Pathogenic theory of schizophrenia

The pathogenic theory of schizophrenia, also called the germ theory of schizophrenia, is a pathogenic theory of disease in which it is thought that a proximal cause of certain cases of schizophrenia is the interaction of the developing fetus with pathogens such as viruses, or with antibodies from the mother created in response to these pathogens (in particular, Interleukin 8). Brown AS, Hooton J, Schaefer CA, Zhang H, Petkova E, Babulas V, Perrin M, Gorman JM, Susser ES.(2004) Elevated maternal interleukin-8 levels and risk of schizophrenia in adult offspring. Am J Psychiatry. 161(5):889-95. PMID 15121655 (free full text) Am. Psych. Assn. Abstract:"OBJECTIVE: Many studies have implicated prenatal infection in the etiology of schizophrenia. Cytokines, a family of soluble polypeptides, are critically important in the immune response to infection and in other inflammatory processes. The goal of this study was to determine whether second-trimester levels of four cytokines—interleukin-8 (IL-8), interleukin-1ß (IL-1ß), interleukin-6 (IL-6), and tumor necrosis factor- (TNF-)—are higher in the mothers of offspring who later developed schizophrenia spectrum disorders than in matched comparison subjects. METHOD: The authors conducted a nested case-control study of maternal serum cytokine levels in a large birth cohort, born 1959–1967. Cases (N=59) were subjects diagnosed with schizophrenia spectrum disorders (mostly schizophrenia and schizoaffective disorder) who had available second-trimester maternal serum samples. Comparison subjects (N=105) were members of the birth cohort, had not been diagnosed with a schizophrenia spectrum disorder or major affective disorder, and were matched to subjects with schizophrenia for date of birth, gender, length of time in the cohort, and availability of maternal sera. Maternal second-trimester serum levels of IL-8, IL-1ß, IL-6, and TNF- were determined by sandwich enzyme-linked immunosorbent assay. RESULTS: The second-trimester IL-8 levels in mothers of offspring with schizophrenia spectrum disorders were significantly higher than those of the mothers of comparison subjects. There were no differences between subjects with schizophrenia and comparison subjects with respect to maternal levels of IL-1ß, IL-6, or TNF-. '''CONCLUSIONS: Using prospectively collected prenatal sera in a large and well-characterized birth cohort, the authors have documented a significant association between maternal IL-8 level during the second trimester and risk of schizophrenia spectrum disorders in the offspring. These findings provide further support for a substantive role of in utero infection or inflammation in the etiology of schizophrenia. Moreover, these results may have important implications for elucidating the mechanisms by which disrupted fetal development raises the risk of this disorder.'''" (Emphasis supplied.)

Substantial research suggests that exposure to certain illnesses (e.g., influenza) in the mother of the neonate (especially at the end of the second trimester) causes defects in neural development which may emerge as a predisposition to schizophrenia around the time of puberty, as the brain grows and develops.