Down syndrome is a chromosomal disorder that includes a combination of birth defects. Affected individuals have some degree of intellectual disability, characteristic facial features and, often, heart defects and other health problems. The severity of these problems varies greatly among affected individuals.
Down syndrome is one of the most common genetic birth defects. About 1 in 700 (or 6,000) babies are born with Down syndrome each year in the United States. According to the National Down Syndrome Society, there are more than 400,000 individuals with Down syndrome in the United States (2).
Down syndrome is caused by extra genetic material from chromosome 21. Chromosomes are the structures in cells that contain the genes.
Each person normally has 23 pairs of chromosomes, or 46 in all. An individual inherits one chromosome per pair from the mother’s egg and one from the father’s sperm. When an egg and sperm join together, they normally form a fertilized egg with 46 chromosomes.
Sometimes something goes wrong before fertilization. A developing egg or sperm cell may divide incorrectly, sometimes causing an egg or sperm cell to have an extra chromosome number 21. When this cell joins with a normal egg or sperm cell, the resulting embryo has 47 chromosomes instead of 46. Down syndrome is called trisomy 21 because affected individuals have three number 21 chromosomes, instead of two. This type of error in cell division causes about 95 percent of the cases of Down syndrome (3).
Occasionally, before fertilization, a part of chromosome 21 breaks off during cell division and becomes attached to another chromosome in the egg or sperm cell. The resulting embryo may have what is called translocation Down syndrome. Affected individuals have two normal copies of chromosome 21, plus extra chromosome 21 material attached to another chromosome. This type of error in cell division causes about 3 to 4 percent of the cases of Down syndrome (3). In some cases, the parent has a rearrangement of chromosome 21, called a balanced translocation, which does not affect his or her health.
About 1 to 2 percent of individuals with Down syndrome have a form called mosaicism (3). In this form, the error in cell division occurs after fertilization. Affected individuals have some cells with an extra chromosome 21 and others with the normal number.
The outlook for individuals with Down syndrome is brighter than it once was. Most of the health problems associated with Down syndrome can be treated, and life expectancy is now about 60 years (2). Individuals with Down syndrome are more likely than unaffected individuals to have one or more of the following health conditions:
Some individuals with Down syndrome may have a number of these problems, while others may have none. The severity of these conditions varies greatly.
A child with Down syndrome may have:
Most children with Down syndrome have some, but not all, of these features.
The degree of intellectual disability varies widely. Most affected individuals have intellectual disabilities within the mild to moderate range (2, 3). With proper intervention, few affected individuals have severe intellectual disability (3). There is no way to predict the mental development of a child with Down syndrome based upon physical features.
Children with Down syndrome usually can do most things that any young child can do, such as walking, talking, dressing and being toilet-trained. However, they generally start learning these things later than unaffected children.
The exact age that these developmental milestones are achieved cannot be predicted. However, early intervention programs beginning in infancy can help these children achieve their developmental milestones sooner.
Yes. There are special programs beginning in the preschool years to help children with Down syndrome develop skills as fully as possible. Along with benefiting from early intervention and special education, many children are integrated into the regular classroom. Many affected children learn to read and write, and some graduate from high school and go on to post-secondary programs or college. Many individuals with Down syndrome participate in diverse childhood activities at school and in their neighborhoods.
While there are special work programs designed for adults with Down syndrome, many people with the disorder hold regular jobs. Today, an increasing number of adults with Down syndrome live semi-independently in community group homes where they take care of themselves, participate in household chores, develop friendships, partake in leisure activities and work in their communities.
There is no cure for Down syndrome. However, some studies suggest that women who have certain versions of some genes that affect how their bodies metabolize (process) the B vitamin folic acid may be at increased risk for having a baby with Down syndrome (5, 6). If confirmed, this finding may provide yet another reason why all women who might become pregnant should take a daily multivitamin containing 400 micrograms of folic acid. Taking folic acid can help reduce the risk of having a baby with certain birth defects of the brain and spinal cord.
