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SNPs for Dihydrofolate Reductase (DHFR)

Discussion in 'Genetic Testing and SNPs' started by nandixon, Sep 25, 2012.

  1. nandixon

    nandixon Senior Member

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    Here are the SNPs that 23andMe gives for dihydrofolate reductase (DHFR). Currently there are twelve of them. This enzyme performs the first two steps in the 4-step transformation of the synthetic form of folate, i.e., folic acid, into biologically active "L-methylfolate" (and folinic acid).

    Since hopefully most people are avoiding folic acid to the extent they can, a more important role for DHFR is in regeneration of tetrahydrobiopterin (BH4) from BH2.

    BH4 is important in the production of neurotransmitters and also for regulation of the enzyme nitric oxide synthase (NOS), which can potentially become dysregulated ("uncoupled") when BH4 is deficient and produce too much nitric oxide and superoxide, leading to peroxynitrite and, theoretically, exacerbating the chronically high levels of oxidative stress that are seen in CFS/ME.

    (The rate-limiting step for production of BH4 itself is GTP cyclohydrolase I, aka GTPCH or GCH1 on 23andMe. I'll be making another thread for GCH1. Mutations in GCH1 can cause a deficiency of BH4, and I think it's worth exploring to see if it may be compounding the problems we seem to have in the methylation cycle genes, i.e., MTHFR, MTRR, CBS, etc.)

    Rich had at one point been interested in what CFS/ME peoples' results might be for DHFR and posted his 23andMe results on another thread. Assuming I've analyzed things correctly, his results appear to be completely normal (homozygous -/- throughout). Mine are identical to his with only one exception: the SNP rs1650697 (aka C35T or G-437A) that overlaps with a coding region for the gene MSH3 is homozygous (+/+) for the variant alleles (AA). I'm not sure whether this single homozygous result by itself is significant, but when paired with another SNP (rs1105525 aka G308A) which 23andMe unfortunately doesn't test for, it can act as a major promoter of DHFR, increasing its production/activity. In theory that actually might be helpful for regenerating BH4. (But it might be bad with respect to cancer growth. Green tea, for example, is an inhibitor of DHFR, thus its anti-cancer benefits.)

    Below are my results for people to compare to theirs. Again, I doubt the one positive SNP is relevant/detrimental for CFS/ME, but other people might have different results for the other SNPs. (I think GCH1 is generally going to be much more problematic.)

    DHFR SNPs:
    rs7387 A or T TT (-/-)
    rs1643659 C or T TT (-/-)
    rs1677693 G or T GG (-/-)
    rs1643649 C or T TT (-/-)
    rs11951910 C or T TT (-/-)
    rs865646 G or T GG (-/-)
    rs13161245 A or G AA (-/-)
    rs10072026 C or T TT (-/-)
    rs11490741 C or T CC (-/-)
    rs863215 C or T CC (-/-)
    rs1478834 A or C CC (-/-)
    DHFR, MSH3 rs1650697 A or G AA (+/+; 4% frequency)
     
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  2. Lotus97

    Lotus97 Senior Member

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    I don't know much about SNPs and I just learned about DHFR an hour ago. Does this mean that SNP determines how much folic acid is needed to slow or block DHFR in an individual?
     
  3. drex13

    drex13 Senior Member

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    My results are identical to yours with the exception of the last one, rs1650697, for which I am AG.
     
  4. Phred

    Phred Senior Member

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    My results differ greatly from yours, as shown in red. This might explain a lot with me. I don't have CFS/ME though. I wound up here following Freddd to do his protocol with a b12 deficiency. When I first saw this I wondered if you had the right letter (haplotype?) for the homozygous negative. As you can see I have 7 of the 12 homozygous positive. Eeek! I'll now be looking up BH4 and BH2.
     
  5. Waverunner

    Waverunner Senior Member

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    My results also differ greatly. I'm +/- for everything except rs10072026 (-/-) and rs11490741 (-/-).
     
  6. nkm

    nkm

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    Just to clarify, the DHFR enzyme is NOT responsible for recycling BH2 to BH4. DHFR is responsible for the first step in the folate cycle which reduces folate/folic acid to dihydrofolate.

    The enzyme DHPR (dihydropteridine reductase) is the one responsible for BH2 to BH4 recycling, using 5MTHF as a cofactor.
     
