Posts Tagged ‘Trisomy 18’

March is Trisomy Awareness Month

Monday, March 13th, 2017

chromosomesWhat is trisomy?

Babies with trisomy are born with an extra copy of a specific chromosome in most or all of their cells. This means that they have three copies of this chromosome in each cell rather than the typical number, which is two. Health conditions that may be associated with trisomy include heart defects, vision or hearing problems, and intellectual and developmental disabilities.

Chromosomes are the structures in cells that contain genes. Each person normally has 23 pairs of chromosomes, or 46 in all. An individual inherits one chromosome from the mother’s egg and one from the father’s sperm. When an egg and sperm join together, they normally form a fertilized egg with 46 chromosomes.

Sometimes a mistake in cell division occurs before a woman gets pregnant. A developing egg or sperm ends up with an extra chromosome. When this cell joins with a normal egg or sperm cell, the resulting embryo has 47 chromosomes instead of 46.

Common trisomy conditions

Although trisomy can occur with any chromosome, here are the conditions that are most often associated with an extra chromosome:

  • Trisomy 21 or Down syndrome: Down syndrome is one of the most common birth defects. In the US, about 6,000 babies (or 1 in 700) are born with Down syndrome each year. Most affected individuals have intellectual disabilities within the mild to moderate range. Although health conditions such as heart defects and vision and hearing problems are associated, most of these can be treated, and life expectancy is now about 60 years.
  • Trisomy 18 is also called Edward syndrome: Trisomy 18 occurs in about 1 in 5,000 live births each year. Affected individuals may have heart defects, significant intellectual and developmental delays, and other life-threatening medical problems.
  • Trisomy 13, also known as Patau syndrome: Trisomy 13 occurs in about 1 in 10,000 to 16,000 live births each year worldwide. Individuals with trisomy 13 often have heart defects, brain or spinal cord abnormalities, severe intellectual and developmental disabilities, and multiple physical problems in many parts of the body.

It is important to understand that every individual with a trisomy is unique and not all of them will have the same symptoms. The severity of the condition and the associated problems depend on:

  • Which chromosome is duplicated: An extra copy of certain chromosomes, like chromosome 1, is not compatible with life and the embryo will not develop.
  • How much of the extra chromosome is present: If only part of the chromosome is present, symptoms may be milder. If the complete chromosome is present, the symptoms may be more severe.
  • How many cells have the extra chromosome: If the copy of the extra chromosome is in only a few cells (mosaicism), the symptoms are usually less severe than if all of the cells in the body are affected.

In the past 10 years, the March of Dimes has invested over 15  million dollars into research for chromosomal conditions, including trisomy. And many March of Dimes grantees are studying basic biological processes of development. This important research should improve our understanding of how genes and other factors affect the development of a baby.

Have questions? Text or email us at AskUs@marchofdimes.org.

Trisomy Awareness Month

Friday, March 4th, 2016

chromosomes1Have you ever heard of “trisomy”? Trisomy is a chromosomal condition that is the result of a mistake in cell division. Chromosomes are the structures in cells that contain genes. Each person normally has 23 pairs of chromosomes, or 46 in all. An individual inherits one chromosome from the mother’s egg and one from the father’s sperm. When an egg and sperm join together, they normally form a fertilized egg with 46 chromosomes.

Sometimes something goes wrong before fertilization. A developing egg or sperm cell may divide incorrectly, causing that egg or sperm to have an extra chromosome. When this cell joins with a normal egg or sperm cell, the resulting embryo has 47 chromosomes instead of 46.

Babies with trisomy are born with an extra copy of a specific chromosome in most or all of their cells. This means that they have three copies of this chromosome in each cell rather than the typical number, which is two.

Although trisomy can occur with any chromosome, there are a few conditions that are most often associated with an extra chromosome. They are:

  • Trisomy 21 or Down syndrome: Down syndrome is one of the most common birth defects. In the US, about 6,000 babies (or 1 in 700) are born with Down syndrome each year. Most affected individuals have intellectual disabilities within the mild to moderate range. Although health conditions such as heart defects and vision and hearing problems are associated, most of these can be treated, and life expectancy is now about 60 years
  • Trisomy 18 is also called Edward syndrome. Trisomy 18 occurs in about 1 in 5,000 live births each year. Affected individuals may have heart defects, significant intellectual and developmental delay, and other life-threatening medical problems.
  • Trisomy 13, also known as Patau syndrome, occurs in about 1 in 10,000 to 16,000 live births each year worldwide. Individuals with trisomy 13 often have heart defects, brain or spinal cord abnormalities, severe intellectual and developmental disabilities, and multiple physical problems in many parts of the body.

It is important to understand that every individual with a trisomy is unique and not all of them will have the same symptoms. The problems depend on which chromosome is duplicated and how much of the extra chromosome is present. Health conditions that may be associated with trisomy include heart defects, vision or hearing problems, and intellectual and developmental disabilities.

