WHAT good is a diagnostic tool if it is too complicated for doctors to use? This is the dilemma facing psychiatry. In the United States the release back in February of a draft version of the latest edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) has triggered a furious row over whether this tool has become too complex. Meanwhile, the World Health Organisation (WHO) points out that more than three-quarters of people with brain disorders in the developing world are not being treated, and on October 7th it released simplified guidelines for diagnosis and treatment designed especially for use by the front-line in medicine: primary-care doctors.

These developments highlight a revolution in psychiatry, the last bastion of symptom-based medicine. In no other medical domain is the symptom (say, anxiety) also the diagnosis. There is a reason for this: the brain is a complex organ and the causes of its disorders remain poorly understood. But thanks to brain imaging and genetics, that is changing fast.

Research into the impact of genetic mutations on brain development has revealed that conditions previously considered distinct often have common genetic underpinnings, so there is bound to be overlap between psychiatric disorders as they have been defined traditionally. One example is a gene called DISC 1 (which stands for disrupted-in-schizophrenia 1). A malfunctioning version of the protein encoded by this gene contributes, as its name suggests, to schizophrenia. But it also contributes to anxiety. Likewise, genes involved in making the myelin sheaths that insulate nerve cells go wrong in both schizophrenic and bipolar patients. In this context it is no surprise that a decade of brain imaging has shown the same neuronal circuits to be involved in many disorders. The reward circuits, for instance, are implicated in addiction, schizophrenia, depression and obsessive-compulsive disorder. According to John Krystal, the editor of Biological Psychiatry, one of the field's leading journals, what seems to be emerging is a completely new way of looking at psychiatric diagnosis in which there is no one-to-one relationship between genes and symptoms but, rather, genes affect the development of brain circuits and this then produces symptoms.

Mind and matter

The authors of DSM-V attempt to capture this less than black-and-white picture by dispensing with the approach taken in previous DSMs, which was based on cut-and-dried checklists of symptoms. Instead, they have adopted a “dimensional” approach, in which patients are assessed for symptoms besides those that match their principal diagnosis, as well as for the severity of their symptoms.

One of the goals is to help medics identify mild forms of severe illnesses such as schizophrenia before people have experienced their first serious psychotic episode, in the hope of stopping the disease progressing. But DSM-V will also propose new conditions, such as “complicated grief”, which describes bereaved people who may benefit from being treated as if for major depression.

The aim is to help doctors offer patients the most appropriate treatment. But an important by-product will be that researchers working on the psychiatric drugs of the future will be able to test them in genetically engineered animal models that more closely resemble human reality. The importance of this was underlined by Eric Nestler of the Mount Sinai Medical Centre, in New York, and Steven Hyman of Harvard University in this month's Nature Neuroscience, when they wrote that drug development for schizophrenia, major depression, bipolar disorder and autism “is at a near standstill”.

The proposed changes, however, worry some psychiatrists, who see in them a creeping medicalisation of normal behaviour. They point out that the DSM carries a lot of weight. Pharmaceutical companies devise new drugs for the conditions it defines, lawyers use it to sue doctors, ordinary people use it to diagnose themselves. They fear that by blurring the boundary between health and disease, DSM-V loses sight of a doctor's first duty: to do no harm.

To overcome this, there have been suggestions in the past that the DSM should be divided into two: a scientific version, for use by researchers and psychiatrists, and a pragmatic version, for everyone else. Writing in the Psychiatric Times in August, Seyyed Nassir Ghaemi of Tufts University in Boston argued that this was not the answer. It would simply lead to the “gerrymandering” of definitions based on outdated and invalid knowledge.

Now the WHO has taken the initiative with its Intervention Guide, in which the organisation's own classification of brain disorders—itself in the process of being revised to make it simpler for non-specialists to use—has been distilled into 100 pages of easy-to-follow flowcharts. The WHO points out that in the developing world nearly 95m people with depression and more than 25m with epilepsy receive no treatment or care.

In the end, says Dr Krystal, the dichotomy between the valid and the useful may turn out to be a false one. The most commonly prescribed psychiatric drugs are effective for many diagnoses, precisely because those diagnoses have underlying features in common. In his view, society's demands are not mutually exclusive. Doctors can continue to do no harm, while researchers brace themselves for exciting, and unsettling, times to come.