About Down Syndrome

Down syndrome is the most commonly occurring chromosomal condition.

What is Down syndrome?​

Down syndrome is the most commonly occurring chromosomal condition. It affects people of all races and economic levels, with an occurrence rate of 1 in every 700 births. Typically, babies receive 23 chromosomes from each parent, totaling 46 chromosomes. However, in the case of Down syndrome, there is an extra copy of the 21st chromosome, resulting in a total of 47 chromosomes. This condition is often referred to as Trisomy 21.

In addition to the most common form of Down syndrome, there are two other, less frequent forms known as mosaic and translocation. Although this extra genetic material can impact a baby’s development, it’s important to note that the baby also inherits many physical and personality traits from their parents. A definitive diagnosis of Down syndrome requires a karyotype, which is a visual display of the baby’s chromosomes.

In the United States alone, there are approximately 350,000 individuals living with Down syndrome. These individuals are active and valued members of their families and communities. We believe that a life with Down syndrome is truly worth living. It’s important to remember that individuals with Down syndrome are more like others than they are different.

What causes Down syndrome?

Down syndrome is usually caused by an error in cell division called non-disjunction. It is not known why this occurs. However, it is known that the error occurs at conception and is not related to anything the mother did during pregnancy. Statistically the incidence of Down syndrome increases with advancing maternal age. However, 80% of children with Down syndrome are born to women under 35 years of age.

How is Down syndrome diagnosed?

Down syndrome is usually identified at birth or shortly thereafter. Initially the diagnosis is based on physical characteristics that are commonly seen in babies with Down syndrome. These include low muscle tone, a single crease across the palm of the hand, a slightly flattened facial profile and an upward slant to the eyes. The diagnosis must be confirmed by a chromosome study known as a karyotype.

Prenatal Screening and Diagnostic Testing

Two types of procedures are available to pregnant women: screening tests and diagnostic tests. The screening tests estimate the likelihood of the baby having Down syndrome. Diagnostic tests tell whether or not the baby actually has Down syndrome.

A common screening test is “The Triple Screen.” This is a combination of three tests that measure quantities of various substances in the blood. These tests are usually done between 15 and 20 weeks of gestation.

Newer screening tests sample for fetal DNA in the mother’s blood and are more accurate than the older “Triple Screen” test. They are still considered screening tests, however, and do not provide certainty about whether the fetus actually has Down syndrome.

Sonograms (ultrasounds) are usually performed in conjunction with other screenings. These can show some physical traits that are helpful in calculating the likelihood of Down syndrome.

Screening tests do not accurately confirm the diagnosis of Down syndrome. In fact, false positives and false negatives can occur.

Diagnostic Tests

Three diagnostic tests are currently available:

Amniocentesis which is performed between 12 and 20 weeks gestation.

Chorionic Villus Sampling (CVS) which is conducted between 8 and 12 weeks gestation.

Percutaneous Umbilical Blood Sampling (PUBS) which is performed after 20 weeks gestation.

We are here to help

On our website, we aim to provide accurate and up-to-date information about Down syndrome, its characteristics, and DSACT’s resources available to support individuals with Down syndrome and their families in Central Texas. We are dedicated to promoting inclusivity, celebrating the unique abilities of individuals with Down syndrome, and fostering a society that embraces diversity.

Explore our website to learn more about Down syndrome and discover the inspiring stories of our members and their families.