Hiroyuki Nodera

Mutations of optineurin in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) has its onset in middle age and is a progressive disorder characterized by degeneration of motor neurons of the primary motor cortex, brainstem and spinal cord. Most cases of ALS are sporadic, but about 10% are familial. Genes known to cause classic familial ALS (FALS) are superoxide dismutase 1 (SOD1), ANG encoding angiogenin, TARDP encoding transactive response (TAR) DNA-binding protein TDP-43 (ref. 4) and fused in sarcoma/translated in liposarcoma (FUS, also known as TLS). However, these genetic defects occur in only about 20–30% of cases of FALS, and most genes causing FALS are unknown. Here we show that there are mutations in the gene encoding optineurin (OPTN), earlier reported to be a causative gene of primary open-angle glaucoma (POAG), in patients with ALS. We found three types of mutation of OPTN: a homozygous deletion of exon 5, a homozygous Q398X nonsense mutation and a heterozygous E478G missense mutation within its ubiquitin-binding domain. Analysis of cell transfection showed that the nonsense and missense mutations of OPTN abolished the inhibition of activation of nuclear factor kappa B (NF-κB), and the E478G mutation revealed a cytoplasmic distribution different from that of the wild type or a POAG mutation. A case with the E478G mutation showed OPTN-immunoreactive cytoplasmic inclusions. Furthermore, TDP-43- or SOD1-positive inclusions of sporadic and SOD1 cases of ALS were also noticeably immunolabelled by anti-OPTN antibodies. Our findings strongly suggest that OPTN is involved in the pathogenesis of ALS. They also indicate that NF-κB inhibitors could be used to treat ALS and that transgenic mice bearing various mutations of OPTN will be relevant in developing new drugs for this disorder.

Electrodiagnostic criteria for diagnosis of ALS

A consensus meeting was held to determine the best use and interpretation of electrophysiological data in the diagnosis of ALS. The utility of needle EMG and nerve conduction studies was affirmed. It is recommended that electrophysiological evidence for chronic neurogenic change should be taken as equivalent to clinical information in the recognition of involvement of individual muscles in a limb. In addition, in the context of a suspected clinical diagnosis of ALS, fasciculation potentials should be taken as equivalent to fibrillation potentials and positive sharp waves in recognising denervation. The importance of searching for instability in fasciculation potentials and in motor unit potentials in ALS is stressed. These changes in the interpretation of electrophysiological data render obsolete the category Probable Laboratory-Supported ALS in the modified El Escorial diagnostic criteria for ALS. Methods for detection of upper motor neuron abnormality appear sensitive but require further study, particularly regarding their value when clinical signs of upper motor neuron lesion are uncertain.

KCNQ channels mediate IKs, a slow K+ current regulating excitability in the rat node of Ranvier

Mutations that reduce the function of KCNQ2 channels cause neuronal hyperexcitability, manifested as epileptic seizures and myokymia. These channels are present in nodes of Ranvier in rat brain and nerve and have been proposed to mediate the slow nodal potassium current IKs. We have used immunocytochemistry, electrophysiology and pharmacology to test this hypothesis and to determine the contribution of KCNQ channels to nerve excitability in the rat. When myelinated nerve fibres of the sciatic nerve were examined by immunofluorescence microscopy using antibodies against KCNQ2 and KCNQ3, all nodes showed strong immunoreactivity for KCNQ2. The nodes of about half the small and intermediate sized fibres showed labelling for both KCNQ2 and KCNQ3, but nodes of large fibres were labelled by KCNQ2 antibodies only. In voltage‐clamp experiments using large myelinated fibres, the selective KCNQ channel blockers XE991 (IC50= 2.2 μm) and linopirdine (IC50= 5.5 μm) completely inhibited IKs, as did TEA (IC50= 0.22 mm). The KCNQ channel opener retigabine (10 μm) shifted the activation curve to more negative membrane potentials by −24 mV, thereby increasing IKs. In isotonic KCl 50% of IKs was activated at −62 mV. The activation curve shifted to more positive potentials as [K+]o was reduced, so that the pharmacological and biophysical properties of IKs were consistent with those of heterologously expressed homomeric KCNQ2 channels. The ability of XE991 to selectively block IKs was further exploited to study IKs function in vivo. In anaesthetized rats, the excitability of tail motor axons was indicated by the stimulus current required to elicit a 40% of maximal compound muscle action potential. XE991 (2.5 mg kg−1i.p.) eliminated all nerve excitability functions previously attributed to IKs: accommodation to 100 ms subthreshold depolarizing currents, the post‐depolarization undershoot in excitability, and the late subexcitability after a single impulse or short trains of impulses. Due to reduced spike‐frequency adaptation after XE991 treatment, 100 ms suprathreshold current injections generated long trains of action potentials. We conclude that the nodal IKs current is mediated by KCNQ channels, which in large fibres of rat sciatic nerve appear to be KCNQ2 homomers.

