MTHFR and Rare hereditary thrombophilia: On the other hand, in a cohort of 176 patients, Fevraleva et al. [21] could not demonstrate a higher risk of thrombotic complications during COVID-19 disease in carriers of the genetic markers for thrombophilia, including G1691A in the FV gene, C677T and A1298C in the MTHFR gene, G20210A in the FII gene, and (-675) 4G/5G in the PAI-I gene, relative to patients without these markers.