Down Syndrome
What is Down syndrome?
Down syndrome is a genetic condition in which a child is born with an extra chromosome.
Normally, an individual is born with 46 chromosomes, however, children born with Down
syndrome have an extra copy of the 21st chromosome. This extra copy changes the body and
brain’s development and causes physical and developmental alterations in children. Even though
people with Down syndrome might have some physical and developmental features in common,
characteristics of Down syndrome can range from mild to severe.
How common is Down syndrome?
Down syndrome is one of the most common genetic birth defects. The Centers for Disease
Control and Prevention (CDC) estimates that each year about 3,357 babies in the United States
are born with Down syndrome, about one in every 733 babies. According to the National Down
Syndrome Society, there are approximately 400,000 individuals living with Down syndrome in
the United States.
Description of characteristics associated with Down syndrome
Individuals with Down syndrome can have medical and physical problems, as well as intellectual
disabilities. Some of the characteristics associated with Down syndrome include:
Characteristics
 Every person with Down syndrome is a unique individual and may possess some of these
physical characteristics to different degrees or not at all:
 A flat face with an upward slant to the eye, a short neck, small ears, and a large tongue
 Tiny white spots on the iris (colored part) of the eye
 Small hands and feet
 A single crease across the palm of the hand
 Small pinky fingers that sometimes curve toward the thumb
 Low muscle tone or loose ligaments
Intellectual Disability
A person with Down syndrome will have an intellectual disability. The severity of the
intellectual disability can vary from mild through to severe or profound. Most individuals
with Down syndrome have an intellectual disability that falls into the mild to moderate range.
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Cardiac
Up to 50 percent of individuals with Down syndrome are born with congenital heart
conditions. The majority of heart conditions in children with Down syndrome are surgically
corrected with resulting long-term health improvements. Other defects are minor and may be
treated with medications. All babies with Down syndrome should be examined by a pediatric
cardiologist and have an echocardiogram within the first two months of life.
Alzheimer's disease
Estimates vary, but approximately 25 percent of individuals with Down syndrome over the
age of 35 will develop the clinical signs and symptoms of Alzheimer's-type dementia. Signs
and symptoms of dementia often appear before age 40. Individuals with Down syndrome are
more likely than unaffected individuals to develop Alzheimer's -type dementia.
Leukemia
Approximately 1% of individuals with Down syndrome will develop leukemia. The majority
of the individuals will have acute megakaryoblastic leukemia, which tends to occur in the
first three years of life, and for which there is a high cure rate. A transient form of leukemia
is also seen in newborns with Down syndrome, disappearing spontaneously during the first
two to three months of life.
Intestinal conditions
About 12 percent of babies with Down syndrome are born with intestinal malformations that
require surgery, such as a blocked small intestine. Celiac disease is another digestive disease
that damages the small intestine so that nutrients from food are not well absorbed.
Hearing impairment
About 75 percent of children with Down syndrome have some hearing loss. Hearing loss
may be due to fluid in the middle ear (which may be temporary), nerve damage or both.
Babies with Down syndrome should be screened for hearing loss at birth or by 3 months of
age. They also should have regular hearing exams to detect fluid in the ears.
Vision impairment
More than 60 percent of children with Down syndrome have vision problems, including
esotropia, near- or far-sightedness, and cataracts (3%). Glasses, surgery or other treatments
usually can improve vision. A child with Down syndrome should be examined by a pediatric
ophthalmologist within the first six months of life and have regular vision exams.
Infectious diseases
Because of abnormalities in their immune systems, those with Down syndrome are much
more susceptible to infectious diseases. Children with Down syndrome tend to have many
colds and ear infections, as well as bronchitis and pneumonia.
Seizures
Between 5 and 13% of individuals with Down syndrome will have seizures. This incidence
is 10 times the incidence in the general population. There is an unusually high incidence of
infantile spasms or seizures in children less than one year of age, some of which are
precipitated by neonatal complications and infections and cardiovascular disease.
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Other conditions
Individuals with Down syndrome are also at risk for other health conditions at greater rates
than the general population. These include obesity, diabetes, thyroid conditions, dental
conditions and behavioral and psychiatric conditions. Appropriate, ongoing medical care is
required.
What causes Down syndrome?
Most of the time, the occurrence of Down syndrome is due to a random event that occurred
during formation of the reproductive cells resulting in an individual having three, rather than
two, copies of the 21st chromosome. The cells in his or her body have 47 chromosomes instead
of the usual 46 chromosomes. This extra chromosome causes the physical signs and additional
problems that can occur among people with Down syndrome.
The cause of the errors that produce the extra chromosome is not well understood. Currently
Down syndrome is not attributable to any behavioral activity of the parents or environmental
factors. The age of the mother is the only factor that has been shown to increase the risk of
having a baby with Down syndrome. This risk increases with every year, especially after the
mother is 35 years of age. However, because younger women have babies in greater numbers
than older women, 80% of babies with Down syndrome are born to women younger than 35
years of age.
Incidence of Down Syndrome in Relationship to Maternal Age
Mothers Age
Incidence
Mothers Age
Incidence
Under 30
< 1 in 1000
40
1 in 105
35
1 in 400
42
1 in 60
36
1 in 300
44
1 in 35
37
1 in 230
46
1 in 20
38
1 in 180
48
1 in 16
39
1 in 135
49
1 in 12
Source: Kozma, C. (2008). Down syndrome and dementia. Topics in Geriatric Rehabilitation,
24, 41-53.
The genetic forms of Down syndrome
Down syndrome is caused by extra genetic material from chromosome 21, but there are three
different genetic mechanisms that result in the extra chromosome.
 Trisomy 21
More than 90 percent of cases of Down syndrome are caused by trisomy 21. A child with
trisomy 21 has three copies of chromosome 21, instead of the usual two copies, in all of his
or her cells. This form of Down syndrome is caused by abnormal cell division during the
development of the sperm cell or the egg cell.
 Mosaic Down syndrome
In this rare form of Down syndrome (1% of all people with Down syndrome), children have
some cells with an extra copy of chromosome 21, but not all cells. This mosaic of normal and
abnormal cells is caused by abnormal cell division after fertilization.
 Translocation Down syndrome
Although uncommon, Down syndrome can also occur when part of chromosome 21 becomes
attached (translocated) onto another chromosome, before or at conception. Children with
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translocation Down syndrome have the usual two copies of chromosome 21, but they also
have additional material from chromosome 21 adhered to the translocated chromosome.
Translocation Down syndrome is the only form of the disorder that can be passed from
parent to child. However, only about 4 percent of children with Down syndrome have
translocation and only about half of these cases are inherited from one of the parents who is
a carrier. The chance of passing on the translocation depends on the sex of the parent who
carries the rearranged chromosome 21. If the father is the carrier, the risk is about 3 percent;
if the mother is the carrier, the risk is about 12 percent.
Prenatal diagnosis
 Screening
The American College of Obstetricians and Gynecologists (ACOG) recommends that all
pregnant women be offered a screening test for Down syndrome, regardless of the woman's
age. Screening may consist of a maternal blood test done in the first trimester (at 11 to 13
weeks of pregnancy), along with a special ultrasound examination of the back of the baby's
neck (called nuchal translucency), or a maternal blood test done in the second trimester (at 15
to 20 weeks). A screening test helps identify pregnancies that are at higher-than-average risk
of Down syndrome but can not diagnose Down syndrome.

