Antibodies affecting ion channel function in acquired neuromyotonia, in seropositive and seronegative myasthenia gravis, and in antibody-mediated arthrogryposis multiplex congenita

A new autoimmune disease affecting the neuromuscular junction has been defined. Acquired neuromyotonia is associated with antibodies to voltage-gated potassium channels that act, at least in part, by reducing potassium channel function with resulting neuronal hyperactivity. This condition is quite frequently associated with thymoma and, in many cases, antibodies to acetylcholine receptors are present as well as antibodies to VGKC. Improvements in techniques and the availability of cloned DNA and recombinant forms of the AChR subunits have led to new observations concerning the specificity and roles of antibodies in myasthenia gravis. The transfection of a cell line with the epsilon subunit means that we can now accurately compare antibodies reactive with adult and fetal human AChR. This may help to determine the relationship between AChR subunit expression in different tissues and the induction of antibodies that bind specifically to the two forms, as well as to clarify the role of antibodies to fetal or adult AChR in causing ocular muscle symptoms. Serum antibodies from a few mothers with obstetric histories of recurrent arthrogryposis multiplex congenita in their babies specifically inhibit the function of fetal AChR. These observations not only explain the cause of some cases of arthrogryposis multiplex congenita, but also suggest that other fetal-specific antibodies might be responsible for other fetal or neonatal conditions. An animal model has been established to enable us to investigate the role of maternal serum factors in causing such disorders. Seronegative MG has been the subject of many studies from our laboratory over the last ten years. The transience of the effects of SNMG plasmas on AChR function strongly suggests that the plasma antibodies do not bind directly to the AChR, but inhibit function by some indirect mechanism. They do not appear to act via the cAMP-dependent protein kinase pathway, and studies are in progress to investigate the involvement of other second messenger systems.

Cricoid pressure: can protective force be sustained?

We studied six operating department assistants performing simulated cricoid pressure on a model of the larynx with the arm either flexed to 90 degrees (flexed position) or fully extended with the elbow locked (extended position). Subjects were asked to maintain forces of 20, 30 and 40 Newtons (N) for a target time of 20 min. Subjects rated pain during each assessment on a four-point verbal rating scale (VRS): 1 = uncomfortable; 2 = hurting; 3 = hurting a lot; and 4 = agony. Times to onset of pain were short and mean times to VRS 3 at each force studied were: 40 N, flexed position 2.3 min, extended position 5.4 min; 30 N, flexed position 4.0 min, extended position 7.5 min; and 20 N, flexed position 9.6 min, extended position 12.5 min. None of our subjects was able to sustain 40 N for the target time. Mean times to release at 40 N were: flexed position 3.7 min, extended position 7.6 min. Only one subject was able to sustain 30 N and then only using the extended arm. Mean times to release at 30 N were: flexed position 6.4 min, extended position (five subjects) 10.8 min. Two subjects with the arm flexed and five with the arm extended achieved the target time at 20 N. Mean times to release at 20 N were: flexed position (four subjects) 13.2 min, extended position (one subject) 14.6 min. Use of the extended arm consistently prolonged times to pain and fatigue. These findings are relevant to the management of cricoid pressure during failed intubation.

Acquired neuromyotonia in a patient with spinal epidural abscess

We report a case of acquired neuromyotonia in a patient with Staphylococcus aureus septicemia and a spinal epidural abscess. Autoantibodies to voltage-gated potassium channels, which are associated with acquired neuromyotonia, were present during the patient's acute illness but became undetectable on clinical recovery. The spinal epidural abscess may have triggered the production of these specific autoantibodies, resulting in clinically and electromyographically detectable neuromyotonia.

A radioimmuno-precipitation assay for antibodies to botulinum A

We quantified antibodies to botulinum A (anti-BTx) by immunoprecipitation of 125I-BTx. We tested seven bioassay-positive sera and 68 coded samples, including 18 from patients who had ceased to respond to BTx treatment. Compared with values from healthy control subjects and 42 neurologic control subjects, all bioassay-positive sera were positive (range, 258 to 2,809 pM) and 49 of 50 patients who continued to respond to BTx were negative (<130 pM). This simple, specific, sensitive, and quantitative assay should prove helpful in the investigation of BTx resistance.

