MTHFR and osteoporosis: One of the subjects with pregnancy-related osteoporosis was also homozygous for the MTHFR gene C677T polymorphism, which has been associated with several health outcomes including fracture risk and low BMD (47) MTHFR encodes for methylenetetrahydrofolate reductase, an enzyme involved in folate, homocysteine and amino acid metabolism.