Psychotic disorders manifest in developmental processes that affect both verbal and nonverbal abilities in the first 20 years of life, according to findings from a prospective, population-based cohort study published in JAMA Psychiatry.
The research sample included individuals from the Avon Longitudinal Study of Parents and Children, which includes all live births between April 1, 1991, and December 31, 1992, in Avon, England. Participants who underwent cognitive testing at 18 months and at 4, 8, 15, and 20 years of age who also had psychiatric assessments at 18 years of age were included (n=4322).
Participants were grouped into 5 groups: participants with psychotic disorder, participants with psychosis with depression, participants with psychotic experiences, participants with depression, and controls. Study outcomes were full-scale, verbal, and nonverbal IQ at age 18 months and at 4, 8, 15, and 20 years of age as well as processing speed, working memory, language, visuospatial ability, and attention at ages 8 and 20 years.
Participants with psychotic disorders had increasing deficits in full-scale IQ (effect size of change [ESΔ] =−1.09; P =.02) and nonverbal IQ (ESΔ =−0.94; P =.008) compared with the other 4 groups.
Participants with psychotic disorders also showed slower growth in measures of processing speed (ESΔ =−0.68; P =.001), working memory (ESΔ =−0.59; P =.004), and attention (ESΔ =−0.44; P =.001) compared with the 4 other groups. They showed significant unchanging deficits in measures of language (ES =−0.87; P =.005) and visuospatial ability (ES =−0.90; P =.001) compared with other groups.
Participants with depression showed a small increasing deficit from age 18 months to 20 years in nonverbal IQ (ESΔ =−0.29; P =.04) compared with other groups.
The study researchers concluded that individuals with psychotic disorders had increasing IQ deficits and delayed developmental growth. This is in contrast to participants with psychosis with depression or psychotic experiences for which weak evidence for cognitive deficits was found.
“Clinically, our findings highlight the importance of early intervention for cognitive deficits,” the researchers wrote. “Verbal abilities may be more amenable to change during childhood, while interventions during adolescence may be most effective for nonverbal abilities.”
Mollon J, David AS, Zammit S, Lewis G, Reichenberg A. Course of cognitive development from infancy to early adulthood in the psychosis spectrum [published online January 31, 2018]. JAMA Psychiatry. doi:10.1001/jamapsychiatry.2017.4327