HINT1 founder mutation causing axonal neuropathy with neuromyotonia in South America: A case report.

BACKGROUND: Recessive loss-of-function mutations in HINT1 are associated with predominantly motor axonal peripheral neuropathy with neuromyotonia. Twenty-four distinct pathogenic variants are reported all over the world, including four confirmed founder variations in Europe and Asia. The majority of patients carry the ancient Slavic founder variant c.110G>C (p.Arg37Pro) that shows a distribution gradient from east to west throughout Europe. METHODS: We report a case of HINT1 neuropathy in South America, identified by massive parallel sequencing of a neuropathy gene panel. To investigate the origin of the variant, we performed haplotyping analysis. RESULTS: A Brazilian adolescent presented with recessive axonal motor neuropathy with asymmetric onset and fasciculations. Neuromyotonia was found on needle electromyography. His parents were not consanguineous and had no European ancestry. The patient carried biallelic pathogenic p.Arg37Pro alterations in the first exon of HINT1. Both alleles were identical by descent and originated from the same ancestral founder allele as reported in Europe. CONCLUSION: Our findings expand the geographic distribution of HINT1 neuropathy to South America, where we describe a recognized founder variant in a Brazilian adolescent with no apparent European ancestry. We confirm the association of the hallmark sign of neuromyotonia with the disease.

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.

Urinary manifestations in Isaacs's syndrome. Our experience in 8 cases.

INTRODUCTION: Isaacs's syndrome (IS), is a rare neurological disorder, characterized by sustained muscular activity, fasciculations, cramps, myokymia, excessive sweating, and occasional elevation of creatine phosphokinase (CPK) enzyme. AIM: To report our experience in patients with IS and urinary manifestations, describing clinical findings, test's results, and response to treatment. Methods An observational, retrospective analysis of patients with IS and urinary manifestations treated at German Hospital of Buenos Aires between 2001 and 2011 was done. Diagnosis was performed with clinical examination and electromyography (EMG) of external sphincter of the anus and/or urethra. Demographic, clinical, and treatment variables were analyzed. International Prognostic Scoring System (IPSS) at diagnosis and follow up was made. RESULTS: Eleven IS patients were recruited, of whom 8 (72.72%) were females with a mean age 47.87 years (DS ± 13.95) and presented associated lower tract urinary symptoms (LUTS). Six of them (75%) had voiding and 2 (25%) filling symptoms. Urodynamic and electromyographic findings reproduced symptomatology in all patients. Patients with voiding symptomatology were treated with combination of alpha-blockers with benzodiazepines; membrane stabilizings agents; antiepileptics; neurotropic; corticoids; posterior tibial nerve stimulation and botulinum toxin, achieving improvement in 4/6. The two patients with storage symptoms were treated in first instance with anticholinergic drugs, one of which did not respond completely was added oral pentosansulfate and electrical stimulation, reversing the symptomatology. Four patients had associated pathologies: Hashimoto's thyroiditis; Sjögren's syndrome; dysautonomia, and myasthenia gravis. CONCLUSIONS: In our experience, IS urinary manifestations are common and usually has a good evolution with adequate treatment for each patient.

Mechanisms of Caspr2 antibodies in autoimmune encephalitis and neuromyotonia.

OBJECTIVE: To determine the pathogenic mechanisms of autoantibodies to the cell adhesion molecule Caspr2 in acquired neuromyotonia and autoimmune encephalitis. METHODS: Caspr2-positive samples were confirmed using a cell-based assay, and their IgG subtypes were determined by enzyme-linked immunosorbent assay and cell-based assay. A solid phase binding assay quantified the binding of Caspr2 to contactin-2 in the presence of Caspr2 autoantibodies. Living cultures of primary rat hippocampal neurons were incubated with Caspr2-positive or control sera, and the distribution of Caspr2-positive immunofluorescent puncta and total surface Caspr2 was quantified. HEK cells transfected to express Caspr2 were incubated with Caspr2-positive or control samples, and cell-surface biotinylation and Western blot were used to assess total, internalized, and surface levels of Caspr2. RESULTS: We confirmed 6 samples with strong Caspr2 reactivity. IgG4 Caspr2 antibodies were present in all 6 cases. Caspr2 interacted with another cell adhesion molecule, contactin-2, with nanomolar affinity in the solid phase assay, and Caspr2 autoantibodies inhibited this interaction. Caspr2 autoantibodies did not affect the surface expression of Caspr2 in rat primary hippocampal neurons or transfected HEK cells. INTERPRETATION: Caspr2 autoantibodies inhibit the interaction of Caspr2 with contactin-2 but do not cause internalization of Caspr2. Functional blocking of cell adhesion molecule interactions represents a potential mechanism with therapeutic implications for IgG4 autoantibodies to cell adhesion molecules in neurological diseases. Ann Neurol 2018;83:40-51.

Acquired neuromyotonia in childhood: case report and review.

Recently characterized as an immune-mediated channelopaty, Isaacs' syndrome (also known as acquired neuromyotonia) was first described in 1961 in two men with persistent, generalized muscle stiffness, in addition to spontaneous, rapid discharges of motor-unit potentials on electromyography. In the peripheral nervous system, antibodies targeted to voltage-gated potassium channels induce hyperexcitability of motor axons, resulting in signs of muscle stiffness or of pseudomyotonia. A spontaneous burst of single motor-unit activity, and myokymic and neuromyotonic discharges, are the most characteristic features found in electromyography studies. This report describes Isaacs' syndrome in a child, in whom the diagnosis was made by clinical features of acquired, spontaneous muscle overactivity and typical electromyographic findings.