Hippocampal aggregation signatures of pathogenic UBQLN2 in amyotrophic lateral sclerosis and frontotemporal dementia

Pathogenic variants in the UBQLN2 gene cause X-linked dominant amyotrophic lateral sclerosis and/or frontotemporal dementia characterised by ubiquilin 2 aggregates in neurons of the motor cortex, hippocampus, and spinal cord. However, ubiquilin 2 neuropathology is also seen in sporadic and familial amyotrophic lateral sclerosis and/or frontotemporal dementia cases not caused by UBQLN2 pathogenic variants, particularly C9orf72-linked cases. This makes the mechanistic role of mutant ubiquilin 2 protein and the value of ubiquilin 2 pathology for predicting genotype unclear. Here we examine a cohort of 44 genotypically diverse amyotrophic lateral sclerosis cases with or without frontotemporal dementia, including eight cases with UBQLN2 variants (resulting in p.S222G, p.P497H, p.P506S, p.T487I (two cases), and p.P497L (three cases)). Using multiplexed (5-label) fluorescent immunohistochemistry, we mapped the co-localisation of ubiquilin 2 with phosphorylated TDP-43, dipeptide repeat aggregates, and p62, in the hippocampus of controls (n = 6), or amyotrophic lateral sclerosis with or without frontotemporal dementia in sporadic (n = 20), unknown familial (n = 3), SOD1-linked (n = 1), FUS-linked (n = 1), C9orf72-linked (n = 5), and UBQLN2-linked (n = 8) cases. We differentiate between i) ubiquilin 2 aggregation together with phosphorylated TDP-43 or dipeptide repeat proteins, and ii) ubiquilin 2 self-aggregation promoted by UBQLN2 pathogenic variants that cause amyotrophic lateral sclerosis/and frontotemporal dementia. Overall, we describe a hippocampal protein aggregation signature that fully distinguishes mutant from wildtype ubiquilin 2 in amyotrophic lateral sclerosis with or without frontotemporal dementia, whereby mutant ubiquilin 2 is more prone than wildtype to aggregate independently of driving factors. This neuropathological signature can be used to assess the pathogenicity of UBQLN2 gene variants and to understand the mechanisms of UBQLN2-linked disease.

Distribution of ubiquilin 2 and TDP-43 aggregates throughout the CNS in UBQLN2 p.T487I-linked amyotrophic lateral sclerosis and frontotemporal dementia

Mutations in the UBQLN2 gene cause amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The neuropathology of such UBQLN2-linked cases of ALS/FTD is characterised by aggregates of the ubiquilin 2 protein in addition to aggregates of the transactive response DNA-binding protein of 43 kDa (TDP-43). ALS and FTD without UBQLN2 mutations are also characterised by TDP-43 aggregates, that may or may not colocalise with wildtype ubiquilin 2. Despite this, the relative contributions of TDP-43 and ubiquilin 2 to disease pathogenesis remain largely under-characterised, as does their relative deposition as aggregates across the central nervous system (CNS). Here we conducted multiplex immunohistochemistry of three UBQLN2 p.T487I-linked ALS/FTD cases, three non-UBQLN2-linked (sporadic) ALS cases, and 8 non-neurodegenerative disease controls, covering 40 CNS regions. We then quantified ubiquilin 2 aggregates, TDP-43 aggregates and aggregates containing both proteins in regions of interest to determine how UBQLN2-linked and non-UBQLN2-linked proteinopathy differ. We find that ubiquilin 2 aggregates that are negative for TDP-43 are predominantly small and punctate and are abundant in the hippocampal formation, spinal cord, all tested regions of neocortex, medulla and substantia nigra in UBQLN2-linked ALS/FTD but not sporadic ALS. Curiously, the striatum harboured small punctate ubiquilin 2 aggregates in all cases examined, while large diffuse striatal ubiquilin 2 aggregates were specific to UBQLN2-linked ALS/FTD. Overall, ubiquilin 2 is mainly deposited in clinically unaffected regions throughout the CNS such that symptomology in UBQLN2-linked cases maps best to the aggregation of TDP-43.

Treatment with sodium butyrate induces autophagy resulting in therapeutic benefits for spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3, also known as Machado Joseph disease) is a fatal neurodegenerative disease caused by the expansion of the trinucleotide repeat region within the ATXN3/MJD gene. Mutation of ATXN3 causes formation of ataxin-3 protein aggregates, neurodegeneration, and motor deficits. Here we investigated the therapeutic potential and mechanistic activity of sodium butyrate (SB), the sodium salt of butyric acid, a metabolite naturally produced by gut microbiota, on cultured SH-SY5Y cells and transgenic zebrafish expressing human ataxin-3 containing 84 glutamine (Q) residues to model SCA3. SCA3 SH-SY5Y cells were found to contain high molecular weight ataxin-3 species and detergent-insoluble protein aggregates. Treatment with SB increased the activity of the autophagy protein quality control pathway in the SCA3 cells, decreased the presence of ataxin-3 aggregates and presence of high molecular weight ataxin-3 in an autophagy-dependent manner. Treatment with SB was also beneficial in vivo, improving swimming performance, increasing activity of the autophagy pathway, and decreasing the presence of insoluble ataxin-3 protein species in the transgenic SCA3 zebrafish. Co-treating the SCA3 zebrafish with SB and chloroquine, an autophagy inhibitor, prevented the beneficial effects of SB on zebrafish swimming, indicating that the improved swimming performance was autophagy-dependent. To understand the mechanism by which SB induces autophagy we performed proteomic analysis of protein lysates from the SB-treated and untreated SCA3 SH-SY5Y cells. We found that SB treatment had increased activity of Protein Kinase A and AMPK signaling, with immunoblot analysis confirming that SB treatment had increased levels of AMPK protein and its substrates. Together our findings indicate that treatment with SB can increase activity of the autophagy pathway process and that this has beneficial effects in vitro and in vivo. While our results suggested that this activity may involve activity of a PKA/AMPK-dependent process, this requires further confirmation. We propose that treatment with sodium butyrate warrants further investigation as a potential treatment for neurodegenerative diseases underpinned by mechanisms relating to protein aggregation including SCA3.

Novel gene-intergenic fusion involving ubiquitin E3 ligase UBE3C causes distal hereditary motor neuropathy

Distal hereditary motor neuropathies (dHMNs) are a group of inherited diseases involving the progressive, length-dependent axonal degeneration of the lower motor neurons. There are currently 29 reported causative genes and four disease loci implicated in dHMN. Despite the high genetic heterogeneity, mutations in the known genes account for less than 20% of dHMN cases, with the mutations identified predominantly being point mutations or indels. We have expanded the spectrum of dHMN mutations with the identification of a 1.35 Mb complex structural variation (SV) causing a form of autosomal dominant dHMN (DHMN1 OMIM %182906). Given the complex nature of SV mutations and the importance of studying pathogenic mechanisms in a neuronal setting, we generated a patient-derived DHMN1 motor neuron model harbouring the 1.35 Mb complex insertion. The DHMN1 complex insertion creates a duplicated copy of the first 10 exons of the ubiquitin-protein E3 ligase gene (UBE3C) and forms a novel gene-intergenic fusion sense transcript by incorporating a terminal pseudo-exon from intergenic sequence within the DHMN1 locus. The UBE3C intergenic fusion (UBE3C-IF) transcript does not undergo nonsense-mediated decay and results in a significant reduction of wild-type full-length UBE3C (UBE3C-WT) protein levels in DHMN1 iPSC-derived motor neurons. An engineered transgenic Caenorhabditis elegans model expressing the UBE3C-IF transcript in GABA-ergic motor neurons shows neuronal synaptic transmission deficits. Furthermore, the transgenic animals are susceptible to heat stress, which may implicate defective protein homeostasis underlying DHMN1 pathogenesis. Identification of the novel UBE3C-IF gene-intergenic fusion transcript in motor neurons highlights a potential new disease mechanism underlying axonal and motor neuron degeneration. These complementary models serve as a powerful paradigm for studying the DHMN1 complex SV and an invaluable tool for defining therapeutic targets for DHMN1.

