This is a pretty technical link...but the paper shows MRI results of those with MTHFR mutations. Discussed also is brain shrinkage.

Common folate gene variant, MTHFR C677T, is associated with brain structure in two independent cohorts of people with mild cognitive impairment

While it is true that the "lay" internet has picked up on the MTHFR SNPs... there are scientific papers out there that back up the importance of treating those with MTHFR errors to prevent brain and cardiovascular diseases. I recall reading a Merck site over a decade ago when they published their papers on MTHFR mutations. Times are very different now, with many non technical sites discussing this now.

We are very lucky in that methylB12 and methylfolate are available OTC at relatively low cost to help with this problem.

The Merck company tried to sequester methylfolate for several years as an RX only product. They removed it from OTC sellers, but that did not last. It is now available again, OTC. The Merck company still holds the patent on methylfolate however.

The competition of folic acid with methylfolate in vivo however is still not clarified yet.