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Down Syndrome

Summary

Down syndrome is a genetic condition that causes mental retardation and some specific physical characteristics. It was named after JohnLangdon Down, the 19th century physician who first described it. The condition occurs in about one in every 800 newborns, according tothe U.S. Centers for Disease Control and Prevention (CDC), and occurs equally among all races and ethnic groups.

Down syndrome is caused by the presence of an extra chromosome. Most cells in the human body have 46chromosomes in 23 pairs.

About Down syndrome

Down syndrome is a condition caused by extra genetic material that results in some degree of mental retardation and certain physicalproblems. Usually, people with Down syndrome have an entire extra chromosome in most of their cells, although occasionally only anextra piece of a chromosome is present.

Down syndrome is among the most common birth defects and is the most common cause of developmental delays and mental retardationin the United States. The condition was named after John Langdon Down, the 19th century physician who first described it. Downsyndrome is associated with certain facial features (e.g., flatter face, upward slanting eyes) that may seem abnormal, particularly for the

childs race.

Most people have 46 chromosomes in 23 pairs in all of their cells -- 22 regular pairs and one pair of sex chromosomes. The mother andfather each contribute one chromosome of each pair. However, people with Down syndrome have triplication of chromosome 21 (anextra copy in the smallest of these chromosome pairs, chromosome 21). This extra copy may be an entire extra chromosome, or only apart of it attached to a different chromosome.

This extra genetic material found in Down syndrome can affect almost every system in the body. It almost always results indevelopmental delays, including mild to moderate mental retardation. The severity of mental retardation and developmental delays in

children with Down syndrome varies widely. Some have a near-normal overall level of functioning, but others require substantialassistance. However, people with Down syndrome tend to demonstrate near-average levels of social functioning. In general, a child'soverall functioning can be improved with proper medical management, therapy, education and a supportive home environment.

e mother and father each contribute one-half of each pair. However, people with Down syndrome have triplication of chromosome 21 (an

extra copy or extra genetic material of the smallest of these chromosomes, chromosome 21) The cause of this chromosomal abnormalityis not known. However, the risk of having a child with Down syndrome increases as a parent ages.

The characteristics, features and potential complications of Down syndrome vary greatly among patients. Down syndrome is commonly

associated with a number of physical features, including a flat facial profile, upward slanting eyes and a single crease along the center ofthe palms. Various medical issues, including an increased susceptibility to infection, poor muscle tone, congenital heart defects and eye,ear, breathing and digestive problems, are also generally associated with Down syndrome.

The extra genetic material present in Down syndrome also results in developmental delays, including mild to moderate mentalretardation. Infants born with Down syndrome are usually born an average size, but tend to grow more slowly than others. Because of

this, most people with Down syndrome will be smaller than their age peers throughout life. Other developmental delays include delays insitting up, walking, talking and toilet training. Early intervention with speech, physical and occupational therapy can help overcome these

delays. Children and adolescents with Down syndrome may attend regular schools, although some may still need special classes to helpwith learning disabilities.

Down syndrome is often detected before birth. Prenatal screening tests may be used to determine the chance that a particular fetus hasDown syndrome. A positive result on a screening test may lead to the use of a diagnostic test such as amniocentesis or chorionic villus

sampling. Prenatal diagnosis of Down syndrome may give parents the time to decide to terminate the pregnancy or to adjust to theupcoming challenges of raising a child with Down syndrome. After an infant is born, Down syndrome can usually be diagnosed by aphysical examination.

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Types and differences of Down syndrome

Down syndrome involves an abnormality in chromosome 21. Each person has 23 pairs of chromosomes in each body cell -- 22 regularpairs and one pair of sex chromosomes. The abnormality associated with Down syndrome and chromosome 21 can occur three ways:

Standard trisomy 21. Three entire copies of chromosome 21 occur in all the nonreproductive cells in a child's body.This form results from a problem that occurs during egg or sperm cell development. The vast majority of Downsyndrome cases are of this type.

Translocation 21. Due to an abnormality in the genes of a parent or an error in egg or sperm cell development, anextra piece of chromosome 21 is attached to a different chromosome. The normal pair of chromosome 21 is stillpresent. This is an uncommon form of Down syndrome.

