Plasma concentrations of magnesium, lead, lithium, copper, and zinc in mentally retarded persons.

The metal magnesium and the trace elements lead, lithium, copper, and zinc were determined by atomic absorption spectrophotometry in the plasma of 107 residents with different types of mental retardation at a state institution in Minnesota. Twenty-six staff volunteers and 29 residents with psychosocial mental retardation served as control subjects. Plasma magnesium concentrations were normal in all retarded subjects. Lead and lithium concentrations were below detection levels in all retarded and nonretarded subjects. Low copper concentrations were found in the plasma of retarded dwarfs and of male microcephalic subjects. The most significant finding was hypozincemia in 49 subjects with Down syndrome of both sexes and all ages. Because this finding was limited to residents with Down syndrome, a nutritional deficiency is most unlikely. The possible etiological factors of hypozincemia in Down syndrome were discussed.