Diagnostics
Each of these three tests is 98 to 99 percent accurate in diagnosing Down syndrome before
birth.
Amniocentesis: Analysis of the chromosomes of the amniotic fluid surrounding the fetus.
Doctors usually perform this test after 15 weeks of gestation. The test carries a risk of
miscarriage of one in 200.
Chorionic villus sampling (CVS): Analysis of cells from the mother's placenta to determine
fetal chromosomes. Typically performed between the ninth and 14th week of pregnancy, this
test carries a risk of miscarriage of one in 100.
Percutaneous umbilical blood sampling (PUBS): Umbilical cord blood is examined for
chromosomal defects. Doctors generally perform this test after 18 weeks of gestation. This
test carries a greater risk of miscarriage than does amniocentesis or chorionic villus sampling.
Generally, this test is only done when speed of diagnosis is essential.
What is the risk that parents of a child with Down syndrome will have
another child with Down syndrome?
The risk depends on the form of Down syndrome. In general, if a woman has a child with Down
syndrome the chance of having another baby with Down syndrome in each subsequent
pregnancy is 1 percent plus any additional risk a mother has because of her age. If, however, the
first child has translocation Down syndrome, the chance of having another child with Down
syndrome may be greatly increased. To determine the risk of having another baby with Down
syndrome, at birth the baby’s chromosomes will be examined to determine which genetic type of
Down syndrome the child has.
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Developmental and health considerations for individuals with Down
syndrome
Development
In general, children with Down syndrome usually meet developmental milestones, but at a
slower rate than a child without Down syndrome. Early intervention such as physical therapy or
speech therapy has been shown to enhance the development of children with Down syndrome
and parents report that the early intervention services and supports were critical for their ability
to assist in promoting their child’s development.
Although each child is individual, here are some resources that are helpful guides for
development of children with Down syndrome
Health
Because of the increased risk of some health conditions in individuals with Down syndrome,
guidelines for screening and evaluations throughout the life span have been developed to assist
health care providers, families and individuals in managing these special health care needs.

