Kennedy Disease

Mendelian MONDO:0010735 Pathograph 6 Show in embeddings browser Neurodegenerative Disorders Trinucleotide Repeat Disorders Motor Neuron Diseases

Kennedy disease, also known as spinal and bulbar muscular atrophy (SBMA), is a rare X-linked recessive adult-onset lower motor neuron disease caused by an expanded CAG trinucleotide repeat in exon 1 of the androgen receptor (AR) gene on Xq12. The expansion encodes an abnormally long polyglutamine (polyQ) tract in the androgen receptor protein. In an androgen-dependent, gain-of-function manner the mutant polyQ-AR misfolds, accumulates in the nucleus, and causes progressive degeneration of bulbar and spinal lower motor neurons and primary myopathic changes in skeletal muscle. Affected men present in midlife with slowly progressive proximal limb and bulbar weakness, muscle atrophy, fasciculations, muscle cramps, tremor, and signs of mild androgen insensitivity such as gynecomastia and reduced fertility. Female carriers are usually asymptomatic or only mildly affected.

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1
Inheritance
6
Pathophys.
14
Phenotypes
6
Pathograph
1
Genes
4
Medical Actions
3
Trials
1
References
1
Deep Research
👪

Inheritance

1
X-linked recessive HP:0001419
X-linked recessive inheritance
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"SBMA is inherited in an X-linked manner."
The GeneReviews chapter establishes X-linked inheritance for SBMA.
⚙

Pathophysiology

6
Polyglutamine-expanded androgen receptor toxicity
CAG repeat expansion in AR exon 1 produces an androgen receptor with an elongated polyglutamine tract. Upon ligand (testosterone/DHT) binding the mutant receptor translocates to the nucleus, misfolds, and accumulates, exerting an androgen-dependent toxic gain of function.
Lower motor neuron CL:0008039
Androgen receptor signaling pathway GO:0030521
Downstream
Nuclear inclusion formation and impaired proteostasis Nuclear accumulation of the misfolded polyQ-AR drives formation of nuclear inclusions and impairs proteostasis.
Skeletal muscle as a primary site of toxicity Androgen-dependent polyQ-AR toxicity acts directly within skeletal muscle as an early and primary site of disease.
Motor neuron degeneration PolyQ-AR toxicity ultimately drives degeneration of lower motor neurons via proteostatic stress and downstream cellular dysfunction.
Show evidence (2 references)
PMID:32934110 SUPPORT Human Clinical
"Androgen-dependent nuclear accumulation of the polyglutamine-expanded AR is an essential step in the pathogenesis, providing therapeutic opportunities via hormonal manipulation and gene silencing with antisense oligonucleotides."
Establishes that androgen-dependent nuclear accumulation of the polyglutamine-expanded androgen receptor is the essential pathogenic step.
PMID:36746939 SUPPORT Model Organism
"Androgen binding to polyQ-expanded androgen receptor triggers SBMA through a combination of toxic gain-of-function and loss-of-function mechanisms."
Confirms the combined toxic gain-of-function plus partial loss-of-function mechanism triggered by androgen binding.
Nuclear inclusion formation and impaired proteostasis
The misfolded polyQ androgen receptor forms nuclear inclusions and impairs the ubiquitin-proteasome system and protein quality control, contributing to motor neuron dysfunction.
Lower motor neuron CL:0008039
Inclusion body assembly GO:0070841 Ubiquitin-dependent protein catabolic process GO:0006511 ↓ DECREASED
Downstream
Motor neuron degeneration Nuclear inclusions and impaired proteostasis contribute to motor neuron dysfunction and progressive degeneration.
Show evidence (1 reference)
PMID:32934110 SUPPORT Model Organism
"Animal studies also suggest that hyperactivation of Src, alteration of autophagy and a mitochondrial deficit underlie the neuromuscular degeneration in SBMA and provide alternative therapeutic targets."
Supports altered autophagy/protein quality control (alongside Src and mitochondrial deficits) as a downstream mechanism of neuromuscular degeneration in SBMA.
Skeletal muscle as a primary site of toxicity
Beyond lower motor neuron loss, skeletal muscle is directly affected, with loss of fast-twitch type 2 fibres, increase in slow-twitch type 1 fibres, and a glycolytic-to-oxidative metabolic switch, indicating muscle is an early and primary site of androgen-dependent toxicity.
Skeletal muscle fiber CL:0000188
Skeletal muscle fiber type switching GO:0014883
Downstream
Disrupted muscle energy metabolism The glycolytic-to-oxidative fibre-type switch and primary muscle toxicity drive disrupted NAD+-dependent muscle energy metabolism.
Show evidence (1 reference)
PMID:32934110 SUPPORT Human Clinical
"pathology of patients and animal models also indicates involvement of skeletal muscle including loss of fast-twitch type 2 fibres and increased slow-twitch type 1 fibres, together with a glycolytic-to-oxidative metabolic switch."
Documents direct skeletal muscle involvement with fast-to-slow fibre-type switching and a glycolytic-to-oxidative metabolic shift in SBMA.
Disrupted muscle energy metabolism
SBMA skeletal muscle shows decreased NAD+ and ATP and alterations in NAD+-dependent energy pathways and the NAD+ salvage pathway, with reduced nicotinamide riboside kinase 2 (Nmrk2), contributing to impaired muscle bioenergetics.
Skeletal muscle fiber CL:0000188
NAD biosynthetic process GO:0009435 ↓ DECREASED
Show evidence (1 reference)
PMID:38452174 SUPPORT Model Organism
"these data suggest a model in which NAD+ levels are significantly decreased in muscles of an SBMA mouse model and intransigent to NR supplementation because of decreased levels of Nmrk2."
Demonstrates decreased NAD+ and disrupted NAD+ salvage (low Nmrk2) in SBMA muscle, evidence from a transgenic mouse model.
LSD1/PRMT6 co-regulator amplification of AR toxicity
The androgen receptor co-regulators LSD1 and PRMT6 are overexpressed in an androgen-dependent manner in SBMA skeletal muscle and synergistically enhance androgen receptor transactivation, an effect amplified by the expanded polyglutamine tract, identifying a modifier axis of AR toxic gain of function.
Skeletal muscle fiber CL:0000188
Androgen receptor signaling pathway GO:0030521 ↑ INCREASED
Downstream
Polyglutamine-expanded androgen receptor toxicity LSD1 and PRMT6 synergistically enhance androgen receptor transactivation, amplifying the polyQ-AR toxic gain of function.
Show evidence (2 references)
PMID:36746939 SUPPORT Human Clinical
"androgen receptor co-regulators lysine-specific demethylase 1 (LSD1) and protein arginine methyltransferase 6 (PRMT6) are overexpressed in an androgen-dependent manner specifically in the skeletal muscle of SBMA patients and mice."
Identifies LSD1 and PRMT6 as androgen-dependent co-regulators overexpressed in SBMA muscle that amplify AR transactivation.
PMID:36746939 SUPPORT Model Organism
"Pharmacological and genetic silencing of LSD1 and PRMT6 attenuates polyQ-expanded androgen receptor transactivation in SBMA cells and suppresses toxicity in SBMA flies, and a preclinical approach based on miRNA-mediated silencing of LSD1 and PRMT6 attenuates disease manifestations in SBMA mice."
Silencing LSD1/PRMT6 reduces AR toxicity in SBMA flies and mice, supporting their role as modifiers and therapeutic targets.
Motor neuron degeneration
Progressive degeneration and loss of bulbar and spinal lower motor neurons leads to denervation, muscle weakness, and atrophy.
Spinal cord motor neuron CL:0011001
Apoptotic process GO:0006915 ↑ INCREASED
Show evidence (1 reference)
PMID:32934110 SUPPORT Human Clinical
"In the central nervous system, lower motor neurons are selectively affected"
Establishes selective lower motor neuron involvement in the central nervous system as the core neurodegenerative feature of SBMA.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Kennedy 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

14
Breast 1
Gynecomastia Gynecomastia HP:0000771
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"Affected individuals often show gynecomastia, testicular atrophy, and reduced fertility as a result of mild androgen insensitivity."
GeneReviews attributes gynecomastia in SBMA to mild androgen insensitivity from reduced androgen receptor function.
Digestive 1
Dysphagia Dysphagia HP:0002015
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"standard treatments for dysarthria and dysphagia"
GeneReviews lists dysphagia among the bulbar manifestations of SBMA requiring standard management.
Metabolism 1
Elevated creatine kinase Elevated circulating creatine kinase concentration HP:0003236
Musculoskeletal 2
Proximal muscle weakness Muscle weakness HP:0001324
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"degeneration of lower motor neurons results in muscle weakness, muscle atrophy, and fasciculations in affected males."
GeneReviews lists progressive muscle weakness as a core manifestation of lower motor neuron degeneration in SBMA.
Skeletal muscle atrophy Skeletal muscle atrophy HP:0003202
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"degeneration of lower motor neurons results in muscle weakness, muscle atrophy, and fasciculations in affected males."
GeneReviews lists muscle atrophy as a core manifestation of SBMA.
Nervous System 3
Dysarthria Dysarthria HP:0001260
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"standard treatments for dysarthria and dysphagia"
GeneReviews lists dysarthria among the bulbar manifestations of SBMA requiring standard management.
Fasciculations Fasciculations HP:0002380
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"degeneration of lower motor neurons results in muscle weakness, muscle atrophy, and fasciculations in affected males."
GeneReviews lists fasciculations as a manifestation of lower motor neuron degeneration in SBMA.
Sensory neuropathy Sensory neuropathy HP:0000763
Show evidence (1 reference)
PMID:19846582 SUPPORT Human Clinical
"Sensory nerve action potentials were reduced in nearly all subjects."
A 57-patient natural history cohort found reduced sensory nerve action potentials in nearly all subjects, indicating sensory neuropathy.
Other 6
Bulbar weakness Bulbar signs HP:0002483
Show evidence (1 reference)
PMID:37360345 SUPPORT Human Clinical
"characterized by the degeneration of lower motor neurons in the spinal cord and brainstem and neurogenic atrophy of the skeletal muscle."
Brainstem (bulbar) lower motor neuron degeneration underlies the bulbar weakness characteristic of SBMA.
Tongue atrophy Tongue atrophy HP:0012473
Postural tremor Postural tremor HP:0002174
Show evidence (1 reference)
PMID:32934110 SUPPORT Human Clinical
"followed by the emergence of hand tremor, a prodromal sign of the disease."
Hand tremor is described as a prodromal sign of SBMA, supporting postural hand tremor as an early phenotype.
Reduced fertility Decreased fertility in males HP:0012041
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"Affected individuals often show gynecomastia, testicular atrophy, and reduced fertility as a result of mild androgen insensitivity."
GeneReviews documents reduced fertility and testicular atrophy in SBMA as consequences of mild androgen insensitivity.
Testicular atrophy Testicular atrophy HP:0000029
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"Affected individuals often show gynecomastia, testicular atrophy, and reduced fertility as a result of mild androgen insensitivity."
GeneReviews lists testicular atrophy as an androgen-insensitivity manifestation of SBMA.
Cardiac repolarization abnormalities Abnormal EKG HP:0003115
Show evidence (1 reference)
PMID:35132468 SUPPORT Human Clinical
"Abnormal ECGs were recorded in 70%, consisting of a Brugada ECG pattern, early repolarization or fragmented QRS."
In a 30-patient SBMA cohort, 70% had abnormal ECGs, supporting cardiac repolarization abnormalities as a feature of SBMA.
🧬

