ORIGINAL RESEARCH published: 01 October 2018 doi: 10.3389/fgene.2018.00424 Specificity: A Phenotypic Comparison of Communication-Relevant Domains Between Youth With Down Syndrome and Fragile X Syndrome Laura del Hoyo Soriano 1,2*, Angela John Thurman 1,2 and Leonard Abbeduto 1,2 1 MIND Institute, University of California, Davis, Sacramento, CA, United States, 2 Department of Psychiatry and Behavioral Sciences, University of California, Davis, Sacramento, CA, United States 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 Edited by: phenotypes require a single comprehensive multi-domain assessment of participants Manuel Mattheisen, with the syndrome groups being well matched on chronological age (CA) and cognitive Universitätsklinikum Würzburg, Germany functioning. The current study was designed to fill this gap by assessing several Reviewed by: important cognitive and behavioral domains relevant to communication, such as: Juko Ando, structural language skills, false belief understanding, as well as pragmatics and behavioral Keio University, Japan difficulties, in 30 adolescents of both sexes with DS and 39 males with FXS, matched on Baptiste Couvy-Duchesne, University of Queensland, Australia CA and nonverbal (NV) cognition. After statistically controlling for NV cognition, we did *Correspondence: not find significant syndrome differences in expressive and receptive structural language Laura del Hoyo Soriano or false belief understanding. In contrast, participants with DS displayed less stereotyped
[email protected] language and fewer behavioral difficulties compared to males with FXS.