Ryuji Kaji

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.

Mutations in COQ2 in familial and sporadic multiple-system atrophy the multiple-system atrophy research collaboration

BACKGROUND Multiple-system atrophy is an intractable neurodegenerative disease characterized by autonomic failure in addition to various combinations of parkinsonism, cerebellar ataxia, and pyramidal dysfunction. Although multiple-system atrophy is widely considered to be a nongenetic disorder, we previously identified multiplex families with this disease, which indicates the involvement of genetic components. METHODS In combination with linkage analysis, we performed whole-genome sequencing of a sample obtained from a member of a multiplex family in whom multiple-system atrophy had been diagnosed on autopsy. We also performed mutational analysis of samples from members of five other multiplex families and from a Japanese series (363 patients and two sets of controls, one of 520 persons and one of 2383 persons), a European series (223 patients and 315 controls), and a North American series (172 patients and 294 controls). On the basis of these analyses, we used a yeast complementation assay and measured enzyme activity of parahydroxybenzoate-polyprenyl transferase. This enzyme is encoded by the gene COQ2 and is essential for the biosynthesis of coenzyme Q10. Levels of coenzyme Q10 in lymphoblastoid cells and brain tissue were measured on high-performance liquid chromatography. RESULTS We identified a homozygous mutation (M78V-V343A/M78V-V343A) and compound heterozygous mutations (R337X/V343A) in COQ2 in two multiplex families. Furthermore, we found that a common variant (V343A) and multiple rare variants in COQ2, all of which are functionally impaired, are associated with sporadic multiple-system atrophy. The V343A variant was exclusively observed in the Japanese population. CONCLUSIONS Functionally impaired variants of COQ2 were associated with an increased risk of multiple-system atrophy in multiplex families and patients with sporadic disease, providing evidence of a role of impaired COQ2 activities in the pathogenesis of this disease. (Funded by the Japan Society for the Promotion of Science and others.).

Multifocal demyelinating motor neuropathy Cranial nerve involvement and immunoglobulin therapy

We report two patients with multifocal demyelinating motor neuropathy whose symptoms improved after immunoglobulin infusion. Clinical signs included atrophy of the tongue and limb muscles, closely resembling that of motor neuron disease. Nerve conduction studies revealed multiple sites of motor conduction block without sensory abnormalities, suggesting selective involvement of motor fibers. Careful documentation of conduction block is required to diagnose this entity, which may be treated with immunoglobulin therapy.

Reduced Neuron-Specific Expression of the TAF1 Gene Is Associated with X-Linked Dystonia-Parkinsonism

X-linked dystonia-parkinsonism (XDP) is a movement disorder endemic to the Philippines. The disease locus, DYT3, has been mapped to Xq13.1. In a search for the causative gene, we performed genomic sequencing analysis, followed by expression analysis of XDP brain tissues. We found a disease-specific SVA (short interspersed nuclear element, variable number of tandem repeats, and Alu composite) retrotransposon insertion in an intron of the TATA-binding protein-associated factor 1 gene (TAF1), which encodes the largest component of the TFIID complex, and significantly decreased expression levels of TAF1 and the dopamine receptor D2 gene (DRD2) in the caudate nucleus. We also identified an abnormal pattern of DNA methylation in the retrotransposon in the genome from the patients caudate, which could account for decreased expression of TAF1. Our findings suggest that the reduced neuron-specific expression of the TAF1 gene is associated with XDP.

Dissociation between contingent negative variation (CNV) and Bereitschaftspotential (BP) in patients with parkinsonism.

