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Motor Neurone Disease (MND) is a term used to cover a number of illnesses of the motor neurone. Amyotrophic Lateral Sclerosis (ALS), Progressive Muscular Atrophy (PMA), Progressive Bulbar Palsy (PBP) and Progressive Lateral Sclerosis (PLS) are all types of MND. MND is the term used internationally while ALS is often used in the United States (where it is also known as Lou Gehrig's disease) to cover all forms of MND. It was first described by Jean-Martin Charcot, a French neurologist, in 1869 and in France the disease is also known as Maladie de Charcot.
Overview
The disorder is characterized by the progressive loss of voluntary muscle contraction due to the destruction of nerve cells in the brain and the spinal cord that are responsible for the stimulation of the voluntary muscles.
The muscles are simply stimulated by a group of neurons located on the frontal portion of the spinal cord projecting to the muscle cells (lower motor neurons) and these nerve cells are stimulated by a group of nerve cells that project from a specific region called the motor area, located on the frontal lobe (upper motor neurons). The latter projection is called the corticospinal tract. The nerve cells of both pathways shrink and die for some unknown reason giving rise to muscle weakness, muscle cramps, speech impairment, difficulty swallowing and breathing. The international support organization uses the abbreviation ALS/MND to refer to the disease.
History
Lou Gehrig brought national and international attention to the disease in 1939 when he abruptly retired from baseball after being diagnosed with ALS/MND. Theoretical physicist Stephen Hawking, ex-Glasgow Celtic football player Jimmy Johnstone and former guitar virtuoso Jason Becker also suffer from the disease. American soap opera veteran Michael Zaslow, Hollywood actor David Niven, jazz giant Charles Mingus, and Hall of Fame pitcher Jim "Catfish" Hunter died from the disease.
Incidence
ALS/MND is indeed the most frequently observed member of a family of disorders called motor neuron diseases. This family of disorders has three major subgroups called primary lateral sclerosis (only the first motor neurons are affected), spinal muscular atrophy (only the second motor neurons are affected) and ALS (both are affected).
The incidence of ALS/MND is approximately 1-5 out of 100,000 people, and men have a 20% higher rate of incidence then women. Approximately 5600 cases are diagnosed in U. S. every year.
The onset of symptoms is usually between 40-70 years of age (avg. 55).
Causes
Some cases with familial forms of the disease were shown to have a mutation on their superoxide dismutase (SOD) 1 genes, which produces an enzyme that reduces the oxidative stress of the nerve cells. So far over 100 different mutations in the SOD1 gene have been found, all of which cause some form of ALS (ALS Online Database (http://www.alsod.org)).
Similar findings led the researchers to assume that the nerve cell death was caused by an excess of free radicals in the cell. This hypothesis is one of many others developed to describe the etiology of ALS/MND and is waiting to be reliably proven. Meanwhile, some experimental drugs are used to reduce the oxidative stress of the cells with very limited success.
At least 4 genes are known to be linked to ALS, these are, SOD1, ALS2, NEFH and VAPB. Only ~10% of cases are identified as genetic/hereditary, the causes for the remaining 90% are unknown.
Diagnosis
The diagnosis is established on both clinical grounds and an electromyography (EMG) examination, which is obligatory to demonstrate the diffuse loss of nervous stimulation of muscles of extremities, face and abdomen.
Clinically, upper motor neuron signs such as spasticity and babinski signs can be found, while the lower motor neurons demonstrate weakness and muscle atrophy. Weakness of bulbar musculature can also be seen (difficulty breathing, swallowing, coughing or speaking).
Neuroimaging examinations can be performed for some occasional cases especially for a mass lesion of upper parts of spinal cord to exclude some disorders that may mimic the symptoms of ALS/MND. The disease has always a grave prognosis and 50% of patients die within the first 3 years, 20% will live 5 years or more, only 10% survive for 10 years or more. Usually due to the later onset of the disease in life, some patients died from complications due to natural aging. There are documented cases of people living 35 years or more after diagnosis; Hawking has lived for more than 40 years since his diagnosis. There is no cure and the treatment is usually supportive and symptomatic.
Pathology
There is a degeneration of the ventral horns of the spinal cord, as well as atrophy of the ventral roots (shrunken in appearance). A degeneration of the motor neurons in the brainstem is seen. Neuronal loss and astrogliosis develops as well. Degeneration of the corticospinal tracts, as well as of the neurons in the motor strip of the cerebral cortex is known.
A mutation can be seen on chromosome 21. There is some evidence of mitochondrial abnormalities in animal models (SOD-1 mutants). There is a role in excitotoxicity and oxidative stress, presumably secondary to mitochondrial dysfunction. In animal models, death by apoptosis has also been identified (tranlocation of Bax to mitochondria, and translocation of cytochrome c to cytosol).
Treatment
Some current promising research towards a cure has focused on gene therapy and the use of stem cells, though the ethical and legal difficulties surrounding the harvesting of stem cells have slowed progress, particularly in the United States.
Riluzole, an inhibitor of glutamate, may delay the progression of ALS in selected patients.
Etymology
Amyotrophic comes from the Greek language. A- means "no", myo refers to muscle, and trophic means nourishment; amyotrophic therefore means "no muscle nourishment," which describes the characteristic atrophication of the sufferer's disused muscle tissue. Lateral identifies the areas in a person's spinal cord where portions of the nerve cells that are affected are located. As this area degenerates it leads to scarring or hardening ("sclerosis") in the region.
External links
Some information gathered from Dr. M Norenberg, Oct 26th, 2004: University of Miami.
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