significant deficits in visual motor integration (mean 57.08, SD 9.26)."

Quantifies the visual-motor integration deficit that occupational therapy addresses.

Ophthalmologic Surveillance

Category: Monitoring Action: vision assessment Ontology label: Vision Assessment NCIT:C156778

Baseline ophthalmologic evaluation at diagnosis with periodic review for changes in visual acuity and strabismus, with refractive correction and strabismus treatment per ophthalmologist when abnormalities are found. Registry data showing 72-76% visual involvement make this a higher-yield surveillance target than earlier clinic-based reports implied.

Show evidence (2 references)

PMID:40228085 SUPPORT Human Clinical

"assess for changes in visual acuity and strabismus per treating ophthalmologist"

GeneReviews surveillance recommendation for ocular manifestations.

PMID:40389839 SUPPORT Human Clinical

"The GenIDA series identified a higher prevalence of visual impairment (76%) and highlighted under-recognized musculoskeletal issues, such as foot deformities, which had previously received little attention."

Quantifies the burden that justifies routine rather than symptom-triggered ophthalmologic review.

Audiologic and Vestibular Surveillance

Category: Monitoring Action: hearing examination Ontology label: Audiometric Test NCIT:C38036

Annual audiology evaluation, extended — on the strength of the first objective vestibulometry performed in this disorder — to comprehensive audiovestibular assessment, since vestibular weakness had never previously been looked for and was found.

Show evidence (3 references)

PMID:40228085 SUPPORT Human Clinical

"audiology evaluation annually or as needed"

GeneReviews surveillance recommendation for hearing.

PMID:38454295 SUPPORT Human Clinical

"We emphasize the importance of comprehensive audiovestibular assessment in children diagnosed with MED13L mutations for effective management of these children."

Extends the standard audiologic recommendation to include vestibular assessment.

PMID:38454295 SUPPORT Human Clinical

"Early intervention with hearing aids and vestibular rehabilitation led to a favorable outcome in terms of speech, communication, and balance."

Documents benefit from combined amplification and vestibular rehabilitation, including on the speech outcome.

Hearing Aids and Vestibular Rehabilitation

Amplification with hearing aids and vestibular rehabilitation for children found to have sensorineural hearing loss or vestibular weakness. Reported to improve speech, communication and balance — meaning an otologic intervention can move the communication outcome that otherwise dominates the disorder.

Target Phenotypes: Hearing impairment HP:0000365

Show evidence (2 references)

PMID:38454295 SUPPORT Human Clinical

"Early intervention with hearing aids and vestibular rehabilitation led to a favorable outcome in terms of speech, communication, and balance."

Documents the outcome benefit of amplification plus vestibular rehabilitation.

PMID:40228085 SUPPORT Human Clinical

"hearing aids may be helpful per otolaryngologist"

GeneReviews management guidance for the hearing arm.

Antiseizure Pharmacotherapy

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

Agent: anticonvulsant agent NCIT:C264

Standard anti-seizure medication selected by seizure type for the minority with epilepsy. There are no MED13L-specific trial data and no evidence for a gene-specific drug choice.

Target Phenotypes: Seizure HP:0001250

Show evidence (1 reference)

PMID:40228085 SUPPORT Human Clinical

"Standardized treatment for developmental, intellectual, and behavioral issues and seizures"

GeneReviews specifies standardized (non-gene-specific) seizure treatment, which is the claim being made here.

Feeding Therapy and Nutritional Support

Action: Supportive Care NCIT:C15747

Feeding therapy with gastrostomy placement as needed, driven by the hypotonia, aspiration risk and the gastrointestinal problems that affect over half of individuals.

Show evidence (2 references)

PMID:40228085 SUPPORT Human Clinical

"feeding therapy; gastrostomy tube placement as needed; social work and family support"

GeneReviews treatment guidance for the feeding/nutritional arm.

PMID:40228085 SUPPORT Human Clinical

"monitor for evidence of aspiration and/or respiratory insufficiency, nutritional status, safety of oral intake, and family needs at each visit"

Establishes the surveillance rationale for ongoing feeding support.

Genetic Counseling

Category: Counseling / Informational Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Counselling at diagnosis and pre-conception. The key point is that a de novo finding does not reduce recurrence risk to the population baseline: parental gonadal/germinal mosaicism is documented, so prenatal or preimplantation genetic testing should be offered once the familial variant is known.

Show evidence (2 references)

PMID:40228085 SUPPORT Human Clinical

"Once the MED13L pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible."

Establishes the reproductive-testing options counselling should cover.

PMID:41403746 SUPPORT Human Clinical

"The study underscores the value of genetic testing and counseling, exemplified by the successful prenatal diagnosis and birth of an unaffected child in the second family."

Worked example of prenatal diagnosis changing a reproductive outcome in a MED13L family.

🔀

Differential Diagnoses

6

Conditions with similar clinical presentations that must be differentiated from MED13L Syndrome:

MED13-related intellectual developmental disorder (MRD61) MONDO:0032485

Overlapping Features The paralogous CKM-hinge disorder. Both are autosomal dominant CDK8-kinase-module disorders with intellectual disability and prominent speech impairment, and the two proteins occupy the same structural position in the module.

Distinguishing Features

MED13L has a recognisable facial gestalt and a far larger reported cohort (~100 vs ~26 cases).
MED13 carries ophthalmologic features not reported in MED13L, notably Duane anomaly.
MED13L syndrome is defined by a motor speech disorder; MED13 is described as producing a language-dominant phenotype.

Show evidence (1 reference)

PMID:29740699 SUPPORT Human Clinical

"Mutations in several other genes encoding subunits of Mediator have been previously shown to associate with DD/ID, including MED13L, a paralog of MED13."

Establishes MED13 and MED13L as paralogous disease genes within the same module, the basis for their mutual differential-diagnosis relationship.

MED12-related intellectual disability syndrome Not Yet Curated MONDO:0100000

Overlapping Features The X-linked member of the CDK8 kinase module allelic series (FG/Opitz-Kaveggia, Lujan-Fryns, Ohdo-Maat-Kievit-Brunner), sharing intellectual disability and hypotonia with MED13L syndrome.

Distinguishing Features

X-linked inheritance with predominantly affected males, versus autosomal dominant de novo events in MED13L.
Distinct facial and behavioural profiles across the MED12 allelic series.

Show evidence (1 reference)

PMID:30905399 SUPPORT Human Clinical

"Mutations in MED12, MED13, and MED13L were previously identified in syndromic developmental disorders with overlapping phenotypes."

States the phenotypic overlap between the MED12, MED13 and MED13L disorders that makes MED12-related intellectual disability a differential for MED13L syndrome.

Chromosome 1p36 deletion syndrome Not Yet Curated MONDO:0011929

Overlapping Features A recurrent microdeletion syndrome that overlaps MED13L syndrome in facial gestalt, particularly straight/horizontal eyebrows, deep-set eyes and midface hypoplasia, and in the combination of intellectual disability with congenital heart disease.

Distinguishing Features

1p36 deletion is detectable on chromosomal microarray, whereas most MED13L variants are not.
Overlapping facial features prompted the explicit recommendation to consider MED13L when 1p36 testing is negative.

Show evidence (1 reference)

PMID:25712080 SUPPORT Human Clinical

"Haploinsufficiency for MED13L should be considered in the differential diagnosis of the 1p36 microdeletion syndrome, due to overlapping dysmorphic facial features in some patients."

Direct recommendation to place MED13L in the 1p36 differential on facial-gestalt grounds.

Kleefstra syndrome MONDO:0012455

Overlapping Features EHMT1-related syndromic intellectual disability whose facial gestalt has been explicitly noted to resemble that of individual MED13L patients.

Distinguishing Features

Resolved by identifying an EHMT1 variant or 9q34.3 deletion on molecular testing.

Show evidence (1 reference)

PMID:28645799 SUPPORT Human Clinical

"The first patient indicates some facial resemblance to Kleefstra syndrome as a novel differential diagnosis, and the second patient shows, for the first time, recurrence of a MED13L missense mutation (p.(Asp860Gly))."

Introduces Kleefstra syndrome as a MED13L differential on the basis of facial resemblance.

22q11.2 deletion syndrome MONDO:0018923

Overlapping Features Shares the combination of intellectual disability with conotruncal congenital heart disease, and the more common MED13L facial gestalt has been noted to resemble it.

Distinguishing Features

22q11.2 deletion adds palatal anomalies, hypocalcaemia and immune deficiency, none of which are MED13L features.
The deletion is detectable on chromosomal microarray.

Show evidence (1 reference)

PMID:28645799 SUPPORT Human Clinical

"The latter are especially important in the differential diagnosis of 1p36 deletion and Kleefstra syndromes, while the more common facial gestalt shows some resemblance to 22q11.2 deletion syndrome."

Places 22q11.2 deletion syndrome in the MED13L facial differential alongside 1p36 and Kleefstra.

Cornelia de Lange syndrome MONDO:0016033

Overlapping Features MED13L variants have been recovered from cohorts clinically suspected of Cornelia de Lange syndrome but negative for cohesin-pathway genes, so MED13L belongs in the CdLS-like differential.

Distinguishing Features

Classic CdLS features (synophrys, limb reduction defects, prenatal growth restriction) are not core MED13L features.
Resolved by identifying NIPBL or another cohesin-pathway variant.

Show evidence (1 reference)

PMID:31337854 SUPPORT Human Clinical

"Systematic clinical evaluation of all patients using a recently proposed clinical scoring system showed that ZMYND11, MED13L, and PHIP abnormality may cause CdLS or CdLS-like."

Demonstrates MED13L variants being ascertained through a CdLS-suspected cohort, establishing the differential empirically.

📊

Related Datasets

1

Cardiomyocyte-specific Deletion of Med13 and Med13L Results in Dysregulated Gene Expression and Lethal Heart Failure geo:GSE298801

Bulk RNA-seq from adult murine cardiomyocytes after inducible knockout of Med13 and Med13L. Included on the MED13L entry because it is the primary evidence for MED13/MED13L functional redundancy, which underpins the paralog-compensation hypothesis for MED13L's variable cardiac penetrance.

mouse BULK RNA SEQ n=8

cardiomyocyte

Conditions: Med13/Med13L cardiomyocyte-specific double knockout wild-type control

Findings

Med13 and Med13L are functionally redundant in adult cardiomyocytes

Combined knockout causes lethal heart failure with fibrotic and calcium-handling gene dysregulation

PMID:40989238

Show evidence (1 reference)

PMID:40989238 SUPPORT Model Organism

"Med13/13L knockout resulted in decreased cardiac function leading to lethal heart failure in a median timeframe of 6 weeks from the start of tamoxifen."

Establishes the redundancy result that this dataset supports and that the paralog-compensation hypothesis rests on.

🔬

Clinical Trials

1

NCT01238250 NOT_APPLICABLE RECRUITING

Simons Searchlight is a prospective observational online registry enrolling individuals with rare genetic neurodevelopmental variants, including MED13L. It provides natural-history, developmental-milestone and behavioural data. There are no interventional trials in MED13L syndrome.

Target Phenotypes: Global developmental delay HP:0001263

🧫

Experimental Models

3

MED13L patient-derived skin fibroblasts PRIMARY_CELL_CULTURE

Fibroblasts from an individual carrying the MED13L S1497F/fs allele, used as the readout system for cyclin C subcellular localisation, mitochondrial morphology, respiration, mtDNA copy number and oxidative-stress sensitivity. The system supports pharmacological rescue and is therefore the closest thing MED13L syndrome currently has to a drug-screening assay.

Organism

human NCBITaxon:9606

Publication

PMID:35198885

Findings

Unstressed patient fibroblasts show cytoplasmic cyclin C, mitochondrial fragmentation and a six-fold respiration deficit

Blocking cyclin C mitochondrial localisation partially restores organelle function

Show evidence (1 reference)

PMID:35198885 SUPPORT In Vitro

"Unstressed MED13L S1497 F/fs patient fibroblasts exhibited aberrant cytoplasmic cyclin C localization, mitochondrial fragmentation, and a 6-fold reduction in respiration."

Defines the assay readouts available in this model system.

In utero electroporation of mouse cortex with MED13L variants OTHER

In utero electroporation of embryonic mouse cortex with wild-type or disease-associated MED13L missense constructs, plus knockdown-with-rescue, giving a variant-level functional readout on subcellular localisation, dendritic growth, spine morphology, migration and axon elongation. This is the closest available assay for classifying MED13L variants of uncertain significance.

Organism

mouse NCBITaxon:10090

Publication

PMID:36798993

Findings

Missense variants differ in nuclear versus cytoplasmic distribution

MED13L knockdown abrogates dendritic growth and is rescued by RNAi-resistant wild-type but not by variant constructs

Show evidence (1 reference)

PMID:36798993 SUPPORT Model Organism

"Furthermore, we show that mMED13L-knockdown abrogated dendritic growth in vivo, and this effect was significantly rescued by co-electroporation of an RNAi-resistant mMED13L, but weakly by the p.T2162M variant, and not at all by the p.S2163L variant."

Demonstrates the rescue-based design that converts the assay into a variant classifier.

iPSC-derived neural progenitor CRISPRi Perturb-seq platform IPSC_DERIVED_MODEL

A scalable Perturb-seq platform (CRISPRi perturbation plus single-cell RNA-seq) in human WTC11 induced pluripotent stem cells carrying dCas9-KRAB, differentiated to neural progenitor cells, applied to 60 high-confidence autism risk genes and read out with structural topic modelling to assess cell fate and differentiation stage simultaneously. MED13L is one of only four genes whose effect replicated in an independent dataset. This is the closest thing MED13L currently has to a human iPSC-derived neuronal model system, and it addresses the gap left by the cyclin-C work, which is fibroblast-only — but note it assays CRISPRi repression of the gene rather than patient variants, so it models dosage loss, not allele-specific effects.

Organism

human NCBITaxon:9606

Cell source

Human WTC11 iPSC line with dCas9-KRAB knocked into the CLYBL safe-harbour locus (Allen Institute), differentiated to neural progenitor cells

Culture

Monolayer forebrain-directed NPC differentiation (dual-SMAD inhibition), transduced with pooled sgRNA lentivirus in two independently differentiated biological replicates and read out by CROP-seq-style sgRNA-enriched single-cell RNA-seq

Publication

PMID:39386704

Findings

MED13L repression alters neural cell fate and differentiation stage, replicated in an independent dataset

Preprint (bioRxiv) with a PubMed record. Recorded because it is the only human neural model system currently reporting a replicated MED13L effect; treat the finding as provisional pending peer review.

Show evidence (2 references)

PMID:39386704 SUPPORT In Vitro

"Repression of ASD risk genes led to changes in topic proportions and effects of four genes (DEAF1, KMT2A, MED13L, and MYT1L) were validated in an independent dataset."

MED13L is one of four genes whose neural-development effect replicated independently in this platform.

PMID:39386704 SUPPORT In Vitro

"To identity convergent pathways in NDD genes, we optimized Perturb-seq, a method combining CRISPR perturbation with single-cell RNA sequencing (scRNA-seq), and applied structural topic modeling (STM) to simultaneously assess impact on cell fate and developmental stage."

Describes the platform and the readouts available in this model system.