Mosaic trisomy 21. Three entire copies of chromosome 21 occur in some, but not all, cells in the child's body. Thisis caused by a problem in embryo development after the sperm and egg have joined. It is a rare form of Downsyndrome.

Infant issues for Down syndrome

Infants with Down syndrome will generally require more frequent medical checkups (e.g., well-child visits) to ensure and maintaingood health. Some symptoms that commonly affect infants with Down syndrome must be identified shortly after birth and monitored. Forexample, babies with heart or gastrointestinal defects may require corrective surgery in infancy.

Infants with Down syndrome are usually born an average size but tend to grow more slowly than others. Because of this, throughout life,

most people with Down syndrome will be smaller than their age peers.

Down syndrome infants frequently have poor muscle tone (hypotonia). This may lead to problems with sucking and feeding. Theseinfants develop more slowly than other infants. They tend to sit up and reach other developmental milestones later than usual. Teethingoften occurs later and the teeth may erupt in an abnormal pattern. Digestive issues such as constipation are also common during infancy.

Early intervention services can be extremely helpful for Down syndrome patients. These are best started as early as possible. Regularphysical therapy, for example, can help to build muscle tone and improve coordination so the infants can learn to sit up and crawl.

Childhood issues for Down syndrome

Children with Down syndrome generally still require frequent medical checkups (e.g.,

well-child visits) to ensure and maintain good health. Many pediatricians recommend visionand hearing tests at every visit. Many children with Down syndrome have sight problems and

suffer from chronic ear infections (e.g., otitis media) in addition to hearing loss , which cancompromise their ability to learn and use language. Identifying vision and hearing problemsearly may minimize their effect on learning and language skills.

Developmental delays continue in childhood. Children with Down syndrome may begin towalk and speak later than other children. It may also take longer for them to become toilettrained and to learn to feed and dress themselves.

Early-intervention services are generally recommended to continue from infancy up to school

age. Physical therapy can continue to help increase muscle tone and coordination.Occupational therapy can be used to improve fine-motor skills, such as hand coordination. Speech therapy may help to improve language

development. Therapists can also teach the parents of children with Down syndrome how to continue to improve these and othercommunication skills at home.

The U.S. Individuals with Disabilities Education Act (IDEA) guarantees educational services to children with Down syndrome who are 3years of age and older. This includes free education that is appropriate for the child's level of development and an individualizededucation plan (IEP). These services are typically provided by the local school district.

Many school-aged children with Down syndrome can attend classes in regular schools. Some may still need special classes to help withany learning disabilities. There are also special programs available for the schooling of children with Down syndrome.

Children with Down syndrome can participate in activities (e.g., music, dance) and usually play sports, although medical problems may

restrict some of these children from certain sports (e.g., football, diving). Many children with Down syndrome participate in the SpecialOlympics, a sports training and athletic competition for people with intellectual disabilities.

Schooling for children with Down syndrome may vary by state and school district. In some areas, classrooms are grouped by age

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regardless of education level. In others, children with disabilities may study separately in groups according to their ability level. Parentsof Down syndrome children can educate themselves about their child's abilities and the programs offered within their districts.

Adolescent issues for Down syndrome

Many adolescents with Down syndrome can still attend the same classes and schools and participate in the same activities as their agepeers. They can often get after-school or summer jobs. Some continue their education through college, and many can look forward toliving at least partially independently.

These adolescents generally have the same desires and interests as other adolescents. They can be concerned over romantic relationships

and having their own families one day. Boys and men with Down syndrome are usually infertile. Girls with Down syndrome reach sexual

maturity and experience menstrual periods, and many can become pregnant. However, a girl or woman with Down syndrome has anincreased chance of having a child who also has Down syndrome.

Risk factors and causes of Down syndrome

Down syndrome is caused by an abnormality in chromosome 21. However, the specific mechanism that causes the abnormality is notknown. Some factors have been identified that may increase the risk of having a child with Down syndrome. These risk factors include:

Advanced parental age. The mother's age is the most prominent and best-established risk factor. The older awoman is when she gives birth, the greater her chance of having a child with Down syndrome. Children born towomen older than 35 have a much higher risk of the condition. A 30-year-old woman has a one-in-1,000 chance ofhaving a child with Down syndrome, according to the American Academy of Family Physicians (AAFP). However,this risk increases to one in 400 at age 35 and one in 60 at age 42.

