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False Starts in Psychiatric Genetics

August 2, 2006

You’ve probably seen the headline a dozen times “Researchers at State College University Discover the Gene for Depression”. And yet it seems like no progress has been made towards understanding the genetic basis for psychiatric diseases. How can this be?

Well the fundamental reason for the lack of progress is that psychiatric diseases, like most interesting genetic traits, are the result of complex interactions between a number of genes. Every study that gets talked about in the media is only a small part of a very complex puzzle. It will take many years of broader more detailed studies to start to uncover the patterns in which these genes interact to cause psychiatric disorders.

However the problem goes deeper than that. The entire search for genetic causes of psychiatric diseases is undermined by the vague and arbitrary nature of psychiatric diagnosis. Many people are shocked to find out that there is no ‘test’ for depression, schizophrenia or any other psychiatric disease. There are only generally accepted guidelines (found in DSM-IV – the current edition of the diagnostic and statistical manual). Human inconsistencies in assigning diagnoses make it extremely difficult to do statistical analysis across studies.

Even more problematic than inconsistency in assigning psychiatric diagnoses, is inconsistency in the diagnoses themselves. Psychiatric diseases are a poorly designed, fuzzy set. That means that patients often fit into the definitions of mulitiple diseases. This ambiguity is a consequence of diagnosis using external symptoms. Because every person is different, their disease manifests in different ways, making it very difficult to identify exactly what their pathology is. Ths suggests that the search for genetic causes to psychiatric diseases may never bear fruit.

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