Whole blood serotonin and plasma beta-endorphin in autistic probands and their first-degree relatives

Background: Whole blood serotonin (5-HT) and C-terminally directed beta-end orphin protein immunoreactivity (C-ter-beta-EP-ir) are known to be elevated in autistic subjects and might be possible markers of genetic liability to autism. This study thus investigates the familial aggregation of 5-HT and of C-ter-beta-EP-ir levels in first degree relatives of autistic probands. Methods: In a sample of 62 autistic subjects and 122 of their first-degree relatives, compared to age and sex-matched controls, we measured 5-HT by ra dioenzymology and C-ter-beta-EP-ir by radioimmunoassay, Results: We confirm the previously reported familiality of hyperserotoninem ia in autism as mothers (51%), fathers (45%) and siblings (87%) have elevat ed levels of 5-HT, and we reveal presence of elevated levels of C-ter-beta- EP-ir in mothers (53%) of autistic subjects. Conclusions: Familial aggregation of quantitative variables, such as concen tration of neurotransmitters, within unaffected relative could serve as an intermediate phenotype and might thus help the search of genetic susceptibi lity factors in autism. (C) 1999 Society of Biological Psychiatry.