Christopher J McDermott

Hereditary spastic paraparesis: a review of new developments

Hereditary spastic paraparesis (HSP) or the Strumpell-Lorrain syndrome is the name given to a heterogeneous group of inherited disorders in which the main clinical feature is progressive lower limb spasticity. Before the advent of molecular genetic studies into these disorders, several classifications had been proposed, based on the mode of inheritance, the age of onset of symptoms, and the presence or otherwise of additional clinical features. Families with autosomal dominant, autosomal recessive, and X-linked inheritance have been described.

Clinico-pathological features in amyotrophic lateral sclerosis with expansions in C9ORF72

Intronic expansion of the GGGGCC hexanucleotide repeat within the C9ORF72 gene causes frontotemporal dementia and amyotrophic lateral sclerosis/motor neuron disease in both familial and sporadic cases. Initial reports indicate that this variant within the frontotemporal dementia/amyotrophic lateral sclerosis spectrum is associated with transactive response DNA binding protein (TDP-43) proteinopathy. The amyotrophic lateral sclerosis/motor neuron disease phenotype is not yet well characterized. We report the clinical and pathological phenotypes associated with pathogenic C9ORF72 mutations in a cohort of 563 cases from Northern England, including 63 with a family history of amyotrophic lateral sclerosis. One hundred and fifty-eight cases from the cohort (21 familial, 137 sporadic) were post-mortem brain and spinal cord donors. We screened DNA for the C9ORF72 mutation, reviewed clinical case histories and undertook pathological evaluation of brain and spinal cord. Control DNA samples (n = 361) from the same population were also screened. The C9ORF72 intronic expansion was present in 62 cases [11% of the cohort; 27/63 (43%) familial, 35/500 (7%) cases with sporadic amyotrophic lateral sclerosis/motor neuron disease]. Disease duration was significantly shorter in cases with C9ORF72-related amyotrophic lateral sclerosis (30.5 months) compared with non-C9ORF72 amyotrophic lateral sclerosis/motor neuron disease (36.3 months, P < 0.05). C9ORF72 cases included both limb and bulbar onset disease and all cases showed combined upper and lower motor neuron degeneration (amyotrophic lateral sclerosis). Thus, clinically, C9ORF72 cases show the features of a relatively rapidly progressive, but otherwise typical, variant of amyotrophic lateral sclerosis associated with both familial and sporadic presentations. Dementia was present in the patient or a close family member in 22/62 cases with C9ORF72 mutation (35%) based on diagnoses established from retrospective clinical case note review that may underestimate significant cognitive changes in late disease. All the C9ORF72 mutation cases showed classical amyotrophic lateral sclerosis pathology with TDP-43 inclusions in spinal motor neurons. Neuronal cytoplasmic inclusions and glial inclusions positive for p62 immunostaining in non-motor regions were strongly over-represented in the C9ORF72 cases. Extra-motor pathology in the frontal cortex (P < 0.0005) and the hippocampal CA4 subfield neurons (P < 0.0005) discriminated C9ORF72 cases strongly from the rest of the cohort. Inclusions in CA4 neurons were not present in non-C9ORF72 cases, indicating that this pathology predicts mutation status.

Mutation analysis of the spastin gene (SPG4) in patients with hereditary spastic paraparesis

BACKGROUND Hereditary spastic paraparesis is a genetically heterogeneous condition. Recently, mutations in the spastin gene were reported in families linked to the common SPG4 locus on chromosome 2p21-22. OBJECTIVES To study a population of patients with hereditary spastic paraparesis for mutations in the spastin gene (SPG4) on chromosome 2p21-22. METHODS DNA from 32 patients (12 from families known to be linked to SPG4) was analysed for mutations in the spastin gene by single strand conformational polymorphism analysis and sequencing. All patients were also examined clinically. RESULTS ThirteenSPG4 mutations were identified, 11 of which are novel. These mutations include missense, nonsense, frameshift, and splice site mutations, the majority of which affect the AAA cassette. We also describe a nucleotide substitution outside this conserved region which appears to behave as a recessive mutation. CONCLUSIONS Recurrent mutations in the spastin gene are uncommon. This reduces the ease of mutation detection as a part of the diagnostic work up of patients with hereditary spastic paraparesis. Our findings have important implications for the presumed function of spastin and schemes for mutation detection in HSP patients.