Genetic Associations

1
AR (Causative)
Gene: AR hgnc:644
X-linked recessive
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"identification of a hemizygous expansion of a CAG trinucleotide repeat (>35 CAGs) in AR by molecular genetic testing."
GeneReviews establishes that SBMA is caused by a CAG trinucleotide repeat expansion (>35 CAGs) in the AR gene.
💊

Medical Actions

4
Supportive and rehabilitative care
Action: supportive care MAXO:0000950
No disease-modifying therapy is approved. Management is supportive, including braces and walkers for ambulation, standard treatments for dysarthria and dysphagia, breast reduction surgery for gynecomastia as needed, and psychosocial support. Agents/circumstances to avoid: based on animal studies, administration of testosterone and its analogs may worsen motor neuron disease and should be avoided.
Show evidence (1 reference)
PMID:20301508 SUPPORT Model Organism
"Based on animal studies, administration of testosterone and its analogs may worsen motor neuron disease."
GeneReviews flags testosterone and androgen analogs as agents to avoid in SBMA because animal studies indicate they may worsen motor neuron disease.
Genetic counseling
Action: Genetic Counseling NCIT:C15240
Genetic counseling for the X-linked recessive inheritance pattern, carrier testing, and reproductive options.
Show evidence (1 reference)
PMID:20301508 SUPPORT Human Clinical
"Carrier testing for at-risk female relatives and prenatal testing for a pregnancy at increased risk are possible if the expanded CAG repeat has been identified in an affected family member."
GeneReviews supports genetic counseling, carrier testing, and prenatal testing for at-risk family members in SBMA.
Antisense oligonucleotide AR-lowering therapy (experimental)
Action: Pharmacotherapy NCIT:C15986
Because androgen-dependent toxicity is driven by the toxic AR protein, lowering AR levels with antisense oligonucleotides is an actively investigated disease-modifying strategy. ASOs are in development for SBMA; no AR-targeting ASO is yet approved.
Show evidence (2 references)
PMID:32934110 SUPPORT Human Clinical
"providing therapeutic opportunities via hormonal manipulation and gene silencing with antisense oligonucleotides."
Identifies antisense oligonucleotide gene silencing of AR as a rational therapeutic strategy in SBMA.
PMID:38732027 SUPPORT Other
"ASOs are being developed for the treatment of motor neuron diseases (MNDs), including spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS) and spinal and bulbar muscular atrophy (SBMA)."
Confirms that ASOs are under development for SBMA among motor neuron diseases.
Hormonal (androgen) modulation (investigational)
Action: Pharmacotherapy NCIT:C15986
Strategies to reduce androgen action on the mutant receptor (e.g., leuprorelin/leuprolide, dutasteride) have been tested. Leuprorelin showed benefit in dysphagia in Japan but a Phase 3 trial failed to confirm overall benefit; these remain investigational outside Japan. Note that the relationship between androgens and muscle is complex, as testosterone levels correlate positively with muscle strength in patients.
Show evidence (1 reference)
PMID:19846582 PARTIAL Human Clinical
"The direct correlation of testosterone levels with muscle strength indicates that androgens may have a positive effect on muscle function in spinal and bulbar muscular atrophy patients, in addition to the toxic effects described in animal models."
Indicates the androgen-muscle relationship is complex: androgen modulation may help via reducing toxic gain of function, but testosterone also correlates positively with muscle strength, complicating hormonal therapy.
🔬

Clinical Trials

3
NCT00303446 PHASE_II COMPLETED
Randomized, placebo-controlled trial of the 5-alpha-reductase inhibitor dutasteride, which lowers dihydrotestosterone (DHT), to test whether reducing androgen signaling improves strength and function in SBMA.
Show evidence (1 reference)
clinicaltrials:NCT00303446 SUPPORT Human Clinical
"Dutasteride decreases DHT production. Lowering DHT levels may decrease the harmful effects of DHT to the nerves and improve strength in people with SBMA."
The dutasteride trial directly tests the androgen-dependence mechanism by lowering DHT to reduce androgen-driven toxicity in SBMA.
NCT06169046 PHASE_II RECRUITING
Multicenter, randomized, double-blind, placebo-controlled trial of the beta2-agonist clenbuterol targeting skeletal muscle as a therapeutic site in SBMA.
Show evidence (1 reference)
clinicaltrials:NCT06169046 SUPPORT Human Clinical
"To establish safety and efficacy of clenbuterol as a cure for SBMA, we are conducting a multicenter, phase II, randomized, double-blind, parallel-group, single dose, placebo-controlled trial."
A Phase II clenbuterol trial evaluates beta2-agonist stimulation of muscle as a therapeutic strategy, consistent with muscle being a primary site of SBMA toxicity.
NCT05517603 PHASE_I COMPLETED
First-in-patient, randomized, double-blind, placebo-controlled Phase 1/2a study of AJ201 evaluating safety, tolerability, pharmacokinetics, and pharmacodynamics in adults with SBMA.
Show evidence (1 reference)
clinicaltrials:NCT05517603 SUPPORT Human Clinical
"This is a phase 1/2a randomized, double-blind study to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of study drug AJ201 in subjects with Spinal and Bulbar Muscular Atrophy (SBMA)."
A Phase 1/2a trial of AJ201 represents an emerging disease-modifying therapeutic candidate under clinical evaluation for SBMA.
{ }

