Since the time of Sir Francis Galton, studies of human twins have provided material with which to study the relative effects of genetics and environment. When identical twins are more similar with respect to some characteristic than fraternal twins, this is taken as evidence of a genetic influence on a particular characteristic. In 1958, the Medical Follow-up Agency began a project to identify white male twins who had jointly entered military service during World War II, an effort funded by the National Institutes of Health and the Veterans Administation. Beginning with birth records provided by 42 vital statistics offices, 108,000 searches were made by hand against VA files to determine veteran status. In the end, nearly 16,000 twin pairs were identified in which both members had served in the military.

Certain baseline data were abstracted from VA and military records, an initial questionnaire was mailed to the twin pairs, and anthropometric and fingerprint data were used to determine zygosity (i.e., to differentiate identical from fraternal twins). Interestingly, the single best question for determining zygosity by self-report was, As children, were you and your twin as alike as two peas in a pod?  This is essentially a translation of a similar item used in the Danish and Swedish twin registries and accurately predicts zygosity roughly 95 percent of the time. Subsequent follow-up data have come primarily from computerized VA records and mail surveys. A subset of roughly 500 twin pairs, the National Heart, Lung, and Blood Institute twins, have been examined by investigators four different times at clinical centers around the country.

More than 200 journal articles have made use of the Twin Registry. Published articles cover a variety of topics. Among these are articles on smoking and respiratory function, schizophrenia, heart disease, bone mass, eye disease, type A behavior, blood chemistry profiles, headache, blood pressure, personality traits, financial earnings, dietary intake, fingerprint patterns, weight change and body fat distribution, alcoholism, cancer, diabetes, antisocial behavior, Alzheimer's disease, alcohol and tobacco consumption, suicide, declines in cognitive functioning, and prostate disease.

Recent studies of the Twin Registry are listed on the left.

Operating Principles:
 

The NAS-NRC Twin Registry operates under a set of principles designed to maintain and protect the Registry as a resource for research. Requests for access to the Registry are carefully considered to protect the twins' privacy against unwarranted intrusion; to avoid unauthorized disclosure of confidential information and unnecessary harm caused by experimental manipulation; to assure that the scientific value of each proposed study is weighed against the financial and socials costs to be incurred; to prevent too frequent contact of the twins by investigators or conflicting demands by different investigators; and to coordinate the efforts of the investigators. For these reasons, every application for access to the Registry is reviewed by the Subcommittee on Twins.

Information on Accessing the Registry

More Information on NAS-NRC WWII Veteran Twins Registry