Down Syndrome (DS) is a chromosomal aberration where 21 chromosome is total or partial duplicate. DS is a common cause for mental retardation and its prevalence in general population is 1/600 to 1/1000 in live borns becoming an important resource spending cause to national public health programs. Embryonary ethiology of DS is associated to non chromosomal disjunction at meiosis I on maternal gametes. However, molecular explanation for this phenomenom is not known. The only epidemiological factor accepted for DS is maternal age. Currently, several research groups have proposed metabolic errors on Folate cycle as a possible factor associated to DS specially genetic mutation on Methylene Tetrahydrofolate Reductase (MTHFR) and Mehionine Synthase Reductase (MTRR). This review shows cur¬rently literature in this topic and proposed an association between high levels of plasmatic homocysteine