The SOD1-mediated ALS phenotype shows a decoupling between age of symptom onset and disease duration

Superoxide dismutase (SOD1) gene variants may cause amyotrophic lateral sclerosis, some of which are associated with a distinct phenotype. Most studies assess limited variants or sample sizes. In this international, retrospective observational study, we compare phenotypic and demographic characteristics between people with SOD1-ALS and people with ALS and no recorded SOD1 variant. We investigate which variants are associated with age at symptom onset and time from onset to death or censoring using Cox proportional-hazards regression. The SOD1-ALS dataset reports age of onset for 1122 and disease duration for 883 people; the comparator population includes 10,214 and 9010 people respectively. Eight variants are associated with younger age of onset and distinct survival trajectories; a further eight associated with younger onset only and one with distinct survival only. Here we show that onset and survival are decoupled in SOD1-ALS. Future research should characterise rarer variants and molecular mechanisms causing the observed variability.

Clinical practice guideline for the management of paediatric Charcot-Marie-Tooth disease

BACKGROUND AND OBJECTIVES

Charcot-Marie-Tooth disease (CMT) is the most common inherited neuropathy and often presents during childhood. Guidelines for the optimal management of common problems experienced by individuals with CMT do not exist, for either children or adults. We formed the Paediatric CMT Best Practice Guidelines Consortium to develop evidence and consensus-based recommendations for the clinical management of children and adolescents with CMT, with the primary objective of promoting optimal, standardised care globally.

METHODS

Development of this clinical practice guideline involved a series of systematic reviews covering 10 clinical questions, modified Delphi methodology involving an international panel of clinicians to generate consensus where evidence did not exist, and application of the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach to evaluate the body of literature and formulate recommendations.

RESULTS

The final guideline includes three evidence-based and 31 consensus-based recommendations. They encompass the management of muscle weakness, balance and mobility impairment, sensory symptoms, muscle cramps, impaired upper limb function, respiratory impairment, maintenance of joint range of motion and non-surgical management of joint deformity. Consensus was not achieved in some management areas, reflecting differences in practice between clinicians and healthcare settings, and highlighting the need for further research.

CONCLUSIONS

This clinical practice guideline provides practical and implementable guidance on the management of common clinical problems experienced by children with CMT and advocates for improved access to multidisciplinary care. Successful dissemination and implementation of these recommendations will be critical in ensuring their application across multiple healthcare settings.

Common and rare variant association analyses in amyotrophic lateral sclerosis identify 15 risk loci with distinct genetic architectures and neuron-specific biology

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with a lifetime risk of one in 350 people and an unmet need for disease-modifying therapies. We conducted a cross-ancestry genome-wide association study (GWAS) including 29,612 patients with ALS and 122,656 controls, which identified 15 risk loci. When combined with 8,953 individuals with whole-genome sequencing (6,538 patients, 2,415 controls) and a large cortex-derived expression quantitative trait locus (eQTL) dataset (MetaBrain), analyses revealed locus-specific genetic architectures in which we prioritized genes either through rare variants, short tandem repeats or regulatory effects. ALS-associated risk loci were shared with multiple traits within the neurodegenerative spectrum but with distinct enrichment patterns across brain regions and cell types. Of the environmental and lifestyle risk factors obtained from the literature, Mendelian randomization analyses indicated a causal role for high cholesterol levels. The combination of all ALS-associated signals reveals a role for perturbations in vesicle-mediated transport and autophagy and provides evidence for cell-autonomous disease initiation in glutamatergic neurons.

Sodium valproate increases activity of the sirtuin pathway resulting in beneficial effects for spinocerebellar ataxia-3 in vivo

Machado-Joseph disease (MJD, also known as spinocerebellar ataxia type 3) is a fatal neurodegenerative disease that impairs control and coordination of movement. Here we tested whether treatment with the histone deacetylase inhibitor sodium valproate (valproate) prevented a movement phenotype that develops in larvae of a transgenic zebrafish model of the disease. We found that treatment with valproate improved the swimming of the MJD zebrafish, affected levels of acetylated histones 3 and 4, but also increased expression of polyglutamine expanded human ataxin-3. Proteomic analysis of protein lysates generated from the treated and untreated MJD zebrafish also predicted that valproate treatment had activated the sirtuin longevity signaling pathway and this was confirmed by findings of increased SIRT1 protein levels and sirtuin activity in valproate treated MJD zebrafish and HEK293 cells expressing ataxin-3 84Q, respectively. Treatment with resveratrol (another compound known to activate the sirtuin pathway), also improved swimming in the MJD zebrafish. Co-treatment with valproate alongside EX527, a SIRT1 activity inhibitor, prevented induction of autophagy by valproate and the beneficial effects of valproate on the movement in the MJD zebrafish, supporting that they were both dependent on sirtuin activity. These findings provide the first evidence of sodium valproate inducing activation of the sirtuin pathway. Further, they indicate that drugs that target the sirtuin pathway, including sodium valproate and resveratrol, warrant further investigation for the treatment of MJD and related neurodegenerative diseases.

Charcot-Marie-tooth disease causing mutation (p.R158H) in pyruvate dehydrogenase kinase 3 (PDK3) affects synaptic transmission, ATP production and causes neurodegeneration in a CMTX6 C. elegans model

Charcot–Marie-Tooth (CMT) is a commonly inherited, non-fatal neurodegenerative disorder that affects sensory and motor neurons in patients. More than 90 genes are known to cause axonal and demyelinating forms of CMT. The p.R158H mutation in the pyruvate dehydrogenase kinase 3 (PDK3) gene is the genetic cause for an X linked form of axonal CMT (CMTX6). In vitro studies using patient fibroblasts and iPSC-derived motor neurons have shown that this mutation causes deficits in energy metabolism and mitochondrial function. Animal models that recapitulate pathogenic in vivo events in patients are crucial for investigating mechanisms of axonal degeneration and developing therapies for CMT. We have developed a C. elegans model of CMTX6 by knocking-in the p.R158H mutation in pdhk-2, the ortholog of PDK3. In addition, we have developed animal models overexpressing the wild type and mutant form of human PDK3 specifically in the GABAergic motor neurons of C. elegans. CMTX6 mutants generated in this study exhibit synaptic transmission deficits, locomotion defects and show signs of progressive neurodegeneration. Furthermore, the CMTX6 in vivo models display energy deficits that recapitulate the phenotype observed in patient fibroblasts and iPSC-derived motor neurons. Our CMTX6 animals represent the first in vivo model for this form of CMT and have provided novel insights into the cellular function and metabolic pathways perturbed by the p.R158H mutation, all the while closely replicating the clinical presentation observed in CMTX6 patients.

