Emily F. Goodall

A distinct clinical, neuropsychological and radiological phenotype is associated with progranulin gene mutations in a large UK series

Mutations in the progranulin gene (GRN) are a major cause of frontotemporal lobar degeneration with ubiquitin-positive, tau-negative inclusions (FTLD-U) but the distinguishing clinical and anatomical features of this subgroup remain unclear. In a large UK cohort we found five different frameshift and premature termination mutations likely to be causative of FTLD in 25 affected family members. A previously described 4-bp insertion mutation in GRN exon 2 comprised the majority of cases in our cohort (20/25), with four novel mutations being identified in the other five affected members. Additional novel missense changes were discovered, of uncertain pathogenicity, but deletion of the entire gene was not detected. The patient collection was investigated by a single tertiary referral centre and is enriched for familial early onset FTLD with a high proportion of patients undergoing neuropsychological testing, MRI and eventual neuropathological diagnosis. Age at onset was variable, but four mutation carriers presented in their 40s and when analysed as a group, the mean age at onset of disease in GRN mutation carriers was later than tau gene (MAPT) mutation carriers and duration of disease was shorter when compared with both MAPT and FTLD-U without mutation. The most common clinical presentation seen in GRN mutation carriers was behavioural variant FTLD with apathy as the dominant feature. However, many patients had language output impairment that was either a progressive non-fluent aphasia or decreased speech output consistent with a dynamic aphasia. Neurological and neuropsychological examination also suggests that parietal lobe dysfunction is a characteristic feature of GRN mutation and differentiates this group from other patients with FTLD. MR imaging showed evidence of strikingly asymmetrical atrophy with the frontal, temporal and parietal lobes all affected. Both right- and left-sided predominant atrophy was seen even within the same family. As a group, the GRN carriers showed more asymmetry than in other FTLD groups. All pathologically investigated cases showed extensive type 3 TDP-43-positive pathology, including frequent neuronal cytoplasmic inclusions, dystrophic neurites in both grey and white matter and also neuronal intranuclear inclusions. Finally, we confirmed a modifying effect of APOE-E4 genotype on clinical phenotype with a later onset in the GRN carriers suggesting that this gene has distinct phenotypic effects in different neurodegenerative diseases.

Mutations in CHMP2B in Lower Motor Neuron Predominant Amyotrophic Lateral Sclerosis (ALS)

Background Amyotrophic lateral sclerosis (ALS), a common late-onset neurodegenerative disease, is associated with fronto-temporal dementia (FTD) in 3–10% of patients. A mutation in CHMP2B was recently identified in a Danish pedigree with autosomal dominant FTD. Subsequently, two unrelated patients with familial ALS, one of whom also showed features of FTD, were shown to carry missense mutations in CHMP2B. The initial aim of this study was to determine whether mutations in CHMP2B contribute more broadly to ALS pathogenesis. Methodology/Principal Findings Sequencing of CHMP2B in 433 ALS cases from the North of England identified 4 cases carrying 3 missense mutations, including one novel mutation, p.Thr104Asn, none of which were present in 500 neurologically normal controls. Analysis of clinical and neuropathological data of these 4 cases showed a phenotype consistent with the lower motor neuron predominant (progressive muscular atrophy (PMA)) variant of ALS. Only one had a recognised family history of ALS and none had clinically apparent dementia. Microarray analysis of motor neurons from CHMP2B cases, compared to controls, showed a distinct gene expression signature with significant differential expression predicting disassembly of cell structure; increased calcium concentration in the ER lumen; decrease in the availability of ATP; down-regulation of the classical and p38 MAPK signalling pathways, reduction in autophagy initiation and a global repression of translation. Transfection of mutant CHMP2B into HEK-293 and COS-7 cells resulted in the formation of large cytoplasmic vacuoles, aberrant lysosomal localisation demonstrated by CD63 staining and impairment of autophagy indicated by increased levels of LC3-II protein. These changes were absent in control cells transfected with wild-type CHMP2B. Conclusions/Significance We conclude that in a population drawn from North of England pathogenic CHMP2B mutations are found in approximately 1% of cases of ALS and 10% of those with lower motor neuron predominant ALS. We provide a body of evidence indicating the likely pathogenicity of the reported gene alterations. However, absolute confirmation of pathogenicity requires further evidence, including documentation of familial transmission in ALS pedigrees which might be most fruitfully explored in cases with a LMN predominant phenotype.

