In this paper, we will try to supply at least a partial answer to the three following questions. First, what language levels are reached by adults with Down syndrome? Second, is there progress in language or some aspects of it beyond adolescence and during the adult years? This question is related to the issue of a critical period for language development raised by Eric Lenneberg (1967). Third, what is the effect of ageing on the language of persons with Down syndrome, including those who develop Alzheimer disease in old age?
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Comblain et al. (1996) studied this question.
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