In addition, research in recent years has increasingly indicated that advanced paternal age also increases the riskof several health problems in children, including birth defects such as Down syndrome. Sperm declines in quality asmen age, swimming more slowly and becoming more genetically defective. One recent study found that men'ssperm usually started showing signs of decline at age 56.

Parental chromosomal abnormality. Men and women with certain chromosomal abnormalities have an increasedrisk of having a child with Down syndrome. In some cases, the parent does not have any extra or missing geneticmaterial, but genes are not located in the normal places. For example, a part of chromosome 21 may occur onanother chromosome but be missing from chromosome 21.

Previous child with Down syndrome. If parents have had one child with Down syndrome, they have a slightlyincreased chance of having another. This may be due to a chromosomal abnormality that has not yet beendetected.

Signs and symptoms of Down syndrome

The characteristics, features and potential complications ofDown syndrome vary greatly among patients. All children with the

condition are different. However, some degree of mental retardation is nearly universal. In most cases, children with Down syndromehave mild to moderate retardation. Severe retardation is uncommon.

Mild retardation is defined as an intelligence quotient (IQ) of 50 to 70, moderate retardation as an IQ of 35 to 50, severe retardation as anIQ of 20 to 35. The overall development is slow in these children but still occurs. In most cases, children with Down syndrome reach allof the developmental goals of infancy and childhood, just not as quickly as usual.

Down syndrome is commonly associated with a number of physical features. Some children with the condition may have many of these.However, some may have few, if any. These physical features include:

A small, short and broad head

A flat facial profile with a flat nasal bridge

Upward slanting eyes with epicanthic folds (eyelid folds at the inner corner of the eyes)

Brushfield spots (speckled discoloration on the iris, the colored part of the eye)

Small ears that may be misshapen or look lower than usual

A small mouth with a large, protruding tongue

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Excess skin at the back of the neck

Short, broad hands with short fingers

A curved fifth finger

Simian crease (single crease along the center of the palms)

Wide gap between the big toe and the second toe

Many medical problems are commonly associated with Down syndrome. Some children with the condition have no other medicalproblems at all. However, others require a great deal of medical attention. Medical problems commonly associated with Down syndromeinclude:

Infections. Most children with Down syndrome are at least slightly more susceptible to infections (e.g., colds, flu)that their peers. When these infections occur, they are likely to last longer than normal.

Low muscle tone and loose joints. Many children with Down syndrome have low muscle tone (hypotonia) and loosejoints. This can result in excessive flexibility and a floppy, rag-doll like appearance. These problems are often worsein infancy and improve with age. Children with Down syndrome have a 6 percent chance of dislocating their hip,according to the American Academy of Pediatrics (AAP). Some children have a characteristic instability with thebones in the neck that may need to be monitored.

Ear problems. Hearing loss occurs in 75 percent of children with Down syndrome, according to the AAP. Thesechildren also have between a 50 and 75 percent risk of ear infections. These problems may be due to structuralproblems or a fluid buildup in the inner ear.

Obstructive sleep apnea. Temporary interruptions in breathing during sleep. Children with Down syndrome have a50 to 75 percent risk of sleep apnea, according to the AAP.

Eye problems. The AAP reports an overall risk of eye disease of 60 percent in children with Down syndrome. Thisincludes a 50 percent risk of vision loss due to severe myopia (nearsightedness), hyperopia (farsightedness) orastigmatism (abnormal shape of the retina). These children also have a 15 percent chance of cataracts, accordingto the AAP. Lazy eye (amblyopia) is also more common in children with Down syndrome.

Congenital heart defects. According to the AAP, about 50 percent of infants with Down syndrome are born withheart defects, such as abnormal openings called septal defects. These conditions can also increase a childs risk ofhigh blood pressure in the lungs (pulmonary hypertension).

Thyroid disease. Children with Down syndrome have a 15 percent risk of thyroid disease (e.g., hypothyroidism),according to the AAP.

Digestive problems. The AAP reports that 12 percent of infants with Down syndrome are born with incomplete orabsent openings (atresia) in their digestive tract. These can include the openings into and out of the stomach,between different parts of the intestines, or a lack of an anus. Poor muscle tone may also increase the risk ofdigestive problems such as constipation. Intestinal obstruction (blockage) may occur due to problems with function(Hirschsprung disease) in 1 percent of Down syndrome infants, according to the AAP. There may be an increasedrisk of celiac disease (gluten intolerance).

