WHAT IS ALS

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Amyotrophic lateral sclerosis (ALS) – also referred to as motor neurone disease in some Commonwealth of Nations countries and as Lou Gehrig's disease in the United States – is a debilitating disease with varied etiology characterized by rapidly progressive weakness, muscle atrophy and fasciculations, muscle spasticity, difficulty speaking (dysarthria), difficulty swallowing (dysphagia), and difficulty breathing (dyspnea).

SIGNS AND SYMPTOMS
The disorder causes muscle weakness and atrophy throughout the body caused by the degeneration of the upper and lower motor neurons. Unable to function, the muscles weaken and atrophy. Individuals affected by the disorder may ultimately lose the ability to initiate and control all voluntary movement, although bladder and bowel sphincters and the muscles responsible for eye movement are usually, but not always, spared until the terminal stages of the disease.

Cognitive function is generally spared for most patients, although some (about 5%) also have frontotemporal dementia. A higher proportion of patients (30–50%) also have more subtle cognitive changes which may go unnoticed, but are revealed by detailed neuropsychological testing. Sensory nerves and the autonomic nervous system are generally unaffected, meaning the majority of people with ALS will maintain hearing, sight, touch, smell, and taste.

INITIAL SYMPTOMS
The earliest symptoms of ALS are typically obvious weakness and/or muscle atrophy. Other presenting symptoms include muscle twitching, cramping, or stiffness of affected muscles; muscle weakness affecting an arm or a leg; and/or slurred and nasal speech. The parts of the body affected by early symptoms of ALS depend on which motor neurons in the body are damaged first. 

About 75% of people contracting the disease experience "limb onset" ALS, i.e., first symptoms in the arms or legs. Patients with the leg onset form may experience awkwardness when walking or running or notice that they are tripping or stumbling, often with a "dropped foot" which drags gently along the ground. Arm-onset patients may experience difficulty with tasks requiring manual dexterity such as buttoning a shirt, writing, or turning a key in a lock. 

About 25% of cases are "bulbar onset" ALS. These patients first notice difficulty speaking clearly or swallowing. Speech may become slurred, nasal in character, or quieter. Other symptoms include difficulty swallowing and loss of tongue mobility. A smaller proportion of patients experience "respiratory onset" ALS, where the intercostal muscles that support breathing are affected first. A small proportion of patients may also present with what appears to be frontotemporal dementia, but later progresses to include more typical ALS symptoms.
Over time, patients experience increasing difficulty moving, swallowing (dysphagia), and speaking or forming words (dysarthria). 

Symptoms of upper motor neuron involvement include tight and stiff muscles (spasticity) and exaggerated reflexes (hyperreflexia) including an overactive gag reflex. An abnormal reflex commonly called Babinski's sign also indicates upper motor neuron damage. Symptoms of lower motor neuron degeneration include muscle weakness and atrophy, muscle cramps, and fleeting twitches of muscles that can be seen under the skin (fasciculations). Around 15–45% of patients experience pseudobulbar affect, also known as "emotional lability", which consists of uncontrollable laughter, crying or smiling, attributable to degeneration of bulbar upper motor neurons resulting in exaggeration of motor expressions of emotion. To be diagnosed with ALS, patients must have signs and symptoms of both upper and lower motor neuron damage that cannot be attributed to other causes.

DISEASE PROGRESSION AND SPREAD
Although the order and rate of symptoms varies from person to person, eventually most patients are not able to walk, get out of bed on their own, or use their hands and arms. The rate of progression can be measured using an outcome measure called the "ALS Functional Rating Scale (Revised)", a 12-item instrument administered as a clinical interview or patient-reported questionnaire that produces a score between 48 (normal function) and 0 (severe disability). Though there is a high degree of variability and a small percentage of patients have much slower disease, on average, patients lose about 1 FRS point per month. Regardless of the part of the body first affected by the disease, muscle weakness and atrophy spread to other parts of the body as the disease progresses. In limb-onset ALS, symptoms usually spread from the affected limb to the opposite limb before affecting a new body region, whereas in bulbar-onset ALS symptoms typically spread to the arms before the legs.

Disease progression tends to be slower in patients who are younger than 40 at onset, have disease restricted primarily to one limb, and those with primarily upper motor neuron symptoms. Conversely, progression is faster and prognosis poorer in patients with bulbar-onset disease, respiratory-onset disease, and frontotemporal dementia.

LATE STAGE DISEASE SYMPTOMS
Difficulty swallowing and chewing make eating normally very difficult and increase the risk of choking or aspirating food into the lungs. In later stages of the disease, aspiration pneumonia and maintaining a healthy weight can become a significant problem and may require insertion of a feeding tube. As the diaphragm and intercostal muscles (rib cage) that support breathing weaken, measures of lung function such as forced vital capacity and inspiratory pressure diminish. In respiratory onset ALS, this may occur before significant limb weakness is apparent. 

External machines such as bilevel positive pressure ventilation (frequently referred to by the tradename BiPAP) are frequently used to support breathing, first at night, and later during the daytime as well. BiPAP is only a temporary remedy, however, and it is recommended that long before BiPAP stops being effective, patients should decide whether to have a tracheotomy and long term mechanical ventilation. At this point, some patients choose palliative hospice care. Most people with ALS die of respiratory failure or pneumonia.

Although respiratory support can ease problems with breathing and prolong survival, it does not affect the progression of ALS. Most people with ALS die from respiratory failure, usually within three to five years from the onset of symptoms. The median survival time from onset to death is around 39 months, and only 4% survive longer than 10 years. The best-known person with ALS, Stephen Hawking, has lived with the disease for more than 50 years, though his is an unusual case.

CAUSE
Where no family history of the disease is present – i.e., in around 95% of cases – there is no known cause for ALS. Potential causes for which there is inconclusive evidence includes head trauma, military service, and participation in contact sports. Many other potential causes, including chemical exposure, electromagnetic field exposure, occupation, physical trauma, and electric shock, have been investigated but without consistent findings.
According to Medical News Today, "A group of investigators from the University of British Columbia and the Vancouver Coastal Health Research Institute have discovered a crucial link between prions and the neurodegenerative disease ALS" 

There is a known hereditary factor in familial ALS (FALS), where the condition is known to run in families. Recently, a genetic abnormality known as a hexanucleotide repeat was found in a region called C9ORF72, which is associated with ALS combined with frontotemporal dementia ALS-FTD, and accounts for some 6% of cases of ALS among white Europeans. The high degree of mutations found in patients that appeared to have "sporadic" disease, i.e. without a family history, suggests that genetics may play a more significant role than previously thought and that environmental exposures may be less relevant.

A defect on chromosome 21 (coding for superoxide dismutase) is associated with approximately 20% of familial cases of ALS, or about 2% of ALS cases overall. This mutation is believed to be autosomal dominant, and has over a hundred different forms of mutation. The most common ALS-causing SOD1 mutation in North American patients is A4V, characterized by an exceptionally rapid progression from onset to death. The most common mutation found in Scandinavian countries, D90A, is more slowly progressive than typical ALS and patients with this form of the disease survive for an average of 11 years.