Down Syndrome

Down syndrome is the most common chromosomal abnormality. It results in mild to moderate mental retardation and other medical conditions. It occurs once in every 800 to 1,000 live births, and affects 350,000 people in the United States, according to the National Down Syndrome Society (NDSS). (Read about "Birth Defects")

What causes it?

Down syndrome is a chromosomal disorder caused by the presence of excess chromosomal material. (Read about "Genetics") A human being normally inherits 23 chromosomes from each of his or her parents, for a total of 46. When there is an extra copy of chromosome number 21, or excess genetic material from this chromosome, it results in Down syndrome.

Most of the time, the occurrence of Down syndrome is due to a random event during formation of the reproductive cells, the egg or sperm. Currently, it is not known to be caused by environmental factors or any behavior on the part of the parents. However, maternal age does seem to play a part in the incidence of Down syndrome, according to NDSS.

Maternal age a factor

Researchers have found that the likelihood that a reproductive cell will contain an extra chromosome number 21 increases dramatically as a woman ages. Therefore, an older woman is more likely than a younger one to have a baby with Down syndrome. The National Institute of Child Health & Human Development (NICHD) says older mothers account for only about nine percent of all live births each year, but 25 percent of Down syndrome births.

The likelihood that a woman under age 30 will have a baby with Down syndrome is less than 1 in 1,000, but those odds increase with age. Here's a look at how the risk increases, from NICHD:

• under age 30 - less than 1 in 1,000
• age 35 - 1 in 400
• age 38 - 1 in 180
• age 40 - 1 in 105
• age 42 - 1 in 60
• age 46 - 1 in 20
• age 49 - 1 in 12

The American College of Obstetricians and Gynecologists (ACOG) suggests that all women be offered screenings for Down syndrome. Because the incidence of Down syndrome increases with maternal age, many doctors recommend that women 35 or older, who become pregnant, undergo additional prenatal testing for Down syndrome. The age of the father may also be a factor.

Prenatal tests

There are two types of procedures that look for Down syndrome, according to NDSS: screening tests and diagnostic tests. Screening tests estimate the risk of the fetus having Down syndrome; diagnostic tests tell whether or not the fetus actually has the condition, according to NDSS.

ACOG suggests first-trimester screening for genetic defects. An ultrasound (Read about "Ultrasound Imaging"), called nuchal translucency that measures the thickness at the back of the neck of the fetus, combined with blood tests for beta human chorionic gonadotropin (ß-hCG) and plasma protein-A (PAPP-A), can indicate an increased risk of Down syndrome and the need for additional diagnostic testing. (Read about "Laboratory Testing") There is also a more sophisticated blood test. Called a Non-Invasive Screening Test (NIPT), it may also be used to screen for Down Syndrome and other chromosomal abnormalities. This test looks for genetic fragments from the fetus that are circulating in the mother's blood, and can be performed after the 10th week of gestation. ACOG says all tests can result in false positives, and the decision to use these tests should be evaluated by a woman and her physician.

In the second trimester, the most common screening tests are the Alpha-fetoprotein Plus and the Triple marker or Quad Marker Screen. They measure various substances in the blood, and together with the woman's age, estimate the risk of her having a child with Down syndrome. These tests are only about 60 percent accurate. The diagnostic tests are about 98 to 99 percent accurate. However, each one carries a small risk of miscarriage as tissue is extracted from the placenta or umbilical cord to analyze the fetus' chromosomes. (Read about "Pregnancy Testing") The three diagnostic tests are amniocentesis, chorionic villus sampling (CVS) and percutaneous umbilical blood sampling (PUBS). Here is some basic information about each test from NICHD:

• Amniocentesis
  • involves the removal and analysis of a small sample of fetal cells from the amniotic fluid
  • cannot be done until the 14-18th week of pregnancy (Read about "Stages of Pregnancy")
  • has lowest risk of miscarriage
• Chorionic villus sampling (CVS)
  • involves extraction of a tiny amount of fetal tissue to be tested for extra material from chromosome 21
  • usually done during 9-11th week of pregnancy
  • Carries a 1-2 percent risk of miscarriage
• Percutaneous umbilical blood sampling (PUBS)
  • involves testing a sample of umbilical tissue for extra material from chromosome 21
  • cannot be done until 18-22nd week of pregnancy
  • carries greatest risk of miscarriage

Diagnosis

A newborn with Down syndrome often has physical features that a doctor can often recognize immediately. They may include a flat facial profile, an upward slant to the eyes, abnormally shaped ears, folds at the inner corner of the eyes, an enlarged tongue, poor muscle tone and a single deep crease across the palm. Some infants may have many of these traits; others may have just a few. If Down syndrome is suspected, a blood test called a chromosomal karyotype can be done to confirm the diagnosis, according to NICHD.

A doctor will not be able to tell right away what intellectual or physical capabilities a child with Down syndrome will have. People with Down syndrome have a wide range of abilities. There is a lot of information for parents whose children are diagnosed with Down syndrome and support groups are available. Your doctor can help you find them.

Associated medical problems

There are increased health risks for individuals with Down syndrome. The greatest risks are for heart disease, leukemia and Alzheimer's disease. (Read about "Coronary Heart Disease" "Leukemia" "Alzheimer's Disease") Nearly half of all children with Down syndrome have some form of heart disease or congenital heart defect. (Read about "Congenital Heart Defects") The risk of childhood leukemia is 15 to 20 times greater. In addition, about 25 percent of adults with Down syndrome will develop the signs and symptoms of Alzheimer's disease, often before they are 40 years old.

They are also at risk for other medical problems that may include:

• seizure disorders (Read about "Seizures")
• hearing loss (Read about "Hearing Loss")
• vision problems (Read about "The Eye" "Eye Exams")
• respiratory problems (Read about "Respiratory System")
• bowel obstructions
• thyroid enlargement (Read about "Thyroid")

However, thanks to medical advances, many of these problems can now be treated with surgeries, medications and physical therapy. (Read about "Rehabilitation") In the last 75 years, the average life expectancy of a person with Down syndrome has gone from 9 years to 55 years, according to NDSS.

Living with Down syndrome

Infants with Down syndrome need to be loved, fed, cuddled and cared for just like any other baby. They usually have developmental delays and will likely take longer to roll over, sit up, walk and talk than other children. They may also teethe later than other babies. But while it may take them longer to reach these milestones, they will eventually get there. (Read about "Child Development") It is also important to have them see a doctor regularly and have their vision and hearing checked. Early intervention, in the form of educational programs and good home and medical care, could be beneficial for children with Down syndrome. This may include working with special educators, speech therapists, occupational therapists and social workers. Your doctor can help you decide what course is best for your child, including what type of schooling to choose. Children can attend a school where most of the kids do not have disabilities (called inclusion) or a school for children with special needs. Inclusion has become more common over the past decade, according to the NICHD. As mentioned, people with Down syndrome are now living to age 50 and beyond, and are leading fuller lives. Many are able to have relationships and eventually marry, to gain the skills to hold jobs and live independently. With the help of their families and the community, people with Down syndrome are able to do more than ever before.

Related Information:

    Brain/Mental Health/Nervous System

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