WASHINGTON, DC--Down Syndrome occurs in about one in every 700 live births, and now a study conducted by the Food and Drug Administration's National Center for Toxicological Research (NCTR) suggests a reason why this condition might occur. The study found that mothers of children with Down syndrome show biochemical and genetic evidence of impaired folate metabolism. Down syndrome, or trisomy 21, is a complex genetic disease that is caused by an extra copy of chromosome 21. The origin of the extra chromosome is maternal in most cases and is due to an error in chromosome separation before conception. The results of the new study indicate that mothers of children with Down syndrome have an imbalance in folate metabolism that may be explained, in part, by a common genetic variation in an enzyme involved in the folic acid pathway. A 1998 mandate of the Federal Drug Administration (FDA) requires that 140 micrograms of folic acid, a B vitamin, to every 100 grams of grain products like flour, breakfast cereals, and pasta. The FDA's decision was based on evidence that inadequate folate status in early pregnancy increases the risk of neural tube defects, and was intended to reduce the incidence of birth defects in the brain and spinal cord in the United States.