While we are all well aware of how our genetic make-up influences a host of individual characteristics, a study conducted by Prof Mark Tomlinson of the Psychology Department at Stellenbosch University, has now revealed a large, hidden role that a child's genetic make-up can play in intervention efforts to maximise his or her development.
The study, which will be published on 28 February in PLoS Medicine, was funded by the Government of Canada through Grand Challenges Canada's Saving Brains programme and sheds new light on why some children benefit more than others from interventions. It also raises complex questions about psychosocial intervention programmes in future.
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"These findings provide the tantalising possibility of being able to better focus intervention efforts to ensure that everybody receives the appropriate interventions that they need to optimise the development of their children," says Principal Investigator Tomlinson who conducted the study in collaboration with other colleagues from Stellenbosch University, University of Cape Town, University of Reading (UK), the University College London, and Ruhr-University Bochum, Germany.
In the original study an intervention was implemented between 1999 and 2003 in which expectant mothers received a home-visiting parenting intervention to improve attachment with their children. Attachment was used as a measure of a child's psychological security and is predictive of future well-being. In that study Tomlinson, together with colleagues from the University of Reading, the University of Cape Town and the Parent Centre, found that the intervention had a small-to-moderate effect on mother-child attachment, which was evaluated once the child reached 18 months of age.
The follow-up study, conducted nine years later, re-examined the original attachment results and revealed something surprising.
"The intervention had in fact worked well for toddlers who had a particular genetic characteristic," says Tomlinson.
In the follow-up study, caregivers and their children were re-enrolled and the original attachment results were re-analysed based on whether the child had the short or long form of gene SLC6A4.
"This enabled the investigators to test whether the original attachment outcomes were influenced by a gene-intervention interaction," says Tomlinson.
The researchers factored in whether the child had the short or long form of gene SLC6A4 — the serotonin transporter gene, which is involved in nerve signalling, and which other studies have linked to anxiety and depression. Serotonin is popularly thought to contribute to feelings of well-being and happiness. Previous studies have also shown that individuals with the short form of SLC6A4 are generally more sensitive or 'susceptible' to psychosocial interventions, in other words, they benefit when they get it, and do not benefit or actively suffer harm when they do not get it.
The attachment of children with the short form of the gene, and whose pregnant mothers received the intervention, were almost four times more likely to be securely attached to their mothers at 18 months old (84%) than children carrying the short form whose mothers did not receive home visits (58%).
Meanwhile, children with the long form of the gene were apparently unaffected by their mother's training or lack thereof: in both cases, the children's rates of secure attachment were almost identical (70 and 71% percent). According to lead author Dr Barak Morgan this "may mean that this group of children appear less susceptible and derived little benefit from the same intervention, and little detriment from not getting it".
"Our findings are subject to further validation," says Tomlinson "but the insight has important implications for scientists designing and evaluating interventions to benefit as many people as possible in South Africa and worldwide. Without taking genetics into account, it is possible that other studies have underestimated the impact of their interventions, as we originally did."
"This is an enormously important insight because, in this case, the subgroup with the short form of the SLC6A4 gene is also the one with the most to lose if not helped," says Morgan.
Indeed, separating the effects of an intervention on different subgroups will allow researchers to better detect when interventions work, and for whom.
Adds Professor Tomlinson: "In the original study, we did not see such a big impact from this intervention because only those with the short gene improved, and this improvement was 'diluted' by the large number of children with the long gene who did not improve."
Tomlinson cautions that, among other limitations, this study involved a relatively small sample and only measured one gene and one outcome – in this case, attachment.
"Going forward, the implications are therefore two-fold. Firstly, measuring genetic differences will allow for proper assessment of the effectiveness or lack of effectiveness of an intervention for a particular outcome in different individuals. Secondly, this information can then be used to find out how to intervene effectively for all – to guide what might be done to improve outcomes for a non-responsive gene-intervention interaction while continuing to optimise outcomes for the responsive one."
Commenting on the findings, Dr Karlee Silver, Vice President: Programs at Grand Challenges Canada says: "This work is fundamentally about better understanding the impact of interventions and shows that some outreach efforts may be much more effective than we thought, especially for those for which it matters most — for children most susceptible to harm from poverty, poor nutrition and other adverse conditions."
"This is an important step forward to creating a world where every child can survive and thrive."