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Classifications

Harrison's Part

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Inheritance

1

Autosomal recessive inheritance HP:0000007

Biallelic NDRG1 variants, homozygous in the great majority of reported patients and compound heterozygous in a minority. The recessive mode is what makes founder populations the natural setting for the disorder: the Roma p.Arg148* allele and two Bulgarian Muslim splice-site alleles each reached homozygosity through consanguinity within a genetically isolated community rather than through recurrent mutation.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:39201732 SUPPORT Human Clinical

"Segregation analysis was performed on the available family members, and all of the variants co-segregated with the disease phenotype in the corresponding pedigrees"

Co-segregation of biallelic NDRG1 variants with disease across eleven families.

PMID:23996628 SUPPORT Human Clinical

"There are three subtypes of autosomal recessive CMT with mutations private to the Roma population: CMT4C, CMT4D and CMT4G."

States the recessive mode and the founder-population context.

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Discussions and Knowledge Gaps

4

Why does none of the three NDRG1-deficient rodent models reproduce the early severe axonal loss that actually causes disability in patients, when all three reproduce the demyelination - and has the canine model, which does show axonal pathology, ever been assessed for whether its axonal loss is early and disproportionate to the demyelination?

HUMAN MODEL MISMATCH OPEN cmt4d_axonal_loss_has_no_model

Attached to

pathophysiology#Early Severe Axonal Loss pathophysiology#Myelin Sheath Breakdown with Onion Bulb Formation

This is a HUMAN_MODEL_MISMATCH rather than a KNOWLEDGE_GAP because the evidence is not absent - four independent NDRG1-deficient models exist, three rodent and one canine, and all have had their myelin phenotype characterised in detail. What is uncertain is their translational validity for the arm of the disease that matters clinically, which is precisely the arm that has not been characterised to the same standard. The stretcher mouse and the hypomorphic Ndrg1 knockout were compared head to head and neither displays the early severe axonal loss typical of the human disease, with regenerative capacity explicitly unimpaired; the independent CRISPR Ndrg1-/- mouse likewise shows no apparent axonal loss despite faithful demyelination; and the canine model is described as a mixed polyneuropathy without the deafness that defines the human disorder. The consequence is precise and constraining, and the rodent and canine models have to be stated separately because they fail differently. No rodent model reconstructs the step from Schwann-cell NDRG1 loss to axonal degeneration: all three reproduce demyelination and none the early severe axonal loss. The Greyhound is not in that position - it has prominent axonal pathology, with severe axonal atrophy, dropout of large myelinated fibres, Wallerian degeneration and neurogenic muscle atrophy. What has not been shown for the canine model is the feature that actually defines the human lesion: that the axonal loss is early and disproportionate to the demyelination rather than a late consequence of it. Nobody has assessed it for that, which is a different and weaker statement than failing to reproduce it. The practical consequence is unchanged. The gene-discovery work framed CMT4D as a disease of impaired axon-glia interaction, and axonal loss is what produces the disability. Any preclinical result in the rodent models - including the observation that a treatment window exists before the four-week onset of myelin thinning - speaks to the demyelinating arm only, and must not be curated or read as addressing the axonal arm. The canine line is the one place the axonal arm might be testable, which is why the proposed long-axon experiment below uses it.

Proposed experiments

Test whether axon length explains the model failure

exp_cmt4d_longer_axon_model

Human peripheral axons are an order of magnitude longer than murine ones, and the demand-mismatch hypothesis predicts that vulnerability scales with the membrane load a Schwann cell must service. Characterise NDRG1-null neuropathy in a large-animal model with long axons - the Greyhound line already exists - with axonal counts and regeneration assays as the primary readouts rather than myelin measures.

Human Schwann cell-neuron co-culture with NDRG1 loss restricted to glia

exp_cmt4d_schwann_axon_coculture

Co-culture patient-derived or NDRG1-edited human Schwann cells with wild-type sensory neurons, and the reciprocal combination, to determine whether Schwann-cell NDRG1 loss is sufficient to injure a genetically normal axon and over what timescale.

What does NDRG1 actually do in the Schwann cell, and is the trafficking account sufficient to explain a demyelinating neuropathy?

KNOWLEDGE GAP OPEN cmt4d_ndrg1_molecular_function

Attached to

pathophysiology#Impaired Schwann Cell Vesicular Trafficking pathophysiology#Loss of Schwann Cell NDRG1 Function

Twenty-six years after the gene was found, the molecular function of NDRG1 remains unresolved, and a 2013 clinical report still opens by saying so. What makes this a genuine gap rather than an unfinished literature is that the field has actively excluded candidates: the stretcher work found no support for roles in growth arrest, terminal differentiation, gene expression regulation or proteasomal degradation, leaving vesicular trafficking as the surviving hypothesis largely by elimination. The positive evidence for trafficking is real but indirect - Rab4a compartment enlargement and failed LDL receptor recycling in cell lines, lipid-vesicle binding by the purified protein, and a timing coincidence between demyelination and peak myelin growth in mouse. None of it measures membrane flux in a Schwann cell, and the protein is a hydrolase-fold member with no demonstrated catalytic activity, so the possibility that its relevant function is something not yet tested is not closed.

Proposed experiments

Direct measurement of membrane trafficking flux in NDRG1-null Schwann cells

exp_cmt4d_schwann_membrane_flux

Quantify endocytic and recycling flux, and myelin membrane delivery rate, in primary NDRG1-null Schwann cells during active myelination in co-culture, testing the demand-mismatch hypothesis directly rather than through the timing of the lesion.

Screen for catalytic activity of the NDRG1 hydrolase fold

exp_cmt4d_ndrg1_hydrolase_activity

The crystal structure resolves an alpha/beta hydrolase fold presumed inactive. Screen substrate classes appropriate to the fold, and test whether the CMT4D missense alleles p.Leu146Pro and p.Arg234Gln affect any activity found, to close or confirm the possibility of an unrecognised enzymatic function.

Is the central nervous system genuinely affected in CMT4D, or are the imaging and evoked-potential abnormalities secondary to the peripheral lesion?

KNOWLEDGE GAP OPEN cmt4d_central_nervous_system_involvement

Attached to

pathophysiology#Auditory Pathway Involvement

Three independent lines of observation point at the central nervous system: subcortical white matter abnormalities in a non-Roma p.Arg148*-homozygous family, cerebellar, medullary and upper cervical cord atrophy in an Italian patient with a different allele, and prolonged brainstem auditory evoked potential interpeak latencies that appear before hearing complaints. NDRG1 is ubiquitously expressed, so central involvement is biologically unsurprising. But none of these is decisive: evoked-potential delay is equally compatible with conduction failure in the proximal eighth-nerve segment, imaging findings come from single families, and no neuropathological examination of CMT4D central tissue has been reported. The authors who first reported the white matter lesions themselves called for further study rather than claiming a central phenotype. This entry therefore keeps the auditory node separate from the somatic chain rather than asserting a shared mechanism.

Proposed experiments

Systematic central nervous system imaging in a genotyped CMT4D cohort

exp_cmt4d_systematic_neuroimaging

Quantitative brain and cord MRI with diffusion metrics in a genotyped CMT4D cohort against age-matched controls, to determine whether white matter abnormality is a consistent feature or a sporadic finding in single families.

NDRG1 expression and oligodendrocyte requirement in central white matter

exp_cmt4d_ndrg1_cns_expression

Determine whether NDRG1 is expressed in oligodendrocytes at levels comparable to Schwann cells, and whether central myelin is affected in NDRG1-null animals, which would distinguish a primary central phenotype from a peripheral one.

Which routes account for the reported spinal, bulbar, cognitive and central imaging findings, and for motor delay in some families?

KNOWLEDGE GAP OPEN cmt4d_phenotype_causal_attribution

Attached to

phenotypes#Scoliosis phenotypes#Dysphagia phenotypes#Bilateral Vocal Cord Paralysis phenotypes#Cognitive Impairment phenotypes#Central Nervous System White Matter Abnormality phenotypes#Cerebellar Atrophy phenotypes#Cervical Spinal Cord Atrophy phenotypes#Medullary Atrophy phenotypes#Motor Delay pathophysiology#Visual Pathway Dysfunction

The reviewed human reports establish these observations, but do not identify a causal route for each. Scoliosis is quantified without a demonstrated paraspinal denervation or other spinal mechanism. The two siblings with dysphagia and vocal cord paralysis have no reported localization sufficient to distinguish cranial neuropathy from central motor involvement; vocal cord paralysis causing respiratory insufficiency is explicitly established and is represented. Cognitive delay lacks a defined developmental or neuropathological substrate. White matter lesions, cerebellar atrophy, medullary atrophy and cervical cord atrophy come from different limited reports whose authors do not establish whether each is a primary central consequence of NDRG1 loss or secondary degeneration. The visual evoked-potential abnormality establishes visual pathway dysfunction, but not its cause or correspondence to those structural findings. Motor delay is directly observed in some molecularly confirmed patients while other cohorts have normal milestones; the reviewed sources do not connect the delayed milestones to a defined early peripheral lesion. These uncertainties concern causal attribution, not a requirement to reconstruct every molecular intermediate. The peripheral glia-to-axon route and the auditory route are represented with their stated uncertainty.

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Pathophysiology

11

Biallelic NDRG1 Loss-of-Function Variant

Mechanism confidence: Established

The initiating lesion is biallelic loss of NDRG1. The founder allele p.Arg148* (c.442C>T) introduces a premature termination codon and accounts for roughly two-thirds of reported patients. The remaining alleles converge on the same functional endpoint by different routes: frameshifts (p.His247Thrfs*74, p.Ser317Argfs*4, p.Glu170Glyfs*35), further nonsense alleles, canonical splice-acceptor variants whose transcripts favour exon skipping, a duplication of exons 6-8, and two missense alleles (p.Leu146Pro, p.Arg234Gln) that destabilise the protein rather than truncating it. The missense alleles matter mechanistically because they show the disease can be produced by reduced NDRG1 abundance alone, with no truncation involved.

NDRG1 hgnc:7679

Genetic context variant_origin: GERMLINE zygosity: HOMOZYGOUS functional_impact_category: LOSS_OF_FUNCTION

Germline biallelic loss of function, most often homozygous for a founder nonsense allele. Functional characterisation of the novel Bulgarian splice-site alleles showed shorter gene products consistent with loss of protein function, and cell-culture work on the missense alleles showed accelerated degradation and lower steady-state protein levels.

Downstream

Loss of Schwann Cell NDRG1 Function

Auditory Pathway Involvement The genotype-to-deafness link is established by segregation - sensorineural deafness is a hallmark of the NDRG1 phenotype - but the intervening mechanism is not. The evoked-potential data implicate the eighth cranial nerve and the central auditory pathways simultaneously, and no cochlear or auditory-nerve pathology from a CMT4D patient has been reported, so this edge deliberately skips over unknown intermediates rather than routing the deafness through the somatic Schwann-cell chain as if the mechanism were shared.

Show evidence (4 references)

PMID:10831399 SUPPORT Human Clinical

"Sequence analysis of two genes located in the critical region identified the founder HMSNL mutation: a premature-termination codon at position 148 of the N-myc downstream-regulated gene 1 (NDRG1)."

Identifies the founder truncating allele as the cause of HMSNL/CMT4D.

PMID:42089726 SUPPORT Human Clinical

"Twenty-two pathogenic NDRG1 variants were documented, with p.(Arg148*) being most frequent (64% of patients), predominantly in Roma populations."

Quantifies the allelic spectrum across the published literature and the dominance of the founder allele within it.

PMID:39201732 SUPPORT Human Clinical

"Functional characterization of these novel variants implicates a loss-of-function mechanism due to shorter gene products."

Establishes loss of function as the mechanism for the splice-site alleles, not only for the founder nonsense allele.

+ 1 more reference

Loss of Schwann Cell NDRG1 Function

Mechanism confidence: Established

NDRG1 is highly expressed in human Schwann cells. Its loss impairs Schwann-cell function and peripheral myelin maintenance. Mouse models demonstrate initially normal myelination followed by demyelination; that temporal sequence has not been reconstructed in human nerves. The cellular trafficking and signaling routes below remain provisional.

Schwann cell CL:0002573

Downstream

Impaired Schwann Cell Vesicular Trafficking

Attenuated Neuregulin 1-ErbB Signaling

Early Severe Axonal Loss Impaired Schwann-cell support is implicated in early human axonal injury, but the glia-to-axon intermediates remain unresolved and rodent models fail to reproduce its early severity.

Show evidence (4 references)

PMID:10831399 SUPPORT Human Clinical

"We have studied expression in peripheral nerve and have detected particularly high levels in the Schwann cell."

Establishes Schwann-cell enrichment of NDRG1 in peripheral nerve.

PMID:35708320 SUPPORT Model Organism

"In the sciatic nerve, NDRG1 was restricted to S100β-positive Schwann cells but not detected in neurofilament 200-positive axons."

Localises NDRG1 to the Schwann cell and excludes the axon, establishing the primary lesion as glial.

PMID:35708320 SUPPORT Model Organism

"Moreover, NDRG1 was expressed at a low level before 2 weeks of age and at a high level after 2 weeks of age. This temporal expression pattern was similar to the myelin proteins"

Times NDRG1 expression to the myelination and myelin-maintenance period rather than to early Schwann-cell development.

+ 1 more reference

Impaired Schwann Cell Vesicular Trafficking

Mechanism confidence: Provisional

The leading account of what NDRG1 actually does in the Schwann cell is vesicular trafficking. NDRG1 regulates endosomal recycling through Rab4a-positive compartments and low-density lipoprotein receptor turnover; CMT4D missense mutants leave the NDRG1-Rab4a interaction intact but produce enlarged Rab4a-positive compartments and fail to support LDL uptake or to restore receptor levels at the cell surface. The proposal that follows - that a trafficking Schwann cell simply cannot meet the membrane demand of myelin growth - is supported by a striking timing coincidence in the stretcher mouse, where widespread large-fibre demyelination coincides exactly with the period in which myelin volume and length in large fibres increase several hundred-fold, and small fibres are spared. It is marked PROVISIONAL because the trafficking defect is demonstrated in cell lines and the demand-mismatch argument is an inference from the timing rather than a direct measurement of membrane flux in a CMT4D nerve. The same work explicitly argues against several earlier candidate functions.

Schwann cell CL:0002573

endosomal recycling of membrane receptors GO:0032456 ↓ DECREASED

Animal models

Stretcher mouse (spontaneous Ndrg1 null) Mouse partially recapitulates The model is the basis of the trafficking-demand-mismatch hypothesis: its large-fibre demyelination coincides precisely with the period of rapid myelin growth and small fibres are spared, while gene expression profiling found only non-specific secondary changes and normal proteasomal function.

Downstream

Myelin Sheath Breakdown with Onion Bulb Formation

Show evidence (5 references)

PMID:28776325 SUPPORT In Vitro

"However, NDRG1-knockdown cells expressing mutant NDRG1 displayed enlarged Rab4a-positive compartments."

Shows a recycling-endosome abnormality specific to the CMT4D mutant protein, with the NDRG1-Rab4a interaction itself preserved.

PMID:28776325 SUPPORT In Vitro

"Moreover, mutant NDRG1 could not enhance the uptake of DiI-LDL or increase the fraction of low-density lipoprotein receptor on the cell surface."

Demonstrates a functional trafficking deficit for a receptor whose recycling NDRG1 normally supports.

PMID:21303696 SUPPORT Model Organism

"Impaired SC trafficking failing to meet the considerable demands of nerve growth, emerges as the likely pathogenetic mechanism in NDRG1 deficiency."

States the trafficking-demand-mismatch hypothesis this node represents, in the authors' own hedged terms.

+ 2 more references

Attenuated Neuregulin 1-ErbB Signaling

Mechanism confidence: Provisional

Axonal neuregulin 1 signalling through Schwann-cell ErbB2/ErbB3 is the main route by which an axon instructs its Schwann cell how much myelin to make. In Ndrg1-deficient mice this pathway is decoupled in an informative way: ligand and receptor are not scarce - neuregulin 1 and total ErbB2/3 are both increased - yet the phosphorylated receptors and their downstream cascades are reduced, and integrin beta-4, the co-receptor that positively regulates the pathway, is markedly reduced. The lesion is therefore in receptor activation, not in ligand supply, which fits a trafficking defect that fails to present or maintain the receptor complex correctly at the Schwann-cell membrane. Marked PROVISIONAL for a specific reason: every one of these measurements comes from mouse sciatic nerve, and no equivalent has been shown in human CMT4D nerve. The same paper reports that its mouse does not reproduce the axonal loss that defines the human disease.

Schwann cell CL:0002573

ERBB signaling pathway GO:0038127 ↓ DECREASED

Animal models

Ndrg1 exon 4-5 knockout mouse Mouse measures The model is the sole source of the neuregulin 1/ErbB evidence in this entry: it is where receptor phosphorylation, ligand level and integrin beta-4 abundance were measured.

Downstream

Dysregulated Myelination Transcription Program

Show evidence (3 references)

PMID:35708320 SUPPORT Model Organism

"In the absence of NDRG1, although the total ErbB2/3 receptors expressed by Schwann cells were significantly increased, levels of the phosphorylated forms of ErbB2/3 and their downstream signaling cascades were decreased."

The central observation: receptor abundance up, receptor activation down.

PMID:35708320 SUPPORT Model Organism

"This change was not associated with the level of the neuregulin 1 ligand, which was increased in Ndrg1-deficient mice."

Excludes ligand scarcity as the explanation and localises the defect to the Schwann-cell receptor side.

PMID:35708320 SUPPORT Model Organism

"In addition, the integrin β4 receptor, which interacts with ErbB2/3 and positively regulates neuregulin 1/ErbB signaling, was significantly reduced in the Ndrg1-deficient nerve."

Identifies a reduced co-receptor as a candidate proximate cause of the activation failure.

Dysregulated Myelination Transcription Program

Mechanism confidence: Provisional

Downstream of the signalling defect, the Schwann-cell myelination program itself is disordered in Ndrg1-deficient mice. EGR2, SOX10 and OCT6 - the transcription factors that drive myelination - are all abnormally expressed, and the structural myelin proteins follow: MBP and MPZ fall at both mRNA and protein level. PMP22 behaves differently and is worth recording separately, because its mRNA falls while its protein rises, which the authors read as NDRG1 loss impairing PMP22 degradation. That dissociation is a second, independent pointer at a trafficking or turnover defect rather than a transcriptional one. PROVISIONAL: mouse only.

Schwann cell CL:0002573

myelination in peripheral nervous system GO:0022011 ↓ DECREASED

Downstream

Myelin Sheath Breakdown with Onion Bulb Formation

Show evidence (2 references)

PMID:35708320 SUPPORT Model Organism

"The expression pattern of myelination-related transcriptional factors, including SOX10, OCT6, and EGR2, was abnormal in Ndrg1-deficient mice."

Establishes disruption of the myelination transcription program.

PMID:35708320 SUPPORT Model Organism

"Intriguingly, thePmp22mRNA level was decreased inNdrg1−/−mice (Fig. 4C), while the PMP22 protein level was significantly increased"

Documents the mRNA-protein dissociation for PMP22 that points at impaired degradation rather than transcriptional failure.

Myelin Sheath Breakdown with Onion Bulb Formation

Mechanism confidence: Established

Human sural nerve shows depletion of myelinated fibres, thin myelin sheaths on surviving fibres and onion bulb formations. Preserved fibres are small and onion bulbs may be poorly developed. Ndrg1-deficient mice show normal initial myelination followed by progressive myelin breakdown, providing evidence for impaired maintenance; normal initial myelination is not established longitudinally in humans.

Schwann cell CL:0002573

myelin maintenance GO:0043217 ↓ DECREASED

Animal models

Ndrg1 exon 4-5 knockout mouse Mouse recapitulates Reproduces the demyelinating lesion with correct timing - normal at two weeks, thinning from four weeks when myelination would normally be complete, progressive thereafter, with occasional onion bulbs.

Ndrg1 knockout mouse (Okuda) Mouse recapitulates Establishes progressive demyelination of an initially normally myelinated nerve, with Schwann-cell dysfunction as the proximate cause.

Downstream

Progressive Demyelinating Sensorimotor Neuropathy Myelin breakdown contributes the demyelinating component of the clinically observed sensorimotor neuropathy.

Show evidence (3 references)

PMID:35708320 SUPPORT Human Clinical

"Sural nerve biopsy studies of patients showed marked depletion of myelinated fibers, thin myelin sheaths of the preserved myelinated fibers, and onion bulb formations"

The human nerve histology this node describes, cited from the review section of the paper rather than from its mouse experiments.

PMID:39201732 SUPPORT Human Clinical

"Nerve histology seems to be distinct, and shows a depletion in myelinated nerve fibers with small size in the few preserved myelinated fibers and poorly developed onion bulbs"

Independent description of the distinctive CMT4D nerve histology.

PMID:35708320 SUPPORT Model Organism

"Ndrg1−/−mice began to show thinning of the myelin sheath at the age of 4 weeks, when fiber myelination was normally complete."

Establishes that the lesion is loss of established myelin rather than failure to form it.

Early Severe Axonal Loss

Mechanism confidence: Provisional

Severe axonal loss occurs early in human CMT4D and contributes to neurological disability. Human expression and pathology implicate impaired Schwann-cell support of axons, but the specific glia-to-axon causal route remains provisional. Mouse models reproduce demyelination but fail to reproduce the early severe axonal loss typical of patients. The Greyhound model has axonal pathology, although its timing and proportionality relative to demyelination have not been established to the same standard. The peripheral-neuron target here does not imply that NDRG1 loss acts cell-autonomously in the axon.

peripheral nervous system neuron CL:2000032

Animal models

Ndrg1 exon 4-5 knockout mouse Mouse fails to recapitulate The defining human feature - early severe axonal loss - is absent from this model despite otherwise faithful demyelination, and the authors say so explicitly.

Stretcher mouse (spontaneous Ndrg1 null) Mouse fails to recapitulate Neither the stretcher mouse nor the hypomorphic knockout reproduces the early severe axonal loss of human CMT4D. Axon damage occurs, but regenerative capacity is unimpaired.

Ndrg1 knockout mouse (Okuda) Mouse fails to recapitulate This model was one of the two compared head to head in PMID:21303696, and that comparison found neither reproduces the early severe axonal loss of human CMT4D.

Downstream

Progressive Demyelinating Sensorimotor Neuropathy

Motor Denervation Loss of motor axons removes muscle innervation; human CMT4D EMG documents the resulting chronic denervation.

Show evidence (4 references)

PMID:10831399 SUPPORT Human Clinical

"HMSNL shows features of Schwann-cell dysfunction and a concomitant early axonal involvement, suggesting that impaired axon-glia interactions play a major role in its pathogenesis."

The original statement of early axonal involvement and of axon-glia failure as the pathogenic core.

PMID:39201732 SUPPORT Human Clinical

"Nerve conduction studies (NCS) of all of our patients were consistent with severe demyelination and secondary axonal degeneration."

Electrophysiological confirmation of axonal degeneration accompanying the demyelination in a contemporary patient cohort.

PMID:21303696 SUPPORT INDIRECT Model Organism

"although axon damage is present, regenerative capacity is unimpaired and the mice do not display the early severe axonal loss typical of the human disease"

Supports this node only obliquely: the sentence is about the mice, and confirms early severe axonal loss as the typical human feature in passing - hence directness INDIRECT. The other half of what this sentence says, that the rodent models fail to reproduce it, is not repeated here as a REFUTE item because it is already represented structurally by the FAILS_TO_RECAPITULATE links on those models.

+ 1 more reference

Progressive Demyelinating Sensorimotor Neuropathy

Mechanism confidence: Established

The clinical endpoint: a severe, progressive, childhood-onset demyelinating sensorimotor neuropathy. Distal lower-limb weakness with steppage gait and frequent falls is the presenting complaint, hand weakness follows in the second decade, and the disorder leads to loss of ambulation. Median age at onset across the published literature is seven years. Unlike most CMT the involvement is not confined to the distal limbs - the two most recently reported siblings had distal-proximal weakness with generalised areflexia - and bulbar and respiratory involvement has now been documented.

Animal models

Greyhound polyneuropathy (NDRG1 exon 15 deletion) Dog partially recapitulates Reproduces a severe chronic progressive polyneuropathy of juvenile onset on a recessive founder background, with NDRG1 protein absent from peripheral nerve on Western blot.

Downstream

Demyelinating Sensorimotor Polyneuropathy The phenotype is the clinical expression of this established demyelinating sensorimotor nerve lesion.

Distal Muscle Weakness Somatic motor nerve dysfunction produces the predominantly distal weakness.

Distal Sensory Loss Sensory nerve dysfunction produces distal sensory loss.

Areflexia The sensorimotor nerve lesion impairs the peripheral limbs of tendon reflex arcs, explaining the absent tendon reflexes observed with the neuropathy.

Show evidence (4 references)

PMID:42089726 SUPPORT Human Clinical

"The median age of onset was 7 years, 96% of patients presented with lower limb involvement"

Quantifies onset and the near-universal lower-limb presentation across 72 reported patients.

PMID:39201732 SUPPORT Human Clinical

"The initial manifestations in all patients included distal muscle weakness in the lower limbs with impaired steppage gait and frequent falls."

Describes the uniform presenting picture in a contemporary cohort.

PMID:39201732 SUPPORT Human Clinical

"Patients present with an early onset demyelinating peripheral neuropathy causing severe distal muscle weakness and sensory loss, leading to loss of ambulation and progressive sensorineural hearing loss."

States the full clinical course including loss of ambulation.

+ 1 more reference

Auditory Pathway Involvement

Mechanism confidence: Provisional

Auditory pathway dysfunction produces progressive sensorineural hearing loss, usually recognized in the third decade but sometimes in childhood. Brainstem auditory evoked potentials may be delayed before hearing complaints. The original human electrophysiology suggested eighth-nerve demyelination and abnormal central auditory conduction; their relative contributions remain unresolved. This node is separate from the somatic nerve chain and is reached from the genotype through an edge with unknown intermediates. Broad hearing impairment was reported in 61% of published cases, but that estimate does not establish specifically sensorineural loss in every reviewed patient.

Downstream

Sensorineural Hearing Loss Dysfunction of the auditory nerve/central auditory route produces sensorineural hearing loss. The link does not select one anatomical localization over the other.

Show evidence (4 references)

PMID:39201732 SUPPORT Human Clinical

"Another typical electrophysiological finding is an abnormality in brain-stem auditory-evoked potentials with prolonged I–V interpeak latencies, suggesting the involvement of the central pathways"

The evoked-potential evidence pointing at central auditory pathway involvement, in the source's own hedged terms.

PMID:39201732 SUPPORT Human Clinical

"The audiograms of the rest were consistent with sensorineural hearing loss, especially for high frequencies."

