Course of cognitive impairment in schizophrenia develops throughout youth
People with psychotic disorder demonstrated a developing course of cognitive impairment throughout their first 20 years of life, leading to verbal and nonverbal dysfunction; however, this course was not seen in other psychiatric disorders, according to findings published in JAMA Psychiatry.
“Important questions remain regarding the course of cognitive impairment in schizophrenia,” Josephine Mollon, PhD, department of psychiatry, Yale University School of Medicine, and colleagues wrote. “Few studies permit examination of cognitive development between late childhood and early adolescence, and studies spanning early childhood or late adolescence are rare, with mixed results. It remains unclear how ... [cognitive] deficits develop and whether a course of increasing impairment is specific to schizophrenia.”
Researchers analyzed data from a population-based cohort in England followed prospectively from birth (born between April 1, 1991 and Dec. 31, 1992) to track the course of general and specific cognitive functions in psychotic disorders, psychotic experiences and depression.
They included individuals who underwent cognitive testing throughout infancy to young adulthood (at ages 18 months and 4, 8, 15 and 20 years) and psychiatric assessment at age 18 years in their study. They measured full-scale, verbal and nonverbal IQ at the same age points along with abilities in processing speed, working memory, language, visuospatial ability and attention at ages 8 and 20 years, comparing outcomes among participants with psychotic disorder, psychosis with depression, psychotic experiences and depression and controls.
Researchers included 511 individuals at age 18 months, 483 at age 4 years, 3,930 at age 8 years, 3,783 at age 15 years, and 257 at age 20 years in their study. Participants with psychotic disorder demonstrated progressively increasing deficits between infancy at age 18 months and young adulthood at age 20 years in full-scale IQ (P = .02) and nonverbal IQ (P = .008), whereas the depression group only showed a small, increasing deficit in nonverbal IQ (P = .04). Verbal functions declined during infancy, while nonverbal functions showed reduced growth during adolescence. Furthermore, examination of full-scale IQ scores between ages 8 and 20 years revealed that most individuals with psychotic disorder (81.3%) showed a decline in IQ, which exceeded the established threshold for reliable change in 62.5% of individuals with psychotic disorder.
Between ages 8 and 20 years, those in the psychotic disorder group showed reduced development in measures of processing speed (P = .001), working memory (P = .004), and attention (P = .001) as well as deficits in measures of language (P = .005) and visuospatial ability (P = .001). Although individuals with psychotic disorder showed widespread, progressive deficits in cognition, those with psychosis with depression, psychotic experiences and depression had only small cognitive lags and deficits in some functions.
“Individuals with psychotic disorder showed a dynamic course of cognitive impairment throughout the first 2 decades of life,” Mollon and colleagues wrote. “Future efforts to elucidate the pathophysiological processes underlying this progressive dysfunction and the developmental periods during which it occurs will inform early detection and intervention strategies.”
Longitudinal studies, like the one used by Mollon and colleagues are the key to better understanding the course of neurodevelopmental disorders like schizophrenia, according to Ruben C. Gur, PhD, brain behavior laboratory in the department of psychiatry at Perelman School of Medicine, University of Pennsylvania.
“Studies such as Mollon [and colleagues] are harvesting the fruits of large-scale, developmental studies of cross-sectional and longitudinal designs that were planned and implemented decades ago,” Gur wrote in a related editorial. “They illustrate how these studies are already advancing us to new levels of understanding and helping predict the course of psychosis and other neurodevelopmental disorders. We should also now leverage new technologies and put efforts into collecting longitudinal data from genotyped samples of individuals who have consented to follow-up.” – by Savannah Demko
Disclosures: The authors report no relevant financial disclosures. Gur reports royalties from the Brain Resource Centre.