Expressive Vocabulary Development in Children With Down Syndrome: A Longitudinal Study

Children with Down syndrome (DS) show a significant delay in their language development, in particular in expressive language. Although many studies have described the development of spoken language skills of children with DS, not many investigated the development of gestures and spoken words more in detail. The aim of this study was to describe the expressive vocabulary development of young children with DS with regard to the nature of vocabulary growth and modality (gesture- and/or verbal production). In addition, the association between cognitive development and vocabulary growth was examined. The study included 26 children with DS aged between 18 and 24 months (age at start: M=19.5, SD=2.1). Expressive vocabulary growth (gestures and spoken words) was longitudinally followed over an 18-month period based on monthly administrations of the Lexi questionnaire. Cognition was determined with the Cognition Scale of the Bayley-III-NL. First, three different vocabulary growth patterns were observed: marginal vocabulary growth (n=8), vocabulary growth without a spurt (n=9), and vocabulary growth spurt (n=9). The average level of cognition of the group of children with a marginal vocabulary growth pattern was significantly lower compared to that of the other two growth pattern groups. Second, between the age of 18 and 33 months, two different modality profiles were observed: predominant use of gestures (G), and use of gestures plus spoken words (GS). Two children changed from a G profile to a GS profile, two children changed from a GS profile to a predominant spoken word (S) profile. In line with earlier studies, the present study underscores the individual variability in expressive vocabulary growth patterns, and in modality profiles of children with DS. The relation of these individual differences to the children's level of cognition, as well as the relation between the different growth patterns and the different modality profiles are discussed.