The Brave New World of Epigenetics: Embracing Complexity in the Study of Speech and Language Disorders

Abstract

The study of causal influences on marked disorders of speech and language have been dominated by dichotomies and reductionist models. However, the emergent evidence of epigenetics forces us to acknowledge the complex mechanisms that underlie such conditions. The purpose of this article is to highlight future directions for studying the causal mechanisms that underlie children's speech and language disorders, with an emphasis on speech sound disorders and specific language impairment. In doing so, we will briefly highlight past methods of studying genetic effects on children's speech sound and language disorder profiles and propose the dynamic systems theory as a meaningful framework for studying the complex landscape of childhood speech-language development. This model challenges traditional dichotomies between genetic and environmental effects and between beneficial versus deleterious effects/factors.

Motor Issues in Specific Language Impairment: a Window into the Underlying Impairment

“…An endophenotype is Bany hereditary characteristic that is normally associated with some condition but is not a direct symptom of that condition [71, p. 10].^If, via the search for endophenotypes, one or more common genetic sources could be found for SLI and other syndromes such as dyslexia where sequencing suffers in both the language and motor domains [72,73], that outcome would further support Ullman and Pierpont's proposal. Preliminary work that has been done in this connection has suggested genetic contributions to SLI [74], though identification of candidate genes [75] has been slowed by the varied diagnostic categories for SLI [76], and more recently the suggestion of complex interactions between genetic and environmental factors [77]. It is too early to tell whether the genetic data bear critically on the sequencing view or the other views that were reviewed here.…”

Causal effects on child language development: A review of studies in communication sciences and disorders

“…Such complexity highlights the value in studying individual developmental trajectories, preferably through a variety of scientific paradigms. At the same time that molecular genetic paradigms are providing increasingly sophisticated means to examine epigenetic effects (Kraft & DeThorne, 2014), longitudinal case studies offer an opportunity to document the emergence and development of behavior ''in the wild,'' including the multitude of factors likely to impinge upon it. At the very least, both quantitative and qualitative studies should be moving toward the inclusion of more contextual information in the study of child language development, incorporating information across levels from individual biology to social-cultural community (see for example Baxendale, Lockton, Adams, & Gaile, 2013or Zubrick et al, 2007.…”

Longitudinal Effects on Early Adolescent Language: A Twin Study

“…Last, behavioral genetic analyses are not well positioned to examine the complexities of epigenetic effects, specifically environmental influences on genetic expression (cf. Kraft & DeThorne, 2014;Rogers, Nulty, Aparicio Betancourt, & DeThorne, 2015).…”