A common MTRR 66A>G polymorphism (rs1801394), resulting in Ile22Met amino acid change, was the second polymorphism of the folate pathway, after the MTHFR 677C>T one, to be associated with the maternal risk of having a birth with DS in North American women (Hobbs et al., 2000). Here, MTHFR is linked to Dravet syndrome.