MTRR and Dravet syndrome: Meta-analyses of published data have been performed to overcome the limits of small case-control cohorts, revealing that both the methylenetetrahydrofolate reductase (MTHFR c.677C>T) and the methionine synthase reductase (MTRR c.66A>G) polymorphisms (both genes are involved in folate metabolism) might represent independent maternal risk factors for the birth of a child with DS [15,16,17].