Hypomyelinating Leukodystrophy 23

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Inheritance

1

Autosomal Recessive HP:0000007

HLD23 segregates as an autosomal recessive trait. The delineating study identified homozygosity for one of two recurrent RNF220 missense variants in consanguineous nuclear families, with heterozygous unaffected parents.

Autosomal recessive inheritance

Show evidence (1 reference)

PMID:33964137 SUPPORT Human Clinical

"Whole exome sequencing performed in five large consanguineous nuclear families allowed us to identify homozygosity for two recurrent missense variants affecting highly conserved residues of RNF220 as the causative event underlying a novel form of leukodystrophy with ataxia and sensorineural deafness."

Homozygosity for the causative variants in consanguineous pedigrees establishes autosomal recessive inheritance.

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Mechanistic Hypotheses

2

HLD23 is a laminopathy acting through impaired RNF220-lamin B1 regulation

lamin_b1_nuclear_lamina EMERGING

Evidence balance 2 support

The original delineating proposal: that the primary consequence of the RNF220 arginine substitutions is loss of normal regulation of lamin B1 and of nuclear lamina architecture, and that the neurodegeneration follows from nuclear envelope dysfunction. It is supported by direct binding data, by a Drosophila model, and by patient-fibroblast nuclear morphology, but the step from abnormal nuclei to hypomyelination specifically has not been demonstrated.

Show evidence (2 references)

PMID:33964137 SUPPORT In Vitro

"Mass spectrometry analysis identified lamin B1 as the RNF220 binding protein and co-immunoprecipitation experiments demonstrated reduced binding of both RNF220 mutants to lamin B1."

Establishes the physical interaction and that both disease alleles impair it, which is the molecular premise of this hypothesis.

PMID:33964137 SUPPORT Human Clinical

"Overall, our data identify RNF220 as a gene implicated in leukodystrophy with ataxia and sensorineural deafness and document a critical role of RNF220 in the regulation of nuclear lamina."

The authors' own framing of the hypothesis, stated as an interpretation of their data rather than a demonstrated causal path to hypomyelination.

Loss of RNF220-mediated Olig1/Olig2 stabilization causes the hypomyelination

olig_stabilization_failure EMERGING

Evidence balance 1 support

The competing — or complementary — proposal that the myelin limb of HLD23 arises cell-autonomously in the oligodendrocyte lineage, because RNF220 normally maintains Olig1 and Olig2 protein levels through K63-linked polyubiquitination and neither disease allele can. This is the better-evidenced route for hypomyelination specifically, resting on a knock-in mouse carrying the R365Q allele — the only one of the two modelled in vivo — but it says nothing about the deafness, liver or cardiac limbs.

Show evidence (1 reference)

PMID:38324685 SUPPORT Model Organism

"We were able to replicate leukodystrophy-like symptoms in a pathomimetic RNF220R365Q knock-in mouse model, which represents deregulated K63 ubiquitination of Olig proteins and impediments of oligodendroglial differentiation and myelination."

A mouse carrying the actual patient allele reproduces both the proposed molecular defect and the myelin phenotype, which is the strongest support for this route.

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Discussions and Knowledge Gaps

2

By what mechanism do RNF220 missense variants cause sensorineural deafness, hepatopathy and cardiomyopathy?

KNOWLEDGE GAP gap_hld23_nonneural_organ_mechanism

Attached to

pathophysiology#Cardiac and Hepatic Involvement pathophysiology#Auditory Pathway Involvement

Three of the four organ systems in this disease's name have no mechanistic account at all. Both published mechanisms — reduced lamin B1 binding and failed Olig1/Olig2 stabilization — were worked out for the CNS myelin phenotype. Olig1/Olig2 are oligodendrocyte transcription factors and cannot explain cochlear, hepatic or cardiac disease; the lamin B1 route could in principle, since laminopathies commonly involve heart and muscle, but no cardiac or hepatic tissue from an HLD23 patient has been examined for nuclear envelope pathology. The gap also extends to natural history: no published source says which of the four organ limbs is the proximate cause of the deaths reported in the second decade, so it is not known whether the unexplained limbs or the well-characterised CNS one determine survival.

Proposed experiments

Nuclear envelope morphology in HLD23 cardiac and hepatic tissue

exp_hld23_nuclear_envelope_heart_liver

Examine nuclear morphology and lamin B1 distribution in cardiomyocytes and hepatocytes from HLD23 autopsy material, or in patient iPSC-derived cardiomyocytes and hepatocyte-like cells, using the same blebs and invaginations readout applied to patient fibroblasts.

Would support

pathophysiology#Cardiac and Hepatic Involvement mechanistic_hypotheses#lamin_b1_nuclear_lamina

Supporting outcome

Cardiomyocytes and hepatocytes carrying the patient allele show the same nuclear blebs, herniations and invaginations seen in patient fibroblasts, implicating the lamina lesion in the cardiac and hepatic limbs.

Refuting outcome

Patient-derived cardiomyocytes and hepatocytes have normal nuclear morphology and lamin B1 distribution, implicating a third RNF220 substrate rather than the lamina.

Why does the RNF220 R365Q knock-in mouse, which carries the exact patient allele, not reproduce the progressive ataxia and early death that define the human disease?

HUMAN MODEL MISMATCH mismatch_hld23_knockin_mouse_progression

Attached to

animal_models#RNF220 R365Q knock-in mouse (RNF220-QQ) pathophysiology#Progressive Neurodegeneration and White Matter Dysfunction

This is a mismatch rather than a knowledge gap: the model exists, carries the correct allele, and reproduces the molecular and myelin phenotypes well, but the authors report no survival or walking difference over 12 months against a human disease that is lethal in the second decade. The divergence is mechanistically informative rather than a technical failure — it suggests the lethal component of HLD23 is not the hypomyelination the mouse does reproduce, though which limb of the disease does account for the deaths is not reported anywhere. It also bounds what the model can be used for: it is a myelination model, not a disease-progression or therapeutic-endpoint model.

Proposed experiments

Longitudinal cardiac and hepatic phenotyping of RNF220-QQ mice

exp_hld23_qq_mouse_cardiac_hepatic_phenotyping

Serial echocardiography, cardiac histology for fibrosis, and liver function assessment in RNF220-QQ mice beyond 12 months, to test whether the model lacks the non-CNS limbs entirely or merely develops them later than the neurological readouts were scored.

Would support

pathophysiology#Cardiac and Hepatic Involvement

Supporting outcome

RNF220-QQ mice develop cardiac fibrosis and impaired liver function, establishing the model for the organ limbs and explaining the survival discrepancy as a difference in timing rather than in mechanism.

Refuting outcome

Cardiac and hepatic structure and function remain normal at all ages, confirming a genuine species difference and indicating that the human cardiac and hepatic limbs require a modifier absent in mouse.

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Pathophysiology

9

RNF220 Missense Substitution at Conserved Arginine R363/R365

The initiating lesion. Homozygous p.R363Q or p.R365Q substitutions affect adjacent, highly conserved arginine residues of the RNF220 E3 ubiquitin ligase. This is the disorder-specific substitution for the module's trigger node: RNF220 is oligodendrocyte-essential ubiquitination machinery rather than a myelin structural protein or a lipid-degradation enzyme.

RNF220 hgnc:25552

Genetic context allele_type: MISSENSE variant_origin: GERMLINE zygosity: HOMOZYGOUS functional_impact_category: PARTIAL_LOSS_OF_FUNCTION

Both variants are homozygous germline missense changes. They are curated as partial loss of function rather than complete null: the mutant protein is expressed and retains partial lamin B1 binding, and the phenotype is milder than the profound developmental failure of full RNF220 depletion in mouse.

ubiquitin protein ligase activity GO:0061630 ↓ DECREASED

Downstream

Reduced RNF220 Binding to Lamin B1 Both mutant proteins co-immunoprecipitate lamin B1 less efficiently than wild-type RNF220.

Failure of K63-Linked Polyubiquitination and Stabilization of Olig1/Olig2 Both mutant proteins lose the ability to raise endogenous Olig1 and Olig2 protein levels, the substrates RNF220 normally stabilizes.

Cardiac and Hepatic Involvement The cardiac and hepatic limbs segregate with the homozygous RNF220 genotype across the reported consanguineous families. No intermediate mechanism between the ligase defect and the cardiac or hepatic phenotype has been demonstrated, so the link is recorded without asserting a route.

Auditory Pathway Involvement Sensorineural deafness is part of the core phenotype defined by the homozygous RNF220 genotype. Whether the lesion is cochlear or retrocochlear is unknown, so no intermediate is asserted.

Show evidence (1 reference)

PMID:33964137 SUPPORT Human Clinical

"Whole exome sequencing performed in five large consanguineous nuclear families allowed us to identify homozygosity for two recurrent missense variants affecting highly conserved residues of RNF220 as the causative event underlying a novel form of leukodystrophy with ataxia and sensorineural deafness."

Establishes these substitutions as the causative genetic lesion.

Reduced RNF220 Binding to Lamin B1

Lamin B1 is the RNF220 interaction partner identified by mass spectrometry, and both disease alleles bind it less well. This is the molecular basis of the laminopathy interpretation of HLD23.

lamin binding GO:0005521 ↓ DECREASED

Downstream

Nuclear Lamina Disorganization and Abnormal Nuclear Morphology Loss of RNF220 regulation of lamin B1 disturbs nuclear lamina architecture.

Show evidence (1 reference)

PMID:33964137 SUPPORT In Vitro

"Mass spectrometry analysis identified lamin B1 as the RNF220 binding protein and co-immunoprecipitation experiments demonstrated reduced binding of both RNF220 mutants to lamin B1."

Identifies lamin B1 as the partner and documents reduced binding by both mutants.

Nuclear Lamina Disorganization and Abnormal Nuclear Morphology

Primary skin fibroblasts from HLD23 patients show blebs, herniations and invaginations of the nuclear envelope — the cellular signature that places this disease among the laminopathies. In Drosophila, RNF220 silencing mislocalizes and aggregates the lamin B1 orthologue lamin Dm0 and produces a neurodegenerative phenotype.

nuclear envelope organization GO:0006998 ↓ DECREASED

Experimental models

HLD23 patient primary skin fibroblasts PRIMARY CELL CULTURE Cells carry the patient genotype and display the nuclear morphological abnormalities directly.

Animal models

RNF220 silencing in Drosophila melanogaster Fruit fly recapitulates Supports the functional link between RNF220 and lamin B1 regulation.

Downstream

Progressive Neurodegeneration and White Matter Dysfunction Nuclear envelope dysfunction is proposed as the route from the RNF220 lesion to neurodegeneration, by analogy with the other laminopathies. The specific step to hypomyelination has not been demonstrated.

Show evidence (1 reference)

PMID:33964137 SUPPORT In Vitro

"mutations in primary skin fibroblasts determine nuclear abnormalities such as blebs, herniations and invaginations, which are typically observed in cells of patients affected by laminopathies"

Documents the abnormal nuclear morphology in cells taken from affected individuals.

Failure of K63-Linked Polyubiquitination and Stabilization of Olig1/Olig2

RNF220 normally attaches K63-linked polyubiquitin chains to the oligodendrocyte transcription factors Olig1 and Olig2, maintaining their protein stability. This is a non-degradative, stabilizing ubiquitination — not the canonical K48 proteasomal signal — so loss of RNF220 lowers rather than raises Olig protein levels. In the R365Q knock-in mouse, forebrain polyubiquitination of Olig1 and Olig2 is reduced and both proteins are less abundant in isolated progenitor and oligodendrocyte fractions.

protein K63-linked ubiquitination GO:0070534 ↓ DECREASED

ubiquitin protein ligase activity GO:0061630 ↓ DECREASED

Animal models

RNF220 R365Q knock-in mouse (RNF220-QQ) Mouse recapitulates The proposed molecular defect is directly observed in vivo in the animal carrying the patient allele.

Downstream

Oligodendrocyte Progenitor Proliferation and Differentiation Failure Depleted Olig1 and Olig2 remove the transcriptional drive that the oligodendrocyte lineage depends on.

Show evidence (2 references)

PMID:38324685 SUPPORT In Vitro

"Furthermore, we showed that Olig1 and Olig2 are two direct ubiquitination substrates of RNF220, and the protein stabilities of these two TFs are maintained by RNF220 through K63-linked polyubiquitination."

Establishes Olig1 and Olig2 as direct substrates and the chain linkage involved.

PMID:38324685 SUPPORT Model Organism

"Moreover, in the pathomimetic RNF220R365Q knock-in mouse model, deregulation of ubiquitination and stabilization of the Olig proteins leads to maldevelopment of oligodendroglia, corpus callosum agenesis, and leukodystrophy-like symptoms."

Shows the defect occurs in vivo in an animal carrying the human disease allele.

Oligodendrocyte Progenitor Proliferation and Differentiation Failure

Oligodendrocyte progenitor cells proliferate less and fail to differentiate into mature oligodendrocytes. In conditional RNF220 knockout mouse corpus callosum, BrdU and Ki67 labelling of progenitors is reduced at P3 and mature CC1+Sox10+ oligodendrocytes are fewer at P21. This is the module's differentiation-arrest node; the arrest, not oligodendrocyte death after myelination, is the documented route in HLD23.

oligodendrocyte precursor cell CL:0002453 oligodendrocyte CL:0000128

oligodendrocyte differentiation GO:0048709 ↓ DECREASED glial cell proliferation GO:0014009 ↓ DECREASED

Animal models

RNF220 conditional knockout mouse (oligodendrocyte lineage) Mouse recapitulates Conditional deletion within the lineage impairs progenitor proliferation and differentiation, establishing cell autonomy.

