Differential Analysis of Gly211Val and Gly286Val Mutations Affecting Sarco(endo)plasmic Reticulum Ca2+-ATPase (SERCA1) in Congenital Pseudomyotonia Romagnola Cattle.

Congenital pseudomyotonia in cattle (PMT) is a rare skeletal muscle disorder, clinically characterized by stiffness and by delayed muscle relaxation after exercise. Muscle relaxation impairment is due to defective content of the Sarco(endo)plasmic Reticulum Ca2+ ATPase isoform 1 (SERCA1) protein, caused by missense mutations in the ATP2A1 gene. PMT represents the only mammalian model of human Brody myopathy. In the Romagnola breed, two missense variants occurring in the same allele were described, leading to Gly211Val and Gly286Val (G211V/G286V) substitutions. In this study, we analyzed the consequences of G211V and G286V mutations. Results support that the reduced amount of SERCA1 is a consequence of the G211V mutation, the G286V mutation almost being benign and the ubiquitin-proteasome system (UPS) being involved. After blocking the proteasome using a proteasome inhibitor, we found that the G211V mutant accumulates in cells at levels comparable to those of WT SERCA1. Our conclusion is that G211/286V mutations presumably originate in a folding-defective SERCA1 protein, recognized and diverted to degradation by UPS, although still catalytically functional, and that the main role is played by G211V mutation. Rescue of mutated SERCA1 to the sarcoplasmic reticulum membrane can re-establish resting cytosolic Ca2+ concentration and prevent the appearance of pathological signs, paving the way for a possible therapeutic approach against Brody disease.

HINT1 neuropathy: Expanding the genotype and phenotype spectrum.

Inherited peripheral neuropathy (IPN) is a heterogeneous group of disorders due to pathogenic variation in more than 100 genes. In 2012, the first cases of IPN associated with HINT1 pathogenic variations were described in 33 families sharing the same phenotype characterized by an axonal neuropathy with neuromyotonia and autosomal recessive inheritance (NMAN: OMIM #137200). Histidine Triad Nucleotide Binding Protein 1 regulates transcription, cell-cycle control, and is possibly involved in neuropsychiatric pathophysiology. Herein, we report seven French patients with NMAN identified by Next Generation Sequencing. We conducted a literature review and compared phenotypic and genotypic features with our cohort. We identified a new HINT1 pathogenic variation involved in NMAN: c.310G>C p.(Gly104Arg). This cohort is comparable with literature data regarding age of onset (7,4yo), neuronal involvement (sensorimotor 3/7 and motor pure 4/7), and skeletal abnormalities (scoliosis 3/7, feet anomalies 6/7). We expand the phenotypic spectrum of HINT1-related neuropathy by describing neurodevelopmental or psychiatric features in six out of seven individuals such as generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), mood disorder and attention deficit hyperactivity disorder (ADHD). However, only 3/128 previously described patients had neuropsychiatric symptomatology or neurodevelopmental disorder. These features could be part of HINT1-related disease, and we should further study the clinical phenotype of the patients.

Ocular Neuromyotonia in Children and Adolescents Following Radiation Treatment of Pediatric Brain Tumors.

PURPOSE: To report five cases of ocular neuromyotonia in children and adolescents following radiation therapy for a variety of pediatric brain tumors. Notably, three cases occurred in children younger than 11 years. METHODS: Case series of five patients with ocular neuromyotonia following proton beam therapy or conventional radiation. RESULTS: Five cases of ocular neuromyotonia were identified following radiation treatment of various pediatric brain tumors. Onset ranged from 5 to 142 months after radiation treatment. The abducens nerve/lateral rectus muscle was affected in three patients, and the trochlear nerve/superior oblique muscle was affected in two patients. Ages at symptom presentation were 4 years (intermittent head tilt), 9 years (intermittent blurry vision and head tilt), 10 years (intermittent blurry vision progressing to intermittent diplopia), 15 years (intermittent diplopia), and 17 years (intermittent diplopia). One patient improved with gabapentin. Two patients experienced spontaneous resolution. One patient died due to meta-static disease, and one patient has planned follow-up. CONCLUSIONS: Ocular neuromyotonia occurs most commonly following radiation to the brain and skull base. Clinicians need to be aware that ocular neuromyotonia presents differently in children (who may not report diplopia) than in adults or adolescents (who typically report diplopia). Two children in this series never reported diplopia, only intermittent head tilt and blurry vision. Ocular neuromyotonia requires a high index of suspicion to diagnose, especially in children. Membrane stabilizers can be used effectively, but observation may be a valid option in children because spontaneous resolution was seen. [J Pediatr Ophthalmol Strabismus. 2022;59(5):338-343.].

