Episodic Detail Production and Semantic Coherence in Down Syndrome and Fragile X Syndrome: Longitudinal Findings from Expressive Language Sampling

Autobiographical memory requires the integration of episodic and semantic information and is closely tied to expressive language abilities. This study examined episodic detail production and narrative coherence in children and adolescents with Down syndrome (DS) and Fragile X syndrome (FXS) using conversational samples from the Expressive Language Sampling (ELS) Conversation task (Abbeduto et al., 2020, 2023). Participants (N = 50) contributed one matched autobiographical topic at two visits approximately 18 months apart. Episodic and semantic details were coded using the Autobiographical Interview (AI) framework (Levine et al., 2002), and narrative coherence was assessed using Semantic Distance (SemDis), a computational measure of conceptual relatedness (Beaty & Johnson, 2021). Multilevel models evaluated whether diagnostic group, expressive language, narrative length, and time predicted autobiographical memory performance. Across aims, children showed substantial variability in narrative output, with greater within-group than between-group differences. Diagnostic group did not significantly predict episodic detail production, and episodic content showed minimal change across time. Word count was the only significant predictor, indicating that children who produced more language provided more episodic content. No demographic or language variables uniquely predicted episodic detail production once narrative length was controlled. Semantic coherence was also stable across visits and did not differ by diagnostic group or narrative length. The only significant effect was a diagnostic group × CELF-FS interaction: higher expressive syntax predicted more coherent narratives among children with DS, whereas children with FXS showed a slight decrease in coherence as expressive syntax increased. Overall, findings indicate that expressive output, rather than diagnostic status, is the primary driver of autobiographical narrative performance in DS and FXS.