A recent study revealed that the fission yeast methylenetetrahydrofolate reductase protein (Met11) is important for maintaining the pericentromeric heterochromatin structure to ensure mitotic and meiotic chromosome segregation fidelity,[14] supporting the original hypothesis by James et al and suggesting that MTHFR polymorphisms promote changes in global DNA methylation during maternal meiosis leading to chromosomal non-disjunction and increasing the maternal risk to have children with DS.[6]. The gene discussed is MTHFR; the disease is Dravet syndrome.