{ }

Source YAML

click to show

name: MED13L Syndrome
creation_date: '2026-07-30T00:00:00Z'
category: Mendelian
synonyms:
- MED13L haploinsufficiency syndrome
- MED13L-related intellectual disability
- MRFACD
- Mental retardation and distinctive facial features with or without cardiac defects
- Asadollahi-Rauch syndrome
- Impaired intellectual development and distinctive facial features with or without
  cardiac defects
description: >
  MED13L syndrome (MRFACD) is an autosomal dominant neurodevelopmental disorder
  caused by heterozygous, predominantly de novo variants in MED13L, the paralog of
  MED13 within the CDK8 kinase module (CKM) of the Mediator transcriptional
  coactivator complex. The core phenotype is moderate-to-severe intellectual
  disability with disproportionately severe speech impairment, hypotonia, motor
  delay, and a recognizable facial gestalt (depressed/broad nasal bridge, bulbous
  nasal tip, hypotonic open mouth, upslanted palpebral fissures). Congenital heart
  defects — historically considered a defining feature because the gene was first
  implicated through isolated dextro-transposition of the great arteries — are now
  recognised as a minority, variably penetrant finding. Deep phenotyping shows the
  speech phenotype is specifically a motor speech disorder (apraxia and/or
  dysarthria) rather than a nonspecific language delay. Loss-of-function alleles
  (whole-gene and intragenic deletions, frameshift, nonsense, canonical splice)
  act through haploinsufficiency; missense variants cluster in two hotspots
  (exons 15-17 and 25-31) and are associated with a more severe, epilepsy-enriched
  presentation, with at least one recurrent allele (p.Pro869Ser) behaving unlike
  simple dosage loss in functional assays. MED13L is one of the more frequently
  implicated genes in syndromic intellectual disability, with roughly 100 cases
  described in the literature.
disease_term:
  preferred_term: MED13L syndrome
  term:
    id: MONDO:0014773
    label: cardiac anomalies - developmental delay - facial dysmorphism syndrome
parents:
- Autosomal dominant syndromic intellectual disability
- Neurodevelopmental disorder
- CDK8-kinase module-associated disorder
notes: >-
  This entry is the MED13L-specific counterpart of `MED13_Syndrome`. MED13L is also
  represented as a molecular subtype of the `Mediator Complex Neurodevelopmental
  Disorder` grouping entry; that entry remains the cross-subtype view, while this
  entry carries the MED13L-specific mechanism graph, variant-class stratification,
  and management detail.
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:40228085
      reference_title: "MED13L Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The diagnosis of MED13L syndrome is established in a proband with a
        heterozygous pathogenic variant in MED13L identified by molecular genetic
        testing.
      explanation: Supports classification as a molecularly defined hereditary disorder.
  - classification_value: NEUROLOGIC
    evidence:
    - reference: PMID:40228085
      reference_title: "MED13L Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        MED13L syndrome is characterized by mild-to-profound developmental delay,
        intellectual disability, and hypotonia.
      explanation: Supports classification as a neurodevelopmental / neurologic disorder.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: BELOW_1_IN_1000000
  notes: >-
    Approximately 100 cases had been reported in the literature as of the early
    2020s, and larger aggregations (102 published cases plus a 41-patient GenIDA
    family-reported series) have since been assembled. No population-based
    prevalence estimate exists. Despite the ultra-rare case count, MED13L is
    repeatedly described as one of the more frequent single-gene causes of
    syndromic intellectual disability in unbiased exome cohorts, so the true
    prevalence is likely higher than the published case count implies.
  evidence:
  - reference: PMID:34654706
    reference_title: "MED13L-related intellectual disability due to paternal germinal mosaicism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The MED13L-related intellectual disability or MRFACD syndrome (Mental
      retardation and distinctive facial features with or without cardiac defects;
      MIM # 616789) is one of the most common forms of syndromic intellectual
      disability with about a hundred cases reported so far.
    explanation: >-
      Establishes both the cumulative published case count (~100) and the
      characterisation of MED13L as one of the more common syndromic ID entities.
  - reference: PMID:40389839
    reference_title: "Contribution of families using the GenIDA database to the description of MED13L syndrome and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This study focused on MED13L syndrome, analyzing data from 41 patients in the
      GenIDA database and comparing it with 102 cases from the scientific literature
      and 6 new descriptions of patients from our medical center.
    explanation: Documents the size of the assembled MED13L literature and registry cohorts.
- population: Unbiased developmental-disorder exome cohorts
  measure_type: UNKNOWN
  prevalence_class: UNKNOWN
  notes: >-
    Ascertainment note rather than a rate: MED13L was identified as one of the most
    commonly mutated intellectual-disability genes in the Deciphering Developmental
    Disorders Study, which is the main argument that clinic-based case counts
    understate the true frequency.
  evidence:
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Despite the fact that MED13L was found to be one of the most common ID genes
      in the Deciphering Developmental Disorders Study
    explanation: >-
      Supports the claim that MED13L is a high-yield gene in unbiased developmental
      disorder cohorts despite a modest published case count.
mechanistic_hypotheses:
- hypothesis_group_id: med13l_haploinsufficiency
  hypothesis_label: MED13L haploinsufficiency (dosage loss) as the primary disease mechanism
  status: CANONICAL
  description: >
    Heterozygous deletion, frameshift, nonsense, and canonical-splice variants
    reduce functional MED13L dosage below a developmental threshold, reducing the
    pool of intact CKM available to dock on core Mediator and dysregulating
    CKM-gated RNA polymerase II transcription during development. Supported by the
    predominance of loss-of-function alleles among patients, a recognisable shared
    phenotype across deletion and truncating cases, and recapitulation in
    heterozygous Med13l mice with embryonic/neonatal lethality of the homozygous
    null.
  applies_to_subtypes:
  - Loss-of-function (deletion / truncating / splice)
  evidence:
  - reference: PMID:23403903
    reference_title: "Dosage changes of MED13L further delineate its role in congenital heart defects and intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Using high resolution molecular karyotyping, we identified two intragenic de
      novo frameshift deletions, likely resulting in haploinsufficiency, in two
      patients with a similar phenotype of hypotonia, moderate ID, conotruncal heart
      defect and facial anomalies.
    explanation: >-
      De novo intragenic dosage-loss alleles produce a shared recognisable phenotype,
      the founding argument for haploinsufficiency.
  - reference: PMID:24781760
    reference_title: "Further confirmation of the MED13L haploinsufficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both patients show features of the MED13L haploinsufficiency syndrome, except
      for the heart defects, thus further confirming the existence of the MED13L
      haploinsufficiency syndrome.
    explanation: >-
      Independent splice and multi-exon deletion alleles reproduce the syndrome,
      confirming dosage loss as the mechanism.
  - reference: PMID:40775066
    reference_title: "Regulation of cortical neurogenesis by MED13L via transcriptional priming and its implications for MED13L syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      While homozygous Med13l knockout exhibit neonatal lethality accompanied by
      reduced brain volume and cortical thickness, heterozygous mice are viable and
      display hallmarks of MED13L syndrome, including impaired learning and memory,
      reduced motor coordination, and heightened anxiety.
    explanation: >-
      Mouse dosage series shows the heterozygous state is sufficient to produce the
      syndrome phenotype while complete loss is lethal.
  - reference: PMID:29511999
    reference_title: "MED13L-related intellectual disability: involvement of missense variants and delineation of the phenotype."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We found that patients carrying missense mutations had more frequently epilepsy
      and showed a more severe phenotype.
    explanation: >-
      Qualifies the pure-dosage model: missense carriers are systematically more
      severely affected than truncating carriers, which simple haploinsufficiency
      does not predict.
- hypothesis_group_id: med13l_missense_non_haploinsufficient
  hypothesis_label: A subset of recurrent missense variants act through a mechanism other than simple dosage loss
  status: EMERGING
  description: >
    Most pathogenic MED13L missense variants destabilise the protein and mislocalise
    it to the cytoplasm, behaving as loss-of-function. At least one recurrent
    exon-15 allele, p.Pro869Ser, retains comparatively stable expression and partial
    nuclear localisation while associating with a more severe, epilepsy-enriched
    phenotype than truncating alleles — a pattern more consistent with a
    dominant-negative or neomorphic effect on the assembled CKM than with
    haploinsufficiency. This remains an inference from cell-based localisation and
    stability assays plus genotype-phenotype correlation; no direct demonstration of
    dominant-negative action on Mediator function has been published.
  applies_to_subtypes:
  - Missense (exon 15-17 and 25-31 hotspots)
  evidence:
  - reference: PMID:40500968
    reference_title: "MED13L pathogenic missense variants impair protein stability and interaction, underlying diverse clinical outcomes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We identified significant reductions in protein stability across these
      variants, with some exhibiting aberrant cytoplasmic localization, suggesting
      disruptions in structural integrity and function.
    explanation: >-
      Functional characterisation of five recurrent missense alleles showing
      heterogeneous, not uniformly loss-of-function, behaviour.
  - reference: PMID:40500968
    reference_title: "MED13L pathogenic missense variants impair protein stability and interaction, underlying diverse clinical outcomes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In particular, exon 15 variants (p.Pro866Leu and p.Pro869Ser) correlated with
      severe phenotypes, including epilepsy and severe motor impairment, whereas
      p.Gly1899Arg and p.Thr2162Met were associated with milder manifestations.
    explanation: >-
      Ties variant position to clinical severity, the genotype-phenotype anchor for
      the non-haploinsufficiency hypothesis.
  - reference: PMID:32646507
    reference_title: "Report of a de novo c.2605C > T (p.Pro869Ser) change in the MED13L gene and review of the literature for MED13L-related intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our case further demonstrates that Pro869Ser is a hotspot mutation of the
      MED13L gene.
    explanation: >-
      Establishes p.Pro869Ser as a recurrent allele, a prerequisite for the
      allele-specific mechanism claim.
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: PARTIAL
    evidence_source: COMPUTATIONAL
    snippet: >-
      Notably, our in silico modelling predicted this missense mutation to decrease
      the stability of an alpha-helix and thereby affecting the MED13L secondary
      structure, while the majority of published missense mutations remain variants
      of uncertain significance.
    explanation: >-
      Counterweight: structural prediction for at least some missense alleles points
      back to destabilisation (loss-of-function), and most missense variants remain
      VUS.
  notes: >-
    Treat the severity stratification as preliminary. The same study that reports
    p.Pro869Ser as stable and nuclear reports four other missense alleles behaving as
    classic loss-of-function, so this hypothesis applies to specific alleles rather
    than to missense variants as a class.
- hypothesis_group_id: med13l_isolated_dtga
  hypothesis_label: MED13L missense variants as a cause of isolated dextro-transposition of the great arteries
  status: DEPRECATED
  description: >
    The gene entered the literature in 2003-2004 as a candidate for isolated
    d-transposition of the great arteries, and that framing persisted for a decade.
    Subsequent syndromic cohorts redefined the entity as a neurodevelopmental
    haploinsufficiency disorder in which congenital heart defects are a minority,
    variably penetrant feature, and the original missense alleles are now largely
    classified as variants of uncertain significance. The isolated-d-TGA association
    is retained here as the historical entry point to the gene, not as a supported
    current mechanism.
  applies_to_subtypes:
  - Isolated d-transposition of the great arteries
  evidence:
  - reference: PMID:15175163
    reference_title: "A set of consensus mammalian mediator subunits identified by multidimensional protein identification technology."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In addition, we identify as Mediator-associated proteins the CDK8-like
      cyclin-dependent kinase CDK11 and the TRAP240-like KIAA1025 protein (MED13L),
      which is mutated in patients with the congenital heart defect transposition of
      the great arteries (TGA).
    explanation: >-
      Records the original framing of MED13L (then KIAA1025/TRAP240-like) as a
      transposition-of-the-great-arteries gene.
  - reference: PMID:25758992
    reference_title: "Redefining the MED13L syndrome."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we report eight patients with predominantly novel MED13L variants who
      lack such complex congenital heart malformations.
    explanation: >-
      Directly refutes obligate cardiac involvement and reframes MED13L as a
      syndromic neurodevelopmental disorder.
  - reference: PMID:23403903
    reference_title: "Dosage changes of MED13L further delineate its role in congenital heart defects and intellectual disability."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings show that MED13L haploinsufficiency in contrast to the previously
      observed missense mutations cause a distinct syndromic phenotype.
    explanation: >-
      Separates the syndromic dosage-loss entity from the earlier isolated-d-TGA
      missense reports.
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Subsequent reports of 22 further patients diagnosed by genome-wide testing
      further delineated the syndrome with expansion of the phenotypic spectrum and
      showed reduced penetrance for congenital heart defects.
    explanation: >-
      Documents reduced cardiac penetrance, undermining a conotruncal-specific gene
      model.
- hypothesis_group_id: med13l_med13_paralog_compensation
  hypothesis_label: MED13/MED13L paralog compensation modulates expressivity
  status: EMERGING
  description: >
    MED13 and MED13L are mutually exclusive occupants of the same structural position
    in the CKM and are partially redundant: combined cardiomyocyte deletion of both is
    lethal where either single deletion is tolerated. Incomplete, tissue-dependent
    compensation by the intact paralog is a candidate explanation for the variable
    expressivity of MED13L syndrome — in particular for why cardiac involvement is
    penetrant in only a minority — and, if druggable, a candidate therapeutic axis.
    No direct human evidence links paralog expression level to phenotype severity.
  evidence:
  - reference: PMID:40989238
    reference_title: "Med13 and Med13L: Critical redundant players in basal cardiac function and gene expression."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Med13 and Med13L are mutually exclusive paralogs within the kinase submodule of
      the Mediator complex that have been shown to have partially redundant functions
      in embryonic development and transcription, but their combined roles have not
      been investigated in the adult heart.
    explanation: >-
      States the mutual exclusivity and partial redundancy that the compensation
      hypothesis rests on.
  - reference: PMID:40989238
    reference_title: "Med13 and Med13L: Critical redundant players in basal cardiac function and gene expression."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Med13/13L knockout resulted in decreased cardiac function leading to lethal
      heart failure in a median timeframe of 6 weeks from the start of tamoxifen.
    explanation: >-
      Combined loss is lethal where single-paralog loss is tolerated, the functional
      signature of redundancy.
  - reference: PMID:40919805
    reference_title: "Heterozygous Med13l mice recapitulate a developmental growth delay and craniofacial anomalies seen in MED13L syndrome."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Med13l HET mice recapitulate MED13L syndrome phenotypes including a
      developmental growth delay and craniofacial anomalies.
    explanation: >-
      Heterozygous Med13l loss produces growth and craniofacial phenotypes but not a
      cardiac functional defect, consistent with — though not proof of — cardiac
      compensation by Med13.
  notes: >-
    The available redundancy evidence is cardiac and murine. Whether the same buffering
    operates in developing human cortex, where the dominant MED13L phenotype arises, is
    untested.
- hypothesis_group_id: med13l_cyclin_c_mitochondrial
  hypothesis_label: Cyclin C nuclear release and mitochondrial fragmentation as a secondary disease mechanism
  status: EMERGING
  description: >
    MED13L tethers the cyclin C-CDK8 kinase module to Mediator; cyclin C also has a
    CKM-independent cytoplasmic role driving stress-induced mitochondrial fission and
    regulated cell death. In patient fibroblasts carrying a MED13L frameshift allele,
    cyclin C is aberrantly cytoplasmic even without stress, with mitochondrial
    fragmentation and markedly reduced respiration; blocking cyclin C mitochondrial
    localisation partially rescues organelle function. If this operates in neurons it
    would add a bioenergetic component to the intellectual disability phenotype and
    would be pharmacologically approachable independently of transcription. Currently
    demonstrated only in fibroblasts from a single patient allele.
  applies_to_subtypes:
  - Loss-of-function (deletion / truncating / splice)
  evidence:
  - reference: PMID:35198885
    reference_title: "Aberrant cyclin C nuclear release induces mitochondrial fragmentation and dysfunction in MED13L syndrome fibroblasts."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Unstressed MED13L S1497 F/fs patient fibroblasts exhibited aberrant cytoplasmic
      cyclin C localization, mitochondrial fragmentation, and a 6-fold reduction in
      respiration.
    explanation: >-
      Primary observation linking a MED13L patient allele to cyclin C mislocalisation
      and a measurable bioenergetic deficit.
  - reference: PMID:35198885
    reference_title: "Aberrant cyclin C nuclear release induces mitochondrial fragmentation and dysfunction in MED13L syndrome fibroblasts."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Pharmacological or genetic approaches preventing cyclin C-mitochondrial
      localization corrected the fragmented mitochondrial phenotype and partially
      restored organelle function.
    explanation: >-
      Rescue experiment establishes cyclin C mislocalisation as causal for the
      mitochondrial phenotype rather than a bystander effect, and defines the
      candidate therapeutic handle.
  notes: >-
    Evidence is from one patient fibroblast line carrying a single frameshift allele.
    Whether the same cyclin C release occurs in MED13L-haploinsufficient neurons, and
    whether it contributes measurably to the neurodevelopmental phenotype, is untested.
pathophysiology:
- name: CKM hinge anchoring by MED13L
  biological_scale: MOLECULAR
  description: >
    MED13L, like its paralog MED13, is the physical hinge of the Mediator CDK8 kinase
    module (CKM, comprising MED13/MED13L, MED12/MED12L, CDK8/CDK19 and cyclin C). The
    subunit adopts an Argonaute-like bi-lobal fold, and a large intrinsically
    disordered region within it forms the principal CKM contact with core Mediator.
    That same disordered region sterically occludes the RNA polymerase II and MED26
    binding surfaces, so MED13L abundance and structural integrity gate reversible
    CKM-core docking and thereby the switch between Mediator's repressive and
    permissive states.
  genes:
  - preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  - preferred_term: MED13
    term:
      id: hgnc:22474
      label: MED13
  biological_processes:
  - preferred_term: regulation of transcription by RNA polymerase II
    term:
      id: GO:0006357
      label: regulation of transcription by RNA polymerase II
  molecular_functions:
  - preferred_term: transcription coregulator activity
    term:
      id: GO:0003712
      label: transcription coregulator activity
  evidence:
  - reference: PMID:39321804
    reference_title: "Structural basis of the human transcriptional Mediator regulated by its dissociable kinase module."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The CKM binds to multiple regions on cMED through both MED12 and MED13,
      including a large intrinsically disordered region (IDR) in the latter.
    explanation: >-
      Cryo-EM of the complete human Mediator identifies the MED13 intrinsically
      disordered region as the CKM-core interface.
  - reference: PMID:39321804
    reference_title: "Structural basis of the human transcriptional Mediator regulated by its dissociable kinase module."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Notably, the MED13 IDR obstructs the recruitment of RNA Pol II/MED26 onto cMED
      by direct occlusion of their respective binding sites, leading to functional
      repression of cMED-dependent transcription.
    explanation: >-
      Defines the structural mechanism by which the hinge subunit represses
      Mediator-dependent transcription, the function lost on MED13L dosage reduction.
  - reference: PMID:33523904
    reference_title: "Structure and noncanonical Cdk8 activation mechanism within an Argonaute-containing Mediator kinase module."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Unexpectedly, Med13 has a characteristic Argonaute-like bi-lobal architecture.
    explanation: Establishes the structural fold of the MED13/MED13L hinge subunit.
  - reference: PMID:33523904
    reference_title: "Structure and noncanonical Cdk8 activation mechanism within an Argonaute-containing Mediator kinase module."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Numerous pathogenic mutations causative for neurodevelopmental disorders and
      cancer congregate in CKM subunits.
    explanation: >-
      Connects the CKM structure to the disease burden carried by its subunits,
      including MED13L.
  - reference: PMID:35198885
    reference_title: "Aberrant cyclin C nuclear release induces mitochondrial fragmentation and dysfunction in MED13L syndrome fibroblasts."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      MED13L controls transcription by tethering the cyclin C-Cdk8 kinase module (CKM)
      to the Mediator complex.
    explanation: States the MED13L-specific tethering role directly.
  downstream:
  - target: MED13L haploinsufficiency
    description: >-
      Reduced MED13L protein reduces the pool of intact CKM competent to dock on core
      Mediator.
  - target: SCF-FBW7 control of MED13L abundance
    description: >-
      Because the hinge is the rate-limiting CKM-core contact, ubiquitin-mediated
      turnover of MED13L sets CKM-core stoichiometry.
- name: SCF-FBW7 control of MED13L abundance
  biological_scale: MOLECULAR
  description: >
    The SCF-Fbw7 ubiquitin ligase binds CDK8-Mediator and targets both MED13 and
    MED13L for proteasomal degradation. This is the only characterised E3-ligase
    control of MED13L abundance, and because MED13/MED13L physically link the CKM to
    Mediator, Fbw7-dependent turnover sets the kinetics of CKM dissociation from the
    core complex. Loss of Fbw7 increases CKM-Mediator association, the reciprocal of
    the dosage reduction seen in MED13L syndrome.
  genes:
  - preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  - preferred_term: FBXW7
    term:
      id: hgnc:16712
      label: FBXW7
  biological_processes:
  - preferred_term: protein ubiquitination
    term:
      id: GO:0016567
      label: protein ubiquitination
  - preferred_term: proteasome-mediated ubiquitin-dependent protein catabolic process
    term:
      id: GO:0043161
      label: proteasome-mediated ubiquitin-dependent protein catabolic process
  evidence:
  - reference: PMID:23322298
    reference_title: "The SCF-Fbw7 ubiquitin ligase degrades MED13 and MED13L and regulates CDK8 module association with Mediator."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We show that Fbw7, a tumor suppressor and ubiquitin ligase, binds to
      CDK8-Mediator and targets MED13/13L for degradation.
    explanation: >-
      Establishes SCF-Fbw7 as the E3 ligase controlling MED13L protein abundance.
  - reference: PMID:23322298
    reference_title: "The SCF-Fbw7 ubiquitin ligase degrades MED13 and MED13L and regulates CDK8 module association with Mediator."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      MED13/13L physically link the CDK8 module to Mediator, and Fbw7 loss increases
      CDK8 module-Mediator association.
    explanation: >-
      Shows MED13L abundance is directly coupled to CKM-core occupancy, the dosage
      axis perturbed in MED13L syndrome.
  downstream:
  - target: MED13L haploinsufficiency
    description: >-
      Turnover of the remaining wild-type allele's product further lowers functional
      MED13L in a haploinsufficient cell, making degradation kinetics a candidate
      modifier and therapeutic target.
- name: MED13L haploinsufficiency
  biological_scale: MOLECULAR
  description: >
    Heterozygous loss-of-function alleles — whole-gene and intragenic deletions,
    frameshift, nonsense, and canonical splice variants — halve functional MED13L
    dosage. The reduced pool of intact CKM dysregulates RNA polymerase II-dependent
    transcriptional programs during development. Dosage loss is sufficient to produce
    the syndrome: heterozygous Med13l mice reproduce growth, craniofacial, learning
    and motor phenotypes, while homozygous loss is embryonic/neonatal lethal.
  genes:
  - preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  biological_processes:
  - preferred_term: transcription by RNA polymerase II
    term:
      id: GO:0006366
      label: transcription by RNA polymerase II
    modifier: DECREASED
  - preferred_term: regulation of transcription by RNA polymerase II
    term:
      id: GO:0006357
      label: regulation of transcription by RNA polymerase II
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:23403903
    reference_title: "Dosage changes of MED13L further delineate its role in congenital heart defects and intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we describe for the first time, three patients with copy number changes
      affecting MED13L and delineate a recognizable MED13L haploinsufficiency
      syndrome.
    explanation: Founding delineation of the dosage-loss syndrome.
  - reference: PMID:37512036
    reference_title: "Molecular and Functional Characterisation of a Novel Intragenic 12q24.21 Deletion Resulting in MED13L Haploinsufficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Based on these findings, heterozygous intragenic 12q24.21 deletion in the
      affected individual resulted in MED13L haploinsufficiency due to the premature
      termination of protein translation, therefore leading to MED13L
      haploinsufficiency syndrome.
    explanation: >-
      Traces an intragenic deletion through premature translation termination to
      haploinsufficiency at the protein level.
  - reference: PMID:40775066
    reference_title: "Regulation of cortical neurogenesis by MED13L via transcriptional priming and its implications for MED13L syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      While homozygous Med13l knockout exhibit neonatal lethality accompanied by
      reduced brain volume and cortical thickness, heterozygous mice are viable and
      display hallmarks of MED13L syndrome, including impaired learning and memory,
      reduced motor coordination, and heightened anxiety.
    explanation: >-
      Establishes the mouse dosage series and shows heterozygous loss is sufficient
      for the syndrome phenotype.
  downstream:
  - target: Neurodevelopmental transcriptional dysregulation
    description: >-
      Reduced CKM-gated transcriptional control perturbs the neurodevelopmental gene
      programs that underlie intellectual disability, speech impairment and hypotonia.
  - target: Neural-crest and cardiac outflow-tract developmental dysregulation
    description: >-
      Dosage loss perturbs neural-crest-dependent craniofacial and cardiac
      outflow-tract morphogenesis.
  - target: Cyclin C nuclear release and mitochondrial dysfunction
    description: >-
      Loss of the MED13L nuclear anchor permits cyclin C to accumulate in the
      cytoplasm, where it drives mitochondrial fission.
- name: MED13L missense destabilisation and mislocalisation
  biological_scale: MOLECULAR
  description: >
    Pathogenic missense variants cluster in two hotspots (exons 15-17 and 25-31).
    Functional characterisation shows they reduce MED13L protein stability, several
    mislocalise the protein to the cytoplasm, and 3D modelling predicts disrupted
    contact with the CDK8 kinase module. Most therefore behave as loss-of-function.
    The exon-15 alleles p.Pro866Leu and p.Pro869Ser stand out clinically, correlating
    with epilepsy and severe motor impairment, and p.Pro869Ser retains relatively
    stable, partly nuclear expression — the basis for the contested non-dosage
    mechanism captured in `med13l_missense_non_haploinsufficient`.
  genes:
  - preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: dendrite morphogenesis
    term:
      id: GO:0048813
      label: dendrite morphogenesis
    modifier: DECREASED
  evidence:
  - reference: PMID:40500968
    reference_title: "MED13L pathogenic missense variants impair protein stability and interaction, underlying diverse clinical outcomes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In this study, we investigated five pathogenic missense variants in
      MED13L-c.2597C>T p.Pro866Leu, c.2605C>T p.Pro869Ser, c.3392G>A p.Cys1131Tyr,
      c.5695G>A p.Gly1899Arg, and c.6485C>T p.Thr2162Met-associated with different
      clinical severities.
    explanation: Defines the characterised missense allele series.
  - reference: PMID:40500968
    reference_title: "MED13L pathogenic missense variants impair protein stability and interaction, underlying diverse clinical outcomes."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      3D protein modeling suggested that these missense variants may disrupt MED13L's
      interaction with the CDK8 kinase module, leading to functional deficits.
    explanation: >-
      Provides the structural rationale linking missense position to impaired CKM
      assembly.
  - reference: PMID:29511999
    reference_title: "MED13L-related intellectual disability: involvement of missense variants and delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Missense variants clustered in two mutation hot-spots, i.e., exons 15-17 and
