Adolescents and young adults experiencing relative declines in cognitive performance have an increased risk for later psychosis, with a decline in verbal ability between 13 and 18 years of age a strong predictor, conclude researchers.
"This suggests that the premorbid cognitive deficit observed in schizophrenia and other psychoses represents a disruption of neurodevelopment during the teenage years," say James MacCabe, from King's College London, UK, and colleagues.
They add: "We believe… relative verbal decline in adolescence and young adulthood reflects a neurodevelopmental process that occurs at a fixed age and puts the individual at an increased lifetime risk for psychosis, as opposed to a prodromal process that occurs shortly before the onset of symptoms."
The team studied a total of 10,717 adolescent boys and young men grouped into four population-based cohorts born in 1953, 1967, 1972, and 1977, and followed them up to the end of 2006. Scores on verbal, spatial, and inductive ability at the age of 13 years and at army conscription, at 18 years, were compared with hospital admissions for nonaffective or affective psychoses in adulthood.
The results, published in JAMA Psychiatry, indicated that all the cognitive test scores correlated positively with one another. Associations between cognitive functioning at 18 years and risk for schizophrenia in adulthood were moderate, but a model including change in functioning between 13 and 18 years revealed that a relative decline in verbal ability scores was the only significant predictor for schizophrenia, at a hazard ratio of 0.60 for each standard deviation increase in verbal ability.
The findings remained significant after adjustments for urbanity, parental educational level, and family history of psychosis.
The team also reports that the results for other non-affective psychoses were similar to those seen in schizophrenia. Interestingly, individuals who later developed bipolar disorder outperformed population norms on all tasks and at all time points.
Running separate analyses excluding individuals who developed psychoses before 25 years of age only served to strengthen the association between verbal decline and schizophrenia, at a hazard ratio of 0.39 per standard deviation increase in verbal ability, and between verbal decline and other non-affective psychoses.
MacCabe and team conclude: "Further research is required to determine what types of longitudinal changes in cognitive functioning occur in the premorbid phase and how they relate to neuroanatomical changes."
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