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Environmental risk for obsessive-compulsive symptoms: findings from a recent genetically-informative study

As a Clinical Psychologist working with young people who suffer from obsessive-compulsive disorder (OCD), I am often asked by my patients: “Why me?”. Young people want to know why it is that they have ended up being burdened with the distressing intrusive thoughts and relentless compulsions that make up OCD. Similarly, their parents question why OCD emerged in their otherwise happy and healthy child, sometimes seemingly out-of-the-blue. At the moment, our answer to the question of why some young people develop OCD is basically: “We don’t know”.

What we do know? What don’t we know?

Twin studies suggest that approximately 50% of the variance of OCD symptoms in youth is accounted for by genetic influences, with the remainder being attributed to the non-shared environment [1]. What’s surprising, is that we know virtually nothing about the specific aspects of the environment that confer risk for OCD. A large range of possible candidates have been suggested, ranging from perinatal complications to parenting style [2]. However, most studies have only shown cross-sectional associations[2]and, as any psychology graduate will tell you, correlation does not imply causation.

Another problem with previous research on environmental risk for OCD is that virtually no studies have attempted to control for genetic confounding [2]. This issue might be a bit trickier to get your head around. Let’s think about stressful life events as an example of an “environmental” risk. Many studies have shown that the likelihood of an individual experiencing stressful life events is influenced their genetic make-up [3]. For example, they might be genetically predisposed to seek out certain environments or evoke particular reactions from their environment, which places them at risk of stressful life events. As I already mentioned, we also know that OCD is partly driven by genetic factors. So what if some of the same genes that affect OCD also influence the likelihood of experiencing stressful life events? It would mean that OCD and stressful life events tend to co-occur, but this association would be (at least partly) due to shared underlying genetic risk.  In order to demonstrate that something is a true environmental risk, independent of genetic effects, we need research using genetically-informative designs.

What is new?

We recently conducted a study of environmental risk factors for adolescent obsessive-compulsive symptoms (OCS), which was published online this week in European Psychiatry [4]. The study used data from the Genesis 12-19 project, a longitudinal twin study. We tested the hypothesis that punitive parenting style and stressful life events are risk factors for obsessive-compulsive symptoms during adolescence. Here are some of the key findings:

  1. Maternal punitive parenting, paternal punitive parenting and stressful life event were all positively associated with concurrent OCS at age 15 and later OCS at age 17.
  2. Earlier punitive parenting from mothers (but not fathers) and stressful life events were independent predictors of later OCS.
  3. Only stressful life events predicted changes in OCS from age 15 to 17 years.
  4. The longitudinal association between stressful life events and change in OCS was due to both genetic (48%) and environmental (52%) influences.

Where next?

Our findings support the notion that stressful life events are an environmental risk factor for OCS, above and beyond genetic confounding But it is also notable that life events only explained a small proportion of the variance in OCS after controlling for genetic effects. They are therefore probably only one small piece of the very large puzzle that makes up environmental risk for OCD. We need more prospective, genetically-informative studies to identify other specific environmental risk factors for OCD. From a clinical-perspective, this is important because at least some of these factors may be modifiable, and provide targets for early intervention and prevention programmes.

 

References

[1] van Grootheest DS, Cath DC, Beekman AT, Boomsma DI. Twin studies on obsessive–compulsive disorder: a review. Twin Research and Human Genetics. 2005;8:450-8.

[2] Brander G, Pérez-Vigil A, Larsson H, Mataix-Cols D. Systematic review of environmental risk factors for Obsessive-Compulsive Disorder: A proposed roadmap from association to causation. Neuroscience & Biobehavioral Reviews. 2016;65:36-62.

[3] Kendler KS, Baker JH. Genetic influences on measures of the environment: a systematic review. Psychological medicine. 2007;37:615-26.

[4] Krebs G, Hannigan L, Gregory A, Rijsdijk F, Maughan B, Eley T. Are punitive parenting and stressful life events environmental risk factors for obsessive-compulsive symptoms in youth? A longitudinal twin study. European Psychiatry. 2019;56:35-42.