Having a baby? Eating food fortified with vitamin B9 during pregnancy unfortunately won’t help prevent your unborn child from having Down Syndrome, but it may protect your grandchildren, according to a recent study.
“Down Syndrome, or trisomy 21, is not a genetic disease-the condition is almost never inherited,” explains Dr. Joel Ray of U of T’s Department of Medicine, chief author of the study, which appeared in the July 30 issue of the American Journal of Medical Genetics. “A child with Down Syndrome, if they were fertile, wouldn’t typically give it to their offspring.” The condition arises when a mother’s eggs are forming during a process called meiosis. In meiosis a normal cell, which has two copies of every chromosome (one inherited from the mother and one from the father), is split apart to create cells with only one copy of each chromosome. Thus when an egg meets a sperm, the result is a cell with a normal number of chromosomes.
People with Down Syndrome, however, possess three copies of chromosome 21. The chromosomes are incorrectly separated during meiosis, and an egg is created that has two copies of chromosome 21. This rarely happens with sperm. “The current belief is that nearly all cases of trisomy 21 originate with the mother,” said Dr. Ray. When such an egg meets a normal sperm, the result is a baby with three copies of chromosome 21. A woman over 35 is more likely to produce such an egg.
It has been known for years that folic acid can help prevent neural tube defects, such as spina bifidia, in which an infant’s spine doesn’t close completely during development and as a result the spinal cord protrudes from the back, covered only by skin or a thin membrane. “In late 1997 the United States initiated a program whereby the white flour industry was required to add a certain amount of folic acid to every kilogram of flour produced for this very reason,” said Dr. Ray, “and as a lot of the flour that was being consumed in the US was being produced in Canada, Canadian flour millers also got on board to meet American requirements-by 1998 Health Canada realized it would be beneficial for Canada to also provide folic acid enriched flour, and so we too began to consume folic acid enriched products.” Some rice and corn products are also enriched with vitamin B9.
As it is known that extra folic acid in a cell can stabilize chromosomes and aid in DNA repair, Dr. Ray and his team suspected that it may help prevent trisomy 21. They investigated the question by examining the number of diagnosed cases of Down Syndrome in Ontario before and after folic acid was added to flour (most cases of trisomy 21 are found during pregnancy). Their results showed that there was no change.
This doesn’t mean, however, that vitamin B9 may not help at all in preventing Down Syndrome. A woman’s eggs are formed in two stages-the first stage occurs when she herself is a fetus, the stage second is just prior to ovulation as an adult. It may be possible that enriching foods with folic acid now may prevent girls born today from having children themselves with trisomy 21. “But we’ll have to wait another 15 or 20 years to see,” said Dr. Ray, “and I’m hoping that if the world is still here by that time I can investigate that question myself.”
Dr. Ray did stress however that although this study might seem a bit negative, it is important to keep in mind that folic acid enrichment is still beneficial. “We used the same methods to look at the occurrence of neural tube defects in Ontario, and found that the rate went down by 50 per cent after 1998,” he said.
“The program that was initiated has done its job.”