Paradoxical pseudomyotonia in English Springer and Cocker Spaniels.

BACKGROUND: Paramyotonia congenita and Brody disease are well-described conditions in humans, characterized by exercise-induced myotonic-like muscle stiffness. A syndrome similar to Brody disease has been reported in cattle. Reports of a similar syndrome in dogs are scarce. OBJECTIVES: To define and describe the clinical, diagnostic, and genetic features and disease course of paradoxical pseudomyotonia in Spaniel dogs. ANIMALS: Seven client-owned dogs (4 English Springer Spaniels and 3 English Cocker Spaniels) with clinically confirmed episodes of exercise-induced generalized myotonic-like muscle stiffness. METHODS: Sequential case study. RESULTS: All dogs were <24 months of age at onset. The episodes of myotonic-like generalized muscle stiffness always occurred with exercise, and spontaneously resolved with rest in <45 seconds in all but 1 dog. Extreme outside temperatures seemed to considerably worsen episode frequency and severity in most dogs. Complete blood count, serum biochemistry including electrolytes, urinalysis, brain magnetic resonance imaging, cerebrospinal fluid analysis, electromyography, motor nerve conduction velocity, ECG, and echocardiography were unremarkable. Muscle biopsy samples showed moderate but nonspecific muscle atrophy. The episodes seemed to remain stable or decrease in severity and frequency in 6/7 dogs, and often could be decreased or prevented by avoiding the episode triggers. The underlying genetic cause is not identified yet, because no disease-causing variants could be found in the coding sequence or splice sites of the 2 major candidate genes, SCN4A and ATP2A1. CONCLUSIONS AND CLINICAL IMPORTANCE: Paradoxical pseudomyotonia is a disease affecting Spaniels. It is of variable severity but benign in most cases.

Novel mutations in HINT1 gene cause the autosomal recessive axonal neuropathy with neuromyotonia.

Autosomal recessive axonal neuropathy with neuromyotonia (ARAN-NM) is a rare form of hereditary neuropathy. Mutations in HINT1 gene have been identified to be the cause of this disorder. We report two unrelated patients who presented gait impairment, progressive distal muscle weakness and atrophy, neuromyotonia and foot deformities. Electrophysiological studies showed axonal motor neuropathy and neuromyotonic discharges. Using Next-generation sequencing, we identified two homozygous mutations, NM_005340.6: c.112T > C; p.(Cys38Arg) and NM_005340.6: c.289G > A; p.(Val97Met) in HINT1 gene. Based on the clinical presentation and molecular genetic analyses, ARAN-NM was diagnosed in both patients and NM_005340.6: c.112T > C; p.(Cys38Arg) and NM_005340.6: c.289G > A; p.(Val97Met) in HINT1 gene were believe to be causative for the disorder.

Neuromyotonia in a horse.

This article describes the clinical and electromyographic findings of neuromyotonia in a 19-month-old male crossbred Quarter Horse that presented with stiffness and muscle asymmetry in the hind limbs as well as sacrococcygeal, paravertebral, and gluteal myokymia. An electromyographic study showed spontaneous continuous muscle fiber activity with high-frequency discharges, fibrillations, positive sharp waves, fasciculation potentials, and complex repetitive discharges. Histological examination of the gluteal muscle showed a mixed neurogenic and myopathic pattern. The findings are consistent with neuromyotonia.

Axonal neuropathy with neuromyotonia: there is a HINT.