Nerve excitability testing and its clinical application to neuromuscular diseases

Non-invasive nerve excitability testing measures the membrane polarization, ion channel function and paranodal/internodal condition of peripheral nerves. This technique has been recently used for various neuromuscular disorders, such as pure motor conduction block in multifocal motor neuropathy, conduction block in carpal tunnel syndrome and Na(+) channel function disorders in diabetic neuropathy, to shed light on their pathophysiology. Here, we review the basics of ion channel functions and membrane properties that influence nerve excitability, the basic principles of nerve excitability testing and the reported findings in various disorders.

Threshold electrotonus in chronic inflammatory demyelinating polyneuropathy: Correlation with clinical profiles

Chronic inflammatory demyelinating polyneuropathy (CIDP) is characterized by multifocal demyelination along the course of the nerves, and involvement of the intermediate segments may correlate with more severe demyelination associated with breakdown of the blood–nerve barrier. Threshold electrotonus was used to study whether altered membrane properties of the median nerve at the wrist (intermediate segment) are associated with clinical profiles in 21 CIDP patients. In response to hyperpolarizing conditioning stimuli, the threshold changes were significantly greater for CIDP patients than for normal controls (n = 49). The pattern was similar to that of 11 patients with Charcot‐Marie‐Tooth disease type 1a, who exhibited abnormally high thresholds to hyperpolarizing currents. The abnormal threshold electrotonus was present in 48% of the CIDP patients and was associated with longer disease duration, more severe disability, poorer response to immune treatments, and slower nerve conduction velocities. Threshold electrotonus can be used to detect demyelination at the tested sites and may provide new information about pathophysiology and distribution patterns of demyelination in CIDP. Muscle Nerve 29: 28–37, 2004

Can Awaji ALS criteria provide earlier diagnosis than the revised El Escorial criteria

BACKGROUND Recently, new electrophysiological ALS criteria incorporating fasciculation potentials (FPs) as evidence for lower motor neuron signs (Awaji Criteria (AC)) was proposed to provide earlier detection of early-stage ALS than revised El Escorial electrophysiological criteria (REEC). However, serial electrophysiological analysis is lacking to ascertain the original intention. The objective for this study was to elucidate whether electrophysiological criteria set for AC detects ALS earlier than REECs counterpart in patients with ALS. METHODS Of the 51 patients who were clinically suspected of ALS, 35 patients prospectively received serial electrophysiological studies every 3 months until (1) both electrophysiological AC and REEC criteria were met in more than two muscles representing both of the cervical and lumbosacral segments or (2) either clinically definite or clinically probable REEC criteria was met. The intervals were determined between the initial disease onset and when the respective electrophysiological criteria were met. RESULTS Electrophysiological diagnostic criteria were met in 94.3% by AC and 40% by REEC at the initial visits. The intervals between the disease onset and the time of meeting the electrophysiological criteria were shorter in AC (mean: 9.0 months) than in REEC (mean: 15.2 months) (P<0.01). Eleven patients who met only AC electrophysiological criteria on the initial study subsequently met REEC electrophysiological criteria with the mean interval of 3.8 months. A higher percentage of bulbar-type ALS (83.3%) met AC than limb-onset ALS (43.4%) (P<0.05). FPs tended to be more frequently observed than fib/psw in the muscles outside the region of initial clinical onset. CONCLUSION Electrophysiological criteria of AC were met earlier than that of REEC in ALS patients, especially in patients with bulbar onset. Early recognition of ALS by AC may allow effective therapeutic intervention in the early disease stage.

