Grantee Research Project Results
2000 Progress Report: Reproductive Health, Serum Dixon, and P450 Genes in Vietnam Veterans
EPA Grant Number: R825817Title: Reproductive Health, Serum Dixon, and P450 Genes in Vietnam Veterans
Investigators: Sweeney, Anne , Symanski, Elaine , Denison, Michael , Cooper, Sharon , Wu, Xifeng , Junco, Deborah del
Current Investigators: Sweeney, Anne , Wun, Chuan-Chuan , Symanski, Elaine , Denison, Michael , Cooper, Sharon , Wu, Xifeng , Junco, Deborah del
Institution: The University of Texas at Houston
EPA Project Officer: Aja, Hayley
Project Period: November 19, 1997 through November 18, 2000 (Extended to November 30, 2002)
Project Period Covered by this Report: November 19, 1999 through November 18, 2000
Project Amount: $874,195
RFA: Issues in Human Health Risk Assessment (1997) RFA Text | Recipients Lists
Research Category: Human Health
Objective:
Recent Institute of Medicine updates regarding the association of Agent Orange exposure and birth defects among the offspring of Vietnam veterans indicate a critical need to reexamine this controversial issue. The major limitations of previous studies were crude exposure assessment, selection bias, and small sample sizes. This is a nested case-control study to test hypotheses regarding dioxin exposure, the CYP1A1 variant allele, and any interactions between these two factors in producing pregnancies affected with a neural tube defect (NTD).Progress Summary:
The investigators elected to utilize a very labor-intensive and time-consuming approach to sampling to reduce potential selection bias that could result from using incomplete or restricted military records as the basis for sampling. The likelihood that this bias was present in previous studies of Vietnam veterans and health effects due to dioxin exposure has been a severe limitation. A registry of all known 2.7 million male and female Vietnam veterans was obtained from the Departments of Defense and Veterans Affairs as the sampling frame. To maximize the probability of identifying veteran parents, the National Center for Health Statistics (NCHS), with the approval of State Vital Statistics Offices, provided available birth and death certificate numbers for NTD births, deaths, and fetal deaths in the United States for the period 1962-1995.The fifty states were trichotomized according to the proportion of Vietnam veterans in the population, with Tier 1 having the highest proportion of veterans. A 2-year effort resulted in Institutional Review Board (IRB) approval from 40 states overall (80%): 10 of 10 in Tier 1; 16 of 17 in Tier 2; and 14 of 23 in Tier 3. Three states (Maryland, Arizona, and Virginia) denied access to any records; other states permitted access to only death certificates; and still others allowed access to death, birth, and fetal death certificates for varying intervals. Due to time and budget constraints, we have restricted this study to 36 states, omitting those states with low proportions of Vietnam veterans in the population.
Parent identifiers were abstracted from these certificates and crosslinked with the veteran registry for a list of "potential" matches (N=5,990), using the MatchWare software program. An interagency agreement with the National Institute for Occupational Safety and Health (NIOSH) and the Internal Revenue Service (IRS) was established to provide current addresses for the veterans. This process was facilitated by the EPA, which serves as the official federal institution requesting this service. This agreement required several months to arrange; therefore, the recruitment of participants was necessarily delayed until we could obtain the current addresses. Those who were not located through this process also were submitted to Metronet, a national tracking company that searches credit and other information sources to find the most current address for an individual.
A screening survey has been mailed to 4,553 (76.0%) of these potential matches for whom an address was available to determine eligibility based on both veteran and parental status. The remaining veterans were not contacted because they were deceased (n=595, 9.9%) or had no current address available (n=842, 14.1%). A total of 1,875 (41.2%) responded to our letters; this is an excellent response rate for this type of mailing survey in this population, and will only improve as we continue to receive many new responses daily. A total of 2,193 (48.1%) have not yet responded, and 485 (10.7%) surveys were returned to us unopened.