Revisiting the pathogenic mechanism of the GJB1 5' UTR c.-103C > T mutation causing CMTX1

The second most common form of Charcot-Marie-Tooth neuropathy (CMT), X-linked CMT type X1 (CMTX1), is caused by coding and non-coding mutations in the gap junction beta 1 (GJB1) gene. The non-coding GJB1 c.-103C > T mutation (NM_000166.5) has been reported to cause CMTX1 in multiple families. This study assessed the internal ribosomal entry site (IRES) activity previously reported for the rat Gjb1 P2 5' untranslated region (UTR). Using a bicistronic assay and transfecting RT4 Schwann cells, IRES activity of the human GJB1 P2 5' UTR was compared to the GJB1 P2 5' UTR containing either the c.-103C > T mutation or the non-pathogenic c.-102G > A variant. No differences in GJB1 P2 5' UTR IRES activity were observed between the negative control, the wild-type P2 5' UTR, the c.-103C > T 5' UTR or the c.-102G > A 5' UTR, irrespective of the GJB1 intron being present (p = .429 with intron, and p = .865 without). A theoretical c.-131A > G variant was predicted to result in the same RNA secondary structure as the GJB1 c.-103C > T P2 5' UTR. However, no significant difference was observed between expression from the wild-type GJB1 P2 5' UTR and the GJB1 c.-131A > G variant (p = .688). Deletion of the conserved region surrounding the c.-103C > T mutation (c.-108_-103del) resulted in significantly higher expression than the c.-103C > T mutation alone (p = .019), suggesting that the conserved c.-108_-103 region was not essential for translation. The reporter assays in this study do not recapitulate the previously reported GJB1 IRES activity and suggest an alternate pathogenic mechanism for the c.-103C > T CMTX1 non-coding mutation.

Genome-wide Meta-analysis Finds the ACSL5-ZDHHC6 Locus Is Associated with ALS and Links Weight Loss to the Disease Genetics

We meta-analyze amyotrophic lateral sclerosis (ALS) genome-wide association study (GWAS) data of European and Chinese populations (84,694 individuals). We find an additional significant association between rs58854276 spanning ACSL5-ZDHHC6 with ALS (p = 8.3 × 10⁻⁹), with replication in an independent Australian cohort (1,502 individuals; p = 0.037). Moreover, B4GALNT1, G2E3-SCFD1, and TRIP11-ATXN3 are identified using a gene-based analysis. ACSL5 has been associated with rapid weight loss, as has another ALS-associated gene, GPX3. Weight loss is frequent in ALS patients and is associated with shorter survival. We investigate the effect of the ACSL5 and GPX3 single-nucleotide polymorphisms (SNPs), using longitudinal body composition and weight data of 77 patients and 77 controls. In patients’ fat-free mass, although not significant, we observe an effect in the expected direction (rs58854276: −2.1 ± 1.3 kg/A allele, p = 0.053; rs3828599: −1.0 ± 1.3 kg/A allele, p = 0.22). No effect was observed in controls. Our findings support the increasing interest in lipid metabolism in ALS and link the disease genetics to weight loss in patients.

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Cross-ethnic meta-analysis finds an association between the ACSL5-ZDHHC6 locus and ALS

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The ACSL5-ZDHHC6 association is replicated in an independent Australian cohort

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ACSL5-ZDHHC6 lead SNP is in ACSL5 and is an eQTL of ZDHHC6 in brain tissues

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ACSL5 SNPs might have an effect on fat-free mass in ALS patients

Impaired NHEJ repair in amyotrophic lateral sclerosis is associated with TDP-43 mutations

Background

Pathological forms of TAR DNA-binding protein 43 (TDP-43) are present in motor neurons of almost all amyotrophic lateral sclerosis (ALS) patients, and mutations in TDP-43 are also present in ALS. Loss and gain of TDP-43 functions are implicated in pathogenesis, but the mechanisms are unclear. While the RNA functions of TDP-43 have been widely investigated, its DNA binding roles remain unclear. However, recent studies have implicated a role for TDP-43 in the DNA damage response.

Methods

We used NSC-34 motor neuron-like cells and primary cortical neurons expressing wildtype TDP-43 or TDP-43 ALS associated mutants (A315T, Q331K), in which DNA damage was induced by etoposide or H₂O₂ treatment. We investigated the consequences of depletion of TDP-43 on DNA repair using small interfering RNAs. Specific non homologous end joining (NHEJ) reporters (EJ5GFP and EJ2GFP) and cells lacking DNA-dependent serine/threonine protein kinase (DNA-PK) were used to investigate the role of TDP-43 in DNA repair. To investigate the recruitment of TDP-43 to sites of DNA damage we used single molecule super-resolution microscopy and a co-immunoprecipitation assay. We also investigated DNA damage in an ALS transgenic mouse model, in which TDP-43 accumulates pathologically in the cytoplasm. We also examined fibroblasts derived from ALS patients bearing the TDP-43 M337V mutation for evidence of DNA damage.

Results

We demonstrate that wildtype TDP-43 is recruited to sites of DNA damage where it participates in classical NHEJ DNA repair. However, ALS-associated TDP-43 mutants lose this activity, which induces DNA damage. Furthermore, DNA damage is present in mice displaying TDP-43 pathology, implying an active role in neurodegeneration. Additionally, DNA damage triggers features typical of TDP-43 pathology; cytoplasmic mis-localisation and stress granule formation. Similarly, inhibition of NHEJ induces TDP-43 mis-localisation to the cytoplasm.

Conclusions

This study reveals that TDP-43 functions in DNA repair, but loss of this function triggers DNA damage and is associated with key pathological features of ALS.

Genome-wide association study identifies genetic factors that modify age at onset in Machado-Joseph disease

Machado-Joseph disease (MJD/SCA3) is the most common form of dominantly inherited ataxia worldwide. The disorder is caused by an expanded CAG repeat in the ATXN3 gene. Past studies have revealed that the length of the expansion partly explains the disease age at onset (AO) variability of MJD, which is confirmed in this study (Pearson’s correlation coefficient R² = 0.62). Using a total of 786 MJD patients from five different geographical origins, a genome-wide association study (GWAS) was conducted to identify additional AO modifying factors that could explain some of the residual AO variability. We identified nine suggestively associated loci (P < 1 × 10⁻⁵). These loci were enriched for genes involved in vesicle transport, olfactory signaling, and synaptic pathways. Furthermore, associations between AO and the TRIM29 and RAG genes suggests that DNA repair mechanisms might be implicated in MJD pathogenesis. Our study demonstrates the existence of several additional genetic factors, along with CAG expansion, that may lead to a better understanding of the genotype-phenotype correlation in MJD.

Genetic and immunopathological analysis of CHCHD10 in Australian amyotrophic lateral sclerosis and frontotemporal dementia and transgenic TDP-43 mice

OBJECTIVE

Since the first report of CHCHD10 gene mutations in amyotrophiclateral sclerosis (ALS)/frontotemporaldementia (FTD) patients, genetic variation in CHCHD10 has been inconsistently linked to disease. A pathological assessment of the CHCHD10 protein in patient neuronal tissue also remains to be reported. We sought to characterise the genetic and pathological contribution of CHCHD10 to ALS/FTD in Australia.

