Wim Robberecht

Purpose of reviewThis review examines the clinical implications of recent breakthroughs in amyotrophic lateral sclerosis (ALS).Recent findingsALS has been found to be a highly variable condition at the clinical, genetic and mechanistic level. The study of newly discovered genetic causes for ALS has demonstrated that in addition to the effect of toxic mutant proteins, abnormalities of RNA householding contribute to motor neuron degeneration. Furthermore, the classic distinction between gain of function and loss of function may be an oversimplification of the biological reality. The most important clinical breakthrough was the finding of intronic hexanucleotide repeat expansions in chromosome 9 open reading frame 72 (C9orf72) as a common cause of ALS, frontotemporal lobar degeneration (FTLD) and ALS with concomitant FTLD. This provides unambiguous evidence that ALS and FTLD represent the ends of one spectrum of neurodegenerative diseases. The high prevalence of C9orf72 mutations in patients without family history further blurs the distinction between sporadic and familial forms of ALS and FTLD. It also opens opportunities for stratified clinical trials in ALS and for the development of targeted therapies.SummaryALS is a heterogeneous disorder that overlaps with FTLD. C9orf72 mutations are the most common cause of ALS, and add to the evidence that disturbances in RNA householding contribute to ALS.

Although the zebrafish (Danio rerio) has been used extensively for many years in neurodevelopmental studies, use of this teleost to study neurological diseases has evolved only recently. Being a vertebrate, this animal offers advantages for the study of human disease over other small animals, such as the fly or worm. Genetic, as well as nongenetic, disorders can be modeled in both the adult organism and the embryo. Genetic manipulation of the embryo to generate stable and transiently expressing transgenic fish, and to knockdown genes to study loss of their function, can be easily achieved. Because of large offspring numbers screening studies can also be readily performed. Here, we describe some of the protocols useful for modeling neurodegenerative disease in zebrafish embryos, with particular emphasis on models to study motor neuron phenotypes.

Mislocalization, aberrant processing and aggregation of TAR DNA-binding protein 43 (TDP-43) is found in the neurons affected by two related diseases, amyotrophic lateral sclerosis (ALS) and frontotemporal lobe dementia (FTLD). These TDP-43 abnormalities are seen when TDP-43 is mutated, such as in familial ALS, but also in FTLD, caused by null mutations in the progranulin gene. They are also found in many patients with sporadic ALS and FTLD, conditions in which only wild type TDP-43 is present. The common pathological hallmarks and symptomatic cross over between the two diseases suggest that TDP-43 and progranulin may be mechanistically linked. In this study we aimed to address this link by establishing whether overexpression of mutant TDP-43 or knock-down of progranulin in zebrafish embryos results in motor neuron phenotypes and whether human progranulin is neuroprotective against such phenotypes. Mutant TDP-43 (A315T mutation) induced a motor axonopathy characterized by short axonal outgrowth and aberrant branching, similar, but more severe, than that induced by mutant SOD1. Knockdown of the two zebrafish progranulin genes, grna and grnb, produced a substantial decrease in axonal length, with knockdown of grna alone producing a greater decrease in axonal length than grnb. Progranulin overexpression rescued the axonopathy induced by progranulin knockdown. Interestingly, progranulin also rescued the mutant TDP-43 induced axonopathy, whilst it failed to affect the mutant SOD1-induced phenotype. TDP-43 was found to be nuclear in all conditions described. The findings described here demonstrate that progranulin is neuroprotective in vivo and may have therapeutic potential for at least some forms of motor neuron degeneration.

Background: The microtubule-associated protein tau is thought to play a pivotal role in neurodegeneration. Mutations in the tau coding gene MAPT are a cause of frontotemporal dementia, and the H1/H1 genotype of MAPT, giving rise to higher tau expression levels, is associated with progressive supranuclear palsy, corticobasal degeneration, and Parkinson disease (PD). Furthermore, tau hyperphosphorylation and aggregation is a hallmark of Alzheimer disease (AD), and reducing endogenous tau has been reported to ameliorate cognitive impairment in a mouse model for AD. Tau hyperphosphorylation and aggregation have also been described in amyotrophic lateral sclerosis (ALS), both in human patients and in the mutant SOD1 mouse model for this disease. However, the precise role of tau in motor neuron degeneration remains uncertain. Methods: The possible association between ALS and the MAPT H1/H2 polymorphism was studied in 3,540 patients with ALS and 8,753 controls. Furthermore, the role of tau in the SOD1^G93A mouse model for ALS was studied by deleting Mapt in this model. Results: The MAPT genotype of the H1/H2 polymorphism did not influence ALS susceptibility (odds ratio = 1.08 [95% confidence interval 0.99–1.18], p = 0.08) and did not affect the clinical phenotype. Lowering tau levels in the SOD1^G93A mouse failed to delay disease onset (p = 0.302) or to increase survival (p = 0.557). Conclusion: These findings suggest that the H1/H2 polymorphism in MAPT is not associated with human amyotrophic lateral sclerosis, and that lowering tau levels in the mutant SOD1 mouse does not affect the motor neuron degeneration in these animals.

