Several factors suggest that spontaneous dyskinesia may be a useful supplemental phenotype for further elucidating the specific nature of the genetic contribution to schizophrenia. For example, involuntary movement abnormalities have been observed in both medicated and unmedicated schizophrenia patients, in individuals with schizotypal personality disorder, and sometimes in siblings of schizophrenia patients. However, there are many inconsistencies present in the literature to date. The current study thus sought to investigate the existence of spontaneous dyskinesia in schizophrenia patient probands, their non-psychotic siblings, and healthy controls in order to clarify its potential value as an "endophenotype" in genetic studies of schizophrenia. Videotaped interviews were coded for the presence of spontaneous, involuntary movement abnormalities by a trained and reliable rater using computer assisted technology who was blind to group and family status. The results of this study indicated that siblings of schizophrenia patients did not display significantly more involuntary movements compared to controls, although tremor was observed in a few siblings. In contrast, schizophrenia patients did display significantly more involuntary movements compared to controls as well as their non-psychotic siblings. The lack of significant differences between siblings and controls argues against a strong association between spontaneous dyskinesia and an "unexpressed" genetic liability to schizophrenia. Thus, it appears that involuntary movement abnormalities may be limited in their utility as endophenotypes in genetic studies of schizophrenia, despite being associated with, and perhaps predictive of, schizophrenia itself. © 2005 Elsevier B.V. All rights reserved.
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