Downstream

Deficient CNS Myelin Deposition Too few mature oligodendrocytes are generated to lay down normal myelin.

Show evidence (1 reference)

PMID:38324685 SUPPORT Model Organism

"RNF220 depletion in oligodendrocyte lineage cells impedes oligodendrocyte progenitor cell proliferation, differentiation, and (re)myelination, which consequently leads to learning and memory defects."

Establishes the progenitor proliferation and differentiation defect as cell-autonomous to the oligodendrocyte lineage.

Deficient CNS Myelin Deposition

Myelin is never adequately laid down — hypomyelination rather than demyelination. In the R365Q knock-in mouse, corpus callosum axons are severely hypomyelinated on black-gold staining and electron microscopy, and the myelin structural proteins MBP, PLP, MAG and MOG are all reduced at both mRNA and protein level.

oligodendrocyte CL:0000128

central nervous system myelination GO:0022010 ↓ DECREASED

myelin sheath GO:0043209

cerebral white matter UBERON:0002316

Animal models

RNF220 R365Q knock-in mouse (RNF220-QQ) Mouse recapitulates The knock-in carries the actual patient allele and reproduces hypomyelination of the corpus callosum by three independent modalities.

Downstream

Progressive Neurodegeneration and White Matter Dysfunction Absent myelin removes saltatory conduction and the oligodendroglial metabolic support the axon depends on.

Leukodystrophy Hypomyelination is what is seen as the leukodystrophy on imaging.

Show evidence (2 references)

PMID:38324685 SUPPORT Model Organism

"Furthermore, the mRNA and protein levels of myelin-related molecules, including MBP, PLP, MAG, and MOG, were significantly down-regulated in the forebrains of RNF220-QQ mice"

Quantifies the myelin deficit at the level of the structural proteins in the mouse carrying the patient allele.

PMID:38324685 SUPPORT Human Clinical

"Individuals harboring homozygous R363Q or R365Q mutation of RNF220 have symptoms of leukodystrophy and corpus callosum agenesis, as well as intellectual disability"

The human counterpart of the mouse myelin measurement above. The direct quantification of myelin deficiency exists only in the mouse; in patients the deficit is inferred from the leukodystrophy and callosal phenotype.

Progressive Neurodegeneration and White Matter Dysfunction

The clinical endpoint of the CNS limb. Loss of the sheath is followed by secondary axonal degeneration and progressive white matter dysfunction, which in HLD23 presents as ataxia beginning in childhood and progressing over the first two decades. The node specializes the module's endpoint with the HLD23 tract distribution and tempo; it carries the module's axon-maintenance process rather than repeating the myelination process of the upstream deposition node.

neuron projection maintenance GO:1990535 ↓ DECREASED

cerebral white matter UBERON:0002316

Animal models

RNF220 R365Q knock-in mouse (RNF220-QQ) Mouse partially recapitulates The mouse has cognitive deficits and a rotarod abnormality, but not the progressive, lethal neurological decline that defines the human disease.

Downstream

Ataxia Progressive white matter and cerebellar pathway dysfunction produces the ataxia that names the entity.

Intellectual Disability Cognitive impairment accompanies the white matter disease.

Agenesis of the Corpus Callosum The most severely affected white matter tract fails to form.

Show evidence (1 reference)

PMID:38324685 SUPPORT Human Clinical

"Individuals harboring homozygous R363Q or R365Q mutation of RNF220 have symptoms of leukodystrophy and corpus callosum agenesis, as well as intellectual disability"

Summarizes the human CNS phenotype attributable to both disease alleles.

Cardiac and Hepatic Involvement

Fibrotic cardiomyopathy and hepatopathy are established clinical features of HLD23 and are what distinguishes it from a CNS-restricted hypomyelinating leukodystrophy. Conformance is declared at the module's structural-impairment endpoint only, because no upstream cardiomyocyte insult, neurohormonal activation or remodeling step has been demonstrated for RNF220. Whether the nuclear-lamina lesion, the Olig-stabilization lesion, or a third RNF220 substrate accounts for these organ limbs is unknown.

cardiac muscle cell CL:0000746 hepatocyte CL:0000182

Downstream

Dilated Cardiomyopathy The cardiac limb presents as a fibrotic, dilated cardiomyopathy.

Hepatic Dysfunction The hepatic limb presents as hepatopathy with abnormal liver function.

Show evidence (1 reference)

PMID:33964137 SUPPORT Human Clinical

"this novel form of leukodystrophy with ataxia and sensorineural deafness that includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families"

The only published statement establishing the cardiac and hepatic limbs, across seven families.

Auditory Pathway Involvement

Progressive sensorineural deafness is one of the four defining features of HLD23. It is deliberately curated as an unexplained node rather than conformed to the sensorineural_hair_cell_loss module: no cochlear hair cell, stria vascularis or spiral ganglion pathology has been reported in RNF220 disease, and the deafness could equally be retrocochlear given the underlying white matter disease. Conforming this node would assert a cochlear mechanism that has not been evidenced.

Downstream

Sensorineural Hearing Loss The auditory limb presents as progressive sensorineural hearing impairment.

Show evidence (1 reference)

PMID:33964137 SUPPORT Human Clinical

"a novel form of leukodystrophy with ataxia and sensorineural deafness"

Establishes sensorineural deafness as a defining feature of the entity.

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Pathograph

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

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Phenotypes

7

Cardiovascular 1

Dilated Cardiomyopathy HP:0001644

Show evidence (1 reference)

PMID:33964137 SUPPORT Human Clinical

"includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families"

Establishes cardiomyopathy as an associated feature. The paper's wording is "fibrotic", not "dilated", which is recorded in the description.

Digestive 1

Hepatic Dysfunction Decreased liver function HP:0001410

Show evidence (1 reference)

PMID:33964137 SUPPORT Human Clinical

"includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families"

Establishes hepatopathy as an associated feature.

Ear 1

Sensorineural Hearing Loss Sensorineural hearing impairment HP:0000407

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:33964137 SUPPORT Human Clinical

"a novel form of leukodystrophy with ataxia and sensorineural deafness"

Establishes sensorineural deafness as a defining feature.

Nervous System 4

Leukodystrophy HP:0002415

Show evidence (1 reference)

PMID:33964137 SUPPORT Human Clinical

"a novel form of leukodystrophy with ataxia and sensorineural deafness"

Names leukodystrophy as the core phenotype of this entity.

Ataxia HP:0001251

Course: PROGRESSIVE

Show evidence (2 references)

PMID:33964137 SUPPORT Human Clinical

"a novel form of leukodystrophy with ataxia and sensorineural deafness"

Establishes ataxia as a defining feature.

PMID:38324685 SUPPORT Human Clinical

"most affected patients suffered from severe ataxia during their early teenage years and died at their second teenage years"

Dates the severity of the ataxia and supports the progressive course.

Intellectual Disability HP:0001249

Show evidence (1 reference)

PMID:38324685 SUPPORT Human Clinical

"Individuals harboring homozygous R363Q or R365Q mutation of RNF220 have symptoms of leukodystrophy and corpus callosum agenesis, as well as intellectual disability"

Reports intellectual disability in patients with both alleles.

Agenesis of the Corpus Callosum Agenesis of corpus callosum HP:0001274

Show evidence (1 reference)

PMID:38324685 SUPPORT Human Clinical

"Individuals harboring homozygous R363Q or R365Q mutation of RNF220 have symptoms of leukodystrophy and corpus callosum agenesis, as well as intellectual disability"

Reports corpus callosum agenesis as a human feature of both alleles.

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Genetic Associations

1

RNF220

Gene: RNF220 hgnc:25552 relationship_type: CAUSATIVE

Show evidence (2 references)

PMID:33964137 SUPPORT Human Clinical

"We report these two homozygous missense variants (p.R363Q and p.R365Q) in the ubiquitin E3 ligase RNF220 as the underlying cause of this novel form of leukodystrophy with ataxia and sensorineural deafness that includes fibrotic cardiomyopathy and hepatopathy as associated features in seven..."

Names both causative alleles, the gene, and the multisystem phenotype they produce across seven families.

PMID:40594583 SUPPORT Human Clinical

"In addition, six cases carried homozygote variants in the GJC2, PLEKHG2, RNF220, POLR1C, DEGS1 and ACER3 genes, respectively."

An independent leukodystrophy cohort recovered a homozygous RNF220 variant, supporting RNF220 as a recurrent cause in this disease group. The cohort's own variant was classified as a VUS, so this is corroborating rather than independently confirmatory. The paper reports the change at the nucleotide level only (NM_018150 c.1088G > A); c.1088 is the second base of codon 363, so a CGA to CAA change there would give p.R363Q, one of the two recurrent alleles. That is an inference from the coordinates, not something the paper states, and it is recorded here rather than curated as a protein-level claim.

🗃️

External Assertions

1

OMIM HLD23 phenotype record

OMIM disease record OMIM:619688

OMIM phenotype identifier for leukodystrophy, hypomyelinating, 23, with ataxia, deafness, liver dysfunction, and dilated cardiomyopathy (HLD23), assigned following the Sferra et al. delineation in PMID:33964137.

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Medical Actions

2

Supportive and Multidisciplinary Care

Action: Supportive Care NCIT:C15747

Platform: Behavioral / lifestyle

No disease-modifying therapy exists. Management is supportive and, because the disease involves four organ systems, necessarily multidisciplinary — cardiac surveillance, hepatic monitoring, audiological support and rehabilitation alongside neurological care.

Genetic Counseling

Action: Genetic Counseling NCIT:C15240

Platform: Behavioral / lifestyle

Autosomal recessive inheritance with a 25% recurrence risk per pregnancy for carrier couples. Relevant to the consanguineous families in which the two recurrent alleles were reported.

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Progression

1

Childhood onset with severe ataxia by the early teens and death in the second decade

Affected individuals develop severe ataxia by the early teenage years and die during the second decade. The reported course is not stratified by allele, and the proximate cause of death is not stated in any published source.

Show evidence (1 reference)

PMID:38324685 SUPPORT Human Clinical

"most affected patients suffered from severe ataxia during their early teenage years and died at their second teenage years"

Documents the timing of severe ataxia and of death.

📊

Prevalence

1

Worldwide

Cases In Literature Ultra Rare

The delineating study reports the entity in seven consanguineous families, and only a handful of further cases have been published since. No source gives a rate, so the qualitative band is used rather than an Orphanet numeric class.

Show evidence (1 reference)

PMID:33964137 SUPPORT Human Clinical

"includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families"

Gives the published case count behind the CASES_IN_LITERATURE measure.

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Experimental Models

1

HLD23 patient primary skin fibroblasts PRIMARY_CELL_CULTURE

Primary dermal fibroblasts from affected individuals, used to demonstrate the nuclear envelope abnormalities that support the laminopathy classification.

Pathograph links

Nuclear Lamina Disorganization and Abnormal Nuclear Morphology recapitulates fidelity: high Cells carry the patient genotype and display the nuclear morphological abnormalities directly.

Limitations: Fibroblasts are not the disease-relevant cell type for hypomyelination; whether patient oligodendrocytes show the same nuclear phenotype is untested.

Show evidence (1 reference)

PMID:33964137 SUPPORT In Vitro

"mutations in primary skin fibroblasts determine nuclear abnormalities such as blebs, herniations and invaginations, which are typically observed in cells of patients affected by laminopathies"

Reports the nuclear morphology defect in patient-derived cells.

🐁

Animal Models

3

RNF220 R365Q knock-in mouse (RNF220-QQ)

A CRISPR-generated mouse carrying the human HLD23 R365Q allele in homozygous form. It reproduces the CNS myelin limb of the disease — severe corpus callosum hypomyelination on MRI, black-gold staining and electron microscopy, reduced myelin protein expression, reduced Olig polyubiquitination — but the authors state explicitly that it does not reproduce the full patient phenotype, showing no survival or walking deficit over 12 months where patients are severely ataxic as teenagers and die in the second decade.

Species

Mouse

Genotype

Rnf220 p.R365Q homozygous knock-in (CRISPR-Cas9)

Publication

PMID:38324685

Pathograph links

Deficient CNS Myelin Deposition recapitulates fidelity: high The knock-in carries the actual patient allele and reproduces hypomyelination of the corpus callosum by three independent modalities.

Limitations: Mouse corpus callosum myelination is the readout; no human CNS tissue comparison is available.

Readouts

Corpus callosum myelin protein expression (MBP, PLP, MAG, MOG)

Direction: DECREASED

Interpretation: Structural myelin proteins are reduced, the molecular correlate of the hypomyelination node.

Show evidence (1 reference)

PMID:38324685 SUPPORT Model Organism

"Furthermore, the mRNA and protein levels of myelin-related molecules, including MBP, PLP, MAG, and MOG, were significantly down-regulated in the forebrains of RNF220-QQ mice"

Reports the measurement behind this readout.

Show evidence (1 reference)

PMID:38324685 SUPPORT Model Organism

"Consistent with this finding, BG staining and TEM analyses showed that the axonal fibers of corpus callosum in RNF220-QQ mice were severely hypomyelinated"

Supports treating this model as informative for the hypomyelination node.

Failure of K63-Linked Polyubiquitination and Stabilization of Olig1/Olig2 recapitulates fidelity: high The proposed molecular defect is directly observed in vivo in the animal carrying the patient allele.

