WHAT IS DOWN SYNDROME?
Down Syndrome (DS) is a condition in which extra genetic material causes delays in the way a child develops, and often leads to mental retardation. It affects 1 in every 800 babies born.
The symptoms of Down Syndrome can vary widely from child to child. While some kids with DS need a lot of medical attention, others lead very healthy and independent lives.
Though Down Syndrome can’t be prevented, it can be detected before a child is born. The health problems that can go along with DS can be treated, and there are many resources within communities to help kids and their families who are living with the condition.
WHAT CAUSES DOWN SYNDROME?
Normally, at the time of conception a baby inherits genetic information from its parents in the form of 46 chromosomes: 23 from the mother and 23 from the father. In most cases of Down Syndrome, however, a child gets an extra chromosome - for a total of 47 chromosomes instead of 46. It’s this extra genetic material that causes the physical and cognitive delays associated with Down Syndrome.
Although no one knows for sure why DS occurs and there’s no way to prevent the chromosomal error that causes it, scientists do know that women age 35 and older have a significantly higher risk of having a child with the condition. At age 30, for example, a woman has less than a 1 in 1,000 chance of conceiving a child with DS. Those odds increase to 1 in 400 by age 35. By 42, it jumps to about 1 in 60.
HOW DOES DOWN SYNDROME AFFECT A CHILD?
Kids with Down Syndrome tend to share certain physical features such as a flat facial profile, an upward slant to the eyes, small ears, a single crease across the center of the palms, and an enlarged tongue.
A doctor can usually tell if a newborn has the condition through a physical exam. Low muscle tone and loose joints are also characteristic of children with DS, and babies in particular may seem especially “floppy.” Though this can and often does improve over time, most children with DS typically reach developmental milestones - like sitting up, crawling, and walking - later than other kids. At birth, kids with DS are usually of average size, but they tend to grow at a slower rate and remain smaller than their peers. For infants, low muscle tone may contribute to sucking and feeding problems, as well as constipation and other digestive issues. In toddlers and older children, there may be delays in speech and self-care skills like feeding, dressing, and toilet teaching. Down Syndrome affects kids’ cognitive abilities in different ways, but most have mild to moderate mental retardation. Kids with DS can and do learn, and are capable of developing skills throughout their lives. They simply reach goals at a different pace - which is why it’s important not to compare a child with DS with typically developing siblings or even other children with the condition. Kids with DS have a wide range of abilities, and there’s no way to tell at birth what they will be capable of as they grow up. Medical Problems Associated with Down Syndrome While some kids with DS have no other health problems, others may experience a host of medical issues that require extra care. For example, half of all children born with DS also have congenital heart defects and are prone to developing pulmonary hypertension (high blood pressure in the lungs).
A pediatric cardiologist can monitor these types of problems, many of which can be treated with medication or surgery. Approximately half of all kids with DS also have problems with hearing and vision. Hearing loss can be related to fluid buildup in the inner ear or to structural problems of the ear itself. Vision problems commonly include amblyopia (lazy eye), near- or farsightedness, and an increased risk of cataracts. Regular evaluations by an audiologist and an ophthalmologist are necessary to detect and correct any problems before they affect a child’s language and learning skills. Other medical conditions that may occur more frequently in children with DS include thyroid problems, intestinal abnormalities, seizure disorders, respiratory problems, obesity, an increased susceptibility to infection, and a higher risk of childhood leukemia.
Fortunately, many of these conditions are treatable. Prenatal Screening and Diagnosis There are two types of prenatal tests available to detect Down Syndrome in a fetus: screening tests and diagnostic tests. Screening tests estimate the risk that a fetus has DS; diagnostic tests can tell whether the fetus actually has the condition. Screening tests are noninvasive and generally painless. But because they can’t give a definitive answer as to whether a baby has DS, mostly they’re used to help parents decide whether to have more diagnostic tests. Diagnostic tests are about 99% accurate in detecting Down Syndrome and other chromosomal abnormalities. However, because they are performed inside the uterus, they are associated with a risk of miscarriage and other complications. For this reason, they are generally recommended only for women age 35 or older, those with a family history of genetic defects, or those who’ve had an abnormal result on a screening test. If you’re unsure about which test, if any, is right for you, your doctor or a genetic counselor can help you sort through the pros and cons of each.
SCREENING TESTS INCLUDE:
- Nuchal translucency testing. This test, performed between 11 and 14 weeks of pregnancy, uses ultrasound to measure the clear space in the folds of tissue behind a developing baby’s neck. (Babies with DS and other chromosomal abnormalities tend to accumulate fluid there, making the space appear larger.) This measurement, taken together with the mother’s age and the baby’s gestational age, can be used to calculate the odds that the baby has DS. Nuchal translucency testing correctly detects DS about 80% of the time; when performed with a maternal blood test, it may offer greater accuracy.
- The triple screen (also called the multiple marker test) and the alpha fetoprotein plus. These tests measure the quantities of various substances in the mother’s blood, and together with the woman’s age, estimate the likelihood that her baby has Down syndrome. They are typically offered between 15 and 20 weeks of pregnancy.
- A detailed ultrasound. This is often performed in conjunction with the blood tests, and it checks the fetus for some of the physical traits associated with Down Syndrome. However, these screening tests are only about 60% accurate and often lead to false-positive or false-negative readings
DIAGNOSTIC TESTS INCLUDE:
- Amniocentesis. This test, performed between 16 and 20 weeks of pregnancy, involves the removal of a small amount of amniotic fluid through a needle inserted in the abdomen. The cells can then be analyzed for the presence of chromosomal abnormalities. Amniocentesis carries a small risk of complications, such as preterm labor and miscarriage.
- Chorionic villus sampling (CVS). CVS involves taking a tiny sample of the placenta, also through a needle inserted in the abdomen. The advantage of this test is that it can be performed earlier than amniocentesis, between 8 and 12 weeks. The disadvantage is that it carries a slightly greater risk of miscarriage and other complications. *
- Percutaneous umbilical blood sampling (PUBS). Usually performed after 20 weeks, this test uses a needle to retrieve a small sample of blood from the umbilical cord. It carries risks similar to those associated with amniocentesis.
After a baby is born, a diagnosis of Down Syndrome can usually be made just by looking at the baby. If the doctor suspects DS, a karyotype - a blood or tissue sample stained to show chromosomes grouped by size, number, and shape - can be performed to verify the diagnosis.