Madras Motor Neuron Disease

Neurological Disorder MONDO:0015307 Pathograph 3 Show in embeddings browser Motor Neuron Disease

Madras motor neuron disease (MMND) is a geographically distinctive, predominantly sporadic juvenile/young-adult-onset motor neuron disease reported chiefly from Southern India (originally described in patients from Madras, now Chennai). It is characterized by onset in the young, atrophy and weakness of the limbs from lower-motor-neuron (anterior horn) degeneration, multiple lower cranial nerve palsies (notably the seventh and ninth-to-twelfth, producing facial weakness, tongue wasting and fasciculation, dysarthria and dysphagia), and a hallmark sensorineural hearing loss (auditory neuropathy); a subset (the MMND variant, MMNDV) additionally shows optic atrophy and cerebellar involvement. Compared with amyotrophic lateral sclerosis it has a much younger age of onset and a comparatively benign, slowly progressive course, though clinical heterogeneity exists. The condition is mostly sporadic, with a recognized familial form (FMMND). The etiology remains unknown: sequencing of the riboflavin transporter genes SLC52A1/SLC52A2/SLC52A3 (the cause of the phenotypically overlapping Brown-Vialetto-Van Laere syndrome) and assessment of the C9ORF72 expansion have been negative in MMND series, distinguishing it as a separate clinico-genetic entity whose cause may involve a combination of genetic and environmental factors. Management is supportive and symptomatic; there is no disease-modifying therapy.

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1
Mappings
4
Pathophys.
6
Phenotypes
3
Pathograph
3
Subtypes
2
Differentials
🔗

Mappings

MONDO
MONDO:0015307 Madras motor neuron disease
skos:exactMatch MONDO
Primary MONDO disease identifier for this entry.
◆

Subtypes

3
Sporadic Madras motor neuron disease
The classic, predominantly sporadic form: young-onset limb wasting and weakness, multiple lower cranial nerve palsies and sensorineural hearing loss, with a comparatively benign course.
Madras motor neuron disease variant (MMNDV)
A clinical variant in which optic atrophy is an invariable feature and cerebellar involvement may occur, with a younger age at onset and more consistent bulbar palsy than classic MMND.
Familial Madras motor neuron disease (FMMND)
A recognized familial form of MMND sharing the core phenotype but with a positive family history.
⚙

