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Vietnam-Era Twin Registry - Mission, History, Formation

In the United States, there is a scarcity of twin registries, which has been a serious impediment to research. Several states possess twin registries.(1-2) The largest national twin registry in the US is the National Academy of Sciences Medical Follow-up Agency (MFUA) WWII Twin Registry.(3) 

The VET Registry is the only other national registry of twins in the United States.(4)


The VETR Registry mission is:

  • To promote and advance high-quality scientific research in partnership with Vietnam-era Veteran twins and their families
  • To maintain a secure and current Registry database and biospecimen repository as a resource for future studies
  • To treat Registry members and their families with respect and maintain their confidentiality


The VET Registry was formed in the early 1980s in response to concerns regarding the long-term health effects of military service during the Vietnam era. Between 1964-1975, nearly 9 million Veterans served on active duty and roughly one-third served overseas in Southeast Asia. As these Veterans returned home, there was concern about the post-discharge health of those who had been deployed. In order to examine the health effects of military service in Southeast Asia, the Department of Veterans Affairs (VA) Cooperative Studies Program (CSP) funded a research project entitled The Vietnam-Era Twin Study. The basic rationale for this study was to compare the health of Veteran twin pairs who both served on active duty during the Vietnam-era. Of particular interest were the subset of twin pairs who were discordant for service in Vietnam (one brother served in Vietnam while his co-twin was in the military but did not serve in the Vietnam theater). An essential first step in this study was the identification of a large sample of Vietnam-era Veteran twin pairs to form the Vietnam-Era Twin Registry.  

The presentation, The VET Registry: A 30 year compendium of scientific research, by Dr. Jack Goldberg explains the VET Registry history and uses publication data to analyze the scientific productivity of the VET Registry.  


The VET Registry is a VA resource originally constructed in the 1980s using military records.  During the Vietnam-era the Department of Defense (DoD) was transitioning their administrative record-keeping from traditional pencil and paper methods to more modern electronic database systems. For all 9 million service personnel who were on active duty during the Vietnam-era, neither the hardcopy records nor the computerized data contained a field that indicated whether a serviceman was a member of a twin pair. Hence, a computerized record matching system was developed to identify pairs of records from the DoD that were likely to represent twins based on the following criteria:  

  • Males
  • Born between 1939 and 1957
  • Served on active duty during the Vietnam era (the interval 1964-1975)
  • Same last name
  • Different first name
  • Same date of birth, and
  • Same first 5 digits of the Social Security number

Then, using information from manual searches of hard-copy discharge records, “twinship” was confirmed when there was an exact match on place of birth and parental names. In total, 7,369 twin pairs (14,738 individuals) were identified. 

When the Registry was constructed, the DoD estimated that only 5.5 million out of the estimated 9 million Vietnam-era Veterans were included in their records. Because of this, the VET Registry does not include all the twins who both served in the military during the Vietnam-era.

The VET Registry is a Closed Cohort

The VET Registry is a closed cohort based on the original 7,369 twin pairs and is not currently recruiting new members. 

Mothers and Offspring of VET Registry Members

In the late 1990s, VET Registry investigators proposed a novel idea to launch studies that involved the offspring of twin pairs and the mothers of the offspring. By adding these new members the investigators felt that the enhanced Registry would better be able to separate the genetic and environmental causes of health and illness. At the time, the Registry only included twin pairs and so a new recruitment was undertaken with a selected group of offspring and offspring mothers. This effort resulted in 2,200 offspring and 1,300 mothers being added to the membership rolls of the Registry. These members continue to be an important component of the VET Registry.

(1) Lykken D. T., et al. (1990). The Minnesota twin family registry: some initial findings. Acta Geneticae Medicae et Gemellologiae, 39(1): 35-70.
(2) Lilley E. C. & J. L. Silberg. (2013). The mid-atlantic twin registry, revisited. Twin Research and Human Genetics, 16(1): 424-428.
(3) Page, W. F. (2006). Update on the NAS-NRC twin registry. Twin Research and Human Genetics, 9(6): 985-7. 
(4) Tsai M. et al. (2013). The vietnam era twin registry: a quarter century of progress.  Twin Research and Human Genetics, 16(1):429-36.