, 2008) (see below). Influencing mutant SOD1 synthesis in muscle cells did not affect motor neuron degeneration in the mutant SOD1 mouse (Miller et al., 2006; Towne et al., 2008). However, overexpression of insulin-like growth factor isoforms exclusively in muscle did slow down progression (Dobrowolny et al., 2005). Therefore, the exact role of muscle in ALS remains an interesting topic of research. The removal of mutant

SOD1, the primary see more cause of motor neuron toxicity, is an obvious therapeutic strategy. This has been achieved by the viral delivery of RNAi against SOD1 (Ralph et al., 2005; Raoul et al., 2005), by intracerebroventricular administration of antisense oligonucleotides (Smith et al., 2006) and by crossbreeding mutant

SOD1 mice with mice that express an shRNA against mutant SOD1 (Xia et al., 2006). Hence, gene silencing holds great promise as a therapy for ALS (and in fact for many neurodegenerative diseases; Maxwell, 2009). The first clinical studies investigating the feasibility of these approaches in humans are under way. As toxicity from aberrant secretion of mutant SOD1 is likely to play a role, targeting this pool of mutant SOD1 may be of interest. The burden of extracellular SOD1 could be reduced using an active or a passive immunization strategy, and this led to a slower disease progression ICG-001 in mutant SOD1 mice (Urushitani et al., 2007). The mutant SOD1 mouse (and rat) has been used extensively

to study compounds or approaches with possible therapeutic value (Turner & Talbot, 2008). The validity of this model has been questioned Methocarbamol because some of the compounds with a positive effect in the mouse were negative in human studies. There may be other explanations. The effects observed in the mouse were often small, and may be easily missed in a clinically and genetically heterogenous human ALS population. Furthermore, the differences in pharmacokinetics between mice and humans were often largely neglected. In addition, the ‘positive’ results obtained in mice often came from (inadequately powered) studies in which administration of the compound began before disease onset, while in humans therapeutic trials are done in patients who have had ALS for at least one, sometimes even several, years. The question is whether the mutant SOD1 mouse is a good model in which to study sporadic ALS. Obviously it is not ideal: sporadic ALS is definitely etiologically different from monogenic mutant SOD1-related familial ALS. Recent studies on transactivation response DNA-binding protein with molecular weight 43 kDa (TDP-43) suggest that there may also be a pathogenic difference, which will be discussed below. The role of TDP-43 was first suspected when it was identified as one of the major constituents of the intraneuronal inclusions characteristically observed in ALS and in frontotemporal lobar degeneration (FTLD)–ubiquitin (FTLD-U; Neumann et al., 2006).