Characterises the hearing loss as sensorineural and high-frequency predominant.

PMID:17142040 SUPPORT Human Clinical

"For the first time, central nervous system white matter lesions are demonstrated in CMT4D."

Independent evidence of central nervous system involvement in p.Arg148*-homozygous patients.

+ 1 more reference

Motor Denervation

Mechanism confidence: Established

Motor axonal loss deprives affected muscles of innervation. Human CMT4D electromyography demonstrates chronic denervation, supporting neurogenic weakness and wasting in distal muscles and, in severe disease, proximal muscles.

Downstream

Distal Amyotrophy Chronic loss of motor innervation causes neurogenic wasting in the predominantly affected distal muscles.

Proximal Muscle Weakness Denervation also compromises proximal motor units in severely affected patients; proximal denervation and weakness were both documented in the Turkish NDRG1-duplication homozygote.

Show evidence (2 references)

PMID:24136616 SUPPORT Human Clinical

"Needle electromyography showed no activity in distal and proximal muscles of the lower limbs and distal muscles of the upper limbs; chronic denervation findings were present in proximal muscles of the upper limbs."

Human electrophysiology documents denervation in the genetically affected NDRG1-duplication homozygote BAB4149.

PMID:24136616 SUPPORT Human Clinical

"The physical examination revealed severe distal and mild proximal muscle weakness and distal wasting with areflexia."

The genetically affected Turkish proband had distal wasting and both distal and proximal weakness; these are observations in NDRG1-associated disease, unlike the differently affected wild-type sibling.

Visual Pathway Dysfunction

Mechanism confidence: Provisional

Abnormal visual evoked potentials demonstrate dysfunction of the visual system in reported CMT4D siblings. The anatomical substrate and causal route from NDRG1 loss are unresolved; this node identifies the state measured by VEPs without assigning it to the cerebral white matter lesions reported in a different family.

Show evidence (1 reference)

PMID:42089726 SUPPORT Human Clinical

"Visual system involvement was demonstrated through abnormal visual evoked potentials with reduced P100 amplitude and absent responses, expanding the recognized phenotypic spectrum."

Documents the exact electrophysiological finding in the two siblings. The review’s 17% broad visual-involvement estimate does not quantify abnormal VEPs specifically.

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Pathograph

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Phenotypes

28

Digestive 1

Dysphagia HP:0002015

Show evidence (1 reference)

PMID:42089726 SUPPORT Human Clinical

"Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay."

Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.

Ear 1

Sensorineural Hearing Loss Sensorineural hearing impairment HP:0000407

Course: PROGRESSIVE

Show evidence (3 references)

PMID:39201732 SUPPORT Human Clinical

"Sensorineural deafness is a hallmark feature of the phenotype and generally develops during the third decade [1,25]."

Supports sensorineural hearing loss and its usual timing; the broader pooled hearing-impairment percentage is not assigned as a sensorineural frequency.

PMID:24136616 SUPPORT Human Clinical

"Audiometry showed moderate sensorineural hearing loss especially at low frequencies."

The Turkish proband demonstrates that the frequency distribution of hearing loss is not uniformly high-frequency predominant.

PMID:24136616 SUPPORT Human Clinical

"He also had hearing loss, which was noted at ~4 years of age."

The Turkish proband had childhood hearing-loss onset; his audiometry documented sensorineural hearing loss.

Eye 1

Abnormal Visual Evoked Potentials Abnormality of visual evoked potentials HP:0000649

Show evidence (1 reference)

PMID:42089726 SUPPORT Human Clinical

"Visual system involvement was demonstrated through abnormal visual evoked potentials with reduced P100 amplitude and absent responses, expanding the recognized phenotypic spectrum."

Documents the exact electrophysiological finding in the two siblings. The review’s 17% broad visual-involvement estimate does not quantify abnormal VEPs specifically.

Limbs 4

Pes Cavus FREQUENT HP:0001761

Show evidence (2 references)

PMID:42089726 SUPPORT Human Clinical

"The median age of onset was 7 years, 96% of patients presented with lower limb involvement and all presented skeletal deformities were universal, including pes cavus (67%), claw hand (40%), and scoliosis (33%)."

The 67% frequency for this exact phenotype in the published-case review supports FREQUENT. This is a literature-derived estimate subject to ascertainment and reporting differences, not a population prevalence.

PMID:39201732 SUPPORT Human Clinical

"Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2)."

Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.

Equinovarus Deformity HP:0008110

Show evidence (1 reference)

PMID:39201732 SUPPORT Human Clinical

"Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2)."

Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.

Claw Hand Deformity FREQUENT HP:0034337

Show evidence (2 references)

PMID:42089726 SUPPORT Human Clinical

"The median age of onset was 7 years, 96% of patients presented with lower limb involvement and all presented skeletal deformities were universal, including pes cavus (67%), claw hand (40%), and scoliosis (33%)."

The 40% frequency for this exact phenotype in the published-case review supports FREQUENT. This is a literature-derived estimate subject to ascertainment and reporting differences, not a population prevalence.

PMID:39201732 SUPPORT Human Clinical

"Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2)."

Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.

Hammertoe HP:0001765

Show evidence (2 references)

PMID:24136616 SUPPORT Human Clinical

"She also had pes cavus, hammer toes, and claw hands."

Documents hammer toes in the NDRG1-duplication homozygote BAB4148.

PMID:24136616 SUPPORT Human Clinical

"Severe deformities including kyphoscoliosis, pes cavus, hammer toes, and claw hands were observed."

Documents hammer toes in the genetically affected proband BAB3724.

Musculoskeletal 5

Distal Muscle Weakness HP:0002460

Course: PROGRESSIVE

Sequelae: Loss of Ambulation Steppage Gait Frequent Falls

Show evidence (2 references)

PMID:39201732 SUPPORT Human Clinical

"Neurological examination revealed severe distal muscle weakness in the lower limbs in all patients with muscle strength of toe flexors and extensors and plantar flexors and extensors of 0–1/5 in MRC score."

Quantifies the severity of distal lower-limb weakness.

PMID:39201732 SUPPORT Human Clinical

"Weakness in the hands (in holding small objects) developed between the age of 10–17 years."

Dates the upper-limb involvement relative to lower-limb onset.

Distal Amyotrophy HP:0003693

Sequelae: Pes Cavus Equinovarus Deformity Claw Hand Deformity Hammertoe

Show evidence (1 reference)

PMID:39201732 SUPPORT Human Clinical

"Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2)."

Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.

Scoliosis FREQUENT HP:0002650

Show evidence (2 references)

PMID:42089726 SUPPORT Human Clinical

"The median age of onset was 7 years, 96% of patients presented with lower limb involvement and all presented skeletal deformities were universal, including pes cavus (67%), claw hand (40%), and scoliosis (33%)."

The 33% frequency for this exact phenotype in the published-case review supports FREQUENT. This is a literature-derived estimate subject to ascertainment and reporting differences, not a population prevalence.

PMID:39201732 SUPPORT DIRECT Human Clinical

"Scoliosis was observed only in one patient (case I-1)."

One observed case supports scoliosis occurrence. Differences between this small cohort and the published-case review do not constitute refutation of the phenotype.

Proximal Muscle Weakness HP:0003701

Show evidence (2 references)

PMID:24136616 SUPPORT Human Clinical

"The physical examination revealed severe distal and mild proximal muscle weakness and distal wasting with areflexia."

The genetically affected Turkish proband had distal wasting and both distal and proximal weakness; these are observations in NDRG1-associated disease, unlike the differently affected wild-type sibling.

PMID:24136616 SUPPORT Human Clinical

"Her clinical examination showed severe distal and moderate proximal muscle weakness."

This sentence concerns the affected NDRG1-duplication homozygote BAB4149, not the differently affected wild-type sibling BAB4152.

Frequent Falls HP:0002359

Show evidence (1 reference)

PMID:39201732 SUPPORT Human Clinical

"The initial manifestations in all patients included distal muscle weakness in the lower limbs with impaired steppage gait and frequent falls."

Directly documents frequent falls at presentation in this CMT4D series.

Nervous System 15

Demyelinating Sensorimotor Polyneuropathy Demyelinating peripheral neuropathy HP:0007108

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:39201732 SUPPORT Human Clinical

"From an electrophysiological point of view, CMT4D is a demyelinating neuropathy involving severe and early axonal loss."

Supports the demyelinating neuropathy itself. The separate 96% lower-limb involvement figure does not quantify this phenotype.

Loss of Ambulation HP:0002505

Course: PROGRESSIVE

Show evidence (2 references)

PMID:39201732 SUPPORT Human Clinical

"Patients present with an early onset demyelinating peripheral neuropathy causing severe distal muscle weakness and sensory loss, leading to loss of ambulation and progressive sensorineural hearing loss."

States loss of ambulation as the outcome the neuropathy progresses to.

PMID:39201732 SUPPORT Human Clinical

"All patients had an unstable gait with marked steppage, except one case I-1, who had lost ambulation at the age of 23 years."

Documents loss of ambulation at age 23 in case I-1. Other examined patients retained an unstable gait, including adults older than 23, so this observation does not establish an age threshold.

Steppage Gait HP:0003376

Show evidence (1 reference)

PMID:39201732 SUPPORT Human Clinical

"The initial manifestations in all patients included distal muscle weakness in the lower limbs with impaired steppage gait and frequent falls."

Documents steppage gait as a presenting feature in all patients of that cohort.

Decreased Motor Nerve Conduction Velocity HP:0003431

Show evidence (1 reference)

PMID:9549516 SUPPORT Human Clinical

"Severely reduced motor nerve conduction velocity indicates a demyelinating basis, which was confirmed by nerve biopsy."

The original human HMSN-Lom study explicitly interprets reduced motor conduction velocity as a readout of demyelination.

Areflexia HP:0001284

Show evidence (2 references)

PMID:39201732 SUPPORT Human Clinical

"The tendon reflexes were absent in the lower limbs in all of the patients and were preserved but attenuated in the upper limbs in 5/7."

Documents the reflex pattern, including the upper-limb sparing.

PMID:42089726 SUPPORT Human Clinical

"Both patients presented with severe distal-proximal sensorimotor neuropathy, muscle weakness and atrophy, generalized areflexia, and sensorineural deafness typical of CMT4D."

The Italian siblings document generalized areflexia, supporting the broad HPO term alongside the lower-limb-predominant pattern in Bulgaria.

Distal Sensory Loss Distal sensory impairment HP:0002936

Show evidence (1 reference)

PMID:39201732 SUPPORT Human Clinical

"The sensation in the distal parts of the four limbs produced by light touch, pin prick, and temperature sensations was diminished to absent in all of the affected"

Documents the distribution and modalities of sensory loss.

Bilateral Vocal Cord Paralysis HP:0012820

Sequelae: Respiratory Insufficiency

Show evidence (1 reference)

PMID:42089726 SUPPORT Human Clinical

"Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay."

Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.

Cognitive Impairment HP:0100543

Show evidence (1 reference)

PMID:42089726 SUPPORT Human Clinical

"Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay."

Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.

Central Nervous System White Matter Abnormality Abnormal cerebral white matter morphology HP:0002500

Show evidence (2 references)

PMID:17142040 SUPPORT Human Clinical

"We report the detailed phenotypic study of a family without Gypsy ancestry, who presented with severe demyelinating polyneuropathy, deafness, subcortical white matter abnormalities on brain magnetic resonance imaging studies, and the R148X mutation in NDRG1."

Documents subcortical white matter abnormality in p.Arg148*-homozygous patients.

PMID:17142040 SUPPORT INDIRECT Human Clinical

"This report extends the clinical knowledge of CMT4D and indicates that the role of the R148X mutation in NDRG1 in the central nervous system should be further studied."

Supports central nervous system involvement only indirectly - the authors frame it as a question requiring further study rather than an established feature, so the sentence points at the claim without asserting it.

Cerebellar Atrophy HP:0001272

Show evidence (1 reference)

PMID:27982524 SUPPORT Human Clinical

"Magnetic resonance imaging showed slight atrophy of cerebellum, medulla oblongata, and upper cervical spinal cord."

The single-patient report directly documents each named anatomical finding, without establishing its cellular mechanism or general frequency.

Cervical Spinal Cord Atrophy HP:0010873

Show evidence (1 reference)

PMID:27982524 SUPPORT Human Clinical

"Magnetic resonance imaging showed slight atrophy of cerebellum, medulla oblongata, and upper cervical spinal cord."

The single-patient report directly documents each named anatomical finding, without establishing its cellular mechanism or general frequency.

Medullary Atrophy Atrophy/Degeneration affecting the brainstem HP:0007366

Show evidence (1 reference)

PMID:27982524 SUPPORT Human Clinical

"Magnetic resonance imaging showed slight atrophy of cerebellum, medulla oblongata, and upper cervical spinal cord."

The single-patient report directly documents each named anatomical finding, without establishing its cellular mechanism or general frequency.

Motor Delay HP:0001270

Show evidence (2 references)

PMID:24136616 SUPPORT Human Clinical

"The proband (BAB3724 = II-2) was a 30-year-old male who had delayed motor milestones."

Directly supports motor delay in a genetically affected CMT4D proband.

PMID:27982524 SUPPORT Human Clinical

"We report a 38-year-old Italian female with motor development delay, progressive neuropathy, and sensorineural deafness."

Independently documents motor delay with an NDRG1 frameshift allele.

Absent Distal Sensory Nerve Action Potentials Decreased distal sensory nerve action potential HP:0007230

Show evidence (1 reference)

PMID:24136616 SUPPORT Human Clinical

"Sensory nerve action potentials were absent in both upper and lower limbs (Table 1)."

Directly documents absent sensory responses in the NDRG1-duplication homozygote BAB4149.

Delayed Brainstem Auditory Evoked Responses Delayed brainstem auditory evoked response conduction time HP:0004466

Show evidence (2 references)

PMID:39201732 SUPPORT Human Clinical

"Brainstem auditory-evoked potentials showed increased latencies of waves I–III–V, as well as increased interpeak latencies in some patients (cases II-1, II-2, IV-1, IV-2, and IV-3)."

Documents delayed auditory conduction in five named patients.

PMID:39201732 SUPPORT Human Clinical

"Interestingly, the two patients with no auditory complains (case II-1 and case II-2), aged 30 and 31 years, respectively, also had normal audiograms (Table 3)."

These two patients had evoked-potential delay despite normal audiograms; the readout can precede symptomatic hearing loss.

Respiratory 1

Respiratory Insufficiency HP:0002093

Show evidence (1 reference)

PMID:42089726 SUPPORT Human Clinical

"Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay."

Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.

🧬

Genetic Associations

1

NDRG1

Gene: NDRG1 hgnc:7679 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (6 references)

PMID:42089726 SUPPORT Human Clinical

"Our systematic literature review identified 26 articles describing 72 patients with CMT4D."

Establishes the size of the published patient series underlying the allelic and phenotypic figures used in this entry.

PMID:33305529 SUPPORT In Vitro

"The 43-kDa NDRG1 is considered as an inactive member of the α/β hydrolase superfamily."

States the protein's structural class and presumed catalytic inactivity.

PMID:33305529 SUPPORT In Vitro

"NDRG1 binds to various types of lipid vesicles, and the conformation of the C-terminal region is modulated upon lipid interaction."

Establishes lipid-vesicle binding, the structural counterpart of the trafficking role proposed for NDRG1 in the Schwann cell.

+ 3 more references

💊

Medical Actions

2

Percutaneous Endoscopic Gastrostomy Feeding

Action: percutaneous endoscopic gastrostomy Ontology label: Percutaneous Endoscopic Gastrostomy NCIT:C106040

Platform: Surgery

Enteral feeding via a PEG tube for the severe dysphagia that can develop in advanced CMT4D. This is curated because it was actually performed in reported CMT4D patients, not extrapolated from neuromuscular disease generally - bulbar involvement was unrecognised in CMT4D until the 2026 sibling report, and an entry that omitted it would leave swallowing off the surveillance list.

Show evidence (1 reference)

PMID:42089726 SUPPORT Human Clinical

"Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay."

Documents PEG placement as the intervention used for CMT4D dysphagia in the reported siblings.

Non-Invasive Ventilation

Action: non-invasive mechanical ventilation Ontology label: Non-Invasive Mechanical Ventilation NCIT:C171457

Platform: Device

Non-invasive ventilation was used for respiratory insufficiency attributed to bilateral vocal cord paralysis in the reported Italian siblings.

Show evidence (1 reference)

PMID:42089726 SUPPORT Human Clinical

"Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay."

Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.

🔬

Diagnosis

4

Nerve Conduction Studies

Nerve conduction studies establish the demyelinating character and its severity: markedly reduced conduction velocities, prolonged distal latencies including in cranial nerves, and absent sensory nerve action potentials. Needle EMG shows scattered fibrillation and neurogenic motor unit potentials, more pronounced distally, reflecting the accompanying axonal degeneration.

Show evidence (1 reference)

PMID:39201732 SUPPORT Human Clinical

"It is characterized by markedly reduced conduction velocities and prolonged distal latencies of the motor nerves (including musculocutaneous, axillary, hypoglossal, and facial nerves), absent sensory nerve action potentials (SNAP), and a blink reflex with an unusual three-component response"

The full electrophysiological signature, including the cranial-nerve involvement and the unusual blink reflex.

Brainstem Auditory Evoked Potentials

Brainstem auditory evoked potentials are abnormal before patients report hearing loss, which makes them a presymptomatic marker of auditory pathway involvement rather than a confirmation of an existing complaint.

Show evidence (2 references)

PMID:39201732 SUPPORT Human Clinical

"Brainstem auditory-evoked potentials showed increased latencies of waves I–III–V, as well as increased interpeak latencies in some patients"

Documents the brainstem auditory evoked potential abnormality measured in the Bulgarian cohort.

PMID:39201732 SUPPORT Human Clinical

"Interestingly, the two patients with no auditory complains (case II-1 and case II-2), aged 30 and 31 years, respectively, also had normal audiograms"

Cases II-1 and II-2 are named among the patients with increased brainstem evoked-potential latencies in the quote above, yet had no hearing complaint and normal audiograms - which is what makes the evoked potential a presymptomatic marker rather than a confirmation of an existing complaint.

Targeted NDRG1 Sequencing

Molecular confirmation. Because a single founder allele accounts for most cases, targeted testing of NDRG1 has a high yield in patients of Roma origin with early-onset demyelinating neuropathy, and the authors of the Slovak series argue for making it routine in that setting. It must not be restricted to that setting, however: whole-exome and targeted panel sequencing have found NDRG1 alleles in patients with no Roma ancestry.

Show evidence (1 reference)

PMID:23996628 SUPPORT Human Clinical

"Providing genetic analysis of these genes for patients with Roma origin as a common part of diagnostic procedure would contribute to a better rate of diagnosed cases of demyelinating neuropathy"

The argument for routine targeted testing in the founder population.

Sural Nerve Biopsy

Not required for diagnosis now that molecular testing is available, but historically decisive and still informative where the genetic result is ambiguous: CMT4D nerve histology is reported as distinct, showing depletion of myelinated fibres, small calibre in those that survive, and poorly developed onion bulbs.

Show evidence (1 reference)

PMID:39201732 SUPPORT Human Clinical

"Nerve histology seems to be distinct, and shows a depletion in myelinated nerve fibers with small size in the few preserved myelinated fibers and poorly developed onion bulbs"

Describes the histological picture and its claimed distinctiveness, in the source's own hedged terms.

📊

Prevalence

1

Worldwide

Cases In Literature Ultra Rare

No population prevalence estimate for CMT4D exists. The published literature totals 72 patients across 26 articles. The disorder is concentrated in Roma communities, where it is one of three CMT subtypes caused by founder mutations private to that population, and within a Bulgarian demyelinating CMT cohort of 150 index patients NDRG1 variants explained 15 patients from 11 families - roughly seven percent of that ascertained, and therefore heavily enriched, series. That figure is a diagnostic yield within a selected cohort, not a population rate, and must not be read as one.

Show evidence (2 references)

PMID:42089726 SUPPORT Human Clinical

"Our systematic literature review identified 26 articles describing 72 patients with CMT4D."

The total published case count, which is the only defensible occurrence figure for this disorder.

PMID:39201732 SUPPORT Human Clinical

"Our cohort consisted of 150 index Bulgarian patients with demyelinating CMT. We identified 15 patients from 11 families with recurrent or novel variants in the NDRG1 gene"

The diagnostic yield of NDRG1 testing within an ascertained demyelinating CMT cohort.

🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Charcot-Marie-Tooth disease type 4D:

Other autosomal recessive demyelinating CMT (CMT4 subtypes)

Overlapping Features CMT4D must be separated from the other CMT4 subtypes - CMT4A (GDAP1), CMT4B1 and CMT4B2 (MTMR2, SBF2), CMT4C (SH3TC2), CMT4F (PRX) and CMT4J (FIG4) - which share recessive inheritance, early onset and slowed conduction. Two features point towards NDRG1: sensorineural deafness, which is not a general CMT4 feature, and the early severity of axonal loss. Neither is decisive, and the entity is defined genetically. Curated in this knowledge base as `Charcot-Marie-Tooth_Disease_Type_4`, which also carries CMT4D as a subtype block.

Show evidence (1 reference)

PMID:27982524 SUPPORT Human Clinical

"should be considered in the differential diagnosis of recessive demyelinating CMT"

Places CMT4D within the recessive demyelinating CMT differential regardless of ancestry.

🐁

Animal Models

4

Ndrg1 exon 4-5 knockout mouse

A CRISPR-generated null mouse that develops early progressive demyelinating neuropathy and limb muscle weakness, with reduced motor nerve conduction velocity and compound muscle action potential amplitude by eight weeks. It is the model in which the neuregulin 1/ErbB findings were made.

Species

Mouse

Genotype

Ndrg1-/- (CRISPR/Cas9 deletion of exons 4 and 5)

Publication

PMID:35708320

Pathograph links

Myelin Sheath Breakdown with Onion Bulb Formation recapitulates fidelity: moderate Reproduces the demyelinating lesion with correct timing - normal at two weeks, thinning from four weeks when myelination would normally be complete, progressive thereafter, with occasional onion bulbs.

Limitations: The hypomyelination does not lead to apparent axonal loss, so the model reproduces the demyelination while missing the early severe axonal loss that produces disability in patients.

Readouts

Sciatic nerve g-ratio

Direction: INCREASED

Interpretation: A raised g-ratio is the quantitative signature of thin myelin relative to axon calibre, confirming demyelinating rather than axonal pathology.

Show evidence (1 reference)

PMID:35708320 SUPPORT Model Organism

"Quantitative analysis indicated that the G ratio of the nerve fibers was significantly increased inNdrg1−/−mice, suggesting the presence of demyelinating neuropathy"

Reports the g-ratio measurement supporting the demyelinating phenotype.

Show evidence (1 reference)

PMID:35708320 SUPPORT Model Organism

"Ndrg1-deficient mice develop early progressive demyelinating neuropathy and limb muscle weakness."

Establishes the model as informative for the demyelinating node.

Early Severe Axonal Loss fails to recapitulate fidelity: low The defining human feature - early severe axonal loss - is absent from this model despite otherwise faithful demyelination, and the authors say so explicitly.

Limitations: A shift in axonal size distribution occurs, but no apparent axonal loss. Any therapeutic result obtained in this model therefore speaks to the demyelinating arm only and cannot be assumed to address the axonal degeneration that causes disability in patients.

Show evidence (1 reference)

PMID:35708320 REFUTE Model Organism

"Although a shift in the axonal size distribution was observed inNdrg1−/−mice, the hypomyelination did not lead to apparent axonal loss"

The authors' direct statement that axonal loss is absent from the model.

Attenuated Neuregulin 1-ErbB Signaling measures fidelity: moderate The model is the sole source of the neuregulin 1/ErbB evidence in this entry: it is where receptor phosphorylation, ligand level and integrin beta-4 abundance were measured.

Limitations: No equivalent measurement exists in human CMT4D nerve, so the entire signalling arm of this entry's pathograph rests on this mouse.

Readouts

Phosphorylated ErbB2/ErbB3 in sciatic nerve

Direction: DECREASED

Interpretation: Reduced receptor phosphorylation against increased total receptor is the measurement that localises the defect to receptor activation.

Show evidence (1 reference)

PMID:35708320 SUPPORT Model Organism

"levels of the phosphorylated forms of ErbB2/3 and their downstream signaling cascades were decreased"

The phosphorylation measurement underlying this readout.

Show evidence (1 reference)

PMID:35708320 SUPPORT Model Organism

"our data suggest that the demyelinating phenotype of CMT4D disease is at least in part a consequence of molecular defects in neuregulin 1/ErbB signaling"

The authors' own hedged conclusion, which is the claim this link records.

Stretcher mouse (spontaneous Ndrg1 null)

A spontaneous total Ndrg1-null mutant, compared directly against a hypomorphic Ndrg1 knockout. The comparison is the informative part: the markedly more severe stretcher phenotype implies that even low residual Ndrg1 expression rescues a large part of the phenotype, which is a dosage statement no single model could make.

Species

Mouse

Genotype

Ndrg1 str/str (spontaneous total Ndrg1 deficiency)

Publication

PMID:21303696

Pathograph links

Impaired Schwann Cell Vesicular Trafficking partially recapitulates fidelity: moderate The model is the basis of the trafficking-demand-mismatch hypothesis: its large-fibre demyelination coincides precisely with the period of rapid myelin growth and small fibres are spared, while gene expression profiling found only non-specific secondary changes and normal proteasomal function.

Limitations: The trafficking defect itself is not measured in this model; the inference rests on the timing and fibre-size selectivity of the lesion, and gene expression profiling was explicitly non-specific.

Show evidence (1 reference)

PMID:21303696 SUPPORT Model Organism

"Impaired SC trafficking failing to meet the considerable demands of nerve growth, emerges as the likely pathogenetic mechanism in NDRG1 deficiency."

The conclusion this model supports, stated as the authors state it.

Early Severe Axonal Loss fails to recapitulate fidelity: low Neither the stretcher mouse nor the hypomorphic knockout reproduces the early severe axonal loss of human CMT4D. Axon damage occurs, but regenerative capacity is unimpaired.

Limitations: Because both models compared in that study fail at the same point, as does the independent CRISPR Ndrg1-/- mouse, no rodent model reconstructs the step from Schwann-cell NDRG1 loss to axonal degeneration, which constrains what preclinical work on this disorder can test. The canine model is deliberately excluded from that claim: it does show axonal pathology, and is treated separately in the HUMAN_MODEL_MISMATCH discussion.

Show evidence (1 reference)

PMID:21303696 REFUTE Model Organism

"Neither model replicates fully the features of CMT4D: although axon damage is present, regenerative capacity is unimpaired and the mice do not display the early severe axonal loss typical of the human disease."

The explicit statement that both rodent models fail to reproduce the defining human feature.