Pathophysiology

4
Lower Motor Neuron and Anterior Horn Degeneration
The core lesion of MMND is degeneration of lower motor neurons in the spinal anterior horn, producing wasting and weakness of the limbs (predominantly distal) on a background of young onset. Electromyography and nerve conduction studies in MMND patients support lower-motor-neuron involvement, and the clinical picture has features of amyotrophic lateral sclerosis but with a much younger age of onset.
lower motor neuron CL:0008039
motor neuron apoptotic process GO:0097049 ↑ INCREASED
Downstream
Multiple Lower Cranial Nerve (Bulbar) Involvement The same motor-neuronal degeneration extends to lower cranial nerve motor nuclei, producing bulbar dysfunction.
Show evidence (2 references)
PMID:18261745 SUPPORT Human Clinical
"The characteristic features are onset in young, weakness and wasting of limbs, multiple lower cranial nerve palsies and sensorineural hearing"
A 116-patient series defines MMND by young-onset limb wasting and weakness, the clinical correlate of lower-motor-neuron degeneration.
PMID:38854224 SUPPORT Human Clinical
"Neurological examination revealed signs consistent with lower motor neuron involvement."
A case report documents examination findings of lower motor neuron involvement in MMND.
Multiple Lower Cranial Nerve (Bulbar) Involvement
MMND characteristically involves multiple lower cranial nerves, particularly the seventh (facial) and the ninth to twelfth, producing facial weakness, tongue wasting and fasciculation, dysarthria and dysphagia. Bulbar palsy is an invariable feature of the MMND variant and is present in a substantial fraction of classic MMND.
lower motor neuron CL:0008039
motor neuron apoptotic process GO:0097049 ↑ INCREASED
Downstream
Cochlear and Auditory Pathway Involvement Auditory pathway involvement parallels the lower cranial nerve and brainstem pathology, manifesting as sensorineural hearing loss.
Show evidence (2 references)
PMID:12686396 SUPPORT Human Clinical
"multiple cranial nerve palsies particularly the seventh, ninth to twelfth and sensorineural hearing loss"
Defines the characteristic multiple lower cranial nerve palsies of MMND, with the seventh and ninth-to-twelfth nerves particularly affected.
PMID:12686396 SUPPORT Human Clinical
"Bulbar palsy was an invariable feature, being present in all patients compared to 38.3% of MMND"
Bulbar palsy was present in all MMNDV patients and in 38.3% of classic MMND, confirming lower cranial nerve (bulbar) involvement.
Cochlear and Auditory Pathway Involvement
A hallmark and near-universal feature of MMND is sensorineural hearing loss; all patients in the largest series had clinical and/or audiological evidence of hearing impairment, and the deficit has been characterized as an auditory neuropathy. Impaired hearing is frequently among the predominant initial manifestations.
spiral ganglion (auditory) neuron CL:0011113
neuron apoptotic process GO:0051402 ↑ INCREASED
Show evidence (2 references)
PMID:18261745 SUPPORT Human Clinical
"All patients had clinical and/or audiological evidence of hearing impairment."
Every patient in the 116-patient series had clinical and/or audiological hearing impairment, establishing auditory pathway involvement as near-universal in MMND.
PMID:18261745 SUPPORT Human Clinical
"young age of onset and presence of auditory neuropathy"
The hearing loss in MMND is characterized as an auditory neuropathy, implicating the auditory (cochlear) neural pathway.
Unknown Etiology with Negative Riboflavin-Transporter and C9ORF72 Genetics
The cause of MMND remains unknown. Despite phenotypic overlap with Brown-Vialetto-Van Laere syndrome (BVVL), sequencing of the riboflavin transporter genes SLC52A1, SLC52A2 and SLC52A3 in MMND probands and sporadic cases identified no defects, and C9ORF72 repeat expansions were absent (all repeats <10), establishing MMND as a distinct clinico-genetic subgroup. The authors propose that MMND may share a common defective biological pathway with BVVL arising from a combination of genetic and environmental factors. No specific causative gene is asserted here.
Show evidence (2 references)
PMID:24139842 SUPPORT Human Clinical
"We sequenced the SLC52A1, SLC52A2 and SLC52A3 in affected probands and sporadic individuals from the MMND series as well as the C9ORF72 expansion. No genetic defects were identified and the C9ORF72 repeats were all less than 10."
Riboflavin transporter genes and C9ORF72 were assessed and found negative in MMND, supporting an as-yet-unidentified etiology.
PMID:24139842 SUPPORT Human Clinical
"these diseases are likely to share a common defective biological pathway that may be a combination of genetic and environmental factors"
The authors hypothesize a shared defective biological pathway with BVVL driven by combined genetic and environmental factors.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Madras Motor Neuron Disease Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