METHODS

Whole-exome and whole-genome sequencing data from 81 familial and 635 sporadic ALS, and 108 sporadic FTD cases, were assessed for genetic variation in CHCHD10. CHCHD10 protein expression was characterised by immunohistochemistry, immunofluorescence and western blotting in control, ALS and/or FTD postmortem tissues and further in a transgenic mouse model of TAR DNA-binding protein 43 (TDP-43) pathology.

RESULTS

No causal, novel or disease-associated variants in CHCHD10 were identified in Australian ALS and/or FTD patients. In human brain and spinal cord tissues, CHCHD10 was specifically expressed in neurons. A significant decrease in CHCHD10 protein level was observed in ALS patient spinal cord and FTD patient frontal cortex. In a TDP-43 mouse model with a regulatable nuclear localisation signal (rNLS TDP-43 mouse), CHCHD10 protein levels were unaltered at disease onset and early in disease, but were significantly decreased in cortex in mid-stage disease.

CONCLUSIONS

Genetic variation in CHCHD10 is not a common cause of ALS/FTD in Australia. However, we showed that in humans, CHCHD10 may play a neuron-specific role and a loss of CHCHD10 function may be linked to ALS and/or FTD. Our data from the rNLS TDP-43 transgenic mice suggest that a decrease in CHCHD10 levels is a late event in aberrant TDP-43-induced ALS/FTD pathogenesis.

Targeted next generation sequencing identifies a genetic spectrum of DNA variants in patients with hemiplegic migraine

Objective:

Hemiplegic migraine in both familial (FHM) and sporadic (SHM) forms is a rare subtype of migraine with aura that can be traced to mutations in the CACNA1A, ATP1A2 and SCN1A genes. It is characterised by severe attacks of typical migraine accompanied by hemiparesis, as well as episodes of complex aura that vary significantly between individuals.

Methods:

Using a targeted next generation sequencing (NGS) multigene panel, we have sequenced the genomic DNA of 172 suspected hemiplegic migraine cases, in whom no mutation had previously been found by Sanger sequencing (SS) of a limited number of exons with high mutation frequency in FHM genes.

Results:

Genetic screening identified 29 variants, 10 of which were novel, in 35 cases in the three FHM genes ( CACNA1A, ATP1A2 and SCN1A). Interestingly, in this suspected HM cohort, the ATP1A2 gene harboured the highest number of variants with 24/35 cases (68.6%), while CACNA1A ranked the second gene, with 5 variants identified in 7/35 cases (20%). All detected variants were confirmed by SS and were absent in 100 non-migraine healthy control individuals. Assessment of variants with the American College of Medical Genetics and Genomics guidelines classified 8 variants as pathogenic, 3 as likely pathogenic and 18 as variants of unknown significance. Targeted NGS gene panel increased the diagnostic yield by fourfold over iterative SS in our diagnostics facility.

Conclusion:

We have identified 29 potentially causative variants in an Australian and New Zealand cohort of suspected HM cases and found that the ATP1A2 gene was the most commonly mutated gene. Our results suggest that screening using NGS multigene panels to investigate ATP1A2 alongside CACNA1A and SCN1A is a clinically useful and efficient method.

Monozygotic twins and triplets discordant for amyotrophic lateral sclerosis display differential methylation and gene expression

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterised by the loss of upper and lower motor neurons. ALS exhibits high phenotypic variability including age and site of onset, and disease duration. To uncover epigenetic and transcriptomic factors that may modify an ALS phenotype, we used a cohort of Australian monozygotic twins (n = 3 pairs) and triplets (n = 1 set) that are discordant for ALS and represent sporadic ALS and the two most common types of familial ALS, linked to C9orf72 and SOD1. Illumina Infinium HumanMethylation450K BeadChip, EpiTYPER and RNA-Seq analyses in these ALS-discordant twins/triplets and control twins (n = 2 pairs), implicated genes with consistent longitudinal differential DNA methylation and/or gene expression. Two identified genes, RAD9B and C8orf46, showed significant differential methylation in an extended cohort of >1000 ALS cases and controls. Combined longitudinal methylation-transcription analysis within a single twin set implicated CCNF, DPP6, RAMP3, and CCS, which have been previously associated with ALS. Longitudinal transcriptome data showed an 8-fold enrichment of immune function genes and under-representation of transcription and protein modification genes in ALS. Examination of these changes in a large Australian sporadic ALS cohort suggest a broader role in ALS. Furthermore, we observe that increased methylation age is a signature of ALS in older patients.

Motor Neuron Abnormalities Correlate with Impaired Movement in Zebrafish that Express Mutant Superoxide Dismutase 1

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of motor neurons. ALS can be modeled in zebrafish (Danio rerio) through the expression of human ALS-causing genes, such as superoxide dismutase 1 (SOD1). Overexpression of mutated human SOD1 protein causes aberrant branching and shortening of spinal motor axons. Despite this, the functional relevance of this axon morphology remains elusive. Our aim was to determine whether this motor axonopathy is correlated with impaired movement in mutant (MT) SOD1-expressing zebrafish. Transgenic zebrafish embryos that express blue fluorescent protein (mTagBFP) in motor neurons were injected with either wild-type (WT) or MT (A4V) human SOD1 messenger ribonucleic acid (mRNA). At 48 hours post-fertilization, larvae movement (distance traveled during behavioral testing) was examined, followed by quantification of motor axon length. Larvae injected with MT SOD1 mRNA had significantly shorter and more aberrantly branched motor axons (p < 0.002) and traveled a significantly shorter distance during behavioral testing (p < 0.001) when compared with WT SOD1 and noninjected larvae. Furthermore, there was a positive correlation between distance traveled and motor axon length (R² = 0.357, p < 0.001). These data represent the first correlative investigation of motor axonopathies and impaired movement in SOD1-expressing zebrafish, confirming functional relevance and validating movement as a disease phenotype for the testing of disease treatments for ALS.

Neuronal cell culture from transgenic zebrafish models of neurodegenerative disease

We describe a protocol for culturing neurons from transgenic zebrafish embryos to investigate the subcellular distribution and protein aggregation status of neurodegenerative disease-causing proteins. The utility of the protocol was demonstrated on cell cultures from zebrafish that transgenically express disease-causing variants of human fused in sarcoma (FUS) and ataxin-3 proteins, in order to study amyotrophic lateral sclerosis (ALS) and spinocerebellar ataxia type-3 (SCA3), respectively. A mixture of neuronal subtypes, including motor neurons, exhibited differentiation and neurite outgrowth in the cultures. As reported previously, mutant human FUS was found to be mislocalized from nuclei to the cytosol, mimicking the pathology seen in human ALS and the zebrafish FUS model. In contrast, neurons cultured from zebrafish expressing human ataxin-3 with disease-associated expanded polyQ repeats did not accumulate within nuclei in a manner often reported to occur in SCA3. Despite this, the subcellular localization of the human ataxin-3 protein seen in cell cultures was similar to that found in the SCA3 zebrafish themselves. The finding of similar protein localization and aggregation status in the neuronal cultures and corresponding transgenic zebrafish models confirms that this cell culture model is a useful tool for investigating the cell biology and proteinopathy signatures of mutant proteins for the study of neurodegenerative disease.