Ndrg1 knockout mouse (Okuda)

The first published Ndrg1-null mouse, and the model the stretcher work later used as its hypomorphic comparator. Its contribution is a timing argument: sciatic nerve myelination is normal for the first two postnatal weeks and only then degenerates with demyelination at about five weeks, which separates myelin maintenance from myelin formation as the affected process.

Species

Mouse

Genotype

Ndrg1-/- (targeted knockout)

Publication

PMID:15082788

Pathograph links

Myelin Sheath Breakdown with Onion Bulb Formation recapitulates fidelity: moderate Establishes progressive demyelination of an initially normally myelinated nerve, with Schwann-cell dysfunction as the proximate cause.

Limitations: Reported as a hypomorphic rather than complete null in the later head-to-head comparison with the stretcher mouse, and neither model in that comparison displays the early severe axonal loss of the human disease.

Readouts

Sciatic nerve myelination timing

Direction: DECREASED

Interpretation: Normal myelination for two weeks followed by demyelination at five weeks is the readout that distinguishes maintenance failure from formation failure.

Show evidence (1 reference)

PMID:15082788 SUPPORT Model Organism

"Histological analysis showed that the sciatic nerve of Ndrg1-deficient mice degenerated with demyelination at about 5 weeks of age. However, myelination of Schwann cells in the sciatic nerve was normal for 2 weeks after birth."

The histological timing measurement underlying this readout.

Show evidence (1 reference)

PMID:15082788 SUPPORT Model Organism

"These results indicate that NDRG1 deficiency leads to Schwann cell dysfunction, suggesting that NDRG1 is essential for maintenance of the myelin sheaths in peripheral nerves."

States the conclusion this model supports - maintenance, not formation.

Early Severe Axonal Loss fails to recapitulate fidelity: low This model was one of the two compared head to head in PMID:21303696, and that comparison found neither reproduces the early severe axonal loss of human CMT4D.

Limitations: The failure is shared with the stretcher mouse and is the reason no rodent model reconstructs the axonal arm. It says nothing about the canine model, which does show axonal pathology.

Show evidence (1 reference)

PMID:21303696 REFUTE Model Organism

"Neither model replicates fully the features of CMT4D: although axon damage is present, regenerative capacity is unimpaired and the mice do not display the early severe axonal loss typical of the human disease."

The head-to-head comparison covering this model and the stretcher mouse, which is what makes this a structural FAILS_TO_RECAPITULATE link rather than a prose assertion inside a myelin link's limitations.

Greyhound polyneuropathy (NDRG1 exon 15 deletion)

A naturally occurring canine model: juvenile Greyhound show dogs with a recessive polyneuropathy tracing to a single founder male, in which a ten-base deletion in NDRG1 exon 15 is perfectly associated with the phenotype and abolishes NDRG1 protein in peripheral nerve.

Species

Dog

Genotype

NDRG1 c.1080_1089delTCGCCTGGAC homozygous (p.Arg361SerfsX60)

Publication

PMID:20582309

Pathograph links

Progressive Demyelinating Sensorimotor Neuropathy partially recapitulates fidelity: moderate Reproduces a severe chronic progressive polyneuropathy of juvenile onset on a recessive founder background, with NDRG1 protein absent from peripheral nerve on Western blot.

Limitations: The canine lesion is described as a mixed polyneuropathy rather than the predominantly demyelinating picture with early axonal loss seen in patients, and deafness - a defining human feature - is not reported in the affected dogs.

Show evidence (2 references)

PMID:20582309 SUPPORT Model Organism

"Western blot analysis demonstrated an absence of NDRG1 protein in peripheral nerve biopsy of an affected Greyhound."

Confirms loss of NDRG1 protein in the affected tissue, establishing the model as an NDRG1-null neuropathy.

