chemicals that inhibit cholinesterase are responsible for the three nervous system-based syndromes (Haley and Kurt, 1997). Results of this study are discussed in Appendix A.

Another study by Haley and collaborators (1999) examined whether genetic susceptibility could play a role in placing some veterans at risk for neurologic damage by organophosphate chemicals. The investigators studied 45 veterans: 25 with chronic neurologic symptoms identified through their earlier factor analysis study and 20 healthy controls from the same battalion. Investigators measured blood butyrylcholinesterase and two types, or allozymes, of paraoxonase/arylesterase-1 (PON1). The genotypes encoding the allozymes were also studied. Results of this study are also discussed in Appendix A.

The Update committee identified one new study by Haley et al. (2009) that looked at abnormal brain response to cholinergic challenge in a small group of Gulf War veterans. Twenty-one Gulf War veterans with symptom complexes used by Haley to define three forms of Gulf War illness and 17 age-, sex- and education-matched controls, underwent a 99mTc-HMPAO-SPECT brain scan with and without an infusion of PB.

Reference Study

The first in a series of studies by Gray et al. (1999) surveyed Seabees who remained on active duty for at least 3 years after the Gulf War. The Seabees were from 14 commands at two locations (Port Hueneme, California, and Gulfport, Mississippi). Those who were deployed to the Gulf War were in mobile construction battalions serving in the same tasks and at the same sites as did the reserve Seabee battalion studied by Haley et al. (1997b), Gray et al. (1999) excluded Gulf War veterans who were no longer on active duty at the time of study.

In 1994, 1497 study subjects were enrolled: 527 Gulf War veterans and 970 nondeployed veterans. The participation rate of eligible Seabees was 53%. The following were administered to the study participants: eight-page questionnaire regarding medical history, Gulf War exposures, postwar symptoms, hospitalization, and pregnancy outcomes; questions regarding the presence of chronic fatigue syndrome and PTSD; laboratory testing—sera, blood, urine; and pulmonary function and handgrip strength tests. Findings of this study can be found in Chapter 4.

Derivative Studies

Beginning in May 1997, Gray et al. (2002) distributed a postal questionnaire to all regular and reserve navy personnel (n = 18,945) who served on active-duty Seabee command during the Gulf War period. The questionnaire collected information regarding medical history, current health status, symptoms, and environmental exposures (for example, PB). Of the 17,559 located participants, 11,868 completed and returned the survey: 3831 Gulf War deployed, 4933 deployed elsewhere, and 4933 nondeployed. Compared with the two control groups, the deployed were more likely to report having more symptoms and being in fair or poor health. Outcome specific results are found in Chapter 4.

Knoke et al. (2000) used the same Seabee cohort to conduct a factor analysis of the symptoms reported by the veterans on the Hopkins Symptom Checklist to determine whether there was a unique Gulf War syndrome.

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