Neural Tube Defects from Even One Gene
Background: Neural tube defects (NTDs) are common birth defects of the
brain and spinal cord that include anencephaly and spina bifida (meningomyelocele).
Deficiency of the vitamin folic acid raises the risk of NTDs,
as does mutation of a gene for an enzyme that processes folic acid. The mutation
is called the C677T variant, or T for short.
Summary: People with two copies of the T mutation are two and a half
times as likely to have a NTD as people with two copies of the normal gene. Now
it has been found that people with just one copy of the T gene are also at
increased risk for an NTD. They are one and a half times more likely to have a
NTD than people with two copies of the normal gene.
Comments: NTDs provide a model of how the environment and genetics can
interact to cause birth defects. The environmental factor is a lack of folic
acid. It can be added to the diet. The gene has to do with the metabolism of
folic acid.
It was thought that there had to be two mutant copies of the gene to raise
the NTD risk. Now it is clear that even one copy of the mutant gene can raise
the NTD risk. Even one gene can spell trouble.
Barbara K. Hecht,
Ph.D.
Frederick Hecht, M.D.
Medical Editors, MedicineNet.com
Related Links
U.S., Irish Researchers Identify
Important Clue to Genetic Basis for
Neural Tube Defects
A team of U.S. and Irish researchers has come one step closer to
understanding why a high proportion of the population is genetically at risk for
neural tube defects, according to a genetic study by researchers in Ireland and
at two of the National Institutes of Health, the
National Institute of Child Health and Human Development, and the National Human Genome Research Institute.
Specifically, the researchers learned that having only
one copy of a variant gene is enough to increase the chances of being born with
a neural tube defect.
Previously, researchers believed that two copies of the gene were needed to
increase someone's risk of being born with a neural tube defect.
The finding underscores the need for all women of childbearing age to follow
the current recommendation to take 400 micrograms of the vitamin folic acid each
day.
The study appears on the Web site of the British Medical Journal, at http://bmj.com
and will appear in the print edition of the journal at a later date.
Neural tube defects are a class of birth defects
affecting the brain and spinal cord. In one type, spina bifida, a piece of the
spinal cord protrudes from the spinal column, causing paralysis below the protrusion. In anencephaly,
a fatal neural tube defect, the brain and skull are grossly underdeveloped.
The study was funded by the NICHD and the Health Research Board of Ireland.
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