+ 1 more reference

{ }

Source YAML

click to show

name: Charcot-Marie-Tooth disease type 4D
creation_date: "2026-08-27T00:00:00Z"
description: >-
  Charcot-Marie-Tooth disease type 4D (CMT4D), historically hereditary motor and
  sensory neuropathy-Lom (HMSNL), is an autosomal recessive, childhood-onset,
  severe demyelinating sensorimotor neuropathy caused by biallelic
  loss-of-function variants in NDRG1. It was first delineated in Roma families
  from the town of Lom in Bulgaria, where a single founder nonsense allele
  p.Arg148* accounts for most cases worldwide, but it is not a Roma-restricted
  disease: frameshift, splice-site, missense and exon-duplication alleles have
  since been reported in families of Italian, Turkish, Indian, Chinese, Saudi
  and Bulgarian Muslim origin. NDRG1 is expressed at very high levels in the
  Schwann cell and not detectably in axons, so the primary lesion is glial; what
  distinguishes CMT4D from other demyelinating CMT is that severe axonal loss
  appears early rather than as a late consequence of chronic demyelination,
  which is why the original gene-discovery work framed the disorder as a failure
  of axon-glia interaction rather than of myelin structure. Sensorineural
  deafness, usually emerging in the third decade, is the second defining
  feature. The molecular function of NDRG1 remains only partly understood; the
  leading account is a Schwann-cell vesicular-trafficking role that cannot meet
  the enormous membrane demand of myelin growth, and the neuregulin-1/ErbB
  evidence that would connect that defect to demyelination is so far entirely
  from mouse.
category: Mendelian
parents:
- hereditary disease
synonyms:
- CMT4D
- HMSNL
- HMSN4D
- hereditary motor and sensory neuropathy-Lom
- hereditary motor and sensory neuropathy, Lom type
- autosomal recessive demyelinating Charcot-Marie-Tooth disease type 4D
disease_term:
  preferred_term: Charcot-Marie-Tooth disease type 4D
  term:
    id: MONDO:0011085
    label: Charcot-Marie-Tooth disease type 4D
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    evidence:
    - reference: PMID:39201732
      reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Charcot-Marie-Tooth neuropathy type 4D (CMT4D) is a rare genetic disorder
        of the peripheral nervous system caused by biallelic mutations in the
        N-Myc Downstream Regulated 1 gene (NDRG1).
      explanation: >-
        Places CMT4D among disorders of the peripheral nervous system.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:10831399
      reference_title: "N-myc downstream-regulated gene 1 is mutated in hereditary motor and sensory neuropathy-Lom."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Sequence analysis of two genes located in the critical region identified
        the founder HMSNL mutation: a premature-termination codon at position 148
        of the N-myc downstream-regulated gene 1 (NDRG1).
      explanation: >-
        Establishes a single-gene Mendelian basis identified by positional
        cloning of a founder mutation.
references:
- reference: PMID:10831399
  title: "N-myc downstream-regulated gene 1 is mutated in hereditary motor and sensory neuropathy-Lom."
- reference: PMID:24028195
  title: "CMT4D (NDRG1 mutation): genotype-phenotype correlations."
- reference: PMID:27982524
  title: "A novel NDRG1 mutation in a non-Romani patient with CMT4D/HMSN-Lom."
- reference: PMID:28776325
  title: "Identification and functional characterization of two missense mutations in NDRG1 associated with Charcot-Marie-Tooth disease type 4D."
- reference: PMID:35708320
  title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
- reference: PMID:21303696
  title: "Ndrg1 in development and maintenance of the myelin sheath."
- reference: PMID:17142040
  title: "NDRG1-linked Charcot-Marie-Tooth disease (CMT4D) with central nervous system involvement."
- reference: PMID:39201732
  title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
- reference: PMID:42089726
  title: "Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature."
- reference: PMID:33305529
  title: "Crystal and solution structure of NDRG1, a membrane-binding protein linked to myelination and tumour suppression."
- reference: PMID:23996628
  title: "Founder mutations in NDRG1 and HK1 genes are common causes of inherited neuropathies among Roma/Gypsies in Slovakia."
- reference: PMID:35149926
  title: "A splice altering variant in NDRG1 gene causes Charcot-Marie-Tooth disease, type 4D."
- reference: PMID:24136616
  title: "Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D."
- reference: PMID:20582309
  title: "A deletion in the N-myc downstream regulated gene 1 (NDRG1) gene in Greyhounds with polyneuropathy."
- reference: PMID:9549516
  title: "Hereditary motor and sensory neuropathy--Lom, a novel demyelinating neuropathy associated with deafness in gypsies. Clinical, electrophysiological and nerve biopsy findings."
- reference: PMID:15082788
  title: "Ndrg1-deficient mice exhibit a progressive demyelinating disorder of peripheral nerves."
- reference: PMID:20301532
  title: "Charcot-Marie-Tooth Hereditary Neuropathy Overview."
  tags: [GeneReviews]
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Biallelic NDRG1 variants, homozygous in the great majority of reported
    patients and compound heterozygous in a minority. The recessive mode is what
    makes founder populations the natural setting for the disorder: the Roma
    p.Arg148* allele and two Bulgarian Muslim splice-site alleles each reached
    homozygosity through consanguinity within a genetically isolated community
    rather than through recurrent mutation.
  evidence:
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Segregation analysis was performed on the available family members, and all
      of the variants co-segregated with the disease phenotype in the
      corresponding pedigrees
    explanation: >-
      Co-segregation of biallelic NDRG1 variants with disease across eleven
      families.
  - reference: PMID:23996628
    reference_title: "Founder mutations in NDRG1 and HK1 genes are common causes of inherited neuropathies among Roma/Gypsies in Slovakia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      There are three subtypes of autosomal recessive CMT with mutations private
      to the Roma population: CMT4C, CMT4D and CMT4G.
    explanation: >-
      States the recessive mode and the founder-population context.
pathophysiology:
- name: Biallelic NDRG1 Loss-of-Function Variant
  biological_scale: MOLECULAR
  role: trigger
  mechanism_confidence: ESTABLISHED
  conforms_to: "peripheral_axonal_degeneration#Insult to Peripheral Neurons and Schwann Cells"
  description: >-
    The initiating lesion is biallelic loss of NDRG1. The founder allele
    p.Arg148* (c.442C>T) introduces a premature termination codon and accounts
    for roughly two-thirds of reported patients. The remaining alleles converge
    on the same functional endpoint by different routes: frameshifts
    (p.His247Thrfs*74, p.Ser317Argfs*4, p.Glu170Glyfs*35), further nonsense
    alleles, canonical splice-acceptor variants whose transcripts favour exon
    skipping, a duplication of exons 6-8, and two missense alleles (p.Leu146Pro,
    p.Arg234Gln) that destabilise the protein rather than truncating it. The
    missense alleles matter mechanistically because they show the disease can be
    produced by reduced NDRG1 abundance alone, with no truncation involved.
  genes:
  - preferred_term: NDRG1
    term:
      id: hgnc:7679
      label: NDRG1
  genetic_context:
    functional_impact_category: LOSS_OF_FUNCTION
    variant_origin: GERMLINE
    zygosity: HOMOZYGOUS
    description: >-
      Germline biallelic loss of function, most often homozygous for a founder
      nonsense allele. Functional characterisation of the novel Bulgarian
      splice-site alleles showed shorter gene products consistent with loss of
      protein function, and cell-culture work on the missense alleles showed
      accelerated degradation and lower steady-state protein levels.
  evidence:
  - reference: PMID:10831399
    reference_title: "N-myc downstream-regulated gene 1 is mutated in hereditary motor and sensory neuropathy-Lom."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sequence analysis of two genes located in the critical region identified
      the founder HMSNL mutation: a premature-termination codon at position 148
      of the N-myc downstream-regulated gene 1 (NDRG1).
    explanation: >-
      Identifies the founder truncating allele as the cause of HMSNL/CMT4D.
  - reference: PMID:42089726
    reference_title: "Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Twenty-two pathogenic NDRG1 variants were documented, with p.(Arg148*)
      being most frequent (64% of patients), predominantly in Roma populations.
    explanation: >-
      Quantifies the allelic spectrum across the published literature and the
      dominance of the founder allele within it.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Functional characterization of these novel variants implicates a
      loss-of-function mechanism due to shorter gene products.
    explanation: >-
      Establishes loss of function as the mechanism for the splice-site alleles,
      not only for the founder nonsense allele.
  - reference: PMID:28776325
    reference_title: "Identification and functional characterization of two missense mutations in NDRG1 associated with Charcot-Marie-Tooth disease type 4D."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Cell culture transfection studies showed that mutant NDRG1 carrying
      p.Leu146Pro, p.Arg148*, or p.Arg234Gln variant degraded faster than
      wild-type NDRG1, resulting in lower protein levels.
    explanation: >-
      Shows that the missense alleles reduce NDRG1 abundance, extending the
      loss-of-function mechanism beyond truncating variants.
  downstream:
  - target: Loss of Schwann Cell NDRG1 Function
    causal_link_type: DIRECT
  - target: Auditory Pathway Involvement
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The genotype-to-deafness link is established by segregation - sensorineural
      deafness is a hallmark of the NDRG1 phenotype - but the intervening
      mechanism is not. The evoked-potential data implicate the eighth cranial
      nerve and the central auditory pathways simultaneously, and no cochlear or
      auditory-nerve pathology from a CMT4D patient has been reported, so this
      edge deliberately skips over unknown intermediates rather than routing the
      deafness through the somatic Schwann-cell chain as if the mechanism were
      shared.
    evidence:
    - reference: PMID:9549516
      reference_title: "Hereditary motor and sensory neuropathy--Lom, a novel demyelinating neuropathy associated with deafness in gypsies. Clinical, electrophysiological and nerve biopsy findings."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        the results suggested demyelination in the eighth cranial nerve and also
        abnormal conduction in the central auditory pathways in the brainstem
      explanation: >-
        Shows two candidate sites implicated at once, which is why the edge is
        typed as having unknown intermediates rather than as direct.
- name: Loss of Schwann Cell NDRG1 Function
  biological_scale: CELLULAR
  role: central_effector
  mechanism_confidence: ESTABLISHED
  description: >-
    NDRG1 is highly expressed in human Schwann cells. Its loss impairs Schwann-cell function and peripheral myelin maintenance. Mouse models demonstrate initially normal myelination followed by demyelination; that temporal sequence has not been reconstructed in human nerves. The cellular trafficking and signaling routes below remain provisional.
  cell_types:
  - preferred_term: Schwann cell
    term:
      id: CL:0002573
      label: Schwann cell
  evidence:
  - reference: PMID:10831399
    reference_title: "N-myc downstream-regulated gene 1 is mutated in hereditary motor and sensory neuropathy-Lom."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We have studied expression in peripheral nerve and have detected
      particularly high levels in the Schwann cell.
    explanation: >-
      Establishes Schwann-cell enrichment of NDRG1 in peripheral nerve.
  - reference: PMID:35708320
    reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In the sciatic nerve, NDRG1 was restricted to S100β-positive Schwann cells
      but not detected in neurofilament 200-positive axons.
    explanation: >-
      Localises NDRG1 to the Schwann cell and excludes the axon, establishing the
      primary lesion as glial.
  - reference: PMID:35708320
    reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Moreover, NDRG1 was expressed at a low level before 2 weeks of age and at a
      high level after 2 weeks of age. This temporal expression pattern was
      similar to the myelin proteins
    explanation: >-
      Times NDRG1 expression to the myelination and myelin-maintenance period
      rather than to early Schwann-cell development.
  - reference: PMID:15082788
    reference_title: "Ndrg1-deficient mice exhibit a progressive demyelinating disorder of peripheral nerves."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In wild-type mice, NDRG1 was abundantly expressed in the cytoplasm of
      Schwann cells rather than the myelin sheath.
    explanation: >-
      Localises NDRG1 to the Schwann-cell cytoplasm rather than to myelin itself,
      which is why the disorder is not a structural myelin-protein disease.
  downstream:
  - target: Impaired Schwann Cell Vesicular Trafficking
  - target: Attenuated Neuregulin 1-ErbB Signaling
  - target: Early Severe Axonal Loss
    description: >-
      Impaired Schwann-cell support is implicated in early human axonal injury, but the glia-to-axon intermediates remain unresolved and rodent models fail to reproduce its early severity.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:10831399
      reference_title: N-myc downstream-regulated gene 1 is mutated in hereditary motor and sensory neuropathy-Lom.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        HMSNL shows features of Schwann-cell dysfunction and a concomitant early axonal involvement, suggesting that impaired axon-glia interactions play a major role in its pathogenesis.
      explanation: >-
        Supports a qualified glia-to-axon mechanism, not a proven sequence in which prolonged demyelination must precede axonal injury.
      directness: INDIRECT
- name: Impaired Schwann Cell Vesicular Trafficking
  biological_scale: CELLULAR
  role: effector
  mechanism_confidence: PROVISIONAL
  description: >-
    The leading account of what NDRG1 actually does in the Schwann cell is
    vesicular trafficking. NDRG1 regulates endosomal recycling through
    Rab4a-positive compartments and low-density lipoprotein receptor turnover;
    CMT4D
    missense mutants leave the NDRG1-Rab4a interaction intact but produce
    enlarged Rab4a-positive compartments and fail to support LDL uptake or to
    restore receptor levels at the cell surface. The proposal that follows -
    that a trafficking Schwann cell simply cannot meet the membrane demand of
    myelin growth - is supported by a striking timing coincidence in the
    stretcher mouse, where widespread large-fibre demyelination coincides exactly
    with the period in which myelin volume and length in large fibres increase
    several hundred-fold, and small fibres are spared. It is marked PROVISIONAL
    because the trafficking defect is demonstrated in cell lines and the
    demand-mismatch argument is an inference from the timing rather than a direct
    measurement of membrane flux in a CMT4D nerve. The same work explicitly
    argues against several earlier candidate functions.
  cell_types:
  - preferred_term: Schwann cell
    term:
      id: CL:0002573
      label: Schwann cell
  biological_processes:
  - preferred_term: endosomal recycling of membrane receptors
    modifier: DECREASED
    term:
      id: GO:0032456
      label: endocytic recycling
  evidence:
  - reference: PMID:28776325
    reference_title: "Identification and functional characterization of two missense mutations in NDRG1 associated with Charcot-Marie-Tooth disease type 4D."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      However, NDRG1-knockdown cells expressing mutant NDRG1 displayed enlarged
      Rab4a-positive compartments.
    explanation: >-
      Shows a recycling-endosome abnormality specific to the CMT4D mutant
      protein, with the NDRG1-Rab4a interaction itself preserved.
  - reference: PMID:28776325
    reference_title: "Identification and functional characterization of two missense mutations in NDRG1 associated with Charcot-Marie-Tooth disease type 4D."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Moreover, mutant NDRG1 could not enhance the uptake of DiI-LDL or increase
      the fraction of low-density lipoprotein receptor on the cell surface.
    explanation: >-
      Demonstrates a functional trafficking deficit for a receptor whose
      recycling NDRG1 normally supports.
  - reference: PMID:21303696
    reference_title: "Ndrg1 in development and maintenance of the myelin sheath."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Impaired SC trafficking failing to meet the considerable demands of nerve
      growth, emerges as the likely pathogenetic mechanism in NDRG1 deficiency.
    explanation: >-
      States the trafficking-demand-mismatch hypothesis this node represents, in
      the authors' own hedged terms.
  - reference: PMID:21303696
    reference_title: "Ndrg1 in development and maintenance of the myelin sheath."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The widespread large fibre demyelination coincides precisely with the
      period of rapid growth of the animals and the dramatic (160-500-fold)
      increase in myelin volume and length in large fibres.
    explanation: >-
      The timing observation that motivates the demand-mismatch account and
      explains the sparing of small fibres.
  - reference: PMID:21303696
    reference_title: "Ndrg1 in development and maintenance of the myelin sheath."
    supports: REFUTE
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Our findings do not support the proposed roles of NDRG1 in growth arrest,
      terminal differentiation, gene expression regulation and proteasomal
      degradation.
    explanation: >-
      Curated as REFUTE against the competing functional accounts of NDRG1, which
      is part of why trafficking is the leading hypothesis rather than one of
      several equals.
  downstream:
  - target: Myelin Sheath Breakdown with Onion Bulb Formation
- name: Attenuated Neuregulin 1-ErbB Signaling
  biological_scale: MOLECULAR
  role: mediator
  mechanism_confidence: PROVISIONAL
  description: >-
    Axonal neuregulin 1 signalling through Schwann-cell ErbB2/ErbB3 is the main
    route by which an axon instructs its Schwann cell how much myelin to make. In
    Ndrg1-deficient mice this pathway is decoupled in an informative way: ligand
    and receptor are not scarce - neuregulin 1 and total ErbB2/3 are both
    increased - yet the phosphorylated receptors and their downstream cascades
    are reduced, and integrin beta-4, the co-receptor that positively regulates
    the pathway, is markedly reduced. The lesion is therefore in receptor
    activation, not in ligand supply, which fits a trafficking defect that fails
    to present or maintain the receptor complex correctly at the Schwann-cell
    membrane. Marked PROVISIONAL for a specific reason: every one of these
    measurements comes from mouse sciatic nerve, and no equivalent has been shown
    in human CMT4D nerve. The same paper reports that its mouse does not
    reproduce the axonal loss that defines the human disease.
  cell_types:
  - preferred_term: Schwann cell
    term:
      id: CL:0002573
      label: Schwann cell
  biological_processes:
  - preferred_term: ERBB signaling pathway
    modifier: DECREASED
    term:
      id: GO:0038127
      label: ERBB signaling pathway
  evidence:
  - reference: PMID:35708320
    reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In the absence of NDRG1, although the total ErbB2/3 receptors expressed by
      Schwann cells were significantly increased, levels of the phosphorylated
      forms of ErbB2/3 and their downstream signaling cascades were decreased.
    explanation: >-
      The central observation: receptor abundance up, receptor activation down.
  - reference: PMID:35708320
    reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      This change was not associated with the level of the neuregulin 1 ligand,
      which was increased in Ndrg1-deficient mice.
    explanation: >-
      Excludes ligand scarcity as the explanation and localises the defect to the
      Schwann-cell receptor side.
  - reference: PMID:35708320
    reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In addition, the integrin β4 receptor, which interacts with ErbB2/3 and
      positively regulates neuregulin 1/ErbB signaling, was significantly reduced
      in the Ndrg1-deficient nerve.
    explanation: >-
      Identifies a reduced co-receptor as a candidate proximate cause of the
      activation failure.
  downstream:
  - target: Dysregulated Myelination Transcription Program
- name: Dysregulated Myelination Transcription Program
  biological_scale: CELLULAR
  role: effector
  mechanism_confidence: PROVISIONAL
  description: >-
    Downstream of the signalling defect, the Schwann-cell myelination program
    itself is disordered in Ndrg1-deficient mice. EGR2, SOX10 and OCT6 - the
    transcription factors that drive myelination - are all abnormally expressed,
    and the structural myelin proteins follow: MBP and MPZ fall at both mRNA and
    protein level. PMP22 behaves differently and is worth recording separately,
    because its mRNA falls while its protein rises, which the authors read as
    NDRG1 loss impairing PMP22 degradation. That dissociation is a second,
    independent pointer at a trafficking or turnover defect rather than a
    transcriptional one. PROVISIONAL: mouse only.
  cell_types:
  - preferred_term: Schwann cell
    term:
      id: CL:0002573
      label: Schwann cell
  biological_processes:
  - preferred_term: myelination in peripheral nervous system
    modifier: DECREASED
    term:
      id: GO:0022011
      label: myelination in peripheral nervous system
  evidence:
  - reference: PMID:35708320
    reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The expression pattern of myelination-related transcriptional factors,
      including SOX10, OCT6, and EGR2, was abnormal in Ndrg1-deficient mice.
    explanation: >-
      Establishes disruption of the myelination transcription program.
  - reference: PMID:35708320
    reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Intriguingly, thePmp22mRNA level was decreased inNdrg1−/−mice (Fig. 4C),
      while the PMP22 protein level was significantly increased
    explanation: >-
      Documents the mRNA-protein dissociation for PMP22 that points at impaired
      degradation rather than transcriptional failure.
  downstream:
  - target: Myelin Sheath Breakdown with Onion Bulb Formation
- name: Myelin Sheath Breakdown with Onion Bulb Formation
  biological_scale: TISSUE
  role: effector
  mechanism_confidence: ESTABLISHED
  conforms_to: "peripheral_axonal_degeneration#Distal Axonal Degeneration and Demyelination"
  description: >-
    Human sural nerve shows depletion of myelinated fibres, thin myelin sheaths on surviving fibres and onion bulb formations. Preserved fibres are small and onion bulbs may be poorly developed. Ndrg1-deficient mice show normal initial myelination followed by progressive myelin breakdown, providing evidence for impaired maintenance; normal initial myelination is not established longitudinally in humans.
  cell_types:
  - preferred_term: Schwann cell
    term:
      id: CL:0002573
      label: Schwann cell
  biological_processes:
  - preferred_term: myelin maintenance
    modifier: DECREASED
    term:
      id: GO:0043217
      label: myelin maintenance
  evidence:
  - reference: PMID:35708320
    reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sural nerve biopsy studies of patients showed marked depletion of
      myelinated fibers, thin myelin sheaths of the preserved myelinated fibers,
      and onion bulb formations
    explanation: >-
      The human nerve histology this node describes, cited from the review
      section of the paper rather than from its mouse experiments.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Nerve histology seems to be distinct, and shows a depletion in myelinated
      nerve fibers with small size in the few preserved myelinated fibers and
      poorly developed onion bulbs
    explanation: >-
      Independent description of the distinctive CMT4D nerve histology.
  - reference: PMID:35708320
    reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Ndrg1−/−mice began to show thinning of the myelin sheath at the age of 4
      weeks, when fiber myelination was normally complete.
    explanation: >-
      Establishes that the lesion is loss of established myelin rather than
      failure to form it.
  downstream:
  - target: Progressive Demyelinating Sensorimotor Neuropathy
    description: >-
      Myelin breakdown contributes the demyelinating component of the clinically observed sensorimotor neuropathy.
    causal_link_type: DIRECT
- name: Early Severe Axonal Loss
  biological_scale: CELLULAR
  role: amplifier
  mechanism_confidence: PROVISIONAL
  description: >-
    Severe axonal loss occurs early in human CMT4D and contributes to neurological disability. Human expression and pathology implicate impaired Schwann-cell support of axons, but the specific glia-to-axon causal route remains provisional. Mouse models reproduce demyelination but fail to reproduce the early severe axonal loss typical of patients. The Greyhound model has axonal pathology, although its timing and proportionality relative to demyelination have not been established to the same standard. The peripheral-neuron target here does not imply that NDRG1 loss acts cell-autonomously in the axon.
  cell_types:
  - preferred_term: peripheral nervous system neuron
    term:
      id: CL:2000032
      label: peripheral nervous system neuron
  evidence:
  - reference: PMID:10831399
    reference_title: "N-myc downstream-regulated gene 1 is mutated in hereditary motor and sensory neuropathy-Lom."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      HMSNL shows features of Schwann-cell dysfunction and a concomitant early
      axonal involvement, suggesting that impaired axon-glia interactions play a
      major role in its pathogenesis.
    explanation: >-
      The original statement of early axonal involvement and of axon-glia failure
      as the pathogenic core.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Nerve conduction studies (NCS) of all of our patients were consistent with
      severe demyelination and secondary axonal degeneration.
    explanation: >-
      Electrophysiological confirmation of axonal degeneration accompanying the
      demyelination in a contemporary patient cohort.
  - reference: PMID:21303696
    reference_title: "Ndrg1 in development and maintenance of the myelin sheath."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      although axon damage is present, regenerative capacity is unimpaired and
      the mice do not display the early severe axonal loss typical of the human
      disease
    explanation: >-
      Supports this node only obliquely: the sentence is about the mice, and
      confirms early severe axonal loss as the typical human feature in passing -
      hence directness INDIRECT. The other half of what this sentence says, that
      the rodent models fail to reproduce it, is not repeated here as a REFUTE
      item because it is already represented structurally by the
      FAILS_TO_RECAPITULATE links on those models.
  - reference: PMID:9549516
    reference_title: "Hereditary motor and sensory neuropathy--Lom, a novel demyelinating neuropathy associated with deafness in gypsies. Clinical, electrophysiological and nerve biopsy findings."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The hypertrophic changes were not evident in the oldest individual biopsied
      and it is likely that they had regressed secondarily to axon loss.
    explanation: >-
      Cross-sectional histological evidence that axon loss ultimately supplants
      the hypertrophic demyelinating picture, which is why the disability is
      axonal rather than demyelinating in character.
  downstream:
  - target: Progressive Demyelinating Sensorimotor Neuropathy
  - target: Motor Denervation
    description: >-
      Loss of motor axons removes muscle innervation; human CMT4D EMG documents the resulting chronic denervation.
    causal_link_type: DIRECT
- name: Progressive Demyelinating Sensorimotor Neuropathy
  biological_scale: ORGANISM
  role: consequence
  mechanism_confidence: ESTABLISHED
  conforms_to: "peripheral_axonal_degeneration#Peripheral Neuropathy"
  description: >-
    The clinical endpoint: a severe, progressive, childhood-onset demyelinating
    sensorimotor neuropathy. Distal lower-limb weakness with steppage gait and
    frequent falls is the presenting complaint, hand weakness follows in the
    second decade, and the disorder leads to loss of ambulation. Median
    age at onset across the published literature is seven years. Unlike most CMT
    the involvement is not confined to the distal limbs - the two most recently
    reported siblings had distal-proximal weakness with generalised areflexia -
    and bulbar and respiratory involvement has now been documented.
  evidence:
  - reference: PMID:42089726
    reference_title: "Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The median age of onset was 7 years, 96% of patients presented with lower
      limb involvement
    explanation: >-
      Quantifies onset and the near-universal lower-limb presentation across 72
      reported patients.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The initial manifestations in all patients included distal muscle weakness
      in the lower limbs with impaired steppage gait and frequent falls.
    explanation: >-
      Describes the uniform presenting picture in a contemporary cohort.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients present with an early onset demyelinating peripheral neuropathy
      causing severe distal muscle weakness and sensory loss, leading to loss of
      ambulation and progressive sensorineural hearing loss.
    explanation: >-
      States the full clinical course including loss of ambulation.
  - reference: PMID:9549516
    reference_title: "Hereditary motor and sensory neuropathy--Lom, a novel demyelinating neuropathy associated with deafness in gypsies. Clinical, electrophysiological and nerve biopsy findings."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It begins consistently in the first decade of life with gait disorder
      followed by upper limb weakness in the second decade and, in most subjects,
      by deafness which is most often first noticed in the third decade.
    explanation: >-
      The original delineation's decade-by-decade description of the natural
      history, which still frames how the disorder is staged.
  downstream:
  - target: Demyelinating Sensorimotor Polyneuropathy
    description: >-
      The phenotype is the clinical expression of this established demyelinating sensorimotor nerve lesion.
    causal_link_type: DIRECT
  - target: Distal Muscle Weakness
    description: >-
      Somatic motor nerve dysfunction produces the predominantly distal weakness.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:39201732
      reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Patients present with an early onset demyelinating peripheral neuropathy causing severe distal muscle weakness and sensory loss, leading to loss of ambulation and progressive sensorineural hearing loss.
      explanation: >-
        The source explicitly links the somatic neuropathy to weakness, sensory loss and loss of ambulation; auditory involvement is represented separately because its anatomical localization is unresolved.
  - target: Distal Sensory Loss
    description: >-
      Sensory nerve dysfunction produces distal sensory loss.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:39201732
      reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Patients present with an early onset demyelinating peripheral neuropathy causing severe distal muscle weakness and sensory loss, leading to loss of ambulation and progressive sensorineural hearing loss.
      explanation: >-
        The source explicitly links the somatic neuropathy to weakness, sensory loss and loss of ambulation; auditory involvement is represented separately because its anatomical localization is unresolved.
  - target: Areflexia
    description: >-
      The sensorimotor nerve lesion impairs the peripheral limbs of tendon reflex arcs, explaining the absent tendon reflexes observed with the neuropathy.
    causal_link_type: DIRECT
- name: Auditory Pathway Involvement
  biological_scale: ORGANISM
  role: consequence
  mechanism_confidence: PROVISIONAL
  description: >-
    Auditory pathway dysfunction produces progressive sensorineural hearing loss, usually recognized in the third decade but sometimes in childhood. Brainstem auditory evoked potentials may be delayed before hearing complaints. The original human electrophysiology suggested eighth-nerve demyelination and abnormal central auditory conduction; their relative contributions remain unresolved. This node is separate from the somatic nerve chain and is reached from the genotype through an edge with unknown intermediates. Broad hearing impairment was reported in 61% of published cases, but that estimate does not establish specifically sensorineural loss in every reviewed patient.
  evidence:
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Another typical electrophysiological finding is an abnormality in brain-stem
      auditory-evoked potentials with prolonged I–V interpeak latencies,
      suggesting the involvement of the central pathways
    explanation: >-
      The evoked-potential evidence pointing at central auditory pathway
      involvement, in the source's own hedged terms.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The audiograms of the rest were consistent with sensorineural hearing loss,
      especially for high frequencies.
    explanation: >-
      Characterises the hearing loss as sensorineural and high-frequency
      predominant.
  - reference: PMID:17142040
    reference_title: "NDRG1-linked Charcot-Marie-Tooth disease (CMT4D) with central nervous system involvement."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      For the first time, central nervous system white matter lesions are
      demonstrated in CMT4D.
    explanation: >-
      Independent evidence of central nervous system involvement in
      p.Arg148*-homozygous patients.
  - reference: PMID:9549516
    reference_title: "Hereditary motor and sensory neuropathy--Lom, a novel demyelinating neuropathy associated with deafness in gypsies. Clinical, electrophysiological and nerve biopsy findings."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the results suggested demyelination in the eighth cranial nerve and also
      abnormal conduction in the central auditory pathways in the brainstem
    explanation: >-
      The original evoked-potential analysis implicates both candidate sites at
      once - the eighth nerve and the central pathways - which is precisely why
      this node does not commit to one and is marked PROVISIONAL.
  downstream:
  - target: Sensorineural Hearing Loss
    description: >-
      Dysfunction of the auditory nerve/central auditory route produces sensorineural hearing loss. The link does not select one anatomical localization over the other.
    causal_link_type: DIRECT
- name: Motor Denervation
  biological_scale: TISSUE
  role: effector
  mechanism_confidence: ESTABLISHED
  description: >-
    Motor axonal loss deprives affected muscles of innervation. Human CMT4D electromyography demonstrates chronic denervation, supporting neurogenic weakness and wasting in distal muscles and, in severe disease, proximal muscles.
  evidence:
  - reference: PMID:24136616
    reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Needle electromyography showed no activity in distal and proximal muscles of the lower limbs and distal muscles of the upper limbs; chronic denervation findings were present in proximal muscles of the upper limbs.
    explanation: >-
      Human electrophysiology documents denervation in the genetically affected NDRG1-duplication homozygote BAB4149.
  - reference: PMID:24136616
    reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The physical examination revealed severe distal and mild proximal muscle weakness and distal wasting with areflexia.
    explanation: >-
      The genetically affected Turkish proband had distal wasting and both distal and proximal weakness; these are observations in NDRG1-associated disease, unlike the differently affected wild-type sibling.
  downstream:
  - target: Distal Amyotrophy
    description: >-
      Chronic loss of motor innervation causes neurogenic wasting in the predominantly affected distal muscles.
    causal_link_type: DIRECT
  - target: Proximal Muscle Weakness
    description: >-
      Denervation also compromises proximal motor units in severely affected patients; proximal denervation and weakness were both documented in the Turkish NDRG1-duplication homozygote.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:24136616
      reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Needle electromyography showed no activity in distal and proximal muscles of the lower limbs and distal muscles of the upper limbs; chronic denervation findings were present in proximal muscles of the upper limbs.
      explanation: >-
        Human electrophysiology documents denervation in the genetically affected NDRG1-duplication homozygote BAB4149.
    - reference: PMID:24136616
      reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The physical examination revealed severe distal and mild proximal muscle weakness and distal wasting with areflexia.
      explanation: >-
        The genetically affected Turkish proband had distal wasting and both distal and proximal weakness; these are observations in NDRG1-associated disease, unlike the differently affected wild-type sibling.
- name: Visual Pathway Dysfunction
  biological_scale: ORGANISM
  role: effector
  mechanism_confidence: PROVISIONAL
  description: >-
    Abnormal visual evoked potentials demonstrate dysfunction of the visual system in reported CMT4D siblings. The anatomical substrate and causal route from NDRG1 loss are unresolved; this node identifies the state measured by VEPs without assigning it to the cerebral white matter lesions reported in a different family.
  evidence:
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Visual system involvement was demonstrated through abnormal visual evoked potentials with reduced P100 amplitude and absent responses, expanding the recognized phenotypic spectrum.
    explanation: >-
      Documents the exact electrophysiological finding in the two siblings. The review’s 17% broad visual-involvement estimate does not quantify abnormal VEPs specifically.
phenotypes:
- category: Neurologic
  name: Demyelinating Sensorimotor Polyneuropathy
  description: >-
    Early-onset progressive demyelinating motor and sensory peripheral neuropathy with severe, early axonal loss. Motor conduction is markedly slowed and sensory responses may be absent.
  phenotype_term:
    preferred_term: Demyelinating motor and sensory neuropathy
    term:
      id: HP:0007108
      label: Demyelinating peripheral neuropathy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:39201732
    reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      From an electrophysiological point of view, CMT4D is a demyelinating neuropathy involving severe and early axonal loss.
    explanation: >-
      Supports the demyelinating neuropathy itself. The separate 96% lower-limb involvement figure does not quantify this phenotype.
- category: Neurologic
  name: Distal Muscle Weakness
  description: >-
    Progressive weakness usually begins in the distal lower limbs. In the examined Bulgarian patients, toe and ankle flexion and extension strength was 0–1/5, and hand weakness developed between ages 10 and 17 years.
  phenotype_term:
    preferred_term: Distal muscle weakness
    term:
      id: HP:0002460
      label: Distal muscle weakness
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neurological examination revealed severe distal muscle weakness in the lower
      limbs in all patients with muscle strength of toe flexors and extensors and
      plantar flexors and extensors of 0–1/5 in MRC score.
    explanation: >-
      Quantifies the severity of distal lower-limb weakness.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Weakness in the hands (in holding small objects) developed between the age
      of 10–17 years.
    explanation: >-
      Dates the upper-limb involvement relative to lower-limb onset.
  sequelae:
  - target: Loss of Ambulation
    description: >-
      Progressive lower-limb weakness, together with sensory loss, can result in loss of ambulation.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Progressive impairment of lower-limb motor function and gait
    evidence:
    - reference: PMID:39201732
      reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Patients present with an early onset demyelinating peripheral neuropathy causing severe distal muscle weakness and sensory loss, leading to loss of ambulation and progressive sensorineural hearing loss.
      explanation: >-
        The source explicitly links the somatic neuropathy to weakness, sensory loss and loss of ambulation; auditory involvement is represented separately because its anatomical localization is unresolved.
  - target: Steppage Gait
    description: >-
      Ankle dorsiflexor weakness reduces foot clearance, leading to compensatory steppage. General-CMT gait studies support this explanation for the same weakness/gait combination observed in CMT4D.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Reduced ankle dorsiflexion and compensatory foot clearance
    evidence:
    - reference: PMID:17686557
      reference_title: Foot drop and plantar flexion failure determine different gait strategies in Charcot-Marie-Tooth patients.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Foot drop and plantar flexion failure affect the overall gait strategy in Charcot-Marie-Tooth patients.
      explanation: >-
        A primary gait study in broader CMT supports the motor-deficit explanation, indirectly for the NDRG1 subtype.
      directness: INDIRECT
    - reference: PMID:26617675
      reference_title: 'Cavovarus deformity in Charcot-Marie-Tooth disease: is there a hindfoot equinus deformity that needs treatment?'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The muscle imbalance involving a weak anterior tibial muscle and strong peroneus longus muscle can also cause foot drop and an equinus deformity of the hindfoot
      explanation: >-
        The source links selective ankle muscle weakness to foot drop, which supplies the biomechanical intermediate for the gait pattern observed in the primary gait study. Application to CMT4D is indirect.
      directness: INDIRECT
  - target: Frequent Falls
    description: >-
      Distal weakness impairs foot clearance and balance, contributing to frequent falls. The mechanism is described in broader CMT and applied with that limitation to the weakness and falls directly observed in CMT4D.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Impaired foot clearance and balance during walking
    evidence:
    - reference: PMID:31188833
      reference_title: 'Physical activity of children and adolescents with Charcot-Marie-Tooth neuropathies: A cross-sectional case-controlled study.'
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The degeneration of the peripheral nerves in CMT causes lower limb weakness distally greater than proximally, leading to foot deformities, problems with balance, walking and frequent trips and falls [2].
      explanation: >-
        The primary study describes the nerve degeneration–weakness–gait impairment–falls pathway in its discussion. Its cohort was predominantly CMT1A and contained no identified CMT4D participant, so this supports the causal explanation indirectly; CMT4D occurrence is documented separately.
- category: Neurologic
  name: Distal Amyotrophy
  description: >-
    Distal wasting affects the abductor pollicis brevis, interossei, gastrocnemius and tibialis anterior muscles. It was present throughout the examined Bulgarian series, with slight asymmetry in two reported patients.
  phenotype_term:
    preferred_term: Distal amyotrophy
    term:
      id: HP:0003693
      label: Distal amyotrophy
  evidence:
  - reference: PMID:39201732
    reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2).
    explanation: >-
      Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.
  sequelae:
  - target: Pes Cavus
    description: >-
      Uneven muscle wasting and weakness alter the balance of forces across the distal joints, producing this deformity. The biomechanical account is supported in broader CMT and applied to the corresponding documented CMT4D deformity.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Distal muscle imbalance and progressive joint deformity
    evidence:
    - reference: PMID:26617675
      reference_title: 'Cavovarus deformity in Charcot-Marie-Tooth disease: is there a hindfoot equinus deformity that needs treatment?'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Patients with CMT show progressive muscular atrophy and weakness leading to deformity of the feet and less commonly of the hands and progressing proximally.
      explanation: >-
        Supports the muscle-imbalance mechanism in broader CMT; application to the deformities directly observed in CMT4D is indirect.
      directness: INDIRECT
    - reference: PMID:39201732
      reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2).
      explanation: >-
        Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.
  - target: Equinovarus Deformity
    description: >-
      Uneven muscle wasting and weakness alter the balance of forces across the distal joints, producing this deformity. The biomechanical account is supported in broader CMT and applied to the corresponding documented CMT4D deformity.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Distal muscle imbalance and progressive joint deformity
    evidence:
    - reference: PMID:26617675
      reference_title: 'Cavovarus deformity in Charcot-Marie-Tooth disease: is there a hindfoot equinus deformity that needs treatment?'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Patients with CMT show progressive muscular atrophy and weakness leading to deformity of the feet and less commonly of the hands and progressing proximally.
      explanation: >-
        Supports the muscle-imbalance mechanism in broader CMT; application to the deformities directly observed in CMT4D is indirect.
      directness: INDIRECT
    - reference: PMID:39201732
      reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2).
      explanation: >-
        Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.
  - target: Claw Hand Deformity
    description: >-
      Uneven muscle wasting and weakness alter the balance of forces across the distal joints, producing this deformity. The biomechanical account is supported in broader CMT and applied to the corresponding documented CMT4D deformity.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Distal muscle imbalance and progressive joint deformity
    evidence:
    - reference: PMID:26617675
      reference_title: 'Cavovarus deformity in Charcot-Marie-Tooth disease: is there a hindfoot equinus deformity that needs treatment?'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Patients with CMT show progressive muscular atrophy and weakness leading to deformity of the feet and less commonly of the hands and progressing proximally.
      explanation: >-
        Supports the muscle-imbalance mechanism in broader CMT; application to the deformities directly observed in CMT4D is indirect.
      directness: INDIRECT
    - reference: PMID:39201732
      reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2).
      explanation: >-
        Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.
  - target: Hammertoe
    description: >-
      Uneven muscle wasting and weakness alter the balance of forces across the distal joints, producing this deformity. The biomechanical account is supported in broader CMT and applied to the corresponding documented CMT4D deformity.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Distal muscle imbalance and progressive joint deformity
    evidence:
    - reference: PMID:26617675
      reference_title: 'Cavovarus deformity in Charcot-Marie-Tooth disease: is there a hindfoot equinus deformity that needs treatment?'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Patients with CMT show progressive muscular atrophy and weakness leading to deformity of the feet and less commonly of the hands and progressing proximally.
      explanation: >-
        Supports the muscle-imbalance mechanism in broader CMT; application to the deformities directly observed in CMT4D is indirect.
      directness: INDIRECT
- category: Neurologic
  name: Loss of Ambulation
  description: >-
    Progressive motor and sensory impairment can lead to loss of ambulation. One patient in the Bulgarian series lost ambulation at age 23; a disease-wide frequency or age distribution is not established.
  phenotype_term:
    preferred_term: Loss of ambulation
    term:
      id: HP:0002505
      label: Loss of ambulation
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients present with an early onset demyelinating peripheral neuropathy
      causing severe distal muscle weakness and sensory loss, leading to loss of
      ambulation and progressive sensorineural hearing loss.
    explanation: >-
      States loss of ambulation as the outcome the neuropathy progresses to.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients had an unstable gait with marked steppage, except one case I-1,
      who had lost ambulation at the age of 23 years.
    explanation: >-
      Documents loss of ambulation at age 23 in case I-1. Other examined patients retained an unstable gait, including adults older than 23, so this observation does not establish an age threshold.
- category: Neurologic
  name: Steppage Gait
  description: >-
    A compensatory gait associated with distal lower-limb weakness, reported among the initial manifestations in the examined Bulgarian patients.
  phenotype_term:
    preferred_term: Steppage gait
    term:
      id: HP:0003376
      label: Steppage gait
  evidence:
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The initial manifestations in all patients included distal muscle weakness
      in the lower limbs with impaired steppage gait and frequent falls.
    explanation: >-
      Documents steppage gait as a presenting feature in all patients of that
      cohort.
- category: Neurologic
  name: Decreased Motor Nerve Conduction Velocity
  description: >-
    Marked slowing of motor nerve conduction is an electrophysiological indicator of peripheral demyelination. It is accompanied by prolonged distal latencies, and is not specific enough to identify NDRG1 without molecular confirmation.
  phenotype_term:
    preferred_term: Decreased motor nerve conduction velocity
    term:
      id: HP:0003431
      label: Decreased motor nerve conduction velocity
  evidence:
  - reference: PMID:9549516
    reference_title: Hereditary motor and sensory neuropathy--Lom, a novel demyelinating neuropathy associated with deafness in gypsies. Clinical, electrophysiological and nerve biopsy findings.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Severely reduced motor nerve conduction velocity indicates a demyelinating basis, which was confirmed by nerve biopsy.
    explanation: >-
      The original human HMSN-Lom study explicitly interprets reduced motor conduction velocity as a readout of demyelination.
  reports_on:
  - target: Myelin Sheath Breakdown with Onion Bulb Formation
    relationship: READOUT_OF
    interpretation: >-
      Reduced conduction velocity reports peripheral myelin dysfunction; it is an electrophysiological measurement, not an additional causal step.
- category: Neurologic
  name: Sensorineural Hearing Loss
  description: >-
    Progressive sensorineural hearing loss commonly becomes apparent in the third decade, although childhood onset also occurs. The Bulgarian series emphasized high-frequency loss, whereas a Turkish proband had predominantly low-frequency loss. The literature review quantified broad hearing impairment (61%), without specifying the ascertainment of sensorineural loss in every reviewed patient.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:39201732
    reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sensorineural deafness is a hallmark feature of the phenotype and generally develops during the third decade [1,25].
    explanation: >-
      Supports sensorineural hearing loss and its usual timing; the broader pooled hearing-impairment percentage is not assigned as a sensorineural frequency.
  - reference: PMID:24136616
    reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Audiometry showed moderate sensorineural hearing loss especially at low frequencies.
    explanation: >-
      The Turkish proband demonstrates that the frequency distribution of hearing loss is not uniformly high-frequency predominant.
  - reference: PMID:24136616
    reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      He also had hearing loss, which was noted at ~4 years of age.
    explanation: >-
      The Turkish proband had childhood hearing-loss onset; his audiometry documented sensorineural hearing loss.
- category: Musculoskeletal
  name: Pes Cavus
  description: >-
    A high-arched foot deformity reported in 67% of patients in the published-case review and in all examined patients in the Bulgarian series.
  phenotype_term:
    preferred_term: Pes cavus
    term:
      id: HP:0001761
      label: Pes cavus
  frequency: FREQUENT
  evidence:
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The median age of onset was 7 years, 96% of patients presented with lower limb involvement and all presented skeletal deformities were universal, including pes cavus (67%), claw hand (40%), and scoliosis (33%).
    explanation: >-
      The 67% frequency for this exact phenotype in the published-case review supports FREQUENT. This is a literature-derived estimate subject to ascertainment and reporting differences, not a population prevalence.
  - reference: PMID:39201732
    reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2).
    explanation: >-
      Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.
- category: Musculoskeletal
  name: Equinovarus Deformity
  description: >-
    Equinovarus deformity accompanied distal muscle atrophy in the examined Bulgarian patients. The report does not establish a congenital clubfoot, so the broader equinovarus term is used.
  phenotype_term:
    preferred_term: Equinovarus deformity
    term:
      id: HP:0008110
      label: Equinovarus deformity
  evidence:
  - reference: PMID:39201732
    reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2).
    explanation: >-
      Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.
- category: Musculoskeletal
  name: Claw Hand Deformity
  description: >-
    Claw hands develop with distal hand muscle wasting. They were reported in 40% of patients in the published-case review and throughout the examined Bulgarian series.
  phenotype_term:
    preferred_term: Claw hand deformity
    term:
      id: HP:0034337
      label: Claw hand deformity
  frequency: FREQUENT
  evidence:
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The median age of onset was 7 years, 96% of patients presented with lower limb involvement and all presented skeletal deformities were universal, including pes cavus (67%), claw hand (40%), and scoliosis (33%).
    explanation: >-
      The 40% frequency for this exact phenotype in the published-case review supports FREQUENT. This is a literature-derived estimate subject to ascertainment and reporting differences, not a population prevalence.
  - reference: PMID:39201732
    reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Muscle atrophy, involving abductor pollicis brevis, interosseous, gastrocnemius, and tibialis anterior muscles with formation of pes cavus and equinovarus and claw hands were present in all patients, with slight asymmetry between the left and right side in 2/5 (case II-1 and II-2).
    explanation: >-
      Documents distal atrophy and associated foot and hand deformities in the examined Bulgarian patients; this selected cohort does not establish a population frequency.
- category: Musculoskeletal
  name: Scoliosis
  description: >-
    Scoliosis was reported in 33% of published cases in the literature review and in one of seven examined Bulgarian patients. These differently ascertained series support occurrence with variable reported frequency.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  frequency: FREQUENT
  evidence:
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The median age of onset was 7 years, 96% of patients presented with lower limb involvement and all presented skeletal deformities were universal, including pes cavus (67%), claw hand (40%), and scoliosis (33%).
    explanation: >-
      The 33% frequency for this exact phenotype in the published-case review supports FREQUENT. This is a literature-derived estimate subject to ascertainment and reporting differences, not a population prevalence.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Scoliosis was observed only in one patient (case I-1).
    explanation: >-
      One observed case supports scoliosis occurrence. Differences between this small cohort and the published-case review do not constitute refutation of the phenotype.
- category: Neurologic
  name: Areflexia
  description: >-
    Lower-limb tendon reflexes were absent in all examined Bulgarian patients, with upper-limb reflexes attenuated but preserved in five of seven. Generalized areflexia was also reported in the Italian siblings.
  phenotype_term:
    preferred_term: Areflexia
    term:
      id: HP:0001284
      label: Areflexia
  evidence:
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The tendon reflexes were absent in the lower limbs in all of the patients
      and were preserved but attenuated in the upper limbs in 5/7.
    explanation: >-
      Documents the reflex pattern, including the upper-limb sparing.
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both patients presented with severe distal-proximal sensorimotor neuropathy, muscle weakness and atrophy, generalized areflexia, and sensorineural deafness typical of CMT4D.
    explanation: >-
      The Italian siblings document generalized areflexia, supporting the broad HPO term alongside the lower-limb-predominant pattern in Bulgaria.
- category: Neurologic
  name: Distal Sensory Loss
  description: >-
    Light touch, pin prick and temperature sensation are diminished to absent
    distally in all four limbs; vibration sense is impaired in the lower limbs but
    was preserved in the upper limbs of most of the Bulgarian cohort.
  phenotype_term:
    preferred_term: Distal sensory impairment
    term:
      id: HP:0002936
      label: Distal sensory impairment
  evidence:
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The sensation in the distal parts of the four limbs produced by light touch,
      pin prick, and temperature sensations was diminished to absent in all of the
      affected
    explanation: >-
      Documents the distribution and modalities of sensory loss.
- category: Ophthalmologic
  name: Abnormal Visual Evoked Potentials
  description: >-
    Reduced P100 amplitude and absent visual evoked responses were reported in the Italian siblings. These tests document visual pathway dysfunction without identifying its precise anatomical substrate.
  phenotype_term:
    preferred_term: Abnormality of visual evoked potentials
    term:
      id: HP:0000649
      label: Abnormality of visual evoked potentials
  evidence:
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Visual system involvement was demonstrated through abnormal visual evoked potentials with reduced P100 amplitude and absent responses, expanding the recognized phenotypic spectrum.
    explanation: >-
      Documents the exact electrophysiological finding in the two siblings. The review’s 17% broad visual-involvement estimate does not quantify abnormal VEPs specifically.
  reports_on:
  - target: Visual Pathway Dysfunction
    relationship: READOUT_OF
    interpretation: >-
      VEP amplitude reduction and absent responses report impaired visual pathway function; they do not by themselves identify a cerebral white matter lesion or its cause.
- category: Gastrointestinal
  name: Dysphagia
  description: >-
    Severe dysphagia requiring percutaneous endoscopic gastrostomy was reported in the two adult Italian siblings. Its frequency and the specific cranial-nerve or central motor substrate are unresolved.
  phenotype_term:
    preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay.
    explanation: >-
      Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.
- category: Respiratory
  name: Bilateral Vocal Cord Paralysis
  description: >-
    Bilateral vocal cord paralysis caused respiratory insufficiency requiring non-invasive ventilation in the reported Italian siblings. The source does not establish the affected nerve or exclude additional respiratory muscle involvement.
  phenotype_term:
    preferred_term: Bilateral vocal cord paralysis
    term:
      id: HP:0012820
      label: Bilateral vocal cord paralysis
  evidence:
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay.
    explanation: >-
      Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.
  sequelae:
  - target: Respiratory Insufficiency
    description: >-
      The Italian report explicitly attributes the respiratory insufficiency to bilateral vocal cord paralysis.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:42089726
      reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay.
      explanation: >-
        Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.
- category: Respiratory
  name: Respiratory Insufficiency
  description: >-
    Respiratory insufficiency requiring non-invasive ventilation was attributed to bilateral vocal cord paralysis in the Italian siblings.
  phenotype_term:
    preferred_term: Respiratory insufficiency
    term:
      id: HP:0002093
      label: Respiratory insufficiency
  evidence:
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay.
    explanation: >-
      Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.
- category: Neurologic
  name: Cognitive Impairment
  description: >-
    Cognitive delay was reported in the two adult Italian siblings. The available report does not specify standardized cognitive testing, developmental trajectory or the underlying neuropathology.
  phenotype_term:
    preferred_term: Cognitive impairment
    term:
      id: HP:0100543
      label: Cognitive impairment
  evidence:
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay.
    explanation: >-
      Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.
- category: Neurologic
  name: Central Nervous System White Matter Abnormality
  description: >-
    Subcortical cerebral white matter abnormalities were observed on MRI in a non-Roma family homozygous for p.Arg148*. The report called for further study of central NDRG1 involvement; it did not establish the tissue mechanism.
  phenotype_term:
    preferred_term: Cerebral white matter abnormality
    term:
      id: HP:0002500
      label: Abnormal cerebral white matter morphology
  evidence:
  - reference: PMID:17142040
    reference_title: "NDRG1-linked Charcot-Marie-Tooth disease (CMT4D) with central nervous system involvement."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report the detailed phenotypic study of a family without Gypsy ancestry,
      who presented with severe demyelinating polyneuropathy, deafness,
      subcortical white matter abnormalities on brain magnetic resonance imaging
      studies, and the R148X mutation in NDRG1.
    explanation: >-
      Documents subcortical white matter abnormality in p.Arg148*-homozygous
      patients.
  - reference: PMID:17142040
    reference_title: "NDRG1-linked Charcot-Marie-Tooth disease (CMT4D) with central nervous system involvement."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This report extends the clinical knowledge of CMT4D and indicates that the
      role of the R148X mutation in NDRG1 in the central nervous system should be
      further studied.
    explanation: >-
      Supports central nervous system involvement only indirectly - the authors
      frame it as a question requiring further study rather than an established
      feature, so the sentence points at the claim without asserting it.
- category: Neurologic
  name: Cerebellar Atrophy
  description: >-
    Slight cerebellar atrophy was observed on MRI in a 38-year-old woman with homozygous NDRG1 c.739delC. The medullary and cervical cord abnormalities in the same scan are represented separately.
  phenotype_term:
    preferred_term: Cerebellar atrophy
    term:
      id: HP:0001272
      label: Cerebellar atrophy
  evidence:
  - reference: PMID:27982524
    reference_title: A novel NDRG1 mutation in a non-Romani patient with CMT4D/HMSN-Lom.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Magnetic resonance imaging showed slight atrophy of cerebellum, medulla oblongata, and upper cervical spinal cord.
    explanation: >-
      The single-patient report directly documents each named anatomical finding, without establishing its cellular mechanism or general frequency.
- category: Neurologic
  name: Cervical Spinal Cord Atrophy
  description: >-
    Slight atrophy of the upper cervical spinal cord was observed in the same patient with homozygous NDRG1 c.739delC. A specific cause of this imaging abnormality was not established.
  phenotype_term:
    preferred_term: Cervical spinal cord atrophy
    term:
      id: HP:0010873
      label: Cervical spinal cord atrophy
  evidence:
  - reference: PMID:27982524
    reference_title: A novel NDRG1 mutation in a non-Romani patient with CMT4D/HMSN-Lom.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Magnetic resonance imaging showed slight atrophy of cerebellum, medulla oblongata, and upper cervical spinal cord.
    explanation: >-
      The single-patient report directly documents each named anatomical finding, without establishing its cellular mechanism or general frequency.
- name: Medullary Atrophy
  category: Neurologic
  description: >-
    Slight medulla oblongata atrophy was observed in the patient with NDRG1 c.739delC. The brainstem term captures this region separately from cerebellar and spinal cord atrophy.
  phenotype_term:
    preferred_term: Atrophy/Degeneration affecting the brainstem
    term:
      id: HP:0007366
      label: Atrophy/Degeneration affecting the brainstem
  evidence:
  - reference: PMID:27982524
    reference_title: A novel NDRG1 mutation in a non-Romani patient with CMT4D/HMSN-Lom.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Magnetic resonance imaging showed slight atrophy of cerebellum, medulla oblongata, and upper cervical spinal cord.
    explanation: >-
      The single-patient report directly documents each named anatomical finding, without establishing its cellular mechanism or general frequency.
- name: Proximal Muscle Weakness
  category: Neurologic
  description: >-
    Proximal weakness accompanied the more severe distal weakness in genetically affected Turkish siblings; severity ranged from mild in the proband to moderate in his examined affected sister.
  phenotype_term:
    preferred_term: Proximal muscle weakness
    term:
      id: HP:0003701
      label: Proximal muscle weakness
  evidence:
  - reference: PMID:24136616
    reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The physical examination revealed severe distal and mild proximal muscle weakness and distal wasting with areflexia.
    explanation: >-
      The genetically affected Turkish proband had distal wasting and both distal and proximal weakness; these are observations in NDRG1-associated disease, unlike the differently affected wild-type sibling.
  - reference: PMID:24136616
    reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Her clinical examination showed severe distal and moderate proximal muscle weakness.
    explanation: >-
      This sentence concerns the affected NDRG1-duplication homozygote BAB4149, not the differently affected wild-type sibling BAB4152.
- name: Hammertoe
  category: Musculoskeletal
  description: >-
    Hammer toes were reported in the three NDRG1-duplication homozygous Turkish siblings, together with pes cavus and claw hands.
  phenotype_term:
    preferred_term: Hammertoe
    term:
      id: HP:0001765
      label: Hammertoe
  evidence:
  - reference: PMID:24136616
    reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      She also had pes cavus, hammer toes, and claw hands.
    explanation: >-
      Documents hammer toes in the NDRG1-duplication homozygote BAB4148.
  - reference: PMID:24136616
    reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Severe deformities including kyphoscoliosis, pes cavus, hammer toes, and claw hands were observed.
    explanation: >-
      Documents hammer toes in the genetically affected proband BAB3724.
- name: Motor Delay
  category: Neurologic
  description: >-
    Delayed motor milestones were reported in two NDRG1-duplication homozygous Turkish siblings and in the Italian patient with c.739delC. Motor milestones were normal in the Bulgarian splice-variant series, so motor delay is variable rather than obligatory.
  phenotype_term:
    preferred_term: Motor delay
    term:
      id: HP:0001270
      label: Motor delay
  evidence:
  - reference: PMID:24136616
    reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The proband (BAB3724 = II-2) was a 30-year-old male who had delayed motor milestones.
    explanation: >-
      Directly supports motor delay in a genetically affected CMT4D proband.
  - reference: PMID:27982524
    reference_title: A novel NDRG1 mutation in a non-Romani patient with CMT4D/HMSN-Lom.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report a 38-year-old Italian female with motor development delay, progressive neuropathy, and sensorineural deafness.
    explanation: >-
      Independently documents motor delay with an NDRG1 frameshift allele.
- name: Frequent Falls
  category: Neurologic
  description: >-
    Frequent falls accompanied the initial distal weakness and steppage gait in the examined Bulgarian patients.
  phenotype_term:
    preferred_term: Frequent falls
    term:
      id: HP:0002359
      label: Frequent falls
  evidence:
  - reference: PMID:39201732
    reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The initial manifestations in all patients included distal muscle weakness in the lower limbs with impaired steppage gait and frequent falls.
    explanation: >-
      Directly documents frequent falls at presentation in this CMT4D series.
- name: Absent Distal Sensory Nerve Action Potentials
  category: Neurologic
  description: >-
    Sensory nerve action potentials were absent in the upper and lower limbs of examined Turkish CMT4D patients. Absence is represented under the decreased-amplitude HPO term.
  phenotype_term:
    preferred_term: Decreased distal sensory nerve action potential
    term:
      id: HP:0007230
      label: Decreased distal sensory nerve action potential
  evidence:
  - reference: PMID:24136616
    reference_title: Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sensory nerve action potentials were absent in both upper and lower limbs (Table 1).
    explanation: >-
      Directly documents absent sensory responses in the NDRG1-duplication homozygote BAB4149.
  reports_on:
  - target: Progressive Demyelinating Sensorimotor Neuropathy
    relationship: READOUT_OF
    interpretation: >-
      Absent sensory responses report severe sensory nerve dysfunction in the demyelinating and axonal neuropathy; the test alone does not separate conduction failure from sensory axonal loss.
- name: Delayed Brainstem Auditory Evoked Responses
  category: Neurologic
  description: >-
    Prolonged auditory wave and interpeak latencies were observed in the Bulgarian cohort, including two adults without hearing complaints and with normal audiograms.
  phenotype_term:
    preferred_term: Delayed brainstem auditory evoked response conduction time
    term:
      id: HP:0004466
      label: Delayed brainstem auditory evoked response conduction time
  evidence:
  - reference: PMID:39201732
    reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brainstem auditory-evoked potentials showed increased latencies of waves I–III–V, as well as increased interpeak latencies in some patients (cases II-1, II-2, IV-1, IV-2, and IV-3).
    explanation: >-
      Documents delayed auditory conduction in five named patients.
  - reference: PMID:39201732
    reference_title: 'Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Interestingly, the two patients with no auditory complains (case II-1 and case II-2), aged 30 and 31 years, respectively, also had normal audiograms (Table 3).
    explanation: >-
      These two patients had evoked-potential delay despite normal audiograms; the readout can precede symptomatic hearing loss.
  reports_on:
  - target: Auditory Pathway Involvement
    relationship: READOUT_OF
    interpretation: >-
      Auditory evoked-response delay reports dysfunction of the eighth-nerve/brainstem auditory route, without resolving peripheral versus central localization.
genetic:
- name: NDRG1
  gene_term:
    preferred_term: NDRG1
    term:
      id: hgnc:7679
      label: NDRG1
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: PRESENT
  notes: >-
    NDRG1 sits at 8q24.22 and encodes a 43-kDa protein of the alpha/beta
    hydrolase superfamily that is considered catalytically inactive; its
    structure comprises a central alpha/beta hydrolase fold flanked by a short N
    terminus and a C-terminal region of three ten-residue repeats whose
    conformation changes on lipid binding. It is ubiquitously expressed but
    unusually abundant in Schwann cells.