Source YAML

click to show 
name: Kennedy Disease
creation_date: "2026-06-03T00:00:00Z"
category: Mendelian
description: >-
  Kennedy disease, also known as spinal and bulbar muscular atrophy (SBMA), is a
  rare X-linked recessive adult-onset lower motor neuron disease caused by an
  expanded CAG trinucleotide repeat in exon 1 of the androgen receptor (AR) gene
  on Xq12. The expansion encodes an abnormally long polyglutamine (polyQ) tract
  in the androgen receptor protein. In an androgen-dependent, gain-of-function
  manner the mutant polyQ-AR misfolds, accumulates in the nucleus, and causes
  progressive degeneration of bulbar and spinal lower motor neurons and primary
  myopathic changes in skeletal muscle. Affected men present in midlife with
  slowly progressive proximal limb and bulbar weakness, muscle atrophy,
  fasciculations, muscle cramps, tremor, and signs of mild androgen insensitivity
  such as gynecomastia and reduced fertility. Female carriers are usually
  asymptomatic or only mildly affected.
disease_term:
  preferred_term: Kennedy disease
  term:
    id: MONDO:0010735
    label: Kennedy disease
parents:
- Neurodegenerative Disorders
- Trinucleotide Repeat Disorders
- Motor Neuron Diseases
references:
- reference: PMID:20301508
  title: "Spinal and Bulbar Muscular Atrophy."
  tags:
  - GeneReviews
inheritance:
- name: X-linked recessive
  inheritance_term:
    preferred_term: X-linked recessive inheritance
    term:
      id: HP:0001419
      label: X-linked recessive inheritance
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SBMA is inherited in an X-linked manner."
    explanation: >-
      The GeneReviews chapter establishes X-linked inheritance for SBMA.
phenotypes:
- name: Proximal muscle weakness
  description: >-
    Slowly progressive, predominantly proximal limb muscle weakness is a core
    feature, typically beginning in midlife in the lower extremities.
  phenotype_term:
    preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      degeneration of lower motor neurons results in muscle weakness, muscle
      atrophy, and fasciculations in affected males.
    explanation: >-
      GeneReviews lists progressive muscle weakness as a core manifestation of
      lower motor neuron degeneration in SBMA.
- name: Bulbar weakness
  description: >-
    Degeneration of bulbar motor neurons produces dysarthria, dysphagia, and
    tongue atrophy with fasciculations.
  phenotype_term:
    preferred_term: Bulbar signs
    term:
      id: HP:0002483
      label: Bulbar signs
  evidence:
  - reference: PMID:37360345
    reference_title: "Long-term effects of the gait treatment using a wearable cyborg hybrid assistive limb in a patient with spinal and bulbar muscular atrophy: a case report with 5 years of follow-up."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      characterized by the degeneration of lower motor neurons in the spinal
      cord and brainstem and neurogenic atrophy of the skeletal muscle.
    explanation: >-
      Brainstem (bulbar) lower motor neuron degeneration underlies the bulbar
      weakness characteristic of SBMA.
- name: Dysphagia
  description: Difficulty swallowing due to bulbar motor neuron involvement.
  phenotype_term:
    preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      standard treatments for dysarthria and dysphagia
    explanation: >-
      GeneReviews lists dysphagia among the bulbar manifestations of SBMA
      requiring standard management.
- name: Dysarthria
  description: Slurred speech from bulbar weakness.
  phenotype_term:
    preferred_term: Dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      standard treatments for dysarthria and dysphagia
    explanation: >-
      GeneReviews lists dysarthria among the bulbar manifestations of SBMA
      requiring standard management.
- name: Tongue atrophy
  description: Wasting of the tongue muscles with fasciculations.
  phenotype_term:
    preferred_term: Tongue atrophy
    term:
      id: HP:0012473
      label: Tongue atrophy
- name: Fasciculations
  description: >-
    Muscle fasciculations, including characteristic perioral and facial-lingual
    fasciculations, reflect lower motor neuron degeneration.
  phenotype_term:
    preferred_term: Fasciculations
    term:
      id: HP:0002380
      label: Fasciculations
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      degeneration of lower motor neurons results in muscle weakness, muscle
      atrophy, and fasciculations in affected males.
    explanation: >-
      GeneReviews lists fasciculations as a manifestation of lower motor neuron
      degeneration in SBMA.
- name: Skeletal muscle atrophy
  description: Progressive wasting of skeletal muscle.
  phenotype_term:
    preferred_term: Skeletal muscle atrophy
    term:
      id: HP:0003202
      label: Skeletal muscle atrophy
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      degeneration of lower motor neurons results in muscle weakness, muscle
      atrophy, and fasciculations in affected males.
    explanation: >-
      GeneReviews lists muscle atrophy as a core manifestation of SBMA.
- name: Postural tremor
  description: A high-frequency postural tremor of the hands is common.
  phenotype_term:
    preferred_term: Postural tremor
    term:
      id: HP:0002174
      label: Postural tremor
  evidence:
  - reference: PMID:32934110
    reference_title: "Disease mechanism, biomarker and therapeutics for spinal and bulbar muscular atrophy (SBMA)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      followed by the emergence of hand tremor, a prodromal sign of the disease.
    explanation: >-
      Hand tremor is described as a prodromal sign of SBMA, supporting postural
      hand tremor as an early phenotype.
- name: Gynecomastia
  description: >-
    Signs of partial androgen insensitivity caused by reduced androgen receptor
    function, including gynecomastia.
  phenotype_term:
    preferred_term: Gynecomastia
    term:
      id: HP:0000771
      label: Gynecomastia
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Affected individuals often show gynecomastia, testicular atrophy, and
      reduced fertility as a result of mild androgen insensitivity.
    explanation: >-
      GeneReviews attributes gynecomastia in SBMA to mild androgen
      insensitivity from reduced androgen receptor function.
- name: Reduced fertility
  description: >-
    Mild androgen insensitivity manifests as reduced fertility, oligospermia or
    azoospermia, and testicular atrophy.
  phenotype_term:
    preferred_term: Decreased fertility in males
    term:
      id: HP:0012041
      label: Decreased fertility in males
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Affected individuals often show gynecomastia, testicular atrophy, and
      reduced fertility as a result of mild androgen insensitivity.
    explanation: >-
      GeneReviews documents reduced fertility and testicular atrophy in SBMA as
      consequences of mild androgen insensitivity.
- name: Testicular atrophy
  description: >-
    Testicular atrophy is a sign of mild androgen insensitivity in SBMA.
  phenotype_term:
    preferred_term: Testicular atrophy
    term:
      id: HP:0000029
      label: Testicular atrophy
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Affected individuals often show gynecomastia, testicular atrophy, and
      reduced fertility as a result of mild androgen insensitivity.
    explanation: >-
      GeneReviews lists testicular atrophy as an androgen-insensitivity
      manifestation of SBMA.
- name: Elevated creatine kinase
  description: Serum creatine kinase is frequently elevated, reflecting myopathy.
  phenotype_term:
    preferred_term: Elevated circulating creatine kinase concentration
    term:
      id: HP:0003236
      label: Elevated circulating creatine kinase concentration
- name: Sensory neuropathy
  description: >-
    Subclinical sensory involvement is common, with reduced sensory nerve
    action potentials in nearly all patients and distal vibration sensory loss.
  phenotype_term:
    preferred_term: Sensory neuropathy
    term:
      id: HP:0000763
      label: Sensory neuropathy
  evidence:
  - reference: PMID:19846582
    reference_title: "Clinical features of spinal and bulbar muscular atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sensory nerve action potentials were reduced in nearly all subjects."
    explanation: >-
      A 57-patient natural history cohort found reduced sensory nerve action
      potentials in nearly all subjects, indicating sensory neuropathy.
- name: Cardiac repolarization abnormalities
  description: >-
    SBMA patients frequently show abnormal ECGs, including a Brugada pattern and
    early repolarization, as well as diffuse myocardial fibrosis, which may
    contribute to increased risk of sudden cardiac death.
  phenotype_term:
    preferred_term: Abnormal EKG
    term:
      id: HP:0003115
      label: Abnormal EKG
  evidence:
  - reference: PMID:35132468
    reference_title: "J wave syndromes in patients with spinal and bulbar muscular atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Abnormal ECGs were recorded in 70%, consisting of a Brugada ECG pattern,
      early repolarization or fragmented QRS.
    explanation: >-
      In a 30-patient SBMA cohort, 70% had abnormal ECGs, supporting cardiac
      repolarization abnormalities as a feature of SBMA.
pathophysiology:
- name: Polyglutamine-expanded androgen receptor toxicity
  description: >-
    CAG repeat expansion in AR exon 1 produces an androgen receptor with an
    elongated polyglutamine tract. Upon ligand (testosterone/DHT) binding the
    mutant receptor translocates to the nucleus, misfolds, and accumulates,
    exerting an androgen-dependent toxic gain of function.
  cell_types:
  - preferred_term: Lower motor neuron
    term:
      id: CL:0008039
      label: lower motor neuron
  biological_processes:
  - preferred_term: Androgen receptor signaling pathway
    term:
      id: GO:0030521
      label: androgen receptor signaling pathway
  evidence:
  - reference: PMID:32934110
    reference_title: "Disease mechanism, biomarker and therapeutics for spinal and bulbar muscular atrophy (SBMA)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Androgen-dependent nuclear accumulation of the polyglutamine-expanded AR
      is an essential step in the pathogenesis, providing therapeutic
      opportunities via hormonal manipulation and gene silencing with antisense
      oligonucleotides.
    explanation: >-
      Establishes that androgen-dependent nuclear accumulation of the
      polyglutamine-expanded androgen receptor is the essential pathogenic step.
  - reference: PMID:36746939
    reference_title: "LSD1/PRMT6-targeting gene therapy to attenuate androgen receptor toxic gain-of-function ameliorates spinobulbar muscular atrophy phenotypes in flies and mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Androgen binding to polyQ-expanded androgen receptor triggers SBMA
      through a combination of toxic gain-of-function and loss-of-function
      mechanisms.
    explanation: >-
      Confirms the combined toxic gain-of-function plus partial
      loss-of-function mechanism triggered by androgen binding.
  downstream:
  - target: Nuclear inclusion formation and impaired proteostasis
    causal_link_type: DIRECT
    description: >-
      Nuclear accumulation of the misfolded polyQ-AR drives formation of nuclear
      inclusions and impairs proteostasis.
  - target: Skeletal muscle as a primary site of toxicity
    causal_link_type: DIRECT
    description: >-
      Androgen-dependent polyQ-AR toxicity acts directly within skeletal muscle
      as an early and primary site of disease.
  - target: Motor neuron degeneration
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - nuclear inclusion formation and impaired proteostasis
    description: >-
      PolyQ-AR toxicity ultimately drives degeneration of lower motor neurons
      via proteostatic stress and downstream cellular dysfunction.
- name: Nuclear inclusion formation and impaired proteostasis
  description: >-
    The misfolded polyQ androgen receptor forms nuclear inclusions and impairs
    the ubiquitin-proteasome system and protein quality control, contributing to
    motor neuron dysfunction.
  cell_types:
  - preferred_term: Lower motor neuron
    term:
      id: CL:0008039
      label: lower motor neuron
  biological_processes:
  - preferred_term: Inclusion body assembly
    term:
      id: GO:0070841
      label: inclusion body assembly
  - preferred_term: Ubiquitin-dependent protein catabolic process
    term:
      id: GO:0006511
      label: ubiquitin-dependent protein catabolic process
    modifier: DECREASED
  evidence:
  - reference: PMID:32934110
    reference_title: "Disease mechanism, biomarker and therapeutics for spinal and bulbar muscular atrophy (SBMA)."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Animal studies also suggest that hyperactivation of Src, alteration of
      autophagy and a mitochondrial deficit underlie the neuromuscular
      degeneration in SBMA and provide alternative therapeutic targets.
    explanation: >-
      Supports altered autophagy/protein quality control (alongside Src and
      mitochondrial deficits) as a downstream mechanism of neuromuscular
      degeneration in SBMA.
  downstream:
  - target: Motor neuron degeneration
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Nuclear inclusions and impaired proteostasis contribute to motor neuron
      dysfunction and progressive degeneration.
- name: Skeletal muscle as a primary site of toxicity
  description: >-
    Beyond lower motor neuron loss, skeletal muscle is directly affected, with
    loss of fast-twitch type 2 fibres, increase in slow-twitch type 1 fibres,
    and a glycolytic-to-oxidative metabolic switch, indicating muscle is an
    early and primary site of androgen-dependent toxicity.
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0000188
      label: cell of skeletal muscle
  biological_processes:
  - preferred_term: Skeletal muscle fiber type switching
    term:
      id: GO:0014883
      label: transition between fast and slow fiber
  evidence:
  - reference: PMID:32934110
    reference_title: "Disease mechanism, biomarker and therapeutics for spinal and bulbar muscular atrophy (SBMA)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      pathology of patients and animal models also indicates involvement of
      skeletal muscle including loss of fast-twitch type 2 fibres and increased
      slow-twitch type 1 fibres, together with a glycolytic-to-oxidative
      metabolic switch.
    explanation: >-
      Documents direct skeletal muscle involvement with fast-to-slow fibre-type
      switching and a glycolytic-to-oxidative metabolic shift in SBMA.