Antibodies to ion-channel proteins in thymoma with myasthenia, neuromyotonia, and peripheral neuropathy

A patient presented with anti-acetylcholine receptor antibody-positive myasthenia gravis. After removal of a thymoma and use of cytotoxic therapy, there was worsening of myasthenia, onset of muscle stiffness and hyperexcitability, and electrophysiologic signs of peripheral neuropathy. Elevated serum titers of antibodies to neuronal voltage-gated K+ channels were present, consistent with neuromyotonia (Isaacs' syndrome). A beneficial response to treatment paralleled changes in antibody titers.

Alpha-Bungarotoxin binding to human muscle acetylcholine receptor: measurement of affinity, delineation of AChR subunit residues crucial to binding, and protection of AChR function by synthetic peptides

Alpha-Bungarotoxin (alpha-BuTx) binds with high affinity to the nicotinic acetylcholine receptor (AChR) of most species, mainly to sequences around the two cysteines at positions 192 and 193 of the alpha-subunit, but other sequences of the alpha-subunit and of the adjacent gamma- or epsilon- and delta-subunits are also important in the native molecule. Alpha-BuTx binds strongly to human AChR but the short alpha neurotoxins, for instance Erabutoxin B, are relatively ineffective at the human neuromuscular junction. In this article we compare the affinity of 125I-alpha-BuTx for Torpedo and human muscle AChR and the ability of neurotoxins to inhibit this binding. We examine the contribution to alpha-BuTx binding of the three amino acids that differ between human and Torpedo AChR alpha-185-196. In addition, we show that an alpha-185-199, peptide that binds strongly to 125I-alpha-BuTx and can inhibit its binding in solution, is also capable of protecting the AChR on a cell line or at the neuromuscular junction. Such peptides might be useful in the treatment of acute envenoming or the autoantibody-mediated block of AChR function that can occur in human disorders.

Autoimmunity in paraneoplastic neurological disorders

Antibodies to neuronal antigens are found in a range of different neurological disorders, both central and peripheral, and often indicate the presence of particular underlying tumours. This conference and workshop was an opportunity to discuss the clinical associations of these antibodies, the relevance of new antibody specificities, and to establish protocols for their detection.

Epitopes expressed in myasthenia gravis (MG) thymomas are not recognized by patients' T cells or autoantibodies

Most thymic epithelial tumours that associate with MG express an epitope that resembles the sequence alpha373-380 from the cytoplasmic loop of the acetylcholine receptor (AChR). It has been proposed that sensitization to this linear epitope initiates autoimmunity to the AChR in thymoma-associated MG. We therefore tested whether MG/thymoma patients have T cell responses or antibodies to this region of the AChR. We found no significant recognition of the alpha309-417 region by their thymoma or peripheral blood T cells, or by their serum anti-AChR antibodies. Instead, the T cell epitopes that were recognized, like the previously characterized B cell epitopes, were in the extracellular AChR domain.

XCoe2, a transcription factor of the Col/Olf-1/EBF family involved in the specification of primary neurons in Xenopus

BACKGROUND

Primary neurogenesis in Xenopus is a model for studying the control of neural cell fate decisions. The specification of primary neurons appears to be driven by transcription factors containing a basic region and a helix-loop-helix (HLH) motif: expression of Xenopus neurogenin-related-1 (X-ngnr-1) defines the three prospective domains of primary neurogenesis, and expression of XNeuroD coincides with neuronal differentiation. The transition between neuronal competence and stable commitment to a neuronal fate remains poorly characterised, however.

RESULTS

Drosophila Collier and rodent early B-cell factor/olfactory-1 define a family of HLH transcription factors containing a previously unknown type of DNA-binding domain. We isolated an orthologous gene from Xenopus, Xcoe2, which is expressed in precursors of primary neurons. Xcoe2 is transcribed after X-ngnr-1 and before XNeuroD. Overexpression of a dominant-negative mutant of XCoe2 prevented neuronal differentiation. Conversely, overexpressed wild-type Xcoe2 could promote ectopic differentiation of neurons, in both the neural plate and the epidermis. In contrast to studies with X-ngnr-1 or XNeuroD, the supernumerary neurons induced by Xcoe2 appeared in a 'salt-and-pepper' pattern, resulting from the activation of X-Delta1 expression and feedback regulation by lateral inhibition.