Association of the H63D polymorphism in the hemochromatosis gene with sporadic ALS

Iron misregulation promotes oxidative stress and abnormally high iron levels have been found in the spinal cords of patients with ALS. The authors investigated whether HFE gene polymorphisms, linked to hemochromatosis, are associated with ALS using two independent populations of patients with sporadic ALS and controls (totaling 379 patients and 400 controls). They found that the H63D polymorphism is overrepresented in individuals with sporadic ALS (odds ratio 1.85, CI: 1.35 to 2.54).

Amyotrophic lateral sclerosis (motor neuron disease): proposed mechanisms and pathways to treatment

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterised by loss of motor neurons. The cause of disease is unknown other than in the rare cases of familial disease arising from mutations in the superoxide dismutase 1 gene. Many theories for pathogenesis have been proposed - including oxidative stress, excitotoxicity, mitochondrial dysfunction and abnormal protein aggregation - based on studies of human post mortem tissue, research on animal models, and in vitro work. Here we review the evidence for the main pathogenic mechanisms and outline how they might interact to cause motor neuron death. Clinical trials have as yet failed to identify any truly effective therapies in ALS, with only riluzole providing a modest improvement in survival. Ongoing trials are exploring the value of antiglutamatergic agents, including the cephalosporin antibiotic ceftriaxone, as well as antioxidants, mitochondrial enhancers and anti-apoptotic drugs. It is likely that effective therapy will involve combinations of agents acting on different mechanisms. Gene therapy with neurotrophic factors will soon be in clinical trials, while work on stem cell therapy remains preclinical. In addition to finding effective therapies, research also needs to identify early disease markers because therapy is likely to be of most benefit when given early in the course of disease.

Neuronal dark matter: the emerging role of microRNAs in neurodegeneration

MicroRNAs (miRNAs) are small, abundant RNA molecules that constitute part of the cells non-coding RNA “dark matter.” In recent years, the discovery of miRNAs has revolutionised the traditional view of gene expression and our understanding of miRNA biogenesis and function has expanded. Altered expression of miRNAs is increasingly recognized as a feature of many disease states, including neurodegeneration. Here, we review the emerging role for miRNA dysfunction in Alzheimers disease, Parkinsons disease, amyotrophic lateral sclerosis (ALS) and Huntingtons disease pathogenesis. We emphasize the complex nature of gene regulatory networks and the need for systematic studies, with larger sample cohorts than have so far been reported, to reveal the most important miRNA regulators in disease. Finally, miRNA diversity and their potential to target multiple pathways, offers novel clinical applications for miRNAs as biomarkers and therapeutic agents in neurodegenerative diseases.

Broad clinical phenotypes associated with TAR-DNA binding protein ( TARDBP ) mutations in amyotrophic lateral sclerosis

The finding of TDP-43 as a major component of ubiquitinated protein inclusions in amyotrophic lateral sclerosis (ALS) has led to the identification of 30 mutations in the transactive response-DNA binding protein (TARDBP) gene, encoding TDP-43. All but one are in exon 6, which encodes the glycine-rich domain. The aim of this study was to determine the frequency of TARDBP mutations in a large cohort of motor neurone disease patients from Northern England (42 non-superoxide dismutase 1 (SOD1) familial ALS (FALS), nine ALS-frontotemporal dementia, 474 sporadic ALS (SALS), 45 progressive muscular atrophy cases). We identified four mutations, two of which were novel, in two familial (FALS) and two sporadic (SALS) cases, giving a frequency of TARDBP mutations in non-SOD1 FALS of 5% and SALS of 0.4%. Analysis of clinical data identified that patients had typical ALS, with limb or bulbar onset, and showed considerable variation in age of onset and rapidity of disease course. However, all cases had an absence of clinically overt cognitive dysfunction.

Increased serum ferritin levels in amyotrophic lateral sclerosis (ALS) patients

Iron misregulation promotes oxidative stress, a proposed pathological mechanism in neurodegenerative disease. The aim of this study was to evaluate serum iron metabolism indicators in 60 amyotrophic lateral sclerosis (ALS) patients and 44 age matched controls. Serum ferritin levels were significantly increased in ALS patients compared to controls (p < 0.001), while no differences in the levels of serum iron, transferrin, iron saturation or total iron binding capacity were found. Likewise no differences in C reactive protein (CRP) or caeruloplasmin were detected, suggesting that the elevated ferritin levels in ALS did not merely indicate an acute phase response. The increased ferritin level may reflect a general increase in stored iron or be a consequence of ongoing muscle degeneration.

