Original Article
Effects of Diagnosis, Race, and Puberty on Platelet Serotonin Levels in Autism and Mental Retardation

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ABSTRACT

Objective

To reevaluate platelet serotonin (5-HT) levels in autism, measuring and controlling for effects of race and puberty. The specificity of hyperserotonemia for autism versus cognitive impairment is also assessed.

Method

Platelet 5-HT levels were measured in 77 individuals, aged 2 through 37 years, with autistic disorder; 65 normal controls; and 22 mentally retarded or otherwise cognitively impaired (MR/CI) prepubertal children. Effects of diagnosis, race, and pubertal status were evaluated by analysis of variance in separate pre- and postpubertal groups. 5-HT levels were expressed as ng/mL blood and ng/μL platelet volume.

Results

Among prepubertal children, significant effects of diagnosis (ng/mL; F2,109 = 5.9, p = .004) and race (F2,109 = 14.7, p < .0005) were found. Autistic youngsters had significantly higher 5-HT concentrations than controls, although the elevation (25%) was less 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 and race effects were nonsignificant in the postpubertal group. Postpubertal subjects had lower 5-HT concentrations than prepubertal subjects (ng/mL; F1,114 = 28.5, p < .0005).

Conclusions

The data underscore the importance of matching for race and pubertal status in neuropsychiatric 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/CI youngsters without autistic features. J. Am. Acad. Child Adolesc. Psychiatry, 1998, 37(7):767–776.

Key Words

platelet serotonin
autism
mental retardation
race
puberty

Cited by (0)

This research was supported by the NIMH (MH44177, MH30929), the Cornell Children's Clinical Research Center (RR06020), a fund established in The New York Community Trust by DeWitt-Wallace, the Caroline and Kenneth Brody Fund, the Korczak Foundation for Autism Research, and the Stallone Fund for Autism Research. Dr. McBride was the recipient of a Teacher-Scientist Award from the Andrew W. Mellon Foundation. The authors thank Laura Hall, M.S., for technical assistance and Ms. Rhonda Higgins for manuscript preparation.