Vitamin B12 responsive homocystinuria and megaloblastic anemia: heterogeneity in methylcobalamin deficiency.
A male infant with methyl-B12 deficiency (cblE) presented at age 6 weeks with lethargy, staring spells, and vomiting. He later became hypotonic and unresponsive to stimuli and required intubation and ventilation. He had homocystinuria and hypomethioninemia with megaloblastic anemia but normal serum folate and vitamin B12 concentrations. No methylmalonic aciduria was detected. Fibroblasts, cultured from the patient, were unable to grow in medium in which homocysteine replaced methionine and incorporated abnormally small amounts of [14C]-methyl-tetrahydrofolate but normal amounts of [14C]-propionate into protein. Methyl-B12 content of fibroblasts was low, while the adenosyl-B12 content was normal. Methionine synthase activity was decreased when the assay was performed under both optimal and suboptimal reducing conditions, suggesting heterogeneity in the cblE disease. The patient responded dramatically to hydroxocobalamin treatment. Homocystinuria disappeared after 10 days of therapy, and methionine was normalized after 3 weeks. Psychometric testing at age 15 months showed a developmental age of 9 months.
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CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL GENE-Y CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL
Methyl-B12 adenosyl-B12 Methionine hydroxocobalamin Vitamin B12 methylcobalamin Methionine synthase methionine methyl-B12 folate vitamin B12 methylmalonic aciduria homocysteine methionine [14C]-methyl-tetrahydrofolate [14C]-propionate