Sleep abnormalities are associated with limitations in vocabulary in very young children with developmental conditions including fragile X syndrome, a study reports.
Although preliminary, the results suggest that strategies aimed at improving sleep in young children with developmental disorders might also help improve language skills.
The study, “Sleep is atypical across neurodevelopmental disorders in infants and toddlers: A cross-syndrome study,” was published in the journal Research in Developmental Disorders.
Children with fragile X and other developmental disorders often have delayed language development. Besides the specific processes linking these conditions to acquiring language skills, other factors may affect language development, especially early in life.
For example, sleep is critical for many aspects of early language development, including learning new vocabulary. Sleep disturbances have been reported in children with Down syndrome and other conditions. This suggests that limitations in language may result from a combination of the underlying processes of these disorders and other factors, including abnormal sleep.
This hypothesis challenges the longstanding view that language delay is inevitable in children with neurodevelopmental disorders and indicates that early treatment could be effective.
A team from the U.K. compared sleep and vocabulary among 30 children with Down syndrome, 15 with fragile X, 30 with Williams syndrome, and 30 typically developing children used as controls. Ages ranged from 10 months to nearly 4.5 years and did not differ across the groups.
To assess sleep habits, caretakers completed the Sleep and Naps Oxford Research Inventory (SNORI), which is a diary to record the child’s sleep over 10 days. This includes parameters such as naps during the day and the proportion of time in bed spent actually sleeping.
The Oxford Communicative Developmental Inventory (OCDI) was used to assess vocabulary. This questionnaire involves asking parents whether their child is able to “understand” or “understand and say” a list of 416 words.
Results showed that sleep was disrupted in the three conditions. On average, controls slept about 50 minutes more per night than children with any of the three disorders — a total of nearly 11 hours in controls and slightly over 10 in affected children.
Typically developing children also spent about 30 fewer minutes awake during bedtime than children with one of the conditions. Put another way, controls had nearly 100% sleep efficiency (percentage of bedtime spent actually asleep), compared with about 95% in children with developmental disorders.
Patterns of napping varied by age — older children tended to take fewer, shorter naps — but did not differ significantly across the groups.
For children with Down or Williams syndrome, nighttime sleep duration was significantly associated with vocabulary: “After accounting for age, for every two minutes of sleep time, language comprehension increased by one word in DS [Down syndrome],” the researchers wrote.
Similar findings were reported for Williams syndrome; fragile X was not analyzed due to the low number of participants.
Interestingly, these differences only applied to language comprehension — differences were in words children could “understand,” not in what they could “understand and say.” According to the researchers, this might occur because speech tends to be more variable. Still, a larger sample size would be needed to confirm these results.
“Our research demonstrates that sleep is disrupted very early in development across various neurodevelopmental disorders, and the indications are that this is contributing to difficulties with learning language,” Dean D’Souza, PhD, the study’s first author from Anglia Ruskin University, said in a press release.
“Further research is needed to explore whether early interventions to improve the sleeping patterns of children with Down’s syndrome, Fragile X syndrome and Williams syndrome would be as beneficial for their language skills as interventions later in their development that specifically target language learning,” he added.