EFFECTS OF DIAGNOSIS, RACE, AND PUBERTY ON PLATELET SEROTONIN LEVELS IN AUTISM AND MENTAL-RETARDATION

Objective: To reevaluate platelet serotonin (5-HT) levels in autism, m easuring and controlling for effects of race and puberty. The specific ity of hyperserotonemia for autism versus cognitive impairment is also assessed. Method: Platelet 5-HT levels were measured in 77 individual s, aged 2 through 37 years, with autistic disorder; 65 normal controls ; and 22 mentally retarded or otherwise cognitively impaired (MR/CI) p repubertal children. Effects of diagnosis, race. and pubertal status w ere evaluated by analysis of variance in separate pre- and postpuberta l groups. 5-HT levels were expressed as ng/mL blood and ng/mu L platel et volume. Results: Among prepubertal children, significant effects of diagnosis (ng/mL; F-2,F-109 = 5.9, p = .004) and race (F-2,F-109 = 14 .7, p <.0005) were found. Autistic youngsters had significantly higher 5-HT concentrations than controls, although the elevation (25%) was l ess than typically reported; MR/CI children had levels very similar to those of controls. White children had significantly lower 5-HT levels than black or Latino youngsters, regardless of diagnosis. Diagnosis a nd race effects were nonsignificant in the postpubertal group. Postpub ertal subjects had lower 5-HT concentrations than prepubertal subjects (ng/mL; F-1,F-114 = 28.5, p <.0005). Conclusions: The data underscore the importance of matching for race and pubertal status in neuropsych iatric research and suggest that the prevalence of hyperserotonemia in autistic individuals may have been overestimated because of a failure to control for both variables. Hyperserotonemia was not found in MR/C I youngsters without autistic features.