  7. nandixon

    nandixon Senior Member

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    Hi nkm,

    No, that's not right. 7,8-dihydrobiopterin (BH2) is recycled to tetrahydrobiopterin (BH4) by dihydrofolate reductase (DHFR).

    A different molecule, quinoid-dihydrobiopterin (q-BH2), is recycled to BH4 by dihydropteridine reductase (DHPR).

    So DHFR and DHPR both produce BH4, but in different regenerative/recycle pathways using different molecules as substrates.

    DHFR is likely to be (much) more important than DHPR in CFS/ ME for a number of reasons, including as I alluded to in my original post the role of DHFR in regulating the ratio of BH4 to BH2 to help maintain endothelial nitric oxide synthase (eNOS) coupling, ie, to prevent damaging superoxide (free radical) and peroxynitrite production. There are a number of articles on this, including:
    http://www.ncbi.nlm.nih.gov/pubmed/21402147/
    ("Dihydrofolate reductase protects endothelial nitric oxide synthase from uncoupling in tetrahydrobiopterin deficiency" 2011)

    Although DHFR does process folic acid, folic acid is not a naturally occurring substrate for that enzyme. It's a synthetic, man-made type of folate and actually inhibits the recycling of BH2 to BH4 by competing as a substrate for DHFR. (This is a good reason, among others, for people to avoid folic acid.) A recent article talks about this:
    http://www.ncbi.nlm.nih.gov/pubmed/23707606/
    ("Human endothelial dihydrofolate reductase low activity limits vascular tetrahydrobiopterin recycling" 2013)
     
    nkm likes this.
  8. nkm

    nkm

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    Thanks for the further information.

    I'm a bit confused though as to the significance for PWC's because the pathway normally discussed involves 5MTHF which catalyses the BH2 to BH4 reaction via DHPR. Perhaps it is more consequential for PWC's who have very elevated peroxynitrite and hence very depleted BH4 may be the ones to have extreme folic acid sensitivity as the DHFR enzyme is less able to protect/maintain the BH4 pool.

    While DHFR can also perform the task of protection/maintenance, wouldn't the DHPR be considered the one of primary significance? Another reason DHPR seems primary is because researchers showed large doses of 5MTHF as mono-therapy (or adjunct to anti-depressants), causes an increase in BH4 and therefore, the monoamine neurotransmitters. Deplin was the end product brought to market based on this research.
     
  9. nandixon

    nandixon Senior Member

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    DHPR doesn't catalyze the reaction of BH2 to BH4. I've seen that mistakenly presented in a number of places, including on the Heartfixer website. DHPR catalyzes the reaction of quinoid-BH2 (q-BH2) to BH4, not 7,8-BH2 (BH2) to BH4, the latter of which is performed by DHFR. See this helpful schematic (Figure 2.9) that Metametrix prepared:
    http://www.metametrixinstitute.org/file.axd?file=2011/6/Page-34.pdf

    And 5-methyltetrahydrofolate (5-MTHF, L-methylfolate) is not directly involved in either the DHFR or DHPR reactions. I think what you're thinking of is the reaction that occurs when the MTHFR enzyme (methylene tetrahydrofolate reductase) runs in reverse due to an excess of 5-MTHF. In that case BH4 is again produced from q-BH2, not BH2. See Figure 4 in this article:
    http://www.altmedrev.com/publications/13/3/216.pdf
    (It also shows BH2 converted to BH4 by DHFR.)

    I'm not aware of any reaction/enzyme that produces BH4 from BH2, other than DHFR. (Not that another one doesn't necessarily exist, I'm just not familiar with it.)
     
    nkm likes this.
  10. LaurieL

    LaurieL Senior Member

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    Midwest
    My results are in green.
     
  11. Valentijn

    Valentijn Activity Level: 3

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    LaurieL : Mine are similar to yours. But several of the DHFR SNPs have exactly the same prevalence in the same sample groups, so are probably inherited as a chunk. One such cluster is red, and the other is green. Our differences from the Richvank genotype are orange.

