Crossing the Threshold: An Epigenetic Alternative to Dimensional Accounts of Mental Disorders

Abstract

Recent trends in psychiatry involve a transition from categorical to dimensional frameworks, in which the boundary between health and pathology is understood as a difference in degree rather than as a difference in kind. A major tenet of dimensional approaches is that no qualitative distinction can be made between health and pathology. As a consequence, these approaches tend to characterize such a threshold as pragmatic or conventional in nature. However, dimensional approaches to psychopathology raise several epistemological and ontological issues. First, we review major sources of evidence usually recruited in support of the dimensional trend (focusing on clinical observation and biological data), and we show that these are connected to different conceptualizations of how dimensional traits extend across health and pathology.Second, we criticize two unquestioned assumptions that stand at the core of the dimensional trend: a) that there is continuity from health to pathology at the symptomatic level; b) that such continuity reflects an underlying continuity in the genetic liability for pathological conditions. Third, we argue against the idea of a conventional threshold by showing that such a view implies a linear relationship between the genotype and the phenotype. Fourth, drawing on epigenetics and developmental biology, we offer a characterization of mental disorders as stable and dynamic constellations of multi-level variables that differ qualitatively from 'healthy states'. We conclude by showing that our account has several theoretical advantages over both categorical and dimensional approaches. Notably, it provides crucial insights into psychological development over time and individual differences, with major implications in terms of intervention and clinical decision-making. Serpico & Petrolini 2023 BJPS 2 Table of contents: 1. Introduction 2. The Dimensional Framework: Its Grounding and Pitfalls 2.1 Methodological and conceptual Issues 3. Unpacking Continuity 3.1 From behaviour to dimensional operationalization 3.2 From genetics data to the quantitative framing of psychopathologies 4. The Conventional-threshold View 4.1 Theoretical issues of the conventional-threshold view 5. The Ontological-threshold Model 5.1 Mental disorders as constellations 5.2 Mental disorders as stable and dynamic qualitative states 5.3. Clinical implications: individual differences and individual development 6. Conclusions

Assessing brain morphological correlates of premenstrual symptoms in young healthy females

“…In doing so, we attempted to capture the spectrum of premenstrual symptom load in the general population of females in their reproductive years. Taking a dimensional approach when looking at potential surrogate markers of mental health traits can be beneficial because of the tendency for behavioral traits in clinical populations to also manifest in non-clinical populations in variable degrees of severity and frequency (Serpico & Petrolini, 2023). Moreover, biological research on mental disorders, especially quantitative genetic research, also support some degree of dimensionality in that healthy and pathological states share common genetic foundations (Serpico & Petrolini, 2023).…”

“…Taking a dimensional approach when looking at potential surrogate markers of mental health traits can be beneficial because of the tendency for behavioral traits in clinical populations to also manifest in non-clinical populations in variable degrees of severity and frequency (Serpico & Petrolini, 2023). Moreover, biological research on mental disorders, especially quantitative genetic research, also support some degree of dimensionality in that healthy and pathological states share common genetic foundations (Serpico & Petrolini, 2023). Brain features, which represent putative intermediate phenotypes between genotypes and behavioral traits (Matoba et al, 2022), should also then show some dimensionality in association to mental health disorders, e.g.…”

“…through additive genetic effects on the brain. Brain morphological studies on mental disorders have indicated both qualitative and quantitative differences, and suggest a highly complex relationship between genetic, brain morphological and behavioral variables (Serpico & Petrolini, 2023). Adding dimensional approaches to biological research on premenstrual symptomology and psychopathology can provide valuable insights into the biological mechanisms and markers that might underlie these conditions and disorders.…”