Screening for TARDBP mutations in Japanese familial amyotrophic lateral sclerosis

TAR-DNA-binding protein 43 (TDP-43), encoded by the TARDBP gene on chromosome 1p36.22, has been identified as the major pathological protein in abnormal inclusions in neurons and glial cells in sporadic amyotrophic lateral sclerosis (SALS), SOD1-negative familial ALS (FALS) and frontotemporal lobar dementia (FTLD). Twenty mutations of TARDBP in SOD1-negative FALS and SALS cases have been reported so far. To investigate the presence and frequency of TARDBP mutations in Japanese SOD1-negative FALS patients, we performed mutational screening of TARDBP in 30 SOD1-negative FALS patients. An N352S mutation was found in one case of FALS, but no TARDBP mutations were found in cases of SALS. It was thought that this mutation increases TDP-43 phosphorylation. This might lead to impaired nuclear cytoplasmic transport or protein-protein interaction, thereby leading to TDP-43 accumulation.

Activity-dependent conduction block in multifocal motor neuropathy Magnetic fatigue test

Background: Multifocal motor neuropathy (MMN) is often misdiagnosed as motor neuron disease, especially when overt evidence of conduction block (CB) is lacking. Activity-dependent CB (ADCB), defined as transient CB induced by brief exercise, has been recently found in MMN but not in ALS. Methods: To test the diagnostic utility of ADCB for differentiating MMN from ALS, the authors recorded the compound muscle action potentials (CMAPs) from small hand muscles by magnetically stimulating nerve roots before and after 1 minute of maximal voluntary contraction (magnetic fatigue test). They examined nine patients with MMN with unequivocal clinical responses to IV immunoglobulins (IVIgs), yet lacked CB according to the conventional criteria. Results: Six MMN patients had postexercise CB/temporal dispersion maximum in the immediate postexercise period. ADCB in an MMN patient improved after IVIg. Further analysis revealed that prolongation of the duration from the onset to the positive peak of the CMAP was the most sensitive indicator for MMN, presumably because the phase cancellation obscures the abnormalities of the other parameters. Conclusion: The magnetic fatigue test is useful in detecting mild conduction block presumably located in a proximal nerve segment in patients with multifocal motor neuropathy who do not fulfill its conventional electrodiagnostic criteria.

Extreme efficacy of intravenous immunoglobulin therapy for severe burning pain in a patient with small fiber neuropathy associated with primary Sjögren's syndrome.

Neurological involvement occurs in approximately 20% of patients with primary Sjögren’s syndrome. Although neurological symptoms can affect the peripheral nervous system and the central nervous system, the most frequent symptom is polyneuropathy. Small fiber neuropathy (SFN) is a form of painful peripheral polyneuropathy that is common in patients with diabetic neuropathy, but may also occur in toxic, infectious, or immune-mediated neuropathy. We show here a patient with Sjögren’s syndrome who developed SFN and was treated with intravenous immunoglobulin (IVIG) therapy, which was immediately and extremely effective. Because of the efficacy of IVIG therapy, we propose that direct immune-mediated mechanisms may be involved in the pathogenesis of SFN complicated by Sjögren’s syndrome.

Neuroprotective effects of Kv7 channel agonist, retigabine, for cisplatin-induced peripheral neuropathy.

Chemotherapy-induced peripheral neuropathy is a major dose-limiting side effect of many commonly used chemotherapeutic agents. One mechanism underlying this neuronal damage is via drug-induced membrane depolarization. Accordingly, one potential approach for preventing chemotherapy-induced neuropathy is via the forced maintenance of normal membrane potential during exposure to the toxic drug. More specifically, intentional elevation of the slow K(+) current, via activation of Kv7 channels with a resultant hyperpolarizing shift, could be theoretically neuroprotective. In this study, in vivo nerve excitability testing in sensory nerves in mice was used to evaluate the potential therapeutic role of retigabine, a Kv7 channel activator, in the prevention of cisplatin-induced neurodegeneration. It was found that cisplatin caused membrane depolarization and peripheral axon loss that were partially prevented by retigabine pretreatment. These results support the general concept that chemotherapy-induced neuropathy can be partially inhibited via Kv7 channel activation.