Gulf War veterans may have an increased risk of developing Lou Gehrig's disease, or ALS, later in life, according to a new report. The neurodegenerative disease causes gradual paralysis and is usually fatal.

A review of five studies, three of which included data from Gulf War veterans, found there was an association between military service and later development of ALS.

The Gulf War veterans were at double the risk of other populations, the researchers observed. One of the studies indicated that people who served in the military prior to the Gulf War experienced 1.5 times the normal risk of acquiring the disease, while another study found no connection between military service and ALS.

Further research is needed, the report authors stressed. If additional studies confirm their findings, then the next step will be to uncover the cause of the link. Exposure to toxins, physical stress and trauma are among the factors scientists might investigate.

There are approximately 25,000 victims of ALS in the US. A neurological disorder, it kills nerve cells, resulting in the loss of muscle control. Patients with ALS gradually become unable to move or speak, but their minds are not affected.

Although most ALS sufferers die from respiratory failure within five years of being diagnosed, the famous theoretical physicist Stephen Hawking has survived over three decades with it.

Despite the possible link between increased risk of the disease and military service -- particularly experience in the Gulf War -- ALS is still considered rare. Overall, it affects just one out of 100,000 people in the general population.