Childhood leukemia. Children with Down syndrome have a greater risk of leukemia than other children. However,this risk is still low, less than 1 percent, according to the AAP. Furthermore, depending on the type of leukemiapresent, children with Down syndrome may have a higher long-term survival rate than other children with the same

type of leukemia.

Other problems, such as:

o Obesityo Seizure disorderso Respiratory problemso Alopecia areata (patchy baldness)

Some of the developmental delays of Down syndrome may worsen the childs experience with physical symptoms. For example, manychildren with Down syndrome have delayed or difficult to understand speech. They also understand language more readily than they can

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use it and may not be able to say when a body part hurts. They may refuse to walk on a hurt foot if they are unable to tell someone aboutthe pain.

Diagnosis methods for Down syndrome

Down syndrome is often detected before birth. Prenatal testing includes screening tests and diagnostic tests. Screening tests identify ahigher likelihood of a given defect but cannot definitively diagnose it. A woman who receives a positive result on a screening test mayelect to have a diagnostic test, which can confirm the presence of Down syndrome in more than 98 percent of cases.

Prenatal screening tests include:

Maternal blood tests . Identify and measure substances in the mothers blood that reveal information about herfetus. There are a number of these tests available, including the triple screen test and quadruple screen test. Thetriple screen identifies the levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG) and estriol. Thequadruple screen tests levels of those three elements plus the inhibin A protein. They are usually performed in the16

thto 18

thweeks of pregnancy.

Detailed ultrasound. Uses sound waves to create an image of inside a mother's womb. This can be used to identifycertain physical features common in Down syndrome, but it is not very accurate without supplementation with otherscreening tests.

Nuchal translucency testing. Ultrasound is used to examine the back of the fetus's neck. Fluid tends to accumulatein this area when Down syndrome or other chromosomal conditions are present. This gives a swollen appearanceon the ultrasound. This test may be performed between 11 and 14 weeks of pregnancy. Recent research indicatesthat nuchal translucency testing combined with a test for HCG and another protein can identify more than 80percent of Down syndrome cases before 13 weeks of gestation, much earlier than some diagnostic tests.

The American College of Obstetricians and Gynecologists began recommending in 2007 that all pregnant women be offered thechoice of having screening tests for Down syndrome, not just higher-risk mothers.

Prenatal diagnostic tests are nearly 99 percent accurate in identifying Down syndrome and certain other chromosomal conditions,according to the American Academy of Family Physicians. However, they are associated with complications, including a risk of

miscarriage and preterm labor. These tests are typically recommended only for women with a high risk of having a child with Downsyndrome, including those over age 35, those with a family history of genetic problems and those who had abnormal results on screeningtests.

Prenatal diagnostic tests include:

Amniocentesis. A needle is inserted through the abdomen and into the uterus. Then, a small amount of amnioticfluid (the fluid in the uterus) is removed for testing. This test is generally performed between 16 and 20 weeks intothe pregnancy.

Chorionic villus sampling (CVS). A sample of the placenta is removed for testing. It may be obtained using either aneedle through the abdomen (as in amniocentesis) or a tube inserted through the vagina. This test can beperformed between eight and 12 weeks of pregnancy.

Percutaneous umbilical blood sampling (PUBS). A needle is used to remove a sample of blood from the fetus'sumbilical cord. This test carries higher risks of complications than amniocentesis or CVS and is typically used onlywhen diagnosis must be made quickly. It is typically performed later in pregnancy, after 20 weeks.

The results of screening and diagnostic tests may provide pregnant women with valuable information about the fetus. Some women maychoose to terminate an affected pregnancy. Others use the information to prepare to care for an infant with special needs.

After an infant has been born, Down syndrome can usually be diagnosed by a physical examination, or even just looking at the infant.The diagnosis is confirmed with a karyotype. This is a chart of the child's chromosomes created using a blood or other tissue sample.

Treatment options and prevention methods

There is no cure for Down syndrome , but the health problems that are often associated with it can be treated.

At one time, death in infancy or childhood was nearly universal for Down syndrome patients. Now, most children born with Downsyndrome survive into older adulthood, as a result of better understanding of the condition and medical advances such as antibiotics andcorrective surgery. However, they do require more frequent medical checkups (e.g., well-child visits) than normal, including regular eye

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and ear examinations.

