The impact of premorbid and current intellect in schizophrenia: cognitive, symptom, and functional outcomes

Background: Cognitive heterogeneity among people with schizophrenia has been defined on the basis of premorbid and current intelligence quotient (IQ) estimates. In a relatively large, community cohort, we aimed to independently replicate and extend cognitive subtyping work by determining the extent of symptom severity and functional deficits in each group. Methods: A total of 635 healthy controls and 534 patients with a diagnosis of schizophrenia or schizoaffective disorder were recruited through the Australian Schizophrenia Research Bank. Patients were classified into cognitive subgroups on the basis of the Wechsler Test of Adult Reading (a premorbid IQ estimate) and current overall cognitive abilities into preserved, deteriorated, and compromised groups using both clinical and empirical ( k -means clustering) methods. Additional cognitive, functional, and symptom outcomes were compared among the resulting groups. Results: A total of 157 patients (29%) classified as ‘preserved’ performed within one s.d. of control means in all cognitive domains. Patients classified as ‘deteriorated’ ( n =239, 44%) performed more than one s.d. below control means in all cognitive domains except estimated premorbid IQ and current visuospatial abilities. A separate 138 patients (26%), classified as ‘compromised,’ performed more than one s.d. below control means in all cognitive domains and displayed greater impairment than other groups on symptom and functional measures. Conclusions: In the present study, we independently replicated our previous cognitive classifications of people with schizophrenia. In addition, we extended previous work by demonstrating worse functional outcomes and symptom severity in the compromised group. Cognitive functioning: Distinct categories for patients with schizophrenia Patients with schizophrenia can be categorized into distinct groups according to their cognitive functioning abilities, say scientists. Cognitive impairment and intellect changes following the onset of schizophrenia are well documented, but recent research suggests that patients are affected in many different ways. Thomas Weickert at the University of New South Wales, Sydney, and co-workers across Australia conducted a large-scale study involving 635 healthy controls and 534 patients with schizophrenic symptoms to verify the presence of three distinct cognitive phenotypes in schizophrenia. Utilizing a test to determine pre-illness intelligence, the team classified patients into