MTHFR is a a key regulatory enzyme in the metabolism of folate. It also refers to a specific gene that plays a major role in the body's methylation process. Both the enzyme and the gene have the same name, MTHFR. The gene's role is very complex, and recent discoveries have been focused around the MTHFR gene polymorphisms (or variants). These polymorphisms are often referred to as 'mutations' or 'defects' because of the problems they cause in the body.
Most often when you hear someone talk about MTHFR, they are actually referring to one of the two common MTHFR gene mutations that causes this MTHFR enzyme to become imperfect and therefore much less effective.
Simply stated, MTHFR most often refers to a genetic mutation that inhibits the body's ability to methylate or convert folic acid from the food we eat into Methylfolate.
Methylfolate is most often referred to as the 'active' or usable form of folate that our cells require. Because the body's cells cannot actually use folic acid, it must first go through a metabolic pathway or 4-step conversion process to become Methylfolate before the cells can use it . It is this metabolic pathway that the MTHFR gene defect inhibits and cause methylation deficiencies and/or neuro-immune syndromes.
The learnings about this gene defect have come out and taught us that there are as many as 50+ variants of the MTHFR gene. However, only two are considered 'common' defects that today’s MTHFR Blood Test checks for and are the: 677 and 1298 (discovered in 1995 and 2001).
Everyone receives one copy of the MTHFR gene from each parent. This means a person could have any one of the following combinations as well as the issues that go with it:
Normal / Normal - Normal for the two common variants, or mutations, 677 and 1298 (no mutation is evident)
Normal / C677T - More susceptible to neuro-immune syndromes, environmental damage, depression, central nervous system issues, etc. (referred to as Heterozygous)
Normal / A1298C - More susceptible to neuro-immune syndromes, environmental damage, depression, central nervous system issues, etc. (referred to as Heterozygous)
A1298C / A1298C - Denoted as 1298CC - Much worse for the above problems (referred to as Homozygous)
C677T / C677T - Denoted as 677TT - Similar to 1298CC plus heart disease, blood clots, and more (referred to as Homozygous)
C677T / A1298C - Susceptible to all of the above and worse for strokes, heart disease, blood clots, etc. (referred to as Compound Heterozygous)
Nutritional Recommendations:

Methylation Complete Sublingual OR
Neuro-Immune Stabilizer Topical Cream
Homozygous for 1298 or C677 or combination: Provide Methylation Complete Sublingual or Neuro-Immune Stabilizer twice daily and add Methyl Folate Plus 1-2x’s daily (Niacinamide is an ingredient in the Methyl Folate Plus to support mitochondria and delivery of tetrahydrofolate)