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Candidate screening of the bovine and feline spinal muscular atrophy genes reveals no evidence for involvement in human motor neuron disorders.

24 October 2018

Spinal muscular atrophy (SMA) is a devastating neuromuscular disease characterised by progressive loss of spinal motor neurons. Mutations in the genes underlying spontaneous bovine and feline models of SMA have recently been described. The clinical and pathological features of these disorders are similar to human forms of SMA making both genes excellent candidates in patients with motor neuron loss of no known aetiology. Here we report that a screen for mutations in coding regions and splice sites of the LIX1 and FVT1 genes in a cohort of 96 non-5q SMA patients and 119 familial and sporadic Amyotrophic Lateral Sclerosis patients identified no obvious pathogenic changes. This study indicates that mutations in these genes do not contribute significantly to the cause of motor neuron diseases in the human population.

Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: a cross-sectional study.

24 October 2018

BACKGROUND: We aimed to accurately estimate the frequency of a hexanucleotide repeat expansion in C9orf72 that has been associated with a large proportion of cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). METHODS: We screened 4448 patients diagnosed with ALS (El Escorial criteria) and 1425 patients with FTD (Lund-Manchester criteria) from 17 regions worldwide for the GGGGCC hexanucleotide expansion using a repeat-primed PCR assay. We assessed familial disease status on the basis of self-reported family history of similar neurodegenerative diseases at the time of sample collection. We compared haplotype data for 262 patients carrying the expansion with the known Finnish founder risk haplotype across the chromosomal locus. We calculated age-related penetrance using the Kaplan-Meier method with data for 603 individuals with the expansion. FINDINGS: In patients with sporadic ALS, we identified the repeat expansion in 236 (7·0%) of 3377 white individuals from the USA, Europe, and Australia, two (4·1%) of 49 black individuals from the USA, and six (8·3%) of 72 Hispanic individuals from the USA. The mutation was present in 217 (39·3%) of 552 white individuals with familial ALS from Europe and the USA. 59 (6·0%) of 981 white Europeans with sporadic FTD had the mutation, as did 99 (24·8%) of 400 white Europeans with familial FTD. Data for other ethnic groups were sparse, but we identified one Asian patient with familial ALS (from 20 assessed) and two with familial FTD (from three assessed) who carried the mutation. The mutation was not carried by the three Native Americans or 360 patients from Asia or the Pacific Islands with sporadic ALS who were tested, or by 41 Asian patients with sporadic FTD. All patients with the repeat expansion had (partly or fully) the founder haplotype, suggesting a one-off expansion occurring about 1500 years ago. The pathogenic expansion was non-penetrant in individuals younger than 35 years, 50% penetrant by 58 years, and almost fully penetrant by 80 years. INTERPRETATION: A common Mendelian genetic lesion in C9orf72 is implicated in many cases of sporadic and familial ALS and FTD. Testing for this pathogenic expansion should be considered in the management and genetic counselling of patients with these fatal neurodegenerative diseases. FUNDING: Full funding sources listed at end of paper (see Acknowledgments).

Review: neuromuscular synaptic vulnerability in motor neurone disease: amyotrophic lateral sclerosis and spinal muscular atrophy.

24 October 2018

Amid the great diversity of neurodegenerative conditions, there is a growing body of evidence that non-somatic (that is, synaptic and distal axonal) compartments of neurones are early and important subcellular sites of pathological change. In this review we discuss experimental data from human patients, animal models and in vitro systems showing that neuromuscular synapses are targeted in different forms of motor neurone disease (MND), including amyotrophic lateral sclerosis and spinal muscular atrophy. We highlight important developments revealing the heterogeneous nature of vulnerability in populations of lower motor units in MND and examine how progress in our understanding of the molecular pathways underlying MND may provide insights into the regulation of synaptic vulnerability and pathology. We conclude that future experiments developing therapeutic approaches specifically targeting neuromuscular synaptic vulnerability are likely to be required to prevent or delay disease onset and progression in human MND patients.

Asymmetrical late onset motor neuropathy associated with a novel mutation in the small heat shock protein HSPB1 (HSP27).

24 October 2018

Distal hereditary motor neuropathy, also known as distal spinal muscular atrophy, is characterised by slowly progressive weakness and wasting of the hands and feet and has a heterogeneous genetic basis. One form of distal hereditary motor neuropathy is associated with mutations in the gene for the small heat shock protein HSPB1 (hsp27). Families have been described in which slowly progressive, symmetrical, lower limb predominant motor weakness is usually evident by middle age. Here we report a novel mutation, G84R, in an elderly patient presenting with strikingly asymmetrical weakness. Expression of this and other known mutations in cell culture demonstrated enhanced aggregation of mutant HSPB1 protein compared with wild-type.

Characterisation of novel point mutations in the survival motor neuron gene SMN, in three patients with SMA.

24 October 2018

We report two novel mutations in three cases of spinal muscular atrophy (SMA), including two distant cousins who followed an unexpectedly severe course. Diagnosis was confirmed by reduced SMN protein and full-length SMN mRNA levels. Sequencing of the non-deleted SMN1 gene revealed a single G insertion at the end of exon 1 in the two cousins and a novel G275S exon 6 missense mutation in the milder case.

