Contributions of phonological and verbal working memory to language development in adolescents with fragile X syndrome

Abstract

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability. Although language delays are frequently observed in FXS, neither the longitudinal course of language development nor its cognitive predictors are well understood. The present study investigated whether phonological and working memory skills are predictive of growth in vocabulary and syntax in individuals with FXS during adolescence. Forty-four individuals with FXS (mean age = 12.61 years) completed assessments of phonological memory (nonword repetition and forward digit recall), verbal working memory (backward digit recall), vocabulary, syntax, and nonverbal cognition. Vocabulary and syntax skills were reassessed at a 2-year follow-up. In a series of analyses that controlled for nonverbal cognitive ability and severity of autism symptoms, the relative contributions of phonological and working memory to language change over time were investigated. These relationships were examined separately for boys and girls. In boys with FXS, phonological memory significantly predicted gains in vocabulary and syntax skills. Further, verbal working memory was uniquely associated with vocabulary gains among boys. In girls with FXS, phonological and working memory skills showed no relationship with language change across the 2-year time period. Our findings indicate that, for adolescent boys with FXS, acquisition of vocabulary and syntax may be constrained by the ability to maintain and manipulate phonological representations online. Implications for the identification and treatment of language disorders in this population are discussed. The present study is the first to identify specific cognitive mechanisms contributing to language growth over time in individuals with FXS.

Growth of Expressive Syntax in Children With Fragile X Syndrome

“…Consistent with previous findings indicating higher language abilities in girls with FXS (Abbeduto et al, 2003;Finestack & Abbeduto, 2010;Pierpont et al, 2011), most girls in our sample demonstrated higher syntactic abilities than boys, although individual differences were noted. That is, only half of the female participants outperformed the male participants.…”

“…Overall, we found a significant linear growth for both the IPSyn and MLU, and these findings coincide with previously reported findings on growth in expressive syntax among participants with FXS (Martin et al, 2013;Pierpont et al, 2011). In addition to the linear trend, there was a small but significant quadratic trend, with a slowing of the growth rate and a slight decline in later ages for some of the participants.…”

“…A primary strength of the current study is the examination of syntactic growth in children with FXS over a 5-year period, a longer time period than previously reported (Martin et al, 2013;Pierpont et al, 2011). This allowed us to gain an extensive look of how FXS affects growth in expressive syntax and relative strengths and weaknesses, both of which are important questions in our attempt to better understand the language phenotype in FXS.…”

“…In terms of language abilities, evidence indicates that girls are not as delayed as boys (Abbeduto et al, 2003;Finestack & Abbeduto, 2010;Fisch et al, 1999). Girls with FXS have generally demonstrated higher receptive (Abbeduto et al, 2003) and expressive (Finestack & Abbeduto, 2010;Finestack, Sterling, & Abbeduto, 2013;Sterling & Abbeduto, 2012) language skills, and tended to acquire specific language skills (i.e., vocabulary, syntax) faster over time than boys with FXS (Pierpont, Richmond, Abbeduto, Kover, & Brown, 2011), with the exception of a small proportion of girls who also have comorbid autism.…”

“…Two recent studies provided data on syntactic development over time. Pierpont et al (2011) examined the contributions of phonological and verbal working memory skills on growth of vocabulary and syntax over a 2-year period among adolescents with FXS. They reported significant relationships between the two memory domains and language growth in boys but not girls with FXS.…”