      25-31.
    explanation: Establishes the positional clustering of pathogenic missense alleles.
  - reference: PMID:36798993
    reference_title: "MED13L and its disease-associated variants influence the dendritic development of cerebral cortical neurons in the mammalian brain."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In overexpression assays using cortical neurons from embryonic mouse cerebral
      cortices transduced by in utero electroporation-mediated gene transfer, we found
      that mouse orthologues of human MED13L-p.P866L and -p.T2162M missense variants
      accumulated in the nucleus, while the p.S2163L and p.S2177Y variants were
      diffusely distributed in the cytoplasm.
    explanation: >-
      In vivo demonstration that disease-associated missense alleles differ in
      subcellular behaviour, supporting allele-specific mechanisms.
  downstream:
  - target: Neurodevelopmental transcriptional dysregulation
    description: >-
      Destabilised or mislocalised MED13L fails to support CKM-gated neurodevelopmental
      transcription.
- name: Neurodevelopmental transcriptional dysregulation
  biological_scale: CELLULAR
  description: >
    Reduced or dysfunctional MED13L dysregulates RNA polymerase II-dependent
    neurodevelopmental gene programs. Mechanistically, MED13L acts by priming
    transcriptional activation of key cortical developmental genes (including Neurod2,
    Sox5, Auts2 and Nfib), a priming step mediated by MED13L binding to core Mediator
    that licenses the complex to associate with RNA Pol II. Loss impairs neural
    progenitor differentiation and cortical neurogenesis, and reduces dendritic
    number and length in cortical pyramidal neurons — the cellular substrate for
    intellectual disability, motor speech impairment, and hypotonia.
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: cerebral cortex development
    term:
      id: GO:0021987
      label: cerebral cortex development
    modifier: DYSREGULATED
  - preferred_term: dendrite morphogenesis
    term:
      id: GO:0048813
      label: dendrite morphogenesis
    modifier: DECREASED
  evidence:
  - reference: PMID:40775066
    reference_title: "Regulation of cortical neurogenesis by MED13L via transcriptional priming and its implications for MED13L syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Single-cell transcriptomics and immunofluorescence reveal severe cortical
      neurogenesis deficits in Med13l knockout embryos, driven by impaired neural
      progenitor differentiation.
    explanation: >-
      Locates the primary cellular defect at neural progenitor differentiation during
      corticogenesis.
  - reference: PMID:40775066
    reference_title: "Regulation of cortical neurogenesis by MED13L via transcriptional priming and its implications for MED13L syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Integrative multi-omics analyses reveal that MED13L orchestrates cortical
      neurogenesis by priming the transcriptional activation of key developmental
      genes, including Neurod2, Sox5, Auts2, and Nfib.
    explanation: >-
      Identifies the specific transcriptional-priming mechanism and its downstream
      target genes.
  - reference: PMID:36798993
    reference_title: "MED13L and its disease-associated variants influence the dendritic development of cerebral cortical neurons in the mammalian brain."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Taken together, our results demonstrate that MED13L expression is relevant to
      corticogenesis and influences the dendritic branching characteristics of
      cortical excitatory neurons.
    explanation: >-
      Establishes a MED13L requirement for dendritic development in cortical
      excitatory neurons.
  downstream:
  - target: Intellectual disability
    description: >-
      Disrupted cortical neurogenesis and dendritic development underlie the core
      cognitive impairment.
  - target: Motor speech disorder
    description: >-
      Impaired corticogenesis in motor-speech networks produces the apraxia/dysarthria
      that dominates the MED13L communication phenotype.
  - target: Global developmental delay
    description: Early milestone acquisition is impaired across domains.
  - target: Generalized hypotonia
    description: >-
      Disrupted neurodevelopmental programs contribute to the near-universal hypotonia.
  - target: Motor delay
    description: Delayed acquisition of motor milestones, with mean walking age near 2 years.
  - target: Seizure
    description: >-
      Disrupted cortical network formation predisposes to seizures, disproportionately
      in missense carriers.
  - target: Gastrointestinal problems
    description: >-
      Hypotonia and impaired oromotor and gut motor control contribute to the
      gastrointestinal and feeding difficulties affecting over half of individuals.
  - target: Abnormality of the musculoskeletal system
    description: >-
      Distal limb, digit and foot deformities arise partly secondary to the central
      hypotonia and reduced motor loading.
  - target: Scoliosis
    description: >-
      Secondary to long-standing axial hypotonia, which is why spinal assessment is
      recommended at every visit.
  - target: Autistic behavior
    description: Neurobehavioral manifestations including autistic features.
  - target: Abnormal brain morphology
    description: >-
      Disturbed corticogenesis and myelination contribute to the MRI abnormalities
      (ventriculomegaly, thin or absent corpus callosum, white matter change).
  - target: Global developmental delay
    description: >-
      Impaired cortical neurogenesis delays milestone acquisition across all domains.
  - target: Absent speech
    description: >-
      At the severe end of the motor-speech phenotype, children remain minimally verbal
      or nonverbal beyond age four.
  - target: Delayed speech and language development
    description: >-
      Near-universal expressive language delay, disproportionate to the degree of
      intellectual disability.
  - target: Ataxia
    description: >-
      Disrupted cerebellar and corticospinal output contributes to ataxia and
      coordination problems.
- name: Neural-crest and cardiac outflow-tract developmental dysregulation
  biological_scale: TISSUE
  description: >
    MED13L dosage reduction perturbs cranial neural crest cell migration and
    neural-crest-dependent morphogenesis, producing the craniofacial gestalt and the
    variable conotruncal and septal congenital heart defects seen in a minority of
    patients. Knockdown of the MED13L zebrafish orthologue med13b causes defective
    cranial neural crest migration and cartilage deformities that phenocopy the human
    craniofacial anomalies, and heterozygous Med13l mice show midfacial hypoplasia.
    The clinical impression of a neurocristopathy predates and motivated this
    mechanistic work.
  cell_types:
  - preferred_term: neural crest cell
    term:
      id: CL:0000333
      label: migratory neural crest cell
  biological_processes:
  - preferred_term: cardiac neural crest cell development involved in heart development
    term:
      id: GO:0061308
      label: cardiac neural crest cell development involved in heart development
    modifier: DYSREGULATED
  - preferred_term: heart development
    term:
      id: GO:0007507
      label: heart development
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:25137640
    reference_title: "Impaired development of neural-crest cell-derived organs and intellectual disability caused by MED13L haploinsufficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Knockdown of MED13L orthologue in zebrafish, med13b, showed early defective
      migration of cranial neural crest cells (NCCs) that contributed to cartilage
      structure deformities in the later stage, recapitulating craniofacial anomalies
      seen in human patients.
    explanation: >-
      Direct model-organism evidence that MED13L loss impairs cranial neural crest
      migration and produces the craniofacial phenotype.
  - reference: PMID:23403903
    reference_title: "Dosage changes of MED13L further delineate its role in congenital heart defects and intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The clinical features suggesting a neurocristopathy may be explained by animal
      model studies indicating involvement of the Mediator complex subunit 13 in
      neural crest induction.
    explanation: >-
      Records the clinical inference of a neurocristopathy that the zebrafish work
      subsequently supported.
  - reference: PMID:40919805
    reference_title: "Heterozygous Med13l mice recapitulate a developmental growth delay and craniofacial anomalies seen in MED13L syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We observed Med13l HET mice are smaller than wildtype (WT) littermates, and over
      60% of them exhibited one of two craniofacial anomalies: a pug snout with
      midface hypoplasia or a crooked snout.
    explanation: >-
      Quantifies the craniofacial penetrance of heterozygous Med13l loss in a mammalian
      model.
  downstream:
  - target: Abnormal heart morphology
    description: >-
      Perturbed outflow-tract morphogenesis contributes to the conotruncal and septal
      defects seen in a minority of patients.
  - target: Abnormal facial shape
    description: >-
      Disrupted cranial neural crest patterning produces the recognisable facial gestalt.
  - target: Bulbous nose
    description: Component of the neural-crest-derived facial gestalt.
  - target: Depressed nasal bridge
    description: Component of the neural-crest-derived facial gestalt.
  - target: Open mouth
    description: >-
      Hypotonic open-mouth appearance, combining the craniofacial and hypotonia arms.
  - target: Low-set ears
    description: Component of the neural-crest-derived facial gestalt.
  - target: Upslanted palpebral fissure
    description: Component of the neural-crest-derived facial gestalt.
  - target: Visual impairment
    description: >-
      Disrupted ocular and periocular development contributes to the high burden of
      visual impairment.
  - target: Strabismus
    description: >-
      Disrupted development of ocular alignment contributes to strabismus.
  - target: Hearing impairment
    description: >-
      Otic and inner-ear structural involvement, including the vestibular abnormality
      documented on imaging, arises from the same neural-crest and placodal programs.
  - target: Recurrent otitis media
    description: >-
      Craniofacial and eustachian-tube anatomy predisposes to recurrent middle-ear
      infection, which compounds the hearing and speech phenotype.
- name: Cyclin C nuclear release and mitochondrial dysfunction
  biological_scale: CELLULAR
  description: >
    Cyclin C is retained in the nucleus by the MED13L-anchored CKM. When MED13L is
    lost, cyclin C is aberrantly released to the cytoplasm even in unstressed cells,
    where its CKM-independent activity drives mitochondrial fission. Patient
    fibroblasts carrying a MED13L frameshift allele show mitochondrial fragmentation,
    a six-fold reduction in respiration, reduced mtDNA copy number and hypersensitivity
    to oxidative stress. This is a candidate secondary, bioenergetic arm of the
    disease; it has been demonstrated in fibroblasts, not neurons.
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  biological_processes:
  - preferred_term: mitochondrial fission
    term:
      id: GO:0000266
      label: mitochondrial fission
    modifier: INCREASED
  - preferred_term: response to oxidative stress
    term:
      id: GO:0006979
      label: response to oxidative stress
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:35198885
    reference_title: "Aberrant cyclin C nuclear release induces mitochondrial fragmentation and dysfunction in MED13L syndrome fibroblasts."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In addition, the fibroblasts exhibited reduced mtDNA copy number, reduction in
      mitochondrial membrane integrity, and hypersensitivity to oxidative stress.
    explanation: >-
      Characterises the mitochondrial phenotype of MED13L-mutant patient cells beyond
      morphology alone.
  - reference: PMID:35198885
    reference_title: "Aberrant cyclin C nuclear release induces mitochondrial fragmentation and dysfunction in MED13L syndrome fibroblasts."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In conclusion, this study found that mitochondrial dysfunction is an underlying
      defect in cells harboring the MED13L S1497 F/fs allele and identified cyclin C
      mis-localization as the likely cause.
    explanation: Attributes the mitochondrial defect specifically to cyclin C mislocalisation.
  downstream:
  - target: Intellectual disability
    description: >-
      A bioenergetic contribution to the cognitive phenotype, predicted if the cyclin C
      release demonstrated in patient fibroblasts also occurs in neurons. Flagged as
      inference: no neuronal data exist.
  - target: Generalized hypotonia
    description: >-
      Reduced oxidative capacity is a plausible contributor to the near-universal
      hypotonia, on the same fibroblast-to-muscle inference as above.
  notes: >-
    Demonstrated in a single patient fibroblast line. Retained as a mechanism node
    rather than folded into the haploinsufficiency node because it is the one MED13L
    mechanism with a pharmacological rescue already shown in patient-derived cells.
    The two downstream edges are explicitly inferential — the cyclin C release is shown
    in fibroblasts, not in neurons or muscle.
phenotypes:
- category: Clinical
  name: Intellectual disability
  frequency: VERY_FREQUENT
  description: >
    Intellectual disability is present in essentially all affected individuals, most
    often in the moderate range but spanning mild to profound. Formal testing places
    full-scale IQ in the borderline-to-intellectual-disability range.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:29511999
    reference_title: "MED13L-related intellectual disability: involvement of missense variants and delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients presented with intellectual disability and severe language
      impairment.
    explanation: >-
      All 36 patients in the largest genotype-phenotype cohort had intellectual
      disability, supporting a VERY_FREQUENT band.
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Review of the reported patients with MED13L haploinsufficiency indicates
      moderate to severe ID and facial anomalies in all patients, as well as severe
      speech delay and muscular hypotonia in the majority.
    explanation: >-
      Literature review confirms intellectual disability in all reported
      haploinsufficiency patients and places the modal severity at moderate-to-severe.
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Full scale IQs fell in the borderline to intellectual disability range,
      consistent with reported cognitive impairment in 97% of the virtual cohort.
    explanation: >-
      Direct standardized cognitive testing quantifies the impairment and its
      near-universal frequency.
- category: Clinical
  name: Global developmental delay
  frequency: VERY_FREQUENT
  description: >
    Global developmental delay affecting speech, motor and cognitive domains is a
    consistent presenting feature, ranging from mild to profound.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MED13L syndrome is characterized by mild-to-profound developmental delay,
      intellectual disability, and hypotonia.
    explanation: GeneReviews places developmental delay among the defining features.
  - reference: PMID:29959045
    reference_title: "Is MED13L-related intellectual disability a recognizable syndrome?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Phenotypically, they all had intellectual disability, speech and motor delay,
      and features of the mouth (open mouth appearance, macroglossia, and/or
      macrostomia).
    explanation: All eight patients in this series had combined speech and motor delay.
- category: Clinical
  name: Motor speech disorder
  frequency: VERY_FREQUENT
  description: >
    The communication phenotype is specifically a motor speech disorder. Every
    individual who completed in-person articulation testing met criteria for speech
    apraxia, dysarthria, or both — a sharper characterisation than the "speech delay"
    recorded in earlier cohorts, and one that changes therapy selection toward
    motor-speech techniques and augmentative communication.
  phenotype_term:
    preferred_term: Speech apraxia
    term:
      id: HP:0011098
      label: Speech apraxia
  evidence:
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All individuals who completed in-person articulation testing met diagnostic
      criteria for speech apraxia, dysarthria, or both.
    explanation: >-
      Deep-phenotyping study establishing motor speech disorder, not generic speech
      delay, as the MED13L communication phenotype.
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MED13L-related disorder is characterized by a high rate of motor speech
      disorders that occur in the context of globally impaired motor, language, and
      cognitive skills.
    explanation: >-
      States the conclusion directly and situates the speech phenotype within global
      motor impairment.
- category: Clinical
  name: Delayed speech and language development
  frequency: VERY_FREQUENT
  description: >
    Severe speech and language delay is near-universal and disproportionate to the
    degree of intellectual disability. Language impairment was present in the entire
    in-person deep-phenotyping cohort and reported for 97% of a larger virtual cohort.
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  evidence:
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Language impairment was present in all of the in-person cohort and reported for
      almost all (97%) of the virtual cohort.
    explanation: >-
      Quantifies language impairment at essentially 100%, supporting VERY_FREQUENT.
  - reference: PMID:25758992
    reference_title: "Redefining the MED13L syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A prominent feature of the MED13L neurocognitive presentation is profound
      language impairment, often in combination with articulatory deficits.
    explanation: >-
      Identifies profound language impairment with articulatory involvement as the
      signature neurocognitive feature.
- category: Clinical
  name: Absent speech
  frequency: OCCASIONAL
  description: >
    A substantial minority of children remain minimally verbal or nonverbal beyond age
    four years, and lack of speech has been reported as a distinguishing finding in
    individual cases.
  phenotype_term:
    preferred_term: Absent speech
    term:
      id: HP:0001344
      label: Absent speech
  evidence:
  - reference: PMID:33930262
    reference_title: "The MED13L haploinsufficiency syndrome associated with de novo nonsense variant (P.GLN1981*)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Uncommon findings like lack of speech, strabismus and self-destructive behaviour
      present in our patient allowed us to further define the phenotypic spectrum of
      mental retardation and distinctive facial features with or without cardiac
      defects syndrome.
    explanation: >-
      Documents complete absence of speech as a recognised but uncommon end of the
      MED13L communication spectrum.
- category: Clinical
  name: Generalized hypotonia
  frequency: VERY_FREQUENT
  description: >
    Hypotonia is one of the three defining features alongside developmental delay and
    intellectual disability, reported in 83% of a systematically phenotyped cohort and
    in the majority of reviewed haploinsufficiency patients.
  phenotype_term:
    preferred_term: Generalized hypotonia
    term:
      id: HP:0001290
      label: Generalized hypotonia
  evidence:
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notable medical features included hypotonia (83%), vision problems (72%),
      recurrent otitis media (58%), gastrointestinal problems (57%), and seizures
      (31%).
    explanation: >-
      Quantifies hypotonia at 83%, supporting the VERY_FREQUENT band (80-99%).
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Review of the reported patients with MED13L haploinsufficiency indicates
      moderate to severe ID and facial anomalies in all patients, as well as severe
      speech delay and muscular hypotonia in the majority.
    explanation: Independent literature review places hypotonia in the majority of patients.
- category: Clinical
  name: Motor delay
  frequency: VERY_FREQUENT
  description: >
    Motor delay is near-universal, with independent walking typically achieved around
    27-28 months.
  phenotype_term:
    preferred_term: Motor delay
    term:
      id: HP:0001270
      label: Motor delay
  evidence:
  - reference: PMID:34654706
    reference_title: "MED13L-related intellectual disability due to paternal germinal mosaicism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Affected individuals share overlapping features comprising intellectual
      disability, hypotonia, motor delay, remarkable speech delay, and a recognizable
      facial gestalt.
    explanation: Lists motor delay among the shared core features of the syndrome.
  - reference: PMID:29959045
    reference_title: "Is MED13L-related intellectual disability a recognizable syndrome?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Phenotypically, they all had intellectual disability, speech and motor delay,
      and features of the mouth (open mouth appearance, macroglossia, and/or
      macrostomia).
    explanation: Motor delay present in all patients of this series.
- category: Clinical
  name: Autistic behavior
  frequency: FREQUENT
  description: >
    Autistic features are part of a broader neurobehavioral profile that also includes
    agitation/aggression, restlessness, self-harm, tantrums, overfriendliness and
    hyperactivity. Autistic features are reported more often in missense than in
    truncating-variant carriers.
  phenotype_term:
    preferred_term: Autistic behavior
    term:
      id: HP:0000729
      label: Autistic behavior
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neurobehavioral manifestations (autistic features, agitation/aggression,
      restlessness, self-harm, tantrums, frustration, overfriendliness, and/or
      hyperactivity) are also reported.
    explanation: >-
      GeneReviews records autistic features within the recognised neurobehavioral
      profile.
  - reference: PMID:32646507
    reference_title: "Report of a de novo c.2605C > T (p.Pro869Ser) change in the MED13L gene and review of the literature for MED13L-related intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Behavioral difficulties and autistic features were observed in 55.6% of the
      patients.
    explanation: >-
      Quantifies behavioural/autistic features at 55.6% in the missense-variant
      literature subset, supporting the FREQUENT band.
- category: Clinical
  name: Seizure
  frequency: FREQUENT
  description: >
    Seizures affect roughly a third of individuals overall — 31% in a systematically
    phenotyped cohort — and are markedly enriched among carriers of missense variants
    (44.4% in the pooled missense literature) relative to truncating variants. Abnormal
    EEG can be present without clinical seizures.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notable medical features included hypotonia (83%), vision problems (72%),
      recurrent otitis media (58%), gastrointestinal problems (57%), and seizures
      (31%).
    explanation: >-
      Quantifies seizures at 31% of a 67-individual cohort, which falls in the FREQUENT
      band (30-79%).
  - reference: PMID:29511999
    reference_title: "MED13L-related intellectual disability: involvement of missense variants and delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We found that patients carrying missense mutations had more frequently epilepsy
      and showed a more severe phenotype.
    explanation: >-
      Establishes the genotype dependence of the seizure risk, which is what makes the
      overall frequency band an average across two different risk groups.
  - reference: PMID:32646507
    reference_title: "Report of a de novo c.2605C > T (p.Pro869Ser) change in the MED13L gene and review of the literature for MED13L-related intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Of these patients, 44.4% had epileptic seizures.
    explanation: >-
      Quantifies the higher seizure frequency specifically within the missense-variant
      subset.
- category: Clinical
  name: Ataxia
  frequency: FREQUENT
  description: >
    Ataxia and coordination problems are recurrent findings, reported as frequent in
    the largest genotype-phenotype cohort and present in roughly 20-50% of reviewed
    patients.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: PMID:29511999
    reference_title: "MED13L-related intellectual disability: involvement of missense variants and delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hypotonia, ataxia, and recognizable facial gestalt were frequent findings, but
      not congenital heart defects.
    explanation: >-
      Ataxia explicitly described as a frequent finding in a 36-patient cohort, and in
      the same sentence contrasted with the non-frequency of cardiac defects.
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Further common signs include abnormal MRI findings of myelination defects and
      abnormal corpus callosum, ataxia and coordination problems, autistic features,
      seizures/abnormal EEG, or congenital heart defects, present in about 20-50% of
      the patients.
    explanation: >-
      Places ataxia and coordination problems in a 20-50% band across reviewed
      patients.
- category: Clinical
  name: Abnormal brain morphology
  frequency: FREQUENT
  description: >
    Brain MRI abnormalities are common and include ventriculomegaly, delayed or absent
    myelination, thin or absent corpus callosum, periventricular foci and subcortical
    white matter change. Reported in roughly 20-50% of reviewed patients, and more
    often in missense-variant carriers.
  phenotype_term:
    preferred_term: Abnormal brain morphology
    term:
      id: HP:0012443
      label: Abnormal brain morphology
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Some individuals have abnormal findings on brain imaging (ventriculomegaly,
      delayed or lack of myelination, thin or absent corpus callosum, periventricular
      foci, and/or subcortical white matter abnormalities).
    explanation: Enumerates the specific neuroimaging abnormalities seen in MED13L syndrome.
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Further common signs include abnormal MRI findings of myelination defects and
      abnormal corpus callosum, ataxia and coordination problems, autistic features,
      seizures/abnormal EEG, or congenital heart defects, present in about 20-50% of
      the patients.
    explanation: Places MRI abnormalities in a 20-50% frequency band.
- category: Clinical
  name: Abnormal heart morphology
  frequency: OCCASIONAL
  description: >
    Congenital heart defects — conotruncal lesions including d-transposition of the
    great arteries, ventricular septal defect and persistent foramen ovale — occur in a
    minority of patients with variable severity. This is a substantive correction to
    the original framing of the gene: cardiac defects were once considered a defining
    feature but are now recognised as reduced-penetrance, and were explicitly absent as
    a frequent finding in the largest cohort.
  phenotype_term:
    preferred_term: Abnormal heart morphology
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  evidence:
  - reference: PMID:29511999
    reference_title: "MED13L-related intellectual disability: involvement of missense variants and delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hypotonia, ataxia, and recognizable facial gestalt were frequent findings, but
      not congenital heart defects.
    explanation: >-
      Explicitly excludes congenital heart defects from the frequent findings in a
      36-patient cohort, the key evidence for the OCCASIONAL band.
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Subsequent reports of 22 further patients diagnosed by genome-wide testing
      further delineated the syndrome with expansion of the phenotypic spectrum and
      showed reduced penetrance for congenital heart defects.
    explanation: Documents reduced penetrance of the cardiac phenotype.
  - reference: PMID:25712080
    reference_title: "Novel de novo heterozygous loss-of-function variants in MED13L and further delineation of the MED13L haploinsufficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Congenital heart diseases are found in some subjects with various degree of
      severity.
    explanation: Confirms cardiac involvement as a variable, subset finding.
  - reference: PMID:29046205
    reference_title: "[Clinical phenotype and genetic analysis of MED13L syndrome]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "echocardiography showed ventricular septal defect"
    explanation: >-
      Case-level documentation of a septal defect, the commonest specific cardiac
      lesion after conotruncal anomalies.
- category: Clinical
  name: Abnormal facial shape
  frequency: VERY_FREQUENT
  description: >
    A recognisable facial gestalt is present in nearly all patients: depressed or broad
    nasal bridge, bulbous nasal tip, hypotonic open mouth, upslanted palpebral fissures,
    broad or prominent forehead, bitemporal narrowing, low-set ears and abnormal chin.
    Macroglossia and horizontal eyebrows occur in a minority.
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  evidence:
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      With reference to facial anomalies, the majority of patients were reported to
      show broad/prominent forehead, low set ears, bitemporal narrowing, upslanting
      palpebral fissures, depressed/flat nasal bridge, bulbous nose, and abnormal chin,
      but macroglossia and horizontal eyebrows were also observed in ∼30%.
    explanation: >-
      Enumerates the component features of the gestalt and their approximate
      frequencies.
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Review of the reported patients with MED13L haploinsufficiency indicates
      moderate to severe ID and facial anomalies in all patients, as well as severe
      speech delay and muscular hypotonia in the majority.
    explanation: >-
      Facial anomalies present in all reviewed haploinsufficiency patients, supporting
      the VERY_FREQUENT band.
- category: Clinical
  name: Bulbous nose
  frequency: FREQUENT
  description: >
    A bulbous nasal tip is one of the most consistently recognised components of the
    MED13L facial gestalt and one of the features that makes the syndrome clinically
    suspectable.
  phenotype_term:
    preferred_term: Bulbous nose
    term:
      id: HP:0000414
      label: Bulbous nose
  evidence:
  - reference: PMID:29959045
    reference_title: "Is MED13L-related intellectual disability a recognizable syndrome?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the syndrome may be suspected in some individuals based on the association of
      developmental delay, speech impairment, bulbous nasal tip, and macroglossia,
      macrostomia, or open mouth appearance.
    explanation: >-
      Bulbous nasal tip named as one of four features that raise clinical suspicion of
      the syndrome.
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dysmorphic facial features, including depressed nasal bridge, bulbous nose, and
      hypotonic open mouth, are present in most individuals.
    explanation: >-
      GeneReviews places bulbous nose among the features present in most individuals.
- category: Clinical
  name: Depressed nasal bridge
  frequency: FREQUENT
  description: >
    A depressed or flat/broad nasal bridge is a core component of the facial gestalt,
