PLATELET SEROTONIN STUDIES IN HYPERSEROTONEMIC RELATIVES OF CHILDREN WITH AUTISTIC DISORDER

Platelet serotonin (5-HT) studies were conducted with 12 hyperserotonemic and 12 normoserotonemic age-, sex-, and relationship-matched relatives of autistic probands. Each group consisted of 7 mothers, 4 fathers, and 1 sister of autistic children and adolescents. The density (B(max)) of platelet 5-HT2 receptor binding sites, labelled with [H-3]-lysergic acid diethylamide (LSD), was significantly lower in 11 hyperserotonemic subjects compared to 12 normoserotonemic subjects (40.9 +/-13.5 fmol/mg protein, 59,6 +/- 13.2; p < 0.004). The affinity (K(d)) for [H-3]-LSD binding did not differ. Although the density (B(max)) of [H-3]-paroxetine binding did not differ between groups, there was a small difference in the affinity (K(d)) of [H-3]-paroxetine binding (hyperserotonemic 47.6 +/- 9.0 pM, normoserotonemic 54.8 +/-12.1; p < 0.05). There were no significant differences in platelet 5-HT uptake, or in thrombin-stimulated 5-HT release. Basal, 5-HT-stimulated, and arginine-vasopressin (AVP)-stimulated inositol phosphate production, as well as basal, prostaglandin E1 (PGE1)-, and forskolin-stimulated cAMP production did not differ. There were signficant correlations between whole blood 5-HT levels and LSD B(max) (r(S) = -0.63, N=23, p < 0.002) and whole blood 5-HT levels and 5-HT uptake V(max) (r(S) = 0.56, N=18, p < 0.02). However, [H-3]-LSD labelled 5-HT2 binding and 5-HT uptake were not correlated with each other. Hyperserotonemia of autism may be heterogeneous with one subgroup of subjects with increased 5-HT uptake and another subgroup with decreased 5-HT2 binding.