Hereditary spastic paraparesis: disrupted intracellular transport associated with spastin mutation.

The commonest cause of hereditary spastic paraplegia (HSP) is mutation in the spastin gene. Both the normal function of spastin in the central nervous system and the mechanism by which mutation in spastin causes axonal degeneration are unknown. One hypothesis is that mutant spastin disrupts microtubule dynamics, causing an impairment of organelle transport on the microtubule network, which leads to degeneration in the distal parts of long axons. To study this neuronal and non‐neuronal cells were transfected with either wild type or mutant spastin proteins. We demonstrated evidence of a transient interaction of wild‐type spastin with microtubules, with resulting disassembly of microtubules, supporting a role for wild‐type spastin as a microtubule‐severing protein. Mutant spastin demonstrated an abnormal interaction with microtubules, colocalizing with but no longer severing microtubules. The abnormal interaction of mutant spastin with microtubules was demonstrated to be associated with an abnormal perinuclear clustering of mitochondria and peroxisomes, suggestive of an impairment of kinesin‐mediated intracellular transport. Our findings indicate that an abnormal interaction of mutant spastin with microtubules, which disrupts organelle transport on the microtubule cytoskeleton, is likely to be the primary disease mechanism in HSP caused by missense mutations in the spastin gene.

Novel FUS/TLS Mutations and Pathology in Familial and Sporadic Amyotrophic Lateral Sclerosis

OBJECTIVE To determine the frequency of and clinicopathologic phenotypes associated with FUS/TLS mutations in a large cohort of amyotrophic lateral sclerosis (ALS) cases from the north of England. DESIGN Genetic screening project with neuropathologic examination of postmortem tissue in selected cases. The clinical details of selected cases are also presented. SETTING Neurology departments of 2 university teaching hospitals in the north of England. PARTICIPANTS The 15 exons of FUS/TLS were sequenced in an initial cohort of 42 familial ALS (FALS) and 117 sporadic ALS (SALS) cases. Exons 14 and 15 were subsequently screened in a larger cohort of 431 SALS cases. Regions mutated in ALS cases were also screened in 293 controls. MAIN OUTCOME MEASURE Evaluation of gene-sequencing chromatographs and detailed histopathologic analysis of the central nervous system. RESULTS Four heterozygous mutations, 1 of which is novel, were identified in 6 patients with ALS (4 with FALS and 2 with SALS). Two of the substitutions were not found to be present in controls, and neuropathology in these cases revealed neuronal and/or glial cytoplasmic inclusions positive for the FUS/TLS protein. One of these cases is also the first reported SALS case with an FUS/TLS mutation. The other 2 substitutions identified were also identified in control cases. Neuropathology in these cases revealed typical SALS pathology, suggesting that they are likely to represent benign polymorphisms. CONCLUSIONS FUS/TLS mutations represented approximately 5% of FALS cases screened. A FUS/TLS mutation was also identified in a single SALS case. Subsequent screening of this region in a larger cohort of SALS cases, however, did not reveal any additional mutations.

Diagnosis and management of motor neurone disease

Motor neurone disease is a devastating illness which leads to progressive paralysis and eventual death. We will discuss the presentation of motor neurone disease in primary care and update non-specialists on progress with regards to life prolonging interventions, better control of disease symptoms, and an increased understanding of disease mechanisms. Motor neurone disease is rare but patients often are aware of it, so this review should help non-specialists reassure patients in whom it is unlikely to be the diagnosis.

