Yes methylation is really important, I have defects here, too. Sadly mercury messes so much enzymatic pathways up, it is also is interfering in methylation pathway.
I don't tolerate ALA only, I need some support for detoxing via the kidneys so I take both, DMSA and ALA. In the beginning I would highly recommend to take DMSA only, later you can add ALA. Be aware that taking ALA will result in a strong mercury dumping. Most people don't even tolerate 1 mg of it when they start.