Working memory subprocesses and catechol-O-methyltransferase Val158Met polymorphism in schizophrenia patients, bipolar disorder patients, and their relatives.

Abstract

The present study had several objectives. It sought to determine if deficits in working memory subprocesses of maintenance, monitoring, and manipulation are specific to schizophrenia or are also present in patients with bipolar disorder. It was of interest to additionally determine if working memory deficits are present in the relatives of schizophrenia patients and relatives of bipolar disorder patients. Finally, the association between the COMT Val158Met polymorphism and working memory ability in schizophrenia patients, bipolar disorder patients, and the relatives of these patient groups was investigated. Genotyping data and performance scores for the Spatial Delayed Response Task (i.e. maintenance), Self Ordered Pointing (i.e. monitoring), Digit Span Backwards (i.e. low demand manipulation) and Letter Number Sequencing (i.e. high demand manipulation) were collected for schizophrenia patients, bipolar disorder patients, relatives of schizophrenia patients, relatives of bipolar disorder patients, and nonpsychiatric controls. Results showed worse performance on the maintenance, low demand manipulation, and high demand manipulation working memory subprocesses for schizophrenia patients compared to nonpsychiatric controls and bipolar disorder patients. The relatives of schizophrenia patients also demonstrated impairment in low demand manipulation and high demand manipulation, as well as a trend for worse maintenance performance compared to nonpsychiatric controls. Although no genotype group differences were revealed when examined in a sample combining all diagnostic groups, a few genotype group differences were detected when examined within a sample of schizophrenia patients. These results will be discussed. The results suggest that schizophrenia and bipolar disorder have distinct pathophysiologies, manipulation is promising as an endophenotype for schizophrenia-relevant disease genes, and there may be Val158Met genotype group differences in working memory within schizophrenia patients.