CONCLUSIONS

XCoe2 may play a pivotal role in the transcriptional cascade that specifies primary neurons in Xenopus embryos: by maintaining Delta-Notch signalling, XCoe2 stabilises the higher neural potential of selected progenitor cells that express X-ngnr-1, ensuring the transition between neural competence and irreversible commitment to a neural fate; and it promotes neuronal differentiation by activating XNeuroD expression, directly or indirectly.

The fetal form of the acetylcholine receptor distinguishes rhabdomyosarcomas from other childhood tumors

The fetal nicotinic acetylcholine receptor (AChR) of muscle is an oligomeric membrane protein with subunit composition alpha2betadeltagamma. After birth, the adult form, in which an epsilon-subunit replaces the gamma-subunit, predominates, and expression of the fetal form is limited to thymic myoid cells, extraocular muscles, and denervated striated muscle. We looked for expression of AChR in rhabdomyosarcomas and other childhood tumors by reverse transcription polymerase chain reaction and immunohistochemistry. mRNA for the AChR gamma-subunit was detected in all embryonal and alveolar rhabdomyosarcomas tested (n = 16) and in some tumors with a rhabdomyomatous component (n = 2) but not in other nonrhabdomyomatous tumors of childhood and adults (n = 45). The fetal form of the AChR was detected immunohistochemically in five of eight embryonal and four of eight alveolar rhabdomyosarcomas and in two Wilms' tumors with a rhabdomyomatous component but not in other tumors or in normal muscle. We conclude that reverse transcription polymerase chain reaction for AChR gamma-subunit could be useful for the diagnosis of rhabdomyosarcoma of childhood and for the detection of micrometastases and minimal residual disease. In addition, the fetal AChR protein is the first extracellular tumor marker that can distinguish rhabdomyosarcomas from nonrhabdomyomatous tumors and from normal muscle. Our findings, therefore, imply that the fetal AChR may be a target for in vivo imaging and, as AChR internalization and degradation is increased by antibody-induced cross-linking, may also provide a sensitive and specific target for immunotherapeutic strategies.

Linkage and physical mapping of prolactin to porcine chromosome 7

Comparative mapping studies between human and pig have shown that there is conserved synteny between human chromosome 6 and pig chromosomes 1 and 7, but some gene locations are not well established. Prolactin (PRL), an anterior pituitary hormone, has been mapped to human chromosome 6, and has tentatively mapped to pig chromosome 7 using Southern-RFLP analysis with a limited number of meioses. To confirm the assignment of prolactin to porcine chromosome 7 by physical and linkage analysis, pig cDNA and human genomic DNA sequences were used to design pig-specific PCR primers. The primers amplified a fragment of approximately 2.8 kb. Two polymorphic restriction sites were identified within this fragment with the restriction endonuclease BstUI. Prolactin was significantly linked to six markers on the published PiGMaP map of pig chromosome 7. Prolactin was physically mapped using a pig x rodent somatic cell hybrid panel. An analysis of these data placed PRL on pig 7p1.1-p1.2 with 100% concordance and was in complete agreement with the linkage data. Both mapping techniques placed PRL in a conserved order with the loci in the syntenic region of human chromosome 6.

Mechanisms of action of anti-GM1 and anti-GQ1b ganglioside antibodies in Guillain-Barré syndrome

Anti-GM1 and anti-GQ1b ganglioside antibodies are found in association with acute and chronic peripheral neuropathies, including Guillain-Barré syndrome. They are believed to arise as a result of molecular mimicry with immunogenic microbial polysaccharides. Although anti-ganglioside antibodies are suspected to play a causal role in neuropathy pathogenesis, the details of this have yet to be proven. The approach in this laboratory to solving this issue has been to generate anti-GM1 and anti-GQ1b monoclonal antibodies from peripheral blood lymphocytes of affected patients and to study their immunolocalization in peripheral nerve and their electrophysiologic effects in animal models in which peripheral nerve sites are exposed to anti-ganglioside antibodies. These data show that anti-ganglioside antibody-reactive epitopes are widely distributed in peripheral nerve and can cause electrophysiologic abnormalities in a variety of model systems; thus, these data support the view that anti-ganglioside antibody-reactive epitopes may directly contribute to neuropathy pathogenesis.

