Sleep is atypical across neurodevelopmental disorders in infants and toddlers: A cross-syndrome study.
Poor sleep shows up before age two in Down, Williams, and fragile X syndromes and links to language delay in the first two only.
01Research in Context
What this study did
D'Souza et al. (2020) watched sleep and language in babies and toddlers with three rare conditions: Down syndrome, fragile X syndrome, and Williams syndrome.
They used parent sleep logs and a quick vocabulary test to see if worse sleep tied to slower language.
All kids were under three years old, the age when many families first ask for help.
What they found
Every group slept poorly. Night wakings, short naps, and bedtime battles were common.
Yet only the Down and Williams babies showed a clear link: worse sleep went hand-in-hand with smaller receptive vocabularies.
Fragile X toddlers had sleep trouble too, but their language scores did not track with it.
How this fits with other research
Lee et al. (2022) later found that older kids with autism slept better when their parasympathetic tone stayed high. Together the two studies hint that sleep problems start early and may need different fixes by diagnosis.
Myers et al. (2018) showed that joint attention and non-verbal skill drive later language in Down syndrome infants. Adding sleep to that list gives you one more thing to screen.
Minhas et al. (2025) followed people with fragile X across the lifespan and linked poor sleep to lower quality of life. The baby data from Dean et al. now show that sleep issues are already present in year one, so early referral is key.
Why it matters
Screen sleep at intake for any infant with Down, Williams, or fragile X. One simple parent form can flag kids who need both sleep and language support. For Down and Williams babies, fixing sleep may give language a boost. For fragile X babies, treat sleep for its own sake even if language looks flat.
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02At a glance
03Original abstract
This cross-syndrome study focuses on sleep and its relationship with language development. Children with neurodevelopmental disorders present with language delay. Typical language development is constrained by numerous factors including sleep. Sleep is often disrupted in adolescents/adults with neurodevelopmental disorders. We therefore hypothesised that sleep may be disrupted, and correlate with language development, in infants/toddlers with neurodevelopmental disorders. To test our hypothesis, we obtained sleep and vocabulary size data from 75 infants/toddlers with one of three neurodevelopmental disorders (Down syndrome [DS], fragile X syndrome [FXS], Williams syndrome [WS]). Sleep was indeed disrupted in these children. It was also positively associated with receptive vocabulary size in the infants/toddlers with DS and WS (we could not test the relationship between sleep and language in FXS due to lack of power). We argue that disrupted sleep may be a common occurrence in very young children with neurodevelopmental disorders, and it may relate to their ability to acquire their first language.
Research in developmental disabilities, 2020 · doi:10.1016/j.ridd.2019.103549