Syntactic Networks as an Endophenotype of Developmental Language Disorders: An Evo-Devo Approach to Clinical Linguistics

Abstract

Usually, developmental language disorders are defined either symptomatically (based on a constellation of linguistic deficits appearing recurrently within a population) or etiologically (on the basis of a common underlying deficit), or both. On paper, each of these clinical categories is expected to be distinguished from other close entities at several levels of analysis (phenotypic, cognitive, neurobiological, genetic, etc.). Nonetheless, this is not typically the case: Comorbidity, variability, and heterogeneity are in fact a common outcome of the clinical practice. Ultimately, different disorders may share the same underlying deficit (e.g., phonological dysfunction in dyslexia and SLI); conversely, different deficits may give rise to the same disorder (e.g., both visual problems and phonological deficits may contribute to dyslexia) (Benitez-Burraco 2013). If we want to achieve a better—and earlier—diagnosis of these conditions, we should improve the tools we employ at present. A promising approach is one relying on the endophenotypes of disorders. Endophenotypes may be defined as cognitive, neuroanatomical, neurophysiological, endocrine, or biochemical quantifiable components of the space between genes and diseases (Gould & Gottesman 2006). Endophenotypes refer to more specific (and more physiological) aspects of the body function, therefore they allow us to gain a more accurate diagnosis of its dysfunction (Gottesman & Gould 2003). Here we would like to advance a putative endophenotype of language disorders that combines four factors: (1) linguistic analysis (syntactic computation), (2) information management (communicative strategies), (3) recent evo-devo insights in the nature of phenotypic variation, and (4) network approaches to emergent properties of complex systems (surely, language it is; Deacon 2005). To begin with, we would like to note that, although the set of pathological conditions already described by clinical linguists is ample, it is not unlimited either. In other words, variation is constrained or canalized, even in pathological states. At the same time, we observe that language is both sensitive to damage (e.g., some aspects of language processing are perturbed in nearly all disorders, like the proper use of inflectional cues in verbal and nominal morphology) and resistant to perturbation (e.g., a nearly functional language faculty may emerge at the term of growth in spite of severe underlying deficits).