Neuropsychological dysfunctions in siblings discordant for schizophrenia

Although cognitive impairments are well recognized in patients with schizophrenia, it is unclear which impairments are due to a genetic predisposition and which are caused by secondary disease effects or phenotype. The aim of this study is to investigate the possible relationship between genetic vulnerability to schizophrenia and cognitive functioning. Three groups of subjects were compared: 14 patients with schizophrenia, 15 healthy siblings and 32 healthy control subjects. All subjects were tested neuropsychologically. The raw test data were rescaled to standard equivalents (z-scores). Subjects' z scores on tests assessing the same cognitive domain were clustered and analyzed. Differences in cognitive functioning were found in the domains of abstraction, attention, executive functioning, spatial memory, and sensory-motor functioning. The schizophrenic probands were impaired on all these five domains whereas the healthy probands showed impairments on executive functioning and partially on sensory-motor functioning. Furthermore, for spatial memory the significant finding could mainly be attributed to impaired functioning in the patients, but not healthy siblings or control subjects, whereas for executive functioning patients and healthy siblings seemed equally impaired as compared to control subjects. The planning time of the Tower of London (TOL) and the initiation time of the Motor Planning Task (MPT) were used for measures of executive functioning, while the 'time to move of the Motor Planning Task' was used as measures of sensory motor functioning. These results suggest that the cognitive abnormalities in schizophrenia that may be related to genotype are represented in the domain of executive functioning and to some extent in the domain of sensory-motor functioning.