Wednesday, November 30, 2016

The genetics of loneliness

So you’ve got a massive social circle, and some of them are actual friends, not just the Facebook kind. But you just can’t shake off that gnawing sense of isolation — like that awkward feeling that washes over you when swaying alone in the corner at a party, cocktail (or more) in hand. You’re probably not being dramatic, and it might not all be in your head. New research suggests that genetics plays a role. In a September Neuropsychopharmacology study, scientists reported that  14 to 27 percent of loneliness can be explained by our genes.

Other factors, like age and marital status, might also play a role. The researchers saw significant genetic similarities among individuals with high levels of loneliness, neuroticism and depressive symptoms, suggesting that people often inherit these traits together.

John Cacioppo of the University of Chicago, a study co-author, has proposed that we crave social contact in much the same way we feel hunger. Just as hunger alerts us to low blood sugar levels and drives us to seek food, loneliness alerts us to possible risks — indeed, earlier studies have cited loneliness as a risk factor for heart disease, cognitive decline and early death — and drives us to seek the company of others. Abraham Palmer, who led the study and whose lab at the University of California, San Diego studies the connection between genes and behavior, wanted to investigate whether genetics would influence how strongly someone feels these lonely urges…

“We’re not measuring whether someone has a lot of social contacts or not, but whether people perceive themselves as being lonely,” Palmer explains. To do that, Palmer and his team measured genetic variations, known as single-nucleotide polymorphisms, or SNPs, in the participants’ DNA and correlated them to their score on the three-question loneliness scale. They found that 14 to 27 percent of loneliness can be explained by genes we inherit. That falls below the 37 to 55 percent heritability that earlier studies had calculated, which could be because the method Palmer’s team used directly measures only common, not rare, genetic variations…

The remaining 73 to 86 percent might be due to life circumstances. Married participants felt less lonely than unmarried participants, and in fact, to Palmer’s surprise, loneliness declined with age. Biological sex had little influence on the tendency to feel lonely.

The researchers also saw strong genetic similarities among people who scored high on loneliness, neuroticism and depressive symptoms. In other words, someone who inherits one of these traits has probably also inherited the other two. Palmer’s team also saw weaker links between loneliness and schizophrenia, bipolar disorder and major depressive disorder.

Like with most psychiatric and personality traits, the researchers found that many genes collectively contribute to loneliness. But since each individual gene makes only a tiny contribution, they couldn’t pinpoint the exact genes involved. They recently launched a follow-up study with threefold the number of participants, which they hope will boost the signal strength of these genes enough so they can identify them.

To be sure, loneliness is a complex psychological state, which the three-question loneliness scale — a shortened version of the original 20-question scale — might not precisely measure, says Francis McMahon of the National Institute of Mental Health. “Are the questions really measuring what we think they’re measuring?” he wonders. Although the researchers noted a high correlation between the shortened and full-fledged scale, loneliness “isn’t like height, for example, or a disease diagnosis. It isn’t something that is necessarily always present,” he says. “It’s tough to measure.” But overall, he believes “it’s a very well-designed, well-executed study.”

And “genetics isn’t destiny,” Palmer says. “There are some people who have genetic tendencies to be one way or another, but the effects are never so strong … as to guarantee one person would be lonely and one person would not.” Still, “lots and lots of aspects of the human experience are influenced by genetics.” So if you find yourself frustrated over quips to “just get over it,” remember that your loneliness might be hardwired, at least to some extent.

1 comment:

  1. Gao J, Davis LK, Hart AB, Sanchez-Roige S, Han L, Cacioppo JT, Palmer AA. Genome-Wide Association Study of Loneliness Demonstrates a Role for Common Variation. Neuropsychopharmacology. 2016 Oct 12. doi: 10.1038/npp.2016.197. [Epub ahead of print]

    Loneliness is a complex biological trait that has been associated with numerous negative health outcomes. The measurement and environmental determinants of loneliness are well understood, but its genetic basis is not. Previous studies have estimated the heritability of loneliness between 37 and 55% using twins and family-based approaches, and have explored the role of specific candidate genes. We used genotypic and phenotypic data from 10 760 individuals aged greater than or equal to50 years that were collected by the Health and Retirement Study (HRS) to perform the first genome-wide association study of loneliness. No associations reached genome-wide significance (p>5 × 10−8). Furthermore, none of the previously published associations between variants within candidate genes (BDNF, OXTR, RORA, GRM8, CHRNA4, IL-1A, CRHR1, MTHFR, DRD2, APOE) and loneliness were replicated (p>0.05), despite our much larger sample size. We estimated the chip heritability of loneliness and examined coheritability between loneliness and several personality and psychiatric traits. Our estimates of chip heritability (14–27%) support a role for common genetic variation. We identified strong genetic correlations between loneliness, neuroticism, and a scale of ‘depressive symptoms.’ We also identified weaker evidence for coheritability with extraversion, schizophrenia, bipolar disorder, and major depressive disorder. We conclude that loneliness, as defined in this study, is a modestly heritable trait that has a highly polygenic genetic architecture. The coheritability between loneliness and neuroticism may reflect the role of negative affectivity that is common to both traits. Our results also reflect the value of studies that probe the common genetic basis of salutary social bonds and clinically defined psychiatric disorders.