    present in most individuals.
  phenotype_term:
    preferred_term: Depressed nasal bridge
    term:
      id: HP:0005280
      label: Depressed nasal bridge
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dysmorphic facial features, including depressed nasal bridge, bulbous nose, and
      hypotonic open mouth, are present in most individuals.
    explanation: Lists depressed nasal bridge among features present in most individuals.
- category: Clinical
  name: Open mouth
  frequency: FREQUENT
  description: >
    A hypotonic open-mouth appearance, often with macroglossia or macrostomia, is a
    characteristic oral feature and part of the clinical gestalt that prompts testing.
  phenotype_term:
    preferred_term: Open mouth
    term:
      id: HP:0000194
      label: Open mouth
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dysmorphic facial features, including depressed nasal bridge, bulbous nose, and
      hypotonic open mouth, are present in most individuals.
    explanation: GeneReviews lists hypotonic open mouth among the majority features.
  - reference: PMID:29959045
    reference_title: "Is MED13L-related intellectual disability a recognizable syndrome?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Phenotypically, they all had intellectual disability, speech and motor delay,
      and features of the mouth (open mouth appearance, macroglossia, and/or
      macrostomia).
    explanation: Oral features present in all eight patients of this series.
- category: Clinical
  name: Low-set ears
  frequency: FREQUENT
  description: >
    Low-set ears are among the facial features reported in the majority of patients.
  phenotype_term:
    preferred_term: Low-set ears
    term:
      id: HP:0000369
      label: Low-set ears
  evidence:
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      With reference to facial anomalies, the majority of patients were reported to
      show broad/prominent forehead, low set ears, bitemporal narrowing, upslanting
      palpebral fissures, depressed/flat nasal bridge, bulbous nose, and abnormal chin,
      but macroglossia and horizontal eyebrows were also observed in ∼30%.
    explanation: Low-set ears listed among features reported in the majority of patients.
- category: Clinical
  name: Upslanted palpebral fissure
  frequency: FREQUENT
  description: >
    Upslanting palpebral fissures are part of the facial gestalt reported in the
    majority of patients.
  phenotype_term:
    preferred_term: Upslanted palpebral fissure
    term:
      id: HP:0000582
      label: Upslanted palpebral fissure
  evidence:
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      With reference to facial anomalies, the majority of patients were reported to
      show broad/prominent forehead, low set ears, bitemporal narrowing, upslanting
      palpebral fissures, depressed/flat nasal bridge, bulbous nose, and abnormal chin,
      but macroglossia and horizontal eyebrows were also observed in ∼30%.
    explanation: Upslanting palpebral fissures listed among majority facial features.
- category: Clinical
  name: Visual impairment
  frequency: FREQUENT
  description: >
    Visual impairment is common and was systematically under-recognised until
    family-reported registry data quantified it. Reported at 72-76% in the two largest
    systematically phenotyped series, well above the frequency implied by earlier
    clinic-based case reports, which is why baseline ophthalmologic review is now
    recommended rather than symptom-triggered referral.
  phenotype_term:
    preferred_term: Visual impairment
    term:
      id: HP:0000505
      label: Visual impairment
  evidence:
  - reference: PMID:40389839
    reference_title: "Contribution of families using the GenIDA database to the description of MED13L syndrome and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The GenIDA series identified a higher prevalence of visual impairment (76%) and
      highlighted under-recognized musculoskeletal issues, such as foot deformities,
      which had previously received little attention.
    explanation: >-
      Family-reported registry data quantify visual impairment at 76% and explicitly
      flag it as previously under-recognised.
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notable medical features included hypotonia (83%), vision problems (72%),
      recurrent otitis media (58%), gastrointestinal problems (57%), and seizures
      (31%).
    explanation: >-
      Independent cohort corroborates the high frequency of vision problems (72%).
- category: Clinical
  name: Strabismus
  description: >
    Strabismus is the specific ocular finding most often named in MED13L case reports and
    is one of the two features GeneReviews flags for ongoing ophthalmologic surveillance.
  phenotype_term:
    preferred_term: Strabismus
    term:
      id: HP:0000486
      label: Strabismus
  evidence:
  - reference: PMID:33930262
    reference_title: "The MED13L haploinsufficiency syndrome associated with de novo nonsense variant (P.GLN1981*)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Uncommon findings like lack of speech, strabismus and self-destructive behaviour
      present in our patient allowed us to further define the phenotypic spectrum of
      mental retardation and distinctive facial features with or without cardiac
      defects syndrome.
    explanation: Case-level documentation of strabismus.
  - reference: PMID:37512036
    reference_title: "Molecular and Functional Characterisation of a Novel Intragenic 12q24.21 Deletion Resulting in MED13L Haploinsufficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This complex neurodevelopmental disorder is characterised by various phenotypic
      features, including plagiocephaly, strabismus, clubfoot, poor speech, and
      developmental delay.
    explanation: Lists strabismus among the characteristic features of the disorder.
  notes: >-
    `frequency` omitted deliberately: strabismus is repeatedly named in case reports and
    in the GeneReviews surveillance guidance, but no source reports a numerator and
    denominator for it separately from the grouped visual-impairment figure.
- category: Clinical
  name: Hearing impairment
  frequency: OCCASIONAL
  description: >
    Hearing impairment is reported in a minority of individuals. A single detailed
    audiovestibular workup additionally documented bilateral vestibular weakness and an
    inner-ear structural abnormality — a previously unreported dimension of the
    phenotype with direct management implications.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Other reported features include seizures and/or hearing impairment.
    explanation: GeneReviews lists hearing impairment among the reported minority features.
  - reference: PMID:38454295
    reference_title: "Cochleovestibular Phenotype in a Rare Genetic MED13L Mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The child showed bilateral sloping sensorineural hearing loss, a bilateral
      vestibular weakness, and an inner ear vestibular structural abnormality on
      imaging.
    explanation: >-
      First objective vestibulometry in MED13L syndrome, extending the otologic
      phenotype beyond hearing loss to vestibular dysfunction.
  - reference: PMID:38454295
    reference_title: "Cochleovestibular Phenotype in a Rare Genetic MED13L Mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hearing loss has been reported very rarely, and vestibular weakness has never
      been reported in the condition.
    explanation: >-
      States the prior rarity of otologic reporting, justifying the OCCASIONAL band and
      the novelty of the vestibular finding.
- category: Clinical
  name: Gastrointestinal problems
  frequency: FREQUENT
  description: >
    Gastrointestinal problems affect roughly half of individuals and, with feeding
    difficulty and aspiration risk, drive a substantial part of routine management
    (feeding therapy, gastrostomy placement where needed).
  phenotype_term:
    preferred_term: Abnormality of the gastrointestinal tract
    term:
      id: HP:0011024
      label: Abnormality of the gastrointestinal tract
  evidence:
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notable medical features included hypotonia (83%), vision problems (72%),
      recurrent otitis media (58%), gastrointestinal problems (57%), and seizures
      (31%).
    explanation: Quantifies gastrointestinal problems at 57%, supporting the FREQUENT band.
- category: Clinical
  name: Recurrent otitis media
  frequency: FREQUENT
  description: >
    Recurrent otitis media affects more than half of individuals and is a plausible
    contributor to the hearing and speech phenotype that is independently modifiable.
  phenotype_term:
    preferred_term: Recurrent otitis media
    term:
      id: HP:0000403
      label: Recurrent otitis media
  evidence:
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notable medical features included hypotonia (83%), vision problems (72%),
      recurrent otitis media (58%), gastrointestinal problems (57%), and seizures
      (31%).
    explanation: Quantifies recurrent otitis media at 58%, supporting the FREQUENT band.
- category: Clinical
  name: Abnormality of the musculoskeletal system
  description: >
    Distal limb and digit anomalies are reported, and family-reported registry data
    surfaced foot deformities as a specific, previously under-attended musculoskeletal
    burden. Scoliosis has been documented at case level and is recommended for
    surveillance at every visit.
  phenotype_term:
    preferred_term: Abnormality of the musculoskeletal system
    term:
      id: HP:0033127
      label: Abnormality of the musculoskeletal system
  evidence:
  - reference: PMID:40389839
    reference_title: "Contribution of families using the GenIDA database to the description of MED13L syndrome and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The GenIDA series identified a higher prevalence of visual impairment (76%) and
      highlighted under-recognized musculoskeletal issues, such as foot deformities,
      which had previously received little attention.
    explanation: >-
      Identifies musculoskeletal involvement, specifically foot deformities, as an
      under-recognised part of the phenotype.
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Distal limb and/or digit anomalies, ocular manifestations and vision issues, and
      congenital heart defects have been reported.
    explanation: GeneReviews records distal limb and digit anomalies in the phenotype.
  notes: >-
    `frequency` deliberately omitted: the registry study establishes that
    musculoskeletal involvement is more common than previously appreciated but does not
    report a numerator/denominator for the grouped term used here.
- category: Clinical
  name: Scoliosis
  frequency: OCCASIONAL
  description: >
    Scoliosis has been documented at case level and is specifically named for clinical
    surveillance at each visit with radiographs as needed.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  evidence:
  - reference: PMID:29046205
    reference_title: "[Clinical phenotype and genetic analysis of MED13L syndrome]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The anteroposterior and lateral films of the spine showed scoliosis
    explanation: Radiographically confirmed scoliosis in a MED13L syndrome proband.
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      clinical assessment for scoliosis at each visit with radiographs as needed
    explanation: >-
      Scoliosis is prominent enough in the phenotype to warrant dedicated surveillance
      in the GeneReviews management guidance.
genetic:
- name: MED13L heterozygous pathogenic variants
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  inheritance:
  - name: Autosomal Dominant
    inheritance_term:
      preferred_term: Autosomal dominant inheritance
      term:
        id: HP:0000006
        label: Autosomal dominant inheritance
    expressivity: VARIABLE
    description: >-
      Missense-variant carriers, particularly at the exon 15-17 hotspot, show a more
      severe phenotype with more frequent epilepsy and cardiac defects than carriers
      of premature-truncating variants.
    evidence:
    - reference: PMID:40228085
      reference_title: "MED13L Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        MED13L syndrome is an autosomal dominant disorder.
      explanation: Confirms the mode of inheritance.
    - reference: PMID:40389839
      reference_title: "Contribution of families using the GenIDA database to the description of MED13L syndrome and literature review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        A comprehensive review of published cases showed that patients with missense
        variants have more severe impairments, including increased cardiac defects,
        global developmental delay, and a higher incidence of epilepsy, than patients
        with premature truncated variants.
      explanation: >-
        Documents variant-class-dependent expressivity across the pooled published
        literature.
  features: >
    MED13L syndrome is caused by heterozygous pathogenic variants in MED13L
    (12q24.21). The great majority arise de novo. The allelic spectrum spans
    whole-gene and intragenic deletions and duplications, frameshift, nonsense and
    canonical-splice variants (all acting through haploinsufficiency) and missense
    variants clustering in two hotspots at exons 15-17 and 25-31. Missense carriers
    are systematically more severely affected. Rare recurrence in siblings is
    explained by parental gonadal/germinal mosaicism, which has been documented
    directly in sperm and is the reason prenatal or preimplantation testing is offered
    despite the predominance of de novo events.
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The majority of probands reported to date whose parents have undergone molecular
      genetic testing have the disorder as the result of a pathogenic variant that
      occurred as a de novo event in the proband.
    explanation: Establishes de novo predominance.
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Rarely, individuals diagnosed with MED13L syndrome have the disorder as the
      result of a pathogenic variant inherited from a mosaic, apparently unaffected
      parent.
    explanation: >-
      Documents parental mosaicism as the recurrence mechanism, the basis for the
      recurrence-risk counselling below.
  - reference: PMID:34654706
    reference_title: "MED13L-related intellectual disability due to paternal germinal mosaicism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We now present the first case of paternal germinal mosaicism for a missense
      MED13L variant causing MRFACD syndrome in one of the father's children and being
      the likely cause of intellectual disability and facial dysmorphism in the other.
    explanation: >-
      First direct demonstration of paternal germinal mosaicism, converting a
      theoretical recurrence risk into a documented one.
  - reference: PMID:34654706
    reference_title: "MED13L-related intellectual disability due to paternal germinal mosaicism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      De novo disruption of the MED13L gene by deletions, duplications, or sequence
      variants has been identified as deleterious.
    explanation: Summarises the breadth of the pathogenic allelic spectrum.
  - reference: PMID:29511999
    reference_title: "MED13L-related intellectual disability: involvement of missense variants and delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We identified seven de novo missense variations, in addition to
      protein-truncating variants and intragenic deletions.
    explanation: Documents the co-occurrence of missense, truncating and CNV alleles.
variants:
- name: MED13L c.2597C>T (p.Pro866Leu)
  description: >-
    Recurrent exon-15 hotspot missense allele. Functionally characterised as
    destabilising with cytoplasmic mislocalisation, consistent with loss of function,
    and clinically associated with a severe phenotype including epilepsy and severe
    motor impairment. In mouse cortical neurons the orthologous variant reduces the
    number and length of dendrites.
  clinical_significance: PATHOGENIC
  type: missense
  gene:
    preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  evidence:
  - reference: PMID:40500968
    reference_title: "MED13L pathogenic missense variants impair protein stability and interaction, underlying diverse clinical outcomes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In particular, exon 15 variants (p.Pro866Leu and p.Pro869Ser) correlated with
      severe phenotypes, including epilepsy and severe motor impairment, whereas
      p.Gly1899Arg and p.Thr2162Met were associated with milder manifestations.
    explanation: Assigns the severe clinical correlate to this exon-15 allele.
  - reference: PMID:36798993
    reference_title: "MED13L and its disease-associated variants influence the dendritic development of cerebral cortical neurons in the mammalian brain."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      There, we found that overexpression of the p.P866L variant resulted in reduced
      number and length of dendrites of cortical layer II/III pyramidal neurons.
    explanation: In vivo neuronal readout of the variant's functional consequence.
- name: MED13L c.2605C>T (p.Pro869Ser)
  description: >-
    Recurrent exon-15 hotspot missense allele and the best-documented MED13L mutational
    hotspot. Unlike the other characterised missense variants it retains comparatively
    stable expression and partial nuclear localisation, which is the principal argument
    for a non-haploinsufficiency (dominant-negative or neomorphic) mechanism, while
    associating clinically with epilepsy and severe motor impairment.
  clinical_significance: PATHOGENIC
  type: missense
  gene:
    preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  evidence:
  - reference: PMID:32646507
    reference_title: "Report of a de novo c.2605C > T (p.Pro869Ser) change in the MED13L gene and review of the literature for MED13L-related intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We used whole-exome sequencing (WES) to detect the genetic aberration of the
      child and found a de novo mutation, c.2605C > T (p.Pro869Ser), in the MED13L
      gene.
    explanation: Documents an independent de novo occurrence of the recurrent allele.
  - reference: PMID:32646507
    reference_title: "Report of a de novo c.2605C > T (p.Pro869Ser) change in the MED13L gene and review of the literature for MED13L-related intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our case further demonstrates that Pro869Ser is a hotspot mutation of the MED13L
      gene.
    explanation: Establishes hotspot status.
  - reference: PMID:40500968
    reference_title: "MED13L pathogenic missense variants impair protein stability and interaction, underlying diverse clinical outcomes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In particular, exon 15 variants (p.Pro866Leu and p.Pro869Ser) correlated with
      severe phenotypes, including epilepsy and severe motor impairment, whereas
      p.Gly1899Arg and p.Thr2162Met were associated with milder manifestations.
    explanation: >-
      Ties the allele to the severe end of the clinical spectrum in a functional
      genotype-phenotype study.
- name: MED13L c.6485C>T (p.Thr2162Met)
  description: >-
    C-terminal missense allele associated with milder manifestations than the exon-15
    hotspot variants, illustrating that missense position, not missense class,
    stratifies severity.
  clinical_significance: PATHOGENIC
  type: missense
  gene:
    preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  evidence:
  - reference: PMID:40500968
    reference_title: "MED13L pathogenic missense variants impair protein stability and interaction, underlying diverse clinical outcomes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In particular, exon 15 variants (p.Pro866Leu and p.Pro869Ser) correlated with
      severe phenotypes, including epilepsy and severe motor impairment, whereas
      p.Gly1899Arg and p.Thr2162Met were associated with milder manifestations.
    explanation: Assigns the milder clinical correlate to this C-terminal allele.
- name: MED13L intragenic deletion of exons 3-10 (12q24.21)
  description: >-
    Novel heterozygous intragenic deletion resolved at cDNA level, predicted to
    truncate the protein and remove the MedPIWI and Med13_C domains, functionally
    confirmed to cause haploinsufficiency.
  clinical_significance: PATHOGENIC
  type: deletion
  gene:
    preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  evidence:
  - reference: PMID:37512036
    reference_title: "Molecular and Functional Characterisation of a Novel Intragenic 12q24.21 Deletion Resulting in MED13L Haploinsufficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The analysis of the proband's cDNA sample allowed for specifying the regions of
      the breakpoints and identifying the heterozygous deletion that spanned exons 3 to
      10 of MED13L, which has not been reported previously.
    explanation: Molecular definition of the deletion allele.
  - reference: PMID:37512036
    reference_title: "Molecular and Functional Characterisation of a Novel Intragenic 12q24.21 Deletion Resulting in MED13L Haploinsufficiency Syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      After MED13L gene editing was performed, reduced cell viability; an accelerated
      aging process; and inhibition of the RB1, E2F1, and CCNC gene expression were
      found to exist.
    explanation: >-
      CRISPR knockdown of MED13L in control fibroblasts reproduces cellular
      consequences, supporting dosage loss as the operative mechanism.
- name: MED13L de novo frameshift variants c.3765delC and c.607dupT
  description: >-
    Two de novo frameshift alleles identified in an ID cohort selected on the facial
    gestalt (bulbous nasal tip, short mouth, straight eyebrows), confirming that
    gestalt-led ascertainment reaches MED13L.
  clinical_significance: PATHOGENIC
  type: frameshift
  gene:
    preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  evidence:
  - reference: PMID:25712080
    reference_title: "Novel de novo heterozygous loss-of-function variants in MED13L and further delineation of the MED13L haploinsufficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We found two de novo frameshift variants in MED13L, consisting in
      single-nucleotide deletion (c.3765delC) and duplication (c.607dupT).
    explanation: Documents the two frameshift alleles and their de novo status.
- name: MED13L splice acceptor variant of exon 5
  description: >-
    De novo splice acceptor variant producing an in-frame deletion of 15 amino acids in
    the conserved MED13L N-terminal domain; the affected proband showed the
    haploinsufficiency phenotype without a heart defect.
  clinical_significance: PATHOGENIC
  type: splice_site
  gene:
    preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  evidence:
  - reference: PMID:24781760
    reference_title: "Further confirmation of the MED13L haploinsufficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The first patient has a de novo mutation in the splice acceptor site of exon 5 of
      MED13L. cDNA analysis showed this mutation results in an in-frame deletion,
      removing 15 amino acids in middle of the conserved MED13L N-terminal domain.
    explanation: >-
      cDNA-level confirmation of the splice consequence, one of the few MED13L alleles
      characterised at the transcript level.
inheritance:
- name: Autosomal Dominant
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  expressivity: VARIABLE
  description: >
    MED13L syndrome is autosomal dominant with variable expressivity: variant class
    stratifies severity, and missense carriers, especially at the exon 15-17 hotspot,
    have more epilepsy, more cardiac defects and more severe global developmental
    delay than carriers of premature-truncating variants.
    Most probands carry a de novo variant;
    recurrence in siblings of unaffected parents is explained by parental gonadal or
    germinal mosaicism, documented directly at ~30-50% of sperm cells in one family.
    Recurrence risk counselling therefore cannot simply quote a de novo population
    baseline.
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MED13L syndrome is an autosomal dominant disorder.
    explanation: Confirms the inheritance mode.
  - reference: PMID:40389839
    reference_title: "Contribution of families using the GenIDA database to the description of MED13L syndrome and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A comprehensive review of published cases showed that patients with missense
      variants have more severe impairments, including increased cardiac defects,
      global developmental delay, and a higher incidence of epilepsy, than patients
      with premature truncated variants.
    explanation: Supports the variable-expressivity statement with a variant-class axis.
diagnosis:
- name: Clinical whole-exome or genome sequencing
  description: >
    The diagnosis is established by identifying a heterozygous pathogenic MED13L
    variant. Sequencing is the primary route because most pathogenic alleles are
    single-nucleotide or small indel variants invisible to microarray, and because the
    facial gestalt overlaps several other syndromic ID entities. Trio testing
    establishes de novo status, which carries pathogenicity weight.
  diagnosis_term:
    preferred_term: clinical whole-exome sequencing
    term:
      id: NCIT:C101295
      label: Whole Exome Sequencing
  results: Heterozygous pathogenic or likely pathogenic MED13L variant
  markers: MED13L
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of MED13L syndrome is established in a proband with a heterozygous
      pathogenic variant in MED13L identified by molecular genetic testing.
    explanation: States the diagnostic criterion.
  - reference: PMID:34211152
    reference_title: "Exome and genome sequencing for pediatric patients with congenital anomalies or intellectual disability: an evidence-based clinical guideline of the American College of Medical Genetics and Genomics (ACMG)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We strongly recommend that ES/GS be considered as a first- or second-tier test
      for patients with CA/DD/ID.
    explanation: >-
      Places exome/genome sequencing in the recommended diagnostic pathway for the
      clinical presentation MED13L patients arrive with.
- name: Chromosomal microarray analysis
  description: >
    Chromosomal microarray remains a first-tier test for unexplained developmental
    delay and detects the intragenic and whole-gene 12q24.21 deletions and duplications
    that account for a minority of MED13L cases. It is normal in most MED13L patients,
    so a normal microarray does not exclude the diagnosis and should prompt sequencing.
  diagnosis_term:
    preferred_term: chromosomal microarray testing
    term:
      id: NCIT:C18477
      label: Microarray Analysis
  results: >-
    Normal in most; detects 12q24.21 intragenic or whole-gene MED13L deletions and
    duplications in the CNV subset
  markers: 12q24.21
  evidence:
  - reference: PMID:23403903
    reference_title: "Dosage changes of MED13L further delineate its role in congenital heart defects and intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Using high resolution molecular karyotyping, we identified two intragenic de novo
      frameshift deletions, likely resulting in haploinsufficiency, in two patients with
      a similar phenotype of hypotonia, moderate ID, conotruncal heart defect and facial
      anomalies.
    explanation: Demonstrates the CNV detection route to a MED13L diagnosis.
  - reference: PMID:20466091
    reference_title: "Consensus statement: chromosomal microarray is a first-tier clinical diagnostic test for individuals with developmental disabilities or congenital anomalies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Available evidence strongly supports the use of CMA in place of G-banded
      karyotyping as the first-tier cytogenetic diagnostic test for patients with
      DD/ID, ASD, or MCA.
    explanation: >-
      Establishes microarray's first-tier position in the diagnostic pathway that
      precedes MED13L sequencing.
- name: Echocardiography
  description: >
    Baseline echocardiography at diagnosis. Because congenital heart defects occur in a
    minority rather than the majority, this is calibrated as a one-time baseline screen
    with cardiology follow-up only if abnormal, not as intensive surveillance.
  diagnosis_term:
    preferred_term: echocardiography
    term:
      id: NCIT:C16525
      label: Echocardiography Test
  results: >-
    Normal in the majority; detects conotruncal defects, ventricular septal defect or
    persistent foramen ovale in the affected minority
  evidence:
  - reference: PMID:29511999
    reference_title: "MED13L-related intellectual disability: involvement of missense variants and delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hypotonia, ataxia, and recognizable facial gestalt were frequent findings, but
      not congenital heart defects.
    explanation: >-
      Supports calibrating cardiac assessment as a baseline screen rather than
      intensive surveillance.
  - reference: PMID:29046205
    reference_title: "[Clinical phenotype and genetic analysis of MED13L syndrome]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "echocardiography showed ventricular septal defect"
    explanation: Illustrates the lesion type detected when echocardiography is abnormal.
- name: Electroencephalography
  description: >
    EEG on clinical suspicion of seizures, with a lower threshold in carriers of
    exon 15-17 missense variants given their markedly higher epilepsy frequency.
  diagnosis_term:
    preferred_term: electroencephalography
    term:
      id: NCIT:C38054
      label: Electroencephalography
  results: Epileptiform abnormalities, which may be present without clinical seizures
  evidence:
  - reference: PMID:32646507
    reference_title: "Report of a de novo c.2605C > T (p.Pro869Ser) change in the MED13L gene and review of the literature for MED13L-related intellectual disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Of these patients, 44.4% had epileptic seizures.
    explanation: >-
      Quantifies the seizure burden in the missense subset that justifies a lower EEG
      threshold in those carriers.
  - reference: PMID:29511999
    reference_title: "MED13L-related intellectual disability: involvement of missense variants and delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We found that patients carrying missense mutations had more frequently epilepsy
      and showed a more severe phenotype.
    explanation: Supports genotype-stratified epilepsy surveillance.
differential_diagnoses:
- name: MED13-related intellectual developmental disorder (MRD61)
  description: >-
    The paralogous CKM-hinge disorder. Both are autosomal dominant CDK8-kinase-module
    disorders with intellectual disability and prominent speech impairment, and the
    two proteins occupy the same structural position in the module.
  distinguishing_features:
  - MED13L has a recognisable facial gestalt and a far larger reported cohort (~100 vs ~26 cases).
  - MED13 carries ophthalmologic features not reported in MED13L, notably Duane anomaly.
  - MED13L syndrome is defined by a motor speech disorder; MED13 is described as producing a language-dominant phenotype.
  disease_term:
    preferred_term: Intellectual developmental disorder 61
    term:
      id: MONDO:0032485
      label: intellectual developmental disorder 61
  evidence:
  - reference: PMID:29740699
    reference_title: "De novo mutations in MED13, a component of the Mediator complex, are associated with a novel neurodevelopmental disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mutations in several other genes encoding subunits of Mediator have been
