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Seattle Epidemiologic Research and Information Center (ERIC)


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Vietnam-Era Twin Registry - Registry, Data & Biospecimen Repository

The Vietnam-Era Twin (VET) Registry is composed of a registry, data repository, and biospecimen repository.


The Registry is a database of contact information for Vietnam-era male twin pairs who met the criteria for “twinship”, according to Department of Veterans Affairs (VA) and Department of Defense (DoD) records at the time the VET Registry was established in the early 1980s. Read more about how the VET Registry was formed at the History & Formation page. Contact information on the twins is updated regularly. We also have contact information from selected offspring of the twins and contact information for the mother of the offspring.

Data Repository

The VET Registry maintains study data in its data repository. Data collected from twin and family members are fully curated and documented for use. Longitudinal data is available on many health and disease phenotypes including post-traumatic stress disorder (PTSD), body mass index, diabetes, cardiovascular disease, depression, and substance use. This information is a valuable tool for researchers who want to study the health outcomes of our members.

We also have genomic and other omic measures as part of the data repository. These data are from a subgroup of the full twin registry membership from whom blood was collected and DNA extracted. Data include measured and imputed genome-wide markers, epigenetic markers, and whole-genome sequencing. 

Biospecimen Repository

The VET Registry collects biological samples, such as blood or saliva, as part of certain Registry studies and projects. If members give their permission, these samples are stored in the biospecimen repository and serve as another valuable tool for researchers. The Registry’s biorepository is located at the Boston VA Massachusetts Veteran Epidemiology Research and Information Center (MAVERIC), which has robotic sample processing and retrieval capabilities.

Storage & Confidentiality

The VET Registry has developed a system of protocols for the collection and storage of biological specimens that assures confidentiality for all participants. The MAVERIC Laboratory staff have no phenotypic (non-genetic) information about VET Registry members, such as identity, disease characteristics, and any other research data collected from VET Registry members.

Before a VET Registry member decides whether to participate in the Biospecimen Repository, the procedures, confidentiality safeguards, and potential risks are explained in great detail. To be able to accommodate the wishes of members, a layered consent process is used so members can choose from several options about how their biological specimen will be used in current or future research studies.

Members are informed that any future use of their samples will be approved by the VET Registry, in addition to an independent ethics committee that protects the rights and welfare of research subjects, this board is more commonly known as an Institutional Review Board or IRB.

Zygosity Testing for Research

DNA from the biorepository can be used to determine if twins are monozygotic (identical) or dizygotic (fraternal). By comparing the DNA of the 2 brothers, we can learn about the extent of relatedness in the 2 DNA samples. The DNA information can then be used to estimate—very accurately—if the twins share complete DNA information (both brothers originating from a single egg fertilized by a single sperm; i.e., monozygotic) or if they share partial information (each brother originating from 2 different eggs fertilized by different sperms; i.e., dizygotic).

The VET Registry conducts DNA-based zygosity if there is DNA is available in the biorepository from both brothers of a twin pair as well as funding to pay for testing. Otherwise, the Registry relies on zygosity estimates based on standard questions twins have answered in past surveys. Zygosity estimates from these types of questionnaires are thought to be accurate 91% to 98% of the time (Forsberg, Goldberg, Sporleder, & Smith, 2010, PMID: 20874468, DOI: 10.1375/twin.13.5.461).