Grantee Research Project Results
Final 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 , 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 Amount: $874,195
RFA: Issues in Human Health Risk Assessment (1997) RFA Text | Recipients Lists
Research Category: Human Health
Objective:
The objective of this research project was 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). 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 project involved a nested case-control study.
Summary/Accomplishments (Outputs/Outcomes):
Completion of Phase I: Establishment of the Cohort
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 of NTD-affected pregnancies, the National Center for Health Statistics, with the approval of State vital statistics offices, provided birth and death certificate numbers for NTD births, deaths, and fetal deaths in the United States for the period 1962-1995. Parent identifiers were abstracted from these certificates and cross linked with the veteran registry for a list of potential matches using the MatchWare TM software program. An interagency agreement with the National Institute for Occupational Safety and Health and the Internal Revenue Service was established to provide current addresses for the veterans.
A screening survey was mailed to potential matches (n = 6,091) to determine eligibility based on both veteran and parental status. Cases were Vietnam veterans with an NTD-affected child; Vietnam veterans with healthy offspring served as controls. Of these, 540 (8.8 percent) were returned as undeliverable by the post office, 106 (1.7 percent) were not Vietnam veterans, and 74 (1.2 percent) were deceased. Of the remaining 5,371 potential participants, 3,226 (60 percent) did not respond. Previous research experience with female Vietnam veterans indicated that death since tour of duty in Southeast Asia must be considered when estimating the sampling frame. To approximate the proportion of the 3,226 nonresponders who were deceased in our national sample, we linked (using Social Security number and last name) all of the nonresponders with Texas addresses (n = 1,163) to the Texas mortality database, which includes all deaths occurring in Texas from 1979 to 2000. A total of 8 percent were deceased. Therefore, if we extrapolate these data with the remaining nonresponders with addresses outside of Texas, approximately 259 also were deceased, yielding a potentially eligible population of 5,112. Of these, 2,967 (58 percent) did not respond to the mailings and 322 (6.3 percent) declined to enroll in the study, yielding 1,823 participants in Phase I of the study for a response rate of 35.7 percent. This response rate is very similar to other studies that employed “cold” contacting approaches to recruiting participants.
The highest number of exposed NTD cases previously reported in studies of Vietnam veterans was 19 (Erickson, et al., 1984); exposure was defined by an Exposure Opportunity Index developed using self-reported exposure data and military records of spraying activity and troop movements. In the project, a total of 143 (7.8 percent) Vietnam veterans reported an NTD pregnancy after their tours in Southeast Asia. Most veterans were willing to provide blood samples for analyses of dioxin levels and genetic susceptibility markers, with 1,362 (74.7 percent) responding yes and 253 (13.9 percent) indicating they would consider this.
Completion of Data Collection for Phase II: Case-Control Study
To be eligibile for this phase of the study, a veteran must have served in Vietnam at any time during the interval 1962-1974 and have had at least one pregnancy after the tour of duty. An indepth survey was developed and sent to the 636 eligible participants from Phase I for complete exposure (military) and reproductive histories. A total of 302 veterans completed the survey, including 76 cases and 226 controls. Data entry and cleaning on these second surveys was completed by May 1, 2002.
Completion of Biological Sampling
From the Phase II respondents, a random sample of the cases (n = 62) and controls (n = 61) were selected for dioxin and genetic polymorphism assays. A total of 55 cases (88.7 percent) and 55 controls (90.2 percent) provided the samples, for a total of 110 blood samples. Budgetary restrictions determined the final number of samples we were able to collect and analyze; there were many additional Vietnam veterans who were willing to participate in this phase of the study but were unableto participate because of limited funds.
All of the samples were sent to Xenobiotics Detection Systems, Inc., for determination of dioxin-like activity using the chemically activated luciferase expression (CALUX) assay (Pauwels, 1999). We then examined the distribution of total toxic equivalency values in the sample, and either dichotomized (high versus low) or trichotomized (high, medium, low) the participants. Again, due to budget constraints, only 30 samples were selected for the complete dioxin analysis by Dr. Olaf Papke at Ergo Laboratories in Germany, weighting towards the more highly exposed veterans identified by the CALUX assay to better understand the potential contribution of specific dioxin congeners to the risk of NTDs.
The analyses comparing the results of the CALUX assay with the dioxin determinations obtained from the gas chromatography/mass spectrometry analysis in Dr. Papke’s laboratory provided a critically needed validation of the CALUX assay. In addition, the M.D. Anderson laboratory performed tests to determine the presence of the wild type versus mutant CYP1A allele under the direction of Dr. Xifeng Wu. Additional tests to determine the levels of insulin-like growth factor-1 (IGF-1), IGF-2, insulin-like growth factor binding-protein-3, and methylenetetrahydrofolate reductase (MTHFR), were performed to enable us to examine their utility as potential biomarkers of exposure and/or effects related to dioxin exposure.
Immediately upon receiving the results of the genetic and dioxin assays from the laboratories, data analysis will begin (expected by summer 2002). The major focus of the analysis will be the relationship between the presence of the wild type allele, serum dioxin level, and occurrence of an NTD among the veterans’ offspring. Multiple analyses are planned to investigate: (1) the relationship between CYP1A polymorphisms, insulin-like growth factors, MTHFR, serum dioxin levels, and NTDs; (2) the association between parenting a child with an NTD and subsequent risk of cancer; and (3) assessment of our dioxin exposure index as a surrogate for serum dioxin analyses in future studies of Vietnam veterans and adverse health effects.
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, neural tube defects, NTD, pesticides, p450 genes, environmental hazard exposures, environmentally caused disease, genetic susceptibility, herbicides, human exposure, human susceptibility, reproductive health,, RFA, Health, Scientific Discipline, Toxics, Genetics, Chemistry, Epidemiology, 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.html Exit
Progress 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.
Project Research Results
- 2002
- 2001 Progress Report
- 2000 Progress Report
- 1999 Progress Report
- 1998 Progress Report
- Original Abstract