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Key points
- A new study on genetic factors and mental health symptoms finds core symptoms are linked to genetic risk.
- Symptoms of conditions that frequently occur, such as anxiety and depression, may share genetic influences.
- Genetic influences on traits important for mental health may affect processes shared across conditions.
- Thinking of mental health conditions as collections of symptoms may help us understand their complex origins.
A person who suffers from a particular mental health condition, such as depression, can show a wide variety of symptoms—problems with sleeping, regulating emotions, and concentrating. But are all symptoms equal? And how do they relate to genetic factors? Our new study looks into the genetic risk for mental health conditions and how it relates to individual symptoms.
Zooming In: Individual symptoms of mental health conditions
Mental health conditions are measured by checking the presence of specific symptoms. For example, a person may experience two weeks of sadness, sleep problems, and concentration problems, which, along with other indicators, may prompt a clinician to diagnose depression. In research, such symptoms are usually aggregated into a single measurement, such as an aggregate score on a psychological scale, measuring how depressed each individual is.
However, symptoms of mental health conditions are not equal in their impact on people’s lives. For instance, specific depression symptoms, such as feeling sad and having problems concentrating, seem to affect work and social life more than others. In much the same way, some symptoms may react more to medication or psychological therapy.
Research also suggests that family history is a strong predictor for mental health problems, and that part of this is due to genetic (not environmental) factors. However, rather than one specific gene, evidence shows many genetic variants contribute to individual differences in mental health. Individual genetic variants have tiny effects, which can be summed to measure each individual’s genetic propensity to develop mental health conditions.
A New Study: Which symptoms are related to genetic risk?
In a new study published in JAMA Psychiatry, we explore the link between individual symptoms of mental health conditions and genetic risk.
We combined network analysis, a statistical technique used to analyse individual symptoms and polygenic scoring, a way to index an individual’s genetic propensity to develop a mental health condition. Using data from a large cohort study (the Avon Longitudinal Study of Parents and Children - ALSPAC), we selected a sample of 5,521 children around 11 years old. To ensure robust results of this analysis, which was largely exploratory, we confirmed our results in a second sample of 4,626 children of the same age (drawn from the Twins Early Development Study, TEDS).
We modeled individual symptoms of common behavioural and mental health problems in children, such as difficulty with social interactions and low mood, as well as problems with social behaviour, emotional responses, and hyperactivity. We tested for the association of each symptom with genetic risk for common mental health conditions, such as ADHD, depression, and anxiety, and for traits that are important for mental health, such as BMI and the highest level of education completed by a person (educational attainment).
What did the study find?
First, the genetic propensity to develop a mental health condition is not related to all individual symptoms. Specifically, we found that the polygenic score for depression was associated with a lack of enjoyment or interest in everyday activities (known as anhedonia), a core symptom of depression, but interestingly it was not associated with low mood. The polygenic score for ADHD was associated with being easily distracted, a key symptom of ADHD. This analysis shows that even within the same condition, not all symptoms are influenced to the same extent by genetic factors.
Second, the genetic risk for each mental health condition is related to both the symptoms of the condition itself and symptoms of other conditions. For example, the polygenic score for anxiety was associated with feeling lonely, while the polygenic score for depression was also associated with being bullied. Thus, genetic risk contributes to the co-occurrence of mental health conditions, such as anxiety and depression, via specific symptoms and possibly specific social processes.
Last, the genetic propensity to develop traits relevant to mental health is related to a wide variety of symptoms. For example, the polygenic score for educational attainment was associated with symptoms of hyperactivity, emotional and conduct problems, problems with peers, and social behaviour. In other words, some genetic risks may be linked to a more general vulnerability to mental health difficulties and may affect symptoms across many conditions.
What do these findings mean?
These findings suggest that when we focus on individual symptoms, instead of measuring overall severity, we can gain new insights into how these conditions might develop.
This study adopts a more nuanced way of thinking about mental health by focusing on its individual components. We find some core symptoms of mental health conditions may be driving the associations with genetic risk which are frequently observed in research studies. Genetic factors may affect these core symptoms in the first place, and their influence may then expand to other symptoms.
Importantly, some of the symptoms related to genetic risk are symptoms of conditions that often occur together. This suggests that individual symptoms may share genetic influences, which may contribute to their co-occurrence.
What’s more, the genetic propensity to develop traits known to be linked to poorer mental health, such as BMI and educational attainment, may contribute to a wide variety of symptoms across the spectrum of mental health conditions. This might mean that the genetic predisposition to these traits also affects social and cognitive processes that play a role in many mental health conditions.
Overall, these findings point to the idea that we should conduct more mental health research at the symptom level.
A caveat of our study is that it is based on correlations (calculated at a specific time point, when children were 11 years old), which limits the insights we can gather from these findings. And although the results were replicated across two different datasets, more mental health studies need to replicate our findings and expand on this study.
In summary, we found new patterns of associations between genetic risk for mental health conditions, traits important for mental health, and individual symptoms. Our findings strengthen the claim that not all symptoms are equal, as they are associated differently with genetic risk. Understanding the structure of symptoms of mental health conditions, and how each symptom is influenced by genetics, may be an important avenue for future research.
Written by Giulia G. Piazza, Eiko Fried, Ph.D., Jonathan Roiser, Ph.D., and Jean-Baptiste Pingault, Ph.D.
