Estimates range from 100,000 to 300,000 individuals exposed to nerve agents.While low-level exposure to nerve agents has been suggested as the cause of GWI, the 2008 report by the U.S. Department of Veterans Affairs (VA) Research Advisory Committee on Gulf War illnesses (RAC) stated that "evidence is inconsistent or limited in important ways." The VAs 2014 RAC report concluded that, "exposure to the nerve gas agents sarin/cyclosarin has been linked in two more studies to changes in structural magnetic resonance imaging findings that are associated with cognitive decrements, further supporting the conclusion from evidence reviewed in the 2008 report that exposure to these agents is etiologically important to the central nervous system dysfunction that occurs in some subsets of Gulf War veterans. "A 2022 study by Dr. Robert W. Haley of the University of Texas Southwestern Medical Center, et al., of 1,016 U.S. Gulf War veterans found evidence of a causal link between GWI and exposure to low levels of sarin, which was released into the air by coalition bombing of Iraqi chemical weapons facilities. Significantly, the study found an increased incidence of GWI not only among veterans who recounted hearing nerve agent alarms, but also among veterans with the RR or QR (as opposed to the QQ) forms of the PON1 gene, which produces an enzyme that deactivates organophosphates (including sarin) through hydrolysis. By contrast, GWI was inversely associated with higher levels of the type Q isozyme, which is more efficient at breaking down sarin than its type R counterpart.
The authors "found that the PON1 genotype and hearing nerve agent alarms were independent and the findings robust to both measured and unmeasured confounding, supporting a mechanistic [gene–environment] interaction. ... Moreover, the change in the combined effect from one category to the next was significantly greater than the sum of the independent effects of the environmental exposure and the genotype". Although organophosphate pesticides could have triggered the nerve agent alarms in use at the time and contributed to neurotoxic symptoms similar to GWI, Haley et al. ruled out pesticides as a primary cause of GWI, citing that pesticide use was "ubiquitous long before the approximately 10,000 alarms began sounding at the start of the air campaign when Coalition bombing of Iraqi chemical weapon facilities released the fallout cloud that reached U.S. troop concentrations just as sarin was detected at multiple sites," while "the PON1 R isoenzyme is the more efficient detoxifier of most pesticides." Less likely causes
According to the VAs 2008 RAC report, "For several Gulf War exposures, an association with Gulf War illness cannot be ruled out. These include low-level exposure to nerve agents, close proximity to oil well fires, receipt of multiple vaccines, and effects of combinations of Gulf War exposures."