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Birth Defects
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Key Findings > Risk Factors for Down
Syndrome (Trisomy 21) |
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Risk Factors for Down Syndrome
(Trisomy 21): Maternal Cigarette Smoking and Oral Contraceptive Use
in a Population-Based Case-Control Study
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CDC and Emory University scientists examined maternal
smoking and oral contraceptive use as possible risk factors for Down
syndrome of maternal origin. This is the first epidemiologic study to
categorize Down syndrome by parental origin and timing of the chromosome
error before assessing possible risk factors.
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Down syndrome, the most commonly identified cause of
mental retardation, occurs in about 1 in 800 births. Despite many years
of research to identify risk factors associated with Down syndrome, only
one factor, advanced maternal age, has been well established.
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Previous studies of risk factors for Down syndrome
have pooled all cases regardless of parental origin or timing of the
chromosome error. With new DNA technology and chromosome 21-specific
genetic markers, determining the parental origin of the chromosome error
and the timing of that error during meiosis is possible. [Meiosis is the
special process of cell division that creates egg and sperm cells so
that each has half the number of chromosomes normally found in other
cells in the body.]
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Younger mothers (<35 years) who smoke and have
meiotic II error are at an increased risk of having children with Down
syndrome. The combined use of cigarettes and oral contraceptives
increased the risk even further.
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This is the first population-based epidemiologic
study to categorize Down syndrome cases by the parental origin and the
timing of the chromosome error to identify important environmental and
maternal health-related risk factors.
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Our results show that categorizing cases of Down
syndrome by parental origin and timing of the meiotic error allows for
more precision in identifying risk factors and may shed light on
mechanisms of meiotic error.
Results published in: Genetics in Medicine 1999;1:80-88.
Date: October 5,
2005
Content source: National Center on Birth Defects and Developmental
Disabilities
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