Quick to laugh or smile? It may be in your genes, says a study

Genes may be responsible for why some people immediately burst into laughter after a humorous moment while others can barely crack a smile, scientists say.

Researchers have found that people with a certain genetic variant - those with short alleles of the gene 5-HTTLPR - smiled or laughed more while watching cartoons or subtly amusing film clips than people with long alleles.

Claudia M Haase of Northwestern University and Ursula Beermann of the University of Geneva co-authored the study, which was conducted in the laboratories of Dacher Keltner and Robert W Levenson at the University of California, Berkeley.

In the study, the scientists looked at short and long alleles of the gene 5-HTTLPR, which is involved in the regulation of serotonin, a neurotransmitter implicated in depression and anxiety.

An allele is a variant of a gene. Each gene has two alleles; humans inherit one allele from mother and one from father.

The new study adds to the growing body of evidence suggesting that people with short alleles also may be more sensitive to the emotional highs of life, researchers said.

"Having the short allele is not bad or risky. Instead, the short allele amplifies emotional reactions to both good and bad environments," said Haase.

"People with short alleles may flourish in a positive environment and suffer in a negative one, while people with long alleles are less sensitive to environmental conditions," Haase added.

The new study combined three experiments from different Berkeley labs. In the first experiment, young adults were shown cartoons from "The Far Side", 'medicalxpress.com' reported.

In the second experiment, young, middle-aged and older adults watched a subtly amusing clip from the film "Strangers in Paradise." The final experiment asked middle-aged and older spouses to discuss an area of disagreement in their marriage. The scientists videotaped the volunteers during the experiments.

Overall, 336 participants were included in the final analysis. The researchers also collected saliva samples from the volunteers to analyse the 5-HTTLPR gene.

The data from the three experiments combined indicated that people with the short allele of 5-HTTLPR showed greater positive emotional expressions.

Specifically, people with the short allele displayed greater genuine smiling and laughing than people with the long allele.