You like big-budget rom-coms, so you know the drill: Opposites attract. Those two characters who can’t stand each other in act one? Chasing each other through an airport by act three. Well…apparently science does not go to the movies. In fact, according to a new study, genetic similarity may determine who’s going to partner with whom—especially if the similarity is in what kind of psychiatric disorder you have.
Here’s the approach: A study in this month’s issue of JAMA Psychiatry looked at 707,263 Swedish people, all with at least one psychiatric disease: ADHD, schizophrenia, bipolar disorder, anxiety and depression, obsessive compulsive disorder, autism spectrum disorders, and others. The study also looked at individuals with physical ailments—diabetes, Crohn’s disease, rheumatoid arthritis, and so on. (How heritable all these things are is open for debate—they cross multiple genes and environment plays a factor. But all have some genetic component.) And for every person with either a physical or psychological condition, five unaffected subjects were included as control.1
From there, the researchers looked at people’s romantic entanglements over 18 months. People with psychiatric disorders were more likely to end up with someone with a psychiatric disorder, and the chances were higher (marginally) that they’d share the same illness. “In the few studies that have examined partner correlations at the level of diagnoses, the methods have generally relied on small volunteer samples or self/informant reports,” says Ashley Nordsletten, a neuroscientist at the Karolinska Institute in Sweden. This one, though, had clinical diagnoses across the board, working from anonymized medical histories on, as Nordsletten says, “psychiatric conditions that varied in terms of age of onset, nature and severity of symptoms, as well as population prevalence.”
This doesn’t mean that your future spouse’s name is spelled out in the As, Ts, Cs, and Gs of your genetic code. Nordsletten’s numbers are significant, but the effect is tiny. Which is probably fine, because sharing the same psychiatric disorder might not necessarily convey compatibility. Successful relationships—the ones in which couples rate themselves as more “satisfied”—tend to feature partners with complementary, not similar traits. “An example of that kind of trait would be dominance,” wrote Vanessa Bohns, a psychologist at Cornell who studies compatibility within relationships, in an email. “Otherwise you’re either going to be stepping all over each other as you go about pursuing your goals (if both of you wants to be the boss) or you’ll never get started on pursuing them (if no one takes the lead).”
On the other hand, Nordsletten’s criterion for a successful relationship isn’t happiness, but fertility. Because many Swedish people co-habitate rather than legally marry, the study focused on people who were either married or had kids. According to Nordsletten, the birth of a child was just about the only viable way to determine if the couples were really “mated.” Given the study’s focus on individuals who have genetically-linked psychiatric disorders, the psychiatric future of those kids is the really interesting part.
The idea that people with certain psychiatric disorders having kids might be perpetuate or increase the incidence of those conditions isn’t a new one. In 2001, WIRED took a deep dive into the surging rates of autism and Asperger’s syndrome in Silicon Valley. Writer Steve Silberman wondered whether the Bay Area, home of tech’s best and brightest and (sometimes) most spectrum-y, was an uncontrolled, accidental experiment in amplifying the expression of autism spectrum disorders. The question is still in play. According to a report by the San Francisco Bay Area Autism Society, the number of autism cases seen by the California Department of Developmental Services is 15 times as high today as it was in 1990.
But this isn’t some weird attempt to justify controlling who marries whom. Nordsletten hopes that her research will help clarify the ways that these disorders are transmitted from parent to child, and allow caregivers to better manage these often ill-understood conditions. So that means the next step is to see how the partners’ diagnoses manifest in their genotypes. And after that? “Following up with the children of these couples would also be a natural companion to this work,” Nordsletten says. Maybe science doesn’t watch movies, but that does sound like a pretty good sequel.
1UPDATE: This story has been updated to correct the representation of the study’s methods.