Dr. Cannon and Colleagues Reply
To the Editor: It is difficult to know how to respond to the comments of Dr. Crow. Our object was not to torture the data but to present them so that readers could see the field for what it is—contradictory—and then to dissect the evidence and expose any truth within it. We were not searching for positive findings. Indeed, we would have been pleased had there been a definitive negative result, something that the correspondent appears to see clearly, despite a lack of evidence. At no stage did we suggest that a causal relationship has been established for any one obstetric risk factor. That would have been foolhardy.
We do not understand the objection to grouping risk factors into categories that may share the same underlying mechanism. This is a well-recognized and useful practice found even in the correspondent’s own research (1, 2). Neither do we understand the objection to the concept of multiple risk factors. Current understanding of causal mechanisms precludes the view that there is a single causal factor for any complex disorder. The concept of multiple risk factors for schizophrenia obviously applies to the genome (3). Why not to the “envirome” as well?
1. Done DJ, Johnstone EC, Frith CD, Golding J, Shepherd PM, Crow TJ: Complications of pregnancy and delivery in relation to psychosis in adult life: data from the British perinatal mortality survey sample. Br Med J 1991; 302:1576-1580Crossref, Medline, Google Scholar
2. Sacker A, Done DJ, Crow TJ, Golding J: Antecedents of schizophrenia and affective illness: obstetric complications. Br J Psychiatry 1995; 166:734-741Crossref, Medline, Google Scholar
3. Straub RE, MacLean CJ, Ma Y, Webb BT, Myakishev MV, Harris-Kerr C, Wormley B, Sadek H, Kadambi B, O’Neill FA, Walsh D, Kendler KS: Genome-wide scans of three independent sets of 90 Irish multiplex schizophrenia families and follow-up of selected regions in all families provides evidence for multiple susceptibility genes. Mol Psychiatry 2002; 7:542-559Crossref, Medline, Google Scholar