When the C allele mutates to a G allele, the corresponding miRNAs cause loss-of-function and the loss of inhibition, while the wild-type CC genotype causes the corresponding miRNAs to bind to the 3'-UTR and leads to mRNA degradation or inhibition of translation, thereby down-regulating MTHFR expression and hyperhomocysteinemia. Here, MTHFR is linked to hyperhomocysteinemia.