Introduction: Intensive insulin therapy (IIT) reduced the incidence of critical illness polyneuropathy and/or myopathy (CIP/CIM) and the need for prolonged mechanical ventilation (MV ≥ 14 days) in two randomised controlled trials (RCTs) on the effect of IIT in a surgical intensive care unit (SICU) and medical intensive care unit (MICU). In the present study, we investigated whether these effects are also present in daily clinical practice when IIT is implemented outside of a study protocol. Methods: We retrospectively studied electrophysiological data from patients in the SICU and MICU, performed because of clinical weakness and/or weaning failure, before and after routine implementation of IIT. CIP/CIM was diagnosed by abundant spontaneous electrical activity on electromyography. Baseline and outcome variables were compared using Student's t-test, Chi-squared or Mann-Whitney U-test when appropriate. The effect of implementing IIT on CIP/CIM and prolonged MV was assessed using univariate analysis and multivariate logistic regression analysis (MVLR), correcting for baseline and ICU risk factors. Results: IIT significantly lowered mean (± standard deviation) blood glucose levels (from 144 ± 20 to 107 ± 10 mg/dl, p < 0.0001) and significantly reduced the diagnosis of CIP/CIM in the screened long-stay patients (125/168 (74.4%) to 220/452 (48.7%), p < 0.0001). MVLR identified implementing IIT as an independent protective factor (p < 0.0001, odds ratio (OR): 0.25 (95% confidence interval (CI): 0.14 to 0.43)). MVLR confirmed the independent protective effect of IIT on prolonged MV (p = 0.002, OR:0.40 (95% CI: 0.22–0.72)). This effect was statistically only partially explained by the reduction in CIP/CIM. Conclusions: Implementing IIT in routine daily practice in critically ill patients evoked a similar beneficial effect on neuromuscular function as that observed in two RCTs. IIT significantly improved glycaemic control and significantly and independently reduced the electrophysiological incidence of CIP/CIM. This reduction partially explained the beneficial effect of IIT on prolonged MV.

Amyotrophic lateral sclerosis is a neurodegenerative disorder that results in the selective death of motor neurons in the central nervous system. This progressive motor neuron degeneration leads to death of the patient on average three to five years after onset of the disease. To date, no therapy is available. Many hypotheses have been formulated to explain the selective degeneration of motor neurons. One of the most studied hypotheses is the putative role of the inflammatory response that accompanies motor neuron death. The proliferation of microglia and astrocytes has been considered to be a secondary phenomenon, but recently, evidence is accumulating in favour of a contributory role of the non-neuronal cell populations to the pathogenesis of the disease. In this review, we will introduce the characteristics of microglial cells in the central nervous system. We will summarize the evidence of the expansion and the activation of the microglial cell population that accompanies motor neuron degeneration. Finally, an overview will be given of the different therapeutic strategies that targeted the inflammatory process in amyotrophic lateral sclerosis.

The angiogenic activity of vascular endothelial growth factor (VEGF) is well known. Recently, it has become evident that VEGF is involved in central nervous system physiology and may play a role in the pathogenesis of neurological diseases. In particular, it may be involved in the mechanism of motor neuron degeneration in amyotrophic lateral sclerosis (ALS), and has been hypothesized to be implicated in the pathogenesis of peripheral neuropathies such as occur in the so‐called POEMS syndrome and diabetes. VEGF is also being studied as a possible treatment option in some of these disorders. In this review we critically analyze the data supporting the notion that VEGF is a factor involved in motor neuron degeneration and review the studies linking VEGF to other diseases of the peripheral and central nervous systems. Muscle Nerve, 2006