WEDNESDAY, April 2 (HealthDay News) -- Mutations responsible for the cblD defect, one of nine defects of intracellular cobalamin (vitamin B12) metabolism, have been found in the MMADHC gene on chromosome 2, according to a report published in the April 3 issue of the New England Journal of Medicine.
David Coelho, Ph.D., from University Children's Hospital in Basel, Switzerland, and colleagues studied fibroblasts from seven patients with the cblD defect. Individual human chromosomes were added to the cells to identify the responsible gene, followed by more refined genetic mapping.
The researchers found that the cblD gene was located on human chromosome 2q23.2 and identified a possible candidate gene, MMADHC (methylmalonic aciduria, cblD type, and homocystinuria). The wild-type gene rescued the defect in adenosylcobalamin and methylcobalamin synthesis, and mutations in the gene were found in all patients. Cells carrying mutant forms of the gene were defective in adenosylcobalamin and methylcobalamin synthesis.
"Mutations in a gene we designated MMADHC are responsible for the cblD defect in vitamin B12 metabolism," Coelho and colleagues conclude. "Various mutations are associated with each of the three biochemical phenotypes of the disorder."
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