DOWN SYNDROME CLINIC OF HOUSTON
About Down Syndrome

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About one in every 700 to 800 babies born in the United States has Down syndrome, according to estimates. Experts do not know what prompts the genetic difference that results in Down syndrome, but they know clearly that it is the most frequent chromosomal disorder in humans.

In the human body, all the genetic information we inherit from our parents is carried on our chromosomes, which get copied into every one of our billions of cells. In a normal body, every cell has 46 chromosomes, arranged into 23 pairs.

But in some pregnancies, for reasons not clear, the very early cell division does not happen properly. When that process of faulty division, called nondisjunction, happens an embryo gets one extra chromosome (or, more accurately, a partial chromosome) that is included from that point onward every time a cell divides in the developing fetus.

Because that extra, partial chromosome locates with the 21st pair of chromosomes, doctors and scientists sometimes refer to Down syndrome as Trisomy 21.

That extra chromosomal material, which becomes copied into every one of an individual’s cells, is the basic characteristic of Down syndrome.

Diagnosis
Formal diagnosis is obtained through chromosomal analysis. A technician looks through a microscope at chromosomes taken either from a blood test or, before birth, from one of three diagnostic procedures:

• Chorionic Villus Sampling (CVS), performed most often between eight and 12 weeks of a pregnancy

• Aminiocentesis, between 12 to 20 weeks gestation

• Percutaneous Umbilical Blood Sampling (PUBS), after 20 weeks

Statistics and history
The condition does not run in families. There is nothing parents did or did not do to cause Down syndrome in their children. There are no common demographics, and Down syndrome seems to be more or less equally distributed among gender, ethnic or socioeconomic groups.

The English physician John Langdon Haydon Down identified, in 1866, many of the outward features and medical conditions that are linked to the syndrome that came to bear his name.

Since the 1930s, Down syndrome births have been linked more often to older mothers, although Down syndrome babies are born to young mothers, too. The chromosomal abnormality was clarified in 1959.

Physical characteristics
Individuals with Down syndrome share certain physical features that can change over time, becoming more apparent, or less so, as a child grows. They include a flat face, low muscle tone, small ears, large tongue, upward-slanting eye creases, single skin crease in the palms and very flexible joints.

These features are obvious in some cases. In others, they are so subtle only chromosomal analysis can firmly establish diagnosis.

In addition, all individuals with Down syndrome present with cognitive delays with IQ scores ranging from 85 (low normal) to 20 (severe mental retardation). Many also have problems in hearing and vision.

Medical needs
Beyond outward physical traits, several medical conditions are frequent among individuals with Down syndrome:

• Certain heart disorders — About 40 percent are born with heart defects that may require careful monitoring and medication, or even surgery. For that reason, echocardiograms are frequently performed on newborns with Down syndrome.

• Gastrointestinal abnormalities — Between 2 percent and 5 percent are born with duodenal atresia, which is a complete obstruction of the small bowel. About another 2 percent have Hirschsprung disease, which inhibits movement of the colon and/or rectum.

• Hearing loss — Malformations in the middle- or inner ear can result in some degree of hearing loss in about 40 percent to 75 percent. Hard-to-heal ear infections can be frequent, too.

• Vision problems — About 60 percent have eye disorders. Most common are congenital cataracts (a cloudy lens), glaucoma (high pressure inside the eye), crossed eyes (called strabismus) and the refractory errors of near- and farsightedness.

• Leukemia — At a rate of one in 150, children with Down syndrome are 20 times more likely than others to develop leukemia.

• Thyroid disorders — About 5 percent have low thyroid levels.

Heart treament
Congenital heart disease was the most frequent cause of death in young patients with Down syndrome until recent advances in care started changing that reality.

Over the past two decades, 70 percent of children with Down syndrome with serious heart disorders survived to their first birthdays, and their survival rates continue to get even better.

Outlook
Thanks to advances in diagnosis and treatment in many specialties, the outlook for all  individuals with Down syndrome is brighter than ever.

Despite needing extra care as children and adults, at least 85 percent of all children with  Down syndrome live past their first year, and half reach the age of 50.