6
Ear 1
Sensorineural hearing loss Sensorineural hearing impairment HP:0000407
Show evidence (2 references)
PMID:18261745 SUPPORT Human Clinical
"All patients had clinical and/or audiological evidence of hearing impairment."
Every patient in the 116-patient series had clinical and/or audiological hearing impairment.
PMID:12686396 SUPPORT Human Clinical
"multiple cranial nerve palsies particularly the seventh, ninth to twelfth and sensorineural hearing loss"
Sensorineural hearing loss is part of the characteristic MMND clinical profile.
Eye 1
Optic atrophy Optic atrophy HP:0000648
Show evidence (1 reference)
PMID:12686396 SUPPORT Human Clinical
"had the additional features of optic atrophy in all and cerebellar involvement in three of them"
Optic atrophy was present in all patients of the MMND variant series.
Musculoskeletal 2
Limb muscle weakness Distal muscle weakness HP:0002460
Show evidence (1 reference)
PMID:38854224 SUPPORT Human Clinical
"gradually progressive weakness of all four limbs, wasting, tongue fasciculation, and bilateral sensorineural hearing loss"
Case report documents progressive four-limb weakness in MMND.
Limb muscle atrophy Skeletal muscle atrophy HP:0003202
Show evidence (1 reference)
PMID:12686396 SUPPORT Human Clinical
"onset in the young, atrophy and weakness of the limbs"
MMND is characterized by atrophy and weakness of the limbs.
Other 2
Bulbar palsy Bulbar palsy HP:0001283
Show evidence (1 reference)
PMID:12686396 SUPPORT Human Clinical
"Bulbar palsy was an invariable feature, being present in all patients compared to 38.3% of MMND"
Bulbar palsy was invariable in MMNDV and present in 38.3% of classic MMND.
Tongue fasciculations Tongue fasciculations HP:0001308
Show evidence (1 reference)
PMID:38854224 SUPPORT Human Clinical
"weakness of all four limbs, wasting, tongue fasciculation, and bilateral sensorineural hearing loss"
Tongue fasciculation documented on examination in an MMND case.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Madras Motor Neuron Disease:

Amyotrophic lateral sclerosis MONDO:0004976
Overlapping Features ALS shares motor neuron degeneration but typically has a much later age of onset and lacks the characteristic sensorineural hearing loss; MMND resembles ALS clinically but presents in the young with auditory neuropathy.
Brown-Vialetto-Van Laere syndrome MONDO:0024537
Overlapping Features BVVL is a childhood motor neuron disease with bulbar palsy and sensorineural hearing loss that overlaps phenotypically with MMND but is caused by riboflavin transporter (SLC52A2/SLC52A3) defects, which are absent in MMND.
{ }