      previously shown to associate with DD/ID, including MED13L, a paralog of MED13.
    explanation: >-
      Establishes MED13 and MED13L as paralogous disease genes within the same module,
      the basis for their mutual differential-diagnosis relationship.
- name: MED12-related intellectual disability syndrome
  description: >-
    The X-linked member of the CDK8 kinase module allelic series (FG/Opitz-Kaveggia,
    Lujan-Fryns, Ohdo-Maat-Kievit-Brunner), sharing intellectual disability and
    hypotonia with MED13L syndrome.
  distinguishing_features:
  - X-linked inheritance with predominantly affected males, versus autosomal dominant de novo events in MED13L.
  - Distinct facial and behavioural profiles across the MED12 allelic series.
  disease_term:
    preferred_term: MED12-related intellectual disability syndrome
    term:
      id: MONDO:0100000
      label: MED12-related intellectual disability syndrome
  evidence:
  - reference: PMID:30905399
    reference_title: "De Novo Missense Substitutions in the Gene Encoding CDK8, a Regulator of the Mediator Complex, Cause a Syndromic Developmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mutations in MED12, MED13, and MED13L were previously identified in syndromic
      developmental disorders with overlapping phenotypes.
    explanation: >-
      States the phenotypic overlap between the MED12, MED13 and MED13L disorders that
      makes MED12-related intellectual disability a differential for MED13L syndrome.
- name: Chromosome 1p36 deletion syndrome
  description: >-
    A recurrent microdeletion syndrome that overlaps MED13L syndrome in facial gestalt,
    particularly straight/horizontal eyebrows, deep-set eyes and midface hypoplasia,
    and in the combination of intellectual disability with congenital heart disease.
  distinguishing_features:
  - 1p36 deletion is detectable on chromosomal microarray, whereas most MED13L variants are not.
  - Overlapping facial features prompted the explicit recommendation to consider MED13L when 1p36 testing is negative.
  disease_term:
    preferred_term: chromosome 1p36 deletion syndrome
    term:
      id: MONDO:0011929
      label: chromosome 1p36 deletion syndrome
  evidence:
  - reference: PMID:25712080
    reference_title: "Novel de novo heterozygous loss-of-function variants in MED13L and further delineation of the MED13L haploinsufficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Haploinsufficiency for MED13L should be considered in the differential diagnosis
      of the 1p36 microdeletion syndrome, due to overlapping dysmorphic facial features
      in some patients.
    explanation: >-
      Direct recommendation to place MED13L in the 1p36 differential on facial-gestalt
      grounds.
- name: Kleefstra syndrome
  description: >-
    EHMT1-related syndromic intellectual disability whose facial gestalt has been
    explicitly noted to resemble that of individual MED13L patients.
  distinguishing_features:
  - Resolved by identifying an EHMT1 variant or 9q34.3 deletion on molecular testing.
  disease_term:
    preferred_term: Kleefstra syndrome
    term:
      id: MONDO:0012455
      label: Kleefstra syndrome
  evidence:
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The first patient indicates some facial resemblance to Kleefstra syndrome as a
      novel differential diagnosis, and the second patient shows, for the first time,
      recurrence of a MED13L missense mutation (p.(Asp860Gly)).
    explanation: >-
      Introduces Kleefstra syndrome as a MED13L differential on the basis of facial
      resemblance.
- name: 22q11.2 deletion syndrome
  description: >-
    Shares the combination of intellectual disability with conotruncal congenital heart
    disease, and the more common MED13L facial gestalt has been noted to resemble it.
  distinguishing_features:
  - 22q11.2 deletion adds palatal anomalies, hypocalcaemia and immune deficiency, none of which are MED13L features.
  - The deletion is detectable on chromosomal microarray.
  disease_term:
    preferred_term: 22q11.2 deletion syndrome
    term:
      id: MONDO:0018923
      label: 22q11.2 deletion syndrome
  evidence:
  - reference: PMID:28645799
    reference_title: "Genotype-phenotype evaluation of MED13L defects in the light of a novel truncating and a recurrent missense mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The latter are especially important in the differential diagnosis of 1p36 deletion
      and Kleefstra syndromes, while the more common facial gestalt shows some
      resemblance to 22q11.2 deletion syndrome.
    explanation: >-
      Places 22q11.2 deletion syndrome in the MED13L facial differential alongside 1p36
      and Kleefstra.
- name: Cornelia de Lange syndrome
  description: >-
    MED13L variants have been recovered from cohorts clinically suspected of Cornelia
    de Lange syndrome but negative for cohesin-pathway genes, so MED13L belongs in the
    CdLS-like differential.
  distinguishing_features:
  - Classic CdLS features (synophrys, limb reduction defects, prenatal growth restriction) are not core MED13L features.
  - Resolved by identifying NIPBL or another cohesin-pathway variant.
  disease_term:
    preferred_term: Cornelia de Lange syndrome
    term:
      id: MONDO:0016033
      label: Cornelia de Lange syndrome
  evidence:
  - reference: PMID:31337854
    reference_title: "Comprehensive genetic analysis of 57 families with clinically suspected Cornelia de Lange syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Systematic clinical evaluation of all patients using a recently proposed clinical
      scoring system showed that ZMYND11, MED13L, and PHIP abnormality may cause CdLS or
      CdLS-like.
    explanation: >-
      Demonstrates MED13L variants being ascertained through a CdLS-suspected cohort,
      establishing the differential empirically.
treatments:
- name: Speech and Language Therapy
  description: >
    The highest-priority developmental intervention. Because the MED13L speech
    phenotype is specifically a motor speech disorder (apraxia and/or dysarthria)
    rather than a nonspecific delay, assessment should screen explicitly for apraxia so
    that motor-speech techniques and, for minimally verbal or nonverbal children,
    augmentative and alternative communication are introduced early.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: speech therapy
    term:
      id: NCIT:C159273
      label: Speech Language Therapy
  target_phenotypes:
  - preferred_term: Speech apraxia
    term:
      id: HP:0011098
      label: Speech apraxia
  - preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  evidence:
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Children would benefit from early referrals to speech therapy to assess their
      speech, language, and support needs.
    explanation: >-
      Direct recommendation from the deep-phenotyping study that established the motor
      speech phenotype.
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All individuals who completed in-person articulation testing met diagnostic
      criteria for speech apraxia, dysarthria, or both.
    explanation: >-
      Justifies apraxia/dysarthria-specific assessment rather than generic language
      therapy.
- name: Physical Therapy
  description: >
    Physiotherapy from infancy for hypotonia, motor delay and the coordination and
    balance problems associated with ataxia and, in some children, vestibular weakness.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  target_phenotypes:
  - preferred_term: Generalized hypotonia
    term:
      id: HP:0001290
      label: Generalized hypotonia
  - preferred_term: Motor delay
    term:
      id: HP:0001270
      label: Motor delay
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      assessment of mobility and self-help skills at each visit
    explanation: >-
      GeneReviews surveillance guidance establishes ongoing motor assessment as
      standard care, the trigger for physiotherapy input.
- name: Occupational Therapy
  description: >
    Occupational therapy as part of the multidisciplinary developmental package,
    targeting self-help skills and the significant visual-motor integration deficits
    demonstrated on standardized testing.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: occupational therapy
    term:
      id: NCIT:C121351
      label: Occupational Therapy
  evidence:
  - reference: PMID:40993520
    reference_title: "MED13L-related disorder characterized by severe motor speech impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Those who were able to complete motor testing demonstrated significant deficits
      in visual motor integration (mean 57.08, SD 9.26).
    explanation: >-
      Quantifies the visual-motor integration deficit that occupational therapy
      addresses.
- name: Ophthalmologic Surveillance
  description: >
    Baseline ophthalmologic evaluation at diagnosis with periodic review for changes in
    visual acuity and strabismus, with refractive correction and strabismus treatment per
    ophthalmologist when abnormalities are found. Registry data showing 72-76% visual
    involvement make this a higher-yield surveillance target than earlier clinic-based
    reports implied.
  action_category: MONITORING
  treatment_term:
    preferred_term: vision assessment
    term:
      id: NCIT:C156778
      label: Vision Assessment
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      assess for changes in visual acuity and strabismus per treating ophthalmologist
    explanation: GeneReviews surveillance recommendation for ocular manifestations.
  - reference: PMID:40389839
    reference_title: "Contribution of families using the GenIDA database to the description of MED13L syndrome and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The GenIDA series identified a higher prevalence of visual impairment (76%) and
      highlighted under-recognized musculoskeletal issues, such as foot deformities,
      which had previously received little attention.
    explanation: >-
      Quantifies the burden that justifies routine rather than symptom-triggered
      ophthalmologic review.
- name: Audiologic and Vestibular Surveillance
  description: >
    Annual audiology evaluation, extended — on the strength of the first objective
    vestibulometry performed in this disorder — to comprehensive audiovestibular
    assessment, since vestibular weakness had never previously been looked for and was
    found.
  action_category: MONITORING
  treatment_term:
    preferred_term: hearing examination
    term:
      id: NCIT:C38036
      label: Audiometric Test
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      audiology evaluation annually or as needed
    explanation: GeneReviews surveillance recommendation for hearing.
  - reference: PMID:38454295
    reference_title: "Cochleovestibular Phenotype in a Rare Genetic MED13L Mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We emphasize the importance of comprehensive audiovestibular assessment in
      children diagnosed with MED13L mutations for effective management of these
      children.
    explanation: >-
      Extends the standard audiologic recommendation to include vestibular assessment.
  - reference: PMID:38454295
    reference_title: "Cochleovestibular Phenotype in a Rare Genetic MED13L Mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Early intervention with hearing aids and vestibular rehabilitation led to a
      favorable outcome in terms of speech, communication, and balance.
    explanation: >-
      Documents benefit from combined amplification and vestibular rehabilitation,
      including on the speech outcome.
- name: Hearing Aids and Vestibular Rehabilitation
  description: >
    Amplification with hearing aids and vestibular rehabilitation for children found to
    have sensorineural hearing loss or vestibular weakness. Reported to improve speech,
    communication and balance — meaning an otologic intervention can move the
    communication outcome that otherwise dominates the disorder.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: hearing aid usage
  target_phenotypes:
  - preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:38454295
    reference_title: "Cochleovestibular Phenotype in a Rare Genetic MED13L Mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Early intervention with hearing aids and vestibular rehabilitation led to a
      favorable outcome in terms of speech, communication, and balance.
    explanation: >-
      Documents the outcome benefit of amplification plus vestibular rehabilitation.
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      hearing aids may be helpful per otolaryngologist
    explanation: GeneReviews management guidance for the hearing arm.
- name: Antiseizure Pharmacotherapy
  description: >
    Standard anti-seizure medication selected by seizure type for the minority with
    epilepsy. There are no MED13L-specific trial data and no evidence for a
    gene-specific drug choice.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: anticonvulsant agent therapy
    term:
      id: NCIT:C64172
      label: Anticonvulsant Therapy
    therapeutic_agent:
    - preferred_term: anticonvulsant agent
      term:
        id: NCIT:C264
        label: Anticonvulsant Agent
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Standardized treatment for developmental, intellectual, and behavioral issues and
      seizures
    explanation: >-
      GeneReviews specifies standardized (non-gene-specific) seizure treatment, which is
      the claim being made here.
- name: Feeding Therapy and Nutritional Support
  description: >
    Feeding therapy with gastrostomy placement as needed, driven by the hypotonia,
    aspiration risk and the gastrointestinal problems that affect over half of
    individuals.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      feeding therapy; gastrostomy tube placement as needed; social work and family
      support
    explanation: GeneReviews treatment guidance for the feeding/nutritional arm.
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      monitor for evidence of aspiration and/or respiratory insufficiency, nutritional
      status, safety of oral intake, and family needs at each visit
    explanation: Establishes the surveillance rationale for ongoing feeding support.
- name: Genetic Counseling
  action_category: COUNSELING_INFORMATIONAL
  description: >
    Counselling at diagnosis and pre-conception. The key point is that a de novo
    finding does not reduce recurrence risk to the population baseline: parental
    gonadal/germinal mosaicism is documented, so prenatal or preimplantation genetic
    testing should be offered once the familial variant is known.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:40228085
    reference_title: "MED13L Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Once the MED13L pathogenic variant has been identified in an affected family
      member, prenatal and preimplantation genetic testing are possible.
    explanation: Establishes the reproductive-testing options counselling should cover.
  - reference: PMID:41403746
    reference_title: "Case Report: Novel mutations in two patients with MED13L-related intellectual disability highlighting the importance of genetic counseling."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The study underscores the value of genetic testing and counseling, exemplified by
      the successful prenatal diagnosis and birth of an unaffected child in the second
      family.
    explanation: >-
      Worked example of prenatal diagnosis changing a reproductive outcome in a MED13L
      family.
animal_models:
- species: Mus musculus
  genotype: Med13l heterozygous germline deletion (exon 11)
  description: >-
    Heterozygous Med13l mice are smaller than wild-type littermates and over 60% show
    craniofacial anomalies (pug snout with midface hypoplasia, or crooked snout), plus
    discontinuous squamosal sutures in a subset. They recapitulate the growth delay and
    craniofacial arm of the human syndrome, and notably do not show a significant
    cardiac functional defect — consistent with the reduced cardiac penetrance now
    recognised in patients.
  genes:
  - preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  associated_phenotypes:
  - Growth delay
  - Midface hypoplasia
  evidence:
  - reference: PMID:40919805
    reference_title: "Heterozygous Med13l mice recapitulate a developmental growth delay and craniofacial anomalies seen in MED13L syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We observed Med13l HET mice are smaller than wildtype (WT) littermates, and over
      60% of them exhibited one of two craniofacial anomalies: a pug snout with midface
      hypoplasia or a crooked snout.
    explanation: Quantifies the growth and craniofacial phenotype of the heterozygous model.
  - reference: PMID:40919805
    reference_title: "Heterozygous Med13l mice recapitulate a developmental growth delay and craniofacial anomalies seen in MED13L syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Med13l HET mice represent a novel research tool for MED13L syndrome.
    explanation: Positions the model as a preclinical research tool for the disorder.
- species: Mus musculus
  genotype: Med13l homozygous and heterozygous knockout
  description: >-
    A dosage series: homozygous Med13l knockout causes neonatal lethality with reduced
    brain volume and cortical thickness, while heterozygous mice are viable and display
    impaired learning and memory, reduced motor coordination, heightened anxiety and
    microcephaly with simplified cortical neuronal morphology. Single-cell
    transcriptomics localises the defect to impaired neural progenitor differentiation.
  genes:
  - preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  associated_phenotypes:
  - Microcephaly
  - Impaired learning and memory
  - Reduced motor coordination
  evidence:
  - reference: PMID:40775066
    reference_title: "Regulation of cortical neurogenesis by MED13L via transcriptional priming and its implications for MED13L syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Additionally, heterozygous mice show microcephaly with simplified neuronal
      morphology in the motor cortex.
    explanation: >-
      Documents the neuroanatomical phenotype of the heterozygous model, including in
      motor cortex, the region relevant to the human motor-speech phenotype.
  - reference: PMID:40775066
    reference_title: "Regulation of cortical neurogenesis by MED13L via transcriptional priming and its implications for MED13L syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Single-cell transcriptomics and immunofluorescence reveal severe cortical
      neurogenesis deficits in Med13l knockout embryos, driven by impaired neural
      progenitor differentiation.
    explanation: Identifies the cellular locus of the neurodevelopmental defect.
- species: Danio rerio
  genotype: med13b morpholino knockdown (morphant)
  description: >-
    Knockdown of the zebrafish MED13L orthologue med13b produces defective cranial
    neural crest cell migration with downstream cartilage deformities and abnormal
    distribution of developing neurons; the neuronal phenotype is rescued by full-length
    human MED13L mRNA, establishing specificity.
  genes:
  - preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  associated_phenotypes:
  - Craniofacial cartilage deformity
  - Defective cranial neural crest migration
  evidence:
  - reference: PMID:25137640
    reference_title: "Impaired development of neural-crest cell-derived organs and intellectual disability caused by MED13L haploinsufficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Knockdown of MED13L orthologue in zebrafish, med13b, showed early defective
      migration of cranial neural crest cells (NCCs) that contributed to cartilage
      structure deformities in the later stage, recapitulating craniofacial anomalies
      seen in human patients.
    explanation: Links MED13L loss to the neural crest migration defect.
  - reference: PMID:25137640
    reference_title: "Impaired development of neural-crest cell-derived organs and intellectual disability caused by MED13L haploinsufficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Notably, we observed abnormal distribution of developing neurons in different
      brain regions of med13b morphant embryos, which could be rescued upon introduction
      of full-length human MED13L mRNA.
    explanation: >-
      Cross-species rescue with human MED13L mRNA establishes that the phenotype is
      MED13L-specific rather than an off-target morpholino effect.
experimental_models:
- name: MED13L patient-derived skin fibroblasts
  description: >-
    Fibroblasts from an individual carrying the MED13L S1497F/fs allele, used as the
    readout system for cyclin C subcellular localisation, mitochondrial morphology,
    respiration, mtDNA copy number and oxidative-stress sensitivity. The system
    supports pharmacological rescue and is therefore the closest thing MED13L syndrome
    currently has to a drug-screening assay.
  experimental_model_type: PRIMARY_CELL_CULTURE
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  publication: PMID:35198885
  findings:
  - statement: Unstressed patient fibroblasts show cytoplasmic cyclin C, mitochondrial fragmentation and a six-fold respiration deficit
  - statement: Blocking cyclin C mitochondrial localisation partially restores organelle function
  evidence:
  - reference: PMID:35198885
    reference_title: "Aberrant cyclin C nuclear release induces mitochondrial fragmentation and dysfunction in MED13L syndrome fibroblasts."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Unstressed MED13L S1497 F/fs patient fibroblasts exhibited aberrant cytoplasmic
      cyclin C localization, mitochondrial fragmentation, and a 6-fold reduction in
      respiration.
    explanation: Defines the assay readouts available in this model system.
- name: In utero electroporation of mouse cortex with MED13L variants
  description: >-
    In utero electroporation of embryonic mouse cortex with wild-type or
    disease-associated MED13L missense constructs, plus knockdown-with-rescue, giving a
    variant-level functional readout on subcellular localisation, dendritic growth,
    spine morphology, migration and axon elongation. This is the closest available
    assay for classifying MED13L variants of uncertain significance.
  experimental_model_type: OTHER
  organism:
    preferred_term: mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  publication: PMID:36798993
  findings:
  - statement: Missense variants differ in nuclear versus cytoplasmic distribution
  - statement: MED13L knockdown abrogates dendritic growth and is rescued by RNAi-resistant wild-type but not by variant constructs
  evidence:
  - reference: PMID:36798993
    reference_title: "MED13L and its disease-associated variants influence the dendritic development of cerebral cortical neurons in the mammalian brain."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Furthermore, we show that mMED13L-knockdown abrogated dendritic growth in vivo,
      and this effect was significantly rescued by co-electroporation of an
      RNAi-resistant mMED13L, but weakly by the p.T2162M variant, and not at all by the
      p.S2163L variant.
    explanation: >-
      Demonstrates the rescue-based design that converts the assay into a variant
      classifier.
- name: iPSC-derived neural progenitor CRISPRi Perturb-seq platform
  description: >-
    A scalable Perturb-seq platform (CRISPRi perturbation plus single-cell RNA-seq) in
    human WTC11 induced pluripotent stem cells carrying dCas9-KRAB, differentiated to
    neural progenitor cells, applied to 60 high-confidence autism risk genes and read out
    with structural topic modelling to assess cell fate and differentiation stage
    simultaneously. MED13L is one of only four genes whose effect replicated in an
    independent dataset. This is the closest thing MED13L currently has to a human
    iPSC-derived neuronal model system, and it addresses the gap left by the cyclin-C
    work, which is fibroblast-only — but note it assays CRISPRi repression of the gene
    rather than patient variants, so it models dosage loss, not allele-specific effects.
  experimental_model_type: IPSC_DERIVED_MODEL
  cell_source: >-
    Human WTC11 iPSC line with dCas9-KRAB knocked into the CLYBL safe-harbour locus
    (Allen Institute), differentiated to neural progenitor cells
  culture_system: >-
    Monolayer forebrain-directed NPC differentiation (dual-SMAD inhibition), transduced
    with pooled sgRNA lentivirus in two independently differentiated biological
    replicates and read out by CROP-seq-style sgRNA-enriched single-cell RNA-seq
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  publication: PMID:39386704
  findings:
  - statement: MED13L repression alters neural cell fate and differentiation stage, replicated in an independent dataset
  evidence:
  - reference: PMID:39386704
    reference_title: "A scalable, high-throughput neural development platform identifies shared impact of ASD genes on cell fate and differentiation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Repression of ASD risk genes led to changes in topic proportions and effects of four
      genes (DEAF1, KMT2A, MED13L, and MYT1L) were validated in an independent dataset.
    explanation: >-
      MED13L is one of four genes whose neural-development effect replicated independently
      in this platform.
  - reference: PMID:39386704
    reference_title: "A scalable, high-throughput neural development platform identifies shared impact of ASD genes on cell fate and differentiation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      To identity convergent pathways in NDD genes, we optimized Perturb-seq, a method
      combining CRISPR perturbation with single-cell RNA sequencing (scRNA-seq), and
      applied structural topic modeling (STM) to simultaneously assess impact on cell fate
      and developmental stage.
    explanation: Describes the platform and the readouts available in this model system.
  notes: >-
    Preprint (bioRxiv) with a PubMed record. Recorded because it is the only human neural
    model system currently reporting a replicated MED13L effect; treat the finding as
    provisional pending peer review.
clinical_trials:
- name: NCT01238250
  phase: NOT_APPLICABLE
  status: RECRUITING
  description: >-
    Simons Searchlight is a prospective observational online registry enrolling
    individuals with rare genetic neurodevelopmental variants, including MED13L. It
    provides natural-history, developmental-milestone and behavioural data. There are
    no interventional trials in MED13L syndrome.
  target_phenotypes:
  - preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  notes: >-
    Recorded without a snippet-validated evidence item. The trial record is a
    ClinicalTrials.gov registry entry rather than a publication, and no citable source
    reports the MED13L-specific cohort size. Data are available to qualified researchers
    via SFARI Base.
external_assertions:
- name: ClinVar variant-interpretation landscape for MED13L
  source: ClinVar
  assertion_type: variant_interpretation_summary
  external_id: hgnc:22962
  url: https://www.ncbi.nlm.nih.gov/clinvar/?term=MED13L%5Bgene%5D
  description: >-
    As of 2026-07-30 ClinVar holds 1,825 MED13L variant records, of which 542 are
    pathogenic or likely pathogenic and 1,058 are of uncertain significance. The
    interpretive burden is the point: VUS outnumber P/LP roughly two to one, which is why
    the functional assays curated in `experimental_models` (protein stability and
    subcellular localisation, in utero electroporation rescue) matter clinically rather
    than only mechanistically.
  notes: >-
    Recorded without an evidence item. ClinVar is not a snippet-validated structured source
    in this repository, so these counts come from a point-in-time NCBI E-utilities query
    (`esearch db=clinvar term="MED13L[gene]"` and its clinsig-filtered variants, run
    2026-07-30) and will drift. They are recorded for scale, not as a citable assertion.
    Note the source pipeline reported different figures (1,813 total / 235 P/LP / 606 VUS)
    from an earlier snapshot; the counts above are the re-queried values.
- name: MONDO disease-gene association for MED13L syndrome
  source: MONDO
  assertion_type: disease_gene_association
  external_id: MONDO:0014773
  description: >-
    MONDO:0014773 asserts MED13L (HGNC:22962) as the causal gene, with xrefs to
    OMIM:616789 and Orphanet:369891. Used here as the named-entity-confusion preflight
    anchor confirming this entry describes MED13L and not the MED13 paralog disorder
    (MONDO:0032485).
  url: https://monarchinitiative.org/MONDO:0014773
  notes: >-
    Recorded without an evidence item: the assertion is the ontology record itself,
    verified locally with `runoak -i sqlite:obo:mondo info MONDO:0014773 -O obo`, not a
    citable publication snippet.
datasets:
- accession: "geo:GSE298801"
  title: Cardiomyocyte-specific Deletion of Med13 and Med13L Results in Dysregulated Gene Expression and Lethal Heart Failure
  description: >-
    Bulk RNA-seq from adult murine cardiomyocytes after inducible knockout of Med13 and
    Med13L. Included on the MED13L entry because it is the primary evidence for
    MED13/MED13L functional redundancy, which underpins the paralog-compensation
    hypothesis for MED13L's variable cardiac penetrance.
  organism:
    preferred_term: mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  data_type: BULK_RNA_SEQ
  sample_count: 8
  sample_types:
  - preferred_term: cardiomyocyte
    tissue_term:
      preferred_term: heart
      term:
        id: UBERON:0000948
        label: heart
  conditions:
  - Med13/Med13L cardiomyocyte-specific double knockout
  - wild-type control
  genes:
  - preferred_term: MED13
    term:
      id: hgnc:22474
      label: MED13
  - preferred_term: MED13L
    term:
      id: hgnc:22962
      label: MED13L
  publication: PMID:40989238
  findings:
  - statement: Med13 and Med13L are functionally redundant in adult cardiomyocytes
  - statement: Combined knockout causes lethal heart failure with fibrotic and calcium-handling gene dysregulation
  evidence:
  - reference: PMID:40989238
    reference_title: "Med13 and Med13L: Critical redundant players in basal cardiac function and gene expression."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Med13/13L knockout resulted in decreased cardiac function leading to lethal heart
      failure in a median timeframe of 6 weeks from the start of tamoxifen.
    explanation: >-
      Establishes the redundancy result that this dataset supports and that the
      paralog-compensation hypothesis rests on.
review_notes: >-
  Curated from an Anthropic-generated systematic-review pipeline output for MED13L that
  was held out from the dismech repository during its own generation. Every claim was
  re-derived here against PubMed abstracts under the dismech evidence policy: the
  pipeline's snippets were verbatim spans of its own review text rather than of source
  abstracts, so none were reused directly. Claims whose only support was a pipeline
  snippet not present in the cited abstract were dropped rather than reworded — notably
  the congenital-heart-defect frequency of 15/72 (20.8%) attributed to PMID:37512036,
  the hypotonia/speech/MRI frequencies of 70%/99%/45% attributed to PMID:33930262, and
  the seizure frequency of 15/68 (22%) attributed to PMID:39619418, all of which appear
  only in those papers' full text. The corresponding phenotype frequency bands here are
  instead anchored on PMID:40993520 and PMID:28645799, which state comparable figures in
  their abstracts. Four sources cited by the pipeline have no PubMed record and were
  therefore not usable under the PMID-plus-verified-snippet policy: DOI
  10.1101/2022.03.30.486486, 10.21508/1027-4065-2022-67-1-101-107, 10.4172/jpb.s2-004,
  and 10.64898/2026.06.01.729270.
references:
- reference: PMID:40228085
  title: "MED13L Syndrome."
  tags:
  - GeneReviews
  findings: []

