What is Down Syndrome?
Down syndrome (DS), also called Trisomy 21, is a condition in
which extra genetic material causes delays in the way a child
develops, both mentally and physically. It affects about 1 in every
800 babies.
The physical features and medical problems associated with Down
syndrome can vary widely from child to child. While some kids with
DS need a lot of medical attention, others lead healthy lives.
Though Down syndrome can't be prevented, it can be detected
before a child is born. The health problems that can go along with
DS can be treated, and there are many resources within communities
to help kids and their families who are living with the
condition.
What Causes It?
Normally, at the time of conception a baby inherits genetic
information from its parents in the form of 46 chromosomes: 23 from
the mother and 23 from the father. In most cases of Down syndrome,
a child gets an extra chromosome 21 - for a total of 47 chromosomes
instead of 46. It's this extra genetic material that causes the
physical features and developmental delays associated with DS.
Although no one knows for sure why DS occurs and there's no
way to prevent the chromosomal error that causes it, scientists do
know that women age 35 and older have a significantly higher risk
of having a child with the condition. At age 30, for example, a
woman has about a 1 in 900 chance of conceiving a child with DS.
Those odds increase to about 1 in 350 by age 35. By 40 the risk
rises to about 1 in 100.
How Down Syndrome Affects Kids
Kids with Down syndrome tend to share certain physical features
such as a flat facial profile, an upward slant to the eyes, small
ears, and a protruding tongue.
Low muscle tone (called
hypotonia
) is also characteristic of children with DS, and babies in
particular may seem especially "floppy." Though this can
and often does improve over time, most children with DS typically
reach developmental milestones - like sitting up, crawling, and
walking - later than other kids.
At birth, kids with DS are usually of average size, but they
tend to grow at a slower rate and remain smaller than their peers.
For infants, low muscle tone may contribute to sucking and feeding
problems, as well as constipation and other digestive issues.
Toddlers and older kids may have delays in speech and self-care
skills like feeding, dressing, and toilet teaching.
Down syndrome affects kids' ability to learn in different
ways, but most have mild to moderate intellectual impairment. Kids
with DS can and do learn, and are capable of developing skills
throughout their lives. They simply reach goals at a different pace
- which is why it's important not to compare a child with DS
against typically developing siblings or even other children with
the condition.
Kids with DS have a wide range of abilities, and there's no
way to tell at birth what they will be capable of as they grow
up.
Medical Problems Associated With DS
While some kids with DS have no significant health problems,
others may experience a host of medical issues that require extra
care. For example, almost half of all children born with DS will
have a
congenital heart defect
.
Kids with Down syndrome are also at an increased risk of
developing pulmonary hypertension, a serious condition that can
lead to irreversible damage to the lungs. All infants with Down
syndrome should be evaluated by a pediatric cardiologist.
Approximately half of all kids with DS also have problems with
hearing and vision. Hearing loss can be related to fluid buildup in
the inner ear or to structural problems of the ear itself. Vision
problems commonly include amblyopia (lazy eye), near- or
farsightedness, and an increased risk of cataracts. Regular
evaluations by an audiologist and an ophthalmologist are necessary
to detect and correct any problems before they affect language and
learning skills.
Other medical conditions that may occur more frequently in kids
with DS include thyroid problems, intestinal abnormalities, seizure
disorders, respiratory problems, obesity, an increased
susceptibility to infection, and a higher risk of childhood
leukemia. Upper neck abnormalities are sometimes found and should
be evaluated by a physician (these can be detected by cervical
spine X-rays). Fortunately, many of these conditions are
treatable.
Prenatal Screening and Diagnosis
Two types of prenatal tests are used to detect Down
syndrome in a fetus: screening tests and diagnostic tests.
Screening tests estimate the risk that a fetus has DS; diagnostic
tests can tell whether the fetus actually has the condition.
Screening tests are cost-effective and easy to perform. But
because they can't give a definitive answer as to whether a
baby has DS, these tests are used to help parents decide whether to
have more diagnostic tests.
Diagnostic tests are about 99% accurate in detecting Down
syndrome and other chromosomal abnormalities. However, because
they're performed inside the uterus, they are associated with a
risk of miscarriage and other complications.
For this reason, invasive diagnostic testing previously was
generally recommended only for women age 35 or older, those with a
family history of genetic defects, or those who've had an
abnormal result on a screening test.
