Mitochondrial abnormalities in myofibrillar myopathies.

Area of Science:

• Neurology
• Mitochondrial Biology
• Muscle Diseases

Background:

• Histological mitochondrial alterations are common in late-onset myofibrillar myopathies (MFMs).
• The precise role of these mitochondrial changes in MFM pathogenesis is not well understood.
• Investigating mitochondrial DNA (mtDNA) deletions and respiratory chain complex activity is crucial.

Purpose of the Study:

• To investigate mitochondrial changes, including COX-deficient fibers and mtDNA deletions, in patients with genetically confirmed MFMs.
• To compare these findings with age- and sex-matched normal controls and patients with nuclear genetic defects causing multiple mtDNA deletions.
• To explore the potential link between mitochondrial alterations and MFM pathology.

Main Methods:

• Analysis of COX-deficient fibers and biochemical activities of respiratory chain complexes.
• Detection of multiple mtDNA deletions using nested long-range PCR in microdissected fibers.
• Comparison of MFM patients (MYOT, DES, ZASP, FLNC) with controls and patients with mitochondrial disorders.

Main Results:

• No overall difference in COX-deficient fibers between MFM patients and controls, but significantly higher in 3 MFM patients.
• Two MFM patients, but no controls, exhibited multiple mtDNA deletions, detected only in COX-deficient fibers.
• Increased citrate synthase activity in MFM patients suggests early mitochondrial alterations, though causality is uncertain.

Conclusions:

• While some MFM patients display specific mitochondrial abnormalities like mtDNA deletions, these findings do not universally correlate with myofibrillar accumulations.
• Increased citrate synthase activity indicates potential mitochondrial dysfunction in MFMs.
• The direct contribution of observed mitochondrial changes to the pathogenesis of MFMs requires further investigation.