fTwin studies compare similarities and differences between identical twins with those between fraternal twins. Stronger similarities between identical twins than between fraternal twins are assumed to be rooted in their genes. Significant differences between twin siblings, whether identical or fraternal, point to environmental influences.

Understanding the environmental versus the genetic contribution is a leg up in a long climb. If you find genetic influences dominate, you can drop your search for environmental causes and go after the genes responsible. If theres only a weak genetic basis, you can skip the gene hunt and start tracking down suspected environmental causes. Either way, you save time and money.

It was that economy that spurred the creation of the SRI Twin Registry 25 years ago.

In 1995, SRI researcher Gary Swan, PhD, initiated the registry to further his nicotine metabolism, addiction and cessation research.

Finding more effective ways to help smokers quit has been a major theme of my career, said Swan, who for many years directed SRIs Center for Health Science. Relapse rates following smoking cessation can be as high as 70% among smokers who want to quit.

Now an adjunct lecturer affiliated with the Stanford Prevention Research Center, Swan has authored or co-authored hundreds of papers tied at least in part to the study of twins. These studies allowed him to show, among other things, that about 50% of addiction is genetic, suggesting that treatments to aid smoking cessation can be tailored to individuals rates of nicotine metabolism.

Several Stanford scientists have used the SRI Twin Registry. About a decade ago, Martin Angst, MD, professor of anesthesiology, perioperative and pain medicine, wanted to know whether patients responsiveness to the analgesic effects of opioids varied because of genetic influences. Angst recruited participants from the registry to find out. In a couple of papers published in 2012, he concluded that of five distinct dimensions of opioids action analgesia, euphoria, nausea, respiratory depression and addiction only one of them, nausea, varied in degree largely due to genetic influences.

Meanwhile, Angst told Davis about the SRI Twin Registry. Davis was contemplating a study on the relative contributions of the environment and genes to immune responsiveness.

The twins in the registry ranged from infancy to 90 years old. This allowed Davis to see whether similarities the researchers observed in the immune responses of young twins were stronger than those found in older twins, which would indicate that twins diverging environments, as they moved away from home and from each other, affected their immune response to influenza vaccination.

In 2015, Davis reported inCellthat the environmental contribution in many ways dwarfed genetic factors.

While there are larger twin registries in the United States and one in China with half a million registrants its the only twin registry in Northern California.

But with Swans retirement in 2014, SRI gradually deprioritized the twin registry. In January 2019, with Swans blessing, Lisa Jack, a senior project manager at SRI, asked Davis if he could take over the registry. He responded enthusiastically.

By November, the transfer was a done deal, and the ITI Institute was actively recruiting twin pairs. In late October, the institute sent emails to most of the intact twin pairs from the SRI registry, offering them a mug emblazoned with a colorful logo: Stanford Twins Registry.

But only if they sign up, Davis said.

So far,600 individuals from the SRI registry and about 500 brand-new recruits have climbed aboard.

Davis wants to get the word out to other Stanford researchers, too. In mid-2019, Philip Grant, MD, assistant professor of infectious diseases and the Stanford Twin Registrys newly appointed director, sent out an anticipatory notice alerting the institutes faculty of the registrys impending transfer.

That was a trial run, Davis said. We want to reach the whole community.

Having the registry reside on campus should mean reduced overhead and less paperwork, making it easier for Stanford scientists of all stripes to explore genetic versus environmental influences on all sorts of human traits and outcomes.

Theres a lot of value in having it here, said Michael Snyder, PhD, professor and chair of genetics and the Stanford W. Ascherman, MD, FACS, Professor in Genetics. Having the registry at Stanford will put it right in front of our researchers faces.

You never know all the possibilities until people show up and start doing things, Davis said. People will find all kinds of ways to study twins thattheyhavent thought of yet.

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Twin peeks: Stanford inherits twin registry, expanding research options - Stanford Medical Center Report