Genetic Testing

What chromosome causes Down Syndrome?

If chromosome 21 is in the presence of three copies. The Howard Hughes Medical Institute researchers have developed a new prenata blood test that accurately detected Down Syndrome and two other serious chromosomal defect in a small study of 18 Pregnant wome. (Citation 6)

Why should I consider screening for Down syndrome?

Many parents-to-be worry that their developing baby may have Down syndrome or some other chromosomal abnormality. Screening tests help you assess your baby's chances of having this kind of problem. The results can help you decide whether to have invasive diagnostic testing to find out for sure about your baby's condition. (Citation 6)

What can a screening test tell me?

Screening tests use blood samples and ultrasound measurements to assess your baby's chances of having certain chromosomal problems, including Down syndrome. They aren't invasive, so they don't pose any risk to you or your baby.

Screening tests can't tell you if your child actually has Down syndrome. Instead, they provide you with a ratio that expresses your baby's chances of having a problem, based on your test results and how old you are. This information may help you decide whether to undergo diagnostic testing.

Diagnostic tests such as chorionic villus sampling (CVS) and amniocentesis can tell you with greater than 99 percent certainty whether your child has a chromosomal abnormality. These tests can identify several hundred genetic disorders by analyzing the genetic makeup of cells from your baby or placenta. However, both procedures carry a small risk of miscarriage. (Citation 6)

How common is Down Syndrome?

Down Syndrome occurs in about 1 in 740 newborns. The chances of having a child with down syndrome increases as the wome gets older. (Citation 6)

What's a chromosomal abnormality?

Chromosomes are threadlike structures in our cells that carry our genes. Most people have 46 chromosomes in each cell, with one set of 23 coming from the mother's egg and the other set from the father's sperm.

Biological errors can happen during the early stages of cell division, causing abnormalities in the chromosomes. For example, some babies develop with 47 chromosomes: Instead of 23 matched pairs, they have 22 pairs plus one set of three, a chromosomal abnormality called trisomy.

Often, a woman who conceives a baby with an abnormal number of chromosomes will miscarry, usually early in pregnancy. But with certain chromosomal abnormalities, the baby may survive and be born with developmental problems and birth defects that can range from mild to severe.

Down syndrome, also known as trisomy 21, occurs when a baby has an extra copy of chromosome 21 in some or all of his cells. Down syndrome is the most common chromosomal abnormality babies can be born with.

Other chromosomal problems that babies can be born with include trisomy 18 and trisomy 13. These abnormalities are almost always associated with profound mental retardation and other congenital malformations. If they survive to birth, these babies rarely live more than a few months.

Anyone can have a baby with a chromosomal abnormality, but the risk rises with the mother's age. For example, your likelihood of carrying a baby with Down syndrome ranges from about 1 in 1295 at age 20 to about 1 in 82 at age 40. (Citation 6)

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