Summary: This article describes the optimization and validation of a protocol for culturing of neurons from transgenic zebrafish for the study of neurodegenerative diseases.

Infantile-Onset Myelin Protein Zero-Related Demyelinating Neuropathy Presenting as an Upper Extremity Monoplegia

We describe an infant with an early-onset demyelinating neuropathy who presented with an upper extremity monoplegia and progressive asymmetric weakness. Neurophysiologic testing revealed a generalized severe neuropathy with marked slowing of nerve conduction. The disproportionate severity and asymmetry of upper extremity involvement at presentation was atypical of inherited neuropathies, and an initial diagnosis of chronic inflammatory demyelinating polyneuropathy was considered. Nerve biopsy showed severe depletion of large myelinated fibers without inflammatory cells, and focally folded myelin sheaths were seen on electron microscopy. Genetic testing revealed a de novo heterozygous mutation in the myelin protein zero gene.

Unique clinical and neurophysiologic profile of a cohort of children with CMTX3

OBJECTIVE

To describe in detail the clinical profile of Charcot-Marie-Tooth disease subtype 3 (CMTX3) to aid appropriate genetic testing and rehabilitative therapy.

METHODS

We reviewed the clinical and neurophysiologic profile and CMT Pediatric Scale (CMTPedS) assessments of 11 children with CMTX3.

RESULTS

Compared with the more common forms of CMT, CMT1A and CMTX, CMTX3 was characterized by early onset with early and progressive hand weakness. Most affected children were symptomatic within the first 2 years of life. The most common presentation was foot deformity in the first year of life. CMTPedS analysis in these children revealed that CMTX3 progressed more rapidly (4.3 ± 4.1 points over 2 years, n = 7) than CMT1A and CMTX1. Grip strength in affected boys was 2 SDs below age- and sex-matched normative reference values (z score -2.05 ± 1.32) in the second decade of life. The most severely affected individual was wheelchair bound at 14 years of age, and 2 individuals had no movement in the small muscles of the hand in the second decade of life. Nerve conduction studies showed a demyelinating sensorimotor neuropathy with motor conduction velocity ≤23 m/s.

CONCLUSIONS

CMTX3 had an earlier onset, severe hand weakness, and more rapidly progressive disability compared to the more common forms of CMT. Understanding the unique phenotype of CMTX3 is essential for directing genetic testing because the CMTX3 insertion will not be seen on a routine microarray or neuromuscular gene panel. Early diagnosis will enable rehabilitation to be started early in this rapidly progressive neuropathy.

Structural variations causing inherited peripheral neuropathies: A paradigm for understanding genomic organization, chromatin interactions, and gene dysregulation

Inherited peripheral neuropathies (IPNs) are a clinically and genetically heterogeneous group of diseases affecting the motor and sensory peripheral nerves. IPNs have benefited from gene discovery and genetic diagnosis using next-generation sequencing with over 80 causative genes available for testing. Despite this success, up to 50% of cases remain genetically unsolved. In the absence of protein coding mutations, noncoding DNA or structural variation (SV) mutations are a possible explanation. The most common IPN, Charcot-Marie-Tooth neuropathy type 1A (CMT1A), is caused by a 1.5 Mb duplication causing trisomy of the dosage sensitive gene PMP22. Using genome sequencing, we recently identified two large genomic rearrangements causing IPN subtypes X-linked CMT (CMTX3) and distal hereditary motor neuropathy (DHMN1), thereby expanding the spectrum of SV mutations causing IPN. Understanding how newly discovered SVs can cause IPN may serve as a useful paradigm to examine the role of topologically associated domains (TADs), chromatin interactions, and gene dysregulation in disease. This review will describe the growing role of SV in the pathogenesis of IPN and the importance of considering this type of mutation in Mendelian diseases where protein coding mutations cannot be identified.

Genome-wide Analyses Identify KIF5A as a Novel ALS Gene

To identify novel genes associated with ALS, we undertook two lines of investigation. We carried out a genome-wide association study comparing 20,806 ALS cases and 59,804 controls. Independently, we performed a rare variant burden analysis comparing 1,138 index familial ALS cases and 19,494 controls. Through both approaches, we identified kinesin family member 5A (KIF5A) as a novel gene associated with ALS. Interestingly, mutations predominantly in the N-terminal motor domain of KIF5A are causative for two neurodegenerative diseases: hereditary spastic paraplegia (SPG10) and Charcot-Marie-Tooth type 2 (CMT2). In contrast, ALS-associated mutations are primarily located at the C-terminal cargo-binding tail domain and patients harboring loss-of-function mutations displayed an extended survival relative to typical ALS cases. Taken together, these results broaden the phenotype spectrum resulting from mutations in KIF5A and strengthen the role of cytoskeletal defects in the pathogenesis of ALS.

A recurrent WARS mutation is a novel cause of autosomal dominant distal hereditary motor neuropathy

Distal hereditary motor neuropathy is a heterogeneous group of inherited neuropathies characterized by distal limb muscle weakness and atrophy. Although at least 15 genes have been implicated in distal hereditary motor neuropathy, the genetic causes remain elusive in many families. To identify an additional causal gene for distal hereditary motor neuropathy, we performed exome sequencing for two affected individuals and two unaffected members in a Taiwanese family with an autosomal dominant distal hereditary motor neuropathy in which mutations in common distal hereditary motor neuropathy-implicated genes had been excluded. The exome sequencing revealed a heterozygous mutation, c.770A > G (p.His257Arg), in the cytoplasmic tryptophanyl-tRNA synthetase (TrpRS) gene (WARS) that co-segregates with the neuropathy in the family. Further analyses of WARS in an additional 79 Taiwanese pedigrees with inherited neuropathies and 163 index cases from Australian, European, and Korean distal hereditary motor neuropathy families identified the same mutation in another Taiwanese distal hereditary motor neuropathy pedigree with different ancestries and one additional Belgian distal hereditary motor neuropathy family of Caucasian origin. Cell transfection studies demonstrated a dominant-negative effect of the p.His257Arg mutation on aminoacylation activity of TrpRS, which subsequently compromised protein synthesis and reduced cell viability. His257Arg TrpRS also inhibited neurite outgrowth and led to neurite degeneration in the neuronal cell lines and rat motor neurons. Further in vitro analyses showed that the WARS mutation could potentiate the angiostatic activities of TrpRS by enhancing its interaction with vascular endothelial-cadherin. Taken together, these findings establish WARS as a gene whose mutations may cause distal hereditary motor neuropathy and alter canonical and non-canonical functions of TrpRS.

Non-nuclear Pool of Splicing Factor SFPQ Regulates Axonal Transcripts Required for Normal Motor Development

Recent progress revealed the complexity of RNA processing and its association to human disorders. Here, we unveil a new facet of this complexity. Complete loss of function of the ubiquitous splicing factor SFPQ affects zebrafish motoneuron differentiation cell autonomously. In addition to its nuclear localization, the protein unexpectedly localizes to motor axons. The cytosolic version of SFPQ abolishes motor axonal defects, rescuing key transcripts, and restores motility in the paralyzed sfpq null mutants, indicating a non-nuclear processing role in motor axons. Novel variants affecting the conserved coiled-coil domain, so far exclusively found in fALS exomes, specifically affect the ability of SFPQ to localize in axons. They broadly rescue morphology and motility in the zebrafish mutant, but alter motor axon morphology, demonstrating functional requirement for axonal SFPQ. Altogether, we uncover the axonal function of the splicing factor SFPQ in motor development and highlight the importance of the coiled-coil domain in this process.

