Adverse Effect of Nitrous Oxide in a Child with 5,10-Methylenetetrahydrofolate Reductase Deficiency

Abstract
Nitrous oxide irreversibly oxidizes the cobalt atom of vitamin B12, thereby inhibiting the activity of the cobalamin-dependent enzyme methionine synthase (or 5-methyltetrahydrofolate–homocysteine S-methyltransferase; Enzyme Commission code EC 2.1.1.13). Methionine synthase catalyzes the remethylation of 5-methyltetrahydrofolate and homocysteine to tetrahydrofolate and methionine ( Figure 1 ). Methionine, by way of its activated form, S-adenosylmethionine, is the principal substrate for methylation in many biochemical reactions, including assembly of the myelin sheath, methyl substitutions in neurotransmitters, and DNA synthesis in rapidly proliferating tissues.1