  downstream:
  - target: Disrupted muscle energy metabolism
    causal_link_type: DIRECT
    description: >-
      The glycolytic-to-oxidative fibre-type switch and primary muscle toxicity
      drive disrupted NAD+-dependent muscle energy metabolism.
- name: Disrupted muscle energy metabolism
  description: >-
    SBMA skeletal muscle shows decreased NAD+ and ATP and alterations in
    NAD+-dependent energy pathways and the NAD+ salvage pathway, with reduced
    nicotinamide riboside kinase 2 (Nmrk2), contributing to impaired muscle
    bioenergetics.
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0000188
      label: cell of skeletal muscle
  biological_processes:
  - preferred_term: NAD biosynthetic process
    term:
      id: GO:0009435
      label: NAD+ biosynthetic process
    modifier: DECREASED
  evidence:
  - reference: PMID:38452174
    reference_title: "Differentially disrupted spinal cord and muscle energy metabolism in spinal and bulbar muscular atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      these data suggest a model in which NAD+ levels are significantly
      decreased in muscles of an SBMA mouse model and intransigent to NR
      supplementation because of decreased levels of Nmrk2.
    explanation: >-
      Demonstrates decreased NAD+ and disrupted NAD+ salvage (low Nmrk2) in
      SBMA muscle, evidence from a transgenic mouse model.
- name: LSD1/PRMT6 co-regulator amplification of AR toxicity
  description: >-
    The androgen receptor co-regulators LSD1 and PRMT6 are overexpressed in an
    androgen-dependent manner in SBMA skeletal muscle and synergistically
    enhance androgen receptor transactivation, an effect amplified by the
    expanded polyglutamine tract, identifying a modifier axis of AR toxic gain
    of function.
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0000188
      label: cell of skeletal muscle
  biological_processes:
  - preferred_term: Androgen receptor signaling pathway
    term:
      id: GO:0030521
      label: androgen receptor signaling pathway
    modifier: INCREASED
  evidence:
  - reference: PMID:36746939
    reference_title: "LSD1/PRMT6-targeting gene therapy to attenuate androgen receptor toxic gain-of-function ameliorates spinobulbar muscular atrophy phenotypes in flies and mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      androgen receptor co-regulators lysine-specific demethylase 1 (LSD1) and
      protein arginine methyltransferase 6 (PRMT6) are overexpressed in an
      androgen-dependent manner specifically in the skeletal muscle of SBMA
      patients and mice.
    explanation: >-
      Identifies LSD1 and PRMT6 as androgen-dependent co-regulators
      overexpressed in SBMA muscle that amplify AR transactivation.
  - reference: PMID:36746939
    reference_title: "LSD1/PRMT6-targeting gene therapy to attenuate androgen receptor toxic gain-of-function ameliorates spinobulbar muscular atrophy phenotypes in flies and mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Pharmacological and genetic silencing of LSD1 and PRMT6 attenuates
      polyQ-expanded androgen receptor transactivation in SBMA cells and
      suppresses toxicity in SBMA flies, and a preclinical approach based on
      miRNA-mediated silencing of LSD1 and PRMT6 attenuates disease
      manifestations in SBMA mice.
    explanation: >-
      Silencing LSD1/PRMT6 reduces AR toxicity in SBMA flies and mice,
      supporting their role as modifiers and therapeutic targets.
  downstream:
  - target: Polyglutamine-expanded androgen receptor toxicity
    causal_link_type: DIRECT
    description: >-
      LSD1 and PRMT6 synergistically enhance androgen receptor transactivation,
      amplifying the polyQ-AR toxic gain of function.
- name: Motor neuron degeneration
  description: >-
    Progressive degeneration and loss of bulbar and spinal lower motor neurons
    leads to denervation, muscle weakness, and atrophy.
  cell_types:
  - preferred_term: Spinal cord motor neuron
    term:
      id: CL:0011001
      label: spinal cord motor neuron
  biological_processes:
  - preferred_term: Apoptotic process
    term:
      id: GO:0006915
      label: apoptotic process
    modifier: INCREASED
  evidence:
  - reference: PMID:32934110
    reference_title: "Disease mechanism, biomarker and therapeutics for spinal and bulbar muscular atrophy (SBMA)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the central nervous system, lower motor neurons are selectively
      affected
    explanation: >-
      Establishes selective lower motor neuron involvement in the central
      nervous system as the core neurodegenerative feature of SBMA.
genetic:
- name: AR
  association: Causative
  inheritance:
  - name: X-linked recessive
    inheritance_term:
      preferred_term: X-linked recessive inheritance
      term:
        id: HP:0001419
        label: X-linked recessive inheritance
  gene_term:
    preferred_term: AR
    term:
      id: hgnc:644
      label: AR
  notes: >-
    The androgen receptor gene on Xq12. A CAG trinucleotide repeat expansion in
    exon 1 beyond ~35 repeats (normal range ~9-36) causes SBMA, encoding an
    elongated polyglutamine tract. Repeat length correlates inversely with age of
    onset. The mechanism is an androgen-dependent toxic gain of function, distinct
    from the loss-of-function mutations in the same gene that cause androgen
    insensitivity syndrome.
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      identification of a hemizygous expansion of a CAG trinucleotide repeat
      (>35 CAGs) in AR by molecular genetic testing.
    explanation: >-
      GeneReviews establishes that SBMA is caused by a CAG trinucleotide repeat
      expansion (>35 CAGs) in the AR gene.
diagnosis:
- name: Molecular genetic testing
  description: >-
    The diagnosis is established in a male proband by identifying a hemizygous
    expansion of a CAG trinucleotide repeat (>35 CAGs) in the AR gene by
    molecular genetic testing.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: MAXO:0000533
      label: molecular genetic testing
    qualifiers:
    - predicate:
        preferred_term: has participant
        term:
          id: RO:0000057
          label: has participant
      value:
        preferred_term: AR
        term:
          id: hgnc:644
          label: AR
  results: >-
    A hemizygous CAG trinucleotide repeat expansion (>35 CAGs) in AR confirms
    the diagnosis.
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of SBMA is established in a male proband by the
      identification of a hemizygous expansion of a CAG trinucleotide repeat
      (>35 CAGs) in AR by molecular genetic testing.
    explanation: >-
      GeneReviews establishes molecular genetic testing for the AR CAG repeat
      expansion as the confirmatory diagnostic test for SBMA.
prevalence:
- population: Italy (nationwide estimate)
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 1.5
  percentage: 1.5 per 100,000
  notes: >-
    Estimated ~1000 affected individuals in Italy at any given time, with an
    annual incidence of 0.19 per 100,000 males.
  evidence:
  - reference: clinicaltrials:NCT06169046
    reference_title: "A Placebo-controlled Study to Evaluate the Efficacy and Safety of Clenbuterol in Patients With Spinal and Bulbar Muscular Atrophy (SBMA)"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      individuals are affected by SBMA in Italy at any given time (prevalence:
      1.5/100000) with an annual incidence of 0.19/100000 males.
    explanation: >-
      An Italian Phase II trial record reports SBMA prevalence of 1.5 per
      100,000 and an annual incidence of 0.19 per 100,000 males.
clinical_trials:
- name: NCT00303446
  phase: PHASE_II
  status: COMPLETED
  description: >-
    Randomized, placebo-controlled trial of the 5-alpha-reductase inhibitor
    dutasteride, which lowers dihydrotestosterone (DHT), to test whether
    reducing androgen signaling improves strength and function in SBMA.
  evidence:
  - reference: clinicaltrials:NCT00303446
    reference_title: "Phase II Clinical Trial to Examine the Efficacy and Safety of Dutasteride in Patients With Kennedy's Disease (Spinal and Bulbar Muscular Atrophy)"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dutasteride decreases DHT production. Lowering DHT levels may decrease the
      harmful effects of DHT to the nerves and improve strength in people with
      SBMA.
    explanation: >-
      The dutasteride trial directly tests the androgen-dependence mechanism by
      lowering DHT to reduce androgen-driven toxicity in SBMA.
- name: NCT06169046
  phase: PHASE_II
  status: RECRUITING
  description: >-
    Multicenter, randomized, double-blind, placebo-controlled trial of the
    beta2-agonist clenbuterol targeting skeletal muscle as a therapeutic site
    in SBMA.
  evidence:
  - reference: clinicaltrials:NCT06169046
    reference_title: "A Placebo-controlled Study to Evaluate the Efficacy and Safety of Clenbuterol in Patients With Spinal and Bulbar Muscular Atrophy (SBMA)"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To establish safety and efficacy of clenbuterol as a cure for SBMA, we
      are conducting a multicenter, phase II, randomized, double-blind,
      parallel-group, single dose, placebo-controlled trial.
    explanation: >-
      A Phase II clenbuterol trial evaluates beta2-agonist stimulation of
      muscle as a therapeutic strategy, consistent with muscle being a primary
      site of SBMA toxicity.
- name: NCT05517603
  phase: PHASE_I
  status: COMPLETED
  description: >-
    First-in-patient, randomized, double-blind, placebo-controlled Phase 1/2a
    study of AJ201 evaluating safety, tolerability, pharmacokinetics, and
    pharmacodynamics in adults with SBMA.
  evidence:
  - reference: clinicaltrials:NCT05517603
    reference_title: "A Phase 1/2a, Randomized, Double-Blind, Placebo-Controlled, First-In-Patient Study Of AJ201 To Evaluate Safety, Tolerability, Pharmacokinetics, And Pharmacodynamics In Adults With Spinal And Bulbar Muscular Atrophy (SBMA)"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This is a phase 1/2a randomized, double-blind study to evaluate the
      safety, tolerability, pharmacokinetics, and pharmacodynamics of study
      drug AJ201 in subjects with Spinal and Bulbar Muscular Atrophy (SBMA).
    explanation: >-
      A Phase 1/2a trial of AJ201 represents an emerging disease-modifying
      therapeutic candidate under clinical evaluation for SBMA.
treatments:
- name: Supportive and rehabilitative care
  description: >-
    No disease-modifying therapy is approved. Management is supportive,
    including braces and walkers for ambulation, standard treatments for
    dysarthria and dysphagia, breast reduction surgery for gynecomastia as
    needed, and psychosocial support. Agents/circumstances to avoid: based on
    animal studies, administration of testosterone and its analogs may worsen
    motor neuron disease and should be avoided.
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Based on animal studies, administration of testosterone and its analogs
      may worsen motor neuron disease.
    explanation: >-
      GeneReviews flags testosterone and androgen analogs as agents to avoid in
      SBMA because animal studies indicate they may worsen motor neuron disease.
- name: Genetic counseling
  description: >-
    Genetic counseling for the X-linked recessive inheritance pattern, carrier
    testing, and reproductive options.
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301508
    reference_title: "Spinal and Bulbar Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Carrier testing for at-risk female relatives and prenatal testing for a
      pregnancy at increased risk are possible if the expanded CAG repeat has
      been identified in an affected family member.
    explanation: >-
      GeneReviews supports genetic counseling, carrier testing, and prenatal
      testing for at-risk family members in SBMA.
- name: Antisense oligonucleotide AR-lowering therapy (experimental)
  description: >-
    Because androgen-dependent toxicity is driven by the toxic AR protein,
    lowering AR levels with antisense oligonucleotides is an actively
    investigated disease-modifying strategy. ASOs are in development for SBMA;
    no AR-targeting ASO is yet approved.
  therapeutic_modality: ANTISENSE_OLIGONUCLEOTIDE
  aso_details:
    aso_mechanism: RNASE_H_KNOCKDOWN
    target_gene:
      preferred_term: AR
      term:
        id: hgnc:644
        label: AR
    target_transcript: AR mRNA
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:32934110
    reference_title: "Disease mechanism, biomarker and therapeutics for spinal and bulbar muscular atrophy (SBMA)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      providing therapeutic opportunities via hormonal manipulation and gene
      silencing with antisense oligonucleotides.
    explanation: >-
      Identifies antisense oligonucleotide gene silencing of AR as a rational
      therapeutic strategy in SBMA.
  - reference: PMID:38732027
    reference_title: "Antisense Oligonucleotides (ASOs) in Motor Neuron Diseases: A Road to Cure in Light and Shade."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      ASOs are being developed for the treatment of motor neuron diseases
      (MNDs), including spinal muscular atrophy (SMA), amyotrophic lateral
      sclerosis (ALS) and spinal and bulbar muscular atrophy (SBMA).
    explanation: >-
      Confirms that ASOs are under development for SBMA among motor neuron
      diseases.
- name: Hormonal (androgen) modulation (investigational)
  description: >-
    Strategies to reduce androgen action on the mutant receptor (e.g.,
    leuprorelin/leuprolide, dutasteride) have been tested. Leuprorelin showed
    benefit in dysphagia in Japan but a Phase 3 trial failed to confirm overall
    benefit; these remain investigational outside Japan. Note that the
    relationship between androgens and muscle is complex, as testosterone levels
    correlate positively with muscle strength in patients.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:19846582
    reference_title: "Clinical features of spinal and bulbar muscular atrophy."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The direct correlation of testosterone levels with muscle strength
      indicates that androgens may have a positive effect on muscle function in
      spinal and bulbar muscular atrophy patients, in addition to the toxic
      effects described in animal models.
    explanation: >-
      Indicates the androgen-muscle relationship is complex: androgen modulation
      may help via reducing toxic gain of function, but testosterone also
      correlates positively with muscle strength, complicating hormonal therapy.
📚

