Ikuya Nonaka

Familial distal myopathy with rimmed vacuole and lamellar (myeloid) body formation

Three cases from 2 families had muscle weakness with predilection for distal extremities, predominantly affecting the tibialis anterior muscles, and onset in early adulthood. The disorder seemed to be inherited through an autosomal recessive trait. The EMG demonstrated a myopathic pattern and CPK was mildly elevated. The striking finding in their muscle biopsies was the presence of rimmed vacuoles which had acid phosphatase-positive autophagic activity and which contained numerous concentric lamellar bodies in various forms (myeloid and cabbage bodies). Despite rapid clinical progression, not only necrotic fibers with phagocytosis, as seen in Duchenne dystrophy, but also evidence of regeneration were virtually absent. Continuous destruction of myofibrils by activation of certain lysosomal proteolytic enzymes might be responsible for the production of atrophic fibers.

Distal myopathy with rimmed vacuoles is allelic to hereditary inclusion body myopathy

Background: Distal myopathy with rimmed vacuoles (DMRV) is an autosomal-recessive disorder with preferential involvement of the tibialis anterior muscle that starts in young adulthood and spares quadriceps muscles. The disease locus has been mapped to chromosome 9p1-q1, the same region as the hereditary inclusion body myopathy (HIBM) locus. HIBM was originally described as rimmed vacuole myopathy sparing the quadriceps; therefore, the two diseases have been suspected to be allelic. Recently, HIBM was shown to be associated with the mutations in the gene encoding the bifunctional enzyme, UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE). Objective: To determine whether DMRV and HIBM are allelic. Methods: The GNE gene was sequenced in 34 patients with DMRV. The epimerase activity in lymphocytes from eight DMRV patients was also measured. Results: The authors identified 27 unrelated DMRV patients with homozygous or compound-heterozygous mutations in the GNE gene. DMRV patients had markedly decreased epimerase activity. Conclusions: DMRV is allelic to HIBM. Various mutations are associated with DMRV in Japan. The loss-of-function mutations in the GNE gene appear to cause DMRV/HIBM.

Werdnig-Hoffmann disease: proposal of a pathogenetic mechanism.

SummaryLight and electron microscopic study and morphometric analysis were performed on the spinal cords and roots from six cases of acute Werdnig-Hoffmann disease and four control cases, in search of the pathogenesis of the selective motor neuron changes considered primarily responsible for Werdnig-Hoffmann disease. This investigation posits a centrifugal traction mechanism based upon the discovery of cylindrical outgrowths of glial bundles, selective loss of large myelinated fibers, and axonal degeneration in the proximal portion of anterior spinal roots (and to a lesser extent in posterior spinal roots) in all six disease cases. This traction mechanism exerts principally upon anterior spinal nerve roots and can account for morphologic and morphometric data characteristically ascribed to Werdnig-Hoffmann disease.

Quantitation of mitochondrial DNA carrying tRNALys mutation in MERRF patients

An A to G transition at nucleotide position 8,344 in tRNALys of mitochondrial DNA has been recently identified as a causative mutation of myoclonus epilepsy associated with ragged-red fibers (MERRF). To investigate if the degree of heteroplasmy of mitochondrial DNA is correlated with the severity of MERRF, we have developed a novel method for quantitation of the mutant mitochondrial DNA by polymerase chain reaction using a mismatched primer. With the method, populations of mutant mtDNAs from 5 cases of MERRF carrying the tRNALys mutation were analyzed. The tight linkage of the severity of symptoms and the degree of heteroplasmies is not necessarily observed for all cases, though there is a tendency that patients with less wild type mtDNAs show severer clinical symptoms and earlier onset.

Satellite cells and muscle regeneration in diseased human skeletal muscles

By virtue of the lanthanum nitrate staining technique applied to biopsied muscle we are able to demonstrate interaction between satellite cells and parent myofibers, as well as development of premyocytes from activated satellite cells. The process of regeneration in diseased muscle appears to differ from that described in experimental myogenesis. Transformation of activated satellite cells to two types of premyocytes in the process of muscle regeneration seems to rely primarily on the state of innervation and recovery rate of the parent cell after injury. Activated satellite cells are characterized morphologically by proliferation of caveolae, first on the parent fiber side, and early T-tubule and myofilament formation and central displacement. In diseased human muscle the satellite cells appear to play significant roles in muscle regeneration both as a source of reinforcement for failing metabolism in the parent cell and as potential replacements for the necrotic segment of the parent cell. This study also demonstrates that the satellite cells are capable of developing into independent myocytes which may fuse with or replace the parent cell, dependent upon the type and extent of the injury sustained. Abnormal fusion among premyocytes or with their parent fiber, resulting in formation of split-or ring-fibers, becomes conceivable when both innervation and recovery from the injury of the parent cell are delayed. Thus, myotube formation, characteristic of usual myogenesis, seldom takes place in the regenerative process instituted by satellite cells in diseased human skeletal muscles.

