Գլխավոր Հիվանդություններ Amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease and motor neurone disease (MND), is a specific disease that causes the death of neurons which control voluntary muscles. Some also use the term motor neuron disease for a group of conditions of which ALS is the most common. ALS is characterized by stiff muscles, muscle twitching, and gradually worsening weakness due to muscles decreasing in size. This results in difficulty in speaking, swallowing, and eventually breathing. The cause is not known in 90% to 95% of cases. About 5–10% of cases are inherited from a person's parents. About half of these genetic cases are due to one of two specific genes. The diagnosis is based on a person's signs and symptoms with testing done to rule out other potential causes. No cure for ALS is known. A medication called riluzole may extend life by about two to three months. Non-invasive ventilation may result in both improved quality and length of life. The disease usually starts around the age of 60 and in inherited cases around the age of 50. The average survival from onset to death is two to four years. About 10% survive longer than 10 years. Most die from respiratory failure. In much of the world, rates of ALS are unknown. In Europe and the United States the disease affects about two people per 100,000 per year. Descriptions of the disease date back to at least 1824 by Charles Bell.[10] In 1869, the connection between the symptoms and the underlying neurological problems was first described by Jean-Martin Charcot, who in 1874 began using the term amyotrophic lateral sclerosis.[10] It became well known in the United States in the 20th century when in 1939 it affected the baseball player Lou Gehrig and later worldwide when physicist Stephen Hawking, diagnosed in 1963 and expected to die within two years, became famous. In 2014 videos of the ice bucket challenge went viral on the Internet and increased public awareness.

Classification ALS is a motor neuron disease, also spelled motor neurone disease which is a group of neurological disorders that selectively affect motor neurons, the cells that control voluntary muscles of the body, including amyotrophic lateral sclerosis (ALS), primary lateral sclerosis, progressive muscular atrophy, progressive bulbar palsy, pseudobulbar palsy, and spinal muscular atrophy. ALS itself can be classified a few different ways - by how fast the disease progresses (slow vs fast progressors), by whether it is inherited or sporadic, and by where it starts. Most commonly (~70% of the time) the limbs are affected first - in this case neurons in the brain (upper motor neurons) and in the spinal cord (lower motor neurons) are dying and this form is called limb onset. In about 25% of cases, muscles in the face, mouth, and throat are affected first because motor neurons in the part of the brain stem called the Medulla oblongata (formerly called the bulb) start to die first along with lower motor neurons - this form is called bulbar onset. In about 5% of cases muscles in the trunk of the body are affected first. In all cases the disease spreads and affects other regions. Signs and symptoms The disorder causes muscle weakness and atrophy throughout the body due to the degeneration of the upper and lower motor neurons. Individuals affected by the disorder may ultimately lose the ability to initiate and control all voluntary movement, although bladder and bowel function and the muscles responsible for eye movement are usually spared until the final stages of the disorder. Cognitive and/or behavioural dysfunction is present in up to half of individuals with ALS. Around half of people with ALS will experience mild changes in cognition and behaviour, and 10 - 15% will show signs of frontotemporal dementia. Repeating phrases or gestures, apathy, and loss of inhibition are frequently reported behavioural features of ALS. Language dysfunction, executive dysfunction, and troubles with social cognition and verbal memory are the most commonly reported cognitive symptoms in ALS; a meta-analysis found no relationship between dysfunction and disease severity. However, cognitive and behavioral dysfunctions have been found to correlate with reduced survival in people with ALS and increased caregiver burden; this may be due in part to deficits in social cognition. About half the people who have ALS experience emotional lability, in which they cry or laugh for no reason. Sensory nerves and the autonomic nervous system are generally unaffected, meaning the majority of people with ALS maintain hearing, sight, touch, smell, and taste. Initial symptoms The start of ALS may be so subtle that the symptoms are overlooked. The earliest symptoms of ALS are muscle weakness and/or muscle atrophy. Other presenting symptoms include trouble swallowing or breathing, 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. In limb onset ALS people first experience awkwardness when walking or running or even tripping over or stumbling may be experienced and often this is marked by walking with a dropped foot which drags gently on the ground. Or if arm-onset, difficulty with tasks requiring manual dexterity such as buttoning a shirt, writing, or turning a key in a