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The auditory event-related P300 amplitude appears to be an endophenotype for schizophrenia, but it is also affected in bipolar disorder patients and may be a marker for psychosis in general, conclude UK researchers.
Decreased P300 positive event-related potential component amplitude, which requires the detection of rare target stimuli, is associated with alcoholism and schizophrenia, and studies have shown that the potential is genetically influenced. However, such studies have different and more complex tasks than those used in clinical studies.
Patricia Bestelmeyer, from the University of Glasgow, and colleagues therefore initially examined the genetic influence on the P300 potential in 14 pairs of healthy monozygotic twins and 14 pairs of healthy dizygotic twins. The team measured the P300 amplitude response to one auditory and one visual paradigm, each of which consisted of 150 stimuli in two blocks, with oddball stimuli appearing at a probability of 20%.
Participants made significantly more errors when reacting to visual than to auditory stimuli on univariate analysis, while a mixed design analysis of variance showed that individuals reacted significantly faster to oddball trials. On multivariate analysis, there were no significant effects of zygosity for reaction time and error rate.
The results, published in the journal Psychiatry Research, indicate that the auditory P300 amplitude was significantly intraclass correlated in monozygotic twins, and the correlation was significantly larger than that seen in dizygotic twins. No significant correlations were seen for auditory P300 latency, or for visual P300 amplitude or latency.
In a second experiment, the team used the same paradigms, procedure, recording condition, and analysis to study visual and auditory P300 in 21 schizophrenia patients, 19 bipolar disorder patients, and 35 healthy unmedicated controls.
Healthy controls made significantly fewer errors in response to auditory stimuli than schizophrenia patients but not compared with bipolar disorder patients. In contrast, healthy controls reacted significantly faster to oddball stimuli than individuals from both patient groups, a pattern that was repeated with standard stimuli. In response to visual stimuli, the only significant difference was between healthy controls and bipolar disorder patients on reaction times, with the former being faster.
Interestingly, while schizophrenia and bipolar disorder patients had significantly lower auditory P300 amplitudes than controls, there were no significant differences between patient groups. A similar pattern was seen for visual P300 amplitudes the centro-parietal electrode site (Pz), although the reduction in bipolar disorder patients versus controls had only a non-significant trend for difference. There were no significant differences in auditory or visual P300 latencies.
The team concludes: “Taken together, our findings imply that the auditory P300 amplitude at Pz may be an endophenotype for psychosis in general rather than specifically for schizophrenia.”
MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009
