Whole-blood serotonin and cognitive functioning in autistic individuals and their first-degree relatives.

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.