The reason I don't recommend going much higher on methylfolate when it is combined with several milligrams of methyl B12 is that this combination takes control of the rate of the methionine synthase enzyme away from the cells and drives it too fast. The result is that too much of the homocysteine is converted to methionine, and there is not enough left to flow into the transsulfuration pathway to support synthesis of glutathione and other sulfur-containing substances that the cells need.
The result is that the methylation cycle gets going well, but glutathione does not come up, as it needs to do for full recovery. There are excess methyl groups produced because of overdriving the methylation cycle. These are shunted off to the folate metabolism by sarcosine, which is produced by the glycine N-methyltransferase reaction, and then they come back to the methylation cycle via methylfolate. It's sort of like a futile cycle, like a squirrel in a rotating cage.
This is not just based on biochemical theory, though it is supported by that. It is based on lab tests that people who have been on this regimen have sent me.
For most PWMEs, this does not work very well in the long run. In Freddd's own case, because of the genetic variations that he apparently has in the CblC complementation group and in MTHFS (not to be confused with MTHFR), it is necessary for him to use a high dosage of methyl B12 to overcome the CblC problem, and it is necessary for him to use a high dosage of methylfolate to feed his folate metabolism, since he cannot use folinic acid or folic acid. (I'm not sure why he cannot use folic acid. Perhaps he has a polymorphism in the DHFR enzyme, also). Freddd cannot tolerate raising glutathione, because it binds cobalamin to form glutathionylcobalamin, and his version of the CblC complementation group is not able to retrieve cobalamin from glutathionylcobalamin. As far as I can tell, this is a rare genetic variation. Most PWMEs are depleted in glutathione, and this is responsible for a large number of the symptoms.
There may be other PWMEs who have one or more of these genetic issues as well, since Freddd reports that there are some others who respond to these supplements in the same way he does, but most do not seem to have them, based on our clinical study and anecdotal reports from quite a few PWMEs.
Best regards,
Rich