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Down syndrome occurs in one out of every 733 live births, and more than 350,000 people in the U.S. have this genetic condition. One of the most frequently occurring chromosomal abnormalities, Down syndrome affects people of all ages, races and economic levels.

What Causes Down Syndrome

The human body is made of cells. All cells contain a center, called a nucleus, in which genes are stored. Genes, which carry the codes responsible for all our inherited characteristics, are grouped along rod-like structures called chromosomes. Normally, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when some or all of a person’s cells have an extra full or partial copy of chromosome 21.

The most common form of Down syndrome is known as Trisomy 21. Individuals with Trisomy 21 have 47 chromosomes instead of the usual 46 in each of their cells. The condition results from an error in cell division called non-disjunction. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body. This error in cell division is responsible for 95 percent of all cases of Down syndrome.

Down syndrome also encompasses two other genetic conditions: 

mosaicism and translocation.

Mosaicism occurs when non-disjunction of chromosome 21 takes place in one of the initial cell divisions after fertilization causing a person to have 46 chromosomes in some of their cells and 47 in others. The least common form of Down syndrome, mosaicism accounts for only 1 to 2 percent of all cases.


Translocation, which accounts for 3 to 4 percent of cases of Down syndrome, occurs when part of chromosome 21 breaks off during cell division and attaches to another chromosome, usually chromosome 14. 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.

The cause of the extra full or partial chromosome is still unknown. What we do know that it is not caused by environmental factors or anything the mother does before or during her pregnancy. Maternal age is the only factor that has been linked to an increased chance of having a baby with Down syndrome resulting from nondisjunction. A 35-year-old woman has a one in 350 chance of conceiving a child with Down syndrome. By age 45, the incidence has increased to one in 30.  However, because younger women have higher fertility rates, 80 percent of babies with Down syndrome are born to women under the age of 35. Once a woman has given birth to a baby with Down syndrome, the chance of having a second child with Down syndrome is about 1 in 100, although age may also be a factor.

Maternal age, however, is not linked to the chance of having a baby with translocation. Most cases are sporadic, chance events, but in about one third of translocation cases, one parent is a carrier of a translocated chromosome. For this reason, the chance of translocation in a second pregnancy is higher than that seen in nondisjunction.

NEW or Expectant Parents


New Parents

New Parent Packets are available for no charge to those requesting one or are given to new parents at area hospitals.  The packets include the book GIFTS (a must-read for new mothers and fathers), an RRVDSS onesie, several information documents about Down syndrome.  Many of these documents can be downloaded in pdf form below.  RRVDSS thanks NDSS, NDSC, and other organizations for making these wonderful resources available. 

Expectant Parent Packets are available through local obstetricians or by contacting RRVDSS.  Packets are filled with information on Down syndrome to help expectant parents understand Down syndrome and the child on the way.

There are several books on Down syndrome that are wonderful resources for new parents.  RRVDSS keeps updating our lending library with copies of these books.  If you would like to find out more about the library and books available, please contact RRVDSS at (903) 783-1922 or by e-mail at  The lending library is located at the Down Syndrome Resource Center in Paris, Texas. 

Diagnosis Down Syndrome: This Web site’s purpose is to inform you of the life realities that a person with Down syndrome can look forward to today which includes stories and photos from parents of children with Down syndrome.

New parents are also encouraged to read or watch "Welcome to Holland", a great story about one parent's experience.

Please contact RRVDSS with questions or comments.  Our organization's mission is to provide support.  We are available to you to help with any concerns, no matter how large or small.  RRVDSS offers a parent network which gives parents the chance to talk to others who have already gone through the same situations with their child with Down syndrome.  We also have a program called "Baby Buddies" which pairs new parents with more experienced parents to offer ongoing support. 

Please call us at (903) 783-1922 or contact us by e-mail at  We are here for you!!!



Grand Parents & other Family Members

Family Member Resources
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