23 April 2012

Environment Matters In Schizophrenia Too

The evidence for that heredity plays a part in causing schizophrenia is more compelling and better documented than almost any other mental health condition (heredity may account for as much as 80% of schizophrenia risk, at least a third of which has been linked to common genetic variants and some of the rest of which may be epigenetic). But, the case that there is also an environmental element to schizophrenia is also compelling according to a recent meta-analysis.

The research, conducted by teams at Liverpool and Maastricht University in the Netherlands, is the first of its kind to bring together and analyse the findings from more than 30 years of studies looking at the association between childhood trauma and the development of psychosis. The researchers looked at more than 27,000 research papers to extract data from three types of studies; those addressing the progress of children known to have experienced adversity; studies of randomly selected members of the population; and research on psychotic patients who were asked about their early childhood.

Across all three types of studies the results led to similar conclusions. Children who had experienced any type of trauma before the age of 16 were approximately three times more likely to become psychotic in adulthood compared to those selected randomly from the population. Researchers found a relationship between the level of trauma and the likelihood of developing illness in later life. Those that were severely traumatised as children were at a greater risk, in some cases up to 50 times increased risk, than those who experienced trauma to a lesser extent.

The Liverpool team also conducted a new study which looked at the relationship between specific psychotic symptoms and the type of trauma experienced in childhood. They found that different traumas led to different symptoms. Childhood sexual abuse, for example, was associated with hallucinations, whilst being brought up in a children's home was associated with paranoia. The research further suggests a strong relationship between environment and the development of psychosis, and provides clues about the mechanisms leading to severe mental illness.

The study described in the material quoted above is R. P. Bentall, S. Wickham, M. Shevlin, F. Varese. "Do Specific Early-Life Adversities Lead to Specific Symptoms of Psychosis? A Study from the 2007 The Adult Psychiatric Morbidity Survey." Schizophrenia Bulletin, 2012; DOI: 10.1093/schbul/sbs049.

One common paradigm, which could be at play in schizophrenia, would be to view the genetic inheritance associated with the condition as vulnerablity to trauma genes, rather than as mental health condition causing genes per se. One might think of them as kindred to the idea that someone has an "eggshell skull" that together with a head trauma leads to much more harm than a typical person would suffer under the same circumstances.

Another possibility is that there is more than one set of circumstances that can present as the set of symptoms (i.e. syndrome) that we call schizophrenia or psychosis. Some cases could have a purely genetic causes, other cases might have a root purely in severe trauma, while yet other cases could be due to a mix of the two causes. For example, if trauma associated schizophrenia has some distinctive features not found in people who develop schizophrenia without a history of trauma, it might be possible to develop diagnostic subtypes of the condition with better identified caused and figure out which treatments work best for which subttypes. For example, maybe psychotherapy works for trauma associated schizophrenia but not purely genetic schizophrenia.

The abstract of the behind the paywall article, doesn't say what proportion of schizophrenia cases involve or do not involve traumas, making the data hard to evaluate.

The gene x environmental model also fits the tendency of the link between mental health conditions and crime being a "mental illness plus" model, in which mental illness alone is not a strong risk factor for crime, but mental illness plus a history of violence and substance abuse are an extremely powerful risk factor for crime. Similarly, college educated people with a mental illness are much less likely to have criminal justice involvement than people who have only high school diplomas or are high school dropouts.

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