About 1 in every 200 babies is born with a chromosomal abnormality. The syndrome, which causes a baby is born with an extra chromosome 21, is one of the most common chromosomal abnormalities whose effects are known by most people.
Children affected with this syndrome have varying degrees of intellectual disabilities, characteristic facial features and, often, heart defects and other problems.
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Apart from Down syndrome, there are many other chromosomal anomalies. Some are less severe but others are more serious and can even cause the death of the baby before birth.
Many of the children who have chromosomal abnormalities, but not all, are characterized by mental retardation, learning disabilities or behavioral problems.
A deeper understanding of the chromosomes can be useful to understand the range of problems that can cause chromosomal abnormalities.
What are Chromosomes?
Chromosomes are tiny filament shaped structures that are present in the body cells. Containing, as it has been estimated between 30.000 to 35.000 pairs of human genes that determine traits like eye color and hair; also they control the growth and development of every part of our physical and biochemical system.
All usually have 23 pairs of chromosomes or 46 in total.
Usually, we inherit one chromosome pair from our mother and one from our father. However, sometimes a baby can be born with a greater or lesser number of chromosomes; with one or more broken chromosomes; or an alteration in structure.
Errors in the number or structure of chromosomes cause a variety of birth defects, which can range from mild to severe.
Causes of Chromosomal Abnormalities
Usually, chromosomal abnormalities result from an error during the development of an egg or sperm cell. The causes of these errors are unknown. However, as far as we know, nothing you do or do either parent before pregnancy or during development can cause chromosomal abnormalities in their child.
- Sperm and egg cells are different from other cells in the body. These reproductive cells have only 23 single chromosomes. When an egg is joined to a cell and begins pregnancy form a fertilized egg with 46 chromosomes. But sometimes something goes wrong before pregnancy begins.
- During cell division, a bug that causes an egg or sperm cell panel with a number of more or less than normal chromosomes.
- When this cell with the wrong number of chromosomes unites with a normal egg or sperm cell, the embryo has a chromosomal abnormality.
- A common type of chromosomal abnormality is Trisomy, which occurs when a person has three copies instead of two, of a specific chromosome.
- Down syndrome is an example of trisomy. Usually, people with Down syndrome have three copies of chromosome 21.
- In most cases, the embryos have a wrong number of chromosomes do not survive. In these cases, the pregnant woman has a spontaneous abortion, often without knowing it.
- Up to 70 percent of spontaneous abortions occur during the first trimester of pregnancy is due to chromosomal abnormalities.
- They can also take place other accidents, usually before pregnancy begins, which could alter the structure of one or more chromosomes.
- Even if a person has the normal number of chromosomes, it may happen that small segments of one or more chromosomes are deleted, duplicated, inverted, alter its normal location or exchanged with a part of another chromosome.
- These structural changes can also cause miscarriage and birth defects.
Common Abnormalities in Chromosomes
Down syndrome is one of the most common chromosomal disorders and affects about one in 800 to 1,000 babies born alive. The risk of this occurring and other trisomies increases with maternal age.
- The risk of a baby being born with Down syndrome is about one in 1,250 women 25 years, one in 1000 for women age 30, one in 400 for women age 35 and one in 100 for women 40 years.
- The outlook for children with Down syndrome is more encouraging than they used to be. Most of them have mental retardation from mild to moderate.
- With early intervention and special education, many of these children learn to read and write and participate in various children’s activities.
- Babies can also be born with extra copies of chromosomes 13 or 18. These trisomies are usually much more severe than Down syndrome, but fortunately less common.
- Babies affected by them are estimated at about one in 5,000.
- Usually, babies with trisomy 13 or 18 have severe mental retardation and many physical birth defects. Unfortunately, most of them die before their first birthday.
One of the 23 pairs of human chromosomes is called “sex chromosomes”. Among the most common chromosomal abnormalities are those that have to do with the absence or presence of additional sex chromosomes (called X and Y).
Normally, women have two X chromosomes and males have one X chromosome and one Y chromosome abnormalities associated with the X and Y chromosomes can affect sexual development and cause infertility, growth abnormalities and, in some cases, behavior problems and learning. However, most affected individuals live a relatively normal life.
Turner syndrome is a sex chromosome abnormality that affects about one in 2,500 girls. Girls with Turner syndrome have only one X chromosome instead of two, which is normal. Usually, they are sterile and do not undergo the normal changes of puberty unless they are treated with sexual hormones.
- Girls affected by this syndrome are short, though treatment with growth hormones and sex can help to increase your height. Some have other health problems, including heart defects type.
