Effect of prednisone on protein metabolism in Duchenne dystrophy.

Prednisone improves strength in Duchenne dystrophy and changes the natural history of the disease. We studied the in vivo effects of prednisone (0.75 mg.kg-1.day-1) on muscle and whole body protein metabolism in six patients with Duchenne dystrophy and three patients with Becker dystrophy. Patients were admitted to the Clinical Research Center for study and consumed a constant flesh-free diet. Strength was measured by manual and quantitative muscle testing. Fractional muscle protein breakdown was estimated by the ratio of 3-methylhistidine to creatinine excretion determined in three consecutive 24-h urine collections. Whole body protein kinetics were studied in the postabsorptive state using a primed continuous infusion of L-[1-13C]leucine. Fractional muscle protein synthesis was determined from tracer incorporation into noncollagen muscle protein obtained by needle biopsy. After 6-8 wk of prednisone treatment, average muscle strength increased by 15% (P < 0.04), and 24-h creatinine excretion (an index of muscle mass) increased by 21% (P = 0.002). 3-Methylhistidine excretion decreased by 10%, but the change was not statistically significant. The ratio of 3-methylhistidine to creatinine excretion decreased by 26% (P < 0.04). Fractional muscle protein synthesis and whole body protein synthesis and breakdown did not change significantly. We conclude that the beneficial effect of prednisone on strength in Duchenne dystrophy appears to be associated with an increase in muscle mass, which may be mediated by inhibition of muscle proteolysis rather than stimulation of muscle protein synthesis.

Ragged red fibers in normal aging and inflammatory myopathy.

Ragged red fibers are an important marker for mitochondrial disease. To evaluate the hypothesis that mitochondrial dysfunction may play a role in the pathogenesis of aging and inclusion body myositis, we studied the frequency of ragged red fibers in muscle biopsy specimens from 15 young and 13 old normal adults, and from 27 patients with inclusion body myositis, polymyositis, or dermatomyositis. Serial transverse cryostat sections were stained with modified Gomori trichrome, modified succinic dehydrogenase, and cytochrome c oxidase. The frequency of ragged red fibers, determined by measuring the percent number of succinic dehydrogenase-positive ragged red fiber equivalents, was significantly higher in old compared to young normal subjects (0.33 vs. 0.02%, p < 0.0001). With the exception of a single polymyositis biopsy specimen showing a large number of ragged red fibers, the frequency of ragged red fibers in patients with polymyositis or dermatomyositis was similar to that of age-matched normal control subjects. The frequency of ragged red fibers was more than 1% in 7 of 8 patients with inclusion body myositis (maximum, 15%). The modified succinic dehydrogenase stain was more sensitive than the modified Gomori trichrome in detecting accumulation of mitochondria in muscle fibers. Cytochrome c oxidase activity was deficient in most ragged red fibers. We conclude that the number of ragged red fibers increases with normal aging and may reflect an age-related decline in muscle mitochondrial oxidative metabolism. The frequent occurrence of ragged red fibers in inclusion body myositis suggests that mitochondrial function may be impaired in this disease.

Dementia of adult polyglucosan body disease. Evidence of cortical and subcortical dysfunction.

OBJECTIVES: To characterize the dementia associated with adult polyglucosan body disease (APBD) and to correlate the cognitive deficits with abnormalities found on magnetic resonance imaging (MRI). METHODS: Quantitative neuropsychological testing and MRI in one man with APBD and a review of the literature. RESULTS: The dementia of APBD affects cortical and subcortical functions. The cognitive deficits correlate with MRI findings of cortical atrophy and white-matter abnormalities. CONCLUSION: Neuropsychological testing and MRI are helpful in the evaluation of patients with APBD.

Intranuclear rods in severe congenital nemaline myopathy.

We compared the muscle pathology and clinical course in eight patients with congenital nemaline myopathy. An abundance of large intranuclear rods was present in the muscle fibers of one patient with a rapid, fatal course. Intranuclear rods were not present in the muscles of seven patients with a benign course. The large intranuclear rods and the smaller sarcoplasmic rods were similar ultrastructurally and exhibited positive immunoperoxidase staining with anti-alpha-actinin antibodies. The accumulation of alpha-actinin within myonuclei may reflect a severe disturbance of normal intracellular processes regulating myofibrillar synthesis. Since two previously reported infants with intranuclear nemaline rods also had a fatal outcome, the presence of intranuclear rods may represent a marker for a severe form of congenital nemaline myopathy.

Forearm 3-methylhistidine efflux in myotonic dystrophy.

Myotonic dystrophy is associated with progressive muscular atrophy. To define the mechanism of muscle wasting in this disease, we studied myofibrillar proteolysis in vivo in 8 men moderately affected with myotonic dystrophy, and compared the results with those of 10 normal men. Myofibrillar proteolysis was estimated by measuring the 3-methylhistidine arteriovenous difference (A-V) and efflux (Q) across the forearm in the postabsorptive state. Plasma 3-methylhistidine concentrations were determined by high-performance liquid chromatography with postcolumn o-phthalaldehyde derivatization and fluorescence detection. Plasma flow to the forearm muscles (F) was estimated to represent 85% of total forearm plasma flow as determined by the indicator-dilution technique. Forearm 3-methylhistidine efflux was calculated as: Q = F(A-V). Mean muscle mass (24-hour creatinine excretion), lean body mass, and forearm volume were decreased in the patients with myotonic dystrophy, confirming the presence of muscle atrophy. Mean forearm 3-methylhistidine arteriovenous difference and efflux were not significantly different in the two groups. We conclude that myofibrillar protein degradation is not increased in myotonic dystrophy, even when measured in a muscle compartment selectively affected by wasting. Muscle atrophy in myotonic dystrophy is probably the result of defective anabolism rather than accelerated catabolism.

Glycogen branching enzyme deficiency in adult polyglucosan body disease.

Branching enzyme activity was assayed in muscle, peripheral nerve, and leukocytes from 2 Ashkenazi-Jewish patients with adult polyglucosan body disease and 1 African-American and 3 Caucasian patients with the same clinical and pathological features. Branching enzyme activity was normal in the muscle specimens from both Jewish and non-Jewish patients. However, the activity was markedly decreased not only in the leukocytes from the 2 Jewish patients (confirming previous findings), but also in peripheral nerve specimens, whereas it was normal in nerve tissue and leukocytes from all non-Jewish patients. These data confirm a branching enzyme deficiency in a subgroup of patients with adult polyglucosan body disease, and show that the defect is tissue-specific, suggesting that adult polyglucosan body disease has more than one biochemical basis.