Source YAML

click to show 
name: Madras Motor Neuron Disease
creation_date: "2026-06-26T00:00:00Z"
description: >-
  Madras motor neuron disease (MMND) is a geographically distinctive, predominantly
  sporadic juvenile/young-adult-onset motor neuron disease reported chiefly from
  Southern India (originally described in patients from Madras, now Chennai). It is
  characterized by onset in the young, atrophy and weakness of the limbs from
  lower-motor-neuron (anterior horn) degeneration, multiple lower cranial nerve palsies
  (notably the seventh and ninth-to-twelfth, producing facial weakness, tongue wasting
  and fasciculation, dysarthria and dysphagia), and a hallmark sensorineural hearing
  loss (auditory neuropathy); a subset (the MMND variant, MMNDV) additionally shows
  optic atrophy and cerebellar involvement. Compared with amyotrophic lateral sclerosis
  it has a much younger age of onset and a comparatively benign, slowly progressive
  course, though clinical heterogeneity exists. The condition is mostly sporadic, with a
  recognized familial form (FMMND). The etiology remains unknown: sequencing of the
  riboflavin transporter genes SLC52A1/SLC52A2/SLC52A3 (the cause of the
  phenotypically overlapping Brown-Vialetto-Van Laere syndrome) and assessment of the
  C9ORF72 expansion have been negative in MMND series, distinguishing it as a separate
  clinico-genetic entity whose cause may involve a combination of genetic and
  environmental factors. Management is supportive and symptomatic; there is no
  disease-modifying therapy.
category: Neurological Disorder
disease_term:
  preferred_term: Madras motor neuron disease
  term:
    id: MONDO:0015307
    label: Madras motor neuron disease
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0015307
      label: Madras motor neuron disease
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: Primary MONDO disease identifier for this entry.
synonyms:
- MMND
- Madras pattern motor neuron disease
parents:
- Motor Neuron Disease
has_subtypes:
- name: Sporadic MMND
  display_name: Sporadic Madras motor neuron disease
  description: >-
    The classic, predominantly sporadic form: young-onset limb wasting and weakness,
    multiple lower cranial nerve palsies and sensorineural hearing loss, with a
    comparatively benign course.
- name: MMNDV
  display_name: Madras motor neuron disease variant (MMNDV)
  description: >-
    A clinical variant in which optic atrophy is an invariable feature and cerebellar
    involvement may occur, with a younger age at onset and more consistent bulbar palsy
    than classic MMND.
- name: FMMND
  display_name: Familial Madras motor neuron disease (FMMND)
  description: >-
    A recognized familial form of MMND sharing the core phenotype but with a positive
    family history.
pathophysiology:
- name: Lower Motor Neuron and Anterior Horn Degeneration
  description: >-
    The core lesion of MMND is degeneration of lower motor neurons in the spinal
    anterior horn, producing wasting and weakness of the limbs (predominantly distal)
    on a background of young onset. Electromyography and nerve conduction studies in
    MMND patients support lower-motor-neuron involvement, and the clinical picture has
    features of amyotrophic lateral sclerosis but with a much younger age of onset.
  cell_types:
  - preferred_term: lower motor neuron
    term:
      id: CL:0008039
      label: lower motor neuron
  biological_processes:
  - preferred_term: motor neuron apoptotic process
    modifier: INCREASED
    term:
      id: GO:0097049
      label: motor neuron apoptotic process
  evidence:
  - reference: PMID:18261745
    reference_title: "Madras motor neuron disease (MMND): clinical description and survival pattern of 116 patients from Southern India seen over 36 years (1971-2007)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The characteristic features are onset in young, weakness and wasting of limbs, multiple lower cranial nerve palsies and sensorineural hearing"
    explanation: >-
      A 116-patient series defines MMND by young-onset limb wasting and weakness, the
      clinical correlate of lower-motor-neuron degeneration.
  - reference: PMID:38854224
    reference_title: "Unveiling a Rare Case: Madras Motor Neuron Disease in an 18-Year-Old Patient."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological examination revealed signs consistent with lower motor neuron involvement."
    explanation: >-
      A case report documents examination findings of lower motor neuron involvement in
      MMND.
  downstream:
  - target: Multiple Lower Cranial Nerve (Bulbar) Involvement
    description: >-
      The same motor-neuronal degeneration extends to lower cranial nerve motor nuclei,
      producing bulbar dysfunction.
- name: Multiple Lower Cranial Nerve (Bulbar) Involvement
  description: >-
    MMND characteristically involves multiple lower cranial nerves, particularly the
    seventh (facial) and the ninth to twelfth, producing facial weakness, tongue wasting
    and fasciculation, dysarthria and dysphagia. Bulbar palsy is an invariable feature
    of the MMND variant and is present in a substantial fraction of classic MMND.
  cell_types:
  - preferred_term: lower motor neuron
    term:
      id: CL:0008039
      label: lower motor neuron
