| 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 (pqac-00000000). Clinical nomenclature and subtype summary in review excerpt (pqac-00000003). |
| 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 (pqac-00000000). Review summary: homozygous NDRG1 variants on 8q24 cause CMT4D (pqac-00000003). |
| 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 (pqac-00000002, pqac-00000004). Review excerpt notes p.P148X as most common mutation (pqac-00000001). |
| 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 (pqac-00000003). 2022 mechanistic paper summarizes early-onset progressive motor and sensory neuropathy with distal weakness, skeletal/foot deformities, and sensorineural hearing loss (pqac-00000001). |
| 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 (pqac-00000003). 2022 paper summary reports sural nerve biopsy with myelinated fiber loss, thin myelin, and onion bulbs (pqac-00000001). |
| 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 (pqac-00000001). 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 (pqac-00000001) and in review excerpt citing Ndrg1-deficient mice with progressive demyelinating peripheral nerve disorder (pqac-00000002). |
| 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 (pqac-00000003). Broader importance of accurate genetic diagnosis in CMT emphasized in general review DOI: https://doi.org/10.23838/pfm.2018.00163 (pqac-00000003). |
| 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 (pqac-00000002, pqac-00000004). Review notes first description in Bulgarian Romani population (pqac-00000003). |
| 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 (pqac-00000000, pqac-00000001, pqac-00000002, pqac-00000003, pqac-00000004). |


*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.*