Secure attachment between mother and infant boosts childrens social, emotional and physical development. Many studies have investigated ways to strengthen maternal-infant attachment and how to implement these strategies for maximum effect, particularly in low- and middle-income countries. But few have asked whether genetics can explain why some children are more likely to benefit than others.

In a new study, Barak Morgan at the University of Cape Town in South Africa and colleagues tested whether a genetic polymorphism of the serotonin transporter gene affects maternal-infant attachment. They reanalyzed data from a previous study that showed that home visits from a parenting program called Thula Sana promoted secure maternal-infant attachment in a low-income community in South Africa. Morgans team used the genetic data collected from approximately half of those who participated in the original trial when they were 13 years of age to compare attachment rates for participants with different polymorphisms of the serotonin transporter gene.

The scientists found that the short allele of the serotonin transporter gene may indeed explain why some infants were more likely than others to form strong attachments with their mothers after the home visits. The probability of forming a secure attachment depended on each childs specific versions, or alleles, of the serotonin transporter gene.

For children whose DNA carried one or two copies of the short allele of the serotonin transporter gene, Thula Sana proved highly effective at improving rates of secure infant attachment. Eighty four percent of children with the short allele formed secure attachment after the program, versus just 58 percent of children with the short allele who did not receive home visits.

Children with two copies of the long allele of the serotonin transporter gene, showed no measurable benefit from the home visits. For these children, the probability of secure maternal-infant attachment was 71 percent if the family received home visits and 70 percent if they did not receive the intervention.

The authors note that past research has operated under the belief that maternal attachment programs such as Thula Sana as well as other strategies to improve early childhood development benefit all children equally. The results of this study challenge this assumption, and indicate that the success of such strategies can vary from child to child and is influenced in part by the genetic polymorphism of the serotonin transporter gene.

The authors call for additional research investigating the interactions between genetics and psychosocial strategies that promote early childhood development. Such research could inform global health policy, which is focused intently on strengthening early childhood development to mitigate the harmful effects of poverty.

Research Article: Morgan B, Kumsta R, Fearon P, Moser D, Skeen S, Cooper P, et al. (2017) Serotonin transporter gene (SLC6A4) polymorphism and susceptibility to a home-visiting maternal-infant attachment intervention delivered by community health workers in South Africa: Reanalysis of a randomized controlled trial. PLoS Med 14(2): e1002237. doi:10.1371/journal.pmed.1002237

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Genetics may influence outcome of efforts to promote maternal attachment - PLOS Research News