The prescription vitamin is Metanx.

This you can do yourself...
methylcobalamin
methylfolate
activated B6 called P5P.

If you have the MTHFR mutation, then it is critical to have
the methyl versions of B12 and folate.
You really should get that DNA test. It is a common mutation.

However, the Metanx is only one part of rebuilding damaged nerves. It requires a good source of Omega-3 fatty acids to provide the building blocks to the nerve membranes. The vitamins are only cofactors. Without Omega-3's not much improvement will be likely.

The entire body needs Omega-3s as well, and they have been traditionally not in our common diets.

Glenn has had later skin biopsies showing improvement over the years. He does the nutrients carefully, and they are probably the factor helping him.
http://neurotalk.psychcentral.com/post1005701-33.html

This is a link to a video at Medscape. Bent98 provided it last year.
It is helpful to illustrate what the dorsal horn of the spinal cord are and it also
suggests how some drugs like gabapentin may help chronic pain.
It does not offer nutrient solutions, like most medical sites avoid discussing. If you do not have a membership to Medscape you can make one easily..and it is free. There are great informational links available there for all sorts of health and drug information.
http://www.medscape.org/viewarticle/754961

There is a genetic subset of patients who cannot rebuild cell damage
at the dorsal root level. There is no test for this as yet. But there is a paper on this forum from research stating that for those people with the defect, stem cells are the only thing so far to help. Evidently most people have the correct genes and DNA in place to fix things at the dorsal roots that have been damaged.