Relationships of whole blood serotonin and plasma norepinephrine within families.

Whole blood serotonin (5HT) and plasma norepinephrine (NE) levels were determined in 47 families of autistic probands to study relationships within families of these measures. Whole blood 5HT, but not plasma NE, was significantly positively correlated between autistic children and their mothers, fathers, and siblings. Twenty-three of the 47 families studied had at least 1 hyperserotonemic member. Of these 23 families, 10 (43.5%) had 2 or more hyperserotonemic members; 5 families were identified in which each family member studied had hyperserotonemia (whole blood 5HT greater than 270 ng/ml). If the autistic child of a family was hyperserotonemic, the first-degree relatives were 2.4 times more likely to be hypersertonemic than if the autistic child was not hyperserotonemic. Mean whole blood 5HT levels were higher in autistic subjects than their parents or siblings. Siblings were found to have lower plasma NE than autistic probands. This study replicates a previous study showing familial relationships of hyperserotonemia within families with autistic children.