Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a progressive neurological disease that destroys nerve cells and causes disability.
The disease causes the death of 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 die. With the loss of motor neurons, the brain is no longer able to move or control muscle movement, and as a result, muscles become smaller and weaker. Within a few years of diagnosis, ALS patients lose the ability to perform everyday tasks like walking up steps, reaching for items, or dressing themselves.
In earlier stages, ALS causes symptoms such as stiff muscles, muscle twitching, and a gradual worsening in muscular strength. As the disease progresses, the body becomes paralyzed, with patients experiencing difficulty in speaking, swallowing, and eventually, breathing.
In 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 experience foot drop and a “slapping” gait.
People with ALS can experience emotional and cognitive difficulties, including bursts of involuntary and inappropriate laughing or crying, depression, impaired critical thinking, or abnormal social behaviors.
As the disease progresses, muscle atrophy becomes more apparent and muscle cramps more common. In advanced stages, patients often experience voice changes, including hypernasality and development of a strained or strangled vocal quality. Speech may eventually be lost completely. Patients may experience drooling and have difficulties swallowing.
Although ALS is not curable, treatment can extend the length and quality of life of patients.
ALS can manifest in different forms, but the two most common are sporadic and familial ALS.
- 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, this often runs in families. The 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.
Causes of ALS
Mutations in several genes have been implicated in familial ALS and 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 between 5,760 to 6,400 new diagnoses per year. The incidence of ALS increases with age, typically starting in the 40s and continuing until around the age of 80. However, ALS can occur in people in their 20s and 30s.
Estimates indicate that four to six people per 100,000 are living with ALS at any given time. Given that the U.S. population is estimated to be 326 million, the prevalence of ALS nationwide is between 12,800 and 19,800 people, 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 database statistics, 93 percent of ALS patients in the U.S. are Caucasian and 60 percent are men. As people age, this gender difference narrows, with the incidence of ALS becoming more equal between men and women.
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