Amyotrophic lateral sclerosis, also called ALS or Lou Gehrig’s disease, is a degenerative neurological disease. Symptoms generally begin as muscle tremors, cramps, or tingling, eventually progressing to debilitating weakness and paralysis of motor neurons, which limits voluntary movement. There are only two drugs currently approved for treating ALS in the United States, largely due to the limited understanding of the disease. Unfortunately, these limits apply to causal factors as well. Here’s a look at what scientists do know about the causes and risk factors of ALS.
Understanding Amyotrophic Lateral Sclerosis
What specifically causes ALS in the human body is unclear, yet experts do have a handle on how the disease wreaks damage on the nervous system. Understanding the meaning of the name can help. Amyotrophic, taken from the original Greek, translates to "no muscle nourishment." Lateral (to the side) is an anatomical description of where on the spine the cells are generally impacted. Sclerosis refers to the scarring and hardening that occurs. Muscles throughout the body begin to weaken and atrophy as the motor neurons, located in the gray matter inside the side of the spine, degenerate, eventually becoming sclerotic.
ALS is a progressive disease. Generally, symptoms start small, like a tremor in the hands or a change in the pitch of your voice. They progress over the months that follow to more severe issues. Eventually, muscles in the diaphragm or the throat weaken significantly enough to make breathing or eating a challenge. Most patients with ALS have about a 3-5 year survival rate.
Genetic Links
Exactly what incites the motor neurons to start dying is a more difficult answer to pinpoint. About 5-10% of patients have what’s called "familial ALS," which develops because of a genetic link. Children of ALS patients have about a 50% chance of developing the disease. Some studies suggest familial ALS might be related to a genetic mutation. Potentially, these mutations could make it more likely certain people will develop the disease, although other factors could still play a role.
Neurochemical Imbalance
Sporadic ALS, or those cases where there is no genetic link, is similar to familial ALS. One of the popular theories makes use of evidence that ALS patients have higher levels of glutamate in their spinal cord than most people. Glutamate is a neurochemical messenger, but too much of it can be dangerous for some types of nerve cells. Riluzole, one of the two medications used to slow the progression, is a glutamate inhibitor.
Dysfunction
Other ways the body may be working against itself include immune dysfunction and an issue with nerve cell proteins. Some studies suggest that the immune system is attacking its own nerve cells, slowly killing them and causing the degeneration of the voluntary motor system. Other studies refer more specifically to a protein found in nerve cells. The abnormal protein can build up, damaging the nerve cells it resides in.
Risk Factors
There are a variety of risk factors when it comes to ALS. Genetics appear to carry the strongest correlation. Age is also important. Most cases of ALS appear between ages 40 to 60. Before age 65, males appear to be slightly more likely to develop the disease than females. After 65, that difference is nonexistent.
Certain environmental factors may be contributing to the development of the disease. Smoking appears to be most influential in postmenopausal women, and it seems to be the only environmental factor with much evidence. However, a few studies do suggest certain chemicals may play a role. Additionally, military veterans are twice as likely to develop ALS as civilians. Exactly what about military service increase the risk of ALS—toxins, exertion, infections, trauma, or some other factor—is still unclear.