Video Abstract

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SFPQ splicing factor is present in motor axons

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Non-nuclear SFPQ is able to drive axon maturation and connectivity

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Loss of axonal SFPQ affects axonal morphology

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Coiled-coil domain of the protein is important for non-nuclear localization

The genotype-phenotype landscape of familial amyotrophic lateral sclerosis in Australia

Amyotrophic lateral sclerosis (ALS) is a clinically and genetically heterogeneous fatal neurodegenerative disease. Around 10% of ALS cases are hereditary. ALS gene discoveries have provided most of our understanding of disease pathogenesis. We aimed to describe the genetic landscape of ALS in Australia by assessing 1013 Australian ALS patients for known ALS mutations by direct sequencing, whole exome sequencing or repeat primed polymerase chain reaction. Age of disease onset and disease duration were used for genotype-phenotype correlations. We report 60.8% of Australian ALS families in this cohort harbour a known ALS mutation. Hexanucleotide repeat expansions in C9orf72 accounted for 40.6% of families and 2.9% of sporadic patients. We also report ALS families with mutations in SOD1 (13.7%), FUS (2.4%), TARDBP (1.9%), UBQLN2 (.9%), OPTN (.5%), TBK1 (.5%) and CCNF (.5%). We present genotype-phenotype correlations between these genes as well as between gene mutations. Notably, C9orf72 hexanucleotide repeat expansion positive patients experienced significantly later disease onset than ALS mutation patients. Among SOD1 families, p.I114T positive patients had significantly later onset and longer survival. Our report highlights a unique spectrum of ALS gene frequencies among patients from the Australian population, and further, provides correlations between specific ALS mutations with disease onset and/or duration.

Quantitative muscle ultrasound as a biomarker in Charcot-Marie-Tooth neuropathy

OBJECTIVE

The utility of quantitative muscle ultrasound as a marker of disease severity in Charcot-Marie-Tooth (CMT) disease subtypes was investigated.

METHODS

Muscle ultrasound was prospectively performed on 252 individual muscles from 21 CMT patients (9 CMT1A, 8 CMTX1, 4 CMT2A) and compared to 120 muscles from 10 age and gender-matched controls. Muscle ultrasound recorded echogenicity and thickness in representative muscles including first dorsal interosseus (FDI) and tibialis anterior (TA).

RESULTS

Muscle volume of FDI and thickness of TA correlated with MRC strength. Muscle echogenicity was significantly increased in FDI (65.05 vs 47.09; p<0.0001) and TA (89.45 vs 66.30; p<0.0001) of CMT patients. In TA, there was significantly higher muscle thickness (23 vs 18 vs 16mm; p<0.0001) and lower muscle echogenicity (80 vs 95 vs 108; p<0.0001) in CMT1A compared to CMTX1 and CMT2A. This corresponded to disease severity based on muscle strength (MRC grading CMT1A vs CMTX1 vs CMT2A: 59 vs 48 vs 44; p=0.002).

CONCLUSION

In CMT, quantitative muscle ultrasound of FDI and TA is a useful marker of disease severity.

SIGNIFICANCE

The current findings suggest that quantitative muscle ultrasound has potential as a surrogate marker of disease progression in future interventional trials in CMT.

Population-based cohort study of variation in the use of emergency cholecystectomy for benign gallbladder diseases

Background

The aims of this prospective population-based cohort study were to identify the patient and hospital characteristics associated with emergency cholecystectomy, and the influences of these in determining variations between hospitals.

Methods

Data were collected for consecutive patients undergoing cholecystectomy in acute UK and Irish hospitals between 1 March and 1 May 2014. Potential explanatory variables influencing the performance of emergency cholecystectomy were analysed by means of multilevel, multivariable logistic regression modelling using a two-level hierarchical structure with patients (level 1) nested within hospitals (level 2).

Results

Data were collected on 4744 cholecystectomies from 165 hospitals. Increasing age, lower ASA fitness grade, biliary colic, the need for further imaging (magnetic retrograde cholangiopancreatography), endoscopic interventions (endoscopic retrograde cholangiopancreatography) and admission to a non-biliary centre significantly reduced the likelihood of an emergency cholecystectomy being performed. The multilevel model was used to calculate the probability of receiving an emergency cholecystectomy for a woman aged 40 years or over with an ASA grade of I or II and a BMI of at least 25·0 kg/m2, who presented with acute cholecystitis with an ultrasound scan showing a thick-walled gallbladder and a normal common bile duct. The mean predicted probability of receiving an emergency cholecystectomy was 0·52 (95 per cent c.i. 0·45 to 0·57). The predicted probabilities ranged from 0·02 to 0·95 across the 165 hospitals, demonstrating significant variation between hospitals.

Conclusion

Patients with similar characteristics presenting to different hospitals with acute gallbladder pathology do not receive comparable care.

NEK1 variants confer susceptibility to amyotrophic lateral sclerosis

To identify genetic factors contributing to amyotrophic lateral sclerosis (ALS), we conducted whole-exome analyses of 1,022 index familial ALS (FALS) cases and 7,315 controls. In a new screening strategy, we performed gene-burden analyses trained with established ALS genes and identified a significant association between loss-of-function (LOF) NEK1 variants and FALS risk. Independently, autozygosity mapping for an isolated community in the Netherlands identified a NEK1 p.Arg261His variant as a candidate risk factor. Replication analyses of sporadic ALS (SALS) cases and independent control cohorts confirmed significant disease association for both p.Arg261His (10,589 samples analyzed) and NEK1 LOF variants (3,362 samples analyzed). In total, we observed NEK1 risk variants in nearly 3% of ALS cases. NEK1 has been linked to several cellular functions, including cilia formation, DNA-damage response, microtubule stability, neuronal morphology and axonal polarity. Our results provide new and important insights into ALS etiopathogenesis and genetic etiology.

Genome-wide association analyses identify new risk variants and the genetic architecture of amyotrophic lateral sclerosis

To elucidate the genetic architecture of amyotrophic lateral sclerosis (ALS) and find associated loci, we assembled a custom imputation reference panel from whole-genome-sequenced patients with ALS and matched controls (n = 1,861). Through imputation and mixed-model association analysis in 12,577 cases and 23,475 controls, combined with 2,579 cases and 2,767 controls in an independent replication cohort, we fine-mapped a new risk locus on chromosome 21 and identified C21orf2 as a gene associated with ALS risk. In addition, we identified MOBP and SCFD1 as new associated risk loci. We established evidence of ALS being a complex genetic trait with a polygenic architecture. Furthermore, we estimated the SNP-based heritability at 8.5%, with a distinct and important role for low-frequency variants (frequency 1-10%). This study motivates the interrogation of larger samples with full genome coverage to identify rare causal variants that underpin ALS risk.

