Schizophrenia (5)

...the proportion of individuals expected to experience the disease at any time in their lives, , is commonly given at 1%.

A 2002 systematic review of many studies, however, found a lifetime prevalence of 0.55%.[3] Despite the received wisdom that schizophrenia occurs at similar rates throughout the world, its prevalence varies across the world,[36] within countries,[37] and at the local and neighbourhood level.[38] One particularly stable and replicable finding has been the association between living in an urban environment and schizophrenia diagnosis, even after factors such as drug use, ethnic group and size of social group have been controlled for.[39] Schizophrenia is known to be a major cause of disability. In a 1999 study of 14 countries, active psychosis was ranked the third-most-disabling condition, after quadriplegia and dementia and before paraplegia and blindness.[40]

Data from a PET study[41] suggests that the less the frontal lobes are activated (red) during a working memory task, the greater the increase in abnormal dopamine activity in the striatum (green), thought to be related to the neurocognitive deficits in schizophrenia.

While the reliability of the diagnosis introduces difficulties in measuring the relative effect of genes and environment (for example, symptoms overlap to some extent with severe bipolar disorder or major depression), evidence suggests that genetic and environmental factors can act in combination to result in schizophrenia.[42] Evidence suggests that the diagnosis of schizophrenia has a significant heritable component but that onset is significantly influenced by environmental factors or stressors.[43] The idea of an inherent vulnerability (or diathesis) in some people, which can be unmasked by biological, psychological or environmental stressors, is known as the stress-diathesis model.[44] The idea that biological, psychological and social factors are all important is known as the "biopsychosocial" model.

Genetic — Estimates of the heritability of schizophrenia tend to vary owing to the difficulty of separating the effects of genetics and the environment although twin studies have suggested a high level of heritability.[45] It is likely that schizophrenia is a condition of complex inheritance, with several genes possibly interacting to generate risk for schizophrenia or the separate components that can co-occur leading to a diagnosis.[46] Recent work has suggested that genes that raise the risk for developing schizophrenia are non-specific, and may also raise the risk of developing other psychotic disorders such as bipolar disorder.[47][48]. Prenatal — It is thought that causal factors can initially come together in early neurodevelopment, including during pregnancy, to increase the risk of later developing schizophrenia. One curious finding is that people diagnosed with schizophrenia are more likely to have been born in winter or spring, (at least in the northern hemisphere).[49] There is now evidence that prenatal exposure to infections increases the risk for developing schizophrenia later in life, providing additional evidence for a link between in utero developmental pathology and risk of developing the condition.[50]

...To be continued