Studies in B12-deficient monkeys with combined system disease. I. B12-deficient patterns in bone marrow deoxyuridine suppression tests without morphologic or functional abnormalities.

A colony of rhesus monkeys made vitamin B12 deficient through dietary deprivation has been maintained since 1970. Deficient animals regularly develop neurologic lesions histologically, ultrastructurally, and topographically indistinguishable from those of human subacute combined degeneration but have failed to develop overt hematologic changes. No megaloblastic alterations, other evidence of impaired blood cell production, or subtle differences in mean red cell size are found. dU suppression tests on bone marrow were performed to determine whether functional B12 deficiency existed. All B12-deficient monkeys had markedly abnormal dU suppression test results after more than 10 months of B12 depviation, corrected by addition of B12 in vitro, whereas controls remained normal. Reasons for these disparate findings are considered, including species differences in metabolism of cobalamin analogues, cobalamin, and transcobalamins; the sensitivity of the dU test; the fact that ability to utilize preformed nucleotides may be greater in monkeys than in humans.