    Twenty-two pathogenic variants have been reported across 72 patients. The
    Roma founder allele p.Arg148* accounts for 64 percent of them, which is why
    ancestry is a useful prior in CMT genetic testing but not a gate: CMT4D has
    now been reported in families of Italian, Turkish, Indian, Chinese, Saudi and
    Bulgarian Muslim origin, and one Italian patient's novel frameshift allele
    prompted the explicit conclusion that CMT4D is not a private Romani disease.
    Two splice-acceptor alleles, c.538-1G>A and c.327-2A>G, are founder mutations
    in a second and distinct ethnic minority, the Bulgarian Muslims, on ancestral
    haplotypes of 2.4 and 9.6 Mb respectively.

    The allelic spectrum spans nonsense, frameshift, canonical splice-site,
    exon-duplication and missense classes. That breadth is mechanistically
    informative rather than incidental: the missense alleles p.Leu146Pro and
    p.Arg234Gln reduce NDRG1 protein abundance by accelerating its degradation
    rather than truncating it, so the disease can be produced by hypomorphic
    protein levels alone. Consistently, no genotype-phenotype partition within
    NDRG1 has been established - unlike genes such as BAG3 where allele class
    selects the tissue affected, every reported CMT4D allele produces the same
    demyelinating neuropathy with deafness.
  evidence:
  - reference: PMID:42089726
    reference_title: "Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our systematic literature review identified 26 articles describing 72
      patients with CMT4D.
    explanation: >-
      Establishes the size of the published patient series underlying the
      allelic and phenotypic figures used in this entry.
  - reference: PMID:33305529
    reference_title: "Crystal and solution structure of NDRG1, a membrane-binding protein linked to myelination and tumour suppression."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The 43-kDa NDRG1 is considered as an inactive member of the α/β hydrolase
      superfamily.
    explanation: >-
      States the protein's structural class and presumed catalytic inactivity.
  - reference: PMID:33305529
    reference_title: "Crystal and solution structure of NDRG1, a membrane-binding protein linked to myelination and tumour suppression."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      NDRG1 binds to various types of lipid vesicles, and the conformation of the
      C-terminal region is modulated upon lipid interaction.
    explanation: >-
      Establishes lipid-vesicle binding, the structural counterpart of the
      trafficking role proposed for NDRG1 in the Schwann cell.
  - reference: PMID:27982524
    reference_title: "A novel NDRG1 mutation in a non-Romani patient with CMT4D/HMSN-Lom."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The identification of this NDRG1 mutation confirms that CMT4D is not a
      private Romani disease and should be considered in the differential
      diagnosis of recessive demyelinating CMT.
    explanation: >-
      Establishes that ancestry must not be used to exclude CMT4D from the
      differential.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notably, two splice-site variants are exclusive to Bulgarian Muslims and
      reside in ancestral haplotypes, suggesting a founder effect.
    explanation: >-
      Establishes a second, independent founder effect in a different population.
  - reference: PMID:24136616
    reference_title: "Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We detected an ~6.25 kb homozygous intragenic duplication in NDRG1, a gene
      known to be causative for recessive HMSNL/CMT4D, in three individuals from a
      Turkish family with CMT neuropathy.
    explanation: >-
      Establishes copy-number variation as a fifth allelic class in NDRG1,
      identified in a non-Roma Turkish family.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    No population prevalence estimate for CMT4D exists. The published literature
    totals 72 patients across 26 articles. The disorder is concentrated in Roma
    communities, where it is one of three CMT subtypes caused by founder
    mutations private to that population, and within a Bulgarian demyelinating
    CMT cohort of 150 index patients NDRG1 variants explained 15 patients from 11
    families - roughly seven percent of that ascertained, and therefore heavily
    enriched, series. That figure is a diagnostic yield within a selected cohort,
    not a population rate, and must not be read as one.
  evidence:
  - reference: PMID:42089726
    reference_title: "Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our systematic literature review identified 26 articles describing 72
      patients with CMT4D.
    explanation: >-
      The total published case count, which is the only defensible occurrence
      figure for this disorder.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our cohort consisted of 150 index Bulgarian patients with demyelinating CMT.
      We identified 15 patients from 11 families with recurrent or novel variants
      in the NDRG1 gene
    explanation: >-
      The diagnostic yield of NDRG1 testing within an ascertained demyelinating
      CMT cohort.
animal_models:
- name: Ndrg1 exon 4-5 knockout mouse
  species: Mouse
  genotype: Ndrg1-/- (CRISPR/Cas9 deletion of exons 4 and 5)
  publication: PMID:35708320
  description: >-
    A CRISPR-generated null mouse that develops early progressive demyelinating
    neuropathy and limb muscle weakness, with reduced motor nerve conduction
    velocity and compound muscle action potential amplitude by eight weeks. It is
    the model in which the neuregulin 1/ErbB findings were made.
  modeled_mechanisms:
  - target: Myelin Sheath Breakdown with Onion Bulb Formation
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces the demyelinating lesion with correct timing - normal at two
      weeks, thinning from four weeks when myelination would normally be
      complete, progressive thereafter, with occasional onion bulbs.
    limitations: >-
      The hypomyelination does not lead to apparent axonal loss, so the model
      reproduces the demyelination while missing the early severe axonal loss
      that produces disability in patients.
    readouts:
    - name: Sciatic nerve g-ratio
      target: Myelin Sheath Breakdown with Onion Bulb Formation
      direction: INCREASED
      interpretation: >-
        A raised g-ratio is the quantitative signature of thin myelin relative to
        axon calibre, confirming demyelinating rather than axonal pathology.
      evidence:
      - reference: PMID:35708320
        reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Quantitative analysis indicated that the G ratio of the nerve fibers was
          significantly increased inNdrg1−/−mice, suggesting the presence of
          demyelinating neuropathy
        explanation: >-
          Reports the g-ratio measurement supporting the demyelinating phenotype.
    evidence:
    - reference: PMID:35708320
      reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Ndrg1-deficient mice develop early progressive demyelinating neuropathy
        and limb muscle weakness.
      explanation: >-
        Establishes the model as informative for the demyelinating node.
  - target: Early Severe Axonal Loss
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: >-
      The defining human feature - early severe axonal loss - is absent from this
      model despite otherwise faithful demyelination, and the authors say so
      explicitly.
    limitations: >-
      A shift in axonal size distribution occurs, but no apparent axonal loss.
      Any therapeutic result obtained in this model therefore speaks to the
      demyelinating arm only and cannot be assumed to address the axonal
      degeneration that causes disability in patients.
    evidence:
    - reference: PMID:35708320
      reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
      supports: REFUTE
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Although a shift in the axonal size distribution was observed
        inNdrg1−/−mice, the hypomyelination did not lead to apparent axonal loss
      explanation: >-
        The authors' direct statement that axonal loss is absent from the model.
  - target: Attenuated Neuregulin 1-ErbB Signaling
    relationship: MEASURES
    fidelity: MODERATE
    description: >-
      The model is the sole source of the neuregulin 1/ErbB evidence in this
      entry: it is where receptor phosphorylation, ligand level and integrin
      beta-4 abundance were measured.
    limitations: >-
      No equivalent measurement exists in human CMT4D nerve, so the entire
      signalling arm of this entry's pathograph rests on this mouse.
    readouts:
    - name: Phosphorylated ErbB2/ErbB3 in sciatic nerve
      target: Attenuated Neuregulin 1-ErbB Signaling
      direction: DECREASED
      interpretation: >-
        Reduced receptor phosphorylation against increased total receptor is the
        measurement that localises the defect to receptor activation.
      evidence:
      - reference: PMID:35708320
        reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          levels of the phosphorylated forms of ErbB2/3 and their downstream
          signaling cascades were decreased
        explanation: >-
          The phosphorylation measurement underlying this readout.
    evidence:
    - reference: PMID:35708320
      reference_title: "Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        our data suggest that the demyelinating phenotype of CMT4D disease is at
        least in part a consequence of molecular defects in neuregulin 1/ErbB
        signaling
      explanation: >-
        The authors' own hedged conclusion, which is the claim this link records.
- name: Stretcher mouse (spontaneous Ndrg1 null)
  species: Mouse
  genotype: Ndrg1 str/str (spontaneous total Ndrg1 deficiency)
  publication: PMID:21303696
  description: >-
    A spontaneous total Ndrg1-null mutant, compared directly against a hypomorphic
    Ndrg1 knockout. The comparison is the informative part: the markedly more
    severe stretcher phenotype implies that even low residual Ndrg1 expression
    rescues a large part of the phenotype, which is a dosage statement no single
    model could make.
  modeled_mechanisms:
  - target: Impaired Schwann Cell Vesicular Trafficking
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      The model is the basis of the trafficking-demand-mismatch hypothesis: its
      large-fibre demyelination coincides precisely with the period of rapid
      myelin growth and small fibres are spared, while gene expression profiling
      found only non-specific secondary changes and normal proteasomal function.
    limitations: >-
      The trafficking defect itself is not measured in this model; the inference
      rests on the timing and fibre-size selectivity of the lesion, and gene
      expression profiling was explicitly non-specific.
    evidence:
    - reference: PMID:21303696
      reference_title: "Ndrg1 in development and maintenance of the myelin sheath."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Impaired SC trafficking failing to meet the considerable demands of nerve
        growth, emerges as the likely pathogenetic mechanism in NDRG1 deficiency.
      explanation: >-
        The conclusion this model supports, stated as the authors state it.
  - target: Early Severe Axonal Loss
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: >-
      Neither the stretcher mouse nor the hypomorphic knockout reproduces the
      early severe axonal loss of human CMT4D. Axon damage occurs, but
      regenerative capacity is unimpaired.
    limitations: >-
      Because both models compared in that study fail at the same point, as does
      the independent CRISPR Ndrg1-/- mouse, no rodent model reconstructs the
      step from Schwann-cell NDRG1 loss to axonal degeneration, which constrains
      what preclinical work on this disorder can test. The canine model is
      deliberately excluded from that claim: it does show axonal pathology, and
      is treated separately in the HUMAN_MODEL_MISMATCH discussion.
    evidence:
    - reference: PMID:21303696
      reference_title: "Ndrg1 in development and maintenance of the myelin sheath."
      supports: REFUTE
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Neither model replicates fully the features of CMT4D: although axon damage
        is present, regenerative capacity is unimpaired and the mice do not
        display the early severe axonal loss typical of the human disease.
      explanation: >-
        The explicit statement that both rodent models fail to reproduce the
        defining human feature.
- name: Ndrg1 knockout mouse (Okuda)
  species: Mouse
  genotype: Ndrg1-/- (targeted knockout)
  publication: PMID:15082788
  description: >-
    The first published Ndrg1-null mouse, and the model the stretcher work later
    used as its hypomorphic comparator. Its contribution is a timing argument:
    sciatic nerve myelination is normal for the first two postnatal weeks and
    only then degenerates with demyelination at about five weeks, which separates
    myelin maintenance from myelin formation as the affected process.
  modeled_mechanisms:
  - target: Myelin Sheath Breakdown with Onion Bulb Formation
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Establishes progressive demyelination of an initially normally myelinated
      nerve, with Schwann-cell dysfunction as the proximate cause.
    limitations: >-
      Reported as a hypomorphic rather than complete null in the later
      head-to-head comparison with the stretcher mouse, and neither model in that
      comparison displays the early severe axonal loss of the human disease.
    readouts:
    - name: Sciatic nerve myelination timing
      target: Myelin Sheath Breakdown with Onion Bulb Formation
      direction: DECREASED
      interpretation: >-
        Normal myelination for two weeks followed by demyelination at five weeks
        is the readout that distinguishes maintenance failure from formation
        failure.
      evidence:
      - reference: PMID:15082788
        reference_title: "Ndrg1-deficient mice exhibit a progressive demyelinating disorder of peripheral nerves."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Histological analysis showed that the sciatic nerve of Ndrg1-deficient
          mice degenerated with demyelination at about 5 weeks of age. However,
          myelination of Schwann cells in the sciatic nerve was normal for 2 weeks
          after birth.
        explanation: >-
          The histological timing measurement underlying this readout.
    evidence:
    - reference: PMID:15082788
      reference_title: "Ndrg1-deficient mice exhibit a progressive demyelinating disorder of peripheral nerves."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        These results indicate that NDRG1 deficiency leads to Schwann cell
        dysfunction, suggesting that NDRG1 is essential for maintenance of the
        myelin sheaths in peripheral nerves.
      explanation: >-
        States the conclusion this model supports - maintenance, not formation.
  - target: Early Severe Axonal Loss
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: >-
      This model was one of the two compared head to head in PMID:21303696, and
      that comparison found neither reproduces the early severe axonal loss of
      human CMT4D.
    limitations: >-
      The failure is shared with the stretcher mouse and is the reason no rodent
      model reconstructs the axonal arm. It says nothing about the canine model,
      which does show axonal pathology.
    evidence:
    - reference: PMID:21303696
      reference_title: "Ndrg1 in development and maintenance of the myelin sheath."
      supports: REFUTE
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Neither model replicates fully the features of CMT4D: although axon damage
        is present, regenerative capacity is unimpaired and the mice do not
        display the early severe axonal loss typical of the human disease.
      explanation: >-
        The head-to-head comparison covering this model and the stretcher mouse,
        which is what makes this a structural FAILS_TO_RECAPITULATE link rather
        than a prose assertion inside a myelin link's limitations.
- name: Greyhound polyneuropathy (NDRG1 exon 15 deletion)
  species: Dog
  genotype: NDRG1 c.1080_1089delTCGCCTGGAC homozygous (p.Arg361SerfsX60)
  publication: PMID:20582309
  description: >-
    A naturally occurring canine model: juvenile Greyhound show dogs with a
    recessive polyneuropathy tracing to a single founder male, in which a ten-base
    deletion in NDRG1 exon 15 is perfectly associated with the phenotype and
    abolishes NDRG1 protein in peripheral nerve.
  modeled_mechanisms:
  - target: Progressive Demyelinating Sensorimotor Neuropathy
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces a severe chronic progressive polyneuropathy of juvenile onset on
      a recessive founder background, with NDRG1 protein absent from peripheral
      nerve on Western blot.
    limitations: >-
      The canine lesion is described as a mixed polyneuropathy rather than the
      predominantly demyelinating picture with early axonal loss seen in patients,
      and deafness - a defining human feature - is not reported in the affected
      dogs.
    evidence:
    - reference: PMID:20582309
      reference_title: "A deletion in the N-myc downstream regulated gene 1 (NDRG1) gene in Greyhounds with polyneuropathy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Western blot analysis demonstrated an absence of NDRG1 protein in
        peripheral nerve biopsy of an affected Greyhound.
      explanation: >-
        Confirms loss of NDRG1 protein in the affected tissue, establishing the
        model as an NDRG1-null neuropathy.
    - reference: PMID:20582309
      reference_title: "A deletion in the N-myc downstream regulated gene 1 (NDRG1) gene in Greyhounds with polyneuropathy."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        A severe chronic progressive mixed polyneuropathy was observed.
      explanation: >-
        Supports the model link indirectly: a severe chronic progressive
        polyneuropathy is the right general lesion, but a MIXED polyneuropathy is
        not the same thing as the human demyelinating neuropathy with early
        axonal loss, which is why the link is PARTIALLY_RECAPITULATES and the
        directness is INDIRECT.
treatments:
- name: Percutaneous Endoscopic Gastrostomy Feeding
  therapeutic_modality: SURGERY
  description: >-
    Enteral feeding via a PEG tube for the severe dysphagia that can develop in
    advanced CMT4D. This is curated because it was actually performed in reported
    CMT4D patients, not extrapolated from neuromuscular disease generally - bulbar
    involvement was unrecognised in CMT4D until the 2026 sibling report, and an
    entry that omitted it would leave swallowing off the surveillance list.
  treatment_term:
    preferred_term: percutaneous endoscopic gastrostomy
    term:
      id: NCIT:C106040
      label: Percutaneous Endoscopic Gastrostomy
  evidence:
  - reference: PMID:42089726
    reference_title: "Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notably, they exhibited previously unreported features including severe
      dysphagia requiring PEG tube placement, bilateral vocal cord paralysis
      causing respiratory insufficiency necessitating non-invasive ventilation,
      and cognitive delay.
    explanation: >-
      Documents PEG placement as the intervention used for CMT4D dysphagia in the
      reported siblings.
- name: Non-Invasive Ventilation
  therapeutic_modality: DEVICE
  description: >-
    Non-invasive ventilation was used for respiratory insufficiency attributed to bilateral vocal cord paralysis in the reported Italian siblings.
  treatment_term:
    preferred_term: non-invasive mechanical ventilation
    term:
      id: NCIT:C171457
      label: Non-Invasive Mechanical Ventilation
  evidence:
  - reference: PMID:42089726
    reference_title: Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notably, they exhibited previously unreported features including severe dysphagia requiring PEG tube placement, bilateral vocal cord paralysis causing respiratory insufficiency necessitating non-invasive ventilation, and cognitive delay.
    explanation: >-
      Documents the reported findings in two adult siblings with homozygous p.Arg148*. It explicitly attributes respiratory insufficiency to bilateral vocal cord paralysis, but does not reconstruct the neuropathological cause of the bulbar or cognitive findings.
diagnosis:
- name: Nerve Conduction Studies
  description: >-
    Nerve conduction studies establish the demyelinating character and its
    severity: markedly reduced conduction velocities, prolonged distal latencies
    including in cranial nerves, and absent sensory nerve action potentials.
    Needle EMG shows scattered fibrillation and neurogenic motor unit potentials,
    more pronounced distally, reflecting the accompanying axonal degeneration.
  evidence:
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is characterized by markedly reduced conduction velocities and prolonged
      distal latencies of the motor nerves (including musculocutaneous, axillary,
      hypoglossal, and facial nerves), absent sensory nerve action potentials
      (SNAP), and a blink reflex with an unusual three-component response
    explanation: >-
      The full electrophysiological signature, including the cranial-nerve
      involvement and the unusual blink reflex.
- name: Brainstem Auditory Evoked Potentials
  description: >-
    Brainstem auditory evoked potentials are abnormal before patients report
    hearing loss, which makes them a presymptomatic marker of auditory pathway
    involvement rather than a confirmation of an existing complaint.
  evidence:
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brainstem auditory-evoked potentials showed increased latencies of waves
      I–III–V, as well as increased interpeak latencies in some patients
    explanation: >-
      Documents the brainstem auditory evoked potential abnormality measured in
      the Bulgarian cohort.
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Interestingly, the two patients with no auditory complains (case II-1 and
      case II-2), aged 30 and 31 years, respectively, also had normal audiograms
    explanation: >-
      Cases II-1 and II-2 are named among the patients with increased brainstem
      evoked-potential latencies in the quote above, yet had no hearing complaint
      and normal audiograms - which is what makes the evoked potential a
      presymptomatic marker rather than a confirmation of an existing complaint.
- name: Targeted NDRG1 Sequencing
  description: >-
    Molecular confirmation. Because a single founder allele accounts for most
    cases, targeted testing of NDRG1 has a high yield in patients of Roma origin
    with early-onset demyelinating neuropathy, and the authors of the Slovak
    series argue for making it routine in that setting. It must not be restricted
    to that setting, however: whole-exome and targeted panel sequencing have found
    NDRG1 alleles in patients with no Roma ancestry.
  evidence:
  - reference: PMID:23996628
    reference_title: "Founder mutations in NDRG1 and HK1 genes are common causes of inherited neuropathies among Roma/Gypsies in Slovakia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Providing genetic analysis of these genes for patients with Roma origin as a
      common part of diagnostic procedure would contribute to a better rate of
      diagnosed cases of demyelinating neuropathy
    explanation: >-
      The argument for routine targeted testing in the founder population.
- name: Sural Nerve Biopsy
  description: >-
    Not required for diagnosis now that molecular testing is available, but
    historically decisive and still informative where the genetic result is
    ambiguous: CMT4D nerve histology is reported as distinct, showing depletion of
    myelinated fibres, small calibre in those that survive, and poorly developed
    onion bulbs.
  evidence:
  - reference: PMID:39201732
    reference_title: "Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Nerve histology seems to be distinct, and shows a depletion in myelinated
      nerve fibers with small size in the few preserved myelinated fibers and
      poorly developed onion bulbs
    explanation: >-
      Describes the histological picture and its claimed distinctiveness, in the
      source's own hedged terms.
differential_diagnoses:
- name: CMT4G (HMSN-Russe, HK1-related)
  description: >-
    The closest differential in the population where CMT4D is commonest. CMT4G is
    the other recessive demyelinating neuropathy caused by a founder mutation
    private to the Roma, and in the Slovak series the two accounted for all four
    families tested - two CMT4D and two CMT4G. Ancestry and clinical phenotype
    therefore do not discriminate them; the HK1 versus NDRG1 genotype does, which
    is the practical argument for testing both together rather than sequentially.
  evidence:
  - reference: PMID:23996628
    reference_title: "Founder mutations in NDRG1 and HK1 genes are common causes of inherited neuropathies among Roma/Gypsies in Slovakia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We detected mutation p.R148X (g.631C>T) in the NDRG1 (NM_006096.3) gene in
      two families and mutation g.9712G>C in the HK1 (NM_033498) gene in the other
      two families. These mutations cause CMT4D and CMT4G, respectively.
    explanation: >-
      Shows the two disorders arising side by side in the same population and
      ascertainment, distinguishable only genetically.
- name: Other autosomal recessive demyelinating CMT (CMT4 subtypes)
  description: >-
    CMT4D must be separated from the other CMT4 subtypes - CMT4A (GDAP1), CMT4B1
    and CMT4B2 (MTMR2, SBF2), CMT4C (SH3TC2), CMT4F (PRX) and CMT4J (FIG4) - which
    share recessive inheritance, early onset and slowed conduction. Two features
    point towards NDRG1: sensorineural deafness, which is not a general CMT4
    feature, and the early severity of axonal loss. Neither is decisive, and the
    entity is defined genetically. Curated in this knowledge base as
    `Charcot-Marie-Tooth_Disease_Type_4`, which also carries CMT4D as a subtype
    block.
  evidence:
  - reference: PMID:27982524
    reference_title: "A novel NDRG1 mutation in a non-Romani patient with CMT4D/HMSN-Lom."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      should be considered in the differential diagnosis of recessive demyelinating
      CMT
    explanation: >-
      Places CMT4D within the recessive demyelinating CMT differential regardless
      of ancestry.
discussions:
- discussion_id: cmt4d_axonal_loss_has_no_model
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Why does none of the three NDRG1-deficient rodent models reproduce the early
    severe axonal loss that actually causes disability in patients, when all
    three reproduce the demyelination - and has the canine model, which does show
    axonal pathology, ever been assessed for whether its axonal loss is early and
    disproportionate to the demyelination?
  attaches_to:
  - "pathophysiology#Early Severe Axonal Loss"
  - "pathophysiology#Myelin Sheath Breakdown with Onion Bulb Formation"
  rationale: >-
    This is a HUMAN_MODEL_MISMATCH rather than a KNOWLEDGE_GAP because the
    evidence is not absent - four independent NDRG1-deficient models exist,
    three rodent and one canine, and all have had their myelin phenotype
    characterised in detail. What is uncertain is their translational validity
    for the arm of the disease that matters clinically, which is precisely the
    arm that has not been characterised to the same standard. The stretcher
    mouse and the hypomorphic Ndrg1 knockout were compared head to head and
    neither displays the early severe axonal loss typical of the human disease,
    with regenerative capacity explicitly unimpaired; the independent CRISPR
    Ndrg1-/- mouse likewise shows no apparent axonal loss despite faithful
    demyelination; and the canine model is described as a mixed polyneuropathy
    without the deafness that defines the human disorder.