References & Deep Research

References

1
PMID:20301508
Spinal and Bulbar Muscular Atrophy.
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Kennedy Disease (Spinal and Bulbar Muscular Atrophy; SBMA): Comprehensive Disease Characteristics Report
Edison Scientific Literature 45 citations 2026-06-03T15:28:18.114669

Kennedy Disease (Spinal and Bulbar Muscular Atrophy; SBMA): Comprehensive Disease Characteristics Report

Summary (knowledge-base ready)

Kennedy disease, also called spinal and bulbar muscular atrophy (SBMA), is an adult-onset, slowly progressive, X-linked neuromuscular disorder primarily affecting males and caused by a CAG trinucleotide repeat expansion in the androgen receptor (AR) gene leading to an expanded polyglutamine tract in AR protein, with androgen-dependent toxicity involving both lower motor neurons (spinal cord/brainstem) and skeletal muscle. (chang2024theroleof pages 11-12, cantara2024antisenseoligonucleotides(asos) pages 14-16, prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, hashizume2020diseasemechanismbiomarker pages 1-5)

Category Key values
Disease name / definition Kennedy disease; spinal and bulbar muscular atrophy (SBMA); an adult-onset, slowly progressive, X-linked neuromuscular / lower motor neuron disease caused by polyglutamine-expanded androgen receptor, with both motor neuron and skeletal muscle involvement (chang2024theroleof pages 11-12, cantara2024antisenseoligonucleotides(asos) pages 14-16, prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, hashizume2020diseasemechanismbiomarker pages 1-5)
Identifiers MONDO: MONDO_0010735 (OpenTargets disease association for Kennedy disease) (OpenTargets Search: Spinal and bulbar muscular atrophy,Kennedy disease-AR); OMIM: 313200 (reported as “X-linked spinal and bulbar muscular atrophy (SMAX1, Kennedy disease, OMIM 313200)”) (wang2020apathogenicmissense pages 1-2); MeSH: Bulbo-Spinal Atrophy, X-Linked D055534 (ClinicalTrials.gov MeSH mapping) (NCT06411912 chunk 2, NCT06169046 chunk 1, NCT00303446 chunk 3)
Synonyms / alternative names Spinal and bulbar muscular atrophy; SBMA; Kennedy disease / Kennedy’s disease; X-linked spinal and bulbar muscular atrophy; X-linked recessive bulbospinal neuronopathy; progressive proximal spinal and bulbar muscular atrophy of late onset (lee2024morethanautophony pages 1-2, debartolo2024differentiallydisruptedspinal pages 14-15, wang2020apathogenicmissense pages 1-2, cantara2024antisenseoligonucleotides(asos) pages 14-16)
Causal gene / locus Gene: AR (androgen receptor); location: Xq11-12 / Xq12; disease caused by CAG trinucleotide expansion in exon 1 producing an expanded polyglutamine tract in AR protein (cantara2024antisenseoligonucleotides(asos) pages 14-16, prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, lee2024morethanautophony pages 1-2, hashizume2020diseasemechanismbiomarker pages 1-5)
Pathogenic repeat ranges / thresholds Common pathogenic thresholds in evidence: ≥38 CAG in trial eligibility and mechanistic literature (NCT06169046 chunk 1, prakasam2023lsd1prmt6targetinggenetherapy pages 1-2); review evidence gives normal 9–36 CAG vs SBMA 39–72 CAG (cantara2024antisenseoligonucleotides(asos) pages 14-16); AJ201 trial used ≥36 repeats for enrollment (NCT05517603 chunk 1)
Inheritance / sex bias X-linked recessive / sex-linked disorder; primarily affects adult males; females are usually carriers and may be mildly affected; androgen dependence explains marked male predominance (cantara2024antisenseoligonucleotides(asos) pages 14-16, prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, NCT00303446 chunk 1, hashizume2020diseasemechanismbiomarker pages 1-5)
Epidemiology Prevalence estimates in cited sources: 1–2 per 100,000 (review) (cantara2024antisenseoligonucleotides(asos) pages 14-16, hashizume2020diseasemechanismbiomarker pages 1-5); 2–5 per 100,000 worldwide (mechanistic study intro) (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2); Italy trial record: about 1,000 affected individuals, prevalence 1.5/100,000, annual incidence 0.19/100,000 males (NCT06169046 chunk 1)
Typical onset / course Adult onset, often 30–40 years (range 18–64 in one review); slowly progressive; tremor may precede weakness by >10 years; wheelchair often needed 10–15 years after onset in some reports (cantara2024antisenseoligonucleotides(asos) pages 14-16, hashizume2020diseasemechanismbiomarker pages 1-5, iijima2023longtermeffectsof pages 1-2)
Hallmark phenotypes Progressive limb and bulbar weakness/atrophy, fasciculations, cramps, postural hand tremor, dysarthria, dysphagia, laryngospasm, reduced/absent reflexes, distal vibration sensory loss; androgen-insensitivity features including gynecomastia, testicular atrophy, erectile dysfunction, infertility/decreased fertility; aspiration pneumonia is a major cause of death (lee2024morethanautophony pages 1-2, hashizume2020diseasemechanismbiomarker pages 1-5, rhodes2009clinicalfeaturesof pages 6-8)
Quality-of-life / functional impact ADL domains notably affected: walking, handwriting, falling, swallowing, speech; SF-36v2 physical component mean 34.3 ± 11.0 in a landmark cohort; substantial diagnostic delay (~2 years to first medical attention plus ~3 more years to diagnosis) (rhodes2009clinicalfeaturesof pages 6-8)
Key diagnostic tests Genetic confirmation of AR CAG expansion is definitive; supportive tests include EMG/neurophysiology, quantitative muscle assessment, timed walk tests, SBMAFRS/ALSFRS-R, tongue pressure, pulmonary metrics (%FVC, %PEF), muscle MRI with Dixon fat quantification, and cardiac ECG/CMR when indicated (NCT06169046 chunk 1, NCT00303446 chunk 1, inagaki2022developmentofa pages 6-7, hashizume2020diseasemechanismbiomarker pages 5-8, steinmetz2022jwavesyndromes pages 1-2)
Biomarkers / outcome measures Prominent biomarkers: serum creatinine (declines before overt weakness), CK/liver enzymes, MRI muscle fat fraction, MUNE, tongue pressure; trial/research outcomes include 6MWT, 2MWD, AMAT, QMA, SBMAFRS, ALSFRS-R, %FVC, %PEF, neurophysiology, and mutant AR in muscle/skin (NCT05517603 chunk 1, NCT06169046 chunk 1, NCT00303446 chunk 1, inagaki2022developmentofa pages 6-7, hashizume2020diseasemechanismbiomarker pages 1-5, hashizume2020diseasemechanismbiomarker pages 5-8)
Notable recent mechanism (2023) LSD1/PRMT6 axis: androgen-dependent overexpression of AR co-regulators LSD1 and PRMT6 specifically in SBMA skeletal muscle; they synergistically enhance AR transactivation, and silencing them suppresses toxic gain-of-function and improves phenotypes in flies and mice (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, prakasam2023lsd1prmt6targetinggenetherapy pages 9-12, prakasam2023lsd1prmt6targetinggenetherapy pages 14-15)
Notable recent mechanism (2023) Early skeletal-muscle pathology: defective excitation-contraction coupling and impaired mitochondrial respiration occur before denervation; early events are androgen-dependent and reversible with castration or AR silencing; patient biopsies and mouse models support muscle as a primary toxicity site (hashizume2020diseasemechanismbiomarker pages 8-12, hashizume2020diseasemechanismbiomarker pages 12-15)
Notable recent mechanism (2024) Energy metabolism / NAD+ biology: SBMA muscle shows reduced NAD+ and ATP, altered nicotinamide/NAD+ salvage pathways, and decreased Nmrk2/NRK2, helping explain why nicotinamide riboside failed to restore muscle NAD+ or improve disease in mice; integrated metabolomics/proteomics implicated glycolysis, PPP, pyruvate, glutathione, and amino-acid pathways (debartolo2024differentiallydisruptedspinal pages 10-12, debartolo2024differentiallydisruptedspinal pages 1-2, debartolo2024differentiallydisruptedspinal pages 8-10)
Notable recent mechanism (2024 preclinical) Synaptic dysregulation / hyperexcitability: early postnatal nuclear accumulation of polyQ-AR in motor neurons dysregulates glutamatergic synaptic genes via Rest/Rest4; iPSC-derived motor neurons are hyperexcitable; antisense correction rescued pathology in mice (preprint evidence) (prakasam2023lsd1prmt6targetinggenetherapy pages 9-12)
Anatomy / cell types chiefly affected Lower motor neurons in spinal cord and brainstem; skeletal muscle is a major primary toxicity site; neuromuscular junction and muscle fiber-type composition are altered; cardiac involvement may occur in a subset (ECG/CMR abnormalities, fibrosis) (hashizume2020diseasemechanismbiomarker pages 1-5, steinmetz2022jwavesyndromes pages 1-2, hashizume2020diseasemechanismbiomarker pages 8-12, hashizume2020diseasemechanismbiomarker pages 12-15)
Cardiac / systemic comorbidity signals In a 30-patient SBMA cohort, 70% had abnormal ECGs; diffuse myocardial fibrosis on T1 mapping in 73.9% vs 9.1% of controls; metabolic comorbidities include glucose intolerance/insulin resistance and dyslipidemia in some patients (debartolo2024differentiallydisruptedspinal pages 1-2, steinmetz2022jwavesyndromes pages 1-2, hashizume2020diseasemechanismbiomarker pages 1-5)
Supportive / real-world implementation Long-term gait rehabilitation using wearable HAL in one 68-year-old patient: 9 courses over ~5 years, 3 sessions/week for 3 weeks each; 2MWD improved from 94 m to 101.8 m, gait item on ALSFRS-R remained stable at 3, and independent walking was maintained (iijima2023longtermeffectsof pages 1-2, iijima2023longtermeffectsof pages 9-10, iijima2023longtermeffectsof pages 2-4)
Historical / completed interventional trials NCT00303446 dutasteride 0.5 mg/day vs placebo for 24 months, phase 2; primary endpoint QMA; failed primary outcome in review summary (NCT00303446 chunk 1, hashizume2020diseasemechanismbiomarker pages 5-8). NCT00004771 leuprolide + testosterone, phase 2; genotype-confirmed by AR exon-1 mutation (NCT00004771 chunk 1). NCT00851461 goserelin (listed as completed) (clinical-trial search context in conversation). NCT02024932 BVS857 / IGF-1 mimetic, phase 2, showed muscle-volume signal in review summary (hashizume2020diseasemechanismbiomarker pages 5-8)
Active / recent trials (2023-2025 records) NCT06169046 clenbuterol 0.04 mg/day for 48 weeks, phase 2, primary endpoint 6MWT, enrollment 90, requires AR CAG ≥38 (NCT06169046 chunk 1); NCT05517603 AJ201 600 mg/day for 12 weeks, phase 1/2a, enrollment 25, pharmacodynamic endpoint mutant AR in skeletal muscle, requires AR CAG ≥36 (NCT05517603 chunk 1); NCT06411912 NIDO-361 in genetically confirmed SBMA, phase 2, enrollment 54 (NCT06411912 chunk 2); NCT06862596 mexiletine hydrochloride phase 2/3 recruiting (clinical-trial search context in conversation)
Expert/consensus interpretation Current expert view is that SBMA combines androgen-dependent toxic gain-of-function of expanded AR with elements of partial AR loss-of-function; skeletal muscle is not merely secondary but a therapeutically relevant primary target, supporting both endocrine modulation and AR-lowering / co-regulator-targeting strategies (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, hashizume2020diseasemechanismbiomarker pages 12-15, hashizume2020diseasemechanismbiomarker pages 1-5)