The birth defects that may be associated with Down syndrome (e.g., heart defects, gastrointestinal atresia) can typically be treatedthrough surgery. After these abnormalities are corrected, they usually cause no more problems. Infections (e.g., colds, ear infections) andother conditions (e.g., thyroid disease, seizure disorders) can be treated with medications. Vision or hearing loss may require corrective

lenses or hearing aids. Obstructive sleep apnea (temporary interruptions in breathing while asleep) can often be treated with atonsillectomy (surgical removal of the tonsils) or adenoidectomy (surgical removal of the adenoids). As with all children, propernutrition and regular physical activity are also very important to maintain good health.

The developmental problems associated with Down syndrome are a lifelong concern. Parents may involve themselves in their children'streatment, therapy and education so the children can achieve to the limits of their abilities in independent living and functioning.

There is no sure way to prevent Down syndrome, but women and men can increase their chances of having healthy children by notdelaying parenthood until later in life.

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Down Syndrome - Exams and Tests

Testing before becoming pregnant

You may want to consider genetic testing for Down syndrome if you are planning to become pregnant and you

have a family history of the condition. Genetic testing can confirm whether you or your partner carry the

translocation chromosome, which increases your risk for having a child with the translocation type of Down

syndrome. But this kind of testing does not detect whether your child is more likely to have the trisomy 21 type,

which accounts for most Down syndrome cases.

Related Articles Shaken Baby Syndrome - Exams and Tests

Down Syndrome - Treatment Overview

Genetic counseling can help you understand why genetic testing is done, what the results mean, and how the

results may affect you and your family.

Screening during pregnancy

Screening does not diagnose Down syndrome but rather provides information about the likelihood that your

fetus will have the condition. Screening tests include:

Fetal ultrasound. This test can detect signs of Down syndrome in the first trimester. A fetal ultrasound

image can show a greater-than-normal amount of fluid at the back of a fetus's neck. The skin fold thickness

measurement estimates the distance between the surface of the skin and the neck bones (nuchal fold). This

test is not yet widely available, because only a specially trained provider can do it.

Maternal serum triple or quadruple screen test. The triple test (triple screen) is done in the second

trimester. It measures the amounts of the following 3 substances in your blood:

Alpha-fetoprotein (AFP)

Human chorionic gonadotropin (hCG)

Estriol (uE3)

The test is called a quadruple screen (quad screen) when a test for inhibin A is added. Inhibin A is a protein

that is produced by the fetus and the placenta. The quadruple test can detect most Down syndrome cases, and

it may be less likely than the triple screen to deliver false-positive results.6

The triple and quad tests can only

be done in the second trimester.

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Should I have the maternal serum triple test or quadruple test (triple or quad screen)?

Other screening options that may be available in the first trimester include:

Combination screening.

Integrated screening.

A combination screening uses both a fetal ultrasound and a blood test to measure levels of human chorionic

gonadotropin (hCG) and pregnancy-associated plasma protein-A (PAPP-A). It has shown to be as exact as the

quad screen for detecting Down syndrome.7

One advantage of this type of screening is that it can be done

earlier in your pregnancy than some other tests.

Integrated screening uses both first and second trimester tests to predict the risk of having a child with Down

syndrome. It is one of the most accurate tests that may be available.7

The results are reported only after both

sets of tests are finished. This can be cause for concern for women who would like to know test results early on.

Screening tests for Down syndrome and other conditions require your consent. Some women find that knowingtheir chances of having a child with Down syndrome helps them to prepare for the possibility. Others are more

comfortable going through their pregnancy without having this information.

Also, the type of screening tests given, alone or in combination, depends on the mother's goals and

preferences. For example, when a mother is most concerned with screening accuracy and does not want to

have amniocentesis, her doctor may recommend a combination of fetal ultrasound and blood test during the first

trimester plus a triple or quad screen during the second trimester.

