Word production inconsistency of Singaporean-English-speaking adolescents with Down Syndrome

Background The nature of speech disorders in individuals with Down Syndrome (DS) remains controversial despite various explanations put forth in the literature to account for the observed speech profiles. A high level of word production inconsistency in children with DS has led researchers to query whether the inconsistency continues into adolescence, and if the inconsistency stems from inconsistent phonological disorder (IPD) or childhood apraxia of speech (CAS). Of the studies that have been published, most suggest that the speech profile of individuals with DS is delayed, while a few recent studies suggest a combination of delayed and disordered patterns. However, no studies have explored the nature of word production inconsistency in this population, and the relationship between word production inconsistency, receptive vocabulary and severity of speech disorder. Aims To investigate in a pilot study the extent of word production inconsistency in adolescents with DS and to examine the correlations between word production inconsistency, measures of receptive vocabulary, severity of speech disorder and oromotor skills in adolescents with DS. Methods & Procedures The participants were 32 native speakers of Singaporean-English adolescents, comprising 16 participants with DS and 16 typically developing (TD) participants. The participants completed a battery of standardized speech and language assessments, including The Diagnostic Evaluation of Articulation and Phonology (DEAP) assessment. Results from each test were correlated to determine relationships. Qualitative analyses were also carried out on all the data collected. Outcomes & Results In this study, seven out of 16 participants with DS scored above 40% on word production inconsistency, a diagnostic criterion for IPD. In addition, all participants with DS performed poorly on the oromotor assessment of DEAP. The overall speech profile observed did not exactly correspond with the cluster symptoms observed in children with IPD or CAS. Conclusions & Implications Word production inconsistency is a noticeable feature in the speech of individuals with DS. In addition, the speech profiles of individuals with DS consist of atypical and unusual errors alongside developmental errors. Significant correlations were found between the measures investigated, suggesting that speech disorder in DS is multifactorial. The results from this study will help to improve differential diagnosis of speech disorders and individualized treatment plans in the population with DS.