A 5-year-old boy with ragged red fibers on muscle biopsy most likely has impairment in which metabolic pathway?

A 5-year-old boy with ragged red fibers on muscle biopsy most likely has impairment in which metabolic pathway?

• A. Oxidative phosphorylation
• B. Fatty acid oxidation
• C. Gluconeogenesis
• D. Pentose phosphate pathway

Answer: (A)

Ragged red fibers point to a mitochondrial myopathy where energy production is impaired at the level of oxidative phosphorylation. When the electron transport chain and ATP synthesis in mitochondria don’t work properly, muscle fibers compensate by increasing the number of mitochondria around the fiber's edge, giving the characteristic ragged appearance on special stains. This is why the most likely pathway affected is oxidative phosphorylation. In these conditions, tissues with high energy demands, like muscle, often show exercise intolerance and can have lactic acidosis due to a shift toward anaerobic metabolism. Fatty acid oxidation defects, gluconeogenesis issues, or the pentose phosphate pathway don’t produce the same mitochondrial proliferation pattern seen as ragged red fibers, so they’re less consistent with this biopsy finding.

Ragged red fibers point to a mitochondrial myopathy where energy production is impaired at the level of oxidative phosphorylation. When the electron transport chain and ATP synthesis in mitochondria don’t work properly, muscle fibers compensate by increasing the number of mitochondria around the fiber's edge, giving the characteristic ragged appearance on special stains. This is why the most likely pathway affected is oxidative phosphorylation. In these conditions, tissues with high energy demands, like muscle, often show exercise intolerance and can have lactic acidosis due to a shift toward anaerobic metabolism. Fatty acid oxidation defects, gluconeogenesis issues, or the pentose phosphate pathway don’t produce the same mitochondrial proliferation pattern seen as ragged red fibers, so they’re less consistent with this biopsy finding.