A multi-level developmental approach to exploring individual differences in Down syndrome: genes, brain, behaviour, and environment.
Michael S C Thomas, Olatz Ojinaga Alfageme, Hana D'Souza and 5 others
PMID 32653761WHAT IT FOUND
Neither family socioeconomic status nor the APOE ε4 gene predicted early vocabulary differences in 84 children with Down syndrome.
Wide individual variation remains unexplained by these common factors, suggesting the genetic syndrome itself drives most of the variability.
Key findings
01Family socioeconomic status, indexed by parental occupation, did not reliably predict receptive or expressive vocabulary size in children with Down syndrome.
02Carrying the APOE ε4 risk allele for Alzheimer's disease was not associated with different levels or rates of early vocabulary development compared to non-carriers.
03There was extensive individual variability in vocabulary development, with some children scoring in the normal range for typically developing peers while others were significantly delayed.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The sample had a restricted range of socioeconomic status, with most families in higher professional categories, which may have obscured an effect. The study was underpowered to detect small genetic effects, particularly for the APOE analysis. The MRI component was a pilot with only five cases, making it impossible to draw conclusions about brain-behaviour links. Vocabulary measures relied partly on parent report, which can be noisy when children have poor speech intelligibility.
Declared interests
No conflicts of interest statement was provided in the text.
The easy way to misread this
Do not interpret the null findings as proof that environment or genetics play no role in Down syndrome development. The SES sample was skewed toward higher incomes, and the study was too small to detect subtle genetic effects, so these factors may still be relevant in different populations.