Levels of some purine metabolizing enzymes in lymphocytes from patients with Down's syndrome.

The activities of a number of purine metabolizing enzymes of erythrocytes and lymphocytes were determined in 18 subjects with Down's syndrome and in 18 age- and sex-matched control subjects. An increase of adenosine deaminase activity (adenosine or deoxyadenosine as substrates) was found in erythrocytes (P less than 0.001) as well as in lymphocytes (P less than 0.001) of Down's syndrome subjects compared to controls. The purine nucleoside phosphorylase activities in lymphocytes and plasma urate concentrations were also significantly higher in Down's syndrome subjects than in controls (P less than 0.001 and less than 0.02, respectively). Adenine phosphoribosyltransferase activities and hypoxanthine-guanine phosphoribosyltransferase activities in lymphocytes were identical in the two groups. In all subjects studied there were positive correlations between the erythrocyte adenosine deaminase activities, lymphocyte adenosine deaminase or deoxyadenosine activities, and plasma urate concentrations (P less than 0.05 in all cases), and between lymphocyte nucleoside phosphorylase and lymphocyte adenosine deaminase or deoxyadenosine deaminase activities (P less than 0.01 and less than 0.05, respectively). The results suggest that increased activities of some purine metabolizing enzymes found in both erythrocytes and lymphocytes may contribute to increased purine degradation and hyperuricemia in subjects with Down's syndrome. In addition, the increased adenosine deaminase and nucleoside phosphorylase activities may be related to the immunological dysfunction found in subjects with Down's syndrome.