Yes. The risk of Down syndrome increases with the mother’s age (7):
Even though the risk is greater as the mother’s age increases, about 80 percent of babies with Down syndrome are born to women under age 35. This is because younger women have more babies than older women (1).
In general, in each subsequent pregnancy the chance of having another baby with Down syndrome is about 1 in 100 up to age 40. After age 40, the risk is based on the mother’s age (8). If, however, the first child has translocation Down syndrome, the chance of having another child with Down syndrome may be greatly increased.
After birth, the provider takes a blood sample from a baby suspected of having Down syndrome and sends it to a laboratory. The lab does a karyotype (examines the chromosomes) to determine if the baby has Down syndrome and what genetic form of Down syndrome the baby has. This information is important in determining the risk in future pregnancies. The provider may refer parents to a genetic counselor who can explain the results of chromosomal tests in detail, including what the recurrence risks may be in another pregnancy.
Yes. 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 be a maternal blood test done in the first trimester (at 11 to 13 weeks of pregnancy) along with a special ultrasound to measure the thickness at the back of the baby’s neck (called nuchal translucency). Or it can be a maternal blood test done in the second trimester (at 15 to 20 weeks) without the ultrasound (9). The screening test helps identify pregnancies that are at higher-than-average risk of Down syndrome. However, the screening test cannot diagnose Down syndrome or other birth defects.
Women who have an abnormal screening test result are offered a diagnostic test, such as amniocentesis or chorionic villus sampling (CVS). These tests are highly accurate at diagnosing or, more likely, ruling out Down syndrome.
ACOG also recommends that pregnant women of all ages have the option of bypassing the screening test and choosing a diagnostic test for Down syndrome instead (9). Until recently, only women over age 35 and others considered at increased risk for having a baby with Down syndrome were offered diagnostic testing because amniocentesis and CVS pose a small risk of miscarriage. In the future, screening for Down syndrome may be able to be accomplished with a simple blood test of the pregnant woman that can find and examine minute amounts of fetal genetic material.
Most parents-to-be receive reassuring news from a screening or diagnostic test for Down syndrome. However, if a prenatal diagnostic test shows that the baby has Down syndrome, parents have an opportunity to consider the diagnosis and their options. They also can prepare medically, emotionally and financially for the birth of a child with special needs, such as arranging for delivery in a medically appropriate setting.
With rare exceptions, men with Down syndrome cannot father a child (3). A woman with Down syndrome has a 50-50 chance of conceiving a child with Down syndrome, but many affected fetuses are miscarried.
Yes. Some March of Dimes grantees are investigating why errors in chromosome division occur to be able to prevent Down syndrome and other birth defects caused by abnormalities in the number or structure of chromosomes. Other grantees are investigating the role of specific genes in causing the brain abnormalities and other health problems associated with Down syndrome, with the goal of developing treatments. For example, one grantee is looking at the role of genes in causing a form of leukemia in children with Down syndrome. Another is exploring the role of genes in causing early Alzheimer’s disease in adults with Down syndrome. An international team of scientists has mapped all the genes of chromosome 21. This information eventually may pave the way for treatment of many features of this disorder.
Many organizations provide information and support for families with children affected by Down syndrome, including:
Dad's exposure to harmful chemicals and substances before conception or during his partner's pregnancy can affect his children. Harmful exposures can include drugs (prescription, over-the-counter and illegal drugs), alcohol, cigarettes, cigarette smoke, chemotherapy and radiation. They also include exposure to lead, mercury and pesticides.
Unlike mom's exposures, dad's exposures do not appear to cause birth defects. They can, however, damage a man's sperm quality, causing fertility problems and miscarriage. Some exposures may cause genetic changes in sperm that may increase the risk of childhood cancer. Cancer treatments, like chemotherapy and radiation, can seriously alter sperm, at least for a few months post treatment. Some men choose to bank their sperm to preserve its integrity before they receive treatment. If you have a question about a specific exposure, contact the Organization of Teratology Information Specialists at www.otispregnancy.org.
