Peripheral and central 5-hydroxytryptamine in trisomy 21

Peripheral and central metabolism of 5-hydroxytryptamine was studied in 16 patients with trisomy 21 and compared to that in 4 karyotypically normal mentally retarded children. Serum 5-hydroxytryptamine was markedly decreased in the trisomics whereas cerebrospinal fluid levels of 5-hydroxytryptamine and 5-hydroxyindole acetic acid were increased in the same groups. These results are discussed with respect to regulatory mechanisms of 5-HT metabolism.