Posts Tagged ‘chromosomes’

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.

Fragile X syndrome

Monday, October 21st, 2013

Fragile X syndrome is the most common inherited form of intellectual disability. It affects about 1 in 4,000 males and 1 in 6,000 to 8,000 females and occurs in all racial and ethnic groups.

Fragile X syndrome is caused by an abnormality in the FMR-1 gene located on the X chromosome.  Each person has 23 pairs of chromosomes, or 46 individual chromosomes. The pair of sex chromosomes (X and Y) determines whether a person is male or female. Females have two X chromosomes, and males have one X chromosome and one Y chromosome. Because females have two X chromosomes, a female who inherits one X chromosome with the abnormal FMR-1 gene still has the other unaffected X chromosome. Therefore, girls are affected by fragile X syndrome less frequently than boys and their symptoms are usually not as severe. Boys are usually more severely affected because they have only one X chromosome, and it contains the abnormal gene.

Fragile X is inherited and passed on through the mother’s side of the family.  Any woman who has a brother or male relative with fragile X syndrome may want to meet with a genetic counselor.  A genetic counselor can help her to better understand the complicated genetics and inheritance of fragile X syndrome.

Children and adults with fragile X syndrome may exhibit a number of signs.  These can range from mild to severe. Some common symptoms include:

• Some degree of intellectual disability or learning problems
• Behavioral problems, such as difficulty paying attention and frequent tantrums
• Autistic-like behaviors, such as hand flapping and hand biting
• Delays in learning how to sit, walk and talk
• Speech problems
• Anxiety and mood problems
• Sensitivity to light, sounds, touch and textures

Most boys with fragile X syndrome have intellectual disabilities, but only about one-third to one-half of affected girls do. However, affected girls with normal intelligence may have some of the following symptoms:

• Learning disabilities involving math
• Attention difficulties
• Speech delays
• Emotional problems, such as anxiety, depression and shyness
• Poor social skills

While most children with fragile X do not have any medical conditions, about 15% of boys and 5% of girls develop seizures.  These can usually be controlled with medication.  Children with fragile X may also be at increased risk for multiple ear infections and they may need to have tubes placed in their ears.  Older children and adults may have heart murmurs, but usually no treatment is necessary.

There is no cure for fragile X syndrome. But, an individualized treatment plan, beginning as soon as possible, can help children reach their full potential. Most children with fragile X syndrome can benefit from treatment by a team of health professionals and special educators. The team may include speech/language therapists, physical and occupational therapists, special educators, psychologists and pediatricians.

What is a molar pregnancy?

Thursday, August 1st, 2013

In a molar pregnancy, the early placenta develops into an abnormal mass (called a hydatidiform mole) that looks a little like a bunch of white grapes. The embryo either does not form at all or is malformed and cannot survive. About 1 in 1,500 pregnancies is molar.

There are two types of molar pregnancy: complete mole (there is no embryo and no normal placental tissue); and partial mole (there is an abnormal embryo, and there may be some normal placental tissue.) Both types of molar pregnancy are caused by an abnormal fertilized egg.

In a complete mole, all of the fertilized egg’s chromosomes (tiny thread-like structures in cells that carry genes) come from the father. Normally, half come from the father and half from the mother. In a complete mole, shortly after fertilization, the chromosomes from the mother’s egg are lost or inactivated, and those from the father are duplicated.

In most cases of partial mole, the mother’s 23 chromosomes remain. However, there are two sets of chromosomes from the father (so the embryo has 69 chromosomes instead of the normal 46). This can happen when two sperm fertilize an egg.

Molar pregnancy poses a threat to the pregnant woman because it can occasionally result in rare pregnancy-related types of cancers called invasive mole and choriocarcinoma.

The most common symptom of a molar pregnancy is abnormal vaginal bleeding in the first three months of pregnancy. Other symptoms may include severe nausea and vomiting, rapid uterine growth, high blood pressure, cysts (fluid-filled sacs) on the ovaries, and hyperthyroidism.

Health care providers use an ultrasound to diagnose a molar pregnancy. The provider also measures the levels of the hormone hCG in the mother’s blood, which often are higher than normal with a molar pregnancy.

A molar pregnancy is a frightening experience. Not only does the woman lose a pregnancy, she learns that she has a slight risk of developing cancer. To protect her, all molar tissue must be removed from the uterus. This usually is done with a D&C. Occasionally, when the mole is extensive and the woman has decided against future pregnancies, she may have a hysterectomy.

After mole removal, her provider again measures the level of hCG. If it has dropped to zero, the woman generally needs no additional treatment. However, the provider will continue to monitor hCG levels for 6 months to 1 year to be sure there is no remaining molar tissue. It’s important that a woman not become pregnant during this time, because a pregnancy would make it difficult to monitor hCG levels.

After the uterus is emptied, about 20 percent of complete moles and less than 5 percent of partial moles continue on. The remaining abnormal tissue may continue to grow in the wall of the uterus. This is called persistent gestational trophoblastic disease (GTD) or invasive mole. The diagnosis is made when hCG blood levels stop decreasing or begin to increase. Treatment with one or more cancer drugs cures persistent GTD nearly 100 percent of the time. Rarely, a cancerous form of GTD, called choriocarcinoma, develops and spreads to other organs. Use of multiple cancer drugs is usually very successful at treating this cancer.

All of this may sound scary, but the good news is that a woman who has had molar pregnancy usually can go on to have healthy pregnancies. The risk that a mole will develop in a future pregnancy is only about 1 to 2 percent.