I agree with what Freddd says. The way in which symptoms of over-methylation / under-methylation are described even by Dr. Lynch seem a bit of a simplification.
Example: Dr.Lynch usually describes overmethylation symptoms as the state of extra agitation, anxiety, edgy feeling etc... caused by excessive intake of methyl-folate and methyl-B12, which can be compensated via niacin.
It's an interesting theory and it's based on strong empirical evidence that mehtyl supplements and niacin can balance each other out until a proper equilibrium is found. Dr Lynch has described many case studies of this phenomenon.
What I don't find very convincing is that this sort of reactions (anxiety, wired feeling etc...) are really correlated to an excessive spinning of the methylation cycle. Looking at my experience and that of folks in this board, it seems that most people with low methylation have these reaction to methyl groups even though their methylation is largely impaired.
In fact, most undermethylators' nervous system can easily go bananas if they don't carefully titrate their metyhl supplements.
In my case I have had all of those problems when trying to increase my dosages of folate and B12, but my blood work still showed high homocysteine and my methylation panel showed total insufficiency in all departments (low glutathione, sam-e, rbc folate etc...)
So I don't think "overmethylation" is a proper label to attach to those symptoms. Additionally real overmethylators, supposedly those with low homocysteine (e.g. < 5), don't necessarily have those kind of symptoms either.
What do you think?