First Signs of Psychotic Disorder May Appear in Childhood With Drop in IQ Interview with:
Josephine Mollon PhD
Department of Psychosis Studies, Institute of Psychiatry, Psychology, and Neuroscience
King’s College London, London, England
Currently with the Department of Psychiatry
Yale University School of Medicine
New Haven, Connecticut What is the background for this study?

Response: Psychotic disorders, such as schizophrenia, are severe mental disorders that cause a range of abnormalities in perception and thinking. Individuals with psychotic disorders also experience severe impairments in IQ and there is evidence that these impairments begin many years before hallucinations and delusions first appear. Understanding how and when individuals with psychotic disorder experience a drop in IQ scores will help us better predict and treat poor cognition in these individuals, and perhaps even the disorder itself. What are the main findings? 

Response: The most surprising finding was that individuals who developed psychotic disorders as adults had normal IQ scores in infancy, but by age 4 their scores had already dropped and continued to drop further throughout childhood, adolescence and early adulthood until they were at 15 points below controls.

Moreover, individuals who later developed a psychotic disorder lagged more and more behind their peers in working memory, processing speed and attention abilities so that by adulthood they were several years behind their healthy peers. Individuals who later developed depression, psychotic symptoms not warranting clinical attention, and even psychotic disorder with depression did not show this drop in IQ score or lags across abilities over time, suggesting that this pattern of intellectual impairment is specific to individuals with psychotic disorder. This is the first time that IQ scores have been examined throughout the entire first two decades of life in individuals with psychotic disorder and the strongest evidence to date that IQ scores drop gradually throughout this period. Moreover, our results suggest that this drop in IQ is not due to a loss in ability over time, but rather to individuals lagging behind their peers because they do not improve at the same rate as their peers across this critical period of development. Importantly, we found that individuals who later developed psychotic disorders showed a drop in both verbal and nonverbal IQ, while previous studies have found that verbal abilities remained stable over time and only nonverbal abilities worsened. Thus, our findings suggest that gradually increasing impairments across both verbal and nonverbal abilities precede the onset of psychotic disorders. What should readers take away from your report? 

Response: Our results suggest that the first signs of psychotic disorder may be seen as early as age 4, when individuals already show a drop in IQ. IQ scores continue to drop gradually throughout the first two decades of life, suggesting the importance of early interventions to improve IQ scores in these individuals. Intervening in childhood or early adolescence may prevent other abilities, such as working memory and processing speed, from worsening in adolescence and may even delay or prevent illness onset. Families of children who start to struggle with schoolwork more and more throughout childhood and adolescence may benefit most from these types of interventions. A critical finding from our study is that this drop in IQ score may not be temporary, but rather a continuous process than worsens over time. This drop in IQ score could be a red flag, but needs to be explored further. Moreover, it is important to bear in mind that many children will experience some difficulties with schoolwork or other intellectual tasks at some point in their lives, but only a small minority will go on to develop a psychotic disorder.  A more general takeaway from our findings is that psychotic disorders do not just begin in adulthood when individuals start to experience symptoms such as hallucinations and delusions, but rather many years prior when difficulties with intellectual tasks emerge and worsen over time. What recommendations do you have for future research as a result of this work? 

Response: We are continuing to follow up these individuals and will examine IQ scores, as well as other abilities, throughout adulthood to see whether scores continue to drop after illness onset. We are also examining brain changes over time in these individuals, as well as potential environmental and genetic risk factors that may predispose individuals to poor cognition, as well as psychotic disorder.


Mollon J, David AS, Zammit S, Lewis G, Reichenberg A. Course of Cognitive Development From Infancy to Early Adulthood in the Psychosis Spectrum. JAMA Psychiatry. Published online January 31, 2018. doi:10.1001/jamapsychiatry.2017.4327

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Last Updated on February 1, 2018 by Marie Benz MD FAAD