Whole Genome Sequencing Identifies a 78 kb Insertion from Chromosome 8 as the Cause of Charcot-Marie-Tooth Neuropathy CMTX3

With the advent of whole exome sequencing, cases where no pathogenic coding mutations can be found are increasingly being observed in many diseases. In two large, distantly-related families that mapped to the Charcot-Marie-Tooth neuropathy CMTX3 locus at chromosome Xq26.3-q27.3, all coding mutations were excluded. Using whole genome sequencing we found a large DNA interchromosomal insertion within the CMTX3 locus. The 78 kb insertion originates from chromosome 8q24.3, segregates fully with the disease in the two families, and is absent from the general population as well as 627 neurologically normal chromosomes from in-house controls. Large insertions into chromosome Xq27.1 are known to cause a range of diseases and this is the first neuropathy phenotype caused by an interchromosomal insertion at this locus. The CMTX3 insertion represents an understudied pathogenic structural variation mechanism for inherited peripheral neuropathies. Our finding highlights the importance of considering all structural variation types when studying unsolved inherited peripheral neuropathy cases with no pathogenic coding mutations.

Pathogenic mechanisms underlying X-linked Charcot-Marie-Tooth neuropathy (CMTX6) in patients with a pyruvate dehydrogenase kinase 3 mutation

Charcot-Marie-Tooth disease (CMT) is the most common inherited peripheral neuropathy. An X-linked form of CMT (CMTX6) is caused by a missense mutation (R158H) in the pyruvate dehydrogenase kinase isoenzyme 3 (PDK3) gene. PDK3 is one of 4 isoenzymes that negatively regulate the activity of the pyruvate dehydrogenase complex (PDC) by reversible phosphorylation of its first catalytic component pyruvate dehydrogenase (designated as E1). Mitochondrial PDC catalyses the oxidative decarboxylation of pyruvate to acetyl CoA and links glycolysis to the energy-producing Krebs cycle. We have previously shown the R158H mutation confers PDK3 enzyme hyperactivity. In this study we demonstrate that the increased PDK3 activity in patient fibroblasts (PDK3(R158H)) leads to the attenuation of PDC through hyper-phosphorylation of E1 at selected serine residues. This hyper-phosphorylation can be reversed by treating the PDK3(R158H) fibroblasts with the PDK inhibitor dichloroacetate (DCA). In the patient cells, down-regulation of PDC leads to increased lactate, decreased ATP and alteration of the mitochondrial network. Our findings highlight the potential to develop specific drug targeting of the mutant PDK3 as a therapeutic approach to treating CMTX6.

Characterizing the molecular phenotype of an Atp7a(T985I) conditional knock in mouse model for X-linked distal hereditary motor neuropathy (dHMNX)

ATP7A is a P-type ATPase essential for cellular copper (Cu) transport and homeostasis. Loss-of-function ATP7A mutations causing systemic Cu deficiency are associated with severe Menkes disease or its milder allelic variant, occipital horn syndrome. We previously identified two rare ATP7A missense mutations (P1386S and T994I) leading to a non-fatal form of motor neuron disorder, X-linked distal hereditary motor neuropathy (dHMNX), without overt signs of systemic Cu deficiency. Recent investigations using a tissue specific Atp7a knock out model have demonstrated that Cu plays an essential role in motor neuron maintenance and function, however the underlying pathogenic mechanisms of ATP7A mutations causing axonal degeneration remain unknown. We have generated an Atp7a conditional knock in mouse model of dHMNX expressing Atp7a(T985I), the orthologue of the human ATP7A(T994I) identified in dHMNX patients. Although a degenerative motor phenotype is not observed, the knock in Atp7a(T985I/Y) mice show altered Cu levels within the peripheral and central nervous systems, an increased diameter of the muscle fibres and altered myogenin and myostatin gene expression. Atp7a(T985I/Y) mice have reduced Atp7a protein levels and recapitulate the defective trafficking and altered post-translational regulatory mechanisms observed in the human ATP7A(T994I) patient fibroblasts. Our model provides a unique opportunity to characterise the molecular phenotype of dHMNX and the time course of cellular events leading to the process of axonal degeneration in this disease.

CCNF mutations in amyotrophic lateral sclerosis and frontotemporal dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are overlapping, fatal neurodegenerative disorders in which the molecular and pathogenic basis remains poorly understood. Ubiquitinated protein aggregates, of which TDP-43 is a major component, are a characteristic pathological feature of most ALS and FTD patients. Here we use genome-wide linkage analysis in a large ALS/FTD kindred to identify a novel disease locus on chromosome 16p13.3. Whole-exome sequencing identified a CCNF missense mutation at this locus. Interrogation of international cohorts identified additional novel CCNF variants in familial and sporadic ALS and FTD. Enrichment of rare protein-altering CCNF variants was evident in a large sporadic ALS replication cohort. CCNF encodes cyclin F, a component of an E3 ubiquitin-protein ligase complex (SCF(Cyclin F)). Expression of mutant CCNF in neuronal cells caused abnormal ubiquitination and accumulation of ubiquitinated proteins, including TDP-43 and a SCF(Cyclin F) substrate. This implicates common mechanisms, linked to protein homeostasis, underlying neuronal degeneration.

Cortical Function in Asymptomatic Carriers and Patients With C9orf72 Amyotrophic Lateral Sclerosis

IMPORTANCE

The identification of the chromosome 9 open reading frame 72 (c9orf72) gene hexanucleotide repeat expansion represents a major advance in the understanding of amyotrophic lateral sclerosis (ALS) pathogenesis. The pathophysiological mechanism by which the c9orf72 gene expansion leads to neurodegeneration is not yet elucidated. Cortical hyperexcitability is potentially an important pathophysiological process in sporadic ALS and familial ALS (FALS).

OBJECTIVE

To investigate whether cortical hyperexcitability forms the pathophysiological basis of c9orf72 FALS using the threshold-tracking transcranial magnetic stimulation technique.

DESIGN, SETTING, AND PARTICIPANTS

Prospective case-control single-center study that took place at hospitals and outpatient clinics from January 1, 2013, to January 1, 2015. Clinical and functional assessments along with transcranial magnetic stimulation studies were taken on 15 patients with c9orf72 FALS and 11 asymptomatic expansion carriers of c9orf72 who were longitudinally followed up for 3 years. Results were compared with 73 patients with sporadic ALS and 74 healthy control participants.

MAIN OUTCOMES AND MEASURES

Cortical excitability variables, including short-interval intracortical inhibition, were measured in patients with c9orf72 FALS and results were compared with asymptomatic c9orf72 carriers, patients with sporadic ALS, and healthy control participants.

RESULTS

Mean (SD) short-interval intracortical inhibition was significantly reduced in patients with c9orf72 FALS (1.2% [1.8%]) and sporadic ALS (1.6% [1.2%]) compared with asymptomatic c9orf72 expansion carriers (10.2% [1.8%]; F = 16.1; P < .001) and healthy control participants (11.8% [1.0%]; F = 16.1; P < .001). The reduction of short-interval intracortical inhibition was accompanied by an increase in intracortical facilitation (P < .01) and motor-evoked potential amplitude (P < .05) as well as a reduction in the resting motor threshold (P < .05) and cortical silent period duration (P < .001).

CONCLUSIONS AND RELEVANCE

This study establishes cortical hyperexcitability as an intrinsic feature of symptomatic c9orf72 expansion-related ALS but not asymptomatic expansion carriers.