Murray Valley encephalitis in an adult traveller complicated by long-term flaccid paralysis: case report and review of the literature.

24 October 2018

Murray Valley encephalitis (MVE) virus, a mosquito-borne flavivirus, is the most common cause of viral encephalitis in the tropical 'Top End' of northern Australia. Clinical encephalitis due to MVE virus has a mortality rate of approximately 30%, with a similar proportion of patients being left with significant neurological deficits. We report the case of a 25-year-old man from the UK who acquired MVE while travelling through northern Australia. He required prolonged admission to the Intensive Care Unit and several years later remains partly ventilator-dependent, with flaccid quadriparesis. To our knowledge, this is the first reported case of MVE virus-induced flaccid paralysis in an adult in northern Australia, although it is well described in children. Paralysis was thought to be due to anterior horn cell involvement in the spinal cord and extensive bilateral thalamic destruction, both of which are well recognised complications of infection with MVE virus. Cases of flaccid paralysis with similar pathology have been described following infection with the related flavivirus Japanese encephalitis virus as well as more recently with West Nile virus. Our case highlights the potential severity of flavivirus-induced encephalitis and the importance of avoiding mosquito bites while travelling through endemic areas.

GARS axonopathy: not every neuron's cup of tRNA.

24 October 2018

Charcot-Marie-Tooth disease type 2D, a hereditary axonal neuropathy, is caused by mutations in glycyl-tRNA synthetase (GARS). The mutations are distributed throughout the protein in multiple functional domains. In biochemical and cell culture experiments, some mutant forms of GARS have been indistinguishable from wild-type protein, suggesting that these in vitro tests might not adequately assess the aberrant activity responsible for axonal degeneration. Recently, mouse and fly models have offered new insights into the disease mechanism. There are still gaps in our understanding of how mutations in a ubiquitously expressed component of the translation machinery result in axonal neuropathy. Here, we review recent reports, weigh the evidence for and against possible mechanisms and suggest areas of focus for future work.

Magnetic resonance spectroscopic imaging--of prognostic value in amyotrophic lateral sclerosis?

24 October 2018

A recurrent loss-of-function alanyl-tRNA synthetase (AARS) mutation in patients with Charcot-Marie-Tooth disease type 2N (CMT2N).

24 October 2018

Charcot-Marie-Tooth (CMT) disease comprises a heterogeneous group of peripheral neuropathies characterized by muscle weakness and wasting, and impaired sensation in the extremities. Four genes encoding an aminoacyl-tRNA synthetase (ARS) have been implicated in CMT disease. ARSs are ubiquitously expressed, essential enzymes that ligate amino acids to cognate tRNA molecules. Recently, a p.Arg329His variant in the alanyl-tRNA synthetase (AARS) gene was found to segregate with dominant axonal CMT type 2N (CMT2N) in two French families; however, the functional consequence of this mutation has not been determined. To investigate the role of AARS in CMT, we performed a mutation screen of the AARS gene in patients with peripheral neuropathy. Our results showed that p.Arg329His AARS also segregated with CMT disease in a large Australian family. Aminoacylation and yeast viability assays showed that p.Arg329His AARS severely reduces enzyme activity. Genotyping analysis indicated that this mutation arose on three distinct haplotypes, and the results of bisulfite sequencing suggested that methylation-mediated deamination of a CpG dinucleotide gives rise to the recurrent p.Arg329His AARS mutation. Together, our data suggest that impaired tRNA charging plays a role in the molecular pathology of CMT2N, and that patients with CMT should be directly tested for the p.Arg329His AARS mutation.

Treatment of vasculitic peripheral neuropathy: a retrospective analysis of outcome.

24 October 2018

BACKGROUND: Vasculitis of the peripheral nervous system (PNS) is rare. There are no controlled treatment trials, and clinical practice is guided by experience from case series and indirectly by analogy with systemic vasculitis. METHODS: We identified patients (n=212) with possible vasculitic peripheral neuropathy (VPN) from the neuropathology and neurophysiology records of two centres over 28 years. Case-notes were available for 181, from which, 106 cases of clinicopathological VPN were identified. Adequate treatment data were available in 100; follow-up data, in 93. RESULTS: Of 106 cases, 95 had systemic vasculitis and 11 had vasculitis confined to the PNS. Pharmacological treatment (94/100 cases) was corticosteroid-based, and included cyclophosphamide in 54; 17 received additional agents. Initial stabilization was achieved in all but six. One-year survival was 90.3%. Of the nine who died in the first years (mean age 73 years), seven had received cyclophosphamide, and all but two had severe, multisystem vasculitis. The neurological relapse rate was 10%. Only one relapse occurred after cyclophosphamide treatment. Outcome was reported as good in 72% (78% in those who relapsed). DISCUSSION: Death and relapse were infrequent in treated patients. Relapse occurred almost exclusively in patients treated with prednisolone alone. Aggressive early treatment with cyclophosphamide may prevent relapse. The current management approach to VPN appears largely effective, especially if cyclophosphamide is used.