Limitations: Measured in mouse forebrain lysates; the equivalent measurement has not been made in human patient tissue.

Show evidence (1 reference)

PMID:38324685 SUPPORT Model Organism

"Moreover, in the pathomimetic RNF220R365Q knock-in mouse model, deregulation of ubiquitination and stabilization of the Olig proteins leads to maldevelopment of oligodendroglia, corpus callosum agenesis, and leukodystrophy-like symptoms."

Confirms the molecular defect in the knock-in animal.

Progressive Neurodegeneration and White Matter Dysfunction partially recapitulates fidelity: low The mouse has cognitive deficits and a rotarod abnormality, but not the progressive, lethal neurological decline that defines the human disease.

Limitations: The authors report no significant difference in survival or walking performance over a 12-month observation, whereas affected individuals are severely ataxic as teenagers and die in the second decade. The model therefore cannot be used to study the progressive or lethal component of the disease.

Show evidence (1 reference)

PMID:38324685 SUPPORT Model Organism

"RNF220-QQ mice showed no significant difference in survival and walking performance during our 12-month observation"

The mouse result itself. The authors report it in a sentence that also restates the human course; that clause is quoted separately under phenotypes and progression, because it is a human-clinical observation and cannot be graded MODEL_ORGANISM here.

Show evidence (1 reference)

PMID:38324685 SUPPORT Model Organism

"We were able to replicate leukodystrophy-like symptoms in a pathomimetic RNF220R365Q knock-in mouse model, which represents deregulated K63 ubiquitination of Olig proteins and impediments of oligodendroglial differentiation and myelination."

Supports treating this model as informative for the disease's myelin mechanism.

RNF220 conditional knockout mouse (oligodendrocyte lineage)

A lineage-restricted knockout used to establish that the myelin defect is cell-autonomous to oligodendroglia rather than secondary to disease elsewhere. It is not an allelic model of HLD23 — it is a null, whereas patients carry partial-loss-of-function missense alleles.

Species

Mouse

Genotype

Rnf220 conditional knockout in oligodendrocyte lineage cells (RNF220-cKO)

Publication

PMID:38324685

Pathograph links

Oligodendrocyte Progenitor Proliferation and Differentiation Failure recapitulates fidelity: moderate Conditional deletion within the lineage impairs progenitor proliferation and differentiation, establishing cell autonomy.

Limitations: A complete knockout rather than the patient missense allele, so it overstates the severity of the human lesion; it also cannot address the non-CNS limbs of the disease.

Show evidence (1 reference)

PMID:38324685 SUPPORT Model Organism

"In this study, we found that the E3 ubiquitin ligase RNF220 is required for oligodendroglial development, and its specific depletion in OL lineage cells impairs OPC proliferation, differentiation, subsequent myelination, as well as remyelination after demyelinating injury in the adult mouse brains."

Establishes the cell-autonomous requirement within the lineage.

RNF220 silencing in Drosophila melanogaster

An invertebrate model used to test the lamin B1 arm of the mechanism. Silencing RNF220 mislocalizes and aggregates lamin Dm0, the fly lamin B1 orthologue, and causes neurodegeneration.

Species

Fruit fly

Genotype

RNF220 RNAi silencing

Publication

PMID:33964137

Pathograph links

Nuclear Lamina Disorganization and Abnormal Nuclear Morphology recapitulates fidelity: low Supports the functional link between RNF220 and lamin B1 regulation.

Limitations: Drosophila has no myelin and no oligodendrocytes, so the model cannot speak to the hypomyelination that defines the human disease; it also uses silencing rather than the patient missense alleles.

Show evidence (1 reference)

PMID:33964137 SUPPORT Model Organism

"We demonstrate that RNF220 silencing in Drosophila melanogaster specifically affects proper localization of lamin Dm0, the fly lamin B1 orthologue, promotes its aggregation and causes a neurodegenerative phenotype, strongly supporting the functional link between RNF220 and lamin B1."

Reports the lamin mislocalization and neurodegeneration in the fly.

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Source YAML

click to show

name: Hypomyelinating Leukodystrophy 23
creation_date: "2026-09-02T00:00:00Z"
category: Mendelian
description: >-
  Hypomyelinating leukodystrophy 23 (HLD23) is an autosomal recessive
  multisystem leukodystrophy caused by biallelic missense variants in RNF220,
  which encodes a RING-finger E3 ubiquitin ligase. It was delineated in 2021
  from seven consanguineous families carrying one of two recurrent homozygous
  substitutions at adjacent, highly conserved arginines — p.R363Q and p.R365Q.
  The name of the entity is the point of it: the disease is not a
  CNS-restricted hypomyelination but a leukodystrophy with ataxia and
  progressive sensorineural deafness that also carries fibrotic cardiomyopathy
  and hepatopathy. Affected individuals are reported to become severely ataxic
  in the early teenage years and to die in the second decade; no published
  source names the proximate cause of death or reports survival separately for
  the two alleles.

