Down Syndrome
Trisomy 21 Chromosome Disorder

Down Syndrome

Contents

• Down Syndrome Facts
• What Are The Symptoms?
• What Are The Causes?
• Age Of The Mother - Risk Factors
• Can I Test For Down Syndrome?

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Birth Defects

Down Syndrome Facts

Down syndrome is a chromosomal disorder (mostly they have too many chromosomes in their cells) which a baby is born with. It results in a variety of health problems as well a characteristic facial appearance. People with Down syndrome suffer different degrees of severity in symptoms ranging from intellectual disabilities, heart defects, thyroid issues, digestive problems like celiac disease or gastroesophageal reflux and other health problems. Given the increased risk of developing significant medical problems, the life expectancy of someone with Down syndrome is about 50, significantly lower than the national average of a 'normal' person. Yet, many adults with Down syndrome have jobs and live independently. Down syndrome affects one in every 800 babies born in the United States each year, and according to the National Down Syndrome Society, there are currently more than 400,000 people living with the disorder in America. In general, Down syndrome is not one of those inherited genetic disorders but rather the result of a random event during the formation of the cells during conception.

What Are The Symptoms?

A child born with this chromosomal disorder will have a characteristic appearance:

• Eyes slant upwards.
• Smaller ears than normal which may fold a little at the top.
• Smaller mouth than normal, gives the tongue the appearance of being larger.
• Short neck.
• Small hands and feet and low muscle tone.
• Generally they will be shorter than the average child or adult.

What Are The Causes?

This disorder is caused by extra genetic material from chromosome 21. Each person normally has 23 pairs of chromosomes (46 in total). One half of the chromosomes come from the father, and the other half from the mother. On occasion however, something goes wrong before fertilization. Sometimes the egg or sperm divide incorrectly, resulting in an extra chromosome 21, which means the resulting embryo ends up with 47 chromosomes instead of 46 (nondisjunction). This process of nondisjunction seems to occur more frequently in older women. It may explain why the risk of having a baby with Down syndrome is greater among women experiencing a pregnancy after 35 and older. Down syndrome is also called trisomy 21 because the individuals end up with three chromosomes 21 instead of the usual two. This type of cell division error causes the vast majority of Down syndrome cases (95 percent). In 3 to 4 percent of cases an embryo may have what is called translocation Down syndrome. This is where part of chromosome 21 breaks off before fertilization and attaches itself to another chromosome. It means the baby will have 2 normal copies of chromosome 21, plus extra chromosome 21 material attached to another chromosome. Finally in 1 to 2 percent of cases, the individuals have a form of Down syndrome called Mosaicism. This is where a cell division error happens after fertilization and the baby ends up with some cells with the two regular chromosomes 21 and others with the abnormal numbers.

Prevention: The best way to reduce the risk factors of having a baby with Down syndrome is to follow a good prenatal care guide, and to start preparing for pregnancy before you even become pregnant. Genetic counselors will also help you assess your personal risk profile.

Age Of The Mother - Risk Factors

Yes. The risks increase incrementally with age, but the most significant increases are after the age of 35. Interestingly enough however, 80 percent of babies born with Down syndrome are born to mothers under 35. This is because statistically a younger woman is likely to have more babies than an older woman.

Statistics
• Age 25 the risk of having a baby with Down syndrome is 1 in 1,250.
• Age 30: risk is 1 in 1,000
• Age 35: risk is 1 in 400
• Age 40: risk is 1 in 100
• Age 45: risk is 1 in 30

Can I Test for Down Syndrome?

Yes. The American College of Obstetricians and Gynecologists (ACOG) recommend that all pregnant women in their first trimester be tested for Down syndrome, regardless of the woman's age. The first test can be carried out in weeks 11 to 13 of pregnancy. This is a maternal blood test in addition to a special ultrasound scan which measures the thickness at the back of the baby's head (called nuchal scan). It can also be carried out in the second trimester at weeks 15 to 20 without ultrasound. Women who have abnormal results from these screenings will then be offered a diagnostic test such as amniocentesis or chorionic villus sampling. These tests are highly accurate when it comes to diagnosing Down syndrome. If you are planning to conceive a child by IVF, then pre-implantation genetic diagnosis can help detect Down syndrome before the embryo is even implanted.

News: New Prenatal Blood Test

A new simple diagnostic blood test developed by Stanford University can check if a pregnant woman is carrying a child with Down syndrome. If proven accurate and affordable it could be further developed to detect hundreds of other genetic and congenital disorders. It works by counting the millions of DNA molecules from both the mother and baby and can determine if there is too much genetic material. The potential market for the new test is huge as an estimated 750,000 out of as out of 4.5 million children born every year in the US are considered high risk due to the age of the mother or genetic family history (in 2010 the prenatal testing market was worth $1.3 billion). This test should prove popular as the current alternative is to undergo amniocentesis and chorionic villus sampling (see genetic testing while pregnant) which involves needles and carries the risk of miscarriage. The blood test has been licensed by biotech companies Verinata Health and Fluidigm Corporation. Known as noninvasive prenatal diagnostics (NIPD) testing, it is expected to be launched commercially to the market in 2012. In the meantime, Sequenom Laboratories have launched their version of the test called MaterniT21. Currently the test can only be ordered by doctors and not directly by consumers . It costs around $1,900, about the same as an amniocentesis. However, for those who are insured it is expected the out-of-pocket costs will be no more than $235.

According to the Boston's Children Hospital, even with current genetic tests however, the rate of Down syndrome has declined 11 percent between 1989 and 2006.

The degree of intellectual difficulties a child born with Down syndrome will experience cannot be predicted at birth, and will only manifest as the child grows older. In general disabilities range from mild to moderate, and with proper intervention few develop severe disabilities. Children with Down syndrome can do can do most things any young child can do, including talking, walking, dressing and being potty-trained. They may just take a little longer, or learn these things later. If you have questions on any other female health topic, see our section womens health questions.

Related Articles on DOWN SYNDROME FACTS

For more birth defects and genetic disorders, see the following:

• Genetic Testing Before Pregnancy
• Third Trimester Prenatal Visit
• Cleft Palate and Clubfoot

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