  biological_processes:
  - preferred_term: motor neuron apoptotic process
    modifier: INCREASED
    term:
      id: GO:0097049
      label: motor neuron apoptotic process
  evidence:
  - reference: PMID:12686396
    reference_title: "Madras motor neuron disease variant, clinical features of seven patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "multiple cranial nerve palsies particularly the seventh, ninth to twelfth and sensorineural hearing loss"
    explanation: >-
      Defines the characteristic multiple lower cranial nerve palsies of MMND, with the
      seventh and ninth-to-twelfth nerves particularly affected.
  - reference: PMID:12686396
    reference_title: "Madras motor neuron disease variant, clinical features of seven patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bulbar palsy was an invariable feature, being present in all patients compared to 38.3% of MMND"
    explanation: >-
      Bulbar palsy was present in all MMNDV patients and in 38.3% of classic MMND,
      confirming lower cranial nerve (bulbar) involvement.
  downstream:
  - target: Cochlear and Auditory Pathway Involvement
    description: >-
      Auditory pathway involvement parallels the lower cranial nerve and brainstem
      pathology, manifesting as sensorineural hearing loss.
- name: Cochlear and Auditory Pathway Involvement
  description: >-
    A hallmark and near-universal feature of MMND is sensorineural hearing loss; all
    patients in the largest series had clinical and/or audiological evidence of hearing
    impairment, and the deficit has been characterized as an auditory neuropathy.
    Impaired hearing is frequently among the predominant initial manifestations.
  cell_types:
  - preferred_term: spiral ganglion (auditory) neuron
    term:
      id: CL:0011113
      label: spiral ganglion neuron
  biological_processes:
  - preferred_term: neuron apoptotic process
    modifier: INCREASED
    term:
      id: GO:0051402
      label: neuron apoptotic process
  evidence:
  - reference: PMID:18261745
    reference_title: "Madras motor neuron disease (MMND): clinical description and survival pattern of 116 patients from Southern India seen over 36 years (1971-2007)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients had clinical and/or audiological evidence of hearing impairment."
    explanation: >-
      Every patient in the 116-patient series had clinical and/or audiological hearing
      impairment, establishing auditory pathway involvement as near-universal in MMND.
  - reference: PMID:18261745
    reference_title: "Madras motor neuron disease (MMND): clinical description and survival pattern of 116 patients from Southern India seen over 36 years (1971-2007)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "young age of onset and presence of auditory neuropathy"
    explanation: >-
      The hearing loss in MMND is characterized as an auditory neuropathy, implicating
      the auditory (cochlear) neural pathway.
- name: Unknown Etiology with Negative Riboflavin-Transporter and C9ORF72 Genetics
  description: >-
    The cause of MMND remains unknown. Despite phenotypic overlap with
    Brown-Vialetto-Van Laere syndrome (BVVL), sequencing of the riboflavin transporter
    genes SLC52A1, SLC52A2 and SLC52A3 in MMND probands and sporadic cases identified no
    defects, and C9ORF72 repeat expansions were absent (all repeats <10), establishing
    MMND as a distinct clinico-genetic subgroup. The authors propose that MMND may share
    a common defective biological pathway with BVVL arising from a combination of genetic
    and environmental factors. No specific causative gene is asserted here.
  evidence:
  - reference: PMID:24139842
    reference_title: "Madras motor neuron disease (MMND) is distinct from the riboflavin transporter genetic defects that cause Brown-Vialetto-Van Laere syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We sequenced the SLC52A1, SLC52A2 and SLC52A3 in affected probands and sporadic individuals from the MMND series as well as the C9ORF72 expansion. No genetic defects were identified and the C9ORF72 repeats were all less than 10."
    explanation: >-
      Riboflavin transporter genes and C9ORF72 were assessed and found negative in MMND,
      supporting an as-yet-unidentified etiology.
  - reference: PMID:24139842
    reference_title: "Madras motor neuron disease (MMND) is distinct from the riboflavin transporter genetic defects that cause Brown-Vialetto-Van Laere syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "these diseases are likely to share a common defective biological pathway that may be a combination of genetic and environmental factors"
    explanation: >-
      The authors hypothesize a shared defective biological pathway with BVVL driven by
      combined genetic and environmental factors.
phenotypes:
- name: Limb muscle weakness
  category: Neuromuscular
  description: >-
    Weakness of the limbs, predominantly distal, reflecting lower-motor-neuron
    degeneration.
  phenotype_term:
    preferred_term: Distal muscle weakness
    term:
      id: HP:0002460
      label: Distal muscle weakness
  evidence:
  - reference: PMID:38854224
