The association of the C677T 5,10methylenetetrahydrofolate reductase variant with elevated maternal serum α-fetoprotein and complications of pregnancy

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Bjorklund, Natalie Kim
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Statement of problem: We have shown that the C677T 5,10 methylenetetrahydrofolate reductase (MTHFR) variant is associated with elevated maternal serum α-fetoprotein (MSAFP), the most common screening test for neural tube defects (NTD). Therefore, past contradictory studies of NTDs and C677T MTHFR may have been biased because of changes in case populations after prenatal diagnosis and termination of pregnancy. Further, an unexplained elevation of MSAFP is known to increase the risk for later pregnancy complications. Is the C677T MTHFR variant a predisposing genetic variant for both NTDs and later complications of pregnancy? Methods: A retrospective study of women with pregnancies resulting in NTD outcome and women with unexplained elevations of MSAFP was undertaken. Women and their partners were genotyped for the C677T MTHFR allele. Couples with a pregnancy resulting in a NTD outcome were compared to couples whose pregnancy outcome did not involve. Couples with unexplained elevations of MSAFP who did and did not have later complications of pregnancy were also compared. Allele frequencies for all groups were then compared against the previously established Manitoba population allele frequency (based on 977 consecutive newborn metabolic screening bloodspots). A review of all studies of NTDs and association with the C677T MTHFR variant was undertaken to determine if the association between the variant and MSAFP is a source of bias. NTD incidence was examined before and after folic acid food fortification introduced in Canada in 1999. Results: There is an increase in the allele frequency of the C677T MTHFR variant in parents with an unexplained elevated MSAFP followed by later complications of pregnancy. The C677T MTHFR variant is also a contributing genetic factor to NTDs worldwide. The incidence of NTDs in Manitoba has decreased by 37% since food fortification with folic acid was introduced. Conclusions: The C677T MTHFR variant is a contributing genetic factor to both later complications of pregnancy after an unexplained elevation of MSAFP and to NTDs. This variant is folate sensitive and folic acid fortification has reduced the incidence of NTDs.
folate, folic acid fortification, neural tube defects, methylenetetrahydrofolate reductase, maternal serum α-fetoprotein, prenatal screening
Björklund, NK, Evans JA, Greenberg CR, Seargeant LE, Schneider C, Chodirker BN. The C677T methylenetetrahydrofolate reductase variant and third trimester obstetrical complications in women with unexpected elevations of maternal serum alpha-fetoprotein. Reprod Biol Endocrinol. 2004 Sep 7;2(1):65
Björklund NK, Chodirker BN, Greenberg CR, Seargeant LE, Evans JA, C677T MTHFR frequencies in different Canadian Provinces. Electronic Letters:, J Med Genet, Nov. 23, 2003
Björklund NK, Evans JA, Greenberg CR. 2000 "Association of thermolabile methylenetetrahydrofolate reductase (C677T) with elevated maternal serum alpha fetoprotein." Am J Hum Genet 67(4) Suppl 2: 417