Mthfr is an enzyme that uses folate to support the process of methylation which is essential to mental and physical health. Even though mthfr is modifying folate to make the methyl group a key part of itself is riboflavin. The way it lowers mthfr activity is to lower its binding affinity for riboflavins. It's sort of like if you were a dude with a prosthetic knee and something made that knee fall out having mthfr c6 77 t1 or another polymorphism can do this.