**Acknowledgements**

This study indicates that SOD1 mutation carriers have normal survival of motor neurones, with as carriers had a full complement of motor neurones during the asymptomatic phase. Significant pre-symptomatic loss of motor neurones did not occur in asymptomatic SOD1 mutation carriers. Sudden and widespread motor neurone death occurs at the time develop‐ ment of the symptomatic symptoms, rather than life-long motor neurone loss. Sudden, catastrophic and multifocal loss of motor neurons occurs immediately prior to the onset of symptoms and the development of MND. This suggests that there may be a biological trigger initiating rapid cell loss, just prior to the onset of symptoms, rather than life-long motor neurone loss. Also, if the trigger initiating motor neurone loss can be identified, it may be possible to prevent motor neurone loss in familial ALS and develop treatments for sporadic MND. The mutant SOD1 protein itself cannot be the trigger, as it is constantly expressed. There may however be a gradual accumulation of a toxic product, possibly SOD1, which has changed into a new toxic conformation or aggregate, resulting in neuronal damage. The possibility of an individual neuron undergoing apoptosis increases as damage accumulates. This cumula‐ tive damage may be due to oxidative stress, resulting in disruption of the cellular structure

Neurofilament heavy polypeptide (NF-H) is an abundant stable cytoplasmic protein located in neuronal cells in large axons and may be used as a cell type marker. Abnormal accumulation of NF-H in motor neurones is associated with ALS, but it is unclear to what extent these contribute to human disease. Analysis of blood serum markers looking for increased levels of NF-H was not performed in this study, but would be interesting to be done in the future to the

The results of this study indicate that the risk of cell death probably remains constant through‐ out life of the neurone and that cell death occurs randomly in time and is independent of that of any other neurone. This suggests a "one-hit" biochemical phenomenon in which the mutation imposes an abnormal mutant steady state on the neurone and a single catastrophic event randomly initiates cell death and apoptosis. Early in the course of MND, the rate of cell death is low as the amount of neuronal damage caused by the mutation is small. The delay in clinical onset was thought to reflect the gradual accumulation of damage within the neurones, as a result of the mutation, which ultimately overwhelms cellular homeostasis leading to cell death. The living mutant neurons function very well for years or decades but the probability that an individual neurone undergoes apoptosis increases as damage accumulates within it. A mutant neurone in an older patient will have accumulated a greater amount of damage and will therefore be more likely to die than in a younger patient. Consequently, early in the course of disease, the chance of a cell containing a sufficient amount of damage to initiate apoptosis is small, and the rate of cell loss is correspondingly low. The mutant neurones appear to function normally for decades, with weakness only occurring once apoptosis and cell death occurs due to a gradual accumulation of damage within the cell. Therapies aimed at preserving motor neurones may be more feasible than trying to replace lost motor neurones. A number of treatment or preventative strategies arise, such as measures to diminish SOD1 aggregation or interactions to specifically reduced apoptosis in motor neurones. As motor neurone loss at

and function.

compare levels of NF-H in the carriers.

218 Current Advances in Amyotrophic Lateral Sclerosis

Prof. Garth Nicholson who introduced me to research into motor neurone disease and his continuing support. Prof. David Burke and Assoc. Prof. Alastair Corbett for their professional guidance and Prof. Jasper Daube for his technical assistance regarding the technique used in this research. The research was supported by the Motor Neurone Disease Association of NSW (Northern Region), ANZAC Health and Medical Research Foundation, Motor Neurone Disease Research Institute of Australia Inc. and the Nerve Research Foundation.

[10] Bensimon, G, Lacomblez, L, & Meiniger, V. (1994). A controlled trial of Riluzole in amyotrophic lateral sclerosis. ALS/Riluzole study group. *N Engl J Med*. , 330(9),

The Role of the Statistical Method of Motor Unit Number Estimation (MUNE) to…

http://dx.doi.org/10.5772/56559

221

[11] Blok, J. H, Van Dijk, J. P, Drenthen, J, Maathuis, E. M, & Stegeman, D. F. Size does matter: the influence of motor unit potential size on statistical motor unit number es‐

[12] Brown, W. F. (1972). A method for estimating the number of motor units in thenar muscles and the changes in motor unit counting with aging*. J Neurol Neurosurg Psy‐*

[13] Bruijn, L. I, Becher, M. W, Lee, M. K, Anderson, K. L, Jenkins, N. A, Copeland, N. G, Sisodia, S. S, Rothstein, J. D, Borchelt, D. R, Price, D. L, & Cleveland, D. W. (1997). ALS-linked SOD1 mutant G85R mediates damage to astrocytes and promotes rapidly

[14] Campbell, M. J, Mccomas, A. J, & Petito, F. (1973). Physiological changes in ageing

[15] Chance, P. F, Rabin, B. A, Ryan, S. G, Ding, Y, Scavina, M, Crain, B, Griffith, J. W, & Cornblath, D. R. (1998). Linkage of the gene for an autosomal dominant form of juve‐ nile amyotrophic lateral sclerosis to chromosome 9q34. *Am J Hum Genet.* , 62, 633-640.

[16] Cheah, B. C, Vucic, S, Krishnan, A. V, & Kiernan, M. C. (2010). Riluzole, neuroprotec‐

[17] Clarke, G, Collins, R. A, Leavitt, B. R, Andrews, D. F, Hayden, M. R, Lumsden, C. J, & Mcinnes, R. R. ((2000). A one hit model of cell death in inherited neuronal degener‐

[18] Clarke, G, Lumsden, C. J, & Mcinnes, R. R. (2001). Inherited neurodegenerative dis‐ ease: the one hit model of neurodegeneration. *Human Molecular Genetics.* , 10,

[19] Cleveland, D. W. (1999). From Charcot to SOD1: Mechanisms of selective motor neu‐

[20] Cudkowicz, M. E, Mckenna-yasek, D, Sapp, P. E, Chin, W, Geller, B, Hayden, D. L, Schoenfeld, D. A, Hosler, B. A, Horvitz, H. R, & Brown, R. H. Jr. ((1997). Epidemiolo‐ gy of mutations in superoxide dismutase in amyotrophic lateral sclerosis. *Ann Neu‐*

[21] Daube, J. R. (1995). Estimating the number of motor units in a muscle. *J Clin Neuro‐*

[22] De Belleroche, J, Orrell, R, & King, A. J. (1995). Medical Genetics. Familial amyotro‐ phic lateral sclerosis/motor neurone disease (FALS): a review of current develop‐

tion and amyotrophic lateral sclerosis. *Curr Med Chem* , 17(18), 1942-49.

progressive disease with SOD1-containing inclusions. *Neuron*. , 18, 327-338.

muscles. *J Neurol Neurosurg Psychiatry*. , 36, 174-182.

timates in healthy subjects. *Clin Neurophysiol.* (2010). Oct; , 121(10), 1772-80.

585-591.

*chiatry*., 35, 845-852.

ations. *Nature.* , 406, 195-199.

ron death in ALS. *Neuron.* , 24, 515-520.

2269-2275.

*rol.* , 41, 210-221.

*physiol*. , 12(6), 585-594.

ments. *J Med Genet.* , 32, 841-847.
