Antibodies against acetylcholine receptors (AChRs) cause pathogenicity in myasthenia gravis (MG) patients through complement pathway-mediated destruction of postsynaptic membranes at neuromuscular junctions (NMJs). However, antibodies against muscle-specific kinase (MuSK), which constitute a major subclass of antibodies found in MG patients, do not activate the complement pathway. To investigate the pathophysiology of MuSK-MG and establish an experimental autoimmune MG (EAMG) model, we injected MuSK protein into mice deficient in complement component five (C5). MuSK-injected mice simultaneously developed severe muscle weakness, accompanied by an electromyographic pattern such as is typically observed in MG patients. In addition, we observed morphological and functional defects in the NMJs of EAMG mice, demonstrating that complement activation is not necessary for the onset of MuSK-MG. Furthermore, MuSK-injected mice exhibited acetylcholinesterase (AChE) inhibitor-evoked cholinergic hypersensitivity, as is observed in MuSK-MG patients, and a decrease in both AChE and the AChE-anchoring protein collagen Q at postsynaptic membranes. These findings suggest that MuSK is indispensable for the maintenance of NMJ structure and function, and that disruption of MuSK activity by autoantibodies causes MG. This mouse model of EAMG could be used to develop appropriate medications for the treatment of MuSK-MG in humans.

To investigate the usefulness of low-dose FK506 for the treatment of myasthenia gravis (MG), we treated 19 patients with generalized MG in a 16-week open clinical trial of FK506 (3-5 mg/day). At the end of the trial, total MG scores (range: 0-27 points) improved by 3 points or more in 7 of 19 patients (37%), and activities of daily living (ADL) scores (range: 0-6 points) also improved by 1 point or more in 8 of 19 patients (42%). Nine of 19 patients (47%) showed improvement in either MG or ADL scores. Significant reduction of anti-acetylcholine receptor antibody titers and interleukin 2 production were observed at the end of this study. Minor but commonly observed side effects were an increase in neutrophil count and a decrease in lymphocyte count. No serious adverse events such as renal toxicity or diabetes mellitus were observed during the 16-week treatment period. FK506 could safely serve as an adjunct to steroid therapy for MG at low dosage.

We investigated the presence of antibodies (Abs) against muscle-specific tyrosine kinase (MuSK) in Japanese myasthenia gravis (MG) patients. MuSK Abs were found in 23 (27%) of 85 generalized seronegative MG (SNMG) patients but not in any of the ocular MG patients. MuSK Ab-positive patients were characterized as having female dominance (M:F, 5:18), age range at onset 18 to 72 (median 45) years old, and prominent oculobulbar symptoms (100%) with neck (57%) or respiratory (35%) muscle weakness. Limb muscle weakness was comparatively less severe (52%), thymoma absent. Most patients had good responses to simple plasma exchange and steroid therapy. MuSK IgG from all 18 patients was exclusively the IgG 4 subclass and bound mainly with the MuSK Ig 1-2 domain. Serial studies of 12 individuals showed a close correlation between the variation in MuSK Ab titers and MG clinical severity (P = 0.01 by Kruskal-Wallis). MuSK Ab titers were sharply decreased in patients who had a good response to early steroid therapy or simple plasma exchange, but there was no change, or a rapid increase on exacerbation after thymectomy. Measurement of MuSK Ab titers aids in the diagnosis of MG and the monitoring of clinical courses after treatment.

Efficacy and safety of long term use of FK506 (2-4.5 mg/ day) for a maximum of two years were evaluated in 12 patients with generalised myasthenia gravis (MG). At the end of the study, eight patients (67%) showed improvement in either MG score or Activities in Daily Living score, and prednisolone dosage could be reduced in seven patients (58%), with a mean reduction ratio of 37%. Long term use of FK506 for MG can be more effective than short term administration, with no serious side effects.

