Multisystem Proteinopathy

Multisystem Proteinopathy

Overview

```mermaid
flowchart TD
classDef gene fill:#0a1f0a,stroke:#4caf50
classDef protein fill:#0a1929,stroke:#2196f3
classDef disease fill:#2d0f0f,stroke:#e91e63
classDef pathway fill:#3e2200,stroke:#ff9800
classDef mechanism fill:#1a0a1f,stroke:#9c27b0
classDef therapeutic fill:#e0f2f1,stroke:#009688
Multisystem_Proteinopathy["Multisystem Proteinopathy"] -->|"associated_with"| Paget_s_Disease_of_Bone["Paget's Disease of Bone"]
Multisystem_Proteinopathy["Multisystem Proteinopathy"] -->|"associated_with"| Myopathy["Myopathy"]
Multisystem_Proteinopathy["Multisystem Proteinopathy"] -->|"associated_with"| Motor_Neuron_Disease["Motor Neuron Disease"]
Multisystem_Proteinopathy["Multisystem Proteinopathy"] -->|"associated_with"| Neurodegeneration["Neurodegeneration"]
Multisystem_Proteinopathy["Multisystem Proteinopathy"] -->|"associated_with"| Bone_Disease["Bone Disease"]
Multisystem_Proteinopathy["Multisystem Proteinopathy"] -->|"associated_with"| Frontotemporal_Dementia["Frontotemporal Dementia"]
Multisystem_Proteinopathy["Multisystem Proteinopathy"] -->|"associated_with"| Paget_S_Disease_Of_Bone["Paget'S Disease Of Bone"]
Multisystem_Proteinopathy["Multisystem Proteinopathy"] -->|"causes"| Myopathy["Myopathy"]
VCP["VCP"] -->|"causes"| Multisystem_Proteinopathy["Multisystem Proteinopathy"]
SQSTM1["SQSTM1"] -->|"causes"| Multisystem_Proteinopathy["Multisystem Proteinopathy"]
HNRNPA2B1["HNRNPA2B1"] -->|"causes"| Multisystem_Proteinopathy["Multisystem Proteinopathy"]
HNRNPA1["

Multisystem Proteinopathy

Overview

Multisystem proteinopathy (MSP), also known as inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia (IBMPFD), is a progressive inherited disorder characterized by a combination of muscle weakness (myopathy), bone disease (Paget disease), neurodegeneration (frontotemporal dementia), and sometimes additional features including parkinsonism and motor neuron disease["@modeling"][@amyotrophic]. The disease is caused by pathogenic variants in the VCP (valosin-containing protein) gene, which encodes a critical AAA+ ATPase involved in ubiquitin-dependent protein quality control. MSP exemplifies how defects in a single molecular hub can produce diverse tissue-specific phenotypes across multiple organ systems.

Genetics and Molecular Biology

VCP Gene

The VCP gene (also known as CDC48 in yeast) is located on chromosome 9p13.3 and encodes a 806-amino acid protein that functions as a AAA+ (ATPases Associated with diverse cellular Activities) ATPase[@modeling]. Over 40 pathogenic variants in VCP have been linked to MSP, with the most common being:

• p.R155H — The most frequent mutation, accounting for ~50% of cases
• p.R155P, p.R155C — Other common R155 variants
• p.A232G — Associated with predominantly myopathic phenotype
• p.D592N — Less severe phenotype

VCP Protein Function

VCP/p97 is a highly conserved hexameric AAA+ ATPase that participates in numerous cellular processes[@modeling]:

• Ubiquitin-dependent protein quality control — Extraction of ubiquitinated proteins from membranes and protein complexes
• Endoplasmic reticulum-associated degradation (ERAD) — Retrotranslocation of misfolded proteins for proteasomal degradation
• [Autophagy](/entities/autophagy) and lysosomal degradation — Processing of autophagosomes and recruitment of autophagy receptors
• Mitophagy — Selective degradation of damaged mitochondria
• DNA damage response — Chromatin remodeling and repair factor recruitment
• Cell cycle regulation — Mitotic spindle assembly and sister chromatid separation

Pathogenic Mechanisms

VCP mutations cause disease through several interconnected mechanisms[@modeling][@amyotrophic]:

Clinical Features

Inclusion Body Myopathy

Muscle weakness is the most common presenting feature, typically beginning in the third or fourth decade[@amyotrophic]:

• Progressive muscle weakness — Affects proximal muscles first, particularly hip girdle muscles
• Scapular winging — Shoulder girdle involvement common
• Respiratory muscle involvement — Can lead to respiratory insufficiency
• Facial weakness — Mild facial muscle involvement in some patients
• Distal weakness — May develop later in disease course

Paget Disease of Bone

Paget disease involves abnormal bone remodeling, typically affecting the pelvis, spine, skull, and long bones[@amyotrophic]:

• Bone pain — Often in the pelvis, lumbar spine, or skull
• Deformities — Bone enlargement and shape abnormalities
• Fractures — Increased fracture risk
• Hearing loss — Temporal bone involvement can affect hearing
• High alkaline phosphatase — Elevated serum marker of bone turnover

Frontotemporal Dementia

Cognitive decline typically presents 10-20 years after myopathy onset[@amyotrophic]:

• Behavioral variant FTD — Most common pattern
• Language variant FTD — Less common
• Executive dysfunction — Impaired planning, judgment, problem-solving
• Personality changes — Apathy, disinhibition, social inappropriateness
• Memory relatively preserved — Unlike [Alzheimer's disease](/diseases/alzheimers-disease)

Additional Features

• Motor neuron disease — ALS-like features in 10-15% of cases
• Parkinsonism — Tremor, bradykinesia, rigidity
