People who experience maltreatment in childhood – such as abuse or neglect – are more likely to report poorer physical and mental health.
A new study published in the Lancet looks at how this may be explained by any number of reasons, including social factors, such as family poverty, or partly genetic factors, such as poor parental mental health, which all may result in both childhood maltreatment and poorer health.
But so far, studies have only shown a link between the two.
None have actually shown that childhood maltreatment directly causes poorer mental and physical health.
Our researcher, Varun Warrier, wanted to know if childhood maltreatment directly causes poor mental and physical health. One way to investigate this is by using genetics.
To begin, data on childhood maltreatment with genetic data in over 180,000 people were combined. This allowed us to check whether the differences in people’s experience of childhood maltreatment was linked to differences in their genetics.
We found that only around 9% of these experiences of childhood maltreatment are linked to genetics. But this does not mean that genetics is causal for experiencing childhood maltreatment.
This also does not mean that a child is to blame, or that childhood maltreatment cannot be reduced regardless of the child’s genetics. The genetic signal reflects the environment a child grows in and it shows how important the environment is (such as the conditions a child is raised in) as a known and modifiable risk factor for addressing childhood maltreatment.
We specifically ask if experiencing childhood maltreatment is causal for mental and physical health conditions. We could not do this using RCTs, so we tried using Mendelian Randomization.
We conducted a GWAS of over 180K people using reports of childhood maltreatment. We observed largely similar heritability and modest/high genetic correlations between subtypes, operationalizations, and reporting methods of childhood maltreatment. – Varun Warrier
What does the genetic signal represent? A child is never to blame, and genetic signal does not imply that genes cause childhood maltreatment, or that a risk for childhood maltreatment is immutable. The signal reflects gene-environment correlations (rge). We used multiple within-family methods to tease the various rge mechanisms better. Our findings provide support for active/reactive rge, but does not demonstrate the absence of passive rge.
Finally, we used MR to ask if childhood maltreatment is potentially causal for mental and physical health conditions. We found a unidirectional causal link between maltreatment and depression, and bidirectional links between maltreatment and both ADHD and schizophrenia.
All of this just reinforces what we already know. We need urgent measures to prevent maltreatment, targeting family dynamics. We need better policies in place to support people who have sadly experienced maltreatment. Changing the environment will reflect in the genetics. (7/8)We address other issues in an FAQ buried in the supplementary (pp 93-95) and in a forthcoming piece. – Varun Warrier
The study did not find evidence to suggest that experiencing childhood maltreatment is causal for later physical health conditions, like type 2 diabetes or coronary artery disease.
Ultimately, our research shows genetics can be used as a tool in answering questions about the role of the environment in many health conditions, including those that are difficult – or even impossible – to address solely using other types of study. Our findings also highlight the urgent need for better protective measures to safeguard children at risk for maltreatment – which would also reduce the risk of mental health conditions later in life.
Read the full article Gene-environment correlations and causal effects of childhood maltreatment on physical and mental health: a genetically informed approach in the Lancet>>
Image credit @plhnk