- Girls with Turner syndrome have normal intelligence, although some have difficulties with mathematics and spatial concepts.
- About one in 1,000 to 2,000 female has one X chromosome, known as triple X. These girls, who are often high, do not follow a consistent pattern in terms of physical abnormalities, have normal puberty and appear to be fertile.
- Their intelligence is normal, but slightly more common learning disabilities. How are you girls are healthy and have a normal appearance, it is likely that parents only know that has this chromosomal abnormality if they have undergone prenatal testing (amniocentesis or CVS ).
- Klinefelter syndrome is a sex chromosome abnormality that affects about one in every 600-800 children.
- Males with Klinefelter syndrome have two, or sometimes more, X chromosomes along with their Y chromosome (males normally have one X chromosome and one Y chromosome).
Affected children often high with normal intelligence, although common learning disabilities. They generally have more problems with judgment and impulse control than XY males. Adult, produce a lower than normal male hormone known as testosterone amount (and often are treated with this hormone) and are infertile.
Other Common Chromosomal abnormalities
Thanks to new techniques for analyzing chromosomes, it has been possible to identify very small abnormalities that may not be visible even under a high-powered microscope.
As a result of this development, the greater the number of parents who learns that his son has a chromosomal abnormality.
- Some of these rare abnormalities include deletions (missing small segments), microdeletions (the lack of a very small amount of material that may contain a single gene), translocations (where part of one chromosome becomes attached to another), and inversion (when part of a chromosome is detached and reattached in reverse).
- Some of these abnormalities are so rare that, in some cases, have affected only one or a few children. In these cases, it may be impossible to predict what medical health and child development long term.
Some rare disorders are caused by chromosomal changes. For example, a very small deletion on chromosome 15 can cause Prader-Willi syndrome (characterized by mental retardation, extreme obesity, and other problems), while a deletion on chromosome 5 causes Cri du chat syndrome, which It characterized by a very high-pitched cry, like the cat, childhood, mental retardation, and physical abnormalities.
Small deletions of a specific segment of chromosome 22 also cause heart defects, cleft palate and other problems seen in DiGeorge syndrome and the VCFS.
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Do children who have the same chromosomal abnormality alike?
If the chromosomal abnormality that has a child is rare or common, it is important to treat it as an individual. Even people with apparently identical chromosomal abnormalities can be very different.
The way a person is affected depends mainly, though not entirely, the exact genetic material involved.
Each chromosome contains hundreds to thousands of genes and each of these influences on a property or function of the different organism.
- In some cases, new techniques for chromosome analysis to identify exactly where the missing or extra genetic material comes.
- If doctors know what genes may contain a certain segment and what role, sometimes parents can provide a more accurate picture of how the future development of your child.
If parents have already had a baby with a chromosomal abnormality, how likely they are to have another child with the same problem?
Parents who have had a baby with a chromosomal abnormality should consult a genetic counselor.
These health professionals help families understand what is known about the causes of a birth defect and the likelihood that the defect recurring in another pregnancy.
- Fortunately, in most cases, the risk to the parents of a baby born with a chromosomal abnormality is small. For example, parents of a baby with Down syndrome usually have a one percent risk of having another affected baby, plus the additional risk that has the mother’s age.
- However, there are exceptions. For example, a small number of parents whose children have Down syndrome has an alteration in chromosome structure (translocation or inversion) does not affect their own health but can be harmful if it is transmitted to their children.
- In some cases, a genetic counselor may recommend that parents perform blood tests to determine if they have this condition and to determine as accurately as possible what is the risk in the next pregnancy.
Where the families affect these chromosomal abnormalities?
The doctor treating an affected baby be able to discuss specific family medical problems in more detail or refer you to a specialist.
It may also be helpful for parents to contact support groups for families of children affected by the same chromosomal abnormality or the like.
Genetic counselors are a good source of information to get in touch with a group of appropriate support.
- American Academy of Pediatrics. Health Supervision for Children with Turner syndrome. Pediatrics, Volume 96, Number 6, December 1995, pages 1166-1173.
- American College of Obstetricians and Gynecologists. Prenatal diagnosis of fetal chromosomal abnormalities. ACOG Practice Bulletin, volume 27, May 2001.
- Barnes, AM and Carey, JC Common problems of Babies With trisomy 18 or 13. Rochester, NY, Support Organization for Trisomy 18, 13, and Related Disorders, January 11, 2002.
- Linden, MG, et al. Intrauterine diagnosis of sex chromosome aneuploidy. Obstetrics & Gynecology, Volume 87, Number 3, March 1996, pages 468-475.