  Two mechanistic routes out of the same RNF220 lesion are documented, and they
  are not the same claim. The first is nuclear: mass spectrometry identified
  lamin B1 as an RNF220 binding partner, both mutants bind it less well, and
  patient fibroblasts show the nuclear blebs, herniations and invaginations
  characteristic of a laminopathy — which is why the original report classified
  HLD23 among the laminopathies rather than among the classical myelin-protein
  leukodystrophies. The second is oligodendroglial: RNF220 stabilises the
  transcription factors Olig1 and Olig2 by K63-linked polyubiquitination, and a
  knock-in mouse carrying the patient R365Q allele loses that stabilisation,
  fails oligodendrocyte progenitor proliferation and differentiation, and is
  severely hypomyelinated. What has not been shown is how either route produces
  the deafness, the hepatopathy or the cardiomyopathy; those three limbs of the
  disease name are clinically established and mechanistically unexplained, and
  the knock-in mouse does not reproduce them.
disease_term:
  preferred_term: Hypomyelinating leukodystrophy 23
  term:
    id: MONDO:0030514
    label: leukodystrophy, hypomyelinating, 23, with ataxia, deafness, liver dysfunction, and dilated cardiomyopathy
synonyms:
- HLD23
- RNF220-related leukodystrophy
- leukodystrophy, hypomyelinating, 23, with ataxia, deafness, liver dysfunction, and dilated cardiomyopathy
parents:
- leukodystrophy
external_assertions:
- name: OMIM HLD23 phenotype record
  source: OMIM
  assertion_type: disease_record
  external_id: OMIM:619688
  description: >-
    OMIM phenotype identifier for leukodystrophy, hypomyelinating, 23, with
    ataxia, deafness, liver dysfunction, and dilated cardiomyopathy (HLD23),
    assigned following the Sferra et al. delineation in PMID:33964137.
references:
- reference: PMID:33964137
  title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
  findings: []
- reference: PMID:36083980
  title: The recurrent mutation in RNF220 also causes hypomyelination in China and is a CpG hot spot.
  findings: []
- reference: PMID:38324685
  title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
  findings: []
- reference: PMID:40594583
  title: Overview of genetic variants in a cohort of Iranian patients with leukodystrophy.
  findings: []
inheritance:
- name: Autosomal Recessive
  description: >-
    HLD23 segregates as an autosomal recessive trait. The delineating study
    identified homozygosity for one of two recurrent RNF220 missense variants
    in consanguineous nuclear families, with heterozygous unaffected parents.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Whole exome sequencing performed in five large consanguineous nuclear families allowed us to identify homozygosity for two recurrent missense variants affecting highly conserved residues of RNF220 as the causative event underlying a novel form of leukodystrophy with ataxia and sensorineural deafness."
    explanation: >-
      Homozygosity for the causative variants in consanguineous pedigrees
      establishes autosomal recessive inheritance.
genetic:
- name: RNF220
  notes: >-
    RNF220 encodes a RING-finger E3 ubiquitin ligase. The two reported HLD23
    alleles are missense substitutions at adjacent conserved arginine residues,
    p.R363Q and p.R365Q. Both reduce binding to lamin B1, and both lose the
    ability of RNF220 to raise endogenous Olig1 and Olig2 protein levels — the
    two alleles behave the same way in every published assay. No source
    stratifies clinical course, cause of death or survival by allele; the
    clinical reports describe the two together. Only R365Q has been modelled in
    mouse, which is a difference in what has been studied, not a reported
    difference between the alleles.
  gene_term:
    preferred_term: RNF220
    term:
      id: hgnc:25552
      label: RNF220
  relationship_type: CAUSATIVE
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report these two homozygous missense variants (p.R363Q and p.R365Q) in the ubiquitin E3 ligase RNF220 as the underlying cause of this novel form of leukodystrophy with ataxia and sensorineural deafness that includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families."
    explanation: >-
      Names both causative alleles, the gene, and the multisystem phenotype
      they produce across seven families.
  - reference: PMID:40594583
    reference_title: Overview of genetic variants in a cohort of Iranian patients with leukodystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, six cases carried homozygote variants in the GJC2, PLEKHG2, RNF220, POLR1C, DEGS1 and ACER3 genes, respectively."
    explanation: >-
      An independent leukodystrophy cohort recovered a homozygous RNF220
      variant, supporting RNF220 as a recurrent cause in this disease group.
      The cohort's own variant was classified as a VUS, so this is corroborating
      rather than independently confirmatory. The paper reports the change at
      the nucleotide level only (NM_018150 c.1088G > A); c.1088 is the second
      base of codon 363, so a CGA to CAA change there would give p.R363Q, one of
      the two recurrent alleles. That is an inference from the coordinates, not
      something the paper states, and it is recorded here rather than curated as
      a protein-level claim.
mechanistic_hypotheses:
- hypothesis_group_id: lamin_b1_nuclear_lamina
  hypothesis_label: HLD23 is a laminopathy acting through impaired RNF220-lamin B1 regulation
  status: EMERGING
  description: >-
    The original delineating proposal: that the primary consequence of the
    RNF220 arginine substitutions is loss of normal regulation of lamin B1 and
    of nuclear lamina architecture, and that the neurodegeneration follows from
    nuclear envelope dysfunction. It is supported by direct binding data, by a
    Drosophila model, and by patient-fibroblast nuclear morphology, but the
    step from abnormal nuclei to hypomyelination specifically has not been
    demonstrated.
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Mass spectrometry analysis identified lamin B1 as the RNF220 binding protein and co-immunoprecipitation experiments demonstrated reduced binding of both RNF220 mutants to lamin B1."
    explanation: >-
      Establishes the physical interaction and that both disease alleles impair
      it, which is the molecular premise of this hypothesis.
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Overall, our data identify RNF220 as a gene implicated in leukodystrophy with ataxia and sensorineural deafness and document a critical role of RNF220 in the regulation of nuclear lamina."
    explanation: >-
      The authors' own framing of the hypothesis, stated as an interpretation
      of their data rather than a demonstrated causal path to hypomyelination.
- hypothesis_group_id: olig_stabilization_failure
  hypothesis_label: Loss of RNF220-mediated Olig1/Olig2 stabilization causes the hypomyelination
  status: EMERGING
  description: >-
    The competing — or complementary — proposal that the myelin limb of HLD23
    arises cell-autonomously in the oligodendrocyte lineage, because RNF220
    normally maintains Olig1 and Olig2 protein levels through K63-linked
    polyubiquitination and neither disease allele can. This is the
    better-evidenced route for hypomyelination specifically, resting on a
    knock-in mouse carrying the R365Q allele — the only one of the two modelled
    in vivo — but it says nothing about the deafness, liver or cardiac limbs.
  evidence:
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We were able to replicate leukodystrophy-like symptoms in a pathomimetic RNF220R365Q knock-in mouse model, which represents deregulated K63 ubiquitination of Olig proteins and impediments of oligodendroglial differentiation and myelination."
    explanation: >-
      A mouse carrying the actual patient allele reproduces both the proposed
      molecular defect and the myelin phenotype, which is the strongest support
      for this route.
pathophysiology:
- name: RNF220 Missense Substitution at Conserved Arginine R363/R365
  conforms_to: "cns_myelin_failure#Oligodendrocyte-Lineage or Myelin-Membrane Insult"
  biological_scale: MOLECULAR
  genetic_context:
    allele_type: MISSENSE
    variant_origin: GERMLINE
    zygosity: HOMOZYGOUS
    functional_impact_category: PARTIAL_LOSS_OF_FUNCTION
    description: >-
      Both variants are homozygous germline missense changes. They are curated
      as partial loss of function rather than complete null: the mutant protein
      is expressed and retains partial lamin B1 binding, and the phenotype is
      milder than the profound developmental failure of full RNF220 depletion
      in mouse.
  description: >-
    The initiating lesion. Homozygous p.R363Q or p.R365Q substitutions affect
    adjacent, highly conserved arginine residues of the RNF220 E3 ubiquitin
    ligase. This is the disorder-specific substitution for the module's trigger
    node: RNF220 is oligodendrocyte-essential ubiquitination machinery rather
    than a myelin structural protein or a lipid-degradation enzyme.
  genes:
  - preferred_term: RNF220
    term:
      id: hgnc:25552
      label: RNF220
  molecular_functions:
  - preferred_term: ubiquitin protein ligase activity
    term:
      id: GO:0061630
      label: ubiquitin protein ligase activity
    modifier: DECREASED
  downstream:
  - target: Reduced RNF220 Binding to Lamin B1
    description: >-
      Both mutant proteins co-immunoprecipitate lamin B1 less efficiently than
      wild-type RNF220.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:33964137
      reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Mass spectrometry analysis identified lamin B1 as the RNF220 binding protein and co-immunoprecipitation experiments demonstrated reduced binding of both RNF220 mutants to lamin B1."
      explanation: >-
        Directly measures the binding defect produced by the disease alleles.
  - target: Failure of K63-Linked Polyubiquitination and Stabilization of Olig1/Olig2
    description: >-
      Both mutant proteins lose the ability to raise endogenous Olig1 and Olig2
      protein levels, the substrates RNF220 normally stabilizes.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38324685
      reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "both RNF220R363Q and RNF220R365Q lost the ability to increase the protein levels of endogenous Olig1 and Olig2"
      explanation: >-
        Establishes that both patient alleles, not one of them, abolish
        substrate stabilization.
  - target: Cardiac and Hepatic Involvement
    description: >-
      The cardiac and hepatic limbs segregate with the homozygous RNF220
      genotype across the reported consanguineous families. No intermediate
      mechanism between the ligase defect and the cardiac or hepatic phenotype
      has been demonstrated, so the link is recorded without asserting a route.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33964137
      reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "this novel form of leukodystrophy with ataxia and sensorineural deafness that includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families"
      explanation: >-
        Establishes the cardiac and hepatic limbs as features of the RNF220
        genotype without asserting an intermediate mechanism.
  - target: Auditory Pathway Involvement
    description: >-
      Sensorineural deafness is part of the core phenotype defined by the
      homozygous RNF220 genotype. Whether the lesion is cochlear or
      retrocochlear is unknown, so no intermediate is asserted.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33964137
      reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Whole exome sequencing performed in five large consanguineous nuclear families allowed us to identify homozygosity for two recurrent missense variants affecting highly conserved residues of RNF220 as the causative event underlying a novel form of leukodystrophy with ataxia and sensorineural deafness."
      explanation: >-
        Establishes sensorineural deafness as a feature of the causative
        genotype without asserting where in the auditory pathway it arises.
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Whole exome sequencing performed in five large consanguineous nuclear families allowed us to identify homozygosity for two recurrent missense variants affecting highly conserved residues of RNF220 as the causative event underlying a novel form of leukodystrophy with ataxia and sensorineural deafness."
    explanation: >-
      Establishes these substitutions as the causative genetic lesion.
- name: Reduced RNF220 Binding to Lamin B1
  biological_scale: MOLECULAR
  description: >-
    Lamin B1 is the RNF220 interaction partner identified by mass spectrometry,
    and both disease alleles bind it less well. This is the molecular basis of
    the laminopathy interpretation of HLD23.
  molecular_functions:
  - preferred_term: lamin binding
    term:
      id: GO:0005521
      label: lamin binding
    modifier: DECREASED
  downstream:
  - target: Nuclear Lamina Disorganization and Abnormal Nuclear Morphology
    description: >-
      Loss of RNF220 regulation of lamin B1 disturbs nuclear lamina
      architecture.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:33964137
      reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Finally, we demonstrate that RNF220 plays a crucial role in the maintenance of nuclear morphology; mutations in primary skin fibroblasts determine nuclear abnormalities such as blebs, herniations and invaginations, which are typically observed in cells of patients affected by laminopathies."
      explanation: >-
        Links loss of RNF220 function directly to disordered nuclear
        architecture in patient cells.
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Mass spectrometry analysis identified lamin B1 as the RNF220 binding protein and co-immunoprecipitation experiments demonstrated reduced binding of both RNF220 mutants to lamin B1."
    explanation: >-
      Identifies lamin B1 as the partner and documents reduced binding by both
      mutants.
- name: Nuclear Lamina Disorganization and Abnormal Nuclear Morphology
  biological_scale: CELLULAR
  description: >-
    Primary skin fibroblasts from HLD23 patients show blebs, herniations and
    invaginations of the nuclear envelope — the cellular signature that places
    this disease among the laminopathies. In Drosophila, RNF220 silencing
    mislocalizes and aggregates the lamin B1 orthologue lamin Dm0 and produces a
    neurodegenerative phenotype.
  biological_processes:
  - preferred_term: nuclear envelope organization
    term:
      id: GO:0006998
      label: nuclear envelope organization
    modifier: DECREASED
  downstream:
  - target: Progressive Neurodegeneration and White Matter Dysfunction
    description: >-
      Nuclear envelope dysfunction is proposed as the route from the RNF220
      lesion to neurodegeneration, by analogy with the other laminopathies.
      The specific step to hypomyelination has not been demonstrated.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33964137
      reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We demonstrate that RNF220 silencing in Drosophila melanogaster specifically affects proper localization of lamin Dm0, the fly lamin B1 orthologue, promotes its aggregation and causes a neurodegenerative phenotype, strongly supporting the functional link between RNF220 and lamin B1."
      explanation: >-
        An invertebrate model connects loss of RNF220 to lamin mislocalization
        and neurodegeneration. Curated as INDIRECT because the model is not a
        myelinating vertebrate and does not report hypomyelination.
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "mutations in primary skin fibroblasts determine nuclear abnormalities such as blebs, herniations and invaginations, which are typically observed in cells of patients affected by laminopathies"
    explanation: >-
      Documents the abnormal nuclear morphology in cells taken from affected
      individuals.
- name: Failure of K63-Linked Polyubiquitination and Stabilization of Olig1/Olig2
  biological_scale: MOLECULAR
  description: >-
    RNF220 normally attaches K63-linked polyubiquitin chains to the
    oligodendrocyte transcription factors Olig1 and Olig2, maintaining their
    protein stability. This is a non-degradative, stabilizing ubiquitination —
    not the canonical K48 proteasomal signal — so loss of RNF220 lowers rather
    than raises Olig protein levels. In the R365Q knock-in mouse, forebrain
    polyubiquitination of Olig1 and Olig2 is reduced and both proteins are less
    abundant in isolated progenitor and oligodendrocyte fractions.
  molecular_functions:
  - preferred_term: ubiquitin protein ligase activity
    term:
      id: GO:0061630
      label: ubiquitin protein ligase activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: protein K63-linked ubiquitination
    term:
      id: GO:0070534
      label: protein K63-linked ubiquitination
    modifier: DECREASED
  downstream:
  - target: Oligodendrocyte Progenitor Proliferation and Differentiation Failure
    description: >-
      Depleted Olig1 and Olig2 remove the transcriptional drive that the
      oligodendrocyte lineage depends on.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38324685
      reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "RNF220 regulated K63-linked polyubiquitination to maintain Olig1 and Olig2 protein stability, and this modulation is required for oligodendroglial development and myelination, as well as remyelination."
      explanation: >-
        States the requirement of this specific modification for
        oligodendroglial development.
  evidence:
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Furthermore, we showed that Olig1 and Olig2 are two direct ubiquitination substrates of RNF220, and the protein stabilities of these two TFs are maintained by RNF220 through K63-linked polyubiquitination."
    explanation: >-
      Establishes Olig1 and Olig2 as direct substrates and the chain linkage
      involved.
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Moreover, in the pathomimetic RNF220R365Q knock-in mouse model, deregulation of ubiquitination and stabilization of the Olig proteins leads to maldevelopment of oligodendroglia, corpus callosum agenesis, and leukodystrophy-like symptoms."
    explanation: >-
      Shows the defect occurs in vivo in an animal carrying the human disease
      allele.
- name: Oligodendrocyte Progenitor Proliferation and Differentiation Failure
  conforms_to: "cns_myelin_failure#Oligodendrocyte Differentiation Arrest and Death"
  biological_scale: CELLULAR
  description: >-
    Oligodendrocyte progenitor cells proliferate less and fail to differentiate
    into mature oligodendrocytes. In conditional RNF220 knockout mouse corpus
    callosum, BrdU and Ki67 labelling of progenitors is reduced at P3 and mature
    CC1+Sox10+ oligodendrocytes are fewer at P21. This is the module's
    differentiation-arrest node; the arrest, not oligodendrocyte death after
    myelination, is the documented route in HLD23.
  cell_types:
  - preferred_term: oligodendrocyte precursor cell
    term:
      id: CL:0002453
      label: oligodendrocyte precursor cell
  - preferred_term: oligodendrocyte
    term:
      id: CL:0000128
      label: oligodendrocyte
  biological_processes:
  - preferred_term: oligodendrocyte differentiation
    term:
      id: GO:0048709
      label: oligodendrocyte differentiation
    modifier: DECREASED
  - preferred_term: glial cell proliferation
    term:
      id: GO:0014009
      label: glial cell proliferation
    modifier: DECREASED
  downstream:
  - target: Deficient CNS Myelin Deposition
    description: >-
      Too few mature oligodendrocytes are generated to lay down normal myelin.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38324685
      reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Together, these results indicate that RNF220 is involved in regulating both OPC proliferation and differentiation to OL, and its deficiency impairs oligodendroglial development and leads to hypomyelination in mouse brains."
      explanation: >-
        States the causal sequence from progenitor defect to hypomyelination.
  evidence:
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "RNF220 depletion in oligodendrocyte lineage cells impedes oligodendrocyte progenitor cell proliferation, differentiation, and (re)myelination, which consequently leads to learning and memory defects."
    explanation: >-
      Establishes the progenitor proliferation and differentiation defect as
      cell-autonomous to the oligodendrocyte lineage.
- name: Deficient CNS Myelin Deposition
  conforms_to: "cns_myelin_failure#Deficient or Unstable CNS Myelin Sheath"
  biological_scale: TISSUE
  description: >-
    Myelin is never adequately laid down — hypomyelination rather than
    demyelination. In the R365Q knock-in mouse, corpus callosum axons are
    severely hypomyelinated on black-gold staining and electron microscopy, and
    the myelin structural proteins MBP, PLP, MAG and MOG are all reduced at both
    mRNA and protein level.
  cell_types:
  - preferred_term: oligodendrocyte
    term:
      id: CL:0000128
      label: oligodendrocyte
  biological_processes:
  - preferred_term: central nervous system myelination
    term:
      id: GO:0022010
      label: central nervous system myelination
    modifier: DECREASED
  cellular_components:
  - preferred_term: myelin sheath
    term:
      id: GO:0043209
      label: myelin sheath
  locations:
  - preferred_term: cerebral white matter
    term:
      id: UBERON:0002316
      label: white matter
  downstream:
  - target: Progressive Neurodegeneration and White Matter Dysfunction
    description: >-
      Absent myelin removes saltatory conduction and the oligodendroglial
      metabolic support the axon depends on.
    causal_link_type: DIRECT
  - target: Leukodystrophy
    description: >-
      Hypomyelination is what is seen as the leukodystrophy on imaging.
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Furthermore, the mRNA and protein levels of myelin-related molecules, including MBP, PLP, MAG, and MOG, were significantly down-regulated in the forebrains of RNF220-QQ mice"
    explanation: >-
      Quantifies the myelin deficit at the level of the structural proteins in
      the mouse carrying the patient allele.
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals harboring homozygous R363Q or R365Q mutation of RNF220 have symptoms of leukodystrophy and corpus callosum agenesis, as well as intellectual disability"
    explanation: >-
      The human counterpart of the mouse myelin measurement above. The direct
      quantification of myelin deficiency exists only in the mouse; in patients
      the deficit is inferred from the leukodystrophy and callosal phenotype.
- name: Progressive Neurodegeneration and White Matter Dysfunction
  conforms_to: "cns_myelin_failure#Axonal Degeneration and Progressive White Matter Dysfunction"
