Hypercobalaminemia (high serum vitamin B12 levels) is a frequent and underestimated anomaly. Clinically, it can be paradoxically accompanied by signs of deficiency, reflecting a functional deficiency linked to qualitative abnormalities, which are related to defects in tissue uptake and action of vitamin B12. The aetiological profile of high serum cobalamin predominantly encompasses severe disea...

BACKGROUND When increased serum cobalamin concentrations are encountered clinically they are usually attributed to parenteral supplementation, dietary factors, or otherwise ignored. However, recently, hypercobalaminaemia has been associated with numerous diseases in humans, most notably neoplastic and hepatic disorders. The aim of this retrospective, observational, cross-sectional study was to ...

Biermer’s disease also called: Addison’s anemia or in old textbooks, pernicious anemia, is an autoimmune disease, caused by impaired absorption of cobalamin (vitamin B12) owing to the neutralization of intrinsic factor action in the setting of immune atrophic gastritis [1]. In adults and elderly patients, this form of megaloblastic anemia is one of the leading causes of cobalamin deficiency, wi...

Developments relating to cobalamin and folate are reviewed. Current work on the relations between these two coenzymes are discussed, particularly those that have emerged in studies using nitrous oxide, which inactivates cobalamin.

Members of the genus Leptospirillum are aerobic iron-oxidizing bacteria belonging to the phylum Nitrospira. They are important members of microbial communities that catalyze the biomining of sulfidic ores, thereby solubilizing metal ions. These microorganisms live under extremely acidic and metal-loaded environments and thus must tolerate high concentrations of reactive oxygen species (ROS). Co...

The megaloblastic anemia of cobalamin deficiency appears secondary to decreased methionine synthetase activity. Decreased activity of this enzyme should cause 5-methyltetrahydrofolate to accumulate intracellularly, and consequently, decrease purine and DNA synthesis; this is the basis of the "methylfolate trap" hypothesis of cobalamin deficiency. However, only some of the clinical and biochemic...

Transcobalamin (TC) I deficiency, like the function of TC I itself, is incompletely understood. It produces low serum cobalamin levels indistinguishable from those of true cobalamin deficiency. Diagnosis is especially elusive when TC I deficiency is mild. To provide new, more substantive definition, the TCN1 gene was examined in two well-characterised families that included members with both se...

Salmonella typhimurium synthesizes cobalamin (vitamin B12) de novo under anaerobic conditions. Of the 30 cobalamin synthetic genes, 25 are clustered in one operon, cob, and are arranged in three groups, each group encoding enzymes for a biochemically distinct portion of the biosynthetic pathway. We have determined the DNA sequence for the promoter region and the proximal 17.1 kb of the cob oper...

This work was presented in part at the meeting ofthe American Society of Human Genetics, San Diego, Calif., October 1977. Dr. Mellman and Dr. Willard are recipients of traineeships from the National Institutes of Health (T01-GM 02299). Dr. Mellman's present address is Laboratory of Cellular Physiology and Immunology, The Rockefeller University, New York 10021. Received for publication 18 May 19...

Background: Cobalamin deficiency and peripheral neuropathy (PN) are commonly seen in HIV-infected adults. The level of urine methylmalonic acid (UMMA), a reliable indicator of tissue cobalamin status, was determined in HIV infected subjects with and without PN to establish this association. Methods: One hundred and ninety-eight (198) consenting HIV infected subjects with and without PN were rec...