lock may be experienced. In bulbar-onset ALS, initial symptoms will mainly be of difficulty speaking clearly or swallowing. Speech may become slurred, nasal in character, or quieter. There may be difficulty in swallowing and loss of tongue mobility. A smaller proportion of people experience respiratory-onset ALS, where the intercostal muscles that support breathing are affected first. Over time, people 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) although twitching is not a diagnostic symptom and more of a side effect so twitching would either occur after or accompany weakness and atrophy. Progression Although the order and rate of symptoms varies from person to person, the disease eventually spreads to unaffected regions and the affected regions become more affected. most people eventually are not able to walk or use their hands and arms, lose the ability to speak and swallow food and their own saliva, and begin to lose the ability to cough and to breathe on their own. The rate of progression can be measured using an outcome measure called the ALS Functional Rating Scale Revised (ALSFRS-R), a 12-item instrument administered as a clinical interview or self-reported questionnaire that produces a score between 48 (normal function) and 0 (severe disability); it is the most commonly used outcome measure in clinical trials and is used by doctors to track disease progression. Though the degree of variability is high and a small percentage of people have a much slower disorder, on average, people with ALS lose about 0.9 FRS points per month. A survey-based study amongst clinicians showed that they rated a 20% change in the slope of the ALSFRS-R as being clinically meaningful. Disorder progression tends to be slower in people who are younger than 40 at onset, are mildly obese, have disorder restricted primarily to one limb, and those with primarily upper motor neuron symptoms. Conversely, progression is faster and prognosis poorer in people with bulbar-onset disorder, respiratory-onset disorder, and frontotemporal dementia. The CX3CR1 allelic variants have also been shown to have an effect on the disorder's progression and life expectancy. Late stages Difficulty in chewing and swallowing makes eating very difficult and increases the risk of choking or of aspirating food into the lungs. In later stages of the disorder, aspiration pneumonia can develop, and maintaining a healthy weight can become a significant problem that may require the insertion of a feeding tube. As the diaphragm and intercostal muscles of the rib cage that support breathing weaken, measures of lung function such as vital capacity and inspiratory pressure diminish. In respiratory-onset ALS, this may occur before significant limb weakness is apparent. 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 between 2 and four years after the diagnosis. Around half of people with ALS die within 30 months of their symptoms beginning, and about 20% of people with ALS live between 5 years and 10 years after symptoms begin. Guitarist Jason Becker has lived since 1989 with the disorder, while physicist Stephen Hawking has survived for more than 50 years, but they are considered unusual cases. Most people with ALS die in their own home, with their breath failing while they sleep; people rarely choke to death. Cause Genetics About 5–10% of cases are directly inherited from a person's parents.[5] Overall, first-degree relatives of an individual with ALS have a 1% risk of developing ALS. A defect on chromosome 21, which codes for superoxide dismutase, is associated with about 20% of familial cases of ALS, or about 2% of ALS cases overall. This mutation is believed to be transmitted in an autosomal dominant manner, and has over a hundred different forms of mutation. The most common ALS-causing mutation is a mutant SOD1 gene, seen in North America; this is characterized by an exceptionally rapid progression from onset to death. The most common mutation found in Scandinavian countries, D90A-SOD1, is more slowly progressive than typical ALS, and people with this form of the disorder survive for an average of 11 years. In 2011, 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 UBQLN2 gene encodes production of the protein ubiquilin 2 in the cell, which is a member of the ubiquilin family and controls the degradation of ubiquitinated proteins. Mutations in UBQLN2 interfere with protein degradation, leading to neurodegeneration and causing dominantly inherited, chromosome X-linked ALS and ALS/dementia. To date, a number of genetic mutations have been associated with various types of ALS. The currently known associations are: SOD1 In 1993, scientists discovered that mutations in the gene (SOD1) that produces the Cu-Zn superoxide dismutase (SOD1) enzyme were associated with around 20% of familial ALS. This enzyme is a powerful antioxidant that protects the body from damage caused by superoxide, a toxic free radical generated in the mitochondria. Free radicals are highly reactive molecules produced by cells during normal metabolism. Free radicals can accumulate and cause damage to DNA and proteins within cells. To date, over 110 different mutations in SOD1 have been linked with the disorder, some of which (such