Mild myopathy is associated with COMP but not MATN3 mutations in mouse models of genetic skeletal diseases

Area of Science:

• Skeletal biology
• Connective tissue disorders
• Myopathology

Background:

• Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) are skeletal dysplasias linked to mutations in COMP, matrilin-3, or collagen IX.
• These conditions typically present with short-limbed dwarfism and premature osteoarthritis, but recent findings suggest associated muscle weakness.

Purpose of the Study:

• To investigate the underlying causes of muscle weakness in PSACH and MED by analyzing specific mouse models.
• To determine if short-limbed dwarfism or specific genetic mutations contribute to muscle pathology in these skeletal disorders.

Main Methods:

• Comparative analysis of two mouse models: ΔD469 T3-COMP (PSACH) and V194D matrilin-3 (MED).
• Grip strength testing to assess muscle function.
• Histological examination of muscle and tendon tissues to identify pathological changes.

Main Results:

• T3-COMP mice exhibited reduced grip strength compared to wild-type littermates, while V194D mice showed no significant difference.
• T3-COMP muscles displayed increased centronuclear fibers at the myotendinous junction.
• T3-COMP tendons were laxer and had thicker collagen fibers, indicating tendon pathology; matrilin-3 mutant tissues were normal.

Conclusions:

• Limb weakness in PSACH/MED is attributable to specific muscle and tendon pathologies, not short-limbed dwarfism itself.
• The observed myopathy is genotype-specific, highlighting the importance of genetic background in disease manifestation.
• This study enhances understanding of PSACH/MED disease progression and aids in recognizing neuromuscular symptoms as potential differential diagnoses.