Recessive mutations in the gene encoding the histidine triad nucleotide binding protein 1 (HINT1) were recently shown to cause a motor-predominant Charcot-Marie-Tooth neuropathy. About 80% of the patients exhibit neuromyotonia, a striking clinical and electrophysiological hallmark that can help to distinguish this disease and to guide diagnostic screening. HINT1 neuropathy has worldwide distribution and is particularly prevalent in populations inhabiting central and south-eastern Europe. With 12 different mutations identified in more than 60 families, it ranks among the most common subtypes of axonal Charcot-Marie-Tooth neuropathy. This article provides an overview of the present knowledge on HINT1 neuropathy with the aim to increase awareness and spur interest among clinicians and researchers in the field. We propose diagnostic guidelines to recognize and differentiate this entity and suggest treatment strategies to manage common symptoms. As a recent player in the field of hereditary neuropathies, the role of HINT1 in peripheral nerves is unknown and the underlying disease mechanisms are unexplored. We provide a comprehensive overview of the structural and functional characteristics of the HINT1 protein that may guide further studies into the molecular aetiology and treatment strategies of this peculiar Charcot-Marie-Tooth subtype.

Structural study of skeletal muscle fibres in healthy and pseudomyotonia affected cattle.

Cattle congenital pseudomyotonia (PMT), recognized as naturally occurring animal model of human Brody disease, is an inherited recessive autosomal muscular disorder due to missense mutations in ATP2A1 gene, encoding sarco(endo)plasmic reticulum Ca(2+)-ATPase protein, isoform 1 (SERCA1). PMT has been described in the Chianina and Romagnola italian cattle breeds and as a single case in Dutch improved Red and White cross-breed. The genetic defect turned out to be heterogeneous in different cattle breeds, even though clinical symptoms were homogeneous. Skeletal muscles of affected animals are characterized by a selective deficiency of SERCA1 in sarcoplasmic reticulum (SR) membranes. Recently, we provided evidence that in Chianina breed, the ubiquitin proteasome system is responsible for SERCA1 mutant premature disposal, even when the mutation does not affect the catalytic properties of the pump. Results presented here show that all SERCA1 mutants described until now, although expressed at low level, are correctly targeted to SR membranes. Ultrastructural studies confirm that in pathological muscle fibres, structure, as well as triads, is well preserved. All together these results suggest that a possible therapeutical approach based on the rescue of the defective protein at SR membranes could be hypothesized. Only fully functionally active missense mutants, whem located at the SR membrane could restore the efficient control of Ca(2+) homeostasis and prevent the appearance of the pathological signs. Moreover, these data demonstrate the increasing importance of domestic animals as genetic models of human pathologies.

Fast-twitch skeletal muscle fiber adaptation to SERCA1 deficiency in a Dutch Improved Red and White calf pseudomyotonia case.

Missense mutations in ATP2A1 gene, encoding SERCA1 protein, cause a muscle disorder designed as congenital pseudomyotonia (PMT) in Chianina and Romagnola cattle or congenital muscular dystonia1 (CMD1) in Belgian Blue cattle. Although PMT is not life-threatening, CMD1 affected calves usually die within a few weeks of age as a result of respiratory complication. We have recently described a muscular disorder in a double muscle Dutch Improved Red and White cross-breed calf. Mutation analysis revealed an ATP2A1 mutation identical to that described in CMD1, even though clinical phenotype was quite similar to that of PMT. Here, we provide evidence for a deficiency of mutated SERCA1 in PMT affected muscles of Dutch Improved Red and White calf, but not of its mRNA. The reduced expression of SERCA1 is selective and not compensated by the SERCA2 isoform. By contrast, pathological muscles are characterized by a broad distribution of mitochondrial markers in all fiber types, not related to intrinsic features of double muscle phenotype and by an increased expression of sarcolemmal calcium extrusion pump. Calcium removal mechanisms, operating in muscle fibers as compensatory response aimed at lowering excessive cytoplasmic calcium concentration caused by SERCA1 deficiency, could explain the difference in severity of clinical signs.

Autoimmune channelopathies in paraneoplastic neurological syndromes.

