Objective To clarify the clinical heterogeneity and genotype-phenotype correlation in dysferlinopathy. Methods Weevaluated clinical parameters of 74 dysferlinopathy patients with knowndysferlin gene mutations who were previously reported in the literature. Results The age at onset varied from 12 to 59 years (mean 21.7 years). Based on the initial distribution of muscle involvement, clinical phenotypes were divided into four subtypes: limb-girdle type, Miyoshi's type, distal anterior compartment type, or scapuloperoneal type. These phenotypic differences were prominent at the early stages, but were difficult to recognize later in the progression of the disease. Patients with missense mutations had significantly moresevere functional status at examination and higher creatine kinase levels than those with frameshift or nonsense mutations.Conclusion Dysferlinopathy exhibited marked heterogeneity in the age at onset, initial distribution of muscle involvement, and rate of disease progression. As this heterogeneity was observed even within the samefamily, some additional factors distinct from dysferlin might be involved. (Internal Medicine 41: 532-536, 2002)

Previous investigators have suggested that proteolysis by calpain, a Ca2+-dependent protease, causes muscle fiber degradation in Duchenne and Becker muscular dystrophies (DMD/BMD). Recent evidence indicates that the nonlysosomal ATP-ubiquitin-dependent proteolytic complex (proteasomes) participates in muscle wasting during various catabolic states and in muscle fiber degradation in physiological or pathological conditions. To elucidate the possible role of proteasomes in dystrophic muscles, routine histochemistry and immunohistochemistry of 26S proteasomes were performed on muscle biopsy specimens obtained from patients with various neuromuscular disorders including DMD/BMD, polymyositis (PM), amyotrophic lateral sclerosis, and peripheral neuropathies, and on normal human muscle specimens. Immunohistochemically, proteasomes were located in the cytoplasm in normal human muscle, but their staining intensity was faint. Compared to control muscles, abnormal increases in both proteasomes and ubiquitin were demonstrated mainly in the cytoplasm of necrotic fibers and to a lesser extent in regenerative fibers in DMD/BMD and PM. Non-necrotic, atrophic fibers in all diseased muscles showed moderate or weak immunoreactions for the proteins; their staining intensities were stronger than those of control muscle fibers. Both proteins often colocalized well. Not all dystrophin-deficient muscle fibers showed a strong reaction for proteasomes. Our results showed increased proteasomes in necrotic and regenerative muscle fibers in DMD/ PMD, although this may not be disease-specific up-regulation. We suggest that the ATP-ubiquitin-dependent proteolytic pathway as well as the nonlysosomal calpain pathway may participate in muscle fiber degradation in muscular dystrophy.

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Objective: Critical illness myopathy (CIM) is an acute myopathy that appears in the setting of critical illness or during exposure to corticosteroids and neuromuscular blocking agents. Its pathological feature is selective loss of thick myosin filaments. Our aim is to gain further insight into the pathomechanism of myosin loss in this myopathy. Methods: To clarify the expression of myosin heavy chain (MHC) and ubiquitin ligase atrogin-1 in this myopathy, histological, immunohistochemical, SDS-PAGE, and semiquantitative reverse transcriptase-polymerase chain reaction studies were performed on innervated and denervated rat soleus muscles after saline and dexamethasone treatments. Results: Denervated muscles from dexamethasone-treated rats showed marked MHC loss. The mRNA expression of ubiquitin ligase atrogin-1 was significantly increased in denervated dexamethasone-treated muscles, suggesting that the ubiquitin-proteasome pathway plays an important role in muscular wasting in CIM. Furthermore, mRNA levels of MHC I, a myosin isoform, were decreased in the denervated dexamethasone-treated muscles. Conclusion: Our findings suggest that an altered transcription rate of myosin, as well as the upregulation of multiple ubiquitin ligases, may be responsible for selective myosin loss in this myopathy.