Neural Tube Defects from Even One Gene (cont.)

In the current study, the researchers tested the DNA of 395 individuals with a neural tube defect and 848 individuals who did not have a neural tube defect. The researchers tested these people to see if they had a variant of a gene known as 5,10-methylenetetrahydro-folate reductase, involved in processing folate. The researchers conducted the study in Ireland because that country has a high proportion of individuals born with neural tube defects.

Human beings typically have two copies of a given gene, one inherited from the father, and one from the mother. Previously, researchers thought that an individual had to have two copies of the C677T variant to be at increased risk of neural tube defects. However, the study authors found that individuals having just one copy of C677T were one and a half times more likely to have a neural tube defect than were people who didn't have a copy of the variant gene. People with two copies of C677T were two and a half times as likely to have a neural tube defect than were people with two normal copies of the gene.

The researchers estimated that about 59 percent of the European population and 53 percent of the North American population has either one or two copies of the C677T variant.

In 1992, the U.S. Public Health Service recommended that all women of childbearing age capable of becoming pregnant consume 400 micrograms of folic acid, the synthetic form of the vitamin folate, from pills or tablets. To reduce the number of neural tube defects, the U.S. Food and Drug Administration required that folic acid be added to the U.S. grain supply in 1998.

The addition of folic acid to grains has cut the amount of neural tube defects in North America by about 50 percent, said the NICHD author of the study, James Mills, M.D., chief of the NICHD's Pediatric Epidemiology Section. Still, he added, on average, U.S. women of childbearing age receive only about 200 micrograms a day of folic acid from fortified grain. Women who don't eat grain products and who don't take a vitamin preparation that contains folic acid may be getting far less. In Ireland, where the study was conducted, grains are not routinely fortified with folic acid.

"...[O]ur study provides new data underscoring the importance of public health intervention programmes of folic acid supplementation and food fortification targeted at all women of childbearing age to prevent neural tube defects," the study authors wrote.

Dr. Mills explained that this gene could not be used as the basis of a prenatal genetic test to diagnose neural tube defects. Although having the gene increases the risk for neural tube defects, not all individuals who have the gene are born with a neural tube defect.

Source: National Institutes of Health News Wire, May 21, 2004

Last Editorial Review: 5/26/2004