Paraneoplastic neurological syndromes and autoimmune encephalitides are immune neurological disorders occurring or not in association with a cancer. They are thought to be due to an autoimmune reaction against neuronal antigens ectopically expressed by the underlying tumour or by cross-reaction with an unknown infectious agent. In some instances, paraneoplastic neurological syndromes and autoimmune encephalitides are related to an antibody-induced dysfunction of ion channels, a situation that can be labelled as autoimmune channelopathies. Such functional alterations of ion channels are caused by the specific fixation of an autoantibody upon its target, implying that autoimmune channelopathies are usually highly responsive to immuno-modulatory treatments. Over the recent years, numerous autoantibodies corresponding to various neurological syndromes have been discovered and their mechanisms of action partially deciphered. Autoantibodies in neurological autoimmune channelopathies may target either directly ion channels or proteins associated to ion channels and induce channel dysfunction by various mechanisms generally leading to the reduction of synaptic expression of the considered channel. The discovery of those mechanisms of action has provided insights on the regulation of the synaptic expression of the altered channels as well as the putative roles of some of their functional subdomains. Interestingly, patients' autoantibodies themselves can be used as specific tools in order to study the functions of ion channels. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

[A case of Isaacs' syndrome causing various central nervous symptoms successfully treated with high-dose intravenous methylprednisolone therapy].

A 44-year-old man with a bilateral hand tremor suffered from a decline in concentration and abnormal vision for several months. He also complained of easily falling down because of muscle stiffness and cramps in his lower limbs. On admission, he demonstrated lower limb stiffness, muscle cramps, diplopia, hyperhidrosis, left upper limb ataxia and dysesthesia in all limbs. Laboratory examination showed a marked elevation in his serum creatine kinase level (26,890 U/l), and needle electromyography demonstrated myokymic discharges in the muscles of his lower extremities. Isaacs' syndrome was diagnosed based on a positive voltage-gated potassium channel antibody titer of 1,007 pM. Administration of an anticonvulsant (phenytoin, 200 mg/day) did not resolve his symptoms; however, high-dose intravenous methylprednisolone therapy (1 g/day for 3 days) resulted in marked clinical improvement. This case suggests that high-dose intravenous methylprednisolone therapy for Isaacs' syndrome might be as effective as other immunosuppressive therapies such as plasma exchange or intravenous immunoglobulin.

Paraneoplastic nerve hyperexcitability.

OBJECTIVES: To provide an overview of paraneoplastic nerve hyperexcitability syndromes. METHODS: An extensive review of the literature on nerve hyperexcitability was performed. Particular attention was paid to Isaacs' syndrome and Morvan's syndrome, as well as their relationship to neoplasia. RESULTS: An overview of the history, clinical manifestations (including neurophysiologic findings), pathophysiology, and management is presented. Clinical differences between the exclusively peripheral nervous system involving Isaacs' syndrome and Morvan's syndrome, which also involves the central nervous system (CNS) are detailed. The role of immune-mediated dysfunction of specific components of the voltage-gated potassium channel (VGKC) complex in the pathophysiology of these syndromes is explained. Finally, the limited data on management of these syndromes, including the use of antiepileptic and immunomodulatory therapies are discussed. CONCLUSION: Nerve hyperexcitability syndrome represents a spectrum of neuroimmunologic diseases, which are often paraneoplastic in etiology.

Inhibition of ubiquitin proteasome system rescues the defective sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA1) protein causing Chianina cattle pseudomyotonia.

A missense mutation in ATP2A1 gene, encoding sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA1) protein, causes Chianina cattle congenital pseudomyotonia, an exercise-induced impairment of muscle relaxation. Skeletal muscles of affected cattle are characterized by a selective reduction of SERCA1 in sarcoplasmic reticulum membranes. In this study, we provide evidence that the ubiquitin proteasome system is involved in the reduced density of mutated SERCA1. The treatment with MG132, an inhibitor of ubiquitin proteasome system, rescues the expression level and membrane localization of the SERCA1 mutant in a heterologous cellular model. Cells co-transfected with the Ca(2+)-sensitive probe aequorin show that the rescued SERCA1 mutant exhibits the same ability of wild type to maintain Ca(2+) homeostasis within cells. These data have been confirmed by those obtained ex vivo on adult skeletal muscle fibers from a biopsy from a pseudomyotonia-affected subject. Our data show that the mutation generates a protein most likely corrupted in proper folding but not in catalytic activity. Rescue of mutated SERCA1 to sarcoplasmic reticulum membrane can re-establish resting cytosolic Ca(2+) concentration and prevent the appearance of pathological signs of cattle pseudomyotonia.

