Genes may influence susceptibility to interventions promoting maternal-infant attachment

Infants with a genetic polymorphism of the serotonin transporter gene may be more susceptible to a psychosocial intervention designed to promote maternal-infant attachment in South Africa, according to a study in PLOS Medicine. In a study led by Mark Tomlinson from Stellenbosch University, South Africa, with lead author Barak Morgan from the University of Cape Town, South Africa and colleagues, data from a randomized controlled trial were reanalysed in light of new genetic data.

In the study, researchers reanalysed data from a randomized controlled trial that was originally published in 2009. This had found that infants whose mothers were visited by lay community workers to provide support and guidance in parenting were significantly more likely to be securely attached to their primary caregiver after 18 months. Using genetic data collected from 220 participants when they were 13 years of age (approximately half of those who participated in the original trial) the researchers were able to compare attachment rates for participants with different polymorphisms of the serotonin transporter gene. Individuals with the short form of the gene, which is involved in nerve signalling in the brain, have previously been found to be sensitive to psychosocial interventions.

The researchers found that, for those with the short allele of the serotonin transporter gene, the probability of secure attachment being observed for those who received the intervention was 84% (95% CI [73%, 94%]), compared to 58% (95% CI [43%, 72%]) in the control group. For those with two copies of the long allele of the serotonin transporter gene, the probability of secure attachment being observed for those who received the intervention was 70% (95% CI [59%, 81%]), compared to 71% (95% CI [60%, 82%]) of infants in the control group.

The researchers note, "[b]eyond illuminating the role of genetic differential susceptibility in early childhood development, the current finding also speaks to a fundamental issue in the quest to understand and mitigate the developmental effects of poverty through psychosocial intervention. The near large effect size reported here for the intervention in children with susceptible genotypes […] is at variance with the general conclusion that psychosocial interventions in the context of poverty produce only small to medium effect sizes […] Without taking account of genetic susceptibility, it is possible that other intervention studies have, at least in some subpopulations, underestimated the impact of their interventions, as we originally did. By the same token […] other studies might also have underestimated the negative impact on susceptible subpopulations of not receiving an intervention […] In short, averaging outcomes across all participants may well lead to an invalid conclusion about the efficacy of an intervention.

The researchers also note, "[a]n important limitation of this study is that we were not able to follow-up all cases of the individuals from the original trial, and there were missing data for attachment and genotype. In total, our primary analysis included 49% (220/449) of the original sample of children whose mothers were randomized to treatment and control conditions. Although the intervention and control groups were highly similar in our follow-up sample, and the follow-up sample was generally very similar to the original sample, there was some evidence of selective loss to follow-up on two variables […] This means that randomization within our follow-up subsample may have been imperfect. Attribution of the primary outcome to causal effects of treatment in the present subsample should therefore be treated with caution.


Research Article


This study was supported by a grant from Grand Challenges Canada, grant reference #0066-03). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests:

MT is a member of the Editorial Board of PLOS Medicine. PF received an honorarium for providing a workshop on attachment at the Meeting of Minds Conference, organised by Shire Pharmaceuticals.


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

Author Affiliations:

Global Risk Governance Program, Department of Public Law, University of Cape Town, Rondebosch, South Africa
NRF Centre of Excellence in Human Development, DVC Research Office, University of
Witwatersrand, Johannesburg, South Africa
Neonatal Unit, Department of Women's and Children's Health, Karolinska Institute, Stockholm, Sweden
Department of Genetic Psychology, Faculty of Psychology, Ruhr University Bochum, Bochum, Germany
Research Department of Clinical, Educational and Health Psychology, Faculty of Brain Sciences, University College London, London, United Kingdom
Department of Psychology, Stellenbosch University, Stellenbosch, South Africa
School of Psychology and Clinical Language Sciences, University of Reading, Reading, United Kingdom
Department of Psychology, University of Cape Town, Rondebosch, South Africa
Department of Psychology, Western University, London, Ontario, Canada


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