    reference_title: "Unveiling a Rare Case: Madras Motor Neuron Disease in an 18-Year-Old Patient."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "gradually progressive weakness of all four limbs, wasting, tongue fasciculation, and bilateral sensorineural hearing loss"
    explanation: >-
      Case report documents progressive four-limb weakness in MMND.
- name: Limb muscle atrophy
  category: Neuromuscular
  description: Wasting of limb muscles from anterior horn cell loss.
  phenotype_term:
    preferred_term: Skeletal muscle atrophy
    term:
      id: HP:0003202
      label: Skeletal muscle atrophy
  evidence:
  - reference: PMID:12686396
    reference_title: "Madras motor neuron disease variant, clinical features of seven patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "onset in the young, atrophy and weakness of the limbs"
    explanation: >-
      MMND is characterized by atrophy and weakness of the limbs.
- name: Bulbar palsy
  category: Neurologic
  description: >-
    Lower cranial nerve dysfunction producing dysarthria and dysphagia; an invariable
    feature of the MMND variant.
  phenotype_term:
    preferred_term: Bulbar palsy
    term:
      id: HP:0001283
      label: Bulbar palsy
  evidence:
  - reference: PMID:12686396
    reference_title: "Madras motor neuron disease variant, clinical features of seven patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bulbar palsy was an invariable feature, being present in all patients compared to 38.3% of MMND"
    explanation: >-
      Bulbar palsy was invariable in MMNDV and present in 38.3% of classic MMND.
- name: Sensorineural hearing loss
  category: Neurologic
  description: >-
    A hallmark feature of MMND; nearly all patients have clinical and/or audiological
    hearing impairment, characterized as an auditory neuropathy.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:18261745
    reference_title: "Madras motor neuron disease (MMND): clinical description and survival pattern of 116 patients from Southern India seen over 36 years (1971-2007)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients had clinical and/or audiological evidence of hearing impairment."
    explanation: >-
      Every patient in the 116-patient series had clinical and/or audiological hearing
      impairment.
  - reference: PMID:12686396
    reference_title: "Madras motor neuron disease variant, clinical features of seven patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "multiple cranial nerve palsies particularly the seventh, ninth to twelfth and sensorineural hearing loss"
    explanation: >-
      Sensorineural hearing loss is part of the characteristic MMND clinical profile.
- name: Tongue fasciculations
  category: Neurologic
  description: Fasciculations of the tongue reflecting hypoglossal lower-motor-neuron involvement.
  phenotype_term:
    preferred_term: Tongue fasciculations
    term:
      id: HP:0001308
      label: Tongue fasciculations
  evidence:
  - reference: PMID:38854224
    reference_title: "Unveiling a Rare Case: Madras Motor Neuron Disease in an 18-Year-Old Patient."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "weakness of all four limbs, wasting, tongue fasciculation, and bilateral sensorineural hearing loss"
    explanation: >-
      Tongue fasciculation documented on examination in an MMND case.
- name: Optic atrophy
  category: Ophthalmologic
  description: >-
    Optic atrophy, an invariable feature of the MMND variant (MMNDV), reflecting optic
    nerve involvement.
  phenotype_term:
    preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
  evidence:
  - reference: PMID:12686396
    reference_title: "Madras motor neuron disease variant, clinical features of seven patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "had the additional features of optic atrophy in all and cerebellar involvement in three of them"
    explanation: >-
      Optic atrophy was present in all patients of the MMND variant series.
differential_diagnoses:
- name: Amyotrophic lateral sclerosis
  description: >-
    ALS shares motor neuron degeneration but typically has a much later age of onset and
    lacks the characteristic sensorineural hearing loss; MMND resembles ALS clinically
    but presents in the young with auditory neuropathy.
  disease_term:
    preferred_term: amyotrophic lateral sclerosis
    term:
      id: MONDO:0004976
      label: amyotrophic lateral sclerosis
- name: Brown-Vialetto-Van Laere syndrome
  description: >-
    BVVL is a childhood motor neuron disease with bulbar palsy and sensorineural hearing
    loss that overlaps phenotypically with MMND but is caused by riboflavin transporter
    (SLC52A2/SLC52A3) defects, which are absent in MMND.
  disease_term:
    preferred_term: Brown-Vialetto-van Laere syndrome 1
    term:
      id: MONDO:0024537
      label: Brown-Vialetto-van Laere syndrome 1
notes: >-
  MMND is rare (fewer than ~200 reported cases, predominantly from Southern India). Mean
  age of onset is in the mid-teens. A familial form (FMMND) is recognized alongside the
  predominantly sporadic disease. The etiology is unknown; no specific causative gene is
  asserted in this entry because none is established in the literature reviewed. The
  comparatively benign/slowly progressive course described in early reports contrasts
  with occasional reports of more rapid deterioration, reflecting clinical heterogeneity.