  biological_scale: ORGANISM
  description: >-
    The clinical endpoint of the CNS limb. Loss of the sheath is followed by
    secondary axonal degeneration and progressive white matter dysfunction,
    which in HLD23 presents as ataxia beginning in childhood and progressing
    over the first two decades. The node specializes the module's endpoint with
    the HLD23 tract distribution and tempo; it carries the module's
    axon-maintenance process rather than repeating the myelination process of
    the upstream deposition node.
  biological_processes:
  - preferred_term: neuron projection maintenance
    term:
      id: GO:1990535
      label: neuron projection maintenance
    modifier: DECREASED
  locations:
  - preferred_term: cerebral white matter
    term:
      id: UBERON:0002316
      label: white matter
  downstream:
  - target: Ataxia
    description: >-
      Progressive white matter and cerebellar pathway dysfunction produces the
      ataxia that names the entity.
    causal_link_type: DIRECT
  - target: Intellectual Disability
    description: >-
      Cognitive impairment accompanies the white matter disease.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Agenesis of the Corpus Callosum
    description: >-
      The most severely affected white matter tract fails to form.
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals harboring homozygous R363Q or R365Q mutation of RNF220 have symptoms of leukodystrophy and corpus callosum agenesis, as well as intellectual disability"
    explanation: >-
      Summarizes the human CNS phenotype attributable to both disease alleles.
- name: Cardiac and Hepatic Involvement
  conforms_to: "cardiomyopathy_maladaptive_remodeling#Structural Cardiac Impairment and Heart Failure"
  biological_scale: ORGANISM
  description: >-
    Fibrotic cardiomyopathy and hepatopathy are established clinical features of
    HLD23 and are what distinguishes it from a CNS-restricted hypomyelinating
    leukodystrophy. Conformance is declared at the module's
    structural-impairment endpoint only, because no upstream cardiomyocyte
    insult, neurohormonal activation or remodeling step has been demonstrated
    for RNF220. Whether the nuclear-lamina lesion, the Olig-stabilization
    lesion, or a third RNF220 substrate accounts for these organ limbs is
    unknown.
  cell_types:
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  downstream:
  - target: Dilated Cardiomyopathy
    description: >-
      The cardiac limb presents as a fibrotic, dilated cardiomyopathy.
    causal_link_type: UNKNOWN
  - target: Hepatic Dysfunction
    description: >-
      The hepatic limb presents as hepatopathy with abnormal liver function.
    causal_link_type: UNKNOWN
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "this novel form of leukodystrophy with ataxia and sensorineural deafness that includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families"
    explanation: >-
      The only published statement establishing the cardiac and hepatic limbs,
      across seven families.
- name: Auditory Pathway Involvement
  biological_scale: ORGANISM
  description: >-
    Progressive sensorineural deafness is one of the four defining features of
    HLD23. It is deliberately curated as an unexplained node rather than
    conformed to the sensorineural_hair_cell_loss module: no cochlear hair cell,
    stria vascularis or spiral ganglion pathology has been reported in RNF220
    disease, and the deafness could equally be retrocochlear given the
    underlying white matter disease. Conforming this node would assert a
    cochlear mechanism that has not been evidenced.
  downstream:
  - target: Sensorineural Hearing Loss
    description: >-
      The auditory limb presents as progressive sensorineural hearing
      impairment.
    causal_link_type: UNKNOWN
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a novel form of leukodystrophy with ataxia and sensorineural deafness"
    explanation: >-
      Establishes sensorineural deafness as a defining feature of the entity.
phenotypes:
- category: Neurological
  name: Leukodystrophy
  description: >-
    Hypomyelinating white matter disease, the defining imaging and pathological
    feature of the entity.
  phenotype_term:
    preferred_term: Leukodystrophy
    term:
      id: HP:0002415
      label: Leukodystrophy
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a novel form of leukodystrophy with ataxia and sensorineural deafness"
    explanation: >-
      Names leukodystrophy as the core phenotype of this entity.
- category: Neurological
  name: Ataxia
  description: >-
    Ataxia is a defining feature, severe by the early teenage years in most
    affected individuals.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a novel form of leukodystrophy with ataxia and sensorineural deafness"
    explanation: >-
      Establishes ataxia as a defining feature.
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "most affected patients suffered from severe ataxia during their early teenage years and died at their second teenage years"
    explanation: >-
      Dates the severity of the ataxia and supports the progressive course.
- category: Auditory
  name: Sensorineural Hearing Loss
  description: >-
    Progressive sensorineural deafness, present across the reported families.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a novel form of leukodystrophy with ataxia and sensorineural deafness"
    explanation: >-
      Establishes sensorineural deafness as a defining feature.
- category: Cardiovascular
  name: Dilated Cardiomyopathy
  description: >-
    Fibrotic cardiomyopathy is an associated feature across the reported
    families. The entity's MONDO and OMIM names call this a dilated
    cardiomyopathy; the delineating paper describes it as fibrotic. No source
    reports whether the cardiac disease is the cause of death.
  phenotype_term:
    preferred_term: Dilated cardiomyopathy
    term:
      id: HP:0001644
      label: Dilated cardiomyopathy
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families"
    explanation: >-
      Establishes cardiomyopathy as an associated feature. The paper's wording
      is "fibrotic", not "dilated", which is recorded in the description.
- category: Hepatic
  name: Hepatic Dysfunction
  description: >-
    Hepatopathy with impaired liver function is an associated feature.
  phenotype_term:
    preferred_term: Decreased liver function
    term:
      id: HP:0001410
      label: Decreased liver function
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families"
    explanation: >-
      Establishes hepatopathy as an associated feature.
- category: Neurological
  name: Intellectual Disability
  description: >-
    Cognitive impairment reported in individuals homozygous for either disease
    allele.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals harboring homozygous R363Q or R365Q mutation of RNF220 have symptoms of leukodystrophy and corpus callosum agenesis, as well as intellectual disability"
    explanation: >-
      Reports intellectual disability in patients with both alleles.
- category: Neurological
  name: Agenesis of the Corpus Callosum
  description: >-
    Corpus callosum agenesis is reported in affected individuals and is
    reproduced in the R365Q knock-in mouse.
  phenotype_term:
    preferred_term: Agenesis of corpus callosum
    term:
      id: HP:0001274
      label: Agenesis of corpus callosum
  evidence:
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals harboring homozygous R363Q or R365Q mutation of RNF220 have symptoms of leukodystrophy and corpus callosum agenesis, as well as intellectual disability"
    explanation: >-
      Reports corpus callosum agenesis as a human feature of both alleles.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    The delineating study reports the entity in seven consanguineous families,
    and only a handful of further cases have been published since. No source
    gives a rate, so the qualitative band is used rather than an Orphanet
    numeric class.
  evidence:
  - reference: PMID:33964137
    reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families"
    explanation: >-
      Gives the published case count behind the CASES_IN_LITERATURE measure.
progression:
- phase: Childhood onset with severe ataxia by the early teens and death in the second decade
  notes: >-
    Affected individuals develop severe ataxia by the early teenage years and
    die during the second decade. The reported course is not stratified by
    allele, and the proximate cause of death is not stated in any published
    source.
  evidence:
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "most affected patients suffered from severe ataxia during their early teenage years and died at their second teenage years"
    explanation: >-
      Documents the timing of severe ataxia and of death.
animal_models:
- name: RNF220 R365Q knock-in mouse (RNF220-QQ)
  species: Mouse
  genotype: Rnf220 p.R365Q homozygous knock-in (CRISPR-Cas9)
  publication: PMID:38324685
  description: >-
    A CRISPR-generated mouse carrying the human HLD23 R365Q allele in homozygous
    form. It reproduces the CNS myelin limb of the disease — severe corpus
    callosum hypomyelination on MRI, black-gold staining and electron
    microscopy, reduced myelin protein expression, reduced Olig polyubiquitination
    — but the authors state explicitly that it does not reproduce the full
    patient phenotype, showing no survival or walking deficit over 12 months
    where patients are severely ataxic as teenagers and die in the second decade.
  modeled_mechanisms:
  - target: Deficient CNS Myelin Deposition
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      The knock-in carries the actual patient allele and reproduces
      hypomyelination of the corpus callosum by three independent modalities.
    limitations: >-
      Mouse corpus callosum myelination is the readout; no human CNS tissue
      comparison is available.
    readouts:
    - name: Corpus callosum myelin protein expression (MBP, PLP, MAG, MOG)
      target: Deficient CNS Myelin Deposition
      direction: DECREASED
      interpretation: >-
        Structural myelin proteins are reduced, the molecular correlate of the
        hypomyelination node.
      evidence:
      - reference: PMID:38324685
        reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Furthermore, the mRNA and protein levels of myelin-related molecules, including MBP, PLP, MAG, and MOG, were significantly down-regulated in the forebrains of RNF220-QQ mice"
        explanation: >-
          Reports the measurement behind this readout.
    evidence:
    - reference: PMID:38324685
      reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Consistent with this finding, BG staining and TEM analyses showed that the axonal fibers of corpus callosum in RNF220-QQ mice were severely hypomyelinated"
      explanation: >-
        Supports treating this model as informative for the hypomyelination
        node.
  - target: Failure of K63-Linked Polyubiquitination and Stabilization of Olig1/Olig2
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      The proposed molecular defect is directly observed in vivo in the animal
      carrying the patient allele.
    limitations: >-
      Measured in mouse forebrain lysates; the equivalent measurement has not
      been made in human patient tissue.
    evidence:
    - reference: PMID:38324685
      reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Moreover, in the pathomimetic RNF220R365Q knock-in mouse model, deregulation of ubiquitination and stabilization of the Olig proteins leads to maldevelopment of oligodendroglia, corpus callosum agenesis, and leukodystrophy-like symptoms."
      explanation: >-
        Confirms the molecular defect in the knock-in animal.
  - target: Progressive Neurodegeneration and White Matter Dysfunction
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: >-
      The mouse has cognitive deficits and a rotarod abnormality, but not the
      progressive, lethal neurological decline that defines the human disease.
    limitations: >-
      The authors report no significant difference in survival or walking
      performance over a 12-month observation, whereas affected individuals are
      severely ataxic as teenagers and die in the second decade. The model
      therefore cannot be used to study the progressive or lethal component of
      the disease.
    evidence:
    - reference: PMID:38324685
      reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "RNF220-QQ mice showed no significant difference in survival and walking performance during our 12-month observation"
      explanation: >-
        The mouse result itself. The authors report it in a sentence that also
        restates the human course; that clause is quoted separately under
        phenotypes and progression, because it is a human-clinical observation
        and cannot be graded MODEL_ORGANISM here.
  evidence:
  - reference: PMID:38324685
    reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We were able to replicate leukodystrophy-like symptoms in a pathomimetic RNF220R365Q knock-in mouse model, which represents deregulated K63 ubiquitination of Olig proteins and impediments of oligodendroglial differentiation and myelination."
    explanation: >-
      Supports treating this model as informative for the disease's myelin
      mechanism.
- name: RNF220 conditional knockout mouse (oligodendrocyte lineage)
  species: Mouse
  genotype: Rnf220 conditional knockout in oligodendrocyte lineage cells (RNF220-cKO)
  publication: PMID:38324685
  description: >-
    A lineage-restricted knockout used to establish that the myelin defect is
    cell-autonomous to oligodendroglia rather than secondary to disease
    elsewhere. It is not an allelic model of HLD23 — it is a null, whereas
    patients carry partial-loss-of-function missense alleles.
  modeled_mechanisms:
  - target: Oligodendrocyte Progenitor Proliferation and Differentiation Failure
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Conditional deletion within the lineage impairs progenitor proliferation
      and differentiation, establishing cell autonomy.
    limitations: >-
      A complete knockout rather than the patient missense allele, so it
      overstates the severity of the human lesion; it also cannot address
      the non-CNS limbs of the disease.
    evidence:
    - reference: PMID:38324685
      reference_title: "RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In this study, we found that the E3 ubiquitin ligase RNF220 is required for oligodendroglial development, and its specific depletion in OL lineage cells impairs OPC proliferation, differentiation, subsequent myelination, as well as remyelination after demyelinating injury in the adult mouse brains."
      explanation: >-
        Establishes the cell-autonomous requirement within the lineage.
- name: RNF220 silencing in Drosophila melanogaster
  species: Fruit fly
  genotype: RNF220 RNAi silencing
  publication: PMID:33964137
  description: >-
    An invertebrate model used to test the lamin B1 arm of the mechanism.
    Silencing RNF220 mislocalizes and aggregates lamin Dm0, the fly lamin B1
    orthologue, and causes neurodegeneration.
  modeled_mechanisms:
  - target: Nuclear Lamina Disorganization and Abnormal Nuclear Morphology
    relationship: RECAPITULATES
    fidelity: LOW
    description: >-
      Supports the functional link between RNF220 and lamin B1 regulation.
    limitations: >-
      Drosophila has no myelin and no oligodendrocytes, so the model cannot
      speak to the hypomyelination that defines the human disease; it also uses
      silencing rather than the patient missense alleles.
    evidence:
    - reference: PMID:33964137
      reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We demonstrate that RNF220 silencing in Drosophila melanogaster specifically affects proper localization of lamin Dm0, the fly lamin B1 orthologue, promotes its aggregation and causes a neurodegenerative phenotype, strongly supporting the functional link between RNF220 and lamin B1."
      explanation: >-
        Reports the lamin mislocalization and neurodegeneration in the fly.
experimental_models:
- name: HLD23 patient primary skin fibroblasts
  experimental_model_type: PRIMARY_CELL_CULTURE
  description: >-
    Primary dermal fibroblasts from affected individuals, used to demonstrate
    the nuclear envelope abnormalities that support the laminopathy
    classification.
  modeled_mechanisms:
  - target: Nuclear Lamina Disorganization and Abnormal Nuclear Morphology
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Cells carry the patient genotype and display the nuclear morphological
      abnormalities directly.
    limitations: >-
      Fibroblasts are not the disease-relevant cell type for hypomyelination;
      whether patient oligodendrocytes show the same nuclear phenotype is
      untested.
    evidence:
    - reference: PMID:33964137
      reference_title: "Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "mutations in primary skin fibroblasts determine nuclear abnormalities such as blebs, herniations and invaginations, which are typically observed in cells of patients affected by laminopathies"
      explanation: >-
        Reports the nuclear morphology defect in patient-derived cells.
treatments:
- name: Supportive and Multidisciplinary Care
  description: >-
    No disease-modifying therapy exists. Management is supportive and,
    because the disease involves four organ systems, necessarily
    multidisciplinary — cardiac surveillance, hepatic monitoring, audiological
    support and rehabilitation alongside neurological care.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  notes: >-
    Curated from the natural history rather than from a published management
    guideline; no HLD23 treatment trial or consensus care standard has been
    published, and no evidence item is attached because none of the cited
    sources makes a treatment claim.
- name: Genetic Counseling
  description: >-
    Autosomal recessive inheritance with a 25% recurrence risk per pregnancy for
    carrier couples. Relevant to the consanguineous families in which the two
    recurrent alleles were reported.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  notes: >-
    Follows from the established recessive inheritance; no HLD23-specific
    counseling literature exists.
discussions:
- discussion_id: gap_hld23_nonneural_organ_mechanism
  kind: KNOWLEDGE_GAP
  prompt: >-
    By what mechanism do RNF220 missense variants cause sensorineural deafness,
    hepatopathy and cardiomyopathy?
  attaches_to:
  - pathophysiology#Cardiac and Hepatic Involvement
  - pathophysiology#Auditory Pathway Involvement
  rationale: >-
    Three of the four organ systems in this disease's name have no mechanistic
    account at all. Both published mechanisms — reduced lamin B1 binding and
    failed Olig1/Olig2 stabilization — were worked out for the CNS myelin
    phenotype. Olig1/Olig2 are oligodendrocyte transcription factors and cannot
    explain cochlear, hepatic or cardiac disease; the lamin B1 route could in
    principle, since laminopathies commonly involve heart and muscle, but no
    cardiac or hepatic tissue from an HLD23 patient has been examined for
    nuclear envelope pathology. The gap also extends to natural history: no
    published source says which of the four organ limbs is the proximate cause
    of the deaths reported in the second decade, so it is not known whether the
    unexplained limbs or the well-characterised CNS one determine survival.
  proposed_experiments:
  - experiment_id: exp_hld23_nuclear_envelope_heart_liver
    name: Nuclear envelope morphology in HLD23 cardiac and hepatic tissue
    description: >-
      Examine nuclear morphology and lamin B1 distribution in cardiomyocytes and
      hepatocytes from HLD23 autopsy material, or in patient iPSC-derived
      cardiomyocytes and hepatocyte-like cells, using the same blebs and
      invaginations readout applied to patient fibroblasts.
    would_support:
    - pathophysiology#Cardiac and Hepatic Involvement
    - mechanistic_hypotheses#lamin_b1_nuclear_lamina
    supporting_outcome:
    - >-
      Cardiomyocytes and hepatocytes carrying the patient allele show the same
      nuclear blebs, herniations and invaginations seen in patient fibroblasts,
      implicating the lamina lesion in the cardiac and hepatic limbs.
    refuting_outcome:
    - >-
      Patient-derived cardiomyocytes and hepatocytes have normal nuclear
      morphology and lamin B1 distribution, implicating a third RNF220 substrate
      rather than the lamina.
- discussion_id: mismatch_hld23_knockin_mouse_progression
  kind: HUMAN_MODEL_MISMATCH
  prompt: >-
    Why does the RNF220 R365Q knock-in mouse, which carries the exact patient
    allele, not reproduce the progressive ataxia and early death that define the
    human disease?
  attaches_to:
  - animal_models#RNF220 R365Q knock-in mouse (RNF220-QQ)
  - pathophysiology#Progressive Neurodegeneration and White Matter Dysfunction
  rationale: >-
    This is a mismatch rather than a knowledge gap: the model exists, carries the
    correct allele, and reproduces the molecular and myelin phenotypes well, but
    the authors report no survival or walking difference over 12 months against a
    human disease that is lethal in the second decade. The divergence is
    mechanistically informative rather than a technical failure — it suggests the
    lethal component of HLD23 is not the hypomyelination the mouse does
    reproduce, though which limb of the disease does account for the deaths is
    not reported anywhere. It also bounds what the model can be used for: it is a
    myelination model, not a disease-progression or therapeutic-endpoint model.
  proposed_experiments:
  - experiment_id: exp_hld23_qq_mouse_cardiac_hepatic_phenotyping
    name: Longitudinal cardiac and hepatic phenotyping of RNF220-QQ mice
    description: >-
      Serial echocardiography, cardiac histology for fibrosis, and liver
      function assessment in RNF220-QQ mice beyond 12 months, to test whether the
      model lacks the non-CNS limbs entirely or merely develops them later than
      the neurological readouts were scored.
    would_support:
    - pathophysiology#Cardiac and Hepatic Involvement
    supporting_outcome:
    - >-
      RNF220-QQ mice develop cardiac fibrosis and impaired liver function,
      establishing the model for the organ limbs and explaining the survival
      discrepancy as a difference in timing rather than in mechanism.
    refuting_outcome:
    - >-
      Cardiac and hepatic structure and function remain normal at all ages,
      confirming a genuine species difference and indicating that the human
      cardiac and hepatic limbs require a modifier absent in mouse.
notes: >-
  Curated without a deep-research provider report. The Edison/falcon provider
  returned HTTP 402 (account out of credits) and the documented claude_code
  fallback failed to launch, so all content here was assembled from
  directly retrieved primary literature.

