Q1.   I've heard that a new study suggests ALS may be caused by a virus. Can you tell me more about these findings?

A.   In the January 2000 issue of the journal Neurology, researchers presented evidence that the genetic material of a particular virus is found in 88 percent of tissue samples taken from people who died of ALS but in only 3 percent of tissue samples from people who died of other causes. Specifically, the viral material was found in the anterior horns of the spinal cord, a region containing motor neurons that's affected in ALS.

The full reference for the article is:

Berger, MM, et al. (2000): Detection and cellular localization of enterovirus RNA sequences in spinal cord of patients with ALS. Neurology, 54:20-25.

These findings were presented by a group of researchers led by M. M. Berger, currently of the University of California, Irvine, and B. Lina, of the National Reference Center for Enterovirus in France.

The virus identified by the researchers is a member of the enterovirus family. This family includes the polio virus and viruses that cause meningitis. The virus identified in the ALS tissue samples most closely resembles a meningitis-causing virus called echovirus-7 and another virus, echovirus-6.

Although these results are intriguing, they show a correlation between the presence of this virus and ALS, not a cause-and-effect relationship. For instance, they don't show whether the virus causes ALS, or whether people with ALS are particularly susceptible to viral infection. More research is needed to determine the role of this virus, if any, in ALS.

Q2.   Is this the first study demonstrating the association of viral infection and ALS?

A.   Researchers have long suspected there might be a viral cause of ALS, and many papers have been published on this topic. To date, researchers have looked for five different types of evidence:

1. Viral particles in tissue samples from people with ALS (viewed by electron microscope)
2. Evidence of inflammatory reactions in the affected nerve tissue of people with ALS (as if the immune system were fighting a viral invader)
3. Evidence that the disease is infectious, meaning that it could be transmitted from humans to other primates or other mammals
4. Evidence of specific antiviral antibodies associated with the occurrence of ALS
5. Evidence of viral genetic material found preferentially in the tissue of people with ALS

So far, no one has been able to link viral infection to ALS through any of the first three means, but this lack of evidence doesn't disprove a connection as there are other valid reasons to explain these negative results.

Evidence of the types described in items 4 and 5 has been reported in relationship to the HIV-1 virus, the Herpes Simplex I virus, the human T-lymphotropic virus (HTLV), the hepatitis B virus and various enteroviruses (including the polio virus). However, in many studies the authors simply report the coexistence of viral infection with ALS in isolated cases. In other instances, study numbers are small and the results are frequently contradicted by subsequent studies.

Together, the studies undertaken up to this point have been inconclusive as to whether or not a viral infection is associated with ALS. They don't address at all the issue of whether a viral infection is the cause of ALS.

This recent article by Berger and colleagues may represent the most convincing evidence to date that a viral infection is associated with ALS in that larger numbers of tissue samples were examined (samples from 17 people with ALS and 29 people who died of other causes), and an extremely sensitive detection method for viral genetic material was used.

Q3.   If a virus is found to cause sporadic ALS, would there be a treatment?

A.   The scientific community has certainly learned a lot about viral suppression from studies of the AIDS virus (HIV), the flu virus and others. In fact, anti-enteroviral drugs already in existence may be of use in slowing or halting the course of the disease if an enterovirus is to blame. It's less likely that such a "treatment" would reverse advanced symptoms of the disease.

Again, although these new findings make a strong case for the association of an enterovirus with ALS, there is no evidence yet that the virus causes ALS.

Q4.   If a virus is found to cause sporadic ALS, does that mean all the other theories concerning glutamate excitotoxicity, oxidative stress, misfolded proteins, etc., are wrong?

A.   These different theories about the cause of ALS aren't mutually exclusive. It's more likely that several different mechanisms play interrelated roles in the disease process. For instance, nerve cells infected with a virus may become susceptible to glutamate toxicity. Or nerve cells already suffering from glutamate toxicity may be more likely to succumb to the effects of a viral infection. Or viral infection may occur as a consequence of glutamate excitotoxicity, but not be, in and of itself, harmful to the nerve cells. More study is necessary to determine if, and how, these processes are related in ALS.

Q5.   Is MDA following up on this new finding?

A.   MDA has been following these developments closely and investigates all legitimate research that may result in a treatment or cure for ALS.