An evaluation of neurophysiological criteria used in the diagnosis of motor neuron disease

Background New criteria for the neurophysiological diagnosis of amyotrophic lateral sclerosis/motor neuron disease (ALS/MND) were recently proposed at an international symposium in Awaji-shima, Japan. They differ from the accepted revised El-Escorial criteria by considering fasciculation potentials to be evidence of acute denervation. In addition, when assessing diagnostic certainty, the Awaji-shima criteria equate electrodiagnostic evidence of lower motor neuron dysfunction with clinical examination findings. Methods A retrospective review of 205 consecutive sets of notes was performed, from patients who underwent neurophysiological assessment for suspected MND. The clinical signs and neurophysiological findings were combined according to the two sets of criteria (revised El-Escorial and Awaji-shima), and the diagnoses reached were compared with the interval diagnosis, to establish the sensitivities and specificities of each protocol. Results An interval diagnosis of MND was recorded in 107 patients. The sensitivity of the Awaji-shima criteria in reaching a diagnosis of MND was 60.7% and the revised El-Escorial 28%, with a specificity of 95.9% for both criteria. The Awaji-shima criteria increased the sensitivity of diagnosis without affecting the specificity. Conclusion Accepting EMG evidence of fasciculations as evidence of acute denervation increases the diagnostic certainty of MND, and the new criteria allow earlier diagnosis of MND without increasing the false-positive rate.

Clinical features of hereditary spastic paraplegia due to spastin mutation

Background: Mutations in the spastin gene are the commonest cause of hereditary spastic paraparesis (HSP), accounting for up to 40% of autosomal dominant cases. The phenotype associated with HSP due to mutation in the spastin gene (SPG4) tends to be pure HSP. Objective: To characterize in more detail the genetic and phenotypic characteristics of SPG4 by examining a large cohort of patients with HSP. Methods: The authors identified patients who tested positive for spastin mutation using a direct sequencing approach of all exons. Results: The authors identified spastin mutations in 53 patients. Twenty-seven of the mutations identified were novel. The phenotype in the majority of patients was of pure HSP. In one individual, a complicated phenotype with progressive bulbar dysfunction and respiratory insufficiency was observed. Evidence of lower motor neuron dysfunction in a subgroup of SPG4 patients was identified. The missense changes S44L and P45Q were identified in patients with other spastin mutations and seemed to be exerting a phenotype-modifying effect. Conclusion: These findings add to the number of spastin mutations identified and demonstrate the importance of screening the whole gene, given the possibility of double mutations and intragenic modifiers. The identification of the complicated phenotypes has important implications for identifying the phenotype of patients in whom spastin screening should be considered. The presence of lower motor neuron dysfunction in a subgroup of SPG4 patients suggests that the cellular dysfunction in SPG4 extends beyond the axonal projections of upper motor neurons and ascending sensory pathways.

Direct evidence for axonal transport defects in a novel mouse model of mutant spastin-induced hereditary spastic paraplegia (HSP) and human HSP patients

Mutations in spastin are the most common cause of hereditary spastic paraplegia (HSP) but the mechanisms by which mutant spastin induces disease are not clear. Spastin functions to regulate microtubule organisation, and because of the essential role of microtubules in axonal transport, this has led to the suggestion that defects in axonal transport may underlie at least part of the disease process in HSP. However, as yet there is no direct evidence to support this notion. Here we analysed axonal transport in a novel mouse model of spastin‐induced HSP that involves a pathogenic splice site mutation, which leads to a loss of spastin protein. A mutation located within the same splice site has been previously described in HSP. Spastin mice develop gait abnormalities that correlate with phenotypes seen in HSP patients and also axonal swellings containing cytoskeletal proteins, mitochondria and the amyloid precursor protein (APP). Pathological analyses of human HSP cases caused by spastin mutations revealed the presence of similar axonal swellings. To determine whether mutant spastin influenced axonal transport we quantified transport of two cargoes, mitochondria and APP‐containing membrane bound organelles, in neurons from mutant spastin and control mice, using time‐lapse microscopy. We found that mutant spastin perturbs anterograde transport of both cargoes. In neurons with axonal swellings we found that the mitochondrial axonal transport defects were exacerbated; distal to axonal swellings both anterograde and retrograde transport were severely reduced. These results strongly support a direct role for defective axonal transport in the pathogenesis of HSP because of spastin mutation.

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.