Lack of effect of Miller Fisher sera/plasmas on transmitter release from PC12 cells

IgG antibodies to GQ1b ganglioside are found in > 90% of patients with the Miller Fisher Syndrome (MFS). MFS sera or IgG preparations have marked effects on neurotransmitter release at the neuromuscular junction, but their mode(s) of action remain unclear. To establish a cell-based system for investigating the mechanism of action of MFS serum preparations, we looked at neurotransmitter release from three cell lines. We failed to demonstrate substantial 14C-acetylcholine release from two motor-neuronal cell lines, VSC4.1 and NSC19, and therefore studied 3H-noradrenaline release from NGF-differentiated PC12 cells, a neural-crest derived catecholaminergic cell line. K(+)-induced release was inhibited by botulinum toxin and basal release was enhanced by alpha-latrotoxin, resembling that at the neuromuscular junction, although K(+)-induced release was dependent on L-type rather than P/Q-type calcium channels. The cells expressed polysialylated gangliosides on the cell surface. Incubation in heat-inactivated or untreated MFS preparations did not, however, affect basal or K(+)-induced release. Thus the PC12 cells do not appear to be sensitive to the effects of serum antibodies from MFS patients.

Family of Ebf/Olf-1-related genes potentially involved in neuronal differentiation and regional specification in the central nervous system

Two novel mouse genes, Ebf2 and Ebf3, have been identified which show high similarity to the rodent Ebf/Olf-1 and the Drosophila collier genes. The strong conservation of the protein regions corresponding to the DNA binding and dimerisation domains previously defined in Ebf strongly suggests that Ebf2 and Ebf3 also constitute DNA sequence-specific transcription factors. Determination of the chromosomal locations of the two genes indicated that the different members of this novel mouse multigene family are not clustered. A detailed analysis of the expression of each of the three Ebf genes in the developing central nervous system revealed partially overlapping patterns with two salient features: 1) In the region extending from the midbrain to the spinal cord, the expression of the three genes correlated with neuronal maturation, with a general activation in early post-mitotic cells, followed by specific patterns of extinction also consistent with the neurogenic gradient. 2) In the forebrain area, although the patterns of expression of the Ebf genes also reflected neuronal maturation, they appeared in addition to be region specific. These data suggest that Ebf genes may be involved in the control of neuronal differentiation in the CNS and in enforcing regional diversity in populations of post-mitotic forebrain neurons.

Effects of tobacco smoking and gender on interhemispheric cognitive function: performance and confidence measures

Cognitive function in tasks involving interhemispheric processing of verbal and spatial information was studied in 31 college students in a 2 x 2 factorial design with chronic smoking status [smoker (10+ cigarettes per day) versus non-smoker (no history of smoking)] and gender as the main between-subject factors. The subjects participated in two sessions on two consecutive days. The same task was repeated within the same session with a 15 min interval: smokers were tested before and after smoking whereas non-smokers rested during the interval. Dependent behavioral variables included those of performance (speed and accuracy) and confidence (low rate of non-responding). The verbal task yielded an expected female advantage, and smoking had the gender-specific effect of increasing both speed and accuracy more clearly in males. In addition, smoking decreased the rate of non-responding (increase confidence) in women, thereby affecting preferred strategies for problem solving by shifting the female pattern towards the male pattern. The spatial task, which probably involved a more perceptual, rather than cognitive, level of functioning, produced no clear effects of smoking and gender, and yielded some laterality effects. The acute within-subject smoking manipulation wherein, among smokers, the first test was preceded by 10+ h of deprivation, whereas the second repeated task was preceded by the smoking of a cigarette (i.e. deprivation followed by partial release) did not affect the behavioral measures. In conclusion, smoking had a gender-specific effect on cognitive function: it improved the performance of males in a verbal task and increased the subjective confidence of females thereby affecting the preferred cognitive strategies for problem solving.

Congenital myasthenic syndromes

Congenital myasthenic syndromes are a rare group of heterogeneous disorders affecting neuromuscular transmission. Recent identification and in-vitro functional analysis of some of the genetic mutations that cause these disorders correlates with previous electrophysiological, biochemical, pathological and therapeutic studies, and has advanced our understanding of neuromuscular transmission.