Causal Pathways for Specific Language Impairment: Lessons From Studies of Twins

Abstract

Purpose This review article summarizes a program of longitudinal investigation of twins' language acquisition with a focus on causal pathways for specific language impairment (SLI) and nonspecific language impairment in children at 4 and 6 years with known history at 2 years. Method The context of the overview is established by legacy scientific papers in genetics, language, and SLI. Five recent studies of twins are summarized, from 2 to 16 years of age, with a longitudinal perspective of heritability over multiple speech, language, and cognitive phenotypes. Results Replicated moderate-to-high heritability is reported across ages, phenotypes, full population estimates, and estimates for clinical groups. Key outcomes are documentation of a twinning effect of risk for late language acquisition in twins that persists through 6 years of age, greater for monozygotic than dizygotic twins (although zygosity effects disappear at 6 years); heritability is greater for grammar and morphosyntax than other linguistic dimensions, from age 2 years through age 16 years, replicated within twin samples at subsequent age levels and across twin samples at age 16 years. Conclusion There is consistent support for legacy models of genetic influences on language acquisition, updated with a more precise growth signaling disruption model supported by twin data, as well as singleton data of children with SLI and nonspecific language impairment. Presentation Video https://doi.org/10.23641/asha.13063727

Disorders of Language and Literacy in the Prison Population: A Scoping Review

“…This model views developmental disorders from a perspective of four levels of explanation: the symptomatic or behavioral level, the cognitive level, the biological level, and the environmental level. The behavioral level concerns what is observable "on the surface", for example problems in morphosyntax [13], slow reading speed [14,15], poor reading comprehension [16,17], or poor spelling skills [18,19]. These behavioral symptoms can originate from deficits at the cognitive level, such as poor phonological processing [20,21], reduced processing speed [22,23], or deficits in working memory [22,[24][25][26].…”

“…These behavioral symptoms can originate from deficits at the cognitive level, such as poor phonological processing [20,21], reduced processing speed [22,23], or deficits in working memory [22,[24][25][26]. The cognitive deficits may in turn be caused by factors at the biological level, which may for example include genetic factors [13,27], or brain structure and function [28][29][30]. Finally, the environmental level continuously influences and modifies the other three levels and comprises conditions such as the educational level of parents and other socio-economic factors [31,32], or school practices and learning environment [33].…”

Advances in Specific Language Impairment Research and Intervention: An Overview of Five Research Symposium Papers

“…The topic of the first paper (Rice, 2020) literally begins with gestation, in investigations of twin pairs of children defined by their biological relationship-that is, monozygotic (MZ) versus dizygotic pairs (DZ). Comparisons of language acquisition between twins and singletons inform us of biological/developmental risks associated with twinning, and comparisons of children within twin pairs inform us of the relative contributions of shared environment versus shared genes as indexed by heritability estimates.…”

“…It will be important to conduct studies in which measures of language, reading, and nonverbal IQ are collected from the same children in a large population-based sample. Methods of analyses in the twin studies (Rice, 2020) generate outcomes most likely to replicate across studies within one lab or across different labs if the measurement methods are precise, including criteria for differentially grouping children as language impaired with or without low nonverbal IQ. Note, it is valuable to also include the children in the population who have low nonverbal IQ with co-occurring language skills within or even above typical range.…”

“…A common theme across the papers is concern with clinical issues related to identification of children with SLI, across a wide age span. Evaluation of diagnostic definitions or clinical markers are addressed in four of the papers (Adlof, 2020;Hadley, 2020;Redmond, 2020;Rice, 2020). Two of the papers focus on intervention methods (Adlof, 2020;Leonard & Deevy, 2020), and a third paper addresses intervention in the literature review (Hadley, 2020).…”