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Research Article Free access | 10.1172/JCI113507

Genetic heterogeneity among patients with methylcobalamin deficiency. Definition of two complementation groups, cblE and cblG.

D Watkins and D S Rosenblatt

Medical Research Council of Canada Genetics Group, Centre for Human Genetics, Montreal, Quebec.

Find articles by Watkins, D. in: JCI | PubMed | Google Scholar

Medical Research Council of Canada Genetics Group, Centre for Human Genetics, Montreal, Quebec.

Find articles by Rosenblatt, D. in: JCI | PubMed | Google Scholar

Published June 1, 1988 - More info

Published in Volume 81, Issue 6 on June 1, 1988
J Clin Invest. 1988;81(6):1690–1694. https://doi.org/10.1172/JCI113507.
© 1988 The American Society for Clinical Investigation
Published June 1, 1988 - Version history
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Abstract

A number of patients with megaloblastic anemia and homocystinuria associated with low levels of methylcobalamin synthesis in cultured cells have been recognized. Methionine biosynthesis by intact cells, as determined by incorporation of label from 5-[14C]methyl-tetrahydrofolate into acid-precipitable material, was deficient in cultured skin fibroblasts that were derived from all of these patients. In one group of patients, activity of the methylcobalamin-dependent enzyme, methionine synthase, in cell extracts was within the normal range when the enzyme was assayed under standard conditions. In a second group of patients, methionine synthase activity was decreased under the same assay conditions. Genetic complementation analysis demonstrated the existence of two complementation classes that corresponded to these two groups of patients. The designation cblE has previously been proposed for normal methionine synthase activity. We propose the designation cblG for the mutation in those patients with methylcobalamin deficiency and decreased synthase activity. The results of these studies suggest that the products of at least two loci are required for cobalamin-dependent methionine biosynthesis in mammalian cells.

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