Table: This table condenses the main evidence-backed facts about Kennedy disease / SBMA, including identifiers, genetics, epidemiology, phenotypes, biomarkers, mechanisms, and clinical trials. It is designed as a quick-reference summary for knowledge-base curation or report drafting.

1. Disease Information

1.1 Definition and overview (current understanding)

SBMA is described as a hereditary neuromuscular disorder caused by CAG trinucleotide expansion in the gene encoding the androgen receptor (AR), with selective involvement of lower motor neurons and clear skeletal muscle pathology. (hashizume2020diseasemechanismbiomarker pages 1-5)

Recent review wording (abstract quote): “Spinal and bulbar muscular atrophy (SBMA) is a hereditary neuromuscular disorder caused by CAG trinucleotide expansion in the gene encoding the androgen receptor (AR).” (Hashizume et al., 2020-09; JNNP; https://doi.org/10.1136/jnnp-2020-322949) (hashizume2020diseasemechanismbiomarker pages 1-5)

A 2024 review similarly defines it as “an X-linked neuromuscular disorder characterized by the progressive loss of motor neurons in the spinal cord and brainstem.” (Chang & Chen, 2024-05; Antioxidants; https://doi.org/10.3390/antiox13060649) (chang2024theroleof pages 11-12)

1.2 Key identifiers (as available from retrieved evidence)

  • MONDO: MONDO_0010735 (“Kennedy disease”) from Open Targets disease entity metadata. (OpenTargets Search: Spinal and bulbar muscular atrophy,Kennedy disease-AR)
  • OMIM: 313200 (“X-linked spinal and bulbar muscular atrophy (SMAX1, Kennedy disease, OMIM 313200)”). (wang2020apathogenicmissense pages 1-2)
  • MeSH: “Bulbo-Spinal Atrophy, X-Linked” (MeSH ID D055534) as used in multiple ClinicalTrials.gov condition mappings. (NCT06411912 chunk 2, NCT06169046 chunk 1)

Not found in retrieved full text: Orphanet identifier and ICD-10/ICD-11 codes were not explicitly present in the gathered sources, so they cannot be cited from this tool run. (wang2020apathogenicmissense pages 1-2, NCT06169046 chunk 1)

1.3 Synonyms / alternative names

Common synonyms in the retrieved literature include Kennedy disease/Kennedy’s disease, spinal and bulbar muscular atrophy (SBMA), X-linked spinal and bulbar muscular atrophy, and “X-linked recessive bulbospinal neuronopathy.” (lee2024morethanautophony pages 1-2, debartolo2024differentiallydisruptedspinal pages 14-15, wang2020apathogenicmissense pages 1-2, cantara2024antisenseoligonucleotides(asos) pages 14-16)

1.4 Evidence-source type

The evidence used here is predominantly aggregated disease-level resources (reviews, clinical trial registries) plus human clinical cohorts/case reports and model organism + in vitro research, rather than EHR-derived analyses. (rhodes2009clinicalfeaturesof pages 6-8, hashizume2020diseasemechanismbiomarker pages 1-5, NCT06169046 chunk 1)

2. Etiology

2.1 Disease causal factors

Primary cause (genetic): CAG repeat expansion in AR exon 1 producing polyglutamine-expanded AR. (cantara2024antisenseoligonucleotides(asos) pages 14-16, prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, hashizume2020diseasemechanismbiomarker pages 1-5)

A landmark clinical cohort explicitly frames the disease as a “ligand-dependent toxic gain of function in the mutant androgen receptor,” linking causality to androgen binding. (Rhodes et al., 2009-10; Brain; https://doi.org/10.1093/brain/awp258) (rhodes2009clinicalfeaturesof pages 2-3)

2.2 Risk factors

  • Sex: adult males are primarily affected due to androgen dependence of toxicity. (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, hashizume2020diseasemechanismbiomarker pages 1-5)
  • Repeat length: longer CAG repeat length correlates with earlier onset and greater severity in reviewed evidence. (cantara2024antisenseoligonucleotides(asos) pages 14-16)
  • Androgen exposure: toxicity requires ligand binding to mutant AR (testosterone/DHT), making androgenic signaling a mechanistic risk factor. (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, hashizume2020diseasemechanismbiomarker pages 8-12)

2.3 Protective factors

Mechanistic protective interventions (preclinical): androgen deprivation and AR silencing are repeatedly reported to prevent or reverse early pathological processes in SBMA models. (debartolo2024differentiallydisruptedspinal pages 16-17, hashizume2020diseasemechanismbiomarker pages 19-25)

A 2024 metabolomics/proteomics study directly tested NAD+ precursor supplementation (nicotinamide riboside) and found no benefit for muscle NAD+/ATP or disease progression in a transgenic SBMA mouse model, indicating that NAD+ precursor supplementation via NR is not protective in that model context. (DeBartolo et al., 2024-03; JCI Insight; https://doi.org/10.1172/jci.insight.178048) (debartolo2024differentiallydisruptedspinal pages 1-2, debartolo2024differentiallydisruptedspinal pages 8-10)

2.4 Gene–environment interactions

The clearest “environmental” interaction is hormonal (androgen) exposure interacting with the expanded AR allele to drive disease: ligand binding triggers nuclear translocation/accumulation and downstream toxicity. (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, hashizume2020diseasemechanismbiomarker pages 8-12)

3. Phenotypes

3.1 Core neuromuscular phenotypes (symptoms/signs)

Commonly reported clinical features include progressive limb and bulbar weakness and atrophy, cramps, fasciculations (including facial/tongue), tremor, dysarthria, dysphagia, laryngospasm, reduced/absent reflexes, and distal sensory loss (often vibration). (hashizume2020diseasemechanismbiomarker pages 1-5, rhodes2009clinicalfeaturesof pages 6-8, lee2024morethanautophony pages 1-2)

A detailed review section states that postural hand tremor can occur “more than ten years before the onset of muscle weakness.” (hashizume2020diseasemechanismbiomarker pages 1-5)

Suggested HPO terms (non-exhaustive): * Muscle weakness (HP:0001324) * Muscle atrophy (HP:0003202) * Fasciculations (HP:0002380) * Muscle cramps (HP:0003394) * Dysarthria (HP:0001260) * Dysphagia (HP:0002015) * Tremor (HP:0001337) * Hyporeflexia/Areflexia (HP:0001265) * Gynecomastia (HP:0000768) * Erectile dysfunction (HP:0100639) * Male infertility (HP:0000027)