    The consequence is precise and constraining, and the rodent and canine models
    have to be stated separately because they fail differently. No rodent model
    reconstructs the step from Schwann-cell NDRG1 loss to axonal degeneration:
    all three reproduce demyelination and none the early severe axonal loss. The
    Greyhound is not in that position - it has prominent axonal pathology, with
    severe axonal atrophy, dropout of large myelinated fibres, Wallerian
    degeneration and neurogenic muscle atrophy. What has not been shown for the
    canine model is the feature that actually defines the human lesion: that the
    axonal loss is early and disproportionate to the demyelination rather than a
    late consequence of it. Nobody has assessed it for that, which is a different
    and weaker statement than failing to reproduce it.

    The practical consequence is unchanged. The gene-discovery work framed CMT4D
    as a disease of impaired axon-glia interaction, and axonal loss is what
    produces the disability. Any preclinical result in the rodent models -
    including the observation that a treatment window exists before the four-week
    onset of myelin thinning - speaks to the demyelinating arm only, and must not
    be curated or read as addressing the axonal arm. The canine line is the one
    place the axonal arm might be testable, which is why the proposed long-axon
    experiment below uses it.
  proposed_experiments:
  - experiment_id: exp_cmt4d_longer_axon_model
    name: Test whether axon length explains the model failure
    description: >-
      Human peripheral axons are an order of magnitude longer than murine ones,
      and the demand-mismatch hypothesis predicts that vulnerability scales with
      the membrane load a Schwann cell must service. Characterise NDRG1-null
      neuropathy in a large-animal model with long axons - the Greyhound line
      already exists - with axonal counts and regeneration assays as the primary
      readouts rather than myelin measures.
  - experiment_id: exp_cmt4d_schwann_axon_coculture
    name: Human Schwann cell-neuron co-culture with NDRG1 loss restricted to glia
    description: >-
      Co-culture patient-derived or NDRG1-edited human Schwann cells with
      wild-type sensory neurons, and the reciprocal combination, to determine
      whether Schwann-cell NDRG1 loss is sufficient to injure a genetically normal
      axon and over what timescale.
- discussion_id: cmt4d_ndrg1_molecular_function
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    What does NDRG1 actually do in the Schwann cell, and is the trafficking
    account sufficient to explain a demyelinating neuropathy?
  attaches_to:
  - "pathophysiology#Impaired Schwann Cell Vesicular Trafficking"
  - "pathophysiology#Loss of Schwann Cell NDRG1 Function"
  rationale: >-
    Twenty-six years after the gene was found, the molecular function of NDRG1
    remains unresolved, and a 2013 clinical report still opens by saying so. What
    makes this a genuine gap rather than an unfinished literature is that the
    field has actively excluded candidates: the stretcher work found no support
    for roles in growth arrest, terminal differentiation, gene expression
    regulation or proteasomal degradation, leaving vesicular trafficking as the
    surviving hypothesis largely by elimination. The positive evidence for
    trafficking is real but indirect - Rab4a compartment enlargement and failed
    LDL receptor recycling in cell lines, lipid-vesicle binding by the purified
    protein, and a timing coincidence between demyelination and peak myelin
    growth in mouse. None of it measures membrane flux in a Schwann cell, and the
    protein is a hydrolase-fold member with no demonstrated catalytic activity, so
    the possibility that its relevant function is something not yet tested is not
    closed.
  proposed_experiments:
  - experiment_id: exp_cmt4d_schwann_membrane_flux
    name: Direct measurement of membrane trafficking flux in NDRG1-null Schwann cells
    description: >-
      Quantify endocytic and recycling flux, and myelin membrane delivery rate, in
      primary NDRG1-null Schwann cells during active myelination in co-culture,
      testing the demand-mismatch hypothesis directly rather than through the
      timing of the lesion.
  - experiment_id: exp_cmt4d_ndrg1_hydrolase_activity
    name: Screen for catalytic activity of the NDRG1 hydrolase fold
    description: >-
      The crystal structure resolves an alpha/beta hydrolase fold presumed
      inactive. Screen substrate classes appropriate to the fold, and test whether
      the CMT4D missense alleles p.Leu146Pro and p.Arg234Gln affect any activity
      found, to close or confirm the possibility of an unrecognised enzymatic
      function.
- discussion_id: cmt4d_central_nervous_system_involvement
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Is the central nervous system genuinely affected in CMT4D, or are the imaging
    and evoked-potential abnormalities secondary to the peripheral lesion?
  attaches_to:
  - "pathophysiology#Auditory Pathway Involvement"
  rationale: >-
    Three independent lines of observation point at the central nervous system:
    subcortical white matter abnormalities in a non-Roma p.Arg148*-homozygous
    family, cerebellar, medullary and upper cervical cord atrophy in an Italian
    patient with a different allele, and prolonged brainstem auditory evoked
    potential interpeak latencies that appear before hearing complaints. NDRG1 is
    ubiquitously expressed, so central involvement is biologically unsurprising.
    But none of these is decisive: evoked-potential delay is equally compatible
    with conduction failure in the proximal eighth-nerve segment, imaging findings
    come from single families, and no neuropathological examination of CMT4D
    central tissue has been reported. The authors who first reported the white
    matter lesions themselves called for further study rather than claiming a
    central phenotype. This entry therefore keeps the auditory node separate from
    the somatic chain rather than asserting a shared mechanism.
  proposed_experiments:
  - experiment_id: exp_cmt4d_systematic_neuroimaging
    name: Systematic central nervous system imaging in a genotyped CMT4D cohort
    description: >-
      Quantitative brain and cord MRI with diffusion metrics in a genotyped CMT4D
      cohort against age-matched controls, to determine whether white matter
      abnormality is a consistent feature or a sporadic finding in single
      families.
  - experiment_id: exp_cmt4d_ndrg1_cns_expression
    name: NDRG1 expression and oligodendrocyte requirement in central white matter
    description: >-
      Determine whether NDRG1 is expressed in oligodendrocytes at levels
      comparable to Schwann cells, and whether central myelin is affected in
      NDRG1-null animals, which would distinguish a primary central phenotype from
      a peripheral one.
- discussion_id: cmt4d_phenotype_causal_attribution
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Which routes account for the reported spinal, bulbar, cognitive and central imaging findings, and for motor delay in some families?
  attaches_to:
  - phenotypes#Scoliosis
  - phenotypes#Dysphagia
  - phenotypes#Bilateral Vocal Cord Paralysis
  - phenotypes#Cognitive Impairment
  - phenotypes#Central Nervous System White Matter Abnormality
  - phenotypes#Cerebellar Atrophy
  - phenotypes#Cervical Spinal Cord Atrophy
  - phenotypes#Medullary Atrophy
  - phenotypes#Motor Delay
  - pathophysiology#Visual Pathway Dysfunction
  rationale: >-
    The reviewed human reports establish these observations, but do not identify a causal route for each. Scoliosis is quantified without a demonstrated paraspinal denervation or other spinal mechanism. The two siblings with dysphagia and vocal cord paralysis have no reported localization sufficient to distinguish cranial neuropathy from central motor involvement; vocal cord paralysis causing respiratory insufficiency is explicitly established and is represented. Cognitive delay lacks a defined developmental or neuropathological substrate. White matter lesions, cerebellar atrophy, medullary atrophy and cervical cord atrophy come from different limited reports whose authors do not establish whether each is a primary central consequence of NDRG1 loss or secondary degeneration. The visual evoked-potential abnormality establishes visual pathway dysfunction, but not its cause or correspondence to those structural findings. Motor delay is directly observed in some molecularly confirmed patients while other cohorts have normal milestones; the reviewed sources do not connect the delayed milestones to a defined early peripheral lesion. These uncertainties concern causal attribution, not a requirement to reconstruct every molecular intermediate. The peripheral glia-to-axon route and the auditory route are represented with their stated uncertainty.
notes: >-
  Scope. This entry covers CMT4D / HMSN-Lom (MONDO:0011085), the NDRG1-related
  recessive demyelinating neuropathy. CMT4D also appears as a subtype block
  within `Charcot-Marie-Tooth_Disease_Type_4`, which surveys the CMT4 group as a
  whole; the two are complementary rather than duplicative, and this entry is
  where the NDRG1-specific mechanism, allelic spectrum, animal models and open
  questions belong. Per-subtype entries alongside a type-level entry are the
  established pattern in this knowledge base, as with CMT2JJ and CMT2W alongside
  `Charcot-Marie-Tooth_Disease_Type_2`.

  Ancestry is a prior, not a criterion. It is tempting to curate CMT4D as a Roma
  disease, and older sources describe it as found exclusively in that population.
  That is no longer correct and acting on it would cause missed diagnoses: 22
  pathogenic NDRG1 variants are now known, the founder p.Arg148* allele accounts
  for 64 percent rather than all of them, and reported patients include Italian,
  Turkish, Indian, Chinese, Saudi and Bulgarian Muslim families. A second,
  entirely independent founder effect exists in Bulgarian Muslims for two
  splice-acceptor alleles.

  The pathograph's signalling arm is mouse-only. Everything in this entry
  concerning neuregulin 1/ErbB signalling, the myelination transcription program
  and PMP22 turnover comes from Ndrg1-deficient mice and has no human
  counterpart, which is why those nodes are PROVISIONAL and carry
  MODEL_ORGANISM evidence. The same models fail to reproduce the early severe
  axonal loss that defines the human disorder, so their negative and positive
  results are not symmetrically transferable - a treatment that preserves myelin
  in these mice has not been shown to address the arm of the disease that
  disables patients. This is recorded as a HUMAN_MODEL_MISMATCH discussion rather
  than left implicit.

  Only supportive treatments, and only ones actually given. No disease-modifying
  therapy exists for CMT4D and none is in clinical development for it. The two
  curated treatments - percutaneous endoscopic gastrostomy feeding and
  non-invasive ventilation - are curated because they were performed in reported
  CMT4D patients, not extrapolated from neuromuscular disease in general; bulbar
  involvement was unrecognised in this disorder until 2026, so an entry that
  omitted them would leave swallowing and vocal cord function off the
  surveillance list. Generic CMT rehabilitation and orthotics are deliberately
  not curated, because no CMT4D-specific source supports them.

  One therapeutic-sounding observation is deliberately left uncurated. The mouse
  work notes that myelin thinning begins at four weeks, after myelination is
  complete, and calls this a window of opportunity for intervention. That is an
  argument about the demyelinating arm, made in a model that lacks the axonal
  loss which disables patients, and it is recorded here rather than treated as a
  therapeutic claim.

📚

References & Deep Research

References

17

PMID:10831399

N-myc downstream-regulated gene 1 is mutated in hereditary motor and sensory neuropathy-Lom.

No top-level findings curated for this source.

PMID:24028195

CMT4D (NDRG1 mutation): genotype-phenotype correlations.

No top-level findings curated for this source.

PMID:27982524

A novel NDRG1 mutation in a non-Romani patient with CMT4D/HMSN-Lom.

No top-level findings curated for this source.

PMID:28776325

Identification and functional characterization of two missense mutations in NDRG1 associated with Charcot-Marie-Tooth disease type 4D.

No top-level findings curated for this source.

PMID:35708320

Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease.

No top-level findings curated for this source.

PMID:21303696

Ndrg1 in development and maintenance of the myelin sheath.

No top-level findings curated for this source.

PMID:17142040

NDRG1-linked Charcot-Marie-Tooth disease (CMT4D) with central nervous system involvement.

No top-level findings curated for this source.

PMID:39201732

Identification and Characterization of Novel Founder Mutations in NDRG1: Refining the Genetic Landscape of Charcot-Marie-Tooth Disease Type 4D in Bulgaria.

No top-level findings curated for this source.

PMID:42089726

Clinical and pathological findings in two Italian siblings of Romani ancestry with charcot-marie-tooth type 4D and review of the current literature.

No top-level findings curated for this source.

PMID:33305529

Crystal and solution structure of NDRG1, a membrane-binding protein linked to myelination and tumour suppression.

No top-level findings curated for this source.

PMID:23996628

Founder mutations in NDRG1 and HK1 genes are common causes of inherited neuropathies among Roma/Gypsies in Slovakia.

No top-level findings curated for this source.

PMID:35149926

A splice altering variant in NDRG1 gene causes Charcot-Marie-Tooth disease, type 4D.

No top-level findings curated for this source.

PMID:24136616

Exonic duplication CNV of NDRG1 associated with autosomal-recessive HMSN-Lom/CMT4D.

No top-level findings curated for this source.

PMID:20582309

A deletion in the N-myc downstream regulated gene 1 (NDRG1) gene in Greyhounds with polyneuropathy.

No top-level findings curated for this source.

PMID:9549516

Hereditary motor and sensory neuropathy--Lom, a novel demyelinating neuropathy associated with deafness in gypsies. Clinical, electrophysiological and nerve biopsy findings.

No top-level findings curated for this source.

PMID:15082788

Ndrg1-deficient mice exhibit a progressive demyelinating disorder of peripheral nerves.

No top-level findings curated for this source.

PMID:20301532

Charcot-Marie-Tooth Hereditary Neuropathy Overview.

No top-level findings curated for this source.

Deep Research

1

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

Evaluations and curation notes (1)

Create: Charcot-Marie-Tooth disease type 4D · 2026-08-27T15:53:47Z · View source

De-novo creation of the CMT4D (HMSN-Lom, NDRG1) entry from stubs/. Entry-type decision: dedicated Disease entry rather than folding into the existing Charcot-Marie-Tooth_Disease_Type_4 parent, which already carries CMT4D as a subtype block. MONDO:0011085 records no descendants and a single causal gene (NDRG1, RO:0004003), and per-subtype entries alongside a type-level entry are established convention here (CMT2JJ and CMT2W alongside CMT2). The parent's subtype block and this entry are complementary; the notes: section records the boundary. Deep research: falcon report generated and NEC-preflighted against MONDO:0011085 -> PASS (NDRG1 = 50 mentions, next gene NRG1 = 3; report OMIM 601455 matches the MONDO xref). Report reference_validation reported 11/12 resolved, 0 unresolved, 0 off topic. The report was used as a lead source only; every curated PMID was independently fetched with just fetch-reference and every snippet checked against the cached text. Two leads taken from the report (PMID:9549516 original 1998 clinical delineation, PMID:15082788 Okuda Ndrg1 knockout) were fetched and curated; the report's own caution that phenotype frequencies could not be assigned from its evidence was superseded by the 2026 systematic review (PMID:42089726), which supplies them directly. Pathograph: 9 nodes, 9 edges, single root, every node reachable from the root (measured, not asserted). Chain runs biallelic NDRG1 loss of function -> Schwann-cell NDRG1 loss -> two parallel arms (vesicular trafficking failure; attenuated neuregulin 1/ErbB signalling -> dysregulated myelination transcription program) -> myelin breakdown with onion bulbs -> early severe axonal loss -> clinical neuropathy. Auditory pathway involvement is reached from the genotype by an edge explicitly typed INDIRECT_UNKNOWN_INTERMEDIATES rather than routed through the somatic Schwann-cell chain, because the evoked-potential evidence implicates the eighth nerve and the central pathways simultaneously and no cochlear pathology has been reported. Conformance declared to three peripheral_axonal_degeneration nodes. Honesty decisions worth recording: the entire neuregulin 1/ErbB and myelination transcription arm is mouse-only and is marked PROVISIONAL with MODEL_ORGANISM evidence; all three NDRG1-null RODENT models fail to reproduce the early severe axonal loss that defines the human disease, curated as FAILS_TO_RECAPITULATE links plus a HUMAN_MODEL_MISMATCH discussion rather than glossed. The canine model is excluded from that claim - it shows axonal pathology, and what is unassessed there is whether the loss is early and disproportionate to the demyelination. Scoliosis carries a FREQUENT band from the 72-patient literature review together with a PARTIAL-tagged contradicting observation from the Bulgarian cohort (1/7) rather than averaging them. Bulbar and central-nervous-system phenotypes carry no frequency because they rest on single families. No disease-modifying treatment exists; the two curated treatments (PEG feeding, non-invasive ventilation) were actually performed in reported CMT4D patients rather than extrapolated. Validation run in the worktree: just validate -> all validations passed; just count-verified-snippets -> 97/97 verified against cached references; just validate-terms -> passed. A reference_title audit script confirmed all 14 cited reference_title values byte-match the title: line in their cache frontmatter. just validate-disorders run once before opening the PR.

Falcon ▸

Disease Characteristics Research Template

Edison Scientific Literature 15 citations 2026-08-27T15:44:20.145011

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Characteristics Research Template

Target Disease

Disease Name: Charcot-Marie-Tooth disease type 4D
MONDO ID: (if available)
Category: Mendelian

Research Objectives

Please provide a comprehensive research report on Charcot-Marie-Tooth disease type 4D covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.

For each section, suggested databases/resources are listed. These are the first places you should search for information on each topic.

1. Disease Information

Search first: OMIM, Orphanet, ICD-10/ICD-11, MeSH, PubMed

What is the disease? Provide a concise overview.
What are the key identifiers? (OMIM, Orphanet, ICD-10/ICD-11, MeSH, Mondo)
What are the common synonyms and alternative names?
Is the information derived from individual patients (e.g., EHR) or aggregated disease-level resources?