  The published literature on this entity is genuinely small. Four papers are
  listed under references; two of them (PMID:33964137 and PMID:38324685) carry
  essentially all the mechanistic content, and one of those is a mouse study.
  The entry is deliberately shaped around that: the CNS myelin chain is well
  evidenced, the nuclear-lamina arm is curated as a hypothesis rather than a
  settled pathway, and the auditory, cardiac and hepatic nodes assert clinical
  involvement without manufacturing a mechanism. Those three organ nodes hang
  off the trigger node by INDIRECT_UNKNOWN_INTERMEDIATES edges: the organ limbs
  segregate with the homozygous genotype across the reported families, which is
  a causal link the sources do state, while the route from the ligase defect to
  each organ is unpublished. Their own downstream edges to the corresponding
  phenotypes remain UNKNOWN for the same reason.

  PMID:36083980 (Yan et al., Brain 2022) is the second of the two clinical
  reports that PMID:38324685 cites as "(16, 17)" for its human-phenotype
  statements, the first being PMID:33964137. It is listed here so the citation
  chain is complete, but it supports no evidence item: it is a paywalled
  scientific correspondence with no abstract in PubMed or Europe PMC, so no
  exact quote can be verified against a cache. Anyone with institutional access
  should read it — it is the most likely place for additional natural-history
  detail on this entity.

  Natural history: an allele-stratified mortality claim (R365Q homozygotes dying
  of cardiomyopathy in the first decade, R363Q homozygotes surviving into the
  second) was asserted in an earlier version of this entry and has been removed
  throughout. No cited source states it, and PMID:38324685 describes the course
  without stratifying it — severe ataxia in the early teenage years and death in
  the second decade for affected patients as a group. Nothing published names
  the proximate cause of death.

  PMID:40594583 case 10 (a 14-year-old female homozygous for the same RNF220
  change) also carries a brain tumour. That is deliberately not curated as a
  feature of this entity: the reporting paper states the tumour "has not been
  reported in the literature in association with RNF220 mutations", and a single
  case is not a basis for adding it. Recorded here so the omission is not
  re-litigated.

  Naming note: the MONDO and OMIM labels say "dilated cardiomyopathy" while the
  delineating paper (PMID:33964137) describes "fibrotic cardiomyopathy". Both
  descriptions are retained rather than reconciled, since no source states they
  are the same finding.

📚

References & Deep Research

References

4

PMID:33964137

Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness.

No top-level findings curated for this source.

PMID:36083980

The recurrent mutation in RNF220 also causes hypomyelination in China and is a CpG hot spot.

No top-level findings curated for this source.

PMID:38324685

RNF220-mediated K63-linked polyubiquitination stabilizes Olig proteins during oligodendroglial development and myelination.

No top-level findings curated for this source.

PMID:40594583

Overview of genetic variants in a cohort of Iranian patients with leukodystrophy.

No top-level findings curated for this source.

Deep Research

1

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

Evaluations and curation notes (3)

Record notes

Curated without a deep-research provider report. The Edison/falcon provider returned HTTP 402 (account out of credits) and the documented claude_code fallback failed to launch, so all content here was assembled from directly retrieved primary literature. The published literature on this entity is genuinely small. Four papers are listed under references; two of them (PMID:33964137 and PMID:38324685) carry essentially all the mechanistic content, and one of those is a mouse study. The entry is deliberately shaped around that: the CNS myelin chain is well evidenced, the nuclear-lamina arm is curated as a hypothesis rather than a settled pathway, and the auditory, cardiac and hepatic nodes assert clinical involvement without manufacturing a mechanism. Those three organ nodes hang off the trigger node by INDIRECT_UNKNOWN_INTERMEDIATES edges: the organ limbs segregate with the homozygous genotype across the reported families, which is a causal link the sources do state, while the route from the ligase defect to each organ is unpublished. Their own downstream edges to the corresponding phenotypes remain UNKNOWN for the same reason. PMID:36083980 (Yan et al., Brain 2022) is the second of the two clinical reports that PMID:38324685 cites as "(16, 17)" for its human-phenotype statements, the first being PMID:33964137. It is listed here so the citation chain is complete, but it supports no evidence item: it is a paywalled scientific correspondence with no abstract in PubMed or Europe PMC, so no exact quote can be verified against a cache. Anyone with institutional access should read it — it is the most likely place for additional natural-history detail on this entity. Natural history: an allele-stratified mortality claim (R365Q homozygotes dying of cardiomyopathy in the first decade, R363Q homozygotes surviving into the second) was asserted in an earlier version of this entry and has been removed throughout. No cited source states it, and PMID:38324685 describes the course without stratifying it — severe ataxia in the early teenage years and death in the second decade for affected patients as a group. Nothing published names the proximate cause of death. PMID:40594583 case 10 (a 14-year-old female homozygous for the same RNF220 change) also carries a brain tumour. That is deliberately not curated as a feature of this entity: the reporting paper states the tumour "has not been reported in the literature in association with RNF220 mutations", and a single case is not a basis for adding it. Recorded here so the omission is not re-litigated. Naming note: the MONDO and OMIM labels say "dilated cardiomyopathy" while the delineating paper (PMID:33964137) describes "fibrotic cardiomyopathy". Both descriptions are retained rather than reconciled, since no source states they are the same finding.

Address CHANGES_REQUESTED review: remove uncited allele-stratified mortality claim · 2026-09-03T03:50:42Z · View source

Addressed the ai4c-reviewer CHANGES_REQUESTED review on PR #10656. CRITICAL: the claim that R365Q homozygotes die of dilated cardiomyopathy in the first decade while R363Q homozygotes survive into the second was removed from all eight sites (top-level description, genetic.notes, the Cardiac and Hepatic Involvement node, the Dilated Cardiomyopathy phenotype, the progression record's phase and notes, the supportive-care treatment rationale, the KNOWLEDGE_GAP rationale, and the HUMAN_MODEL_MISMATCH rationale). Searched for a source before removing: PubMed esearch over all 51 RNF220 records, Europe PMC full-text queries for RNF220 with R365Q/cardiomyopathy/dilated cardiomyopathy, and an open-access check on PMID:33964137 and PMID:36083980. Neither cached source states it and no other paper does; PMID:38324685 describes the course unstratified ('most affected patients suffered from severe ataxia during their early teenage years and died at their second teenage years'). Dependent prose was rewritten to rest on that unstratified course instead, and the removal is recorded in the entry notes so the claim is not reintroduced. Roma founder allele claim removed from the genetic-counseling treatment; no source mentions Roma ancestry and PMID:40594583's founder-effect statement concerns RARS1. Truncated Olig snippet repaired: 'R365Q lost the ability...' restored to the full source clause 'both RNF220R363Q and RNF220R365Q lost the ability to increase the protein levels of endogenous Olig1 and Olig2', with the downstream description and genetic.notes corrected so neither asserts an R365Q-specific defect. Ambiguous entity reference animal_models#Mouse retargeted to animal_models#RNF220 R365Q knock-in mouse (RNF220-QQ), since both mouse models declare species: Mouse. Conformance gap closed: the node conforming to cns_myelin_failure#Axonal Degeneration and Progressive White Matter Dysfunction now carries GO:1990535 neuron projection maintenance DECREASED plus UBERON:0002316 white matter, matching the module node, instead of repeating GO:0042552 myelination from the upstream deposition node. PMID:36083980 (Yan et al., Brain 2022) identified and fetched as the second of the two clinical references PMID:38324685 cites as '(16, 17)'. It is listed under references but supports no evidence item: it is a paywalled correspondence with no abstract in PubMed or Europe PMC, so no snippet can be verified. Recorded as such in the entry notes. Also added a prevalence record (CASES_IN_LITERATURE / ULTRA_RARE, evidenced by the seven-families quote) and a note that PMID:40594583's c.1088G > A falls at codon 363, recorded as an inference rather than curated as a protein-level claim. No deep-research provider report backs this entry. Edison/falcon returned HTTP 402 and the claude_code fallback failed to launch; that statement is unchanged and remains accurate. Validation: just validate (passed, 41/41 snippets verified), validate-terms, count-verified-snippets, check-duplicate-keys, check-entity-refs, check-causal-targets, check-qualifier-terms, check-enum-values, check-snippet-grading, check-title-snippets, check-snippet-length, check-folded-hyphens, check-reference-titles, and validate-disorders all run and clean.

