Twins Research

With their similar genetic makeup, twins represent an ideal opportunity to study health and behavior issues. From twin studies, it is possible to determine how genetic and environmental factors influence health. Studies can also provide scientific insights into twins and genetics, including conditions such as diabetes, heart disease, and obesity, as well as the effects of alcohol and tobacco use. By identifying the genetic components of these health problems and others through twins research, it is possible to develop early interventions and treatments.

For the National Institutes of Health and other clients, researchers at SRI's Center for Health Sciences conduct twins research studies on the pharmacokinetics of nicotine, the metabolism of commonly used medications, genetic susceptibility to cancer-causing chemicals, and sleep patterns in young twins.

The continually growing and diverse Twin Research Registry at SRI International™  includes more than 3,000 members who volunteer to participate in SRI twin research studies.

Twin Facts and Figures

Fascination with twins is part of every culture -- and dates back centuries. Some interesting twin "facts and figures" include:

  • In ancient times, doubleness in nature was often interpreted as a manifestation of the supernatural or intervention by the gods -- that is why many gods in different religions are twins or supertwins.

  • In the Aztecs, Babylonian, Zuni and Ashanti cultural myths, twins took the form of warriors, builders, healers, symbols of light, water or thunder.

  • Native American tribes in the Northwest believed that twins were actually salmon in human disguise.

  • The frequency of twin births reported vary from country to country and range from 1 in 80 to 1 in 140.

  • When it comes to phobias -- like fear of heights, of closed spaces, or of open spaces -- twins often respond similarly. Twins often share phobias, and more often than not if one twin harbors an irrational fear, the other does too.

For more information on twins research and twin registries, watch these videos about "Twins: Unlocking the Secrets of Nature-Nurture Interactions": Background on twins research and an overview of Twin Registries from Dr. Gary Swan's talk at Cafe Scientifique Silicon Valley.


An SRI vaccine researcher in protective clothing and a mask

To help prepare for next-generation pandemics, SRI is partnering with Stanford University to examine vaccination responses.

Twins on bicycles

SRI studied twins to gain more clinical insight into physiologic response to powerful opioid painkillers. Study results should help to optimize pain relief and minimize adverse effects.

twin boys

SRI established the Twin Research Registry as part of its scientific research and efforts to discover more about human behavior. Fraternal and identical twins and multiples of all ages are invited to join the Registry for consideration for research studies.

Press Releases

SRI International, an independent nonprofit research and development institute, is seeking healthy fraternal and identical twin pairs for the second year of a flu vaccine study sponsored by the National Institutes of Health.

Topics: Twins Research

SRI In the News

This article reports that the work of Gary Swan, director of the Center for Health Sciences at SRI International inspired the Center for Health Sciences to create the Twin Research Registry™ at SRI International.

Topics: Twins Research

This article discusses the importance of twin registries and twin studies, and says that the Twin Registry at SRI is currently seeking twins for a number of studies, including a seasonal flu vaccine study, sponsored by the National Institutes of Health to develop more effective flu vaccines.

Topics: Twins Research


To assess the relative contribution of heritable versus non-heritable factors, we have performed a systems-level analysis of 210 healthy twins between 8 and 82 years of age. Members of SRI's Twin Research Registry participated in the study.

Natural killer (NK) cells play critical roles in immune defense and reproduction, yet remain the most poorly understood major lymphocyte population. Their cell diversity and function are closely linked.

Topics: Twins Research

The clinical utility of opioids is limited by adverse drug effects including respiratory depression, sedation, nausea, and pruritus. In addition, abuse of prescription opioids is problematic.

Topics: Twins Research

Opioids are the cornerstone medication for the management of moderate to severe pain. Unfortunately, vast inter-individual differences in dose requirements complicate their effective and safe clinical use.

Topics: Twins Research

Blog Posts

Through twin studies, scientists understand the interplay between genetics and the environment in ways that the study of unrelated people–or even other types of siblings–is unable to do.