AdB12 is not involved in methylation. So you would basically be dosing with just methylfolate. It would combine with any B12 you got from food or was stored in your body. If you don't have much B12 stored, doing folate without B12 may possibly cause depletion of B12, at least that's what it seems like in my case based on symptoms. So that could explain getting good results, and then not. The methylfolate used whatever B12 you had to make methyl groups, then you ran out, so you stopped methylation and the problems returned.
400-600mg is actually pretty much, unless you're one of those people who requires a whole bunch. Rich Van Konynenburg had suggested 200mcg methylfolate, along with 200mcg folinic acid. Those are the final doses, not starting doses. Always Start Low and Go Slow to minimize adverse effects.
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You have one First Priority mutation which is CBS A360A. This is the minor one, which people don't usually have a problem with, but you have two mutations, and you also have all the BHMTs, which can add to the problem. And you reported methyl B12 and TMG caused anxiety. This could be CBS causing this, so it would be good to do some testing to see if that's expressed. Then, if so, treat for that so you can tolerate methyl supplements. Look at Heartfixer or Yasko for more info on testing and treatment.
You have MTHFR A1298C, so some methylfolate for that.
You only have one B12 mutation, which is MTRR (B12 recycling), yet your B12 is low. You said you have gut absorption problems. My suggestion would be to start with the gut first. Do some stool testing and see why you have problems. Then use a 4R gut rebuilding program to address them.
For your COMT/VDR combo, Yasko would suggest hydroxycobalamin, adenosylcobalamin and also methylcobalamin, but less of that.
You have all the BHMTs, which is the secondary pathway, so some TMG and phosphatidyl serine for that.
MAO A +/+ would be consistent with mental health issues. Yasko suggests treating this SNP after the other ones have been addressed.
Check out the links in my signature for more info.
ps. if you're on any SSRIs or other psych meds, you'll likely need to taper off them very slowly. Your doc won't know about this and will likely give you too fast of a taper schedule. If you're having problems, reducing by 10% of the previous dose every 3-6 weeks has worked for many people. See the Paxil Progress forum for more info.