If your baby or someone in your family has a trisomy, you may want to talk to a genetic counselor. A genetic counselor is a person who is trained to know about genetics, birth defects and other medical problems that run in families. She can help you understand the causes of chromosomal conditions, what kind of testing is available, and your chances of having a baby with these conditions. If you already have a baby with a trisomy, the chances of having another baby with the same condition are usually low.

Have questions? Email us at AskUs@marchofdimes.org.

What is trisomy?

Friday, March 6th, 2015

chromosomes1Trisomy is a condition in which individuals are born with an extra copy of a specific chromosome in most or all of their cells. This means that they have three copies of a given chromosome in each cell rather than the typical number, which is two.

Chromosomes are the structures in cells that contain genes. Each person normally has 23 pairs of chromosomes, or 46 in all. An individual inherits one chromosome from the mother’s egg and one from the father’s sperm. When an egg and sperm join together, they normally form a fertilized egg with 46 chromosomes.

Sometimes something goes wrong before fertilization. A developing egg or sperm cell may divide incorrectly, causing that egg or sperm to have an extra chromosome. When this cell joins with a normal egg or sperm cell, the resulting embryo has 47 chromosomes instead of 46.

There are a variety of health conditions that may be associated with trisomy. Common physical problems for individuals with a trisomy include heart defects, vision or hearing problems, and intellectual and developmental disabilities.

Although trisomy can occur with any chromosome, there are three conditions that are most often associated with an extra chromosome. They are:

  • Trisomy 21 or Down syndrome: Down syndrome is one of the most common birth defects. In the US, about 6,000 babies (or 1 in 700) are born with Down syndrome each year. Most affected individuals have intellectual disabilities within the mild to moderate range. Although health conditions such as heart defects and vision and hearing problems are associated, most of these can be treated, and life expectancy is now about 60 years
  • Trisomy 18 is also called Edward syndrome. Trisomy 18 occurs in about 1 in 5,000 live births each year. Affected individuals may have heart defects, significant intellectual and developmental delay, and other life-threatening medical problems.
  • Trisomy 13, also known as Patau syndrome, occurs in about 1 in 10,000 to 16,000 live births each year worldwide. Individuals with trisomy 13 often have heart defects, brain or spinal cord abnormalities, severe intellectual and developmental disabilities, and multiple physical problems in many parts of the body.

It is important to understand that every individual with a trisomy is unique and not all of them will have the same symptoms. The problems depend on which chromosome is duplicated and how much of the extra chromosome is present.

March of Dimes grantees are studying basic biological processes of development to better understand the process of early cell division and how a trisomy may occur. In the past five years, the March of Dimes has invested $5,274,554 in trisomy research.

New prenatal blood test

Thursday, December 13th, 2012

New prenatal tests can give some parents piece of mind that the baby they’re expecting doesn’t have a disorder.  The tests are given sooner and with greater accuracy and less risk of miscarriage than current tests.

The new tests, which use fetal DNA suspended in the mother’s blood, can test for chromosomal disorders such as Down syndrome (trisomy 21) and trisomy 18, and Rh blood incompatibility. They also can determine the baby’s gender, which allows health care providers to screen for disorders such as hemophilia.

During pregnancy, fetal cells and cell-free fetal genetic material circulate in the mother’s bloodstream.  This DNA can be used to screen for certain genetic disorders without having to perform invasive procedures such as amniocentesis or CVS (chorionic villus sampling).

At present four widely used procedures assist health care providers in prenatal diagnosis. They are:
Amniocentesis: a procedure that collects some of the amniotic fluid that surrounds the fetus for analysis. This is a diagnostic test.
Chorionic villus sampling (CVS): a procedure that obtains tissue from around the placenta. This is a diagnostic test.
• Maternal blood tests: screening tests that use mother’s blood to help identify problems with the fetal brain, spinal cord, intestines or chromosomes. These tests include alpha-fetoprotein (AFP), hCG and other hormones. As with all forms of screening, abnormal results require follow-up testing to make a diagnosis.
Ultrasound: a scan using sound waves to visualize the fetus.

Cell-free DNA methods of screening are a new option. “Prenatal diagnosis gives parents important information about the health of their baby and the status of their pregnancy. More often than not, prenatal screening reassures parents that their baby is healthy and that these disorders are not present,” says Joe Leigh Simpson, MD, March of Dimes senior vice president for Research and Global Programs.  “For a high-risk infant, prenatal diagnosis gives parents and health care providers options that may include planning for a health problem or arranging for delivery in a medically appropriate setting. The first step toward treating these problems is diagnosing them, and cell-free DNA methods, without the need for invasive measures, are welcomed.”

