Down Syndrome (cont.)

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How do the extra genes lead to Down syndrome?

Exactly how the extra genes from chromosome 21 lead to Down syndrome is still not clear. Scientists believe that the increased presence of specific genes alters the interaction between these and other genes. Some genes will become more active and others less active than normal, leading to changes in the development and maintenance of the body. Why some individuals are more severely affected than others might have to do with how many and which specific extra genes were inherited.

Scientists are trying to find out which genes from chromosome 21, when present in three copies, are responsible for the different characteristics of Down syndrome. Currently, about 400 genes on chromosome 21 have been identified, but the functions of most are still unknown. Through human studies and animal models, scientists are making progress in understanding the functions of individual genes.

What are the risk factors for conceiving a child with Down syndrome?

The only well known risk factor for conceiving a child with Down syndrome is advanced maternal age. The older the woman is at conception, the greater the risk of having a child with Down syndrome.

Mother's age at conception Risk of Down syndrome

  • 25 years 1 in 1,250
  • 30 years 1 in 1,000
  • 35 years 1 in 400
  • 40 years 1 in 100
  • 45 years 1 in 30

Parents who have conceived a child with Down syndrome have a 1% increased risk of conceiving another child with Down syndrome. If a parent is a carrier of a chromosome 21 translocation, the risk increases.

Women with Down syndrome have a 50% risk of conceiving a child with Down syndrome. If the father has Down syndrome, the risk of conceiving a child with Down syndrome is also increased.

Medically Reviewed by a Doctor on 1/4/2014

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Down Syndrome - Symptoms Question: Are you caring for someone with Down syndrome? What symptoms is he/she experiencing with Down syndrome?
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Down Syndrome - Coping and Management Question: In what ways does having a child with Down syndrome affect your life and family?
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