About Down Syndrome

In 1910, children with Down syndrome in the U.S. were expected to survive to age nine.  In 1983, people with Down syndrome only lived to be 25 years old.  Today adults can live into their 60s and older, largely because of medical advances and societal changes.  Now a new generation wants what other adults have—love, work, and independence.

Basic Stats, United States

  • 400,000 people have Down syndrome
  • 5,000 new births per year
  • Frequency of incidence is 1 in 733 births
  • 80% of babies with Down are born to women younger then 35

General Facts

Down syndrome affects people of all races and economic levels. All people with Down syndrome have an extra, critical portion of chromosome 21 present in all or some of their cells.

An Extra Portion of Chromosome 21

Trisomy 21 involves an extra copy of the 21st chromosome, and is the most common type of Down syndrome.  Mosaicism occurs when you have two distinct cell groupings—some cells have an extra 21st chromosome, and others do not.  With Translocation, part of chromosome 21 breaks off during cell division and attaches to another chromosome. While the total number of chromosomes in the cells remains 46, the presence of an extra part of chromosome 21 causes the characteristics of Down syndrome.

Frequently Asked Questions

Who has the highest risk of having a child with Down syndrome? The incidence of births of children with Down syndrome increases with the age of the mother. But due to higher fertility rates in younger women, 80% of children with Down syndrome are born to women under 35 years of age.

If a woman with Down syndrome becomes pregnant, will the baby have Down syndrome? At least half of all women with Down syndrome do ovulate and are fertile. Between 35 and 50 percent of children born to mothers with Down syndrome are likely to have trisomy 21 or other developmental disabilities.

Are males with Down syndrome fertile? Scientific information about the fertility of men with Down syndrome is limited. There have been at least two documented cases where the paternity of a man with Down syndrome was confirmed. It is likely that additional cases will be recognized – especially since more men with Down syndrome have an increased life expectancy, the opportunity to live in the community, and develop intimate relationships. It is not known if the offspring of men with Down syndrome are more likely to have Down syndrome.  But it does seem clear that, in general, men with Down syndrome have a significantly lower overall fertility rate than that of other men their age.  Contraception should always be used, unless a couple has decided upon parenthood.

Thanks to the National Down Syndrome Society for their helpful online resources.

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