Dr. Lee P. Shulman of Northwestern University says, “while this represents a profound improvement in our ability to identify women at increased risk for carrying fetuses with the most common chromosome abnormalities, still, this technology represents a limited screening protocol and should not serve as a substitute for diagnostic tests such as chorionic villus sampling and amniocentesis, which provide the most accurate and comprehensive assessment by the direct analysis of fetal tissue.”

The American College of Obstetricians and Gynecologists and the American College of Medical Genetics recommend that information on prenatal genetic screening and diagnosis should be made available to all pregnant women and those considering pregnancy.

With all the above options for testing available, it’s important to discuss what is best for you and your pregnancy with your health care provider.

Do those blood tests confuse you?

Monday, August 9th, 2010

For those of you who are pregnant, sometime between 15-20 weeks of pregnancy, you will be offered maternal serum screening.  What is this?  And more importantly, what do the results mean?  I think maternal blood screening is one of the most misunderstood tests in pregnancy.  And for some women it can be a very nerve-wracking experience.

The American College of Obstetricians and Gynecologists (ACOG) recommends that all pregnant women regardless of age be offered a screening test for Down syndrome and certain other birth defects.  This is a blood test that looks at the levels of either 3 or 4 (depending on the test) chemicals that are present in a pregnant woman’s blood.  The chemicals are AFP (alpha fetoprotein), hCG (human chorionic gonadotropin—the same chemical that a home pregnancy test measures), estriol, and recently most labs have added a fourth substance, inhibin A.  These chemicals are present in every pregnant woman’s blood.  Some of them are produced by the fetus while others are hormones produced by the placenta.

Maternal serum tests such as the triple screen or the quad screen as they are commonly called, look at the levels of these 3 or 4 chemicals in the mother’s blood and the woman’s age, weight, race, number of fetuses (e.g. twins) and whether she has diabetes that requires insulin treatment.  Then given all of those factors and the levels of the 3 or 4 chemicals the laboratory can determine the chance that a woman has a baby with Down syndrome, a neural tube defect (spina bifida), trisomy 18, or abdominal wall defects.

There are two different ways that the results may be reported.  A woman may receive her test result as a ratio. For example, her baby has a 1 in 500 chance for Down syndrome. Or, in some cases, a woman’s test results are reported as normal (screen negative) or abnormal (screen positive), depending on whether her results fall below or above a cut-off point (usually about 1 in 270).

The test is NOT a diagnosis of any of these conditions though.  This is where there is a lot of confusion.  By definition, screening tests do not diagnose a condition.  They only determine whether there is an increased risk for the condition.  The good news is that of all of the women who screen positive, only a small percentage will actually have a baby with one of these disorders.  Many times women have an abnormal result simply because their fetus is a few weeks older or younger than previously thought.

For women with abnormal results, the next step is usually an ultrasound. This test can check the gestational age of the fetus and show if a woman is carrying multiples. If either of these factors accounts for the abnormal test result, no further testing is needed. If ultrasound does not explain the abnormal test result, amniocentesis will be offered.  An amniocentesis is an invasive test where the doctor uses a needle to remove some of the amniotic fluid around the baby.  Although amnio does pose a very slight risk of miscarriage (1/4 of one percent or 1/500), it is extremely accurate and usually can give a pregnant woman a definitive answer.  Should a problem exist, arrangements can be made in advance for special care of the newborn at delivery.

Screening for birth defects

Tuesday, September 9th, 2008

At my last prenatal appointment I had a combination of tests done to screen for birth defects such as Down syndrome and Trisomy 13 and 18. I was nervous going, but my husband was with me for support. My visit started with an ultrasound. The doctor rubbed a hand-held device (called a transducer) across my belly. The baby was face up and the doctor needed him/her to turn to the side in order to measure the thickness at the back of the neck (called nuchal translucency).  We waited and waited, but he/she wouldn’t budge. I certainly didn’t mind because I was able to admire the beautiful image on the screen longer.

After several minutes, the doctor finally called for a nurse. She brought me a very sweet orange drink and the doctor said he would be back in less than 10 minutes. I was thinking, “yeah right, this isn’t going to work.” Well, wouldn’t you know it. When he came back and put the transducer on my belly, there it was — the most perfect profile. I guess the baby just needed a little energy. Using the mouse on the ultrasound machine, he was able to measure the back of the neck.

Then I was passed off to the nurse who took a blood sample. I don’t know if this is always the case with maternal blood screening, but she pricked my finger and placed about 5 or 6 drops of blood on a card. The office sent the blood sample to a lab and I would get the results back in about four days. The lab calculated my risk of chromosomal birth defects, using the combined results of my blood test and ultrasound exam.

I received a call a few days later. I was told that based on my age, blood work and ultrasound my risk for Down syndrome was 1 in 1, 610 and my risk for Trisomy 18/13 was 1 in > 10,000. I know that no test can gaurantee the birth of a healthy baby, but I was so relieved. It’s always nice to here reassuring news. Waiting for test results can be so stressful.