In Reply

We would like to thank Dr. Sachdev for his interest in our study. We concur with his argument that traumatic brain injury (TBI) is a significant risk factor for psychosis that deserves further study. Studies of monozygotic twins report that the concordance rate for schizophrenia is roughly 50%.¹ This would suggest that environmental factors are also important. Thus far much of the attention in environmental factors has focused on birth complications and illness or maternal stressors during gestation.¹ The size effects for these factors, however, are relatively small (between 2 and 3).¹ Results from Dr. Sachdev's study as well as ours would suggest that TBI may be another significant risk factor for persons with and without a genetic predisposition for schizophrenia.^2,3 Indeed there is evidence that many psychiatric patients have sustained TBI within one year prior to hospitalization.⁴ Moreover, in many other cases a prior TBI is undocumented in the medical chart.⁴ We hope that both studies will motivate further investigations into the relationship between traumatic brain injury and psychosis.