Of the 1,875 who responded to date, 78 (4.2%) claimed non-Vietnam veteran status and thus were not eligible. Of the remaining 1,797, 1,458 (81.1%) completed the screening survey. It is impossible to estimate what proportion of the eligible veterans this represents, as letters were sent to potential matches, many of whom would not be eligible based on parental or military status. Cases are Vietnam veterans of an NTD-affected child; Vietnam veterans of healthy offspring serve as controls. Of the eligible respondents, 265 (14.7%) declined to participate, and 6 (0.3%) either returned forms with no information (n=4) or were "unable" to participate (n=2). A total of 1,005 (68.9%) reported having fathered (or conceived) at least one pregnancy after their tour of duty in southeast Asia. Of these, 136 cases have been identified to date, representing 13.5 percent of respondents who met both the military and reproductive history eligibility requirements. (The highest number of NTD cases in any previous study of Vietnam veterans was 19). The screening questionnaire also asks if the veteran would be willing to answer another more detailed survey and provide a blood sample for dioxin analysis and genotyping. Of the 1,005 respondents who were both Vietnam veterans and had at least one pregnancy after their tour of duty, 757 (75.3%) were willing to answer the second survey, 161 (16.0%) indicated they "may be willing," and 83 (8.3%) declined. Somewhat surprisingly, slightly more were willing to provide blood samples (n=765, 76.1%), 148 (14.7%) "may be" willing, and 85 (8.5%) declined to give a blood sample.
Upon determination of eligibility and willingness to participate, the veteran is sent a second, in-depth survey to obtain complete military and reproductive histories. A subset of 75 cases and 75 controls will be selected from this sample for dioxin and genetic polymorphism assays. It was intended that every eligible veteran receive this survey, but due to budgetary restraints, this will be targeted to a subset of cases and controls. The first batch of followup surveys was mailed to all of the cases identified to date in Texas (n=22) and 22 controls residing in Texas. As of June 1, 2001, 72.7 percent of cases and 36.4 percent of controls had returned the second survey. Surveys also were sent to 380 controls from around the United States, with a response rate to date of 36.6 percent, similar to the Texas controls. We are in the process of contacting the nonrespondents by telephone?if the number is available?or by letter.
Future Activities:
During the remaining 5 months of the project, we will complete the mailing of the second survey to the extent that the budget permits. Blood samples will be collected and analyzed for dioxin and P450 polymorphism determinations. A total of 75 cases and 75 controls will be selected from those returning the second survey for these analyses. Blood sample collection already has begun among the Texas participants, with a registered nurse driving to the participant's home to draw the samples. Arrangements have been made with the laboratories that will be performing the analyses on the blood samples. Dr. Xifeng Wu will perform genotyping for the CYP1A1 polymorphism at the MD Anderson Cancer Center in Houston, Texas. Xenobiotics Detection Systems, Inc., of North Carolina, will perform the CALUX assay to measure dioxin-like activity in the samples, under the direction of Dr. George Clark. Finally, ERGO Laboratory in Hamburg, Germany, under the supervision of Dr. Olaf Papke, will be performing the analysis documenting 2,3,7,8-TCDD levels in 20 samples, selected to represent low, medium, and highly exposed veterans based on the results of the CALUX assay. The correlation between these two assays will be determined. An Exposure Index has been developed, which will be used to categorize participants according to likelihood of exposure to dioxin (high, medium, or low probability). If the results of the CALUX assay are validated, using GC/MS as the gold standard, the Exposure Index will be correlated with the CALUX assay. If there is a strong correlation between these two measures, it will permit us to model the serum dioxin levels in the remaining participants for whom there was insufficient funding to allow for 2,3,7,8-TCDD analysis.Analysis of the relation between serum dioxin levels and NTDs, as well as interactions between serum dioxin and the variant allele in producing pregnancies afflicted with NTDs, will be conducted. In addition to the major hypothesis of the study, a doctoral student here at the University of Texas School of Public Health is conducting a study to examine the association between dioxin exposure and cancer, as well as any potential coexistence between birth defects and cancer in this population.
Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectSupplemental Keywords:
exposure, risk assessment, teratogen, health effects, vulnerability, sensitive populations, genetic polymorphisms, dioxin, birth defects, Vietnam veterans., RFA, Health, Scientific Discipline, Toxics, Genetics, Epidemiology, Chemistry, pesticides, Risk Assessments, Susceptibility/Sensitive Population/Genetic Susceptibility, genetic susceptability, Biology, dioxin, sensitive populations, Vietnam veterans, spina bifida, P450 genes, exposure, human exposure, genetic polymorphisms, environmentally caused disease, human susceptibility, reproductive health, herbicides, dioxin exposure, genetic susceptibilityRelevant Websites:
http://www.sph.uth.tmc.edu/research/va/vietnamvets/index.htmlProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.