Iraq veterans and Lou Gehrig’s Disease

by revere, cross-posted at Effect Measure

Bush has announced he will reduce the forces in Iraq by 8000 by early 2009. My first thought (after “that’s it? I thought we were victorious”; and let’s get all of them out now as fast as we can) was to wonder what condition they will be in and what’s in store for them in the future? I thought about that particularly because of the emerging scientific literature on strange and rare diseases in Gulf region veterans. One of these diseases is Lou Gehrig’s Disease (medical name, amyotrophic lateral sclerosis or ALS). ALS, while rare (about 1 – 2 cases per 100,000 population in the US each year), is not the only disease of its kind, but one of a group of diseases called motor neuron diseases (MNDs). The physicist Stephen Hawking has a MND but it isn’t ALS, although it is frequently mistakenly identified as such. Unlike the disease Hawking has, ALS kills pretty fast, usually within 3 years of onset.

ALS, however, has been reported to be high in Gulf War I. veterans. One paper (Horner et al.) has made the further argument that the excess in Gulf War vets occurs specifically in the decade following service, but the paper is at best suggestive. The same research group (Duke and the University of Cincinnati) has just published a study of where the ALS cases were in the Gulf region and identified some areas of higher relative odds but have yet to tie any environmental factor to these locations that might account for it. This seems to be preliminary work and the methods are not well described so I don’t know what to make of it.

Is it plausible that service in the first Gulf War (and by inference Iraq) could result in this deadly disease? It is the subject of intense scrutiny by the Department of Veterans Affairs (see, for example, this paper on a new ALS registry set up to study it) and new studies in veterans on interactions between genetic and environmental factors are underway. But ALS is one of the more mysterious diseases and whether it is plausible or not is hard to say since we know so little about it. Here’s some of what we know.

ALS is a progressive degenerative disease of the neuromuscular system that begins with weakness and clumsiness and spreads to become a universal paralysis that kills within a few years by paralyzing the respiratory system. It rarely strikes before the age of 40 but after that increases with each decade of life. The basic components of your neuromuscular system are a long nerve cell from your brain down to your spinal cord (the upper motor neuron) that connects to another nerve cell (the lower motor neuron) that goes from your spinal cord to the muscle it makes move. Both the upper and lower motor neurons die off in ALS, beginning with the lower neuron. This leads to muscle weakness and other abnormalities related to the lost nerve connection (this is the amyotrophic part of the name of the disease); and as the nerve cells die off they are replaced by harder non-nerve cells in the outer (lateral) part of the spinal cord (lateral sclerosis, where sclerosis is a general term for “hardening”).

Whites are slightly more affected than non-whites and males slightly more than females but in the US there seems to be no geographic pattern. Most cases of ALS are of unknown origin and appear random (they are called sporadic cases and constitute 90% of US cases. About 10% of cases in the US are clearly hereditary (called familial cases). While rare, however, the familial cases have been the subject of much study since it was discovered in 1993 that they were caused by a specific mutation in the super oxide dismutase I gene (SOD1). This has been a fruitful line of investigation but to date the results have been confusing (there is a news piece on recent results in Nature; subscription required, alas).

Is there any reason to suspect environmental or occupational factors? There is a Western Pacific variant of ALS-like MND, especially on the island of Guam, that has been associated with eating Cycads (Cycas circinalis), a seed plant used to make starch. The cycads contain an amino acid that overexcites nerve cells and in animals causes an ALS-like condition. But all sorts of toxins, including heavy metals like lead, have also been suggested as triggers for ALS. With so little known about the mechanism causing the motor neuron die off, we don’t even know where to look.

So we will welcome home Iraq soldiers with relief and the hope the deadly peril of combat will not be replaced by the deadly peril of a fatal neurological disease.