Distal myopathy with rimmed vacuoles

Distal myopathy with rimmed vacuoles is an autosomal recessively inherited disorder with preferential involvement of the anterior tibial muscle. Recently the gene was discovered to be mapped to chromosome 9, the same region as in familial inclusion body myopathy (rimmed vacuole myopathy sparing the quadriceps). The onset of the disease was in young adults 20-40 years of age, averaging 26 years. The disease was progressive and most of the patients became non-ambulant within 12 years after the onset. The striking and common pathologic finding was the presence of rimmed vacuoles in muscle fibers with little evidence of necrotic or regenerative processes. Nuclear change with tubulofilamentous inclusions probably induces focal myofibrillar degeneration which activates the lysosomal system, resulting in active autophagocytosis and myelin body formation, i.e. rimmed vacuole formation.

Muscle fiber degeneration in distal myopathy with rimmed vacuole formation

In 11 patients with distal myopathy with rimmed vacuole formation (DMRV), a well-known autosomal recessively inherited disorder, the rimmed vacuole formation appears to be the main pathological change accounting for the progressive muscle fiber degeneration. To gain a better understanding of the pathophysiology of the vacuole formation, we applied Congo red and immunohistochemical stains to muscle biopsies from these patients and the results were compared with those of patients with inclusion body myositis (IBM). The vacuoles in DMRV contained Congophilic amyloid material and deposits immunoreactive for β-amyloid protein, both the NH2 and COOH termini of β-amyloid protein precursor, ubiquitin, and tau protein. These results were similar to those seen in our present cases of IBM as well as in previously reported cases. Therefore, there may be no pathogenetic differences in the formation of rimmed vacuoles in DMRV and IBM. Nevertheless, the degenerative process involved in rimmed vacuole formation in various diseases may share a common pathogenetic mechanism with that in amyloid-plaque formation in Alzheimers disease brain as has been proposed previously.

Sarcolemmal indentation in cardiomyopathy with mental retardation and vacuolar myopathy

Muscle biopsies from three patients with cardiomyopathy, mental retardation and increased serum creatine kinase levels revealed scattered fibers with tiny intracytoplasmic vacuoles containing basophilic and acid phosphatase-positive material and slightly increased amounts of PAS-positive granules. These findings are consistent with those seen in the so-called lysosomal glycogen storage disease with normal acid maltase. In addition to the vacuoles, there were occasional folds or indentations in the sarcolemma which were connected to the membrane enclosing the vacuoles. These membranes were well demonstrated histochemically by the nonspecific esterase and acetylcholinesterase stains. On electron microscopy, most of the vacuoles were bounded by membranes with basal lamina. The vacuolar membrane stained positively with antibodies raised to dystrophin, dystrophin-associated glycoproteins, laminin and type 4 collagen, and it was identical to the sarcolemma and its basal lamina. Therefore, the membrane abnormality which causes sarcolemmal folding is probably critical to understanding the pathomechanism of this disease.

Clonal heterogeneity of thymic muscle-cell precursors

Three myoid-cell clones were established from the thymuses of two Wistar rats; one thymus yielded two clones, RBISA and R615B2, and the other yielded one clone, R613Ad. The three clones were divided into two subtypes. Both subtypes were able to form myofibrils, expressed AChR on their cell-surface membrane, and contained myofibrillar ATPase characteristic of und ifferentiated type-2C fibers, but they differed from each other in morphology, expression of Thy 1 antigen, spontaneous contractility, and qualitative accumulation of AChR. Immunolocalization studies using antisera against the respective cell subtypes also indicated regional differences in their cellular origin. These results show that the thymus contains heterogenous myoid-cell precursors.

Two-step mechanism of myofibrillar protein degradation in acute plasmocid-induced muscle necrosis

Acute muscle necrosis was induced in rats by intramuscular injection of plasmocid, a known myotoxic agent. A single injection of 5 mg/ml plasmocid produced massive fiber necrosis with extensive phagocytosis. Plasmocid administration led to a preferential decrease of alpha-actinin with preservation of other structural proteins within 3 h after injection, and large increases (2-7-fold) in the activities of acid hydrolases, cathepsins B and L, cathepsin D and alpha-galactosidase within 48 h after injection. The plasmocid-induced stimulation of alpha-actinin loss seen at 3 h, when no increases of acid hydrolases occurred, could be inhibited by a cysteine protease inhibitor, Ep-475 (E-64-c), and EGTA. On the other hand, increased lysosomal enzyme activity seemed to have a close correlation with the appearance of invading mononuclear cells, probably macrophages, and not muscle lysosomes. These observations suggest that a two step mechanism of protein degradation (nonlysosomal and lysosomal processes) possibly occurs in plasmocid-induced muscle degradation and macrophages can serve as a main endogenous reservoir of proteases in pathological states.