📚

References & Deep Research

References

1

PMID:40228085

MED13L Syndrome.

No top-level findings curated for this source.

Deep Research

1

MED13L Syndrome — Anthropic systematic-review pipeline output ▸

MED13L Syndrome — Anthropic systematic-review pipeline output

Provider: Anthropic Claude systematic-review pipeline (multi-phase: literature retrieval, structured curation, claim-triple verification). Subject: MED13L syndrome (MRFACD), MONDO:0014773 Run date: 2026-06-24 (MED13) / 2026-06-23 (MED13L); artifacts received 2026-07-09. Deposited: 2026-07-30, as the source artifact for dismech PR #7186.

AI-Generated Content — Not Medical Advice. This document was generated with substantial AI assistance and is not medical advice. It is a research literature synthesis intended for scientific and educational use. It has not been independently reviewed by a licensed physician for clinical accuracy and must not be used as a substitute for professional medical advice, diagnosis, or treatment. AI systems can produce errors, including plausible-sounding statements that are incorrect; verify every claim against the cited primary literature before use.

How this artifact was used

The dismech repository was held out during this pipeline run — no sub-agent fetched or read kb/disorders/MED13_Syndrome.yaml or the rendered dismech site. The two curations are therefore independent, and their overlap is convergent evidence rather than derivation.

Critical caveat for anyone reusing this file. The pipeline's own provenance block states its evidence snippets are "verbatim spans from the post-P19 review.md, not from source abstracts". They are therefore not valid dismech evidence snippets and must not be copied into a KB entry. Every claim curated into dismech from this artifact was re-derived against PubMed abstracts (and cached full text where available) using linkml-reference-validator. Claims whose only support was a pipeline snippet absent from the cited source were dropped rather than reworded. See PR #7186 for the full list of what was dropped and why.

References here are given as DOIs; dismech requires PMIDs. 74 of 78 DOIs resolved to PubMed records; the four that did not are listed in the PR description.

Part 1 — Curation preview (DisMech format)

Description AI-GENERATED

MED13L syndrome is an autosomal dominant neurodevelopmental disorder caused by heterozygous, predominantly de novo, loss-of-function or missense variants in MED13L, which encodes a subunit of the CDK8 kinase module of the Mediator transcriptional coactivator complex. The phenotype comprises moderate intellectual disability, marked speech delay, hypotonia, a recognisable facial gestalt, and variable congenital heart defects. Missense variants are associated with a more severe presentation including epilepsy, and the disorder belongs to the broader CDK8-module Mediatorpathy spectrum.

Parents: MONDO:0002320MONDO:0015159MONDO:0100547MONDO:0100601

AI-generated mechanistic hypotheses AI-GENERATED (5)

These 5 hypotheses are the pipeline's integrative reasoning layer: each synthesises across the mechanism nodes below to propose a testable claim. Per-citation context (DisMech explanation) is collapsed under each evidence item, not shown as headline reasoning.

MED13L haploinsufficiency (dosage loss) is the primary disease mechanismCANONICALAI reasoning

Heterozygous deletion, frameshift, nonsense and canonical-splice variants reduce functional MED13L dosage below a developmental threshold, dysregulating CKM-gated Mediator transcription. Supported by the predominance of LoF alleles in patients, the recognisable phenotype across deletion and truncating cases, and recapitulation in Med13l+/- mice with embryonic lethality of the null.

Applies to: LoF (deletion/truncating/splice)

Evidence: for 4 · against 1

4 supporting citations

“Results: The 17 kb out-of-frame de novo deletion encompassing exon 2 of MED13L (MIM *608771) in patient 56366, together with overlapping cases, were instrumental to define a recognisable haploinsufficiency syndrome that we reported and discussed in detail elsewhere.” de novo intragenic deletion defines recognisable haploinsufficiency syndrome literature · 10.1136/jmedgenet-2014-102588

“The first patient has a de novo mutation in the splice acceptor site of exon 5 of MED13L. cDNA analysis showed this mutation results in an in-frame deletion, removing 15 amino acids in middle of the conserved MED13L N-terminal domain.” splice and exonic deletion alleles confirm haploinsufficiency phenotype literature · 10.1038/ejhg.2014.69

“Results: Due to embryonic lethality, we characterize the Med13l heterozygous germline deletion (Figure 1E).” Med13l null is embryonic lethal; heterozygote phenocopies syndrome literature · 10.1002/dvdy.70079

“Congenital cardiac and neurodevelopmental deficits have been recently linked to the mediator complex subunit 13-like protein MED13L, a subunit of the CDK8-associated mediator complex that functions in transcriptional regulation through DNA-binding transcription factors and RNA polymerase II.” haploinsufficiency causes the cardiac+neurodevelopmental phenotype literature · 10.1038/ejhg.2015.26

1 contrary citation

“We found that patients carrying missense mutations had more frequently epilepsy and showed a more severe phenotype.” missense carriers show a more severe phenotype than expected from pure dosage loss literature · 10.1007/s10048-018-0541-0

Subset of recurrent missense variants act via dominant-negative or neomorphic gain-of-functionEMERGINGAI reasoning

Recurrent missense variants (notably p.Pro869Ser) retain stable nuclear expression yet associate with a more severe, epilepsy-enriched phenotype than truncating alleles, consistent with a dominant-negative or neomorphic effect on the assembled CKM rather than simple dosage loss.

Applies to: missense (exon-15 hotspot, C-terminal)

Evidence: for 3 · against 2

3 supporting citations

“Discussion: We observed that the p.Pro866Leu mutant variant shared similarities with the other studied variants—p.Cys1131Tyr, p.Gly1899Arg, and p.Thr2162Met—with cytoplasmic localization and protein instability, consistent with a loss-of-function pathogenic mechanism, while p.Pro869Ser exhibited more stable protein expression and partial nuclear localization, closely resembling the WT condition, arguing for the dominant-negative effect of the mutant protein or the possibility of a neomorphic effect with dominant or semi-dominant properties.” p.Pro869Ser stable+nuclear, arguing for dominant-negative/neomorphic effect literature · 10.1016/j.xhgg.2025.100467

“We found that patients carrying missense mutations had more frequently epilepsy and showed a more severe phenotype.” missense → more frequent epilepsy and more severe phenotype literature · 10.1007/s10048-018-0541-0

“Discussion: Our case further demonstrates that Pro869Ser is a hotspot mutation of the MED13L gene.” Pro869Ser is a recurrent hotspot mutation literature · 10.1186/s13052-020-00847-y

2 contrary citations

“Discussion: We observed that the p.Pro866Leu mutant variant shared similarities with the other studied variants—p.Cys1131Tyr, p.Gly1899Arg, and p.Thr2162Met—with cytoplasmic localization and protein instability, consistent with a loss-of-function pathogenic mechanism, while p.Pro869Ser exhibited more stable protein expression and partial nuclear localization, closely resembling the WT condition, arguing for the dominant-negative effect of the mutant protein or the possibility of a neomorphic effect with dominant or semi-dominant properties.” four other missense variants behave as LoF (cytoplasmic, unstable) literature · 10.1016/j.xhgg.2025.100467

“Notably, our in silico modelling predicted this missense mutation to decrease the stability of an alpha-helix and thereby affecting the MED13L secondary structure, while the majority of published missense mutations remain variants of uncertain significance.” missense variant predicted to destabilise structure (LoF-like) literature · 10.1016/j.ejmg.2017.06.004

MED13L missense variants cause isolated dextro-transposition of the great arteriesREFUTEDAI reasoning

The founding 2003 PROSIT240 study reported MED13L missense variants in 3/97 isolated d-TGA patients, proposing MED13L as a conotruncal-CHD gene. Subsequent syndromic cohorts show low CHD penetrance, no isolated-d-TGA enrichment, and the original missense alleles are now classified as VUS — the association has not replicated and is regarded as the historical entry point to the gene.

Applies to: isolated d-TGA

Evidence: for 1 · against 3

1 supporting citation

“In addition, we identify as Mediator-associated proteins the CDK8-like cyclin-dependent kinase CDK11 and the TRAP240-like KIAA1025 protein (MED13L), which is mutated in patients with the congenital heart defect transposition of the great arteries (TGA).” MED13L (KIAA1025) noted as mutated in TGA patients (citing the founding study) literature · 10.1016/j.molcel.2004.05.006

3 contrary citations

“Congenital cardiac and neurodevelopmental deficits have been recently linked to the mediator complex subunit 13-like protein MED13L, a subunit of the CDK8-associated mediator complex that functions in transcriptional regulation through DNA-binding transcription factors and RNA polymerase II.” redefinition of MED13L syndrome as a neurodevelopmental haploinsufficiency disorder; cardiac defects variable literature · 10.1038/ejhg.2015.26

“Notably, our in silico modelling predicted this missense mutation to decrease the stability of an alpha-helix and thereby affecting the MED13L secondary structure, while the majority of published missense mutations remain variants of uncertain significance.” majority of published missense variants remain VUS literature · 10.1016/j.ejmg.2017.06.004

“The first patient has a de novo mutation in the splice acceptor site of exon 5 of MED13L. cDNA analysis showed this mutation results in an in-frame deletion, removing 15 amino acids in middle of the conserved MED13L N-terminal domain.” LoF alleles cause syndromic ID, not isolated d-TGA literature · 10.1038/ejhg.2014.69

MED13 paralogue partially compensates for MED13L loss (and vice versa)EMERGINGAI reasoning

MED13 and MED13L are mutually exclusive in the CKM and show compensatory upregulation in knockout models, buffering some MED13L-dependent functions; incomplete compensation may explain variable expressivity (e.g. cardiac penetrance) and is a candidate therapeutic axis.

Applies to: all

Evidence: for 3 · against 2

3 supporting citations

“The difference between these two phenotypes may be explained by the compensatory upregulation of Med13l , a Med13 paralog, which develops in MED13 KOs during a rather long transcriptionally active stage of oocyte growth. However, postimplantation development is not rescued by MED13L [ 31 ].” Med13l compensatorily upregulates in MED13 KOs during oocyte growth literature · 10.3390/ijms24119330

“Clones generated for cryo-EM: However, probably because CH12 cells also express med13L , this strategy did not improve the purification and thus was unnecessary and omitted in other mutants.” MED13L expression buffers MED13 knockout in CH12 cells literature · 10.1016/j.cell.2019.07.011

“Interestingly, 3 subunits of the kinase module have undergone independent gene duplications in vertebrates to generate the paralog pairs MED12/MED12L, MED13/ MED13L, and CDK8/CDK19.” MED13/MED13L are vertebrate paralogue pair from independent gene duplication literature · 10.4172/jpb.s2-004

2 contrary citations

“The difference between these two phenotypes may be explained by the compensatory upregulation of Med13l , a Med13 paralog, which develops in MED13 KOs during a rather long transcriptionally active stage of oocyte growth. However, postimplantation development is not rescued by MED13L [ 31 ].” MED13L does not rescue postimplantation development in MED13 KO literature · 10.3390/ijms24119330

“Results: The preponderance of MED13 crosslinks over MED13L ones is likely explained by a report indicating that MED13 preferentially associates with CKM-MED, while MED13L is present in complexes that also contain MED26 35 .” MED13 preferentially associates with CKM-MED while MED13L is in MED26-containing complexes (non-equivalent roles) literature · 10.1016/j.molcel.2024.06.006

Aberrant cytoplasmic cyclin C release drives mitochondrial fragmentation contributing to neuronal dysfunctionEMERGINGAI reasoning

Loss of the MED13L nuclear anchor releases cyclin C to the cytoplasm in unstressed patient fibroblasts, triggering mitochondrial fission, reduced respiration and ATP output; if operative in neurons this would link MED13L haploinsufficiency to a metabolic component of the ID phenotype.

Applies to: LoF (deletion/truncating/splice)

Evidence: for 3 · against 2

3 supporting citations

“Cyclin C exhibits aberrant cytoplasmic localization in unstressed MED13L S1497 F/fs fibroblasts: MED13L +/ fs cells exhibit cyclin C nuclear release and mitochondrial dysfunction” MED13L+/fs fibroblasts show cytoplasmic cyclin C and mitochondrial dysfunction literature · 10.1016/j.isci.2022.103823

“5.4. Diseases Associated with MED13 Biology: In MED13L, mutant fibroblast cyclin C is aberrantly released into the cytoplasm, leading to mitochondrial fragmentation and increased mitochondrial dysfunction [ 303 ].” cyclin C release leads to mitochondrial fragmentation in MED13L mutant fibroblasts literature · 10.3390/cells14090636

“MED13L syndrome mechanism: It is hypothesized that in MED13L Haploinsufficiency Syndrome, the transcriptional process related to the mediator complex interaction with RNA polymerase II may be disrupted. Cyclin C is aberrantly released into the cytoplasm, increasing susceptibility to cell death through mitochondrial fragmentation, decreased oxygen consumption as well as decreased ATP production. 50 , 53” cyclin C release decreases oxygen consumption and ATP production literature · 10.1177/26330040241290252

2 contrary citations

Pathophysiology AI-CURATED (6 mechanism nodes)

mn-ckm-hinge high

MED13L (with its paralogue MED13) is the physical hinge of the Mediator CDK8 kinase module (CKM): it carries an Argonaute-like fold whose large intrinsically disordered region forms the sole CKM contact with core Mediator and sterically occludes the RNA Pol II / MED26 binding surface, so MED13L abundance and integrity gate reversible CKM-core docking and the switch between Mediator's repressive and activating states.

Causes →: mn-haploinsufficiencymn-fbw7-turnover

Genes: HGNC:22962HGNC:22474HGNC:11957HGNC:1779HGNC:1581

Gene products: MED13LMED13MED12CDK8Cyclin C

GO process: GO:0006366

GO function: GO:0003713

Complexes: CKM (CDK8 kinase module)Mediator complex

Structures: AF-Q71F56-F1

5 evidence

“The structure of the dissociable CKM: Despite exhibiting low sequence homology to classical Argonaute (Ago) proteins, the Med13 possesses an Ago-like architecture, comprising four globular domains (N, PAZ, MID and PIWI) and two linker domains (L1 and L2) ( Figure 3d )[ 42 ].” MED13/MED13L has Argonaute-like four-domain architecture forming the CKM hinge literature · 10.1016/j.sbi.2024.102892

“Architecture of human CKM: Notably, MED13 harbors a large and unique insertion between its PAZ and L2 domains, corresponding to its large IDR (residues 350 – 1069) ( Figures 2A and 2C ).” MED13 IDR occludes Pol II/MED26 binding surface on core Mediator literature · 10.1016/j.molcel.2024.09.001

“Kinase module function and regulation The Mediator kinase module (~430 kDa in yeast; ~560 kDa in humans) is nominally comprised of four subunits: MED13, MED12, CycC and CDK8, with paralogs of all but CycC identified in humans and some vertebrates (discussed below) ( Borggrefe et al. , 2002 ; Bourbon, 2008 ; Hengartner et al. , 1995 ; Sato et al. , 2004 ).” kinase module = MED13/MED12/CycC/CDK8 with vertebrate paralogues literature · 10.3109/10409238.2015.1064854

“Congenital cardiac and neurodevelopmental deficits have been recently linked to the mediator complex subunit 13-like protein MED13L, a subunit of the CDK8-associated mediator complex that functions in transcriptional regulation through DNA-binding transcription factors and RNA polymerase II.” MED13L is a CDK8-associated Mediator subunit linked to cardiac and neurodevelopmental deficits literature · 10.1038/ejhg.2015.26

AlphaFold model for UniProt:Q71F56 (MED13L, mediator complex subunit 13L) structure of MED13L database · alphafold · AF-Q71F56-F1

mn-haploinsufficiency high

Heterozygous loss-of-function alleles (whole-gene/intragenic deletions, frameshift, nonsense, canonical splice) halve functional MED13L dosage, reducing the pool of intact CKM available to dock with core Mediator and dysregulating Pol II-dependent transcriptional programmes during development. Heterozygous deletion is sufficient to produce the phenotype in mouse, while homozygous loss is embryonic lethal.

Causes →: mn-neurodev-transcriptionmn-ncc-cardiac

Genes: HGNC:22962

Gene products: MED13L

GO process: GO:0006366GO:0006357

Complexes: CKM (CDK8 kinase module)

5 evidence

“Results: The 17 kb out-of-frame de novo deletion encompassing exon 2 of MED13L (MIM *608771) in patient 56366, together with overlapping cases, were instrumental to define a recognisable haploinsufficiency syndrome that we reported and discussed in detail elsewhere.” de novo intragenic deletion defines a recognisable haploinsufficiency syndrome literature · 10.1136/jmedgenet-2014-102588

“The first patient has a de novo mutation in the splice acceptor site of exon 5 of MED13L. cDNA analysis showed this mutation results in an in-frame deletion, removing 15 amino acids in middle of the conserved MED13L N-terminal domain.” de novo splice/exonic LoF variants confirm haploinsufficiency literature · 10.1038/ejhg.2014.69

“Results: Due to embryonic lethality, we characterize the Med13l heterozygous germline deletion (Figure 1E).” homozygous Med13l KO is embryonic lethal; heterozygous mice model the syndrome literature · 10.1002/dvdy.70079

“MED13L syndrome mechanism: It is hypothesized that in MED13L Haploinsufficiency Syndrome, the transcriptional process related to the mediator complex interaction with RNA polymerase II may be disrupted. Cyclin C is aberrantly released into the cytoplasm, increasing susceptibility to cell death through mitochondrial fragmentation, decreased oxygen consumption as well as decreased ATP production. 50 , 53” haploinsufficiency disrupts Mediator–Pol II transcription and cyclin C retention literature · 10.1177/26330040241290252

pLI=1; LOEUF=0.060; mis_z=6.46 extreme LoF constraint consistent with haploinsufficiency database · gnomad · gene/MED13L

mn-missense-destabilisation medium

Recurrent missense variants clustering in conserved domains (notably exon 15 hotspot p.Pro866Leu/p.Pro869Ser and C-terminal residues) destabilise MED13L secondary structure, drive cytoplasmic mislocalisation, and impair dendritic growth in cortical neurons; most behave as loss-of-function, but at least p.Pro869Ser retains nuclear localisation and stable expression consistent with a dominant-negative or neomorphic effect, and missense carriers show a more severe phenotype with epilepsy.

Causes →: mn-neurodev-transcription

Genes: HGNC:22962

Gene products: MED13L

GO process: GO:0048813

4 evidence

“Notably, our in silico modelling predicted this missense mutation to decrease the stability of an alpha-helix and thereby affecting the MED13L secondary structure, while the majority of published missense mutations remain variants of uncertain significance.” in silico modelling predicts alpha-helix destabilisation by missense variant literature · 10.1016/j.ejmg.2017.06.004

“In overexpression assays using cortical neurons from embryonic mouse cerebral cortices transduced by in utero electroporation-mediated gene transfer, we found that mouse orthologues of human MED13L-p.P866L and -p.T2162M missense variants accumulated in the nucleus, while the p.S2163L and p.S2177Y variants were diffusely distributed in the cytoplasm.” missense variants alter nuclear/cytoplasmic localisation and impair dendritic growth in mouse cortical neurons literature · 10.1111/jnc.15783

“Discussion: We observed that the p.Pro866Leu mutant variant shared similarities with the other studied variants—p.Cys1131Tyr, p.Gly1899Arg, and p.Thr2162Met—with cytoplasmic localization and protein instability, consistent with a loss-of-function pathogenic mechanism, while p.Pro869Ser exhibited more stable protein expression and partial nuclear localization, closely resembling the WT condition, arguing for the dominant-negative effect of the mutant protein or the possibility of a neomorphic effect with dominant or semi-dominant properties.” four missense variants show cytoplasmic mislocalisation/instability (LoF); p.Pro869Ser stable+nuclear (possible DN/neomorph) literature · 10.1016/j.xhgg.2025.100467

“We found that patients carrying missense mutations had more frequently epilepsy and showed a more severe phenotype.” missense carriers have more frequent epilepsy and a more severe phenotype literature · 10.1007/s10048-018-0541-0

mn-fbw7-turnover high

SCF(FBW7) ubiquitin ligase recognises a CDK8/19-primed phosphodegron on MED13/MED13L and targets both paralogues for proteasomal degradation, providing the only known E3-ligase control of MED13L abundance and thereby the kinetics of CKM dissociation from core Mediator.

Causes →: mn-haploinsufficiency

Genes: HGNC:22962HGNC:16712HGNC:22474HGNC:1779HGNC:19338

Gene products: FBW7 (FBXW7)MED13LMED13

GO process: GO:0006511

Complexes: SCF(FBW7) E3 ubiquitin ligaseCKM (CDK8 kinase module)

2 evidence

“We show that Fbw7, a tumor suppressor and ubiquitin ligase, binds to CDK8-Mediator and targets MED13/13L for degradation.” Fbw7 binds CDK8-Mediator and targets MED13/13L for degradation literature · 10.1101/gad.207720.112

“The Clurman lab demonstrated that MED13 and its paralog MED13L are ubiquitylated by the ubiquitin ligase FBW7, and this modification regulates MED13 and MED13L abundance and stability (Davis et al ., 2013 ).” FBW7 ubiquitylation regulates MED13/MED13L abundance and stability literature · 10.3109/10409238.2013.840259

mn-neurodev-transcription high

Reduced or dysfunctional MED13L dysregulates RNA Pol II-dependent neurodevelopmental gene programmes, impairing cortical neurogenesis, radial migration, dendrite outgrowth and callosal axon projection, providing the cellular substrate for intellectual disability, speech impairment and hypotonia.

Causes →: []

Genes: HGNC:22962

Gene products: MED13L

GO process: GO:0021987GO:0048813GO:0006366

3 evidence

“Med13l KO impairs cortical neurogenesis and dendrite development.” Med13l KO impairs cortical neurogenesis and dendrite development literature · 10.1038/s42003-025-08532-8

“In overexpression assays using cortical neurons from embryonic mouse cerebral cortices transduced by in utero electroporation-mediated gene transfer, we found that mouse orthologues of human MED13L-p.P866L and -p.T2162M missense variants accumulated in the nucleus, while the p.S2163L and p.S2177Y variants were diffusely distributed in the cytoplasm.” MED13L missense variants impair dendritic growth in mouse cortical neurons literature · 10.1111/jnc.15783

“Discussion: Functional validation experiments showed that overexpression of PlxnA4 partially rescued both the radial migration and callosal projection defects in Med13-silencing neurons, establishing PlxnA4 as a critical downstream effector of Med13 for these two processes.” Med13 silencing impairs radial migration and callosal projection (paralogue evidence) literature · 10.1038/s42003-026-09704-w

mn-ncc-cardiac medium

MED13L dosage reduction perturbs neural-crest-dependent cardiac outflow-tract morphogenesis, yielding the variable conotruncal and septal congenital heart defects observed in a minority of patients; supported by neural-crest defects in CKM-mutant zebrafish and craniofacial anomalies in Med13l heterozygous mice.

