Influence of methylenetetrahydrofolate reductase gene polymorphisms on homocysteine concentrations after nitrous oxide anesthesia.
BACKGROUND
Mutations in the methylenetetrahydrofolate reductase (MTHFR) gene (677C>T, 1298A>C) cause elevated plasma homocysteine concentrations and have been linked to fatal outcomes after nitrous oxide anesthesia. This study tested the hypothesis that patients with common MTHFR 677C>T or 1298A>C mutations develop higher plasma homocysteine concentrations after nitrous oxide anesthesia than wild-type patients.


METHODS
In this prospective, observational cohort study with blinded, mendelian randomization, the authors included 140 healthy patients undergoing elective surgery. All patients received 66% nitrous oxide for at least 2 h. The main outcome variable, plasma total homocysteine, and folate, vitamin B12, and holotranscobalamin II were measured before, during, and after surgery. After completion of the study, all patients were tested for their MTHFR 677C>T or 1298A>C genotype.


RESULTS
Patients with a homozygous MTHFR 677C>T or 1298A>C mutation (n = 25) developed higher plasma homocysteine concentrations (median [interquartile range], 14.9 [10.0-26.4] microm) than wild-type or heterozygous patients (9.3 [7.5-15.5] microm; n = 115). The change in homocysteine after nitrous oxide anesthesia was tripled in homozygous patients compared with wild-type (5.6 microm [+60%] vs. 1.8 microm [+22%]). Only homozygous patients reached average homocysteine levels considered abnormal (> 15 microm). Plasma 5-methyl-tetrahydrofolate concentrations increased uniformly by 20% after nitrous oxide anesthesia, indicating the inactivation of methionine synthase and subsequent folate trapping. Holotranscobalamin II concentrations remained unchanged, indicating no effect of nitrous oxide on vitamin B12 plasma concentrations.


CONCLUSIONS
This study shows that patients with a homozygous MTHFR 677C>T or 1298A>C mutation are at a higher risk of developing abnormal plasma homocysteine concentrations after nitrous oxide anesthesia.
Nagele
Peter
P
Department of Anesthesiology, Critical Care Medicine and Pain Therapy, Medical University of Vienna, Vienna, Austria. nagelep@wustl.edu
Zeugswetter
Barbara
B
Wiener
Caspar
C
Burger
Hansjörg
H
Hüpfl
Michael
M
Mittlböck
Martina
M
Födinger
Manuela
M
D000328:Adult; D000769:Anesthesia, Inhalation / Q000009:adverse effects*; D015331:Cohort Studies; D005260:Female; D005838:Genotype; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D008297:Male; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics* / Q000378:metabolism; D008875:Middle Aged; D009609:Nitrous Oxide / Q000009:adverse effects*; D011110:Polymorphism, Genetic / Q000187:drug effects / Q000235:genetics*; D011446:Prospective Studies; D016037:Single-Blind Method
D006710:Homocysteine; D042965:Methylenetetrahydrofolate Reductase (NADPH2); D009609:Nitrous Oxide