(hashizume2020diseasemechanismbiomarker pages 1-5, rhodes2009clinicalfeaturesof pages 6-8, lee2024morethanautophony pages 1-2)

3.2 Endocrine / androgen insensitivity phenotypes

Androgen insensitivity manifestations in SBMA include gynecomastia, testicular atrophy, erectile dysfunction, and decreased fertility. (hashizume2020diseasemechanismbiomarker pages 1-5)

3.3 Onset, progression, and frequency

A 2024 review reports typical onset “around 30–40 years of age, with a range of 18–64 years.” (cantara2024antisenseoligonucleotides(asos) pages 14-16)

3.4 Quality of life and functional impact (quantitative)

In a landmark clinical characterization study, self-reported impairment was greatest for walking/handwriting/falling/swallowing/speech, and quality of life was reduced with an SF-36v2 physical component summary mean of 34.3 (SD 11.0). (rhodes2009clinicalfeaturesof pages 6-8)

The same cohort reported substantial diagnostic delay (~2 years from symptom onset to first medical attention and ~3 more years to clinical diagnosis). (rhodes2009clinicalfeaturesof pages 6-8)

4. Genetic / Molecular Information

4.1 Causal gene

AR (androgen receptor) is the causal gene for SBMA/Kennedy disease in all retrieved mechanistic and clinical sources. (cantara2024antisenseoligonucleotides(asos) pages 14-16, prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, hashizume2020diseasemechanismbiomarker pages 1-5)

Ontology suggestion: HGNC:644 (AR) (gene symbol supported by evidence; HGNC ID not present in retrieved text and is provided here as a conventional mapping without direct citation).

4.2 Pathogenic variant class and repeat ranges

SBMA is caused by an expansion of a polymorphic tandem CAG repeat in the AR coding region; in one review, healthy range is 9–36 and SBMA range 39–72 with repeat length correlating with age of onset and severity. (cantara2024antisenseoligonucleotides(asos) pages 14-16)

Clinical trial inclusion criteria operationalize this as AR CAG repeat number ≥38 for genetic confirmation in an ongoing Phase 2 clenbuterol trial. (NCT06169046 chunk 1)

4.3 Functional consequences

Current expert synthesis supports combined toxic gain-of-function (androgen-dependent nuclear accumulation/aggregation and transcriptional dysregulation) plus partial loss-of-function manifested as androgen insensitivity. (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, hashizume2020diseasemechanismbiomarker pages 1-5, hashizume2020diseasemechanismbiomarker pages 8-12)

4.4 Modifier genes / co-regulators (recent, 2023)

A 2023 Nature Communications study highlights AR co-regulators LSD1 and PRMT6 as androgen-dependently overexpressed in SBMA skeletal muscle, synergistically enhancing AR transactivation (with amplification by expanded polyQ), and shows that silencing these co-regulators ameliorates SBMA phenotypes in flies and mice. (Prakasam et al., 2023-02; https://doi.org/10.1038/s41467-023-36186-9) (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, prakasam2023lsd1prmt6targetinggenetherapy pages 9-12)

Abstract quote: “Spinobulbar muscular atrophy (SBMA) is caused by CAG expansions in the androgen receptor gene.” (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2)

4.5 Epigenetic information

A mechanistic review notes downstream “epigenetic dysregulation” (including histone and DNA methylation-related changes) as part of the nuclear toxic cascade after ligand-dependent nuclear entry and aggregation. (hashizume2020diseasemechanismbiomarker pages 19-25, hashizume2020diseasemechanismbiomarker pages 8-12)

5. Environmental Information

No infectious etiology is implicated in SBMA in the retrieved evidence. (hashizume2020diseasemechanismbiomarker pages 1-5)

Non-genetic environmental contributors are not well-defined in the retrieved texts; the most actionable non-genetic factor is hormonal milieu (androgen signaling), which is mechanistically required for toxicity and therefore constitutes a biologically grounded exposure factor rather than an external toxin or pathogen. (hashizume2020diseasemechanismbiomarker pages 8-12)

6. Mechanism / Pathophysiology

6.1 High-level causal chain (upstream → downstream)

A consensus mechanistic chain supported across review and primary research is: 1) AR CAG expansion → polyQ-expanded AR (genetic trigger). (hashizume2020diseasemechanismbiomarker pages 1-5, prakasam2023lsd1prmt6targetinggenetherapy pages 1-2) 2) Androgen binding (testosterone/DHT) triggers N/C interaction, dissociation from chaperones, and nuclear translocation/accumulation, described as “an essential step in the pathogenesis.” (hashizume2020diseasemechanismbiomarker pages 1-5, hashizume2020diseasemechanismbiomarker pages 8-12) 3) In nucleus and cytoplasm, mutant AR undergoes aggregation/inclusion formation and aberrant transcriptional/co-regulator interactions, driving toxic gain-of-function. (hashizume2020diseasemechanismbiomarker pages 19-25, hashizume2020diseasemechanismbiomarker pages 8-12) 4) Downstream dysfunction includes: * Proteostasis and autophagy impairment, with impaired autophagic flux (LC3/p62 accumulation) supporting accumulation of insoluble AR species. (hashizume2020diseasemechanismbiomarker pages 12-15) * Akt/mTOR signaling hyperactivation in muscle (described as compensatory in one review) coupled to fiber-type and metabolic switching. (hashizume2020diseasemechanismbiomarker pages 12-15) * Mitochondrial deficits (mitochondrial depolarization, altered oxidative phosphorylation proteins, mitophagy) and excitation–contraction coupling / Ca2+ dysregulation, linking molecular pathology to reduced muscle contractility. (hashizume2020diseasemechanismbiomarker pages 12-15, hashizume2020diseasemechanismbiomarker pages 19-25) 5) Tissue-level pathology manifests in lower motor neurons (spinal cord/brainstem) and skeletal muscle, with growing evidence that muscle can be an early and primary site of toxicity. (hashizume2020diseasemechanismbiomarker pages 1-5, hashizume2020diseasemechanismbiomarker pages 12-15)

6.2 Multi-omics / pathway-level evidence (2024)

A 2024 JCI Insight study integrated metabolomics and proteomics in SBMA mouse quadriceps and reported decreased NAD+ and ATP in muscle but not spinal cord, with joint pathway analysis implicating nicotinamide metabolism and NAD+-dependent pathways (pentose phosphate, pyruvate, glutathione, amino acid metabolism). (debartolo2024differentiallydisruptedspinal pages 8-10)

This study also identified decreased Nmrk2/NRK2 as a likely bottleneck explaining why nicotinamide riboside supplementation failed to restore muscle NAD+ or modify progression in vivo. (debartolo2024differentiallydisruptedspinal pages 1-2, debartolo2024differentiallydisruptedspinal pages 8-10)

6.3 Recent mechanistic developments (2023–2024 prioritized)

  • AR co-regulator overexpression as a therapeutic node (2023): androgen-dependent muscle-specific overexpression of LSD1/PRMT6 amplifies AR transactivation, and dual silencing reduces aggregates/denervation markers and improves motor phenotypes in SBMA models. (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, prakasam2023lsd1prmt6targetinggenetherapy pages 9-12)
  • Metabolic NAD+ pathway constraint (2024): decreased Nmrk2 and inability of NR supplementation to raise muscle NAD+/ATP suggests a “salvage pathway entry” limitation rather than simple NAD+ precursor deficiency. (debartolo2024differentiallydisruptedspinal pages 1-2, debartolo2024differentiallydisruptedspinal pages 8-10)

6.4 Expert schematic (visual evidence)

A compact schematic of androgen-dependent nuclear translocation and downstream SBMA pathogenic mechanisms is provided as a figure in Hashizume et al. 2020. (hashizume2020diseasemechanismbiomarker media 00f97023)

6.5 Suggested ontology terms

GO Biological Process (suggested): * Androgen receptor signaling pathway * Protein aggregation * Autophagy * Mitochondrial dysfunction / oxidative phosphorylation * Regulation of mTOR signaling * Regulation of cytosolic calcium ion concentration / excitation–contraction coupling

(hashizume2020diseasemechanismbiomarker pages 12-15, hashizume2020diseasemechanismbiomarker pages 19-25, debartolo2024differentiallydisruptedspinal pages 8-10)

CL Cell types (suggested): * Spinal cord motor neuron (lower motor neuron) * Skeletal muscle fiber cell (myofiber)

(hashizume2020diseasemechanismbiomarker pages 1-5, hashizume2020diseasemechanismbiomarker pages 12-15)

7. Anatomical Structures Affected

7.1 Primary organs/systems

  • Nervous system: spinal cord and brainstem lower motor neurons. (chang2024theroleof pages 11-12, hashizume2020diseasemechanismbiomarker pages 1-5)
  • Skeletal muscle: direct involvement including fiber-type and metabolic switching, and multi-pathway pathology. (hashizume2020diseasemechanismbiomarker pages 1-5, hashizume2020diseasemechanismbiomarker pages 12-15)

7.2 Secondary/associated involvement

Cardiac structural and electrophysiologic abnormalities have been reported in SBMA cohorts, motivating screening in some patients. (steinmetz2022jwavesyndromes pages 1-2)

7.3 Suggested UBERON terms

  • Spinal cord (UBERON:0002240)
  • Brainstem (UBERON:0002298)
  • Skeletal muscle tissue (UBERON:0001134)
  • Neuromuscular junction (UBERON:0001255)

(steinmetz2022jwavesyndromes pages 1-2, hashizume2020diseasemechanismbiomarker pages 1-5)

8. Temporal Development

8.1 Onset

SBMA is adult-onset with typical onset described in the 30–60 year range in a rehabilitation case report and review sources. (iijima2023longtermeffectsof pages 1-2, cantara2024antisenseoligonucleotides(asos) pages 14-16)

8.2 Progression

It is slowly progressive and can lead to major mobility impairment over years to decades; aspiration pneumonia is emphasized as a major cause of death in clinical reviews. (hashizume2020diseasemechanismbiomarker pages 1-5)

9. Inheritance and Population

9.1 Inheritance

SBMA is X-linked (sex-linked) and predominantly manifests in adult males; females are generally carriers with milder or absent manifestations. (cantara2024antisenseoligonucleotides(asos) pages 14-16, hashizume2020diseasemechanismbiomarker pages 1-5)

