Search
for a Cure
The
following was provided by the National Institute of Neurological
Disorders and Stroke, part of the National Institutes of Health.
What
causes ALS?
The
cause of ALS is not known, and scientists do not yet know
why ALS strikes some people and not others. An important step
toward answering that question came in 1993 when scientists
supported by the National Institute of Neurological Disorders
and Stroke (NINDS) discovered that mutations in the gene that
produces the SOD1 enzyme were associated with some cases of
familial ALS. This enzyme is a powerful antioxidant that protects
the body from damage caused by free radicals. Free radicals
are highly unstable molecules produced by cells during normal
metabolism. If not neutralized, free radicals can accumulate
and cause random damage to the DNA and proteins within cells.
Although it is not yet clear how the SOD1 gene mutation leads
to motor neuron degeneration, researchers have theorized that
an accumulation of free radicals may result from the faulty
functioning of this gene. In support of this, animal studies
have shown that motor neuron degeneration and deficits in
motor function accompany the presence of the SOD1 mutation.
Studies
also have focused on the role of glutamate in motor neuron
degeneration. Glutamate is one of the chemical messengers
or neurotransmitters in the brain. Scientists have found that,
compared to healthy people, ALS patients have higher levels
of glutamate in the serum and spinal fluid. Laboratory studies
have demonstrated that neurons begin to die off when they
are exposed over long periods to excessive amounts of glutamate.
Now, scientists are trying to understand what mechanisms lead
to a buildup of unneeded glutamate in the spinal fluid and
how this imbalance could contribute to the development of
ALS.
Autoimmune
responses, which occur when the body's immune system attacks
normal cells, have been suggested as one possible cause for
motor neuron degeneration in ALS. Some scientists theorize
that antibodies may directly or indirectly impair the function
of motor neurons, interfering with the transmission of signals
between the brain and muscles.
In
searching for the cause of ALS, researchers have also studied
environmental factors such as exposure to toxic or infectious
agents. Other research has examined the possible role of dietary
deficiency or trauma. However, as of yet, there is insufficient
evidence to implicate these factors as causes of ALS.
Future
research may show that many factors, including a genetic predisposition,
are involved in the development of ALS.
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