In term of pathophysiology, the influence of MTHFR mutations should not be overlooked in the treatment of endometriosis, especially in patients referred for significant duration of infertility.15,27–29 As mentioned earlier, the c.677C>T isoform carries the heaviest penalty: the compound heterozygote c.677C>T; c.1298A>C is by no means benign, as demonstrated by increased levels of circulating Hcy.15 However, the T677T MTHFR SNP cannot be regarded as an initiator of endometriosis, as WT patients can also be affected. This evidence concerns the gene MTHFR and endometriosis.