Genetic basis of hindlimb loss in a naturally occurring vertebrate model

Here we genetically characterise pelvic finless, a naturally occurring model of hindlimb loss in zebrafish that lacks pelvic fin structures, which are homologous to tetrapod hindlimbs, but displays no other abnormalities. Using a hybrid positional cloning and next generation sequencing approach, we identified mutations in the nuclear localisation signal (NLS) of T-box transcription factor 4 (Tbx4) that impair nuclear localisation of the protein, resulting in altered gene expression patterns during pelvic fin development and the failure of pelvic fin development. Using a TALEN-induced tbx4 knockout allele we confirm that mutations within the Tbx4 NLS (A78V; G79A) are sufficient to disrupt pelvic fin development. By combining histological, genetic, and cellular approaches we show that the hindlimb initiation gene tbx4 has an evolutionarily conserved, essential role in pelvic fin development. In addition, our novel viable model of hindlimb deficiency is likely to facilitate the elucidation of the detailed molecular mechanisms through which Tbx4 functions during pelvic fin and hindlimb development.

Summary: Here we genetically characterise mutations in tbx4 which underlie pelvic finless, a naturally occurring model of hindlimb loss in zebrafish that lacks pelvic fin structures.

Mutation analysis of genes within the dynactin complex in a cohort of hereditary peripheral neuropathies

The cytoplasmic dynein-dynactin genes are attractive candidates for neurodegenerative disorders given their functional role in retrograde transport along neurons. The cytoplasmic dynein heavy chain (DYNC1H1) gene has been implicated in various neurodegenerative disorders, and dynactin 1 (DCTN1) genes have been implicated in a wide spectrum of disorders including motor neuron disease, Parkinson's disease, spinobulbar muscular atrophy and hereditary spastic paraplegia. However, the involvement of other dynactin genes with inherited peripheral neuropathies (IPN) namely, hereditary sensory neuropathy, hereditary motor neuropathy and Charcot-Marie-Tooth disease is under reported. We screened eight genes; DCTN1-6 and ACTR1A and ACTR1B in 136 IPN patients using whole-exome sequencing and high-resolution melt (HRM) analysis. Eight non-synonymous variants (including one novel variant) and three synonymous variants were identified. Four variants have been reported previously in other studies, however segregation analysis within family members excluded them from causing IPN in these families. No variants of disease significance were identified in this study suggesting the dynactin genes are unlikely to be a common cause of IPNs. However, with the ease of querying gene variants from exome data, these genes remain worthwhile candidates to assess unsolved IPN families for variants that may affect the function of the proteins.

MORC2 mutations cause axonal Charcot-Marie-Tooth disease with pyramidal signs

OBJECTIVE

To use linkage analysis and whole exome sequencing to identify the genetic mutation in a multigenerational Australian family with Charcot-Marie-Tooth disease type 2 (CMT2) and pyramidal signs.

METHODS

Genome-wide linkage analysis was performed to map the locus. Whole exome sequencing was undertaken on selected individuals (3 affected, 1 normal), and segregation analysis and mutation screening were carried out using high-resolution melt analysis. The GEM.app database was queried to identify additional families with mutations.

RESULTS

Significant linkage (2-point LOD score ≥ +3) and haplotype analysis mapped a new locus for CMT2 and pyramidal signs to a 6.6Mb interval on chromosome 22q12.1-q12.3. Whole exome sequencing identified a novel mutation (p.R252W) in the microrchidia CW-type zinc finger 2 (MORC2) gene mapping within the linkage region. The mutation fully segregated with the disease phenotype in the family. Screening additional families and querying unsolved CMT2 exomes, we identified the p.R252W mutation in 2 unrelated early onset CMT2 families and a second mutation p.E236G in 2 unrelated CMT2 families. Both the mutations occurred at highly conserved amino acid residues and were absent in the normal population.

INTERPRETATION

We have identified a new locus in which MORC2 mutations are the likely pathogenic cause of CMT2 and pyramidal signs in these families. MORC2 encodes the human CW-type zinc finger 2 protein, which is a chromatin modifier involved in the regulation of DNA repair as well as gene transcription.

Transanal rectal resection: an initial experience of 20 cases

AIM

Low anterior resection (LAR) can present a formidable surgical challenge, particularly for tumours located in the distal third of the rectum. Transanal total mesorectal excision (taTME) aims to overcome some of these difficulties. We report our initial experience with this technique.

METHOD

From June 2013 to September 2014, 20 selected patients underwent transanal rectal resection for various malignant and benign low rectal pathologies. All patients with rectal cancer were discussed at a multidisciplinary team meeting. Data were entered into a prospective managed international database.

RESULTS

Of the 20 patients (14 male), seventeen (85%) had rectal cancer lying at a median distance of 2 cm (range 0-7) from the anorectal junction. The operations performed included LAR (16). Abdominoperineal excision (2) and completion proctectomy (2), all of which were performed by a minimally invasive approach with three conversions. The mean operation time was 315.3 min. There were six postoperative complications of which two (10%) were Clavien-Dindo Grade IIIb (pelvic haematoma and a late contained anastomotic leakage). The median length of stay was 7 days. The TME specimen was intact in 94.1% of cancer cases. The mean number of harvested lymph nodes was 23.2. There was only one positive circumferential resection margin (tumour deposit; R1 rate 5.9%). One patient developed a distant recurrence (median follow-up 10 months, range 6-21).

CONCLUSION

TaTME was safe in this small series of patients. It is especially attractive in patients with a narrow and irradiated pelvis and a tumour in the lower third of the rectum. TaTME is technically demanding, but the good outcomes should prompt randomized studies and prospective registration of all taTME cases in an international registry.

Laparoscopic rectopexy is feasible and safe in the emergency admission setting

AIM

External rectal prolapse may require emergency admission in the elderly and comorbid population. We report the safety and efficacy of laparoscopic ventral rectopexy in patients having an emergency admission with external rectal prolapse.

METHOD

A retrospective analysis was performed of a prospective database of all rectopexies performed from 2006. Outcome and follow-up data were assessed.

RESULTS

Of 812 rectopexies performed, 28 were included for analysis. The mean length of hospital stay was 13.0 days. All operations were completed successfully and without intra-operative complications. Four patients developed a postoperative complication. Two patients developed a recurrence of prolapse.

CONCLUSION

Laparoscopic correction of rectal prolapse following emergency admission is both feasible and safe. It can be considered for both recurring cases and cases with multiple comorbidities.

Novel TBK1 truncating mutation in a familial amyotrophic lateral sclerosis patient of Chinese origin

Missense and frameshift mutations in TRAF family member-associated NF-kappa-B activator (TANK)-binding kinase 1 (TBK1) have been reported in European sporadic and familial amyotrophic lateral sclerosis (ALS) cohorts. To assess the role of TBK1 in ALS patient cohorts of wider ancestry, we have analyzed whole-exome sequence data from an Australian cohort of familial ALS (FALS) patients and controls. We identified a novel TBK1 deletion (c.1197delC) in a FALS patient of Chinese origin. This frameshift mutation (p.L399fs) likely results in a truncated protein that lacks functional domains required for adapter protein binding, as well as protein activation and structural integrity. No novel or reported TBK1 mutations were identified in FALS patients of European ancestry. This is the first report of a TBK1 mutation in an ALS patient of Asian origin and indicates that sequence variations in TBK1 are a rare cause of FALS in Australia.