For a study, researchers sought to investigate neurodevelopmental and neurodegenerative hypotheses of psychotic diseases by the following cognition from elementary school to old age.

The data came from the Suffolk County Mental Health Project, a first-admission longitudinal cohort study of people with psychotic illnesses. Participants were drawn from Suffolk County’s 12 inpatient psychiatric hospitals. The study looked at 428 people with at least two general cognitive ability estimations. Data were gathered between September 1989 and October 2019; analysis occurred between January 2020 and October 2021. Cognitive ratings for readmission were obtained from school and medical data. Neuropsychological testing was used to determine postonset cognitive scores at 6-month, 24-month, 20-year, and 25-year intervals.

About 254 (59.6%) of the 428 participants (212 with schizophrenia and 216 with other psychotic diseases) were male, and the mean (SD) age at psychosis start was 27 years. The cognitive change was seen in three stages: normal, decreasing, and worsening. Cognition was steady during the first phase. About 14 years before the onset of psychosis, those with schizophrenia began to experience cognitive decline at a rate of 0.35 intelligence quotient (IQ) points per year (95% CI, 0.29-0.42; P<.001), significantly faster than those with other psychotic disorders (0.15 IQ points per year; 95% CI, 0.08-0.22, P<.001). Both groups deteriorated at a rate of 0.59 IQ points per year 22 years after beginning (95% CI, 0.25-0.94; P<.001). 

Cognitive trajectories in schizophrenia were consistent with a neurodevelopmental and neurodegenerative pattern in this cohort research, resulting in a loss of 16 IQ points during observation. The cognitive decline occurred well before the onset of psychosis, suggesting that the opportunity for primary prevention is earlier than previously assumed. Secondary preventive opportunities occur in the third decade of disease when cognitive deficits increase in people with schizophrenia and other psychotic illnesses.