In order to clarify the generator mechanism of the late component of contingent negative variation (CNV), we compared the late CNV with Bereitschaftspotential (BP) in patients with parkinsonism (Parkinsons disease and progressive supranuclear palsy). In patients with mild symptoms (Hoehn Yahr grade I and II) both the late CNV and BP were clearly seen. In patients with severe symptoms (Hoehn Yahr grade III, IV and V) the BP was normally seen, but the late CNV was significantly smaller or absent (P < 0.001 at Cz) and it was also significantly smaller than that obtained from age-matched normals. In one patient (H-Y grade II) who had normal BP, the late CNV was diminished selectively at the midline area. Since it was reported that the late CNV arises from at least the supplementary motor area (SMA), selective diminution of the late CNV at the midline could be explained by the decreased activity of the SMA in parkinsonism. It was also previously reported that the BP was absent but the late CNV was normally present in a patient with cerebellar efferent lesion (Ikeda et al., 1994). Taken together with the experimental results indicating that movement-related neurons in the putamen behave contingent on external stimuli, it is suggested that subcortical generating mechanism is different for the late CNV and BP although both commonly share at least some cortical generators, and that the basal ganglia are most likely responsible for the generation of the late CNV and the cerebellar efferent system for the generation of the BP.

Physiology of conduction block in multifocal motor neuropathy and other demyelinating neuropathies

Conduction block is an important functional consequence of demyelination whereby nervous transmission is abolished. Its mechanism has been discussed with respect to the loss of insulation due to disruption of myelin. Recent development of threshold tracking techniques, which enabled noninvasive assessment of axonal membrane potentials and ion channels, has provided evidence that axonal excitability changes significantly and contributes to conduction failure. This view, based upon axo‐glial interaction, clarifies the mechanism of muscle fatigue and fasciculation associated with peripheral demyelination and possibly explains selective motor involvement in multifocal motor neuropathy. Muscle Nerve 27: 285–296, 2003

Functional anatomy of the basal ganglia in X-linked recessive dystonia-parkinsonism.

Dystonia is a neurological syndrome characterized by sustained muscle contractions that produce repetitive twisting movements or abnormal postures. X‐linked recessive dystonia parkinsonism (XDP; DYT3; Lubag) is an adult‐onset disorder that manifests severe and progressive dystonia with a high frequency of generalization. In search for the anatomical basis for dystonia, we performed postmortem analyses of the functional anatomy of the basal ganglia based on the striatal compartments (ie, the striosomes and the matrix compartment) in XDP. Here, we provide anatomopathological evidence that, in the XDP neostriatum, the matrix compartment is relatively spared in a unique fashion, whereas the striosomes are severely depleted. We also document that there is a differential loss of striatal neuron subclasses in XDP. In view of the three‐pathway basal ganglia model, we postulate that the disproportionate involvement of neostriatal compartments and their efferent projections may underlie the manifestation of dystonia in patients with XDP. This study is the first to our knowledge to show specific basal ganglia pathology that could explain the genesis of dystonia in human heredodegenerative movement disorders, suggesting that dystonia may result from an imbalance in the activity between the striosomal and matrix‐based pathways. Ann Neurol 2005

F-wave latency serves as the most reproducible measure in nerve conduction studies of diabetic polyneuropathy: multicentre analysis in healthy subjects and patients with diabetic polyneuropathy

Aims/hypothesis. For use in future drug development for diabetic polyneuropathy, we conducted multicentre trials to assess the reproducibility of nerve conduction studies.¶Methods. All measurements were repeated twice at a time interval of 1–4 weeks in 132 healthy subjects (63 men) and 172 patients (99 men) with diabetic polyneuropathy. Using a standardised method, 32 centres participated in the study of control subjects and 65, in patients with diabetic polyneuropathy. Motor nerve conduction studies consisted of stimulating the left median and tibial nerves and recording the compound action potential from abductor policis and adductor hallucis for measuring amplitude, terminal latency and minimal F-wave latency. For sensory conduction studies, sensory nerve action potentials were recorded antidromically from the second digit and the posterior aspect of the lateral malleous after distal stimulation of the left median and sural nerves. We also calculated motor conduction velocity, F-wave conduction velocity and sensory conduction velocity. The relative intertrial variation and intraclass correlation coefficient were used as an index of reproducibility.¶Results. Of all the measurements, F-wave latency yielded the highest intraclass correlation coefficient with the smallest relative intertrial variation for both median and tibial nerves in both groups.¶Conclusion/interpretation. Median and tibial F-wave latency provide the most reproducible measures for a nerve conduction study, serving as one of the best measures in multicentre drug trials for diabetic polyneuropathies. [Diabetologia (2000) 43: 915–921]