The Rh factor may be a problem if mom is Rh-negative but dad is Rh-positive. If dad is Rh-negative, there is no risk.
If your baby gets her Rh-positive factor from dad, your body may believe that your baby's red blood cells are foreign elements attacking you. Your body may make antibodies to fight them. This is called sensitization.
If you're Rh-negative, you can get shots of Rh immune globulin (RhIg) to stop your body from attacking your baby. It's best to get these shots at 28 weeks of pregnancy and again within 72 hours of giving birth if a blood test shows that your baby is Rh-positive. You won't need anymore shots after giving birth if your baby is Rh-negative. You should also get a shot after certain pregnancy exams like an amniocentesis, a chorionic villus sampling or an external cephalic version (when your provider tries to turn a breech-position baby head down before labor). You'll also want to get the shot if you have a miscarriage, an ectopic pregnancy or suffer abdominal trauma.
A cleft lip or cleft palate that extends into the upper gums (where top teeth develop) can cause your baby to have certain dental problems, including:
Every baby with a cleft lip or palate should get regular dental checkups by a dentist with experience taking care of children with oral clefts. Dental problems caused by cleft lip or palate usually can be fixed. If needed, your baby can get ongoing care by a team of experts, including:
See also: Cleft lip and cleft palate
Cleft lip does not cause ear problems.
Babies with cleft palate, however, are more likely than other babies to have ear infections and, in some cases, hearing loss. This is because cleft palate can cause fluid to build up in your baby’s middle ear. The fluid can become infected and cause fever and earache. If fluid keeps building up with or without infection, it can cause mild to moderate hearing loss.
Without treatment , hearing loss can affect your baby’s language development and may become permanent.
With the right care, this kind of hearing loss is usually temporary. Your baby’s provider may recommend:
See also: Cleft lip and cleft palate
Babies with only a cleft lip usually don’t have trouble breastfeeding. Most of the time, they can breastfeed just fine. But they may need some extra time to get started.
Babies with cleft lip and palate or with isolated cleft palate can have:
Most babies with cleft palate can’t feed from the breast. If your baby has cleft palate, he can still get the health benefits of breastfeeding if you feed him breast milk from a bottle. Your provider can show you how to express (pump) milk from your breasts and store breast milk.
Your baby’s provider can help you start good breastfeeding habits right after your baby is born. She may recommend:
Children with cleft lip generally have normal speech. Children with cleft lip and palate or isolated cleft palate may:
Most children can develop normal speech after having cleft palate repair. However, some children may need speech therapy to help develop normal speech.
See also: Cleft lip and cleft palate
The choroid plexus is the area of the brain that produces the fluid that surrounds the brain and spinal cord. This is not an area of the brain that involves learning or thinking. Occasionally, one or more cysts can form in the choroid plexus. These cysts are made of blood vessels and tissue. They do not cause intellectual disabilities or learning problems. Using ultrasound, a health care provider can see these cysts in about 1 in 120 pregnancies at 15 to 20 weeks gestation. Most disappear during pregnancy or within several months after birth and are no risk to the baby. They aren't a problem by themselves. But if screening tests show other signs of risk, they may indicate a possible genetic defect. In this case, testing with higher-level ultrasound and/or amniocentesis may be recommended to confirm or rule out serious problems.
If you didn’t take folic acid before getting pregnant, it doesn't necessarily mean that your baby will be born with birth defects. If women of childbearing age take 400 micrograms of folic acid every day before and during early pregnancy, it may help reduce their baby’s risk for birth defects of the brain and spin called neural tube defects (NTDs). But it only works if you take it before getting pregnant and during the first few weeks of pregnancy, often before you may even know you’re pregnant.
Because nearly half of all pregnancies in the United States are unplanned, it's important that all women of childbearing age (even if they're not trying to get pregnant) get at least 400 micrograms of folic acid every day. Take a multivitamin with folic acid before pregnancy. During pregnancy, switch to a prenatal vitamin, which should have 600 micrograms of folic acid.
Last reviewed November 2012