In SIDS compared to control cases, our results show: (1) increased levels of plasma and intra-platelet 5-HT, (2) decreased levels of platelet 14–3–3ζ protein, (3) decreased levels of platelet surface adhesion receptor GPIX, and (4) in this independent cohort, confirmation of our previous finding14 of elevated serum 5-HT. The gene discussed is GP9; the disease is sudden infant death syndrome.