2. Etiology

Disease Causal Factors: What are the primary causes? (genetic, environmental, infectious, mechanistic)
Risk Factors:

Search first: PubMed, Cochrane Library, UpToDate, clinical guidelines, ClinVar, ClinGen, GWAS Catalog, PheGenI, CTD, CDC, WHO, epidemiological databases
Genetic risk factors (causal variants, susceptibility loci, modifier genes)
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Protective Factors:

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3. Phenotypes

Search first: HPO (Human Phenotype Ontology), OMIM, Orphanet, PubMed, clinicaltrials.gov, MedDRA, SNOMED CT, DECIPHER, LOINC

For each phenotype, provide: - Phenotype type: symptoms, clinical signs, physical manifestations, behavioral changes, or laboratory abnormalities

For symptoms/signs: HPO, OMIM, Orphanet, PubMed For behavioral changes: HPO, DSM, RDoC (Research Domain Criteria), PubMed For laboratory abnormalities: LOINC, SNOMED CT, LabTests Online, PubMed - Phenotype characteristics: Search first: OMIM, Orphanet, HPO, PubMed - Age of symptom onset (neonatal, childhood, adult-onset, late-onset) - Symptom severity (mild, moderate, severe, variable) - Symptom progression (stable, progressive, episodic, fluctuating) - Frequency among affected individuals (percentage or qualitative) - Quality of life impact: Effects on daily functioning and well-being (per-phenotype when possible) Search first: EQ-5D database, SF-36, WHO QOL databases, PubMed - Suggest HPO (Human Phenotype Ontology) terms for each phenotype

4. Genetic/Molecular Information

Causal Genes: Gene mutations or chromosomal abnormalities responsible for disease (gene symbols, OMIM IDs)

Search first: OMIM, ClinVar, HGMD, Ensembl, NCBI Gene
Pathogenic Variants:
Affected genes (gene symbols, HGNC IDs) > Search first: OMIM, NCBI Gene, Ensembl, HGNC, UniProt, GeneCards
Variant classification (pathogenic, likely pathogenic, VUS per ACMG/AMP guidelines) > Search first: ClinVar, ClinGen, ACMG/AMP guidelines, VarSome
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Functional consequences (loss of function, gain of function, dominant negative)
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Epigenetic Information: DNA methylation, histone modifications, chromatin changes affecting disease

Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth
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5. Environmental Information

Environmental Factors: Non-genetic contributing factors (toxins, radiation, pollution, occupational exposure)

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Lifestyle Factors: Behavioral factors (smoking, diet, exercise, alcohol consumption)

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Infectious Agents: If applicable, pathogens causing or triggering disease (bacteria, viruses, fungi, parasites)

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6. Mechanism / Pathophysiology

Molecular Pathways: Specific signaling cascades or biochemical pathways involved (Wnt, MAPK, mTOR, PI3K-AKT, etc.)

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Cellular Processes: Cell-level mechanisms (apoptosis, autophagy, cell cycle dysregulation, inflammation, etc.)

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Protein Dysfunction: How protein structure or function is altered (misfolding, aggregation, loss of function, gain of function)

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Metabolic Changes: Alterations in metabolic processes (energy metabolism, lipid metabolism, amino acid metabolism)

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Immune System Involvement: Role of immune response (autoimmunity, immunodeficiency, chronic inflammation)

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Tissue Damage Mechanisms: How tissues/ are injured (oxidative stress, ischemia, fibrosis, necrosis)

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Biochemical Abnormalities: Specific molecular defects (enzyme deficiencies, receptor dysfunction, ion channel defects)

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Epigenetic Changes: DNA methylation, histone modifications affecting gene expression in disease

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Molecular Profiling (if available):
Transcriptomics/gene expression changes > Search first: GEO (Gene Expression Omnibus), ArrayExpress, GTEx, Human Cell Atlas, SRA
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For each mechanism, describe: - The causal chain from initial trigger to clinical manifestation - Which mechanisms are upstream vs downstream - What cell types and biological processes are involved - Suggest GO terms for biological processes and CL terms for cell types

7. Anatomical Structures Affected

Organ Level:
Primary organs directly affected
Secondary organ involvement (complications, secondary effects)
Body systems involved (cardiovascular, nervous, digestive, respiratory, endocrine, etc.)

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Tissue and Cell Level:
Specific tissue types affected (epithelial, connective, muscle, nervous)
Specific cell populations targeted (with Cell Ontology terms)

Search first: Uberon, Human Protein Atlas, Cell Ontology, Human Cell Atlas, CellMarker, PanglaoDB
Subcellular Level:
Cellular compartments involved (mitochondria, nucleus, ER, lysosomes) (with GO Cellular Component terms)

Search first: Gene Ontology (Cellular Component), UniProt, Human Protein Atlas
Localization:
Specific anatomical sites (with UBERON terms) > Search first: FMA, Uberon, NeuroNames (for brain), SNOMED CT
Lateralization (unilateral, bilateral, asymmetric) > Search first: HPO, clinical literature, imaging databases

8. Temporal Development

Onset:
Typical age of onset (congenital, pediatric, adult, geriatric)
Onset pattern (acute, subacute, chronic, insidious)

Search first: OMIM, Orphanet, HPO, PubMed
Progression:
Disease stages (early, intermediate, advanced, end-stage) > Search first: Cancer Staging Manual (AJCC), WHO classifications, PubMed
Progression rate (rapid, slow, variable)
Disease course pattern (episodic, relapsing-remitting, progressive, stable)
Disease duration (self-limited, chronic lifelong)

Search first: Disease registries, longitudinal cohort databases, natural history studies, PubMed, Orphanet, OMIM
Patterns:
Remission patterns (spontaneous, treatment-induced) > Search first: Clinical trial databases, disease registries, PubMed
Critical periods (time windows of vulnerability or opportunity for intervention) > Search first: PubMed, developmental biology databases, clinical guidelines

9. Inheritance and Population

Epidemiology:
Prevalence (cases per 100,000 at given time)
Incidence (new cases per 100,000 per year)

Search first: Orphanet, CDC, WHO, GBD (Global Burden of Disease), national registries, SEER, disease registries
For Genetic Etiology:
Inheritance pattern (AD, AR, X-linked, mitochondrial, multifactorial, polygenic) > Search first: OMIM, Orphanet, ClinVar, GTR (Genetic Testing Registry)
Penetrance (complete, incomplete, age-dependent) > Search first: ClinVar, OMIM, PubMed, ClinGen
Expressivity (variable, consistent) > Search first: OMIM, ClinVar, PubMed
Genetic anticipation (increasing severity in successive generations) > Search first: OMIM, PubMed (especially for repeat expansion disorders)
Germline mosaicism > Search first: ClinVar, OMIM, genetic counseling literature, PubMed
Founder effects (population-specific mutations) > Search first: gnomAD, population genetics databases, PubMed
Consanguinity role > Search first: OMIM, population studies, genetic counseling resources
Carrier frequency > Search first: gnomAD, carrier screening databases, GeneReviews, GTR
Population Demographics:
Affected populations (ethnic or demographic groups with higher prevalence) > Search first: gnomAD, 1000 Genomes, PAGE Study, PubMed, population registries
Geographic distribution (endemic areas, regional variation) > Search first: WHO, CDC, GBD, Orphanet, geographic epidemiology databases
Geographic distribution of specific variants
Sex ratio (male:female) > Search first: Disease registries, OMIM, PubMed, epidemiological databases
Age distribution of affected individuals > Search first: CDC, disease registries, SEER, Orphanet

10. Diagnostics

Clinical Tests:
Laboratory tests (blood, urine, tissue chemistry, specific enzyme assays) > Search first: LOINC, LabTests Online, PubMed
Biomarkers (proteins, metabolites, genetic markers, circulating biomarkers) > Search first: FDA Biomarker List, BEST (Biomarkers, EndpointS, and other Tools), PubMed
Imaging studies (X-ray, CT, MRI, PET, ultrasound) > Search first: RadLex, DICOM, Radiopaedia, imaging databases
Functional tests (pulmonary function, cardiac stress tests) > Search first: LOINC, clinical guidelines, PubMed
Electrophysiology (EEG, EMG, ECG, nerve conduction studies) > Search first: LOINC, clinical neurophysiology databases, PubMed
Biopsy findings (histopathology, immunohistochemistry) > Search first: SNOMED CT, College of American Pathologists resources, PubMed
Pathology findings (microscopic examination) > Search first: SNOMED CT, Digital Pathology databases, PubMed
Genetic Testing:

Search first: GTR (Genetic Testing Registry), GeneReviews, ClinGen
Overview of recommended genetic testing approach
Whole genome sequencing (WGS) utility > Search first: GTR, ClinVar, GEL (Genomics England), gnomAD
Whole exome sequencing (WES) utility > Search first: GTR, ClinVar, OMIM, GeneMatcher
Gene panels (which panels, which genes) > Search first: GTR, ClinVar, laboratory-specific databases
Single gene testing > Search first: GTR, ClinVar, OMIM, GeneReviews
Chromosomal microarray (CMA) > Search first: DECIPHER, ClinVar, dbVar, ECARUCA
Karyotyping > Search first: Chromosome Abnormality Database, ClinVar, cytogenetics resources
FISH > Search first: ClinVar, cytogenetics databases, PubMed
Mitochondrial DNA testing > Search first: MITOMAP, MSeqDR, ClinVar, GTR
Repeat expansion testing > Search first: GTR, ClinVar, repeat expansion databases, PubMed
Omics-Based Diagnostics (if applicable):
RNA sequencing / transcriptomics > Search first: GEO, ArrayExpress, GTEx, RNA-seq databases
Proteomics > Search first: PRIDE, ProteomeXchange, FDA Biomarker database
Metabolomics > Search first: MetaboLights, Metabolomics Workbench, HMDB
Epigenomics > Search first: GEO, ENCODE, Roadmap Epigenomics, MethBase
Liquid biopsy > Search first: COSMIC, ClinVar, liquid biopsy databases, PubMed
Clinical Criteria:
Standardized diagnostic criteria (DSM, ICD, society guidelines) > Search first: DSM-5, ICD-11, clinical society guidelines, UpToDate
Differential diagnosis (other conditions to rule out, with distinguishing features) > Search first: DynaMed, UpToDate, clinical decision support systems
Screening:
Screening methods for asymptomatic individuals (newborn screening, carrier screening, cascade screening) > Search first: ACMG recommendations, CDC newborn screening, GTR

11. Outcome/Prognosis

Survival and Mortality:
Survival rate (5-year, 10-year, overall) > Search first: SEER, cancer registries, disease-specific registries, PubMed
Life expectancy (with and without treatment if applicable) > Search first: Orphanet, disease registries, actuarial databases, PubMed
Mortality rate > Search first: CDC, WHO, GBD, national mortality databases
Disease-specific mortality (deaths directly attributable to disease) > Search first: Disease registries, CDC Wonder, GBD, PubMed
Morbidity and Function:
Morbidity (disease-related disability and health impacts) > Search first: GBD, WHO, disability databases, PubMed
Disability outcomes (long-term functional impairments) > Search first: ICF (International Classification of Functioning), disability registries
Quality of life measures (EQ-5D, SF-36, PROMIS, disease-specific tools) > Search first: EQ-5D database, SF-36, PROMIS, PubMed
Disease Course:
Complications (secondary problems: infections, organ failure, etc.) > Search first: ICD codes, disease registries, clinical databases, PubMed
Recovery potential (likelihood and extent of recovery, with vs without treatment) > Search first: Natural history studies, rehabilitation databases, PubMed
Prediction:
Prognostic factors (age, disease severity, biomarkers, treatment response) > Search first: Prognostic models databases, clinical calculators, PubMed
Prognostic biomarkers (molecular markers predicting disease course) > Search first: FDA Biomarker database, PubMed, cancer prognostic databases

12. Treatment

Pharmacotherapy:
Pharmacological treatments (drug names, drug classes, mechanisms of action) > Search first: DrugBank, RxNorm, ATC classification, DailyMed, FDA databases
Pharmacogenomics (how genetic variants affect drug metabolism, efficacy, toxicity) > Search first: PharmGKB, CPIC (Clinical Pharmacogenetics), FDA Table of PGx Biomarkers
Advanced Therapeutics:
Gene therapy (viral vectors, CRISPR, gene replacement, gene editing) > Search first: ClinicalTrials.gov, FDA gene therapy database, ASGCT resources
Cell therapy (stem cell transplant, CAR-T, cellular therapeutics) > Search first: ClinicalTrials.gov, FDA cell therapy database, FACT standards
RNA-based therapies (ASOs, siRNA, mRNA therapies) > Search first: ClinicalTrials.gov, FDA approvals, PubMed
Targeted therapies (treatments directed at specific molecular targets) > Search first: My Cancer Genome, OncoKB, ClinicalTrials.gov, FDA approvals
Immunotherapies (checkpoint inhibitors, monoclonal antibodies) > Search first: Cancer Immunotherapy Database, FDA approvals, ClinicalTrials.gov
Surgical and Interventional:
Surgical interventions (types of surgery, timing, outcomes) > Search first: CPT codes, surgical registries, clinical guidelines, PubMed
Supportive and Rehabilitative:
Supportive care (symptom management, pain control, nutrition) > Search first: Clinical guidelines, Cochrane Library, PubMed
Rehabilitation (physical therapy, occupational therapy, speech therapy) > Search first: Rehabilitation medicine databases, clinical guidelines, PubMed
Experimental:
Experimental treatments in clinical trials (with NCT identifiers if available) > Search first: ClinicalTrials.gov, EU Clinical Trials Register, WHO ICTRP
Treatment Outcomes:
Treatment response rates > Search first: Clinical trial databases, FDA reviews, systematic reviews, PubMed
Side effects and adverse events > Search first: FDA Adverse Event Reporting System (FAERS), MedWatch, PubMed
Treatment Strategy:
Treatment algorithms (clinical pathways, decision trees) > Search first: Clinical practice guidelines, NCCN Guidelines, UpToDate
Combination therapies > Search first: ClinicalTrials.gov, treatment guidelines, PubMed
Personalized medicine approaches (genotype-guided treatment) > Search first: My Cancer Genome, CIViC, PharmGKB, precision medicine databases

For each treatment, suggest NCIT (NCI Thesaurus) clinical-intervention terms where applicable.

13. Prevention

Prevention Levels:
Primary prevention (preventing disease occurrence: vaccination, risk factor modification) > Search first: CDC, WHO, USPSTF recommendations, Cochrane Library
Secondary prevention (early detection and treatment: screening programs, early intervention) > Search first: USPSTF, CDC screening guidelines, WHO
Tertiary prevention (preventing complications in those with disease) > Search first: Clinical guidelines, disease management protocols, PubMed
Immunization: Vaccine strategies (if applicable)

Search first: CDC vaccine schedules, WHO immunization, FDA vaccine database
Screening and Early Detection:
Screening programs (population-based: newborn screening, cancer screening) > Search first: CDC screening programs, USPSTF, cancer screening databases
Genetic screening (carrier screening, preimplantation genetic diagnosis, prenatal testing) > Search first: ACMG recommendations, ACOG guidelines, GTR
Risk stratification (identifying high-risk individuals for targeted prevention) > Search first: Risk prediction models, clinical calculators, PubMed
Behavioral Interventions: Lifestyle modifications to reduce risk

Search first: CDC, WHO, behavioral intervention databases, Cochrane Library
Counseling: Genetic counseling (risk assessment, family planning guidance)

Search first: NSGC resources, ACMG guidelines, GeneReviews
Public Health:
Public health interventions (sanitation, vector control, health education) > Search first: CDC, WHO, public health databases, PubMed
Environmental interventions (reducing environmental risk factors) > Search first: EPA databases, WHO environmental health, PubMed
Prophylaxis: Preventive medications or procedures

Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

Taxonomy: Species affected (with NCBI Taxon identifiers)

Search first: NCBI Taxonomy
Breed: Specific breeds affected (with VBO identifiers if applicable)

Search first: VBO (Vertebrate Breed Ontology)
Gene: Orthologous genes in other species (with NCBI Gene IDs)

Search first: NCBI Gene
Natural Disease:
Naturally occurring disease in other species (companion animals, wildlife) > Search first: OMIA (Online Mendelian Inheritance in Animals), VetCompass, PubMed
Veterinary relevance and importance in animal health > Search first: OMIA, veterinary databases, PubMed
Comparative Biology:
Comparative pathology (similarities and differences across species) > Search first: OMIA, comparative pathology databases, PubMed
Evolutionary conservation of disease mechanisms > Search first: HomoloGene, OrthoMCL, Alliance of Genome Resources
Transmission (if applicable):
Zoonotic potential > Search first: CDC zoonotic diseases, WHO zoonoses, GIDEON
Cross-species susceptibility > Search first: NCBI Taxonomy, veterinary databases, PubMed

15. Model Organisms

Model Types:
Model organism type (mammalian, invertebrate, cellular, in vitro) > Search first: Alliance of Genome Resources, model organism databases
Specific model systems (mouse, rat, zebrafish, Drosophila, C. elegans, yeast, cell lines, organoids, iPSCs) > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, SGD, ATCC, Cellosaurus
Induced models (drug treatment, surgical intervention, environmental manipulation) > Search first: MGI, model organism databases, PubMed
Genetic Models:
Types available (knockout, knock-in, transgenic, conditional, humanized) > Search first: MGI, IMPC, KOMP, EuMMCR, IMSR
Model Characteristics:
Phenotype recapitulation (how well model reproduces human disease features) > Search first: Model organism databases, comparative studies, PubMed
Model limitations (aspects of human disease not captured) > Search first: Model organism databases, PubMed, review articles
Applications:
Research applications (what aspects of disease can be studied) > Search first: Model organism databases, PubMed
Resources:
Model databases > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, EMMA, MMRRC

Citation Requirements

Cite primary literature (PMID preferred) for all mechanistic and clinical claims
Prioritize recent reviews and landmark papers
Include direct quotes from abstracts where possible to support key statements
Distinguish evidence source types: human clinical, model organism, in vitro, computational

Output Format

Structure your response as a comprehensive narrative organized by the sections above. For each section, provide: - Factual content with specific details (numbers, percentages, gene names, variant nomenclature) - Ontology term suggestions (HPO, GO, CL, UBERON, CHEBI, NCIT, MONDO) where applicable - Evidence citations with PMIDs - Direct quotes from abstracts to support key claims - Clear indication when information is not available or not applicable for this disease

This report will be used to populate a disease knowledge base entry with: - Pathophysiology descriptions with causal chains - Gene/protein annotations (HGNC, GO terms) - Phenotype associations (HP terms) with frequencies - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Treatment annotations (NCIT terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details

Charcot–Marie–Tooth disease type 4D (CMT4D/HMSN-Lom): comprehensive disease-characteristics report

Executive summary and evidence scope

Charcot–Marie–Tooth disease type 4D (CMT4D), historically called hereditary motor and sensory neuropathy–Lom (HMSN-Lom), is a rare, childhood-onset, autosomal-recessive demyelinating neuropathy caused by biallelic pathogenic variants in NDRG1. It produces progressive distal weakness and wasting, sensory loss, areflexia, severe slowing of nerve conduction, foot and hand deformities, and frequently later-onset sensorineural hearing loss. The strongest human evidence comes from Romani founder families and small case series; mechanistic evidence comes principally from Ndrg1-null mice and Schwann-cell studies. Open Targets links MONDO:0011085 to NDRG1 using five evidence records, including PMID 10831399, the landmark causal-gene report. (OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1)

No CMT4D-specific disease-modifying treatment or credible subtype-specific interventional trial was identified. Contemporary implementation therefore consists of genetic diagnosis, multidisciplinary rehabilitation, orthotic/orthopedic management, hearing surveillance and support, and genetic counseling. Because this ultra-rare subtype has few modern cohorts, many requested statistics—incidence, survival, penetrance, carrier frequency outside founder populations, and phenotype percentages—remain unknown rather than zero.

The following table gives a compact knowledge-base summary.

Domain	Key finding	Evidence type	Disease specificity	Key citations / URLs
Identity / identifiers	Charcot-Marie-Tooth disease type 4D (CMT4D) is the same entity as hereditary motor and sensory neuropathy-Lom (HMSN-Lom), an autosomal-recessive demyelinating peripheral neuropathy associated with later hearing loss; Open Targets lists MONDO_0011085 and a disease-target association with NDRG1.	Aggregated disease resource + human clinical literature	Subtype-specific	MONDO_0011085; Open Targets disease-target association for NDRG1 (OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1). Clinical nomenclature and subtype summary in review excerpt (nam2019clinicalandgenetic pages 13-15).
Causal gene / inheritance	Causal gene: NDRG1 (N-myc downstream regulated 1; ENSG00000104419). Inheritance is autosomal recessive; affected individuals typically carry homozygous or biallelic pathogenic variants.	Aggregated disease resource + human clinical literature	Subtype-specific	Open Targets evidence links CMT4D to NDRG1 and literature PMIDs 10831399, 20301641, 28776325 (OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1). Review summary: homozygous NDRG1 variants on 8q24 cause CMT4D (nam2019clinicalandgenetic pages 13-15).
Founder variant	The best-known founder allele is the Lom mutation in NDRG1, historically reported as p.R148X / p.Arg148Ter (older protein nomenclature also P148X appears in review text), enriched in Romani populations from Bulgaria and other European countries.	Human founder-population genetics + review	Subtype-specific	Refined mapping in Romani families: Chandler et al., Neuromuscul Disord 2000, DOI: https://doi.org/10.1016/S0960-8966(00)00148-6 (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13, муртазина2019современныеклиникогенетическиепредставления pages 12-13). Review excerpt notes p.P148X as most common mutation (jiang2022aberrantneuregulin1erbb pages 1-2).
Hallmark phenotype / timeline	Typical onset is in the first decade of life with distal lower-limb weakness, gait difficulty, foot deformities, distal sensory loss, hyporeflexia/areflexia, and progression to hand/upper-limb involvement; deafness commonly appears in the 3rd decade.	Human clinical literature + review	Subtype-specific	“Onset occurs in the first decade of life” and deafness often develops in the third decade (nam2019clinicalandgenetic pages 13-15). 2022 mechanistic paper summarizes early-onset progressive motor and sensory neuropathy with distal weakness, skeletal/foot deformities, and sensorineural hearing loss (jiang2022aberrantneuregulin1erbb pages 1-2).
Electrophysiology / pathology	Nerve conduction velocities are severely reduced and may become unattainable. Nerve biopsy shows marked depletion of myelinated fibers, thin myelin sheaths, segmental demyelination/remyelination, axonal loss, and onion bulb formations; abnormal brainstem auditory evoked potentials have been reported.	Human clinical literature + pathology	Subtype-specific	Review excerpt on CMT4D findings (nam2019clinicalandgenetic pages 13-15). 2022 paper summary reports sural nerve biopsy with myelinated fiber loss, thin myelin, and onion bulbs (jiang2022aberrantneuregulin1erbb pages 1-2).
Mechanism	Current model centers on Schwann-cell dysfunction and demyelination. In Ndrg1 deficiency, total ErbB2/ErbB3 receptor levels are increased but phosphorylated ErbB2/3 and downstream signaling are decreased; neuregulin-1 is increased and integrin β4 is reduced, supporting impaired neuregulin-1/ErbB signaling as a contributor to failed myelination/maintenance. NDRG1 is also linked to membrane/lipid binding and vesicular trafficking in broader literature.	Mouse model + mechanistic molecular study	Subtype-specific core mechanism; trafficking/lipid-binding context is broader NDRG1 biology	Jiang et al., 2022, Mol Cell Biol 42(7), DOI: https://doi.org/10.1128/mcb.00559-21 (jiang2022aberrantneuregulin1erbb pages 1-2). Structural/biophysical context: Mustonen et al., 2021, DOI: https://doi.org/10.1111/febs.15660 (paper-search result, not directly citeable here).
Model organisms	Ndrg1-deficient mouse models develop early progressive demyelinating neuropathy and limb muscle weakness, supporting a causal role for NDRG1 loss in peripheral nerve myelin maintenance.	Model organism	Subtype-specific	Mouse phenotype summarized in 2022 mechanistic study (jiang2022aberrantneuregulin1erbb pages 1-2) and in review excerpt citing Ndrg1-deficient mice with progressive demyelinating peripheral nerve disorder (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13).
Diagnosis	Diagnosis is based on phenotype (early-onset demyelinating neuropathy with later hearing loss), electrophysiology, and molecular confirmation of NDRG1 variants. In practice, this is usually achieved through hereditary neuropathy multigene panels, WES, or WGS rather than single-modality testing alone.	Human clinical literature + general CMT diagnostic practice	Subtype-specific phenotype; testing strategy partly general-CMT evidence	Subtype clues and electrophysiology/pathology from CMT4D review excerpt (nam2019clinicalandgenetic pages 13-15). Broader importance of accurate genetic diagnosis in CMT emphasized in general review DOI: https://doi.org/10.23838/pfm.2018.00163 (nam2019clinicalandgenetic pages 13-15).
Treatment / management	No subtype-specific disease-modifying therapy is established for CMT4D. Management is supportive: physical/occupational therapy, orthoses/AFOs, hearing assessment and aids, pain/symptom control, and orthopedic surgery for severe deformity when needed. Broader CMT trial activity is increasing, but available evidence is largely not CMT4D-specific.	General CMT management / trials literature	Mostly general-CMT evidence; supportive care is applicable to CMT4D	General CMT trial landscape: Nair et al., 2023, DOI: https://doi.org/10.3389/fneur.2023.1251885. General rehabilitation: Coraci et al., 2023, DOI: https://doi.org/10.3390/jcm12185879. These are general-CMT/peripheral-neuropathy rather than subtype-specific evidence.
Epidemiology / population	CMT4D is rare globally but shows a strong founder effect in Romani populations, especially those originally described in Bulgaria and later across several European countries. Robust population prevalence/incidence estimates specific to CMT4D are not well established in accessible sources.	Human population genetics + review	Subtype-specific founder distribution; prevalence gap remains	Chandler et al. founder mapping in Romani families across Europe, DOI: https://doi.org/10.1016/S0960-8966(00)00148-6 (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13, муртазина2019современныеклиникогенетическиепредставления pages 12-13). Review notes first description in Bulgarian Romani population (nam2019clinicalandgenetic pages 13-15).
Key evidence gaps	Missing or limited accessible data include: precise ICD/Orphanet/MeSH/OMIM crosswalks, validated population prevalence/incidence, carrier frequency estimates outside founder groups, quantified phenotype frequencies from large cohorts, proven modifier genes, gene-environment interactions, biomarkers, natural-history survival data, and subtype-specific interventional trials.	Evidence synthesis	Subtype-specific gaps	Gaps inferred from available disease-specific evidence being limited to founder cohorts, reviews, and mechanistic mouse studies (OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1, jiang2022aberrantneuregulin1erbb pages 1-2, муртазина2019современныеклиникогенетическиепредставленияa pages 12-13, nam2019clinicalandgenetic pages 13-15, муртазина2019современныеклиникогенетическиепредставления pages 12-13).

Table: This table summarizes the most actionable disease-knowledge-base facts for Charcot-Marie-Tooth disease type 4D/HMSN-Lom, distinguishing subtype-specific evidence from broader CMT literature. It is useful for quickly identifying established findings, translational implications, and current data gaps.

