Posts Tagged ‘trisomy 21’

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.

What causes Down syndrome?

Thursday, September 26th, 2013

Down syndrome is caused by extra genetic material from chromosome 21. Chromosomes are the structures in cells that contain the genes.

Each person normally has 23 pairs of chromosomes, or 46 in all. An individual inherits one chromosome per pair 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, sometimes causing an egg or sperm cell to have an extra chromosome number 21. When this cell joins with a normal egg or sperm cell, the resulting embryo has 47 chromosomes instead of 46. Down syndrome is called trisomy 21 because affected individuals have three number 21 chromosomes, instead of two. This type of error in cell division causes about 95 percent of the cases of Down syndrome.

Occasionally, before fertilization, a part of chromosome 21 breaks off during cell division and becomes attached to another chromosome in the egg or sperm cell. The resulting embryo may have what is called translocation Down syndrome. Affected individuals have two normal copies of chromosome 21, plus extra chromosome 21 material attached to another chromosome. This type of error in cell division causes about 3 to 4 percent of the cases of Down syndrome. In some cases, the parent has a rearrangement of chromosome 21, called a balanced translocation, which does not affect his or her health.

About 1 to 2 percent of individuals with Down syndrome have a form called mosaicism. In this form, the error in cell division occurs after fertilization. Affected individuals have some cells with an extra chromosome 21 and others with the normal number.

The risk of Down syndrome increases with the mother’s age. Even though the risk is greater as the mother’s age increases, about 80 percent of babies with Down syndrome are born to women under age 35. This is because younger women have more babies than older women.

To learn more about Down syndrome and the types of health problems someone with Down syndrome might have, read this article.

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.