    RSID........ALLELE.....RICH...LAURIEL....VAL...
    rs7387......A or T...TT (-/-) AT (+/-) AT (+/-)
    rs1643659...C or T...TT (-/-) CT (+/-) CT (+/-)
    rs1677693...G or T...GG (-/-) GT (+/-) GT (+/-)
    rs1643649...C or T...TT (-/-) CT (+/-) CT (+/-)
    rs11951910..C or T...TT (-/-) CT (+/-) TT (-/-)
    rs865646....G or T...GG (-/-) GT (+/-) GT (+/-)
    rs13161245..A or G...AA (-/-) AC (+/-) ?? (?/?)
    rs10072026..C or T...TT (-/-) TT (-/-) TT (-/-)
    rs11490741..C or T...CC (-/-) CC (-/-) CC (-/-)
    rs863215....C or T...CC (-/-) CT (+/-) CT (+/-)
    rs1478834...A or C...CC (-/-) AC (+/-) AC (+/-)
    rs1650697...A or G...AA (-/-) AG (+/-) AG (+/-)

    So we have the same "red" and "green" groups, which are different from Richvank's, as well as rs7387 and rs1650697. Our only difference from each other is that I have the Richvank version of rs11951910.
     
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  12. LaurieL

    LaurieL Senior Member

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    What I find interesting, is doing my sons at the same time. I have all the mutations in DHFR and he does not. But when looking at GCH1, he has most of the variations, where as I do not.
     
  13. Sea

    Sea Senior Member

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    Mine are the same as Rich except for a CT for rs10072026, which is different from all of you
     
  14. nkm

    nkm

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    That does provide me with more clarity but it raises a major question at the same time...

    I had referred to the neuro-research that led to the development of active L-methylfolate (Deplin). The question is if DHPR is not involved in BH4 recycling, how does giving mass doses of methylfolate lead to an increase in monoamine neurotransmitters via the actions of increased serotonin and tyrosine hydroxylase enzymes, which require BH4 as a co-factor?

    I understand genetics and other theory may say differently but the above is also scientifically backed and now, more and more, is backed by real life results. If you have any technical info on this matter, I would love to read it.
     
  15. nandixon

    nandixon Senior Member

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    Giving large amounts of methylfolate causes the MTHFR enzyme reaction to run in reverse, producing methylene THF from the excess methylfolate, and BH4 from q-BH2. The BH4 can then be used to increase production of the monoamines.

    DHPR is involved in the recycling of BH4, but via q-BH2 (not BH2).

    So both DHPR and MTHFR (in the reverse direction) effectively recycle BH4 from q-BH2.

    On the other hand, DHFR recycles BH4 from BH2...
     
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  16. nkm

    nkm

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    What would be the practical difference between qBH2 and BH2 for an individual wanting to increase BH4 and monoamine neurotransmitter levels? Or is it just two pathways achieving the same result?
     
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  17. nandixon

    nandixon Senior Member

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    To assist in producing more BH4 from q-BH2 (via MTHFR - in reverse) you could take L-methylfolate.

    To assist in producing more BH4 from BH2 (via DHFR) you would want to avoid the known inhibitors of DHFR, including folic acid and green tea (especially green tea extracts, eg, EGCG).
     
    LaurieL likes this.
  18. nkm

    nkm

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    Do you think the other component of green tea, L-theanine, can inhibit DHFR? I ask because someone I know who has problems with methylation cycle reacted badly to L-theanine when we thought it would have helped to calm the CNS down.
     
  19. BFG

    BFG

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    my DHFR genes are the exact same as Nandixon's except for the MSH3

    DHFR79924791rs7387A or T TT
    DHFR79934836rs1643659C or T TT
    DHFR79936318rs1677693G or T GG
    DHFR79939449rs1643649C or T TT
    DHFR79939471rs11951910C or T TT
    DHFR79942357rs865646G or T GG
    DHFR79944733rs13161245A or G AA
    DHFR79945140rs10072026C or T TT
    DHFR79947998rs11490741C or T CC
    DHFR79948005rs863215C or T CC
    DHFR79949575rs1478834A or C CC
    DHFR, MSH379950781rs1650697A or G AG
     
  20. LynnD

    LynnD

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    So which snp does what?
    DHFR
    rs7387 AT
    rs1643659 CT
    rs1677693 GT
    rs1643649 CT
    rs11951910 TT
    rs865646 GT
    rs13161245A or Gno call
    rs10072026C or TTT
    rs11490741C or TCC
    rs863215 CT
    rs1478834 AC
    rs1650697AG
     

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