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Full namemethylenetetrahydrofolate reductase (NAD(P)H)
# SNPs30
  Max Magnitude Chromosome position Summary
Rs12121543 11,794,614
Rs121434294 0 11,800,251
Rs121434295 0 11,801,166
Rs121434296 0 11,794,766
Rs121434297 0 11,795,161
Rs13306560 0 11,806,126
Rs13306561 11,805,747
Rs1476413 11,792,243
Rs1537514 11,788,011
Rs17037390 11,800,786
Rs17037396 0 11,801,990
Rs17367504 0 11,802,721
Rs17375901 0 11,792,459
Rs17421511 11,797,731
Rs1801131 2.1 11,794,419
Rs1801133 2.1 11,796,321 elevated homocysteine levels
Rs2066462 0 11,794,839
Rs2066470 0 11,803,000
Rs2274976 0 11,790,870
Rs267606886 0 11,795,114
Rs267606887 0 11,795,158
Rs3737964 11,806,987
Rs3737965 0 11,806,394
Rs45590836 0 11,791,216
Rs4846048 11,786,195
Rs4846049 11,790,308
Rs4846051 0 11,794,400
Rs59514310 11,796,321
Rs7533315 11,800,626
Rs9651118 11,802,157

The MTHFR gene encodes the vitamin-dependent enzyme, methylenetetrahydrofolate reductase. Several conditions or defects caused by functionally impaired forms of the MTHFR protein can be improved through dietary supplementation by folate.

There are 3 common SNPs giving rise to MTHFR alleles:

It is likely that there are numerous other variations that are much rarer. When the MTHFR genes of 564 individuals of diverse ethnicities were fully sequenced, in addition to the 3 common alleles mentioned above, 11 other nonsynonymous changes were found, each with a frequency under 1%. Four of these 11 rarer alleles affected enzyme function (as did A222V) based on tests in yeast, most of which could be fixed with higher folate supplementation (in yeast; this is not yet tested in humans). Since all five impaired alleles map to the N-terminal catalytic domain of the enzyme, it seems likely that additional SNPs causing nonsynonymous changes in this region could have similar effects.10.1073/pnas.0802813105

SNP rs1801133, A222V, is not thought to be a major risk factor for neural tube defects [PMID 17035141] except in certain populations. For example, Dutch and Irish populations indicate an increased risk for (T;T) carriers [PMID 10090889], but this same genotype (ie carriers of the thermolabile T allele) appears to have a protective effect in an Italian population studied [PMID 12111380].

[PMID 16672082] a SNP in MTHFR which affects Neural-tube defects (Birth defects)