A New Understanding of Mental Illness

The causes of psychiatric disorders are poorly understood. Now, in work by researchers at McGill University, there is evidence that a wide range of early psychiatric problems (from depression, anxiety and addictions to dyslexia, bulimia and ADHD) can be largely due to the combination of only three factors. The first is biological, in the form of individual variability in the dopamine reward pathway in the brain. The second is social and emphasizes the important role of neglect or abuse in early childhood. And the third is psychological and relates to temperament, and in particular tendencies to impulsivity and difficulty in controlling emotions. These findings have implications for understanding both the causes of a wide range of psychiatric disorders and the characteristics that merit targeting in early intervention efforts.

“Until recently, psychiatric disorders were thought to reflect distinct disease entities, each with their own unique causes,” says Marco Leyton, lead author of a recent study published in Neuropsychopharmacology and Professor in the Department of Psychiatry at McGill and Principal Scientist at the Research Institute of the McGill University Health Center. “The present research overturns this idea, suggesting instead that most early-onset disorders largely reflect differential expressions of a small number of biological, psychological and social factors.”

First study to combine three key factors: temperament, trauma and dopamine

Previous research has suggested that each of the three factors, in isolation, has at least modest effects on the development of psychiatric disorders. In comparison, the authors of this new study had the very first opportunity to examine all three factors together. Fifty-two young people, residing in the regions of Montreal or Quebec (30 women and 22 men), followed since their birth by Jean Séguin (University of Montreal) and Michel Boivin (Laval University), underwent brain scans (PET and MRI) which measured characteristics of their dopamine reward pathway. These brain characteristics were then combined with information about their temperament traits and history of adversity early in life.

High precision and potential predictive value of the approach

Surprisingly, this combination of just three factors predicted, with over 90% accuracy, which participants had mental health issues in the past or during the study’s three-year follow-up period. Indeed, since the results are so new and potentially so important, CIHR provided an additional $ 2 million to double the sample size and follow participants into their mid-twenties. “And the results need to be replicated, both in larger and more ethnically diverse groups,” said the paper’s first author, Maisha Iqbal, a graduate student of McGill’s Integrated Neuroscience Program. “If replicated, our research could transform the way we think about mental illness. “

The paper: “A Three-Factor Model of Common Early-Onset Psychiatric Disorders: Temperament, Adversity, and Dopamine” by Maisha Iqbal et al in

DOI: 10.1038 / s41386-021-01187-z

The research was funded through CIHR, Brain Canada, CRSH, FRQS, FRQSC

About McGill University

Founded in 1821, McGill University is home to exceptional students, faculty and staff from across Canada and around the world. It is regularly ranked among the best universities, both nationally and internationally. It is a world-renowned higher education institution with research activities spanning three campuses, 11 faculties, 13 vocational schools, 300 study programs and over 40,000 students, including over 10,200 graduate students. representing 31% of the student body. More than half of McGill students say they have a mother tongue other than English, including around 19% of our students who say French is their mother tongue.


Katherine Gombay
Media Relations Office, McGill University
(514) 717-2289
[email protected]

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