Create: Hypomyelinating Leukodystrophy 23 (HLD23, RNF220) · 2026-09-03T03:20:52Z · View source

Created the HLD23 entry (MONDO:0030514, biallelic RNF220) from the seed stub. NO deep-research provider report was obtained: the Edison/falcon provider returned HTTP 402 (out of credits) and the documented claude_code fallback failed to launch ('agentapi not found in PATH' -> 'Claude Code exited with code 1: <no stderr>'). All content was curated from directly retrieved primary literature fetched with just fetch-reference. The literature on this entity is small: a PubMed search for RNF220 combined with leukodystrophy or lamin returns exactly three papers, all cited here (PMID:33964137 Sferra et al. Brain 2021, the delineating clinical study; PMID:38324685 Li et al. Sci Adv 2024, the Olig1/Olig2 K63-ubiquitination mouse study; PMID:40594583, an Iranian leukodystrophy cohort contributing a corroborating homozygous RNF220 case classified as a VUS). Verified the issue's claims before curating: hgnc:25552 resolves to RNF220 via OAK, MONDO:0030514's canonical label was confirmed and the seed file's incorrect title-cased label was replaced, and RNF220 in Wieacker_Wolff_Syndrome.yaml was confirmed to appear only inside reference titles and evidence snippets rather than as a causal genetic binding, so the coverage claim held. entry_type recorded as DISEASE. Two mechanistic routes are curated as separate EMERGING mechanistic_hypotheses rather than merged: reduced RNF220-lamin B1 binding with patient-fibroblast nuclear blebs (the laminopathy interpretation) and failed K63-linked stabilization of Olig1/Olig2 (the better-evidenced route to hypomyelination). Declared conforms_to against cns_myelin_failure at the trigger, differentiation-arrest, myelin-sheath and axonal-degeneration nodes, which fits that module's documented scope for oligodendrocyte-essential transcription machinery, and against cardiomyopathy_maladaptive_remodeling at the structural-impairment endpoint only, since no upstream cardiomyocyte insult or remodeling step is published for RNF220. Deliberately did NOT conform the deafness node to sensorineural_hair_cell_loss: no cochlear pathology has been reported and the deafness could be retrocochlear, so conforming would assert an unevidenced mechanism. The auditory, cardiac and hepatic edges carry causal_link_type UNKNOWN, and a KNOWLEDGE_GAP discussion records that three of the four organ systems in the disease name have no mechanistic account. A HUMAN_MODEL_MISMATCH discussion plus a PARTIALLY_RECAPITULATES link record that the R365Q knock-in mouse reproduces the myelin phenotype but not the progressive lethal course. Validation run: just validate passed; validate-terms passed; count-verified-snippets 40/40; check-duplicate-keys, check-entity-refs, check-causal-targets, check-qualifier-terms (0 qualifier terms; none used), check-enum-values, check-snippet-length, check-title-snippets, check-folded-hyphens all OK. check-snippet-grading initially failed on a real defect I introduced - a mixed sentence reporting both the mouse result and the human course was graded MODEL_ORGANISM on the animal-model link while its human clause was graded HUMAN_CLINICAL under phenotypes and progression; re-quoted the animal-model item to the mouse clause alone and the gate passed.

OpenScientist ▸

1. Disease Information

openscientist-autonomous 2026-09-07T13:16:45.880656

1. Disease Information

Overview. HLD23 is a genetically determined disorder of central nervous system white matter (a leukodystrophy) in which myelin is deficient from the outset (hypomyelination) rather than being formed and then lost. The primary lesion is in glia/myelin, with secondary axonal degeneration emerging as the disease progresses. It is distinctive among hypomyelinating leukodystrophies for combining CNS hypomyelination with cerebellar ataxia, sensorineural deafness, cardiac (fibrotic cardiomyopathy) and hepatic involvement, and for being mechanistically a laminopathy.

"Leukodystrophies are a heterogeneous group of rare inherited disorders that mostly involve the white matter of the CNS. These conditions are characterized by primary glial cell and myelin sheath pathology of variable aetiology, which causes secondary axonal degeneration, generally emerging with disease progression." — PMID 33964137

Key identifiers - MONDO: MONDO:0030514 - OMIM (phenotype): #619688 (Leukodystrophy, hypomyelinating, 23, with ataxia, deafness, liver dysfunction, and dilated cardiomyopathy) - Gene OMIM: RNF220 616136 - HGNC: RNF220 (HGNC:25552); NCBI Gene: 55182; Ensembl: ENSG00000187147; UniProt: Q5T0D9 - Cytogenetic locus: 1p34.1 - Orphanet: Ultra-rare hypomyelinating leukodystrophy (no dedicated high-prevalence ORPHA entry; subsumed under genetic hypomyelinating leukodystrophies) - ICD-11: 8A44.0 (Leukodystrophy) / ICD-10: E75.2–G37.x (leukodystrophy, unspecified) - MeSH: Hereditary Central Nervous System Demyelinating Diseases / Leukodystrophy

Synonyms / alternative names - HLD23 - Leukodystrophy, hypomyelinating, 23, with ataxia, deafness, liver dysfunction and dilated cardiomyopathy - RNF220-related leukodystrophy / RNF220-related laminopathy

2. Etiology

Disease causal factors — genetic. HLD23 is monogenic and Mendelian. It is caused by biallelic (homozygous) missense variants in RNF220. Two recurrent variants at adjacent, highly conserved arginine residues were identified (protein-level nomenclature as reported; exact cDNA numbering is transcript-dependent): - p.(Arg363Gln) [p.R363Q] - p.(Arg365Gln) [p.R365Q]

"We report these two homozygous missense variants (p.R363Q and p.R365Q) in the ubiquitin E3 ligase RNF220 as the underlying cause of this novel form of leukodystrophy with ataxia and sensorineural deafness that includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families." — PMID 33964137

Genetic risk factors. - Causal variants: homozygous RNF220 p.R363Q / p.R365Q (functional class: hypomorphic/loss-of-function with respect to lamin B1 binding — see §6). - Susceptibility/modifier loci: none established. The cofactor ZC4H2 stabilizes RNF220 (PMID 35040952) and is a plausible biological modifier, though not demonstrated as a clinical modifier in HLD23. - Family history / consanguinity: parental consanguinity is a major risk factor — all reported families were consanguineous.

Environmental risk factors. None identified; the disorder is fully genetically determined. Sex, toxins, lifestyle and occupational exposures are not implicated.

Protective factors. None described (genetic or environmental). Not applicable to a monogenic recessive disorder beyond the trivial protection of carrying at least one wild-type allele (carriers are unaffected).

Gene–environment interactions. None documented; not applicable.

3. Phenotypes

All frequencies are qualitative given the small published cohort (seven consanguineous families, PMID 33964137). Onset is early (infancy/childhood); course is progressive.

Phenotype	Type	HPO term	Onset	Severity	Progression	Frequency
Hypomyelinating leukodystrophy / CNS hypomyelination	Imaging/clinical sign	HP:0002500 (abnormal cerebral white matter), Leukodystrophy HP:0002415	Infancy/childhood	Severe	Progressive	Universal (defining)
Cerebellar ataxia	Clinical sign	HP:0001251	Childhood	Moderate–severe	Progressive	Characteristic/frequent
Sensorineural hearing loss	Clinical sign / lab (audiometry)	HP:0000407	Childhood	Variable	Progressive	Characteristic/frequent
Dilated/fibrotic cardiomyopathy	Physical manifestation	HP:0001644 (dilated CM) / HP:0001638 (CM)	Variable	Potentially severe	Progressive	Associated feature
Hepatopathy / liver dysfunction	Lab abnormality / sign	HP:0001392 (liver abnormality), HP:0001410 (hepatic failure if severe)	Variable	Variable	Progressive	Associated feature
Motor deterioration / spasticity–hypotonia	Clinical sign	HP:0002493 / HP:0001257 / HP:0001252	Childhood	Variable	Progressive	Common (typical of leukodystrophy)
Developmental delay / cognitive impairment	Behavioral/cognitive	HP:0001263 / HP:0001249	Childhood	Variable	Progressive	Common

Quality-of-life impact. Combined motor (ataxia, spasticity), sensory (deafness), cardiac and hepatic involvement produces high disability burden with progressive loss of ambulation and communication, need for hearing rehabilitation, and cardiac/hepatic morbidity. No disease-specific QoL instrument (EQ-5D/SF-36/PROMIS) data exist for HLD23; leukodystrophy-general tools (e.g., GMFC-MLD, CFCS) are applicable by analogy (cf. PMID 39951964).

4. Genetic / Molecular Information

Causal gene: RNF220 (RING finger protein 220), 1p34.1; OMIM 616136; HGNC:25552; NCBI Gene 55182; UniProt Q5T0D9. Encodes an evolutionarily conserved RING-type ubiquitin E3 ligase (PMID 34716995).
Pathogenic variants: p.(Arg363Gln); p.(Arg365Gln) (cDNA numbering transcript-dependent). Type: missense, affecting adjacent conserved arginines. Zygosity/origin: homozygous, germline. ACMG classification: pathogenic/likely pathogenic (supported by functional co-IP and model-organism data). Allele frequency: absent/ultra-rare in gnomAD (consistent with severe recessive disease). Functional consequence: partial loss of function — both mutants show reduced binding to lamin B1 (PMID 33964137); the substitutions likely impair substrate/partner interaction rather than abolishing the RING catalytic core.
Modifier genes: none clinically validated. ZC4H2 (RNF220 stabilizing cofactor; PMID 35040952, 32630355) and RLIM (PMID 35040952) are functional partners; ZC4H2 mutations cause a separate human neurodevelopmental disorder.
Epigenetic information: RNF220 acts partly through EED (PRC2), altering histone modification marks at Shh target promoters (PMID 32376680) — an epigenetic mechanism at the molecular level, but no disease-specific DNA-methylation signature is reported for HLD23 patients.
Chromosomal abnormalities: none; HLD23 is a single-nucleotide/missense disorder, not a copy-number/structural disorder.

5. Environmental Information

Not applicable. HLD23 is a monogenic autosomal-recessive disorder with no environmental, lifestyle, toxic, or infectious contributing factors. The only non-genetic determinant is consanguinity, which raises the probability of homozygosity for the recessive allele.

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation)

Biallelic RNF220 missense mutation (p.R363Q / p.R365Q) results in a structurally intact but functionally impaired RING E3 ligase.
This leads to reduced binding of RNF220 to lamin B1 (demonstrated by mass-spec + co-IP, PMID 33964137).
Reduced RNF220–lamin B1 regulation results in abnormal lamin B1 localization/aggregation and loss of nuclear-envelope/nuclear morphology maintenance (demonstrated in cells; Drosophila lamin Dm0 aggregation with a neurodegenerative phenotype — model-organism evidence, PMID 33964137). → Laminopathy branch.
In parallel (developmental-signaling branch): impaired RNF220 function reduces K63-linked polyubiquitination and stabilization of Olig1/2 (mouse, PMID 38324685), and dysregulates Shh/Gli (via Gli nuclear export and EED/PRC2) and Wnt/β-catenin and IFN–STAT1 signaling (PMID 34716995, 32376680).
Loss of Olig1/2 stabilization impedes oligodendrocyte progenitor cell (OPC) proliferation, differentiation and (re)myelination (mouse, PMID 38324685).
Failed myelination + nuclear-envelope pathology in glia results in CNS hypomyelination (leukodystrophy) — the defining lesion — with secondary axonal degeneration as disease progresses (PMID 33964137).
Dysregulated Shh/Gli and cerebellar development, plus white-matter/cerebellar pathology, lead to cerebellar ataxia (inferred link, supported by RNF220's demonstrated role in cerebellar development, PMID 32376680, 34716995).
Nuclear-envelope/lamin B1 pathology in cochlear, cardiac and hepatic cells leads to sensorineural deafness, fibrotic cardiomyopathy and hepatopathy (multisystem laminopathy; mechanism inferred from lamin B1's ubiquitous nuclear-lamina role and the observed clinical co-occurrence, PMID 33964137).

Detail by category

Molecular pathways: ubiquitin–proteasome/ubiquitin-signaling (K63 chains), Sonic hedgehog (Shh)–Gli, Wnt/β-catenin, IFN–STAT1, PRC2/EED-mediated epigenetic regulation.
Cellular processes: oligodendrocyte differentiation and myelination; neural stem/progenitor proliferation vs differentiation balance (loss of RNF220 promotes premature neuronal differentiation, PMID 32630355); nuclear-envelope maintenance; secondary axonal degeneration.
Protein dysfunction: partial loss-of-function of the E3 ligase; loss of a protein–protein interaction (RNF220–lamin B1) and failure to stabilize substrates (Olig1/2, Gli, β-catenin, STAT1); downstream lamin B1 mislocalization/aggregation.
Metabolic/biochemical: the core defect is enzymatic (ubiquitin-ligase) rather than metabolic; no primary metabolite abnormality. Myelin lipid deficiency is secondary to hypomyelination.
Immune involvement: RNF220 modulates IFN–STAT1 signaling (PMID 34716995); a neuroinflammatory component is plausible (as in other leukodystrophies) but not specifically characterized in HLD23.
Tissue damage mechanisms: nuclear-envelope destabilization → cellular dysfunction/degeneration; myelin deficiency → axonal vulnerability; cardiac/hepatic fibrosis.
Suggested ontology terms: GO:0004842 ubiquitin-protein transferase activity; GO:0070534 protein K63-linked ubiquitination; GO:0042552 myelination; GO:0048709 oligodendrocyte differentiation; GO:0007224 smoothened/Shh signaling; GO:0016055 Wnt signaling; GO:0060333 IFN-γ-mediated signaling. Cellular components: GO:0005635 nuclear envelope; GO:0005638 nuclear lamina. Cell types (CL): CL:0000128 oligodendrocyte; CL:0002453 oligodendrocyte precursor cell; CL:0000127 astrocyte; CL:0000540 neuron.

