A new understanding of mental illness

Three key factors might offer 90% accuracy in predicting wide range of psychiatric disorders
Published: 8 December 2021

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

“Until recently, it was thought that psychiatric disorders reflected discrete disease entities, each with their own unique causes,” says Marco Leyton, the senior author on a recent study published in Neuropsychopharmacology and a professor in McGill’s Department of Psychiatry and Senior Scientist at the Research Institute of the McGill University Health Centre. “The present research upends 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

Earlier 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 first ever opportunity to examine all three factors together. Fifty-two young people, living in the Montreal or Quebec City areas (30 women and 22 men), who have been followed since birth by Jean Séguin (Université de Montréal) and Michel Boivin (Université Laval), had brain imaging scans (PET and MRI) that measured features of their dopamine reward pathway. These brain features were then combined with information about their temperamental traits and histories of early life adversity.

High accuracy & potential predictive value of approach

Strikingly, this combination of just three factors predicted, with over 90% accuracy, which participants had mental health problems either in the past or during the study’s three-year follow-up period. Indeed, since the results are so novel and potentially so important, CIHR has provided an additional two million dollars to double the sample size and follow the participants through to their mid-20s. “And the results do need to be replicated, both in larger and ethnically more diverse groups,” emphasizes the paper’s first author, Maisha Iqbal, a graduate student in McGill’s Integrated Program in Neuroscience. “If replicated, our research could transform the way we think about mental illnesses.”

About the study

“A three-factor model of common early onset psychiatric disorders: temperament, adversity, and dopamine” by Maisha Iqbal et al in Neuropsychopharmacology



About McGill University

Founded in Montreal, Quebec, in 1821, McGill University is Canada’s top ranked medical doctoral university. McGill is consistently ranked as one of the top universities, both nationally and internationally. It  is a world-renowned institution of higher learning with research activities spanning three campuses, 11 faculties, 13 professional schools, 300 programs of study and over 40,000 students, including more than 10,200 graduate students. McGill attracts students from over 150 countries around the world, its 12,800 international students making up 31% of the student body. Over half of McGill students claim a first language other than English, including approximately 19% of our students who say French is their mother tongue.


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