PRINT
E-MAIL
THIS PAGE
CHAPTER TEST 
LEARNING
OBJECTIVESMETABOLIC MYOPATHIES
Glycogenosis type 5 (phosphorylase deficiency, McArdle disease), and type 7 (phosphofructokinase deficiency) are glycolytic enzyme defects that impair the use of glycogen for energy. They cause weakness, cramps, and myonecrosis on exertion. Between episodes, the muscle may look normal. There are specific histochemical and biochemical tests for their diagnosis. |
 |
| Adult acid maltase deficiency | Lipid storage myopathy |
Disorders of lipid metabolism impair the use of lipid for energy. Carnitine carries fatty acids into the mitochondria. Carnitine deficiency causes weakness and a lipid storage myopathy. Carnitine palmitoyl transferase (CPT) transfers fatty acids from carnitine to acetyl-CoA. CPT deficiency causes myonecrosis, often precipitated by exercise.
 |
 |
| Ragged red fibers | Mitochondria in RRF |
Deficiencies of enzymes of the respiratory chain affect more severely muscle and brain which are heavily dependent on oxidative phosphorylation. Several mitochondrial encephalopathy and encephalomyopathy syndromes have been described. Muscle involvement is characterized by weakness and ophthalmoplegia. Mitochondrial myopathies that impair intramitochondrial protein synthesis are associated with a characteristic histological abormality, the "ragged red fiber" (RRF). This term refers to an abnormality seen in frozen sections of muscle stained with the Gomori trichrome stain. The red color of these fibers is due to large numbers of abnormal mitochondria that represent a compensatory proliferation. In addition to their red color, the abnormal fibers are coarse and disorganized. Electron microscopy shows clusters of large, irregular mitochondria with crystal-like inclusions.
