Juvenile amyotrophic lateral sclerosis (JALS) is a rare group of motor neuron disorders with gene association in 40% of cases. JALS is defined as onset before age 25. We conducted a literature review of JALS and gene mutations associated with JALS. Results of the literature review show that the most common gene mutations associated with JALS are FUS, SETX, and ALS2. In familial cases, the gene mutations are mostly inherited in an autosomal recessive pattern and mutations in SETX are inherited in an autosomal dominant fashion. Disease prognosis varies from rapidly progressive to an indolent course. Distinct clinical features may emerge with specific gene mutations in addition to the clinical finding of combined upper and lower motor neuron degeneration. In conclusion, patients presenting with combined upper and lower motor neuron disorders before age 25 should be carefully examined for genetic mutations. Hereditary patterns and coexisting features may be useful in determining prognosis.

Synaptotagmins are integral synaptic vesicle membrane proteins that function as calcium sensors and regulate neurotransmitter release at the presynaptic nerve terminal. Synaptotagmin‐2 (SYT2), is the major isoform expressed at the neuromuscular junction. Recently, dominant missense variants in SYT2 have been reported as a rare cause of distal motor neuropathy and myasthenic syndrome, manifesting with stable or slowly progressive distal weakness of variable severity along with presynaptic NMJ impairment. These variants are thought to have a dominant‐negative effect on synaptic vesicle exocytosis, although the precise pathomechanism remains to be elucidated. Here we report seven patients of five families, with biallelic loss of function variants in SYT2, clinically manifesting with a remarkably consistent phenotype of severe congenital onset hypotonia and weakness, with variable degrees of respiratory involvement. Electrodiagnostic findings were consistent with a presynaptic congenital myasthenic syndrome (CMS) in some. Treatment with an acetylcholinesterase inhibitor pursued in three patients showed clinical improvement with increased strength and function. This series further establishes SYT2 as a CMS‐disease gene and expands its clinical and genetic spectrum to include recessive loss‐of‐function variants, manifesting as a severe congenital onset presynaptic CMS with potential treatment implications.

Introduction Patients with mutations in C9orf72 can have amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), or ALS‐FTD. The goals were to establish whether cortical hyperexcitability occurs in C9orf72 patients with different clinical presentations. Methods: Cortical thresholds and silent periods were measured in thenar muscles in 19 participants with C9orf72 expansions and 21 healthy controls using transcranial magnetic stimulation (TMS). El Escorial and Rascovsky criteria were used to diagnose ALS and FTD. Fourteen participants with C9orf72 expansions were re‐tested 6 months later. Correlations with finger‐tapping speed, timed peg test, the ALS functional rating scale, and Dementia Rating Scale were examined. Results: Most participants with C9orf72 expansions had normal or low cortical thresholds. Among them, ALS patients had the lowest thresholds and significantly shorter silent periods. Thresholds correlated with timed peg‐test scores. TMS did not correlate with the Dementia Rating Scale. Conclusions: TMS measures of cortical excitability may serve as noninvasive biomarkers of ALS disease activity. Muscle Nerve, 2016 Muscle Nerve 54: 264–269, 2016

Microtubules are formed from heterodimers of alpha- and beta-tubulin, each of which has multiple isoforms encoded by separate genes. Pathogenic missense variants in multiple different tubulin isoforms cause brain malformations. Missense mutations in TUBB3, which encodes the neuron-specific beta-tubulin isotype, can cause congenital fibrosis of the extraocular muscles type 3 (CFEOM3) and/or malformations of cortical development, with distinct genotype–phenotype correlations. Here, we report fourteen individuals from thirteen unrelated families, each of whom harbors the identical NM_006086.4 (TUBB3):c.785G>A (p.Arg262His) variant resulting in a phenotype we refer to as the TUBB3 R262H syndrome. The affected individuals present at birth with ptosis, ophthalmoplegia, exotropia, facial weakness, facial dysmorphisms, and, in most cases, distal congenital joint contractures, and subsequently develop intellectual disabilities, gait disorders with proximal joint contractures, Kallmann syndrome (hypogonadotropic hypogonadism and anosmia), and a progressive peripheral neuropathy during the first decade of life. Subsets may also have vocal cord paralysis, auditory dysfunction, cyclic vomiting, and/or tachycardia at rest. All fourteen subjects share a recognizable set of brain malformations, including hypoplasia of the corpus callosum and anterior commissure, basal ganglia malformations, absent olfactory bulbs and sulci, and subtle cerebellar malformations. While similar, individuals with the TUBB3 R262H syndrome can be distinguished from individuals with the TUBB3 E410K syndrome by the presence of congenital and acquired joint contractures, an earlier onset peripheral neuropathy, impaired gait, and basal ganglia malformations.

Background: Tandutinib (MLN 518, Millennium Pharmaceuticals, Cambridge, MA) is an orally active multitargeted tyrosine kinase inhibitor that is currently under evaluation for the treatment of glioblastoma and has been used in the treatment of leukemia. In prior clinical and animal studies, a dose-dependent muscular weakness has been observed with this drug, though the etiology of the weakness has not been defined. Methods: Standard neurophysiologic techniques, including repetitive nerve stimulation, needle EMG, and single-fiber EMG, were used to evaluate patients who developed weakness while being treated with tandutinib and bevacizumab (Avastin, Genentech, South San Francisco, CA) for glioblastoma (NCT00667394). Results: Six patients were observed to develop a reversible weakness that correlated with the administration of the tandutinib. The onset of weakness after starting tandutinib occurred within 3 to 112 days and in less than 15 days in 3 patients. Electrophysiologic studies showed that all patients developed abnormal repetitive nerve stimulation studies. Four patients had short duration motor unit potentials. Two of these patients also had abnormal single-fiber EMG, as did a third patient who did not have standard needle EMG. The clinical and electrophysiologic abnormalities improved with the termination or reduction in the dose of tandutinib. Conclusion: These observations suggest that tandutinib is toxic to the neuromuscular junction, possibly by reversibly binding to a molecule on the postsynaptic acetylcholine receptor complex. Classification of evidence: This study provides Class III evidence that tandutinib 500 mg twice daily induces reversible muscle weakness and electrophysiologic changes consistent with neuromuscular junction dysfunction.