Health Care Guidelines
 National Down Syndrome Society
http://www.ndss.org/index.php?option=com_content&view=article&id=70&Itemid
=139
 National Down Syndrome Congress
http://www.ndsccenter.org/resources/healthcare.pdf

Growth Charts
 National Down Syndrome Society
http://www.ndss.org/index.php?option=com_content&view=article&id=71:growthcharts&catid=38:healthcare&Itemid=91

Associated Conditions
 National Down Syndrome Society
http://www.ndss.org/index.php?option=com_content&view=category&id=60&Item
id=88

Developmental Milestones
o Pennsylvania Child Welfare Training Program, University of Pittsburg
http://www.pacwcbt.pitt.edu/Curriculum/316936BeAllThatCanBeCaringfor
aChildwithDownSyndrome/Overheads/Overhead8DevelopmentalMilestones
andSkillsTable.pdf
 National Down Syndrome Society
http://www.ndss.org/images/stories/NDSSresources/developmental_milestones.pdf
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Issues across the life span
In addition to the health and developmental concerns, other issues come up throughout the life
span of a person with Down syndrome. It is important for early intervention providers to be
aware of these issues and consider them in the planning of services. Some of the more common
ones include:
 Understanding early intervention and educational systems
 Finding appropriate preschool and day care
 Inclusion with peers in school
 Socialization and friendships
 Planning for transition to adulthood
 Sexuality
 Life planning
 Postsecondary education
 Employment
 Independent living
 Self advocacy
What types of intervention are available for young children with Down
syndrome?
Education
Children with Down syndrome are eligible to receive early intervention services and special
education and related services. Children with Down syndrome often attend school and
receive instruction in classrooms with typically developing children.
Therapeutic
Physical therapy, speech-language pathology, occupational therapy and others therapies are
used to help a child develop motor, communication, cognitive and adaptive skills as fully as
possible. For example, babies with Down syndrome have low muscle tone, so a physical
therapist can help a baby learn to roll over, sit up, and walk, a speech-language pathologist
may help with feeding and the development of language, communication, and speech skills ,
or an occupational therapist may help with feeding, hand coordination, and visual-motor
skills.
Medical
Children with Down syndrome should receive regular pediatric care as would all children.
Depending on the extent of medical complications, they also may be seen by pediatric
cardiologists, gastrointestinal specialists, ophthalmologists, audiologist, and neurologists.
References
Fidler,D.J. & Nadel, L. (2007). Education and children with Down syndrome: Neuroscience,
development and intervention. Mental Retardation and Developmental Disabilities Research
Reviews. 13, 262-271.
Hanson, M.J. (2003). Twenty-five years after early intervention: A follow-up of children with
Down syndrome and their families. Infants and Young Children. 16 (4), 354-365.
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Kozma, C. (2008). Down syndrome and dementia. Topics in Geriatric Rehabilitation, 24, 41-53.
Roberts, J.E, Price, J. & Malkin, C. (2007). Language and communication development in Down
syndrome. Mental Retardation and Developmental Disabilities Research Reviews. 13, 26-35.
Roizen, N.J. The early interventionist and the medical problems of the child with Down
syndrome. Infants and Young Children. 16(1), 88-95.
Winders, P. C. (1997). Gross Motor Skills in Children with Down Syndrome: A Guide for
Parents and Professionals. Bethesda, MDL: Woodbine House.
Resources
American Academy of Pediatrics Committee on Genetics. Health Supervision for Children with
Down Syndrome. Pediatrics, volume 107, number 2, February 2001, pages 442-449.
American College of Obstetricians and Gynecologists (ACOG). Your Pregnancy and Birth, 4th
Edition. ACOG, Washington, DC, 2005; Chromosomal Abnormalities. ACOG Practice Bulletin,
number 77, January 2007.
The Arc of the United States
http://www.thearc.org
Centers for Disease Control and Prevention, Down Syndrome
http://www.cdc.gov/ncbddd/birthdefects/DownSyndrome.htm
March of Dimes
http://www.modimes.org/
National Down Syndrome Congress
http://www.ndsccenter.org/
National Down Syndrome Society
http://www.ndss.org/
National Information Center for Children and Youth with Disabilities
http://www.nichcy.org/
National Institute of Child Health and Human Development (NICHD).
http://www.nichd.nih.gov/health/topics/Down_Syndrome.cfm
Cite As: Georgetown University Center for Child and Human Development. Contemporary
Practices in Early Intervention: Down Syndrome Primer. 2009. Available online at
http://www.teachingei.org.
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