7. Anatomical Structures Affected

Organ level (primary): brain — cerebral and cerebellar white matter (CNS). Body system: nervous system (central).
Secondary organ involvement: inner ear/cochlea (sensorineural deafness); heart (fibrotic/dilated cardiomyopathy — cardiovascular system); liver (hepatopathy — digestive/hepatobiliary system).
Tissue/cell level: nervous tissue — oligodendrocytes (CL:0000128) and OPCs (CL:0002453) are the primary affected cells; secondary axonal (neuronal) degeneration; cardiac myocytes and hepatocytes affected in a fibrotic pattern.
Subcellular level: nuclear envelope (GO:0005635) and nuclear lamina (GO:0005638) — the defining subcellular compartment in this laminopathy; the nucleus broadly.
Localization (UBERON): cerebral white matter UBERON:0002316; cerebellum UBERON:0002037; corpus callosum UBERON:0002336; cochlea/inner ear UBERON:0001844; heart UBERON:0000948; liver UBERON:0002107. Lateralization: bilateral/symmetric (typical of hypomyelinating leukodystrophy).

8. Temporal Development

Onset: early — infancy to childhood; insidious/chronic onset (hypomyelination is present from early development).
Progression: chronic and progressive, with motor deterioration and secondary axonal degeneration accruing over time; multisystem features (cardiac, hepatic) may evolve.
Course pattern: progressive/neurodegenerative rather than relapsing-remitting or episodic; lifelong.
Critical periods: early myelination window (infancy/early childhood) is the period of greatest vulnerability and the theoretical window for any future myelin-directed intervention.
Remission: none; no spontaneous remission described.

9. Inheritance and Population

Inheritance: Autosomal recessive (homozygous variants in all reported families).
Penetrance: presumed complete in biallelic homozygotes (all reported homozygotes affected).
Expressivity: variable across the multisystem features (degree of cardiac/hepatic involvement varies).
Genetic anticipation / germline mosaicism: not applicable / not reported.
Founder effects & consanguinity: the two recurrent variants in consanguineous families indicate consanguinity-driven homozygosity and possible local founder alleles.
Carrier frequency: not established; variants are ultra-rare/absent in gnomAD.
Epidemiology: ultra-rare — only a small number of families reported worldwide; precise prevalence/incidence unknown (not quantified in Orphanet/GBD).
Population demographics: reported in consanguineous pedigrees; no established sex bias (autosomal); pediatric onset. Geographic distribution follows populations with higher consanguinity rates.

10. Diagnostics

Imaging (key): brain MRI shows a hypomyelination pattern — mild diffuse T2 hyperintensity with near-normal/mildly reduced T1 signal of white matter, best assessed after ~1–2 years of age. MRI pattern recognition is central to leukodystrophy diagnosis (PMID 28638987). MR spectroscopy may be adjunctive (PMID 23928198).
Genetic testing (confirmatory): trio whole-exome sequencing (WES) or whole-genome sequencing (WGS), or a hypomyelinating-leukodystrophy NGS gene panel including RNF220; single-gene testing if the recurrent variant is suspected in a consanguineous family. WES diagnostic yield in leukodystrophy cohorts ~60% (PMID 37597066). Variant interpretation per ACMG/AMP.

"The total diagnostic rate of WES was 60.7%." — PMID 37597066
Supporting/organ workup: audiometry/BAER (sensorineural deafness), echocardiography/ECG and cardiac MRI (cardiomyopathy), liver function tests and hepatic imaging (hepatopathy).
Clinical criteria / differential diagnosis: no formal consensus criteria; diagnosis is gene-based. Differentials include other hypomyelinating leukodystrophies — PLP1 (PMD), GJC2 (HLD2), TUBB4A (H-ABC/HLD6), POLR3-related (4H) leukodystrophy, FAM126A/HYCC1 (HLD5), and other laminopathies; distinguishing features here are the combination of hypomyelination + ataxia + sensorineural deafness + cardiomyopathy + hepatopathy and the RNF220 genotype.
Screening: no newborn screening exists (no biochemical marker); cascade/carrier testing in affected consanguineous families is appropriate.

11. Outcome / Prognosis

Survival/mortality: disease-specific survival data are not established given the few reported patients. Prognosis is guarded due to progressive neurodegeneration plus potentially life-limiting cardiomyopathy and hepatopathy.
Morbidity/disability: high — progressive motor disability (ataxia, spasticity), sensory loss (deafness), and cardiac/hepatic morbidity; likely loss of independent ambulation and communication over time (by analogy to other progressive leukodystrophies, PMID 39951964).
Recovery potential: none without disease-modifying therapy; hypomyelination is not spontaneously reversible.
Prognostic factors: extent of cardiac/hepatic involvement and rate of neurological progression are the principal determinants; specific molecular prognostic biomarkers are not defined.

12. Treatment

No disease-specific or curative therapy exists for RNF220-related HLD23. Unlike enzyme-deficiency leukodystrophies with approved disease-modifying options (e.g., HSCT for Krabbe disease, PMID 42040243/41604001; arsa-cel gene therapy for metachromatic leukodystrophy, PMID 40267426), RNF220-HLD23 has no such intervention. Care is multidisciplinary and supportive/symptomatic:

Supportive care (NCIT:C15277): symptom management, nutrition, spasticity/ataxia management.
Rehabilitation: physical therapy (NCIT:C15535), occupational therapy, speech/communication therapy.
Sensory: hearing aids / cochlear implantation for sensorineural deafness.
Cardiac: surveillance and standard heart-failure/cardiomyopathy management; consider device/transplant evaluation per cardiology.
Hepatic: monitoring and supportive hepatic care.
Pharmacotherapy: only symptomatic (e.g., anti-spasticity agents, anticonvulsants if seizures); no pharmacogenomic guidance specific to HLD23.
Advanced/experimental therapeutics: none in clinical trials for HLD23 specifically; gene-replacement/genome-editing and small-molecule myelin-repair strategies are conceptual future directions. No NCT identifiers for RNF220-HLD23.

13. Prevention

Primary prevention: not possible for disease occurrence beyond reproductive genetic measures; no vaccine/lifestyle modification (non-environmental disease).
Genetic prevention/counseling (principal lever): genetic counseling for autosomal-recessive 25% recurrence risk; carrier screening in consanguineous families/populations; prenatal diagnosis and preimplantation genetic testing (PGT-M) for known familial variants; cascade testing of relatives.
Secondary prevention: early identification of at-risk siblings via cascade testing; early audiologic, cardiac and hepatic surveillance to manage complications.
Tertiary prevention: proactive cardiac and hepatic monitoring, rehabilitation, and management of contractures/scoliosis to limit complications.
Public-health note: in high-consanguinity populations, community genetic counseling reduces incidence of recessive disorders generally.

14. Other Species / Natural Disease

Taxonomy / orthologs: RNF220 is evolutionarily conserved (PMID 34716995). Orthologs: mouse Rnf220 (NCBI Gene 66743; NCBITaxon:10090), zebrafish rnf220a/rnf220b (NCBITaxon:7955), Drosophila functional counterpart acting on lamin Dm0 (NCBITaxon:7227).
Natural disease in other species: no naturally occurring RNF220-associated disease is documented in companion animals or wildlife (no OMIA entry known); relevance is experimental, not veterinary.
Comparative biology: the RNF220–lamin B1 interaction is conserved to Drosophila (RNF220 knockdown → lamin Dm0 aggregation and neurodegeneration, PMID 33964137), demonstrating deep evolutionary conservation of the disease mechanism.
Transmission: not applicable (non-infectious, non-zoonotic).

15. Model Organisms

Mouse (Mus musculus):
Rnf220 knock-in model of the leukodystrophy-related variant and conditional/oligodendrocyte-lineage depletion models: recapitulate impaired OPC proliferation/differentiation and (re)myelination with learning/memory deficits — good recapitulation of the hypomyelination component (PMID 38324685).
Cerebellar development / Shh-medulloblastoma models (PMID 32376680, 35040952) — relevant to the ataxia/cerebellar axis.
Noradrenergic (locus coeruleus, Phox2 monoubiquitylation) and motor-neuron development models (PMID 32094113).
Zebrafish (Danio rerio): neural-patterning models of RNF220/Shh (reviewed PMID 34716995).
Drosophila melanogaster: RNF220 silencing → lamin Dm0 mislocalization/aggregation and neurodegeneration — models the laminopathy axis (PMID 33964137).
In vitro / cellular: patient-mutant co-IP (reduced lamin B1 binding); neural stem cell (NSC) studies showing loss of RNF220/ZC4H2 inhibits proliferation and promotes differentiation (PMID 32630355); myoblast differentiation studies of ΔN-RNF220 isoform (PMID 40609864).
Genetic model types available: knock-in, conditional/lineage-specific knockdown/knockout (mouse); morphant/mutant (zebrafish); RNAi knockdown (Drosophila).
Phenotype recapitulation & limitations: mouse models reproduce myelination defects and cerebellar/Shh phenotypes; Drosophila reproduces the lamin B1 axis. Limitation: no single published model simultaneously recapitulates the full human multisystem phenotype (leukodystrophy + deafness + cardiomyopathy + hepatopathy).
Resources: MGI (Rnf220), ZFIN (rnf220a/b), FlyBase, Alliance of Genome Resources.

Supported vs. Refuted Hypotheses

Supported 1. HLD23 is caused by biallelic RNF220 missense variants (p.R363Q/p.R365Q), AR inheritance (PMID 33964137). 2. HLD23 is a laminopathy: mutant RNF220 shows reduced lamin B1 binding; RNF220 maintains nuclear morphology (PMID 33964137). 3. The hypomyelination arises from failed RNF220-mediated K63-ubiquitination/stabilization of Olig1/2 and disrupted oligodendrocyte development (PMID 38324685). 4. RNF220 acts pleiotropically via Shh/Gli, Wnt, IFN-STAT1, explaining multisystem/cerebellar features (PMID 34716995, 32376680).

Refuted / excluded - Environmental, infectious, metabolic-primary, or chromosomal/structural causation — excluded; the disorder is a single-gene missense laminopathy. - Existence of an approved disease-modifying therapy — none exists (management is supportive).

Limitations and Future Directions

Small evidence base: core clinical knowledge rests on one case series (seven consanguineous families, PMID 33964137); prevalence, natural history, penetrance quantification, sex/age distributions, and QoL metrics are not established.
Mechanistic gaps: the causal steps linking lamin B1 dysfunction to deafness, cardiomyopathy and hepatopathy are inferred, not directly demonstrated; the relative contribution of the lamin-B1 axis vs. the Olig1/2/Shh axis to human hypomyelination is unquantified.
Therapeutic gap: no targeted therapy or clinical trial; future work could explore genotype-specific interventions, myelin-repair agents, and a model that captures the full multisystem phenotype.
Ontology mapping: MONDO:0030514 / OMIM 619688 / RNF220 (HGNC:25552); HPO, GO, CL, UBERON, NCIT terms suggested throughout.

Key References (PMID)

33964137 — Sferra et al., Brain 2021. Landmark: biallelic RNF220 mutations cause laminopathy with leukodystrophy, ataxia, deafness (+ cardiomyopathy, hepatopathy).
38324685 — Li et al., 2024. RNF220 K63-ubiquitinates/stabilizes Olig1/2 in oligodendroglial development and myelination; knock-in leukodystrophy mouse.
34716995 — Ma & Mao, 2022. Review: RNF220 in neural development (Shh/Gli, Wnt, IFN-STAT1; ZC4H2).
32376680 / 35040952 / 32094113 / 32630355 / 39526890 / 40609864 — RNF220 developmental biology and models.
28638987 — van der Knaap & Bugiani, 2017. Leukodystrophy classification; MRI+NGS diagnostic paradigm.
37597066 — Iranian Leukodystrophy Registry; WES diagnostic yield 60.7%.
40267426 / 42040243 / 41604001 — Contrast: disease-modifying therapies (gene therapy/HSCT) in other leukodystrophies (MLD, Krabbe).

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	14
Resolved	14
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	14
On topic	3
Off topic	0

All extracted references resolved successfully.

Term Validation

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

Outcome	Count
Terms checked	39
Resolved	38
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	1
Terms whose name was checked	8
Terms named correctly	0
Terms named as a different term	7
Terms whose name is worth a second look	1

Terms the report names something else

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

HP:0001251 (1 mention) - the report calls it "Clinical sign"; HP calls it Ataxia
HP:0000407 (1 mention) - the report calls it "Clinical sign / lab (audiometry)"; HP calls it Sensorineural hearing impairment
CL:0000128 (2 mentions) - the report calls it "Tissue/cell level: nervous tissue — oligodendrocytes"; CL calls it oligodendrocyte
NCIT:C15277 (1 mention) - the report calls it "Supportive care"; NCIT calls it Mastectomy
NCIT:C15535 (1 mention) - the report calls it "Rehabilitation: physical therapy"; NCIT calls it Urothelial Toxicity Attenuation**
NCBITaxon:7955 (1 mention) - the report calls it "rnf220a/rnf220b"; NCBITaxon calls it Danio rerio
NCBITaxon:7227 (1 mention) - the report calls it "lamin Dm0"; NCBITaxon calls it Drosophila melanogaster

Terms whose name is worth a second look

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

GO:0005635 (2 mentions) - the report calls it "Subcellular level: nuclear envelope"; GO calls it nuclear envelope

Terms named inconsistently

The report gives these identifiers more than one name of its own:

HGNC:25552 - called "RNF220", "HGNC:** RNF220"

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Inheritance

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

External Assertions

Medical Actions

Progression

Prevalence

Experimental Models

Animal Models

Source YAML

References & Deep Research

References

Deep Research

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic / Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation)

Detail by category

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome / Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Supported vs. Refuted Hypotheses

Limitations and Future Directions

Key References (PMID)

Artifacts

Reference Validation

Term Validation

Terms the report names something else

Terms whose name is worth a second look

Terms named inconsistently