Down Syndrome

Down SyndromeWhat is Down syndrome?
Down syndrome is a disorder that includes a combination of birth defects; among them, some degree of mental retardation, characteristic facial features and, often, heart defects, increased infections, problems with vision and hearing, and other health problems. The severity of all of these problems varies greatly among affected individuals. Down syndrome is one of the most common genetic birth defects, affecting approximately one in 800 to 1,000 babies. It generally is caused by an extra chromosome, the structures in cells that contain the genetic information (genes).

According to the National Down Syndrome Society, there are approximately 350,000 individuals with Down syndrome in this country. Life expectancy among adults with Down syndrome is about 55 years, though life span varies depending on the individual and his or her medical condition.

What causes Down syndrome?
Normally, each egg and sperm cell contains 23 chromosomes. The union of these creates 23 pairs, or 46 chromosomes in total. Sometimes, an accident occurs when an egg or sperm cell is forming, causing it to have an extra chromosome number 21. When this cell contributes the extra chromosome 21 to the embryo, Down syndrome results. All of the features and birth defects associated with Down syndrome result from having this extra chromosome 21 in each of the body's cells. Down syndrome also is called trisomy 21 because of the presence of three number 21 chromosomes.

Occasionally, the extra chromosome 21 is attached to another chromosome in the egg or sperm; this may result in what is called translocation Down syndrome. This is the only form of Down syndrome that can be inherited from a parent. In such cases, the parent has a rearrangement of chromosome 21, called a balanced translocation, which does not affect his or her health.

Rarely, a form of Down syndrome called mosaic Down syndrome may occur when an accident in cell division occurs after fertilization. Affected individuals have some cells with an extra chromosome 21 and others with the normal number.

What health problems might a child with Down syndrome have?
Almost half of babies with Down syndrome have heart defects. Some defects are minor and may be treated with medications, while others may require surgery. All babies with Down syndrome should be examined by a pediatric cardiologist, a doctor who specializes in heart diseases of children, and have an echocardiogram in the first 2 months of life so that any heart defects can be treated.

About 10 percent of babies with Down syndrome are born with intestinal malformations that require surgery. More than 50 percent have some visual or hearing impairment. Common visual problems include crossed eyes (esotropia), near- or far-sightedness and cataracts. Most can be improved with glasses, surgery or other treatments. A pediatric ophthalmologist should be consulted, usually within the first six months of life. Children with Down syndrome may have hearing loss due to fluid in the middle ear, a nerve defect or both. Babies with Down syndrome should be screened for hearing loss at birth or by 3 months of age. Children with Down syndrome should have regular vision and hearing examinations so any problems can be treated before they hinder development of language and other skills.

Children with Down syndrome tend to have many colds and ear infections, as well as bronchitis and pneumonia. They also are at increased risk of thyroid problems and leukemia. Children with the disorder should receive regular medical care including standard childhood immunizations.

What does a child with Down syndrome look like?
A child with Down syndrome may have eyes that slant upward and small ears that may fold over a little at the top. His/her mouth may be small, making the tongue appear large. His/her nose may also be small, with a flattened nasal bridge. Some babies with Down syndrome have short necks and small hands with short fingers and, due to less muscle tone, appear somewhat "floppy."

The child or adult with Down syndrome is often short and has unusual looseness of the joints. Most children with Down syndrome will have some, but not all, of these features.

How serious is the mental retardation?
The degree of mental retardation varies widely, from mild to moderate to severe. Most fall within the mild to moderate range, and studies suggest that, with proper intervention, fewer than 10 percent will have severe mental retardation. There is no way to predict the mental development of a child with Down syndrome based upon physical features.

What can a child with Down syndrome do?
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 other children.

The exact age that these developmental milestones will be achieved cannot be predicted. However, early intervention programs beginning in infancy can help these children achieve their developmental milestones sooner.

Can a child with Down syndrome go to school?
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 in the regular classroom. The outlook for these children is far brighter than it once was. More mildly affected children can learn to read and write and participate in diverse childhood activities both at school and in their neighborhoods.

While there are special work programs designed for adults with Down syndrome, many people with the disorder can 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.

Can Down syndrome be cured or prevented?
There is no cure for Down syndrome, nor is there any prevention for the chromosomal accident that causes Down syndrome. However, recent studies suggest that some women who have had a baby with Down syndrome had an abnormality in how their bodies metabolize (process) the B vitamin folic acid.  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 (which has been shown to reduce the risk of certain birth defects of the brain and spinal cord).

Who has the greatest risk of having a baby with Down syndrome?
Parents who have already had a baby with Down syndrome, mothers or fathers who have a rearrangement involving chromosome 21, and mothers over 35 years old are at greatest risk. The risk of Down syndrome increases with age, from about 1 in 1,250 for a woman at age 25, to 1 in 1,000 at age 30, 1 in 400 at age 35, and 1 in 100 at age 40. However, about 80 percent of babies with Down syndrome are born to women who are under age 35, as younger women have far more babies.

Can Down syndrome be diagnosed before the child is born?
Yes. Prenatal testing using amniocentesis or a newer test called chorionic villus sampling can diagnose or, far more likely, rule out Down syndrome. As both procedures carry a small risk of infection and/or miscarriage, doctors generally offer them only to women at increased risk of having a baby with chromosomal or certain other birth defects.

A doctor may suggest amniocentesis if a woman receives an abnormal result on a blood test (often called the triple screen) done around the 16th week of pregnancy. However, this blood test does not provide a conclusive diagnosis: it simply means that additional tests such as amniocentesis should be considered. Ultrasound can also be used to detect many cases of Down syndrome.

Any family with a mentally retarded child or a child with other birth defects can discuss these tests with their doctor or health professional. He or she may refer the family for genetic counseling to learn more about their particular problem and the risks involved in having another child.

What is the risk that parents of a child with Down syndrome will have another affected child?
In general, in each subsequent pregnancy, the chance of having another baby with Down syndrome is 1 percent plus whatever additional risk a mother has, based upon her age.  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 doctor usually takes a blood sample from a baby suspected of having Down syndrome to do a chromosomal analysis (called a karyotype). This determines if the baby has Down syndrome and what the underlying chromosomal abnormality is. This information is important in determining the risk in future pregnancies. The doctor 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.

Can people with Down syndrome marry?
Some people with Down syndrome marry. With rare exceptions, men with Down syndrome cannot father a child. In any pregnancy, a woman with Down syndrome has a 50-50 chance of conceiving a child with Down syndrome, but many affected fetuses are miscarried. A substantial number of adults with Down syndrome (15 to 20 percent) develop Alzheimer’s disease in middle age.