Researchers found that mothers with a genetic abnormality that hinders folic acid metabolism were 2.6 times more likely to have a child with Down syndrome than mothers without that genetic defect, concludes the study published Tuesday in the American Journal of Clinical Nutrition.
Down syndrome is a genetic abnormality that is a leading cause of mental retardation in newborns.
This link comes on the heels of previous evidence that low levels of folate also contributes to brain and spinal cord defects. The evidence that led the FDA in 1998 to require that some foods be enriched in folic acid.
Although researchers still don't know what role folic acid plays in Down syndrome, there is enough evidence of benefits that women should make sure they're getting enough before and after pregnancy.
One way to get folic acid is by eating a variety of the natural foods that contain the B vitamin, like green leafy vegetables, liver, tuna, asparagus, beans, orange juice, eggs. Another is by eating foods enriched with folic acid, such as some pasta, cereal and bread. Folic acid supplements are another good way to ensure you're getting enough.
The discovery is only one piece in the complicated puzzle of Down syndrome, cautioned FDA Commissioner Jane Henney. That's because millions of women appear to have this genetic abnormality, yet the risk of having a child with Down syndrome is small - one in 600 births.
So something else has to help trigger the devastating condition.
"If you have this mutation and you happen to have a very poor diet, it magnified the problem," explained S. Jill James, an FDA biochemist who led the study. "We call it a gene-nutrient interaction."
Women who eat 400 micrograms of folic acid a day cut in half their chances of having babies with birth defects of the brain and spinal cord, such as spina bifida. Whether a baby develops these defects is determined in the first days after conception - well before a woman knows she is pregnant. And even with food fortification, it can be hard to eat enough. Health experts recommend that every woman of childbearing age take a daily dietary supplement, such as a multivitamin, containing 400 micrograms of folic acid.
There have been hints that folic acid might play a role in other birth defects, too, but the FDA research is the first good evidence.
Normally, each egg and sperm cell contains 23 chromosomes. When either an egg or a sperm carries a certain extra chromosome, Down syndrome results. In most cases, the problem arises during ovulation, when a woman's body produces an abnormal egg.
The gene MTHFR plays a role in how chromosomes separate during ovulation, and in how much folic acid people need for various bodily reactions.
James studied whether an MTHFR abnormality also could affect Down syndrome. She compared 57 mothers of Down syndrome children with 50 mothers of healthy children and concluded the gene abnormality did indeed increase the risk of Down syndrome.
The FDA researchers did not give women folic acid supplements to see if they would prove enough - and at what dose to counter the genetic defect. Experts said a treatment study is the necessary next step.