The relationship between cognitive-intellectual abilities and whole-
blood serotonin (5-hydroxytryptamine; 5-HT) in 18 autistic probands and
their first-degree relatives (n = 21 parents, n = 13 siblings) was
investigated. Whole-blood 5-HT was significantly negatively associated with
verbal-expressive/symbolic abilities for the entire sample. The proportion
of variance in cognitive-intellectual performances attributable to
whole-blood 5-HT was substantial in the context of variance attributable to
familial classification. The relationship between verbal-expressive
abilities and whole-blood 5-HT, adjusted for race and familial
classification, was noteworthy. Simple correlations between 5-HT and
cognitive-intellectual performances were conducted. However, bias related
to covariance attributable to race seriously limits such findings. The
issue of bias and its relevance to previous research is discussed
further.
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