The mean length of utterance (MLU) in a person with DS can range from single words to more sophisticated language, depending on mental age (Fabbretti, Pizzuto, Vicari, & Volterra, 1997). This may be due not only to speech motor issues but to short-term memory issues noted in individuals with DS (Bunn, Roy, & Elliott, 2007).
Bunn, L., Roy, E. A., & Elliott, D. (2017). Speech perception and motor control in children with Down syndrome. Child Neuropsychology, 13(3). 262-275.
Fabbretti, D., Pizzuto, E., Vicari, S., & Volterra, V. (1997). A story description task in children with Down’s syndrome: Lexical and morphosyntactic abilities. Journal of Intellectual Disability Research, 41(2), 165-179.