Specificity: A Phenotypic Comparison of Communication-Relevant Domains Between Youth With Down Syndrome and Fragile X Syndrome

Abstract

Despite the shared presence of an intellectual disability (ID), there is a growing literature documenting important phenotypic differences between Down syndrome (DS) and fragile X syndrome (FXS). These conclusions, however, are based on a synthesis across studies, each of which typically includes only measures of a limited number of constructs, and with differing participant characteristics. Firmer conclusions regarding specific phenotypes require a single comprehensive multi-domain assessment of participants with the syndrome groups being well matched on chronological age (CA) and cognitive functioning. The current study was designed to fill this gap by assessing several important cognitive and behavioral domains relevant to communication, such as: structural language skills, false belief understanding, as well as pragmatics and behavioral difficulties, in 30 adolescents of both sexes with DS and 39 males with FXS, matched on CA and nonverbal (NV) cognition. After statistically controlling for NV cognition, we did not find significant syndrome differences in expressive and receptive structural language or false belief understanding. In contrast, participants with DS displayed less stereotyped language and fewer behavioral difficulties compared to males with FXS. Within-syndrome associations among the targeted domains are described. Finally, females with DS were less impaired than males with DS in almost all structural language domains, whereas no significant sex-related differences were observed in NV cognition, false belief understanding, pragmatics, or behavior. Clinical and methodological implications of the findings are discussed.

Expressive language development in adolescents with Down syndrome and fragile X syndrome: change over time and the role of family-related factors

“…Although individuals with DS and those with FXS both show impairments in receptive language, these impairments tend to be consistent with expectations based on their levels of cognitive functioning [8][9][10][11]. In contrast, expressive language development typically lags behind receptive language and cognition for both individuals with DS [12] and males with FXS [13].…”

“…In general, pragmatic language delays are often noted in individuals with DS, particularly relative to expectations based on nonverbal cognition [26,[35][36][37][38]. That said, pragmatic strengths are often observed in DS, when compared to individuals with other neurodevelopmental disorders [8,39,40]. Sensory and motor impairments, as well as cognitive functioning (e.g., nonverbal MA), have been found to contribute to the expressive language problems of individuals with DS; however, these factors account for a relatively small proportion of the variance in expressive language outcomes [21,23,[29][30][31][32][33][34]36], suggesting a need for research to identify additional factors.…”

“…In addition, several studies have demonstrated that the profile of relative impairment across various areas of expressive language differs between individuals with FXS and those with DS beginning in early childhood [6,[14][15][16]. However, most of these studies have been based on comparisons between the diagnostic group at a single point in time and often for groups of participants representing wide age ranges [8,15]. Consequently, little is known about how expressive language profiles change over the course of development for individuals DS or FXS and how they compare.…”

“…Adolescence, however, is a particularly important developmental period in individuals with ID due to the fact that there is variation across syndromes in terms of whether intellectual development is stable or slows during this period [21], which can have consequences for language development during this same period. Moreover, expressive language difficulties are known to be a significant predictor of adult independence given the influences of these skills on social success, adaptive functioning, and learning [8].…”

Expressive language sampling as a source of outcome measures for treatment studies in fragile X syndrome: feasibility, practice effects, test-retest reliability, and construct validity

“…Advances in genomics, however, have now identified more than 100 genes that have a causal role [3] and that collectively account for half of all cases of ID [4]. Moreover, research spanning multiple levels of analysis, from the cellular to the behavioral, has uncovered both commonalities and differences in the phenotypes of conditions resulting from disparate etiologies, such as fragile X syndrome (FXS) and Down syndrome [5]. This research also has led to etiology-or disorder-specific treatments, with dozens of pharmaceuticals already tested in clinical trials [6][7][8] and more trials planned.…”