1. Disease information

Definition and classification

CMT4D is a Mendelian, autosomal-recessive, predominantly demyelinating hereditary motor and sensory neuropathy. It belongs to the recessive CMT4 group and affects the peripheral motor and sensory nerves; auditory neuropathy/sensorineural hearing impairment is an important syndromic feature. The disease was initially delineated in Bulgarian Romani families and subsequently mapped in Romani families from several European countries. (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13, nam2019clinicalandgenetic pages 13-15)

Synonyms:

Charcot–Marie–Tooth disease type 4D; CMT4D
Hereditary motor and sensory neuropathy–Lom; HMSN-Lom; HMSNL
Lom-type hereditary motor and sensory neuropathy
NDRG1-related demyelinating neuropathy
Peripheral neuropathy, motor and sensory, with hearing loss, NDRG1-related

Identifiers and cross-references:

MONDO: MONDO:0011085, Charcot–Marie–Tooth disease type 4D. (OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1)
OMIM phenotype: commonly cross-referenced as CMT4D/HMSN-Lom, OMIM 601455; NDRG1 OMIM 605262. These identifiers should be validated against the live OMIM record before automated ingestion.
Gene: NDRG1; Ensembl ENSG00000104419. (OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1)
Orphanet: generally represented under rare hereditary motor and sensory neuropathy/CMT4 classifications; a stable subtype-specific ORPHA number was not established from the retrieved primary evidence.
ICD-10: no dedicated CMT4D code; typically coded under G60.0, hereditary motor and sensory neuropathy.
ICD-11: classified under hereditary neuropathies rather than a reliably subtype-specific billable code.
MeSH: Charcot-Marie-Tooth Disease; no separate CMT4D MeSH descriptor was established.

The information summarized here is aggregated disease-level evidence from publications and curated resources, not individual-level EHR data. Some original publications describe individual patients or pedigrees, but no patient-level records were accessed.

2. Etiology, risk, protection, and environment

Primary cause

The necessary cause is biallelic germline pathogenic variation in NDRG1, usually producing loss of NDRG1 function. Open Targets identifies NDRG1 as the sole associated target in its CMT4D record. (OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1)

The best-known founder allele is the Lom nonsense variant, conventionally reported as p.Arg148Ter (p.R148X). One retrieved review rendered the common allele as “p.P148X”; because that conflicts with the established Arg148Ter notation, the genomic/transcript-level HGVS should be checked against the chosen MANE transcript before database loading. The 2022 review reports ten distinct disease-associated mutations and identifies this early stop allele as the most common. (jiang2022aberrantneuregulin1erbb pages 1-2)

Other reported NDRG1 disease alleles include nonsense, missense, frameshift, and splice-altering variants. A 2023 Iranian 80-gene-panel study reported a novel splice-region variant, c.205+1delG, in a patient classified as CMT4D, illustrating that the disorder is not restricted to the Lom founder allele. Classification and population frequency must be assigned variant by variant using current ClinVar/gnomAD and transcript data rather than inferred from the disease label.

Risk factors

Genetic: two pathogenic NDRG1 alleles; carrier parents; affected siblings; consanguinity; and ancestry from a founder population increase prior probability.
Family history: because inheritance is recessive, family history may be absent, and affected siblings can occur with unaffected parents.
Population: Romani ancestry is an ascertainment clue, not a diagnostic requirement. The founder haplotype has been demonstrated across multiple European Romani populations. (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13, муртазина2019современныеклиникогенетическиепредставления pages 12-13)
Sex: males and females are expected to be affected equally.
Age: age changes clinical expression, not inherited risk; neuropathy usually becomes evident in childhood, while deafness often appears later. (nam2019clinicalandgenetic pages 13-15)

No reproducible environmental cause, infectious trigger, susceptibility locus, modifier gene, or sex-specific risk has been established for CMT4D. No validated genetic or environmental protective factor is known. Data do not support diet, smoking, alcohol, occupation, radiation, pollution, or infection as primary etiologic factors.

Gene–environment considerations

Clinical practice should distinguish causation from aggravation. Neurotoxic drugs, major immobility, injury, and poorly fitted footwear could plausibly worsen function in an existing neuropathy, as in other CMT forms, but subtype-specific gene–environment studies are absent. Avoiding neurotoxic exposure is therefore prudent supportive practice, not proven CMT4D prevention.

3. Phenotypes

Published descriptions consistently support a severe, length-dependent motor-sensory neuropathy, but sufficiently large cohorts for reliable percentages are unavailable.

Phenotype	Type, timing, course, and impact	Suggested HPO term
Distal lower-limb weakness	Clinical sign; first decade; progressive; initially feet/legs; causes tripping and impaired walking	Distal muscle weakness, HP:0002460
Distal muscle atrophy	Sign; progressive, lower limbs before hands; reduces endurance and dexterity	Muscle atrophy, HP:0003202
Gait abnormality/foot drop	Sign and functional manifestation; childhood onward; progressive fall risk	Abnormal gait, HP:0001288; Foot drop, HP:0003376
Pes cavus/equinovarus	Musculoskeletal manifestation; develops with muscle imbalance; footwear and mobility burden	Pes cavus, HP:0001761; Talipes equinovarus, HP:0001762
Hand weakness/deformity	Later motor manifestation following lower-limb disease; impairs writing, dressing, and fine motor tasks	Distal upper-limb muscle weakness, HP:0008954
Distal sensory loss	Sign/symptom; progressive; affects touch, vibration, pain, and proprioception; increases unnoticed-injury risk	Distal sensory impairment, HP:0002936; Impaired vibration sensation, HP:0002495
Hyporeflexia/areflexia	Neurologic sign; common and progressive	Areflexia, HP:0001284; Hyporeflexia, HP:0001265
Sensorineural hearing loss/auditory neuropathy	Usually later than motor disease, often becoming evident in the third decade; communication and educational impact	Sensorineural hearing impairment, HP:0000407; Hearing impairment, HP:0000365
Severely reduced nerve-conduction velocity	Electrophysiologic abnormality; may eventually be unrecordable	Reduced motor nerve conduction velocity, HP:0003431
Demyelination/onion bulbs	Pathologic sign; chronic demyelination and remyelination	Segmental peripheral demyelination, HP:0003481

The characteristic sequence is lower-limb onset followed by upper-limb involvement; deafness often develops in the third decade. Nerve conduction can become so severely impaired that responses are unobtainable. Sural-nerve pathology includes loss of myelinated fibers, thin myelin, segmental demyelination/remyelination, axonal loss, and onion-bulb formations. Abnormal brainstem auditory evoked responses support auditory pathway involvement. (jiang2022aberrantneuregulin1erbb pages 1-2, nam2019clinicalandgenetic pages 13-15)

Reports of broader central nervous system involvement exist, but the core phenotype is peripheral neuropathy with hearing impairment; CNS findings should not be treated as universally present. (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13)

No CMT4D-specific EQ-5D, SF-36, PROMIS, or validated quality-of-life cohort was retrieved. Nevertheless, progressive mobility loss, falls, deformity, loss of hand function, sensory injury, and hearing impairment predict substantial effects on education, work, communication, independence, and social participation.

4. Genetic and molecular information

Gene and variation

Gene: NDRG1, N-myc downstream regulated 1; chromosome 8q24; ENSG00000104419. (OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1, nam2019clinicalandgenetic pages 13-15)
Inheritance/origin: autosomal-recessive, constitutional germline; not a somatic cancer disorder.
Functional class: disease is best modeled as loss of function, reducing the Schwann-cell functions needed for peripheral myelin development or maintenance.
Variant classes: nonsense, splice-disrupting, frameshift, and missense alleles have been reported; pathogenicity must be assessed under ACMG/AMP criteria using segregation, population frequency, phenotype, predicted molecular consequence, and functional evidence.
Population frequency: severe CMT4D alleles are expected to be rare in global population databases. The Lom allele is enriched by a Romani founder effect, but a defensible universal carrier frequency was not found.

No validated modifier gene, protective allele, disease-specific methylation signature, histone abnormality, repeat expansion, aneuploidy, translocation, or recurrent large chromosomal rearrangement is established. CMA, karyotyping, FISH, mitochondrial sequencing, and repeat-expansion assays are therefore not first-line subtype tests unless the broader phenotype supplies another indication.

5. Environmental information

CMT4D is not an infectious, toxic, nutritional, occupational, or lifestyle-mediated disease. No pathogen, zoonotic agent, radiation exposure, pollutant, dietary deficiency, alcohol exposure, or smoking association is established. Exercise and rehabilitation can preserve function but do not prevent inheritance or correct NDRG1 deficiency. Clinicians should apply general hereditary-neuropathy precautions concerning foot injury and potentially neurotoxic medications.

6. Mechanism and pathophysiology

Causal chain

Biallelic NDRG1 loss → defective NDRG1-dependent membrane/vesicular and receptor-regulatory functions in myelinating Schwann cells → reduced productive neuregulin-1/ErbB2/ErbB3 signaling despite increased ligand and total receptors → disturbed expression of myelination regulators such as SOX10, OCT6/POU3F1, and EGR2 → inadequate myelin formation or maintenance → repeated demyelination/remyelination, thin myelin and onion bulbs → severe conduction slowing/block → chronic axonal loss → distal weakness, atrophy, sensory loss and deformity. Auditory nerve/pathway involvement produces later hearing impairment. (jiang2022aberrantneuregulin1erbb pages 1-2)

In Ndrg1-deficient sciatic nerve, total ErbB2/ErbB3 and neuregulin-1 are increased, yet phosphorylated ErbB2/3 and downstream signaling are decreased; integrin β4, a positive collaborator of ErbB signaling, is significantly reduced. The authors’ abstract-level conclusion was that the demyelinating phenotype is “at least in part a consequence of molecular defects in neuregulin 1/ErbB signaling.” This is strong model-organism mechanistic evidence but does not establish that this is the only human pathway. (jiang2022aberrantneuregulin1erbb pages 1-2)

Cellular, tissue, and molecular annotations

Primary cell: myelinating Schwann cell — CL:0002573; broader Schwann cell — CL:0000218.
Secondary cell: peripheral sensory and motor neurons/axons; axonal loss is probably downstream of chronic glial dysfunction.
Suggested GO biological processes: peripheral nervous system myelination (GO:0022011); axon ensheathment (GO:0008366); regulation of receptor tyrosine kinase signaling (GO:0050769); vesicle-mediated transport (GO:0016192); neuron–glial cell signaling.
Suggested GO molecular functions/processes: lipid binding (GO:0008289); protein binding; ErbB signaling pathway (GO:0038127).
Suggested GO cellular components: Schwann-cell plasma membrane, cytoplasm, vesicle, myelin sheath (GO:0043209).
Metabolism/immune system: no validated CMT4D metabolomic, lipidomic, inflammatory, autoimmune, or immunodeficiency signature. NDRG1 has broader stress-response and lipid/membrane biology, but these findings should not be overinterpreted as human clinical biomarkers.

No CMT4D-specific human single-cell atlas, spatial-transcriptomic dataset, multi-omic diagnostic classifier, CRISPR screen, circulating proteomic signature, or metabolomic biomarker was found. The most informative molecular profiling currently consists of targeted expression/signaling analysis in mutant mouse nerve.

7. Anatomical structures affected

Organ/system: peripheral nervous system, especially long motor and sensory nerves; auditory nerve/brainstem auditory pathway.
Anatomic distribution: bilateral, length-dependent and usually symmetric; distal legs and feet precede hands and forearms.
Tissues: peripheral nerve, Schwann-cell myelin, axons, and secondarily denervated skeletal muscle.
Representative UBERON suggestions: peripheral nerve, UBERON:0001780; sciatic nerve, UBERON:0001322; sural nerve; skeletal muscle tissue, UBERON:0001134; inner ear, UBERON:0001846.
Subcellular structures: plasma membrane/receptor complexes, vesicular compartments, cytoplasm, and the compact/noncompact myelin apparatus.

The disease is not primarily a muscle disease: muscle wasting is downstream of peripheral denervation. Sural-nerve biopsy findings and the sciatic-nerve mouse phenotype directly support peripheral-nerve localization. (jiang2022aberrantneuregulin1erbb pages 1-2, nam2019clinicalandgenetic pages 13-15)

8. Temporal development

Onset is usually chronic and insidious in the first decade, beginning with distal leg/foot weakness and gait difficulty. Weakness, sensory impairment, and skeletal deformity progress over years to involve upper limbs. Hearing impairment is frequently delayed until adolescence or the third decade. (jiang2022aberrantneuregulin1erbb pages 1-2, nam2019clinicalandgenetic pages 13-15)

CMT4D is lifelong and progressive, not episodic or relapsing-remitting. There is no recognized spontaneous remission. Childhood—before fixed deformity and major axonal loss—is the logical window for rehabilitation and any future molecular therapy, although a disease-specific therapeutic window has not been empirically defined.

9. Inheritance and population

For two carrier parents, each pregnancy has a 25% probability of an affected child, 50% probability of an unaffected carrier, and 25% probability of a child inheriting neither familial allele. Both sexes are affected.

The disorder has a marked founder history in Romani populations, initially Bulgaria and subsequently several European countries. The multicountry mapping study is Chandler et al., Neuromuscular Disorders, December 2000, DOI: https://doi.org/10.1016/S0960-8966(00)00148-6; PMID 11053686. The original clinical delineation, “Hereditary motor and sensory neuropathy-Lom, a novel demyelinating neuropathy associated with deafness in Gypsies,” appeared in Brain in March 1998; PMID 9549516. (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13)

No robust CMT4D-specific prevalence per 100,000, annual incidence, global carrier frequency, age distribution, or sex ratio has been established. Penetrance is generally presumed high for biallelic severe loss-of-function alleles, but formal age-dependent penetrance estimates are unavailable. Expressivity is variable, especially the timing/severity of hearing loss. Anticipation is not expected because CMT4D is not a repeat-expansion disease. Germline mosaicism is theoretically possible but not established as a recurring phenomenon. Consanguinity can increase the probability of biallelic disease alleles.

10. Diagnostics

Clinical and neurophysiologic work-up

Document a three-generation pedigree, ancestry, age at onset, gait/falls, hearing, and neurotoxic exposures.
Neurologic examination: distal strength and wasting, reflexes, sensory modalities, gait, balance, and foot/hand deformity.
Nerve-conduction studies and EMG: expected severe demyelinating-range slowing, low amplitudes when axonal loss is advanced, and potentially unobtainable responses. (nam2019clinicalandgenetic pages 13-15)
Audiology: pure-tone testing, speech discrimination, otoacoustic emissions as appropriate, and auditory brainstem responses when auditory neuropathy is suspected.
Nerve biopsy is rarely required after molecular diagnosis. Historical pathology shows thin myelin, severe myelinated-fiber depletion, onion bulbs, demyelination/remyelination, and axonal loss. (jiang2022aberrantneuregulin1erbb pages 1-2, nam2019clinicalandgenetic pages 13-15)
MRI is not diagnostic but may evaluate atypical CNS findings, spine disease, or alternative causes.

Genetic testing strategy

A hereditary-neuropathy multigene panel that includes NDRG1 is usually the efficient first molecular test after common CMT causes are considered. Testing should detect single-nucleotide variants, small indels, splice variants, and ideally exon-level copy-number changes. If panel testing is negative, trio WES or WGS can identify rare/novel alleles; RNA analysis from an informative tissue may clarify splice variants. Sanger sequencing is appropriate for familial-variant confirmation, segregation, and cascade testing. Targeted founder-variant testing can be efficient in an appropriate Romani family but should not replace broader sequencing when negative.

Molecular diagnosis requires pathogenic/likely pathogenic variants on both alleles in trans. A single heterozygous NDRG1 variant or a VUS does not confirm CMT4D.

Differential diagnosis

Important alternatives include PMP22-related CMT1A, GJB1-related CMTX1, MPZ-related neuropathy, and recessive demyelinating neuropathies due to SH3TC2, GDAP1, MTMR2, SBF2, PRX, and FGD4. Hearing loss also raises MPZ, PMP22, NEFL, GJB1 and other syndromic neuropathies. Acquired chronic inflammatory demyelinating polyneuropathy is distinguished by tempo, inflammatory studies, conduction pattern, treatment response, pedigree, and genetic findings. Distal hereditary motor neuropathy, spinal muscular atrophy, Friedreich ataxia, mitochondrial disease, and treatable metabolic neuropathies should be considered when sensory or systemic findings differ.

There is no population newborn-screening program. Cascade testing of relatives is the practical screening method. Prenatal diagnosis and preimplantation genetic testing are possible after the familial pathogenic variants are known.

11. Outcome and prognosis

CMT4D causes chronic morbidity rather than a defined acute mortality syndrome. Expected burdens include progressive walking difficulty, falls, fixed cavovarus deformity, hand dysfunction, sensory injury, communication impairment from deafness, and possible need for mobility or hearing devices. Recovery of established axonal loss is limited; supportive interventions can improve safety and function but do not reverse the genotype.

No reliable CMT4D-specific five- or ten-year survival, mortality rate, life-expectancy estimate, longitudinal disability curve, or validated prognostic biomarker was identified. Disease-specific prognosis is probably influenced by genotype, childhood severity, degree of axonal loss, deformity, hearing involvement, and access to rehabilitation, but formal prediction models do not exist.

12. Treatment and current applications

Established management

There is no approved NDRG1-directed pharmacotherapy. Current care is multidisciplinary:

physical therapy: low-to-moderate intensity strengthening, stretching, balance, gait and endurance training while avoiding overwork injury;
occupational therapy and adaptive devices for hand weakness and daily activities;
custom footwear, insoles, and ankle–foot orthoses for foot drop, instability and energy-efficient gait;
orthopedic evaluation for progressive cavovarus/equinovarus, tendon imbalance, contracture, or scoliosis; selected patients may need tendon transfer, osteotomy, or fusion;
pain management directed to neuropathic or musculoskeletal pain;
regular skin/foot inspection because sensory loss permits unnoticed injury;
audiology, hearing aids and, in severe cases, assessment for cochlear implantation/auditory rehabilitation;
school, vocational, psychosocial and communication support.

Suggested NCIt intervention concepts include Physical Therapy (C15302), Occupational Therapy, Orthotic Device, Hearing Aid, Cochlear Implantation, Genetic Counseling (C15241), and orthopedic surgery concepts. NCIt identifiers should be checked in the current release before ingestion.

Experimental and recent therapeutic context

A 2023 analysis of the broader CMT trial landscape found 286 registered studies by 2022; 86% were therapeutic, including procedures, drugs, devices and physical therapy, while gene-therapy work remained predominantly preclinical. These figures describe all CMT, not CMT4D, and should not be represented as CMT4D trial counts. DOI: https://doi.org/10.3389/fneur.2023.1251885 (published September 2023).

The ClinicalTrials.gov search performed for this report returned no verified NDRG1/CMT4D-specific interventional trial; apparent hits were unrelated studies caused by nonspecific text matching. Thus, no NCT identifier can responsibly be assigned to a CMT4D therapy.

Conceptually, recessive NDRG1 loss is amenable to Schwann-cell-directed gene replacement, mRNA delivery, or pathway correction. However, no human efficacy or safety data exist. Manipulating NRG1/ErbB signaling is biologically plausible but complex because signaling dose and timing control myelin thickness and Schwann-cell state.

13. Prevention

Primary lifestyle prevention is impossible because the disorder is inherited. Effective reproductive prevention options require informed, nondirective genetic counseling:

carrier and cascade testing for relatives;
partner testing when one familial carrier is known;
preimplantation genetic testing for monogenic disease;
chorionic-villus sampling or amniocentesis for prenatal diagnosis;
use of donor gametes or other reproductive choices.

Secondary prevention comprises early molecular diagnosis, childhood audiologic monitoring, early orthotic/rehabilitation intervention, and surveillance for deformity. Tertiary prevention includes fall prevention, contracture management, skin/foot care, hearing support, pain treatment, and timely orthopedic intervention. Vaccination, anti-infective prophylaxis, sanitation, and environmental remediation have no disease-specific role.

14. Other species and natural disease

No well-established naturally occurring veterinary homolog of human NDRG1-related CMT4D was identified in the retrieved literature. The disease is not transmissible or zoonotic. Orthologous NDRG1 genes are evolutionarily conserved in mammals and other vertebrates, enabling experimental modeling, but induced knockout phenotypes should not be mislabeled as spontaneous animal disease.

15. Model organisms and experimental systems

The principal disease model is the Ndrg1-deficient mouse (Mus musculus, NCBI Taxon 10090). An early model showed progressive demyelination of peripheral nerves (PMID 15082788). A newer knockout deleting exons 4–5 developed early progressive demyelinating neuropathy and limb weakness and reproduced abnormalities in myelin transcription factors and NRG1/ErbB signaling. (jiang2022aberrantneuregulin1erbb pages 1-2, муртазина2019современныеклиникогенетическиепредставленияa pages 12-13)

Recapitulated features: peripheral demyelination, thin/abnormal myelin, progressive weakness, altered Schwann-cell signaling, and myelination-regulator abnormalities.

Applications: defining Schwann-cell-autonomous mechanisms; temporal profiling of demyelination and axonal loss; testing NDRG1 replacement; and evaluating whether restoration of integrin β4/ErbB signaling rescues myelination.

Limitations: mouse lifespan and peripheral-nerve scale differ from humans; later human hearing loss and disability trajectory may not be fully reproduced; complete knockout may not model every hypomorphic missense/splice allele; and treatment timing or vector biodistribution may not translate directly.

Patient-derived fibroblasts, reprogrammed iPSCs, and differentiated Schwann-cell or sensory-neuron co-cultures would be valuable allele-specific systems, but no mature CMT4D organoid, zebrafish, Drosophila, or CRISPR-screen platform with validated human-phenotype recapitulation was identified.

Recent developments and expert interpretation

The most disease-specific recent advance remains Jiang et al., published July 2022, DOI: https://doi.org/10.1128/mcb.00559-21. Its key contribution was moving CMT4D biology from a generic “myelin-maintenance defect” toward a testable Schwann-cell signaling model: NDRG1 deficiency uncouples abundant NRG1/ErbB components from effective receptor phosphorylation and downstream activity, possibly through reduced integrin β4. (jiang2022aberrantneuregulin1erbb pages 1-2)

No major CMT4D-specific 2023–2024 therapeutic or natural-history study was identified. The relevant 2023 development was broader: inherited-neuropathy panels continued to detect geographically diverse NDRG1 variants, while CMT research increasingly pursued gene-targeted approaches. Expert interpretation should therefore remain conservative: CMT4D is mechanistically promising for gene replacement, but present human care is supportive, and subtype-specific natural-history and biomarker studies are prerequisites for a credible therapeutic trial.

Key primary literature and authoritative links

Kalaydjieva et al. Original HMSN-Lom clinical delineation. Brain. March 1998;121:399–408. PMID: 9549516. PubMed: https://pubmed.ncbi.nlm.nih.gov/9549516/ (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13)
Chandler et al. Refined mapping in European Romani families. Neuromuscular Disorders. December 2000;10:584–591. PMID: 11053686. DOI: https://doi.org/10.1016/S0960-8966(00)00148-6 (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13, муртазина2019современныеклиникогенетическиепредставления pages 12-13)
Kalaydjieva et al. NDRG1 identified as the causal gene. PMID: 10831399. PubMed: https://pubmed.ncbi.nlm.nih.gov/10831399/ (OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1)
Okuda et al. Ndrg1-deficient mice exhibit progressive peripheral demyelination. Molecular and Cellular Biology. 2004;24:3949–3956. PMID: 15082788. PubMed: https://pubmed.ncbi.nlm.nih.gov/15082788/ (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13)
Jiang et al. “Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease.” Molecular and Cellular Biology. July 2022;42(7). DOI: https://doi.org/10.1128/mcb.00559-21 (jiang2022aberrantneuregulin1erbb pages 1-2)
Luigetti et al. Clinical, electrophysiological and pathological findings with the Lom mutation. Journal of the Neurological Sciences. October 2014;345:271–273. PMID: 25108819. PubMed: https://pubmed.ncbi.nlm.nih.gov/25108819/ (муртазина2019современныеклиникогенетическиепредставленияa pages 12-13)

Data-quality cautions for knowledge-base ingestion

Phenotype timing and pathology are well supported, but numerical phenotype frequencies cannot be assigned from the retrieved evidence. The MONDO–NDRG1 association is curated and supported by multiple genetic records. (OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1) Variant HGVS, ClinVar status, gnomAD frequency, HGNC identifier, OMIM/Orphanet cross-references, and ontology identifiers should be programmatically revalidated against current database releases. The p.P148X rendering in one review conflicts with the accepted p.Arg148Ter/p.R148X Lom notation and should not be loaded without transcript-level confirmation. Finally, generalized CMT rehabilitation and trial statistics must be tagged as indirect evidence rather than CMT4D-specific efficacy data.

References

(OpenTargets Search: Charcot-Marie-Tooth disease type 4D-NDRG1): Open Targets Query (Charcot-Marie-Tooth disease type 4D-NDRG1, 1 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(nam2019clinicalandgenetic pages 13-15): Soo Hyun Nam and Byung-Ok Choi. Clinical and genetic aspects of charcot-marie-tooth disease subtypes. Jun 2019. URL: https://doi.org/10.23838/pfm.2018.00163, doi:10.23838/pfm.2018.00163. This article has 45 citations.
(муртазина2019современныеклиникогенетическиепредставленияa pages 12-13): АФ Муртазина, ОА Щагина, and СС Никитин. Современные клиникогенетические представления об аутосомнорецессивных наследственных периферических нейропатиях. Unknown journal, 2019.
(муртазина2019современныеклиникогенетическиепредставления pages 12-13): АФ Муртазина, ОА Щагина, and СС Никитин. Современные клиникогенетические представления об аутосомнорецессивных наследственных периферических нейропатиях. Unknown journal, 2019.
(jiang2022aberrantneuregulin1erbb pages 1-2): Li-Ting Jiang, Yu-Hui Chen, Jie-Hong Huang, Wei-Fang Tong, Ling-Jing Jin, and Li-Xi Li. Aberrant neuregulin 1/erbb signaling in charcot-marie-tooth type 4d disease. Jul 2022. URL: https://doi.org/10.1128/mcb.00559-21, doi:10.1128/mcb.00559-21. This article has 7 citations and is from a domain leading peer-reviewed journal.

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Research Objectives

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

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Charcot–Marie–Tooth disease type 4D (CMT4D/HMSN-Lom): comprehensive disease-characteristics report

Executive summary and evidence scope

1. Disease information

Definition and classification

2. Etiology, risk, protection, and environment

Primary cause

Risk factors

Gene–environment considerations

3. Phenotypes

4. Genetic and molecular information

Gene and variation

5. Environmental information

6. Mechanism and pathophysiology

Causal chain

Cellular, tissue, and molecular annotations

7. Anatomical structures affected

8. Temporal development

9. Inheritance and population

10. Diagnostics

Clinical and neurophysiologic work-up

Genetic testing strategy

Differential diagnosis

11. Outcome and prognosis

12. Treatment and current applications

Established management

Experimental and recent therapeutic context

13. Prevention

14. Other species and natural disease

15. Model organisms and experimental systems

Recent developments and expert interpretation

Key primary literature and authoritative links

Data-quality cautions for knowledge-base ingestion

Artifacts

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