Causes →: []

Genes: HGNC:22962HGNC:11957

Gene products: MED13L

GO process: GO:0061308GO:0007507

3 evidence

“Congenital cardiac and neurodevelopmental deficits have been recently linked to the mediator complex subunit 13-like protein MED13L, a subunit of the CDK8-associated mediator complex that functions in transcriptional regulation through DNA-binding transcription factors and RNA polymerase II.” congenital cardiac and neurodevelopmental deficits linked to MED13L literature · 10.1038/ejhg.2015.26

“Homozygous kto mutant zebrafish embryos show defects in brain, neural crest, and kidney development and die at approximately 6 days postfertilization.” CKM (med12) mutant zebrafish embryos show neural-crest defects literature · 10.1073/pnas.0509457102

“Conclusions and Discussion: We classify a Med13l HET mouse model as a possible resource to begin deciphering the correlation between mutations and phenotypes.” Med13l HET mouse recapitulates craniofacial anomalies (neural-crest-derived) literature · 10.1002/dvdy.70079

Genetic (1)

4 evidence

“The paper describes three clinical cases of MED13L-associated intellectual disability with an autosomal dominant inheritance.” MED13L-associated ID with autosomal dominant inheritance literature · 10.21508/1027-4065-2022-67-1-101-107

“Results: The 17 kb out-of-frame de novo deletion encompassing exon 2 of MED13L (MIM *608771) in patient 56366, together with overlapping cases, were instrumental to define a recognisable haploinsufficiency syndrome that we reported and discussed in detail elsewhere.” de novo MED13L deletion is causal literature · 10.1136/jmedgenet-2014-102588

“The first patient has a de novo mutation in the splice acceptor site of exon 5 of MED13L. cDNA analysis showed this mutation results in an in-frame deletion, removing 15 amino acids in middle of the conserved MED13L N-terminal domain.” de novo splice-site MED13L variant is causal literature · 10.1038/ejhg.2014.69

symbol=MED13L; name='mediator complex subunit 13L'; uniprot=Q71F56; ensembl=ENSG00000123066 gene identity database · hgnc · HGNC:22962 |

Variants

1 evidence

total=1813; P/LP=235; VUS=606 variant census database · clinvar · gene=MED13L |

1 evidence

“Discussion: We observed that the p.Pro866Leu mutant variant shared similarities with the other studied variants—p.Cys1131Tyr, p.Gly1899Arg, and p.Thr2162Met—with cytoplasmic localization and protein instability, consistent with a loss-of-function pathogenic mechanism, while p.Pro869Ser exhibited more stable protein expression and partial nuclear localization, closely resembling the WT condition, arguing for the dominant-negative effect of the mutant protein or the possibility of a neomorphic effect with dominant or semi-dominant properties.” p.Pro866Leu shows cytoplasmic localisation and protein instability (LoF mechanism) literature · 10.1016/j.xhgg.2025.100467 |

2 evidence

“Discussion: Our case further demonstrates that Pro869Ser is a hotspot mutation of the MED13L gene.” Pro869Ser is a recurrent hotspot mutation literature · 10.1186/s13052-020-00847-y

“Discussion: We observed that the p.Pro866Leu mutant variant shared similarities with the other studied variants—p.Cys1131Tyr, p.Gly1899Arg, and p.Thr2162Met—with cytoplasmic localization and protein instability, consistent with a loss-of-function pathogenic mechanism, while p.Pro869Ser exhibited more stable protein expression and partial nuclear localization, closely resembling the WT condition, arguing for the dominant-negative effect of the mutant protein or the possibility of a neomorphic effect with dominant or semi-dominant properties.” p.Pro869Ser stable nuclear expression, possible dominant-negative/neomorphic literature · 10.1016/j.xhgg.2025.100467 |

1 evidence

“As depicted in Figure 2A , a heterozygous stop-gain variant of MED13L c.5278C > T (p.Arg1760 ∗ ) was detected in a female newborn diagnosed with spina bifida.” heterozygous stop-gain p.Arg1760* identified in spina bifida newborn literature · 10.3389/fcell.2021.641831 |

1 evidence

“Results: The 17 kb out-of-frame de novo deletion encompassing exon 2 of MED13L (MIM *608771) in patient 56366, together with overlapping cases, were instrumental to define a recognisable haploinsufficiency syndrome that we reported and discussed in detail elsewhere.” 17 kb out-of-frame de novo deletion of exon 2 defines the haploinsufficiency syndrome literature · 10.1136/jmedgenet-2014-102588 |

Inheritance (1)

| HP:0000006 | Autosomal dominant inheritance | complete (assumed; no non-penetrant carriers reported) | variable — wide intrafamilial variability documented; missense (esp. exon 15/17) carriers tend to a more severe phenotype than PTV carriers |

3 evidence

“, Variants are primarily de novo, autosomal dominant, and considered to be loss-of-function (LoF); thus, MED13L syndrome is historically considered a haploinsufficiency syndrome.” literature · 10.1177/26330040241290252

“Sixteen of 17 variants were de novo, with inferred germline mosaicism for the two families with affected siblings (Table ).” literature · 10.1186/s11689-025-09645-1

“Results: 1). We identified the presence of the MED13L mutation in ∼30%–50% of the sperm cells (predicted on the basis of the peak heights on the sequencing electropherograms) accountable for a high recurrence risk in the couple's future pregnancies and advised on either preimplantation genetic diagnosis or insemination with donor sperm cells.” literature · 10.1101/mcs.a006124 |

Phenotypes (22 HPO)

| HPO | Label | Freq | Sev | Dx | Evidence |

| HP:0001249 | Intellectual disability | 36/36 (100%) | moderate | ✓ |

2 evidence

“All patients presented with intellectual disability and severe language impairment.” literature · 10.1007/s10048-018-0541-0

“Neurodevelopmental evaluation: ID severity was classified in 30 of 41 patients with 23% classified as mild, 47% as moderate, and 30% as severe to profound (Table 1).” literature · 10.1186/s11689-025-09618-4 |

| HP:0001263 | Global developmental delay | 8/8 (100%) | moderate | ✓ |

3 evidence

“Phenotypically, they all had intellectual disability, speech and motor delay, and features of the mouth (open mouth appearance, macroglossia, and/or macrostomia).” literature · 10.1016/j.ejmg.2018.06.014

“MED13L syndrome clinical symptoms: Minimal or absent speech and impaired motor capabilities dominate the presentation of global developmental delay, with 99% (81/82) and 98% (80/82) of individuals presenting with minimal/absent speech or impaired motor capabilities, respectively.” literature · 10.1177/26330040241290252

frequency=HP:0040281; evidence=PCS phenotype.hpoa annotation database · hpoa · OMIM:616789|HP:0001263 |

| HP:0000750 | Delayed speech and language development | 81/82 (99%) | severe | ✓ |

3 evidence

“MED13L syndrome clinical symptoms: Minimal or absent speech and impaired motor capabilities dominate the presentation of global developmental delay, with 99% (81/82) and 98% (80/82) of individuals presenting with minimal/absent speech or impaired motor capabilities, respectively.” literature · 10.1177/26330040241290252

“Discussion: Hypotonia, speech delay and brain abnormalities in MRI are quite common among these patients (70%, 99% and 45%, respectively).” literature · 10.34763/jmotherandchild.20202403.2021.d-20-00003

frequency=HP:0040281; evidence=TAS phenotype.hpoa annotation database · hpoa · ORPHA:369891|HP:0000750 |

1 evidence

“Almost all individuals (97%) from the full cohort of 67 reported a diagnosis of language disorder during the developmental history interview, with about a third of children described by their caregivers as minimally verbal or nonverbal beyond the age of 4 years.” literature · 10.1186/s11689-025-09645-1 |

| HP:0001270 | Motor delay | 80/82 (98%) | moderate | ✓ |

3 evidence

“MED13L syndrome clinical symptoms: Minimal or absent speech and impaired motor capabilities dominate the presentation of global developmental delay, with 99% (81/82) and 98% (80/82) of individuals presenting with minimal/absent speech or impaired motor capabilities, respectively.” literature · 10.1177/26330040241290252

“[SECTION: Motor evaluation] There was no significant difference in the mean age of walking between patients in the GenIDA series ( n = 41) and those in the literature series ( n = 65) with ages of 28 and 27 (SD = 6.59) months, respectively.” literature · 10.1186/s11689-025-09618-4

frequency=HP:0040281; evidence=PCS phenotype.hpoa annotation database · hpoa · OMIM:616789|HP:0001270 |

| HP:0001290 | Generalized hypotonia | 70% | moderate | ✓ |

2 evidence

“Discussion: Hypotonia, speech delay and brain abnormalities in MRI are quite common among these patients (70%, 99% and 45%, respectively).” literature · 10.34763/jmotherandchild.20202403.2021.d-20-00003

frequency=n/a; evidence=TAS phenotype.hpoa annotation database · hpoa · OMIM:616789|HP:0001290 |

3 evidence

“Case presentation: Behavioral difficulties, such as self-harm and autistic features, were seen in 55.6% of the patients.” literature · 10.1186/s13052-020-00847-y

“Compared with the overall incidence in all MED13L-related patients summarized by Torring et al. and Smol et al., patients with missense mutations have a higher incidence of seizures (44.4% vs 16%), MRI abnormalities (66.7% vs 45%) and autistic features (55.6% vs 23%)” literature · 10.1186/s13052-020-00847-y

frequency=HP:0040282; evidence=TAS phenotype.hpoa annotation database · hpoa · ORPHA:369891|HP:0000729 |

| HP:0000708 | Atypical behavior | 55.6% | | |

2 evidence

“Case presentation: Behavioral difficulties, such as self-harm and autistic features, were seen in 55.6% of the patients.” literature · 10.1186/s13052-020-00847-y

frequency=HP:0040282; evidence=TAS phenotype.hpoa annotation database · hpoa · ORPHA:369891|HP:0000708 |

| HP:0001250 | Seizure | 15/68 (22%) | | |

2 evidence

“Documented seizure presence is about 22% (15/68) in publications. 2 , 8 , 10 , 27 , 32 , 37 , 38 Of these, 17 individuals with missense variants are evaluated, with 10 having seizures. 10 , 39 Most seizure types are not characterized, though absence seizures ( n = 3) are most common. 8 , 32 , 38 The average age of individuals with reported seizures is 12 years.” literature · 10.1177/26330040241290252

“Compared with the overall incidence in all MED13L-related patients summarized by Torring et al. and Smol et al., patients with missense mutations have a higher incidence of seizures (44.4% vs 16%), MRI abnormalities (66.7% vs 45%) and autistic features (55.6% vs 23%)” literature · 10.1186/s13052-020-00847-y |

| HP:0001251 | Ataxia | 20–50% | | |

2 evidence

“Further common signs include abnormal MRI findings of myelination defects and abnormal corpus callosum, ataxia and coordination problems, autistic features, seizures/abnormal EEG, or congenital heart defects, present in about 20-50% of the patients.” literature · 10.1016/j.ejmg.2017.06.004

frequency=HP:0040283; evidence=PCS phenotype.hpoa annotation database · hpoa · OMIM:616789|HP:0001251 |

| HP:0012443 | Abnormal brain morphology | 45% | | |

2 evidence

“Discussion: Hypotonia, speech delay and brain abnormalities in MRI are quite common among these patients (70%, 99% and 45%, respectively).” literature · 10.34763/jmotherandchild.20202403.2021.d-20-00003

“Further common signs include abnormal MRI findings of myelination defects and abnormal corpus callosum, ataxia and coordination problems, autistic features, seizures/abnormal EEG, or congenital heart defects, present in about 20-50% of the patients.” literature · 10.1016/j.ejmg.2017.06.004 |

| HP:0001627 | Abnormal heart morphology | 15/72 (20.8%) | | |

3 evidence

“[4. Discussion] The congenital heart defects, previously highlighted as one of the main features of MED13L haploinsufficiency syndrome, were diagnosed in only 15 (20.8%) individuals (Supplementary Table S2).” literature · 10.3390/medicina59071225

“Congenital heart defects 12/64 –” literature · 10.34763/jmotherandchild.20202403.2021.d-20-00003

frequency=HP:0040283; evidence=TAS phenotype.hpoa annotation database · hpoa · ORPHA:369891|HP:0001627 |

| HP:0000414 | Bulbous nose | 75% | mild | ✓ |

2 evidence

“Common dysmorphic features, seen in at least 50%, are bulbous nasal tip (75%), open mouth appearance (62%), low set ears (52%), and depressed/broad nasal bridge (58%).” literature · 10.1016/j.ejmg.2018.06.014

frequency=HP:0040282; evidence=TAS phenotype.hpoa annotation database · hpoa · OMIM:616789|HP:0000414 |

| HP:0000194 | Open mouth | 62% | mild | ✓ |

3 evidence

“Common dysmorphic features, seen in at least 50%, are bulbous nasal tip (75%), open mouth appearance (62%), low set ears (52%), and depressed/broad nasal bridge (58%).” literature · 10.1016/j.ejmg.2018.06.014

“the syndrome may be suspected in some individuals based on the association of developmental delay, speech impairment, bulbous nasal tip, and macroglossia, macrostomia, or open mouth appearance.” literature · 10.1016/j.ejmg.2018.06.014

frequency=HP:0040282; evidence=PCS phenotype.hpoa annotation database · hpoa · OMIM:616789|HP:0000194 |

| HP:0000369 | Low-set ears | 52% | mild | |

2 evidence

“Common dysmorphic features, seen in at least 50%, are bulbous nasal tip (75%), open mouth appearance (62%), low set ears (52%), and depressed/broad nasal bridge (58%).” literature · 10.1016/j.ejmg.2018.06.014

frequency=HP:0040282; evidence=PCS phenotype.hpoa annotation database · hpoa · OMIM:616789|HP:0000369 |

| HP:0005280 | Depressed nasal bridge | 58% | mild | |

2 evidence

“Common dysmorphic features, seen in at least 50%, are bulbous nasal tip (75%), open mouth appearance (62%), low set ears (52%), and depressed/broad nasal bridge (58%).” literature · 10.1016/j.ejmg.2018.06.014

frequency=HP:0040283; evidence=TAS phenotype.hpoa annotation database · hpoa · OMIM:616789|HP:0005280 |

| HP:0000341 | Narrow forehead | | | |

1 evidence

frequency=n/a; reference=PMID:25758992; evidence_code=PCS HPO annotation file database · hpoa · OMIM:616789|HP:0000341 |

| HP:0002465 | Poor speech | | | |

1 evidence

frequency=n/a; reference=OMIM:616789; evidence_code=TAS HPO annotation file database · hpoa · OMIM:616789|HP:0002465 |

| HP:0000582 | Upslanted palpebral fissure | | | |

1 evidence

frequency=n/a; reference=OMIM:616789; evidence_code=TAS HPO annotation file database · hpoa · OMIM:616789|HP:0000582 |

| HP:0002342 | Moderate intellectual disability | | | |

1 evidence

frequency=n/a; reference=PMID:25167861; evidence_code=PCS HPO annotation file database · hpoa · OMIM:616789|HP:0002342 |

| HP:0000486 | Strabismus | | | |

1 evidence

frequency=n/a; reference=OMIM:616789; evidence_code=TAS HPO annotation file database · hpoa · OMIM:616789|HP:0000486 |

| HP:0003593 | Infantile onset | | | |

1 evidence

frequency=n/a; reference=OMIM:616789; evidence_code=TAS HPO annotation file database · hpoa · OMIM:616789|HP:0003593 |

Diagnosis (4)

| MAXO:0001612 | chromosomal microarray testing | Normal in most; detects 12q24.21 intragenic deletions/duplications in the CNV-associated subset; ACMG-recommended first-tier ID test. | 12q24.21 CNV, MED13L intragenic deletion |

2 evidence

“A chromosomal microarray, as recommended by the American College of Medical Genetics (ACMG), had been previously conducted and was found to be normal, prompting the decision to proceed with WES.” literature · 10.7759/cureus.59904

“Using high resolution molecular karyotyping, we identified two intragenic de novo frameshift deletions, likely resulting in haploinsufficiency, in two patients with a similar phenotype of hypotonia, moderate ID, conotruncal heart defect and facial anomalies.” literature · 10.1038/ejhg.2013.17 |

| MAXO:0009004 | clinical whole-exome sequencing | Heterozygous de novo MED13L pathogenic variant (PTV, intragenic CNV, or recurrent missense); trio confirmation of de novo status anchors PS2 pathogenicity. | MED13L (NM_015335.5) PTV, MED13L missense (exon 15/17 cluster), de novo status |

2 evidence

“A six-year-old male patient presenting with heart malformation, ID, and hypotonia was further examined using whole exome sequencing of genomic DNA extracted from a peripheral blood sample.” literature · 10.1016/j.isci.2022.103823

“However, due to some similarity to other syndromes with ID such as FG syndrome caused by MED12 mutation, 1p36 deletion syndrome or 22q11.2 deletion syndrome and proved variable clinical expression, the use of NGS is recommended for disease differential diagnosis. 6 , 7 Key points Pathogenic variants in MED13L are common in the autosomal dominant form of syndromic intellectual disability.” literature · 10.34763/jmotherandchild.20202403.2021.d-20-00003 |

| MAXO:0010203 | echocardiography | Normal in ~80%; detects conotruncal CHD (d-TGA, VSD, persistent foramen ovale) in 19–21%; baseline echocardiogram recommended at diagnosis. | VSD, d-TGA, conotruncal defect |

2 evidence

“echocardiography showed ventricular septal defect” literature · 10.7499/j.issn.1008-8830.2017.10.010

“[4. Discussion] The congenital heart defects, previously highlighted as one of the main features of MED13L haploinsufficiency syndrome, were diagnosed in only 15 (20.8%) individuals (Supplementary Table S2).” literature · 10.3390/medicina59071225 |

| MAXO:0000932 | electroencephalography | Abnormal in ~20–50% (epileptiform discharges including spike-and-slow-wave) even without clinical seizures; higher yield in missense carriers. | spike-and-slow-wave, absence seizures |

2 evidence

“She had no clinically observed seizures but had abnormal EEG showing spike and slow wave colligation and multi-spike and slow waves in the bilateral occipital and posterior temporal regions, as well as rapid rhythm distribution in the occipital area (Fig. 2 ).” literature · 10.1186/s13052-020-00847-y

“Documented seizure presence is about 22% (15/68) in publications. 2 , 8 , 10 , 27 , 32 , 37 , 38 Of these, 17 individuals with missense variants are evaluated, with 10 having seizures. 10 , 39 Most seizure types are not characterized, though absence seizures ( n = 3) are most common. 8 , 32 , 38 The average age of individuals with reported seizures is 12 years.” literature · 10.1177/26330040241290252 |

Differential diagnoses (5)

| MONDO:0011929 | chromosome 1p36 deletion syndrome | Overlapping straight eyebrows, deep-set eyes, midface hypoplasia, 1p36 deletion detectable on CMA; MED13L locus is 12q24.21 |

1 evidence

“Haploinsufficiency for MED13L should be considered in the differential diagnosis of the 1p36 microdeletion syndrome, due to overlapping dysmorphic facial features in some patients.” literature · 10.1038/ejhg.2015.19 |

| MONDO:0012455 | Kleefstra syndrome | Facial gestalt resemblance noted in individual MED13L patients, Distinguished by EHMT1 variant / 9q34.3 deletion on molecular testing |

1 evidence

“The first patient indicates some facial resemblance to Kleefstra syndrome as a novel differential diagnosis, and the second patient shows, for the first time, recurrence of a MED13L missense mutation (p.(Asp860Gly)).” literature · 10.1016/j.ejmg.2017.06.004 |

| MONDO:0018923 | 22q11.2 deletion syndrome | Shared ID + conotruncal CHD; 22q11.2 adds palatal anomalies, hypocalcaemia, immune deficiency, 22q11.2 deletion detectable on CMA |

1 evidence

“However, due to some similarity to other syndromes with ID such as FG syndrome caused by MED12 mutation, 1p36 deletion syndrome or 22q11.2 deletion syndrome and proved variable clinical expression, the use of NGS is recommended for disease differential diagnosis. 6 , 7 Key points Pathogenic variants in MED13L are common in the autosomal dominant form of syndromic intellectual disability.” literature · 10.34763/jmotherandchild.20202403.2021.d-20-00003 |

| MONDO:0100000 | MED12-related intellectual disability syndrome | X-linked inheritance (FG/Opitz-Kaveggia, Lujan, Ohdo MKB) vs autosomal-dominant de novo for MED13L, Congenital diaphragmatic hernia in 42% (3/7) of female MED12 LoF — not reported in MED13L |

1 evidence

“However, due to some similarity to other syndromes with ID such as FG syndrome caused by MED12 mutation, 1p36 deletion syndrome or 22q11.2 deletion syndrome and proved variable clinical expression, the use of NGS is recommended for disease differential diagnosis. 6 , 7 Key points Pathogenic variants in MED13L are common in the autosomal dominant form of syndromic intellectual disability.” literature · 10.34763/jmotherandchild.20202403.2021.d-20-00003 |

| MONDO:0016033 | Cornelia de Lange syndrome | MED13L LoF variants identified in cohesinopathy-negative CdLS-suspected cohorts, CdLS classically has synophrys, limb-reduction defects, growth restriction — not core MED13L features |

1 evidence

“Furthermore, pathogenic CNVs were detected in NIPBL, MED13L, and EHMT1, along with pathogenic SNVs in ZMYND11, MED13L, and PHIP.” literature · 10.1038/s10038-019-0643-z |

Treatments (9)

speech therapy developmental therapy

Recommendation with broadest support across reports; addresses near-universal expressive-language impairment and articulatory deficits; consider AAC for minimally/non-verbal children.

MAXO: MAXO:0000930

Regimen: Early referral (before age 3) and ongoing

Addresses: HP:0000750HP:0001344

2 evidence

“First, children with known P/LP variants in MED13L would benefit from early referrals to speech therapy to assess their speech, language, and support needs.” literature · 10.1186/s11689-025-09645-1

“A prominent feature of the MED13L neurocognitive presentation is profound language impairment, often in combination with articulatory deficits.” literature · 10.1038/ejhg.2015.26

physical therapy developmental therapy

Addresses hypotonia, motor delay (mean walking age 27–28 mo) and coordination/balance problems.

MAXO: MAXO:0000011

Regimen: From infancy; standard early-intervention schedule

Addresses: HP:0001270HP:0001290HP:0001251

1 evidence

“[SECTION: Motor evaluation] There was no significant difference in the mean age of walking between patients in the GenIDA series ( n = 41) and those in the literature series ( n = 65) with ages of 28 and 27 (SD = 6.59) months, respectively.” literature · 10.1186/s11689-025-09618-4

occupational therapy developmental therapy

Part of multidisciplinary developmental-therapy package alongside speech and physical therapy.

MAXO: MAXO:0001351

Regimen: Standard early-intervention schedule

Addresses: HP:0001270HP:0001263

1 evidence

“[Discussion] Audiovestibular rehabilitation should be prompt, appropriate, and effective and should be part of a holistic multidisciplinary effort for a maximally favorable outcome.” literature · 10.5152/iao.2024.231284

vision assessment surveillance

Visual disorders reported in 78% (32/41) by caregivers (strabismus, hypermetropia); registry-recommended.

MAXO: MAXO:0000971

Regimen: Baseline at diagnosis; periodic ophthalmologic review

Addresses: HP:0000486HP:0000540HP:0000504

1 evidence

“[Discussion] Hearing and visual screening are recommended to improve the management of these patients.” literature · 10.1186/s11689-025-09618-4

hearing examination surveillance

Hearing problems in 32% (13/41) GenIDA; audiovestibular rehabilitation when hearing loss/balance dysfunction present.

MAXO: MAXO:0000873

Regimen: Baseline at diagnosis; audiometric testing (MAXO:0000125) as indicated

Addresses: HP:0000365

2 evidence

“[Discussion] Hearing and visual screening are recommended to improve the management of these patients.” literature · 10.1186/s11689-025-09618-4

“[Discussion] Audiovestibular rehabilitation should be prompt, appropriate, and effective and should be part of a holistic multidisciplinary effort for a maximally favorable outcome.” literature · 10.5152/iao.2024.231284

echocardiography surveillance

CHD in ~20% (15/72); calibrated to a minority feature — baseline screen rather than intensive surveillance.

