Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a progressive neurological disease that destroys nerve cells and causes disability. It is the most common degenerative disease of the central nervous system.
The disease causes the death of the motor neurons, which control voluntary muscles. Upper motor neurons send messages from the brain to the spinal cord, and lower motor neurons send messages from the spinal cord to the muscles
Over time, ALS causes the motor neurons in the brain and spinal cord to shrink and disappear. With the degeneration of the motor neurons, the brain is no longer able to move or control muscle movement, and as a result, they become smaller and weaker. With the loss of voluntary muscle action, ALS patients will eventually no longer do everyday things like walk up a few steps or reach for something.
ALS causes symptoms such as stiff muscles, muscle twitching, and gradual worsening weakness due to muscles decreasing in size. As the disease progresses, the body becomes paralyzed, with patients experiencing difficulty speaking, swallowing, and eventually breathing.
In about 75 to 80 percent of patients, symptoms of ALS begin with arms, hands, and legs, such as tripping, stumbling, or awkwardness when running. People with ALS also have foot drop and a “slapping” gait.
People with ALS also experience emotional and cognitive difficulties including involuntary laughing or crying, depression, impaired executive function, or abnormal social behaviors.
As the disease progresses, muscle atrophy becomes more apparent, with muscle cramps that become more common. In advanced stages of the disease, patients often experience voice changes, including hypernasality and development of a strained, strangled vocal quality. Speech may eventually be lost completely. Patients may also have swallowing difficulties and drooling.
Although ALS is incurable, treatment can extend the length and quality of life of patients.
ALS can manifest in several different forms:
- Sporadic ALS: This is the most common form of the disease in the U.S., accounting for 90 to 95 percent of all cases. This form of the disease occurs in people with no apparent history of the disorder in their families, and patients usually first develop features of the condition in their late 50s or early 60s.
- Familial or inherited ALS: This type is genetic and occurs more than once in a family. It accounts for 5 to 10 percent of all cases in the U.S. The signs and symptoms of familial ALS typically first appear in the late 40s or early 50s.
- Guamanian ALS: An extremely high incidence of ALS was observed in Guam and the Trust Territories of the Pacific in the 1950s. The exact cause of this is still not clear.
- ALS-parkinsonism-dementia complex: A rare form of ALS that often runs in families. This disorder is characterized by the signs and symptoms of ALS, in addition to a pattern of movement abnormalities known as parkinsonism, including symptoms such as unusually slow movements (bradykinesia), stiffness, and tremors.
Mutations in several genes have been implicated in familial ALS and also contribute to the development of sporadic ALS. Mutations in the C9orf72 gene account for 30 to 40 percent of familial ALS in the U.S. and Europe. SOD1 gene mutations cause 15 to 20 percent of familial ALS worldwide, and TARDBP and FUS gene mutations each account for about 5 percent of cases. Other genes have also been implicated in the disease but in a smaller proportion of cases.
Many environmental factors are thought to cause sporadic ALS. These include toxins such as beta-methylamino-l-alanine (BMAA), found in commercial seafood; smoking; metals; solvents; radiation and electromagnetic fields; pesticides; and viruses.
Incidence and prevalence of ALS
According to the ALS Association, the incidence rate of ALS is projected to be 1.8 to 2 per 100,000 people, which equates to 5,760 to 6,400 new diagnoses per year. The number of new cases of ALS varies with age, which increases until around the age of 80. However, ALS can sometimes occur in younger people who are in their 20s and 30s.
Estimates indicate that four to six people per 100,000 are living with ALS at any given time. Using the estimated U.S. population number of approximately 320,000,000, the prevalence of ALS would be from 12,800 to 19,800, according to the ALS Association.
The ALS Patient Care Database (1996-2005), the first large-scale effort to track the disease course of ALS patients in the U.S., enrolled 6,337 patients from 323 sites for long-term follow-up through patient questionnaires, clinical assessment, and caregiver assessment.
According to the patients enrolled in the database, 93 percent of ALS patients are Caucasian and 60 percent are men. Most people who develop the disease are between the ages of 40 and 70. As age increases, the incidence of ALS becomes more equal between men and when.
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