Schizophrenia environmental factors

These data show that for three psychotic disorders (schizophrenia, bipolar disorder and unipolar depression) the genetic contribution is over 50% but for reactive depression (in response to a traumatic life event ) and tuberculosis, an infectious disease caused by a species of Mycobacterium, environmental factors account for over 90% of the variance. 

Environmental factors, such as prenatal maternal infections and perinatal complications, have been implicated in the pathogenesis of schizophrenia. Also, the correlation of only 0.6 for age of onset in monozygotic twins concordant for schizophrenia suggests that non-genetic factors play a role in determining the age of onset (Kendler et ah, 1987). A greater frequency or severity of these factors could conceivably result in an earlier onset of schizophrenia. 

Emerging evidence suggests that patients with a very early onset of schizophrenia have greater levels of both early and later neurodevelopmental abnormalities. Environmental factors are not increased, while genetic... 

The exact cause of schizophrenia has been the subject of extensive research. It appears that genetic factors (i.e., chromosomal abnormalities that cause deviations in brain structure and function) are the primary risk factors in the majority of people with schizophrenia (70% to 80%).15,23 Environmental factors (social stresses, prenatal or childhood brain injury, and so forth) seem to be the underlying cause in the remaining 20% to 30% of people with schizophrenia.23 The precise role of these factors, and the interplay between genetic and environmental factors, continues to be elucidated.28,50 61... 

Environmental factors that contribute to the development of schizophrenia also converge on NMDA receptors. For example, it has been hypothesized that perinatal hypoxia, an important risk factor for schizophrenia, leads to the neurotoxic degeneration of NMDA-bearing cells, an effect that may only produce behavioral symptoms later in development (Olney et al., 1999). 

Environmental factors such as exposure to viral infections (Leweke et al., 2004) autoimmune, toxic or traumatic insults and stress during gestation, birth or childhood (Marcelis et al., 1998 Cannon et al., 2000 Rosso et al., 2000) have been implied in the pathogenesis of schizophrenia. Lately, models based on epigenic factors and interaction between a susceptible genotype and the environmental factors have been proposed for this complex disease (Petronis, 2004). 

We propose that a redox/antioxidant dysregulation due to GSH deficit could represent a vulnerability factor at the early phase of brain development in at least a subgroup of schizophrenia patients. Combined with other genetic factors and environmental factors, such as stress, obstetrical complications or viral infections, it could favor the development of the disease. The role of the GSH deficit proposed allows integration in a causal way many phenomenological aspects of schizophrenia. It is compatible with both the DA and the glutamate/NMDA hypotheses and with the neuropathological observations. In contrast to... 

Proposed model of genetic and environmental factors contributing to GSH deficit and neurobiological anomalies leading to schizophrenia phenotypes. Evidences are given in the text (O Section 2.5.5)... 

Q9 Schizophrenia appears to involve both genetic and environmental factors. Possible causes of schizophrenia are ... 

---