as H46R) have a very long clinical course, while others, such as A4V, are exceptionally aggressive. When the defenses against oxidative stress fail, programmed cell death (apoptosis) is upregulated. A defect in SOD1 could be a loss or gain of function. A loss of SOD1 function could lead to an accumulation of free radicals. A gain of SOD1 function could be toxic in other ways. Aggregate accumulation of mutant SOD1 is suspected to play a role in disrupting cellular functions by damaging mitochondria, proteasomes, protein folding chaperones, or other proteins. Any such disruption, if proven, would lend significant credibility to the theory that aggregates are involved in mutant SOD1 toxicity. Critics have noted that in humans, SOD1 mutations cause only 2% or so of overall cases and the etiological mechanisms may be distinct from those responsible for the sporadic form of the disease. To date, the ALS-SOD1 mice remain the best model of the disease for preclinical studies, but it is hoped that more useful models will be developed. Head injury While moderate to severe traumatic brain injury is a risk for ALS, it is unclear if mild traumatic brain injury increases rates.' In 1994 the National Institute for Occupational Safety and Health (NIOSH) reported a nonsignificant increase in nervous system disorders due to four cases of ALS among NFL football players. It was unclear if this was due to chance or not. Another study from 2012 also found a possible increase in ALS in NFL football players. An older study did not find an increased risk among high school football players. A 2007 review found an increased risk among soccer players.ALS may also occur more often among the US military veterans however the reason is unknown. This may be due to head injury. Other factors Where no family history of the disease is present – i.e., in around 90% of cases – no cause is known for ALS. Possible associations for which evidence is inconclusive include military service, frequent drug use, and participation in contact sports. Studies also have focused on the role of glutamate in motor neuron degeneration. Glutamate is one of the neurotransmitters in the brain. Scientists have found, compared with healthy people, people with ALS have higher levels of glutamate in their serum and spinal fluid.[28] Riluzole is currently the only FDA-approved drug for ALS and targets glutamate transporters. It only has a modest effect on survival, however, suggesting that excess glutamate is not the sole cause of the disease. Certain studies suggested a link between sporadic ALS, specifically in athletes, and a diet enriched with branched-chain amino acids, a common dietary supplement among athletes, which cause cell hyperexcitability resembling that usually observed in people with ALS. The proposed underlying mechanism is that cell hyperexcitability results in increased calcium absorption by the cell, and thus brings about cell death of neuronal cells, which have particularly low calcium buffering capabilities.[49] Some evidence supports superoxide dismutase 1 (SOD1) protein misfolding propagates between molecules in a similar fashion to prions. Similarly, it has been proposed that incorporation of the cyanobacterial toxin β-methylamino-l-alanine (BMAA) leads to another prion-like protein misfolding propagation. Another very common factor associated with ALS is a lesion to the motor system in areas such as the frontotemporal lobes. Lesions in these areas often show signs of early deficit, which can be used to predict the loss of motor function, and result in the spread of ALS. The mechanisms of ALS are present long before any signs or symptoms become apparent. Before any muscular atrophy becomes apparent during ALS, roughly one-third of the motor neurons must be destroyed. Other potential risk factors including chemical exposure, electromagnetic field exposure, occupation, physical trauma, and electric shock, have been investigated, but are without consistent findings. There is a tentative association with exposure to a number of pesticides including the organochlorine insecticides aldrin, dieldrin, DDT, and toxaphene. Pathophysiology The defining feature of ALS is the death of both upper and lower motor neurons in the motor cortex of the brain, the brain stem, and the spinal cord. Prior to their destruction, motor neurons develop protein-rich inclusions in their cell bodies and axons. This may be partly due to defects in protein degradation. These inclusions often contain ubiquitin, and generally incorporate one of the ALS-associated proteins: SOD1, TAR DNA binding protein (TDP-43, or TARDBP), and/or FUS. Diagnosis No test can provide a definite diagnosis of ALS, although the presence of upper and lower motor neuron signs in a single limb is strongly suggestive. Instead, the diagnosis of ALS is primarily based on the symptoms and signs the physician observes in the person and a series of tests to rule out other diseases. Physicians obtain the person's full medical history and usually conduct a neurologic examination at regular intervals to assess whether symptoms such as muscle weakness, atrophy of muscles, hyperreflexia, and spasticity are worsening.

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