Oral zinc supplementation in Down's syndrome: restoration of thymic endocrine activity and of some immune defects.

Eighteen non-institutionalized Down's syndrome (DS) children (mean age: 7.0 +/- 10/12 years) with a history of respiratory tract, auditory and skin infections, low plasma levels of a nonapeptide thymic hormone, i.e. Serum Thymic Factor (STF), high plasma levels of inactive zinc-unbound STF molecules, and reduced absolute number of circulating T-lymphocytes, were given an oral non-pharmacological supplementation of zinc sulphate (1 mg Zn++/kg body weight/day for 2 months; two cycles, 10 months apart) and monitored immunologically before and after each cycle. A dramatic increase of plasma STF level and concomitantly an almost complete disappearance of inactive STF molecules was observed after each cycle. The absolute number of circulating T-lymphocytes was significantly increased by zinc treatment. The marginal zinc deficiency was also corrected without any appreciable influence on copper plasma levels. A reduction of recurrent infections and an improvement in school attendance after zinc supplementation were recorded. These beneficial effects of zinc supplementation were also noted in those DS children who did not show an apparent zinc deficiency, as assessed by measuring zinc plasma level. The reduced number of circulating B lymphocytes and the impaired lymphocyte responsiveness to phytohaemagglutinin and concanavalin A were not restored. On the whole, these findings suggest that there exists a defect in the bio-availability and/or in the utilization of zinc in DS. This alteration, of unknown origin, can be underestimated on the simple basis of the zinc plasma level and can be corrected with moderate nutritional zinc supplementation.