MAXO: MAXO:0010203

Regimen: Baseline echocardiogram at diagnosis; cardiology follow-up if abnormal

Addresses: HP:0001627HP:0001669

2 evidence

“[4. Discussion] The congenital heart defects, previously highlighted as one of the main features of MED13L haploinsufficiency syndrome, were diagnosed in only 15 (20.8%) individuals (Supplementary Table S2).” literature · 10.3390/medicina59071225

“echocardiography showed ventricular septal defect” literature · 10.7499/j.issn.1008-8830.2017.10.010

electroencephalography surveillance

Seizures in 14–22%; EEG abnormalities can be present without clinical seizures; lower threshold in missense (esp. exon 15/17) carriers.

MAXO: MAXO:0000932

Regimen: Baseline EEG; repeat on clinical suspicion of seizures

Addresses: HP:0001250

2 evidence

“Documented seizure presence is about 22% (15/68) in publications. 2 , 8 , 10 , 27 , 32 , 37 , 38 Of these, 17 individuals with missense variants are evaluated, with 10 having seizures. 10 , 39 Most seizure types are not characterized, though absence seizures ( n = 3) are most common. 8 , 32 , 38 The average age of individuals with reported seizures is 12 years.” literature · 10.1177/26330040241290252

“She had no clinically observed seizures but had abnormal EEG showing spike and slow wave colligation and multi-spike and slow waves in the bilateral occipital and posterior temporal regions, as well as rapid rhythm distribution in the occipital area (Fig. 2 ).” literature · 10.1186/s13052-020-00847-y

anticonvulsant agent therapy symptom-directed pharmacotherapy

Valproic acid initiated for focal bilateral abnormal EEG in one report; no MED13L-specific ASM trial data.

MAXO: MAXO:0000167

Regimen: Standard anti-seizure medication per seizure type

Addresses: HP:0001250

1 evidence

“[Results] Focal bilateral abnormal waves on electroencephalogram (EEG) necessitated the initiation of valproic acid.” literature · 10.1101/mcs.a006124

genetic counseling counselling

De novo in 94–100% of cases but parental gonadal mosaicism documented in ≥4 families; offer prenatal/preimplantation diagnosis to exclude recurrence.

MAXO: MAXO:0000079

Regimen: At diagnosis and pre-conception

2 evidence

“Given the de novo nature of the mutation and the autosomal dominant inheritance model of MED13L , we suggested that her mother receive a molecular prenatal diagnosis by amniocentesis to rule out gonadal mosaicism and prevent the recurrence of another affected child, despite the low risk of recurrence.” literature · 10.3389/fgene.2025.1669849

“We assume the presence of gonadal mosaicism in the mother, which allows to recommend families with confirmed cases of MED13L-associated intellectual disability to plan pregnancies with prenatal or preimplantational diagnostics.” literature · 10.21508/1027-4065-2022-67-1-101-107

Prevalence (2)

global (published cases) — Unknown; ~100 patients described in the literature as of 2025; <1/1,000,000 (Orphanet category)

“There are currently around 100 patients described in the scientific literature, either in case reports or in the form of series of patients who have undergone gene panel, exome or genome analysis, with brief clinical descriptions [ 4 – 6 ].” literature · literature · caumes2025

global — Unknown; <1/1,000,000 (Orphanet point prevalence class)

Orphanet prevalence class for ORPHA:369891 prevalence orphadata · orphadata · ORPHA:369891 (epidemiology)

Clinical trials (1)

Animal/experimental models (8)

| organism | model | models_node |

| NCBITaxon:10090 | Germline heterozygous Med13l mouse — postnatal growth delay, midfacial skeletal anomalies (~61% by micro-CT at 9 mo); no significant cardiac functional defect | mn-haploinsufficiency |

| NCBITaxon:10090 | Conditional Med13l knockout in developing cerebral cortex — loss of transcriptional priming of neurogenesis genes (proteomics + bulk/scRNA-seq) | mn-neurodev-transcription |

| NCBITaxon:10090 | In-utero electroporation of mouse cortex (shRNA knockdown ± WT/missense rescue) — dendritic growth and spine-formation readouts for variant-level function | mn-neurodev-transcription |

| NCBITaxon:7955 | Zebrafish med13b morpholino knockdown (morphant) — defective cranial neural-crest-cell migration and craniofacial cartilage deformities at embryonic/larval stages | mn-ncc-cardiac |

| NCBITaxon:7227 | Drosophila CDK8–Cyclin C kinase-module manipulation in wing disc — Mad-dependent Dpp-target transcription; demonstrates context-dependent direction of CKM effect | mn-ckm-hinge |

| system | description | models_node |

| CL:0000057 | Patient-derived MED13L+/− skin fibroblasts (single +/fs line {chang2022}; 12-line/11-variant collection {campbell2026}) — cyclin-C localisation and mitochondrial-morphology readouts | mn-ckm-hinge |

| CL:0011020 | Human iPSC-derived neurons / neural progenitors carrying MED13L variants (CRISPR-perturbation neural-development platform {wang2024}) | mn-neurodev-transcription |

| CL:0000010 | HEK293 transfection with FLAG-tagged WT vs MED13L missense variants — protein stability (Western) and subcellular localisation (immunofluorescence) {smol2025} | mn-haploinsufficiency |

External assertions (3)

gnomAD: MED13L pLI=1, LOEUF=0.060 · link

ClinVar: 235 P/LP and 606 VUS of 1813 MED13L records · link

Reactome: MED13L mapped to: PPARA activates gene expression; Transcriptional regulation of white adipocyte differentiation; RSV-host interactions · link

References (18 cited in this entry)

10.1186/s11689-025-09618-4

10.1177/26330040241290252

10.1002/dvdy.70079

10.1101/2024.09.25.614184

10.1016/j.isci.2022.103823

10.64898/2026.06.01.729270

10.1371/journal.pgen.1008832

10.1186/s11689-025-09645-1

10.4172/jpb.s2-004

10.1038/ejhg.2013.17

10.1016/j.ejmg.2018.06.014

10.1016/j.xhgg.2025.100467

10.1101/gad.207720.112

10.1016/j.jmccpl.2025.100481

10.1002/humu.22636

10.1111/jnc.15783

10.1101/2022.03.30.486486

10.1038/s42003-025-08532-8

Provenance

{ "creation_date": "2026-06-23 18:39:36.509614+00:00", "updated_date": "2026-06-23 18:39:36.509614+00:00", "curation_history": [ { "date": "2026-06-23 18:39:36.509614+00:00", "agent": "pipeline module / Anthropic Claude (frame 5f9723cd)", "change": "Initial curation entry generated from systematic review run (pipeline run directory)" }, { "date": "2026-06-23 18:39:36.509614+00:00", "agent": "data-validation db-fetch", "change": "Database evidence injected: MONDO/HGNC/gnomAD/ClinVar/AlphaFold/Reactome/HPOA/Orphadata." } ], "notes": [ "research.clinical_trials: ClinicalTrials.gov search for 'MED13L' returned 1 record at curation time; gap recorded.", "Monarch Initiative API blocked by sandbox allowlist (non-critical; MONDO resolved via OLS4).", "ClinGen gene-validity API endpoint returned non-JSON / 404 for direct query; assertion not retrieved (gap).", "completeness_honesty: mechanism.biochemical, mechanism.histopathology, mechanism.environmental, mechanism.infectious, clinical.stages, research.computational_models, research.surrogate_endpoints \u2014 not applicable / no curatable evidence; intentionally omitted.", "validity.reference_validity: all literature snippets sourced verbatim from Phase-5 evidence_package claim_source_sentence fields, which were extracted from abstracts/full-text in Phase 2 with COMPLIANCE_RATE 0.9982." ], "review_notes": [ "Missense vs PTV mechanism (hyp-missense-dn-gof) is EMERGING and contested; treat severity stratification as preliminary.", "FBXW7/SCF dosage-modulation hypothesis carries an oncogene-substrate safety caveat (see hypothesis packet hyp-haploinsufficiency / mn-fbw7-turnover)." ] }

Part 2 — Post-hoc comparison against the held-out dismech entry

⚠️ AI—Generated Content — Not Medical Advice

This document was generated with substantial AI assistance and is not medical advice. It is a research literature synthesis intended for scientific and educational use. It has not been independently reviewed by a licensed physician for clinical accuracy and must not be used as a substitute for professional medical advice, diagnosis, or treatment. Patients, caregivers, and clinicians should rely on qualified healthcare providers and primary sources for any decision regarding a medical condition. AI systems can produce errors, including plausible-sounding statements that are incorrect; verify every claim against the cited primary literature before use. We are pursuing this work with our research partners because we want AI to become more useful in helping people learn about health and medical topics. One day, further research and testing may bring us to a different point — but today is not that day. This is early-stage work, and AI should not be interpreted as providing medical advice or as any substitute for qualified professional care.

Unbiased comparison — the pipeline MED13L outputs vs DisMech `MED13_Syndrome` page

Generated 2026-06-23T23:40:18Z · this report is a static comparison; per the user's instruction, nothing in the pipeline review was modified based on DisMech content.

0. Subject-identity caveat (read first)

	the pipeline (this run)	DisMech page linked
Disease	MED13L syndrome	MED13 syndrome (MRD61)
MONDO	MONDO:0014773	MONDO:0032485
Gene	MED13L (HGNC:22962, 12q24.21)	MED13 (HGNC:22474, 17q23.2)
OMIM	616789	618009
Reported cases	>300 (registry + cohort)	~26 (per the DisMech `description` field)

The page at https://dismech.monarchinitiative.org/pages/disorders/MED13_Syndrome.html covers the paralog gene MED13, not MED13L. A MED13L page does not exist in DisMech: probes of kb/disorders/MED13L*.yaml (repo) and pages/disorders/MED13L*.html (site) all returned 404 against the 1391-disorder kb. The two are sister CKM-hinge disorders with substantial mechanistic and clinical overlap, so a format-and-method comparison is informative — but every content divergence below must be read as paralog biology, not pipeline disagreement.

For an apples-to-apples comparison on structure and evidence model, the pipeline side uses two artifacts: - the narrative review (med13l_review_v3.pdf, 67 pp, 11 394 body-prose words, 120 cited references), and - the structured curation entry (curation-entry.yaml, 87 KB) + pathograph.json — these are the pipeline artefacts that occupy the same role as a DisMech YAML.

1. Format and scope

Dimension	the pipeline MED13L (review v3 + curation-entry)	DisMech MED13_Syndrome
Artifact type	Systematic narrative review (PDF/HTML/MyST) plus schema-backed YAML curation entry	Schema-backed YAML rendered to a single HTML page
Source file size	review_v3.md ≈ 18.9k words (16.1k pre-Methods); curation-entry.yaml 87 KB	YAML 59 429 B; rendered HTML 612 KB
Page count	67 pp PDF	single scrolling page
Top-level YAML sections	6 (identity, mechanism, clinical, research, provenance, companion_artifacts)	12 (name, creation_date, category, synonyms, description, disease_term, parents, pathophysiology, phenotypes, genetic, treatments, datasets)
Rendered prose sections	Intro + §1–§10 + §6b + conclusion + Methods	Pathophysiology, Pathograph, Phenotypes, Genetic Associations, Medical Actions, Related Datasets, Source YAML, References & Deep Research (which embeds two 15-section "deep research" reports)
Structured pathograph	12 nodes / 12 edges (6 mechanism + 6 phenotype), JSON	7 pathophysiology nodes with `downstream` edges; CX2/NDEx export linked
Figures	3 body + 2 Methods	0 (renderer-generated pathograph only)
Tables	12	1 phenotype table + 1 medical-actions table (renderer-generated)
Authoring date range	2026-06-19 → 2026-06-23	2026-04-11 → 2026-06-19 (3 commits)
Authoring agent	Anthropic Claude (literature-review/data-validation/clinical-critic roles)	per-repo Claude Code `/curate` workflow (cmungall + bot, per commit log)

Interpretation. DisMech is a structured KB record: terse, ontology-bound, slot-per-claim, designed for cross-disease query and programmatic export (Mondo EMC, NDEx, ontology-score browser). the pipeline is a PRISMA-style narrative review with a structured KB record alongside — the narrative carries argument, conflict adjudication, and a Methods section the DisMech page does not attempt.

2. Evidence model

	the pipeline review v3	the pipeline curation-entry.yaml	DisMech MED13 YAML
Reference identifier	DOI (cite-key → bib)	`DOI:` CURIE in `evidence[*].source`	`PMID:` in `evidence[*].reference`
Distinct cited references	120	34 distinct DOIs across 113 evidence items	12 PMIDs across 49 evidence items
Evidence items (slot-level)	n/a (prose)	113 (83 with verbatim snippet, 5 empty stubs)	49 (49 with snippet)
Snippet-to-source verification	1 149 claim–citation triples → 91.7 % CLEAN (0 hallucinated, 0 chimeric, 0 broken-DOI) via 5-step blinded protocol	110/110 snippets matched verbatim against the Phase-5 evidence corpus (gate)	per-snippet "validated against PubMed abstracts" (DisMech reference-validator); pass status not exposed on the page
Reference titles stored inline	no (resolved at build from `references.bib`)	no	yes (`reference_title` on every evidence item)
Evidence typing	n/a	`kind: literature` only	`evidence_source` enum (e.g. `HUMAN_CLINICAL`) + `supports` enum (e.g. `SUPPORT`)

Interpretation. the pipeline cites an order of magnitude more sources (120 vs 12) — expected, since MED13L has ~10× the literature MED13 has, and a narrative review's job is comprehensive coverage rather than a curated minimum. DisMech's evidence model is richer per item (typed evidence_source + supports enum + inline reference_title + explanation) and PMID-native; the pipeline's is DOI-native with a separate bibliography resolution step. Both store verbatim supporting snippets; both verify them, but against different oracles (DisMech: PubMed abstract text; the pipeline: its own full-text/abstract evidence corpus, then a separate CrossRef metadata check). the pipeline's curation-entry has 5 empty evidence stubs (e.g. animal_models[0] — source/snippet blank) that DisMech's validator would flag.

3. Ontology binding

Slot	the pipeline curation-entry	DisMech MED13
Disease term	MONDO:0014773 (+ OMIM/ORPHA/GARD/ICD-10 in crossrefs.yaml)	MONDO:0032485
Gene term	HGNC:22962 (+ UniProt, Ensembl, Entrez, AlphaFold)	HGNC:22474
Phenotype HPO	22 terms (numeric `n/N (%)` frequencies)	22 terms (Orphanet `VERY_FREQUENT/FREQUENT/OCCASIONAL` enum)
Treatment MAXO	9 terms	4 terms (1 with `therapeutic_modality`)
Biological process GO	per-node lists (e.g. GO:0006366)	per-node `biological_processes` lists
Cell type CL	none in YAML (covered in prose)	per-node `cell_types` lists
Differential MONDO	5 terms	— (slot absent)
Model organism NCBITaxon	5 (mouse×3, zebrafish, Drosophila)	1 (mouse, via `datasets` only)
Mappings (`mondo_mappings`)	not populated under that key (xrefs in separate file)	not populated

HPO overlap (despite being different diseases): 6/22 shared — HP:0000750, HP:0001249, HP:0001250, HP:0001263, HP:0001270, HP:0001627. This is exactly the CKM-disorder core triad (ID, GDD, speech delay, motor delay, seizures, abnormal heart morphology). The remaining 16-per-side reflect genuine paralog divergence: DisMech-MED13 carries Duane anomaly (HP:0009921), supernumerary tooth (HP:0011069), aganglionic megacolon (HP:0002251), retinal atrophy (HP:0001105) — none reported as MED13L features. pipeline module carries the dysmorphism granularity (bulbous nose HP:0000414, open mouth HP:0000194, depressed nasal bridge HP:0005280, low-set ears HP:0000369) and ataxia (HP:0001251) — the MED13L gestalt. Neither side is "wrong"; they describe sister disorders.

Frequency encoding is the sharper methodological difference: DisMech uses the Orphanet-style 5-band enum; the pipeline records the observed numerator/denominator (e.g. 15/72 (20.8%)) plus per-variant-subset splits (55.6% (missense subset); 23%…). The numeric form preserves the underlying cohort sizes and the ascertainment-method dependence the review's Act-II argument turns on; the enum form is what cross-KB queries and the Orphanet frequency model expect.

4. Mechanism / pathophysiology

	the pipeline	DisMech MED13
Mechanism nodes	6 (`mn-ckm-hinge`, `mn-haploinsufficiency`, `mn-missense-destabilisation`, `mn-fbw7-turnover`, `mn-neurodev-transcription`, `mn-ncc-cardiac`)	7 (Mediator transcriptional dysregulation, MED13 phosphodegron disruption, neurodev transcriptional dysreg, brain-structural/excitability, cardiac dev dysreg, craniofacial/ocular/sensory, somatic-growth/skeletal)
Node identifiers	stable `mn-*` ids (machine-referenced from treatments/models/hypotheses)	`name` strings only
Causal edges	explicit `causes:` lists → 12-edge pathograph JSON	`downstream:` lists per node → CX2/NDEx pathograph
Mechanism hypotheses (separate from established nodes)	5 ranked hypotheses (separate `mechanistic_hypotheses` slot + 5 standalone hypothesis-packet artifacts)	— (no hypothesis slot in DisMech schema)
Variant-class mechanism split	5-row `variants` block (PTV, missense-hotspot, intragenic del/dup, whole-gene CNV, d-TGA-associated noncoding)	encoded as a 529-char free-text `genetic[0].features` string

Interpretation. Coverage is comparable (6 vs 7 nodes; both span the CKM-hinge → tissue-specific dysregulation chain). DisMech's nodes carry richer per-node ontology context (cell_types, biological_processes on every node); the pipeline's carry richer cross-linking (causes ids, confidence, GO+MF+complex+structure lists, and a separate testable-hypothesis layer). DisMech encodes the variant-mechanism split as prose in a string slot; the pipeline as a typed list — neither is the Disease-class genetic shape the dismech schema prefers (which is per-feature dicts, as in larger entries like Kabuki).

5. Coverage gaps (slots one side populates and the other does not)

Populated by the pipeline, absent in DisMech MED13 YAML: - differential_diagnoses (5 MONDO-bound entries with distinguishing features) - diagnosis (4 entries — diagnostic pathway / criteria) - prevalence / epidemiology (2 entries; numeric estimates with source) - animal_models / experimental_models (5 + 3 entries) - mechanistic_hypotheses (5, ranked, with experiment-design packets) - clinical_trials (1) - progression / natural-history narrative - Separate Methods, PRISMA flow, verification ledger, conflict adjudication - mappings to OMIM/ORPHA/GARD/ICD-10/UniProt/Ensembl/AlphaFold

Populated by DisMech MED13, absent in the pipeline curation-entry: - parents (3 disease-ontology parents — the pipeline has identity.parents 4× but as labels, not MONDO-bound parent terms in DisMech's sense) - datasets (1 GEO accession geo:GSE298801 + 1 ClinicalTrials.gov record clinicaltrials:NCT01238250, each with organism/data-type binding) — the pipeline's research.datasets slot is the literal string '[]', not a structured list - per-evidence evidence_source enum and supports enum - per-evidence inline reference_title - per-node cell_types (CL terms) - the page-embedded "References & Deep Research" report (two 15-section research dossiers rendered alongside the structured data)

6. Quality-control surface

Check	the pipeline	DisMech
Schema validation	`gate_curation_entry` (term_validity 22/22 HPO, 10/10 MONDO, 11/11 MAXO; reference_validity 110/110 snippet-match; pass)	`linkml-validate --target-class Disease` (PR-time hook); per-file compliance score in QC dashboard
Reference validation	5-step blinded triple verification (DOI resolve → title → author → metadata → claim), 1 149 triples, 91.7 % clean	`linkml-reference-validator` against PubMed abstracts (pass implied by merge)
Ontology-term validation	OLS4 lookups at build; 0 bad terms	dismech-terms skill (OAK-backed term resolution)
Human review	story-coherence + clinical-critic (7-check clinical critic) — automated, no human in loop	PR review by Monarch curators (cmungall et al., per commit log)
Audit trail	phase_ledger.json (16 versions), gate_* JSONs, fix_ledger	git history (3 commits) + per-PR review threads

Interpretation. the pipeline's QC is deeper per claim (every numeric/citation triple individually verified) but entirely automated; DisMech's QC is lighter per claim but ends in human curator review, which catches things automated checks do not (the Delpire–McNeill PR thread shows reviewers catching a GoF/LoF mislabel and a too-generic CL term — exactly the class of error clinical-critic also targets).

7. Net assessment

As a structured KB record, the pipeline curation-entry is a near-superset of the DisMech slot inventory (it populates 8 slot families DisMech-MED13 leaves empty), with two real gaps to close before it would pass a DisMech PR review: (a) PMID identifiers alongside DOIs, (b) structured datasets with GEO/SRA accessions, plus the 5 empty evidence stubs.
As a reader-facing page, DisMech is leaner and more ontology-navigable — every term is a hyperlink into MONDO/HPO/GO/CL/MAXO and the pathograph is exportable to NDEx; the pipeline review is far more comprehensive and argued (120 vs 12 sources; conflict adjudication; ascertainment-bias analysis; ranked research priorities) but the curation-entry is not yet rendered as a standalone clickable page.
Subject-identity remains the dominant caveat: the only valid scientific-content comparison is mechanism-node structure, not content, because MED13 ≠ MED13L. A like-for-like content comparison would require a kb/disorders/MED13L_Syndrome.yaml in DisMech — which does not yet exist.

Sources read for this comparison: kb/disorders/MED13_Syndrome.yaml @ main (59 429 B), rendered page (612 KB), src/dismech/schema/dismech.yaml, app/data.js MED13 row, repo commit log; the pipeline review_v3.md, curation-entry.yaml, pathograph.json, crossrefs.yaml, gate_curation_entry.json.

Ask OpenScientist

OpenScientist Report

Classifications

Inheritance

Mechanistic Hypotheses

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Differential Diagnoses

Related Datasets

Clinical Trials

Experimental Models

Source YAML

References & Deep Research

References

Deep Research

MED13L Syndrome — Anthropic systematic-review pipeline output

How this artifact was used

Part 1 — Curation preview (DisMech format)

Description AI-GENERATED

AI-generated mechanistic hypotheses AI-GENERATED (5)

MED13L haploinsufficiency (dosage loss) is the primary disease mechanismCANONICALAI reasoning

Subset of recurrent missense variants act via dominant-negative or neomorphic gain-of-functionEMERGINGAI reasoning

MED13L missense variants cause isolated dextro-transposition of the great arteriesREFUTEDAI reasoning

MED13 paralogue partially compensates for MED13L loss (and vice versa)EMERGINGAI reasoning

Aberrant cytoplasmic cyclin C release drives mitochondrial fragmentation contributing to neuronal dysfunctionEMERGINGAI reasoning

Pathophysiology AI-CURATED (6 mechanism nodes)

mn-ckm-hinge high

mn-haploinsufficiency high

mn-missense-destabilisation medium

mn-fbw7-turnover high

mn-neurodev-transcription high

mn-ncc-cardiac medium

Genetic (1)

Variants

Inheritance (1)

Phenotypes (22 HPO)

Diagnosis (4)

Differential diagnoses (5)

Treatments (9)

speech therapy developmental therapy

physical therapy developmental therapy

occupational therapy developmental therapy

vision assessment surveillance

hearing examination surveillance

echocardiography surveillance

electroencephalography surveillance

anticonvulsant agent therapy symptom-directed pharmacotherapy

genetic counseling counselling

Prevalence (2)

Clinical trials (1)

Animal/experimental models (8)

External assertions (3)

References (18 cited in this entry)

Provenance

Part 2 — Post-hoc comparison against the held-out dismech entry

Unbiased comparison — the pipeline MED13L outputs vs DisMech MED13_Syndrome page

0. Subject-identity caveat (read first)

1. Format and scope

2. Evidence model

3. Ontology binding

4. Mechanism / pathophysiology

5. Coverage gaps (slots one side populates and the other does not)

6. Quality-control surface

7. Net assessment

Unbiased comparison — the pipeline MED13L outputs vs DisMech `MED13_Syndrome` page