Editorial: Distinguishing between the challenges posed by surface and deep forms of heterogeneity to diagnostic systems: do we need a new approach to subtyping of child and adolescent psychiatric disorders.

Diagnostic formulations attempt to impose order on the messy reality of psychopathological phenomena. By doing this, so their advocates argue, they provide both the platform necessary for systematic scientific study, and, crucially, the bridge of shared terms and concepts vital if psychiatric science is to be truly translational; where scientific endeavour is guided by clinical priorities and, in-turn, scientific findings innovate clinical practice. The diagnostic schemes we currently work with, taking DSM-5 as the obvious case, are the product of an interesting historical process of ongoing revision - at the same time pragmatic and scientific. On the one hand, it is a process both anchored firmly in historical precedent and constrained by the practical needs of clinicians, patients and health insurance companies. On the other hand, it is a process open to new empirical data about how to best cluster symptomatic expressions and differentiate clinical presentations - so that over historical time diagnostic categories achieve an increasingly accurate mapping of the taxonomy (i.e., underlying structure), and related pathophysiology, of psychiatric phenomenon. Resolving the inevitable tensions that arise when trying to reconcile these pragmatic (economic and professional) and scientific priorities has proved to be both challenging and contentious. The study of heterogeneity as exemplified by the articles highlighted in this editorial indicate a range of different approaches that can be effectively used to refine psychiatric taxonomies by incorporating developmental and pathophysiological data to help identify new putative subtypes of potential therapeutic significance.