SUMMARY1. The whole-cell variation of the patch-clamp technique was used to record ionic currents in Schwann cells obtained from enzyme-treated mouse sciatic nerves before and after the onset of myelination.2. Only outward currents were evoked in embryonic Schwann cells, which had no myelin, at membrane potentials more positive than -40 mV. Neonatal myelinating cells developed depolarization-activated outward currents and hyperpolarizationactivated inward currents. For large hyperpolarizations below -160 mV, inward currents exhibited a sag following a peak which appeared to be mainly due to Na+ blockade.3. Membrane potentials of neonatal myelinating cells were more negative than those of embryonic cells. The depolarization of the membrane potentials per 10-fold increase in external K+ concentrations in neonatal myelinating cells was 57 mV which fits the Nernst equation for a K+ electrode.4. Quinine (0-5-2 mm) blocked the outward currents in embryonic cells and Ba2+ (2 mM) blocked both outward and inward currents in neonatal myelinating cells leaving quinine-sensitive outward currents of the embryonic type. External Cs+ (5 mM) blocked mainly inward currents and internal Cs+ blocked outward currents.5. Developmental changes of these voltage-gated K+ currents in myelinating cells showed that Ba2+-sensitive K+ currents disappeared rapidly during the first week of life in association with the membrane potential becoming more positive. In contrast, quinine-sensitive outward K+ currents of the embryonic type disappeared slowly during the first 3-4 weeks after birth.6. It is concluded that neonatal myelinating Schwann cells developed new voltage-gated K+ channels, which are Ba2+-sensitive and set a new membrane potential, in addition to the voltage-gated K+ channels of embryonic type. The Ba2+-sensitive K+ channels in myelinating cells were suggested to play an important role in siphoning K+ ions accumulated in periaxonal space during nerve activities.

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SUMMARY1. Ionic currents in Schwann cells cultured from enzymatically dissociated sciatic nerves of newborn mice were recorded by the whole-cell variation of the patch-clamp technique.2. In these cells only the voltage-dependent K+ currents were recorded. The K+ current was suppressed by quinine, 4-aminopyridine (4-AP) or tetraethylammonium (TEA), their half-suppression concentrations being 22 /tM, 0-3 mm and 15 mM, respectively.3. The peak amplitudes and density of the K+ currents in these Schwann cells increased rapidly during the first 2 days of the culture.4. In an investigation of the linkage between K+ channels and Schwann cell proliferation, three different K+ channel blockers (quinine, 4-AP and TEA) were added to the medium at different stages of the culture. In media containing sublethal doses of quinine or 4-AP, the start of cell proliferation was delayed when these drugs were added at 12 h or on day 3. The same doses of these drugs applied on day 6, when the Schwann cells were proliferating, did not affect cell proliferation. TEA showed a discrepancy between the dose-dependent blocking of K+ channels and cell proliferation because of its additional cytotoxic effects.5. It is concluded that voltage-dependent K+ channels in mouse Schwann cells are similar to those observed in human and murine T lymphocytes. These K+ channels are suggested to be involved in Schwann cell proliferation at early stages of development.

We investigated a family manifesting amyotrophic lateral sclerosis (ALS) with a heterozygous E478G mutation in the optineurin (OPTN) gene. Clinically, slow deterioration of motor function, mood and personality changes, temporal lobe atrophy on neuroimaging, and bizarre finger deformity were noted. Neuropathologically, TAR DNA-binding protein 43 (TDP-43)-positive neuronal intracytoplasmic inclusions were observed in the spinal and medullary motor neurons. In these cells, the immunoreactivity of nuclear TDP-43 was reduced. Consecutive sections revealed that the inclusions were also reactive with anti-ubiquitin and anti-p62 antibodies, but noticeably negative for OPTN. In addition, TDP-43/p62-positive glial cytoplasmic inclusions (GCIs) were scattered throughout the spinal cord and the medullary motor nuclei. Furthermore, Golgi fragmentation was identified in 70% of the anterior horn cells (AHCs). The presence of AHCs with preserved nuclear TDP-43 and a fragmented Golgi apparatus, which are unrecognizable in sporadic ALS, indicates that patients with the E4787G OPTN mutation would manifest Golgi fragmentation before loss of nuclear TDP-43. In the neocortex, GCIs were sparsely scattered among the primary motor and temporal cortices, but no neuronal TDP-43-positive inclusions were detected. In the amygdala and the ambient gyrus, argyrophilic grains and ballooned neurons were seen. The thorough neuropathologic investigations performed in this work demonstrated that OPTN-positive inclusion bodies, if any, were not prominent. We postulate that optineurinopathy is closely linked with TDP-proteinopathy and speculate that this heterozygous E478G mutation would cause ALS by acting through a dominant-negative mechanism.