Decreased ATPase and Increased Sodium Content of Platelets in Down's Syndrome

Abstract

ATPase activity and sodium and potassium concentrations were studied in platelets from normal subjects and patients with Down's syndrome. Platelet ATPase activity of the patients was significantly decreased (p < 0.001 )-136.8 ± 5.2 (±S.E.M.) nm per hour per 108 platelets as compared to 173.2 ± 7.3 nm per hour per 108 normal platelets. Platelet potassium content of the patients was also decreased, 13.12 ± 0.48 μg per 109 platelets as compared to 19.78 ± 0.72 μg per 109 normal platelets (p < 0.001). Platelet sodium content of the patients was increased, 6.79 ± 0.40 μg per 109 platelets as compared to 3.32 ± 0.21 μg per 109 normal platelets (p < 0.001). The potassium-sodium ratios in the platelets of the patients had no overlap with values obtained in the normal controls. Decreased platelet ATPase activity of patients with Down's syndrome could cause decreased outward sodium transport, resulting in an increased platelet sodium content. Since the transport of serotonin into platelets is coupled to inward sodium transport, we propose that the observed decreased concentration of serotonin in platelets of these patients results from the decreased inward sodium transport. (N Engl J Med 291:950–953, 1974)