• Cardiac involvement — Cardiomyopathy in some families
• Cataracts — Premature cataract formation
• Diabetes mellitus — Metabolic abnormalities reported

Pathology

Muscle Pathology

• Rimmed vacuoles — Autophagic vacuoles with basophilic debris
• [TDP-43](/mechanisms/tdp-43-proteinopathy) inclusions — Phosphorylated TDP-43 aggregates
• Muscle fiber atrophy — Type 2 fiber predominance
• Inflammatory infiltrates — Mild perivascular inflammation
• Mitochondrial abnormalities — Ragged-red fibers in some cases

Bone Pathology

• Increased osteoclast activity — Excessive bone resorption
• Disorganized bone matrix — Mosaic pattern of lamellar bone
• Elevated bone turnover markers — Alkaline phosphatase, N-telopeptide

Brain Pathology

• TDP-43 proteinopathy — Phosphorylated TDP-43 inclusions in [neurons](/entities/neurons) and glia
• Frontotemporal atrophy — Frontotemporal lobe volume loss
• Neuronal loss — Particularly in frontal and temporal cortices
• Spinal cord involvement — Anterior horn cell loss in cases with ALS features

Diagnosis

Clinical Diagnostic Criteria

The diagnosis is based on meeting clinical criteria for the combination of[@amyotrophic]:

Genetic Testing

• Sequencing — VCP gene sequencing identifies pathogenic variants
• Variant interpretation — ACMG guidelines for variant classification
• Family testing — Cascade screening for at-risk relatives

Diagnostic Studies

• Creatine kinase — Usually mildly elevated
• Electromyography — Myopathic changes with possible neurogenic features
• Muscle MRI — Fat infiltration pattern characteristic
• Bone scan — Increased uptake in Paget lesions
• Brain MRI — Frontotemporal atrophy
• Neuropsychological testing — Cognitive profile characterization

Treatment and Management

Myopathy Management

• Physical therapy — Maintain strength and function
• Assistive devices — As needed for mobility
• Respiratory monitoring — Pulmonary function testing
• Cardiac surveillance — Regular echocardiography

Paget Disease Treatment

• Bisphosphonates — First-line therapy
• Zoledronic acid — 5 mg IV single dose; long-lasting effect
• Alendronate — 40 mg daily orally
• Risedronate — 30 mg daily orally
• Calcitonin — Second-line option
• Vitamin D and calcium — Bone health maintenance

Frontotemporal Dementia Management

• Behavioral interventions — Structured environment, caregiver support
• SSRIs — For depression, anxiety, disinhibition
• Occupational therapy — Safety assessments, functional adaptation
• Speech therapy — For language variant

Disease-Modifying Therapies

Currently no approved disease-modifying treatments, but several approaches are in development[@genetic]:

• AAV-VCP gene therapy — Experimental gene replacement
• Autophagy modulators — Enhancing autophagic flux
• Small molecule VCP modulators — Targeting mutant protein function
• Antisense oligonucleotides — Reducing mutant VCP expression

Monitoring

• Annual neurological examination
• Pulmonary function testing
• Cardiac evaluation
• Bone density scanning
• Cognitive assessment

Research Directions

Biomarker Development

• [Neurofilament light](/biomarkers/neurofilament-light-chain-nfl) chain (NfL) — Blood marker for neurodegeneration
• VCP protein levels — In muscle and blood
• Autophagy markers — LC3, p62 in muscle biopsies

Therapeutic Targets

• Autophagy enhancement — [mTOR](/mechanisms/mtor-signaling-pathway)-independent activators
• ER stress modulation — Chemical chaperones
• Proteostasis network support — Heat shock protein inducers
• TDP-43 aggregation inhibitors — Small molecule approaches

Gene Therapy

AAV-mediated VCP gene delivery is being explored in preclinical models, with challenges including:

• Targeting multiple tissue types
• Achieving sufficient CNS delivery
• Balancing wild-type and mutant expression

See Also

• [VCP Gene](/genes/vcp) — Gene causing MSP
• [Frontotemporal Dementia](/diseases/frontotemporal-dementia) — Neurodegenerative component
• [ALS](/diseases/amyotrophic-lateral-sclerosis) — Motor neuron disease component
• [Autophagy-Lysosomal Pathway](/mechanisms/autophagy-lysosomal-pathway) — Dysregulated pathway
• [Proteostasis](/mechanisms/proteostasis-mechanisms) — Protein quality control

Recent Research (2024-2026)

This section highlights recent publications relevant to this disease.

• [Modeling amyotrophic lateral sclerosis (ALS) in vitro: from mechanistic studies to translatable drug discovery.](https://pubmed.ncbi.nlm.nih.gov/41498587/) (2026 Mar 4) - Lab on a chip
• [Amyotrophic Lateral Sclerosis (ALS) Genetics and Microbiota: A Comprehensive Review.](https://pubmed.ncbi.nlm.nih.gov/41752118/) (2026 Feb 19) - International journal of molecular sciences
• [Genetic Spectrum and Phenotypic Variability in Chinese Patients with Multisystem Proteinopathy and Related Disorders.](https://pubmed.ncbi.nlm.nih.gov/41737544/) (2026) - Degenerative neurological and neuromuscular disease
• [Missense variants in TUBA4A cause myo-tubulinopathies.](https://pubmed.ncbi.nlm.nih.gov/41678358/) (2026 Feb 12) - Brain : a journal of neurology
• [Evaluation of Skin Biopsy Techniques for the Diagnosis of Systemic Amyloidosis.](https://pubmed.ncbi.nlm.nih.gov/41368718/) (2026 Feb) - The Journal of dermatology

References