However, the American College of Obstetrics and Gynecology
(ACOG) now recommends that all pregnant women be offered screening
with the option for invasive diagnostic testing for Down syndrome,
regardless of age.
If you're unsure about which test, if any, is right for you,
your doctor or a
genetic counselor
can help you sort through the pros and cons of each.
Screening tests include:
-
Nuchal translucency testing.
This test, performed between 11 and 14 weeks of pregnancy, uses
ultrasound to measure the clear space in the folds of tissue
behind a developing baby's neck. (Babies with DS and other
chromosomal abnormalities tend to accumulate fluid there, making
the space appear larger.) This measurement, taken together with
the mother's age and the baby's gestational age, can be
used to calculate the odds that the baby has DS. Nuchal
translucency testing is usually performed along with a maternal
blood test.
-
The triple screen or quadruple screen
(also called the multiple marker test). These tests measure the
quantities of normal substances in the mother's blood. As the
names imply, triple screen tests for three markers and quadruple
screen includes one additional marker and is more accurate. These
tests are typically offered between 15 and 18 weeks of
pregnancy.
-
Integrated screen.
This uses results from first trimester screening tests (with or
without nuchal translucency) and blood tests with second
trimester quad screen to come up with the most accurate screening
results.
-
A genetic ultrasound.
A detailed ultrasound is often performed at 18 to 20 weeks in
conjunction with the blood tests, and it checks the fetus for
some of the physical traits abnormalities associated with Down
syndrome.
Diagnostic tests include:
-
Chorionic villus sampling (CVS).
CVS involves taking a tiny sample of the placenta, either through
the cervix or through a needle inserted in the abdomen. The
advantage of this test is that it can be performed during the
first trimester, between 8 and 12 weeks. The disadvantage is that
it carries a slightly greater risk of miscarriage as compared
with amniocentesis and has other complications.
-
Amniocentesis.
This test, performed between 15 and 20 weeks of pregnancy,
involves the removal of a small amount of amniotic fluid through
a needle inserted in the abdomen. The cells can then be analyzed
for the presence of chromosomal abnormalities. Amniocentesis
carries a small risk of complications, such as preterm labor and
miscarriage.
-
Percutaneous umbilical blood sampling (PUBS).
Usually performed after 20 weeks, this test uses a needle to
retrieve a small sample of blood from the umbilical cord. It
carries risks similar to those associated with
amniocentesis.
After a baby is born, if the doctor suspects DS based on the
infant's physical characteristics, a karyotype - a blood or
tissue sample stained to show chromosomes grouped by size, number,
and shape - can be performed to verify the diagnosis.
Getting Help
If you're the parent of a child diagnosed with Down
syndrome, you may at first feel overwhelmed by feelings of loss,
guilt, and fear. Talking with other parents of kids with DS may
help you deal with the initial shock and grief and find ways to
look toward the future. Many parents find that learning as much as
they can about DS helps alleviate some of their fears.
Experts recommend enrolling kids with Down syndrome in
early-intervention services as soon as possible. Physical,
occupational, and speech therapists and early-childhood educators
can work with your child to encourage and accelerate
development.
Many states provide free early-intervention services to kids
with disabilities from birth to age 3, so check with your doctor or
a social worker to learn what resources are available in your
area.
Once your child is 3 years old, he or she is guaranteed
educational services under the Individuals with Disabilities
Education Act (IDEA). Under IDEA, local school districts must
provide "a free appropriate education in the least restrictive
environment" and an individualized education plan (IEP) for
each child.
Where to send your child to school can be a difficult decision.
Some kids with Down syndrome have needs that are best met in a
specialized program, while many others do well attending
neighborhood schools alongside peers who don't have DS. Studies
have shown that this type of situation, known as inclusion, is
beneficial for both the child with DS as well as the other
kids.
Your school district's child study team can work with you to
determine what's best for your child, but remember, any
decisions can and should involve your input, as you are your
child's best advocate.
Today, many kids with Down syndrome go to school and enjoy many
of the same activities as other kids their age. A few go on to
college. Many transition to semi-independent living. Still others
continue to live at home but are able to hold jobs, thus finding
their own success in the community.
Reviewed by:
Charles I. Scott, MD
Date reviewed: August 2008
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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