Sir

We would like to suggest a possible reason for the disputes and failures in the search for a genetic basis for mental illnesses that was not mentioned in your News Feature 'Psychiatric genetics: the brains of the family' (Nature 454, 154–157; 2008) or Editorial 'An unnecessary battle' (Nature 454, 137–138; 2008). It is that the discrete categories defined by the American Psychiatric Association's fourth Diagnostic and Statistical Manual of Mental Disorders (DSM) checklists are essentially arbitrary, rarely or never corresponding to a particular and consistent underlying biological dysfunction.

The DSM identifies human troubles as patterns of feelings and behaviours, given in generic verbal descriptions and grouped together into categories defined by checklists. The feelings and behaviours figuring on a particular checklist are described as “symptoms” of the condition that the checklist supposedly identifies.

A symptom is the manifestation of a particular disease state, but the DSM checklists rarely capture any such thing. The diagnostic categories are complex, vague and subjective. There is considerable overlap between conditions and inconsistency within them, both in 'symptoms' and 'treatments'. Their character is entirely generic, failing to incorporate personal histories of patients into a description of their situation. And they are cut from whole cloth by committees whose members have an inherent professional interest in drawing human difficulties into their purview as clinicians and researchers. The well known interconnections between scientific and commercial outcomes in this area are also problematic.

Rather than identifying discrete and universal biological disease phenomena, then, DSM categories may best be viewed as expedient, arbitrary distinctions, used to justify psychiatry's claims to scientific legitimacy and to simplify the task of gaining approval for standardized medical responses to complex human problems.

Assuming that all variations in human experience and character are mediated in part by variations in body chemistry, biological correlates for these groupings of feelings and behaviours can presumably be turned up with enough searching. The associated problems may nonetheless be better understood and dealt with in the context of human lives, relationships, societies and environments, without depending on such categorization.

Contemporary psychiatry is in far too deep to accept such a challenge easily. However, that should not prevent us from considering it.

See also: Mental health: don't overlook environment and its risk factors Mental health: drop ideological baggage in favour of best tools