Concurrence of multiple sclerosis and amyotrophic lateral sclerosis in patients with hexanucleotide repeat expansions of C9ORF72

Background Crossover in the pathogenic mechanisms of amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS) has been described but is poorly understood. A GGGGCC hexanucleotide repeat expansion of C9ORF72 has recently been identified in a significant proportion of patients with ALS. Methods In approximately 650 patients diagnosed with ALS from the North of England we identified seven patients who initially presented with MS. DNA obtained from five patients with MS-ALS and 215 patients with MS alone was screened for the C9ORF72 expansion. Post-mortem material was examined from two patients with MS-ALS. Gene expression profiling was performed on lymphoblastoid cells and levels of CXCL10 were measured in cerebrospinal fluid (CSF) from patients with ALS with and without the C9ORF72 expansion and controls. Results Concurrence of MS and ALS is higher than expected in our population. The C9ORF72 expansion was identified in 80% of patients with MS-ALS but not in those with MS alone. In the presence of preceding MS, C9ORF72-ALS was more rapidly progressive. MetaCore analysis identified alteration of the NF-кB pathway in C9ORF72-ALS and non-C9ORF72-ALS. NF-кB activation is associated with increased expression of the neuroprotective cytokine CXCL10 but, in C9ORF72-ALS, CXCL10 is downregulated and CSF levels are reduced. Conclusions We propose that MS-associated neuroinflammation may affect penetrance and progression of the C9ORF72 expansion. In particular, the NF-кB pathway is activated in MS and appears to be dysfunctional in C9ORF72-ALS. Aberrant downregulation of CXCL10 may explain the predisposition of C9ORF72 expansion carriers to develop ALS in the context of MS and NF-кB activation, and offers a potential therapeutic target.

Gene expression signatures in motor neurone disease fibroblasts reveal dysregulation of metabolism, hypoxia-response and RNA processing functions

Amyotrophic lateral sclerosis (ALS) and primary lateral sclerosis (PLS) are two syndromic variants within the motor neurone disease spectrum. As PLS and most ALS cases are sporadic (SALS), this limits the availability of cellular models for investigating pathogenic mechanisms and therapeutic targets. The aim of this study was to use gene expression profiling to evaluate fibroblasts as cellular models for SALS and PLS, to establish whether dysregulated biological processes recapitulate those seen in the central nervous system and to elucidate pathways that distinguish the clinically defined variants of SALS and PLS.

Oligogenic inheritance of optineurin (OPTN) and C9ORF72 mutations in ALS highlights localisation of OPTN in the TDP-43-negative inclusions of C9ORF72-ALS.

Amyotrophic lateral sclerosis (ALS) is characterized by motor neurone loss resulting in muscle weakness, spasticity and ultimately death. 5‐10% are caused by inherited mutations, most commonly C9ORF72, SOD1, TARDBP and FUS. Rarer genetic causes of ALS include mutation of optineurin (mt OPTN). Furthermore, optineurin protein has been localized to the ubiquitylated aggregates in several neurodegenerative diseases, including ALS. This study: (i) investigated the frequency of mt OPTN in ALS patients in England; (ii) characterized the clinical and neuropathological features of ALS associated with a mt OPTN; and (iii) investigated optineurin neuropathology in C9ORF72‐related ALS (C9ORF72‐ALS). We identified a heterozygous p.E322K missense mutation in exon 10 of OPTN in one familial ALS patient who additionally had a C9ORF72 mutation. This patient had bulbar, limb and respiratory disease without cognitive problems. Neuropathology revealed motor neurone loss, trans‐activation response DNA protein 43 (TDP‐43)‐positive neuronal and glial cytoplasmic inclusions together with TDP‐43‐negative neuronal cytoplasmic inclusions in extra motor regions that are characteristic of C9ORF72‐ALS. We have demonstrated that both TDP‐43‐positive and negative inclusion types had positive staining for optineurin by immunohistochemistry. We went on to show that optineurin was present in TDP‐43‐negative cytoplasmic extra motor inclusions in C9ORF72‐ALS cases that do not carry mt OPTN. We conclude that: (i) OPTN mutations are associated with ALS; (ii) optineurin protein is present in a subset of the extramotor inclusions of C9ORF72‐ALS; (iii) It is not uncommon for multiple ALS‐causing mutations to occur in the same patient; and (iv) studies of optineurin are likely to provide useful dataregarding the pathophysiology of ALS and neurodegeneration.