9.2 Epidemiology (statistics)

Prevalence estimates vary by source: * 1–2 per 100,000 in a clinical review. (hashizume2020diseasemechanismbiomarker pages 1-5) * 2–5 per 100,000 worldwide in a 2023 mechanistic study introduction. (prakasam2023lsd1prmt6targetinggenetherapy pages 1-2) * Italy-specific estimate from a 2024 trial record: “prevalence: 1.5/100000” and “annual incidence of 0.19/100000 males.” (NCT06169046 chunk 1)

10. Diagnostics

10.1 Clinical tests and monitoring

Beyond confirmatory genetic testing, commonly used quantitative measures include quantitative muscle assessment (QMA), timed walk tests (2-minute, 6-minute), AMAT, SBMAFRS, pulmonary function (%FVC/%PEF), tongue pressure, neurophysiology measures (including motor unit number estimation), and skeletal muscle MRI (fat quantification). (hashizume2020diseasemechanismbiomarker pages 5-8, rhodes2009clinicalfeaturesof pages 2-3, inagaki2022developmentofa pages 6-7)

A 2022 methods paper developed a composite (SBMAFC) combining tongue pressure, grip power, %PEF, timed walking, and %FVC to create a more sensitive outcome measure; it enrolled 97 genetically confirmed SBMA patients and 36 controls. (Inagaki et al., 2022-10; Scientific Reports; https://doi.org/10.1038/s41598-022-22322-w) (inagaki2022developmentofa pages 6-7)

10.2 Biomarkers

Serum creatinine is repeatedly highlighted as a promising progression biomarker that begins declining before overt weakness, and MRI-based muscle/fat evaluation is noted as useful for tracking progression. (hashizume2020diseasemechanismbiomarker pages 1-5)

10.3 Electrophysiology and cardiac screening

A 2022 cohort study (30 SBMA vs 11 controls) reported abnormal ECGs in 70% of SBMA and diffuse myocardial fibrosis by T1 mapping in 73.9% vs 9.1% of controls, supporting ECG screening and consideration of CMR in cardiac risk assessment. (Steinmetz et al., 2022-02; J Neurol; https://doi.org/10.1007/s00415-022-10992-5) (steinmetz2022jwavesyndromes pages 1-2)

10.4 Genetic testing approach

Definitive diagnosis is via repeat expansion testing of AR CAG repeat length, with thresholds operationalized in trials (e.g., ≥38) and reviewed pathogenic ranges (39–72). (NCT06169046 chunk 1, cantara2024antisenseoligonucleotides(asos) pages 14-16)

11. Outcome / Prognosis

SBMA is chronic and slowly progressive with meaningful disability; a key morbidity driver is progressive bulbar dysfunction leading to aspiration pneumonia. (hashizume2020diseasemechanismbiomarker pages 1-5)

Quantitative functional impacts include reduced SF-36 physical component score (34.3 ± 11.0) in a landmark cohort and significant ADL impacts on walking and bulbar function. (rhodes2009clinicalfeaturesof pages 6-8)

12. Treatment

12.1 Current standard management (supportive)

No curative therapy is established; supportive management uses symptomatic approaches and structured monitoring/outcome measures (strength, function, respiration, swallowing, imaging/biomarkers). (hashizume2020diseasemechanismbiomarker pages 5-8, hashizume2020diseasemechanismbiomarker pages 1-5)

12.2 Pharmacologic and endocrine modulation (historical and ongoing)

Dutasteride (5α-reductase inhibitor; reduces DHT): A Phase 2, randomized, placebo-controlled trial used dutasteride 0.5 mg/day for 24 months with QMA as primary endpoint and multiple secondary outcomes (AMAT, 2-min walk, SF-36v2, neurophysiology, CK, hormone levels). (ClinicalTrials.gov NCT00303446; first posted 2006; https://clinicaltrials.gov/study/NCT00303446) (NCT00303446 chunk 1)

Leuprolide + testosterone (hormonal suppression/replacement strategy): A Phase 2 trial aimed to “Evaluate the effects of androgen suppression with leuprolide and androgen replacement with testosterone enanthate on muscle strength.” (ClinicalTrials.gov NCT00004771; first posted 1992; https://clinicaltrials.gov/study/NCT00004771) (NCT00004771 chunk 1)

A mechanistic/clinical review summarizes that a Phase 3 trial of leuprorelin (n=204) “failed to confirm benefit” after earlier Phase 2 signals. (hashizume2020diseasemechanismbiomarker pages 5-8)

12.3 Muscle-targeting / anabolic pathway approaches

BVS857 (IGF-1 mimetic): A completed Phase 2 randomized study evaluated safety/tolerability and change in thigh muscle volume (MRI), with functional endpoints (AMAT) and DXA lean mass; results were posted on ClinicalTrials.gov (results first posted 2017-08-11). (ClinicalTrials.gov NCT02024932; https://clinicaltrials.gov/study/NCT02024932) (NCT02024932 chunk 1)

12.4 Emerging disease-modifying strategies (2023–2024 prioritized)

AJ201: A completed Phase 1/2a randomized placebo-controlled trial evaluated safety and pharmacodynamics, including change from baseline in mutant AR protein levels in skeletal muscle, enrolling adult males with confirmed AR expansion (≥36 repeats). (ClinicalTrials.gov NCT05517603; https://clinicaltrials.gov/study/NCT05517603) (NCT05517603 chunk 1)

NIDO-361: A Phase 2 record includes endpoints such as accelerometer-based free-living physical activity and grip strength (HHD) in ambulatory genetically confirmed males. (ClinicalTrials.gov NCT06411912; https://clinicaltrials.gov/study/NCT06411912) (NCT06411912 chunk 2)

Clenbuterol (β2-agonist): A recruiting Phase 2 multicenter RCT uses 0.04 mg/day for 48 weeks with primary endpoint 6MWT and multiple secondary outcomes including SBMA-FRS, AMAT, FVC, serum creatinine, and quality-of-life scales; eligibility includes AR CAG ≥38. (ClinicalTrials.gov NCT06169046; posted 2024; https://clinicaltrials.gov/study/NCT06169046) (NCT06169046 chunk 1)

12.5 RNA-based therapies (expert synthesis)

ASO-based AR lowering is repeatedly described as a rational disease-modifying direction because androgen-dependent toxicity is driven by the toxic AR protein; a review states: “Probably the best therapeutic approach for SBMA is reducing levels of the toxic AR protein” and highlights preclinical ASO benefit. (hashizume2020diseasemechanismbiomarker pages 12-15)

Suggested MAXO terms (non-exhaustive): * Androgen deprivation therapy * Antisense oligonucleotide therapy * Physical therapy / gait training * Assistive device therapy (exoskeleton-assisted gait training)

(NCT06169046 chunk 1, NCT00303446 chunk 1, hashizume2020diseasemechanismbiomarker pages 12-15, iijima2023longtermeffectsof pages 1-2)

13. Prevention

No primary prevention is established for SBMA; key preventive strategies are genetic counseling, carrier detection in families, and anticipatory guidance for complications (swallowing/respiratory risk, fall risk, cardiac screening where appropriate). The retrieved evidence supports downstream complication prevention (e.g., aspiration pneumonia as major cause of death) but does not provide formal prevention guidelines. (hashizume2020diseasemechanismbiomarker pages 1-5)

14. Other Species / Natural Disease

No naturally occurring SBMA orthologous disease in non-human species (OMIA/veterinary) was identified in the retrieved evidence for this run. (hashizume2020diseasemechanismbiomarker pages 8-12, prakasam2023lsd1prmt6targetinggenetherapy pages 9-12)

15. Model Organisms

15.1 In vivo models

Multiple SBMA mouse models are described across mechanistic and therapeutic studies, including AR-97Q, AR100Q, AR112Q/AR113Q, and BAC fxAR121, which recapitulate androgen dependence, AR aggregation, neuromuscular weakness, fiber-type/metabolic switching, and signaling/metabolic abnormalities. (hashizume2020diseasemechanismbiomarker pages 8-12, prakasam2023lsd1prmt6targetinggenetherapy pages 9-12, cantara2024antisenseoligonucleotides(asos) pages 14-16, debartolo2024differentiallydisruptedspinal pages 8-10)

A Drosophila model expressing human polyQ-expanded AR (e.g., AR52Q) is used to score toxicity phenotypes such as eye degeneration and to test genetic suppressors/therapeutics. (prakasam2023lsd1prmt6targetinggenetherapy pages 14-15)

15.2 Human-derived and in vitro models

Human patient muscle biopsies are directly used to confirm muscle pathology and molecular changes, and multiple cell models (HEK293T, MN1, LNCaP) are used to measure AR transactivation and toxicity modulation. (prakasam2023lsd1prmt6targetinggenetherapy pages 9-12, prakasam2023lsd1prmt6targetinggenetherapy pages 14-15)

15.3 Model limitations (evidence-based)

A key translational limitation highlighted in ASO work is CNS accessibility: some gapmers do not cross the blood–brain barrier, producing peripheral but not spinal cord AR knockdown unless delivered intracerebroventricularly. (cantara2024antisenseoligonucleotides(asos) pages 14-16)

Current applications and real-world implementations

A notable real-world implementation is long-term rehabilitation using a wearable cyborg Hybrid Assistive Limb (HAL). In a 5-year follow-up case report (published 2023-06-08), the patient completed nine multi-week courses and improved 2MWD from 94 m to 101.8 m while maintaining ALSFRS-R gait item stability (score 3), suggesting sustained functional maintenance despite progressive disease. (Iijima et al., 2023; Frontiers in Neurology; https://doi.org/10.3389/fneur.2023.1143820) (iijima2023longtermeffectsof pages 1-2)

Abstract quote: “2MWD improved from 94 m to 101.8 m, and the ALSFRS-R gait items remained unchanged (score 3) for approximately 5 years.” (iijima2023longtermeffectsof pages 1-2)

Notes on citation requirements (PMID)

Where possible, primary literature should be referenced by PMID. In this tool run, the retrieved full-text snippets did not consistently include PMID metadata; therefore, this report provides DOI URLs and publication dates from the retrieved sources and clinical trial registry URLs/identifiers. (hashizume2020diseasemechanismbiomarker pages 1-5, prakasam2023lsd1prmt6targetinggenetherapy pages 1-2, NCT06169046 chunk 1)

References

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