A novel association of ocular neuromyotonia with brainstem demyelination: two case reports.

Ocular neuromyotonia (ONM) is a rare disorder of ocular mal-alignment in which painless, transient spontaneous or gaze-induced abnormal deviation of the eye manifests as episodic diplopia. With only a few cases reported in the literature, ONM mostly follows months to years after cranial irradiation for sellar or suprasellar lesions. Here we present two patients with this rare ocular condition, secondary to brainstem demyelination, the association of which is hitherto unreported in the literature. Both patients were 15-year-old girls who presented to us with episodic forced-eye deviation with diplopia. Examination during these attacks revealed ONM involving the superior rectus and medial rectus in the first and second patient, respectively. There was clinical evidence of intrinsic brainstem involvement with downbeat nystagmus and skew deviation in one patient without any other cerebellar or long tract signs. MRI showed evidence of demyelination involving the brainstem in both, with CSF showing positive immunological markers and with positive aquaporin-4 antibody in one patient. Both patients responded remarkably to immunomodulatory therapy and are asymptomatic at follow-up. That ONM can occur with brainstem demyelination has not been reported in the literature. This association may help in explaining the pathophysiology of ONM as secondary to segmental demyelination.

Lack of neuropathy-related phenotypes in hint1 knockout mice.

Mutations in HINT1, the gene encoding histidine triad nucleotide-binding protein 1 (HINT1), cause a recessively inherited peripheral neuropathy that primarily involves motor dysfunction and is usually associated with neuromyotonia (i.e. prolonged muscle contraction resulting from hyperexcitability of peripheral nerves). Because these mutations are hypothesized to cause loss of function, we analyzed Hint1 knockout mice for their relevance as a disease model. Mice lacking Hint1 appeared normal and yielded normal behavioral test results or motor performance, although they moved more slowly and for a smaller fraction of time in an open-field arena than wild-type mice. Muscles, neuromuscular junctions, and nodes of Ranvier were anatomically normal and did not show evidence of degeneration or regeneration. Axon numbers and myelination in peripheral nerves were normal at ages 4 and 13 months. Axons were slightly smaller than those in wild-type mice at age 4 months, but this did not cause a decrease in conduction velocity, and no differences in axon diameters were detected at 13 months. With electromyography, we were unable to detect neuromyotonia even after using supraphysiologic stimuli and stressors such as reduced temperature or 3,4-diaminopyridine to block potassium channels. Therefore, we conclude that Hint1 knockout mice may be useful for studying the biochemical activities of HINT1, but these mice do not provide a disease model or a means for investigating the basis of HINT1-associated neuropathy and neuromyotonia.

Partial third nerve palsy and ocular neuromyotonia from displacement of posterior communicating artery detected by high-resolution MRI.

Ocular neuromyotonia is an unusual condition in which sustained, undesired contraction of one or more extraocular muscles occurs after normal muscle activation. Although most commonly reported after paraseller cranial irradiation for tumor, chronic nonaneurysmal vascular compression of the third nerve can produce partial ocular motor nerve paresis and ocular neuromyotonia. A 75-year-old woman presented with intermittent left-gaze-evoked binocular diplopia. She had an incomplete right third nerve palsy but became symptomatically diplopic and esotropic upon sustained left gaze. High-resolution brain magnetic resonance imaging showed displacement of the right posterior communicating artery and contact with the right third nerve. Gaze-evoked diplopia resolved with carbamazepine, but a partial third nerve paresis remained.

Frostbite-like skin lesion as an autonomic symptom of Isaacs' syndrome.

A 25-year-old woman complained of numbness of the extremities, following muscle rigidity and tenderness. The presence of anti-voltage-gated potassium channel antibody led to the diagnosis of Isaacs' syndrome. Twenty-seven months after the first symptom, she developed a pricking pain sensation in the lateral left foot, and then gradually developed a purple skin lesion resembling frostbite. The lesion completely disappeared 2 days later. An incidental episode occurred at the same site 8 months later. Frostbite-like skin lesions may be a rare autonomic manifestation in Isaacs' syndrome.