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I don’t do this blog at work, but I do recall what has been discussed and shared. This week. let’s think about psychiatric diagnosis. There efforts in psychiatric nosology, or description of disorders, over the last 30 years has been towards reliability. But the validity of what we are doing is being questioned at the highest level.

It is becoming increasingly evident that the usefulness of diagnostic categories in psychiatry has been overemphasized. These categories have been initially charged with implications in terms of pointing to a specific treatment and prospectively a specific etiology and/or pathogenesis, in complete analogy with the other branches of medicine. More recently, they have been more modestly charged with relative, not absolute, pragmatic implications in terms of guiding the formulation of a management plan and the prediction of outcomes (the two main elements of “clinical utility”). The underlying concept has been that we are dealing with “patterns” of intercorrelated reported experiences (in medical jargon, symptoms) and observed behaviours (in medical jargon, signs) which allow significant inferences about further course and management, whereas there is no assumption that these patterns are all “natural kinds” (i.e., discrete disease entities marking a real division in nature). Indeed, improving the clinical utility of psychiatric diagnoses has been the declared main objective of both the DSM?5 and, even more explicitly, the ICD-11.

Unfortunately, even these more modest implications of diagnostic categories in psychiatry have turned out to be overestimated. This is not to say that our current diagnoses do not have clear implications in terms of treatment choice and prediction of outcomes. The fact is, however, that these implications are less significant than originally believed and still assumed by most treatment guidelines.

Maj, M. (2018), Why the clinical utility of diagnostic categories in psychiatry is intrinsically limited and how we can use new approaches to complement them. World Psychiatry, 17: 121-122.

One of my colleagues noted that in GWAS, all the psychiatric disorders lump together, looking at a paper in Science

Common variant risk for psychiatric disorders was shown to correlate significantly, especially among attention deficit hyperactivity disorder (ADHD), bipolar disorder, major depressive disorder (MDD), and schizophrenia. By contrast, neurological disorders appear more distinct from one another and from the psychiatric disorders, except for migraine, which was significantly correlated to ADHD, MDD, and Tourette syndrome. We demonstrate that, in the general population, the personality trait neuroticism is significantly correlated withalmost every psychiatric disorder and migraine.

The Brainstorm Consortium, Analysis of shared heritability in common disorders of the brain Science 22 Jun 2018:Vol 360, Issue 6395, eaap8757

The trouble with these papers is that many would then suggest that because our classification is debunked, there is no differentiation between psychiatric syndromes, and there is no need to look further. This is an error. The data set is mixed, and a when one looks at the symptom level — as is the case in the early intervention literature — then there are some clues.

A genetic relationship was identified between clinical schizophrenia and positive, cognitive, and negative psychotic?like experience trait domains in adolescence. A higher genetic risk for schizophrenia significantly predicted adolescents having more cognitive disorganization, anhedonia, and parent?rated negative symptoms, as well as more paranoia and hallucinations (this last finding was in the non?zero scorers). Thus our findings suggest that psychotic?like experience trait domains in adolescence comprise partly of the genetically?influenced phenotypic manifestation of schizophrenia. Furthermore, higher genetic risk for major depression significantly predicted having more self?rated anhedonia and parent?rated negative symptoms as a teenager. Our results discredit the hypothesis that psychotic?like experience trait domains in the general population are epiphenomena that do not share biological pathways with clinically?recognized psychiatric disorders.

Genetic risk for schizophrenia and major depression in adulthood predicted 0.08–0.11% variance in psychotic?like experience domains in adolescence.

Pain O, Dudbridge F, Cardno AG, Freeman D, Lu Y, Lundstrom S, Lichtenstein P, Ronald A. Genome-wide analysis of adolescent psychotic-like experiences shows genetic overlap with psychiatric disorders. Am J Med Genet B Neuropsychiatr Genet. 2018 Jun;177(4):416-425.

what is clear, to me, is that our current classification system is broken, for it is seeking a false level of reliability without valid nosological constructs. This may change. But it will not be without a struggle.

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