Diagnosis during pregnancyA chromosomal analysis, called a karyotype test, can diagnose Down syndrome during pregnancy. A sample is

taken directly from the fetus or placenta using one of the following techniques:

Amniocentesis. This usually is done at 15 to 18 weeks or later in your pregnancy. The liquid (amniotic

fluid) that surrounds your fetus contains cells that have been shed by your developing baby. These cells can

be checked for the number and size of chromosomes to see if there are any problems that put the baby at r isk

for certain conditions, such as Down syndrome. The test is done by inserting a needle through your abdomen

into your uterus. Approximately 2 Tbsp (30 mL) of the amniotic fluid is collected and examined. Amniocentesis

has a 1 in 370 risk of causing miscarriage.8

It is 99.8% accurate in detecting Down syndrome. Results of

amniocentesis usually take about 2 weeks.

Chorionic villus sampling (CVS). This test is done earlier than amniocentesis, ideally between weeks

10 and 12 of your pregnancy. Chorionic villi are tiny finger-shaped growths found in the placenta. The

genetic material in chorionic villus cells is identical to the genetic material in fetal cells. A biopsy of these cells

can provide doctors with genetic information about your fetus. Doctors can then let you know whether your

fetus is likely to have certain conditions, such as Down syndrome, that can develop from chromosomes that

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are not normal. The chorionic villus sample is usually collected through the mother's vagina. The doctor inserts

a speculum to gently spread apart the vaginal walls, and a catheter is guided through the cervix to the

placenta using ultrasound. When the catheter is correctly placed, a sample of chorionic villus cells is collected.

Less often, the sample of chorionic villus cells is collected by inserting a needle through the abdomen into the

woman's uterus. CVS has a 1 in 360 risk of causing a miscarriage.8

Results of CVS are usually available

within several days.

Should I have chorionic villus sampling?Should I have an amniocentesis?

Because there are risks associated with amniocentesis and CVS, they are not done routinely. The tests usually

are offered to pregnant women with an increased risk for having a fetus with abnormal chromosomes. This

includes women who have had an abnormal nuchal fold ultrasound or triple or quad screen test, who are age 35

or older, who have a child with Down syndrome, or who have a family history of the condition.

It is always your choice whether to have your fetus tested for Down syndrome. A diagnosis of Down syndrome

made early in fetal development allows you the option of terminating your pregnancy. If termination is not an

option for you, early awareness can help you prepare emotionally and plan for the special needs of your child.

A genetic counselor can help you during this process.

If a fetus is diagnosed with Down syndrome, a doctor may recommend fetal echocardiography to screen for

heart defects and fetal ultrasound to help detect digestive system problems. Any suspected defects will be

further investigated after birth.

Diagnosis after your baby is born

If Down syndrome was not diagnosed before birth with a karyotype test (using amniocentesis or chorionic villussampling), a baby's physical features at birth often give doctors a clear sense of whether the child has Down

syndrome. But traits can be subtle in a newborn, depending on the type of Down syndrome that he or she has.

In general, a preliminary diagnosis can often be made from observation of physical features and:

Results of earlier triple or quad screening tests (if any are available).

Details about the parents' medical histories.

Physical exam of the baby for other medical problems.

A newborn will also have a blood sample taken for chromosomal analysis to confirm the diagnosis. It may take 2

to 3 weeks to get the complete results of this test.

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Testing at birth and throughout life

Screening guidelines were developed by the American Academy of Pediatrics and the Down Syndrome Medical

Interest Group (DSMIG) for people with Down syndrome according to age. Doctors screen for common

problems seen in people with Down syndrome, such as heart, hearing, or vision problems.

Testing for newborns (birth to 1 month of age)

Testing for infants (age 1 month to 1 year)

Testing during early childhood (age 1 to 5 years)

Testing during middle and late childhood (age 5 to 13 years)

Testing during adolescence and young adulthood (age 13 to 21 years)

Testing during adulthood

Early Detection

Testing for Down syndrome during pregnancy (prenatal testing), which requires your consent, may be

recommended if you:

Are 35 or older.

Have a family history of Down syndrome or your partner has a family history of Down syndrome.

Know that you or your partner carry the gene for the translocation type of Down syndrome.

Screening for Down syndrome is done with the maternal triple screen test. Prenatal testing for a formal

diagnosis of Down syndrome requires karyotyping. The sample used for this testing is taken during

amniocentesis or chorionic villus sampling.

Genetic counseling offers a lot of information and help for couples who are planning to become pregnant. For

example, couples who have a child with Down syndrome can use genetic counseling to help determine their risk

for having another child with the condition.