Immunological and purine enzyme studies on hyperuricaemic and normouricaemic patients with Down's syndrome.

Hyperuricaemia in Down's syndrome is unreleated to the activity of phosphoribosylamidotransfrease, which catalyses the activity of the first specific step on the purine biosynthetic pathway, and to the activity of hypoxanthine phosphoribosyltransferase and phosphoribosylpyrophosphate synthetase, abnormalities of which are known to be associated with hyperuricaemia. Immunological studies involving serum immunoglobulins, natural E. coli antibodies, test immunization with pneumococcal polysaccharide type III (PnPS), in vitro lymphocyte transformation to mitogens, and pokeweed mitogen (PWM) induced immunoglobulin production showed no difference between hyperuricaemic or normouricaemic Down's patients and institutionalized controls. The Down's patients had higher serum IgA, IgG and IgE, and some also produced more immunoglobulin in PWM-stimulated lymphocyte cultures when compared to normal healthy controls. However, both patients with Down's syndrome and the institutionalized controls had significantly lower responses to PnPs than normal healthy controls. The only deficiency confined to the Down's patients was a signficant depression in delayed hypersensitivity to dinitrochlorobenzene. These findings indicate that the in vivo abnormality of depressed cellular and humoral immunity in Down's patients is not paralleled by in vitro function as measured by PHA lymphocyte transformation and immunoglobulin production by PWM-stimulated lymphocytes. There is also no apparent link between a putative defect in purine metabolism in Down's patients and any immunological abnormalities.