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Histochemical and ultrastructural analysis of the mitochondrial changes in a familial mitochondrial myopathy
Abstract:
Two familial cases of progressive external ophthalmoplegia with involvement of pharyngeal and distal muscles are presented. 'Ragged-red' fibres were found in both cases. Excessive amounts of RNA, as evidenced by the acridine orange-induced fluorescence, were noted in many muscle fibres, mostly in the 'ragged-red' fibres. At the ultrastructural level, numerous mitochondrial changes with paracrystalline formations were noted. Those formations were observed in three forms and three-dimensional reconstruction is proposed which suggests that the paracrystalline formations consist of undulating parallel leaflets joined along the top of the undulations. Small transverse bridges between neighbouring cristae and between cristae and paracrystalline formations are also emphasized. All those mitochondrial abnormalities are thought to represent the morphological expression of a biochemical deficiency in the inner membrane. They are interpreted thus: firstly, the biochemical defect leads to a multiplication of the mitochondria with increase in their volume and proliferation of the cristae in order to improve energy production; secondly, bridges between the modified inner membranes induce attachment of the neighbouring cristae and result in paracrystalline formations.
Insights
This study presents two familial cases of progressive external ophthalmoplegia, a muscle disorder. Researchers observed mitochondrial abnormalities and excessive RNA in muscle fibers, suggesting a biochemical defect.
Area of Science:
- Neurology
- Mitochondrial Biology
- Muscle Physiology
Background:
- Progressive external ophthalmoplegia (PEO) is a rare neuromuscular disorder.
- Familial cases suggest a genetic component.
- Muscle biopsy is crucial for diagnosing mitochondrial myopathies.
Observation:
- Two familial cases of PEO with pharyngeal and distal muscle involvement were studied.
- 'Ragged-red' fibers and excessive RNA (acridine orange fluorescence) were observed in muscle samples.
- Ultrastructural analysis revealed significant mitochondrial abnormalities, including paracrystalline formations.
Findings:
- Paracrystalline formations in mitochondria were characterized in three forms.
- Three-dimensional reconstruction suggests these formations comprise undulating parallel leaflets.
- Mitochondrial abnormalities are interpreted as morphological evidence of an inner membrane biochemical deficiency.
Implications:
- The findings suggest a link between biochemical defects and mitochondrial structural changes in PEO.
- Understanding these mitochondrial alterations may lead to improved diagnostic markers.
- Further research into the specific biochemical pathways affected is warranted.