A chromosomal dysgenesis syndrome consisting of a variable constellation of abnormalities caused by triplication or translocation of chromosome 21. The abnormalities include mental retardation, retarded growth, flat hypoplastic face with short nose, prominent epicanthic skin folds, small low-set ears with prominent antihelix, fissured and thickened tongue, laxness of joint ligaments, pelvic dysplasia, broad hands and feet, stubby fingers, and transverse palmar crease. Lenticular opacities and heart disease are common. The incidence of leukemia is increased and Alzheimer disease is almost inevitable by age 40. Syn: trisomy 21 syndrome.
The human body is made of cells. All cells contain a center, called a nucleus, in which genes are stored. Genes, which carry the codes responsible for all our inherited characteristics, are grouped along rod-like structures called chromosomes. Normally, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when some or all of a person's cells have an extra full or partial copy of chromosome 21.
Chromosomes are structures that carry genetic information in cells. They carry the instructions that tell cells what functions they are to perform. They determine the way a person's body looks and the way it functions.
Cells normally carry two matched sets of twenty-three chromosomes for a total of forty-six chromosomes. One set of twenty-three chromosomes comes from each parent. Down's syndrome occurs when one chromosome pair is damaged. That pair is designated as chromosome #21.
Chromosome #21 can be damaged, for example, if one parent has two chromosomes at location 21, rather than one. A child will then get two #21 chromosomes from one parent and one #21 chromosome from the other parent, for a total of three #21 chromosomes. This form of Down's syndrome is called trisomy 21, meaning that the #21 chromosome has three units rather than two. Overall, the child has forty-seven chromosomes, rather than forty-six chromosomes. This pattern of changes occurs in more than 90 percent of all Down's patients.
Chromosome #21 can also be damaged during cell replication. Cells grow and reproduce over time. As they do so, they make copies of the original chromosomes from the parents. Sometimes, the chromosomes from the parents are normal but a problem occurs when the new cells are reproducing. Two normal chromosomes at location 21 become three chromosomes in some cells.
This condition is known as a mosaic disorder. People with this disorder have some cells containing forty-six chromosomes, and some containing forty-seven chromosomes. They may have less severe symptoms than a person whose cells all contain forty-seven chromosomes. A mosaic condition occurs rarely. Less than 2 percent of all Down's cases are caused by mosaic disorder.
Chromosome #21 can also be damaged when a normal chromosome from the parent breaks into two pieces. One piece of the chromosome becomes attached to another chromosome. This process is called translocation. Translocation occurs in about 3 to 4 percent of all Down's patients.
Down's syndrome occurs in about 1 out of every 800 to 1000 births. It affects an equal number of females and males. The most common cause of Down's syndrome is an extra #21 chromosome in the mother's egg. As a woman grows older, she faces a greater risk of having a baby with Down's syndrome. For example, a woman in her twenties faces a risk of about 1 in 4,000. By the age of thirty-five, that risk has increased to 1 in 400 and, by the age of forty-five, to 1 in 35.
The opportunities currently available to individuals with Down syndrome have never been greater. However, it is only through the collective efforts of parents, professionals, and concerned citizens that acceptance is becoming even more widespread. It is the mission of the National Down Syndrome Society to ensure that all people with Down syndrome are provided the opportunity to achieve their full potential in all aspects of their lives.
Even though people with Down syndrome may have some physical and mental features in common, symptoms of Down syndrome can range from mild to severe. Usually, mental development and physical development are slower in people with Down syndrome than in those without the condition.
Mental retardation is a disability that causes limits on intellectual abilities and adaptive behaviors (conceptual, social, and practical skills people use to function in everyday lives). Most people with Down syndrome have IQs that fall in the mild to moderate range of mental retardation. They may have delayed language development and slow motor development.
Some common physical signs of Down syndrome include:
Decreased muscle tone at birth.
- Excessive skin at the nape of the neck.
- Flattened nose.
- Separated sutures (joints between the bones of the skull).
- Single crease in the palm of the hand.
- Small ears.
- Small mouth.
- Upward slanting eyes.
- Wide, short hands with short fingers.
- White spots on the colored part of the eye (Brushfield spots).
There are a variety of other health conditions that are often seen in people who have Down syndrome, including:
Congenital heart disease.
Causes and Risk factors:
- Hearing problems.
- Intestinal problems, such as blocked small bowel or esophagus.
- Celiac disease.
- Eye problems, such as cataracts.
- Thyroid dysfunctions.
- Skeletal problems.
- Dementia—similar to Alzheimer's.
Most of the time, the occurrence of Down syndrome is due to a random event that occurred during formation of the reproductive cells, the ovum or sperm. As far as we know, Down syndrome is not attributable to any behavioral activity of the parents or environmental factors. The probability that another child with Down syndrome will be born in a subsequent pregnancy is about 1 percent, regardless of maternal age.
For parents of a child with Down syndrome due to translocation trisomy 21, there may be an increased likelihood of Down syndrome in future pregnancies. This is because one of the two parents may be a balanced carrier of the translocation. The translocation occurs when a piece of chromosome 21 becomes attached to another chromosome, often number 14, during cell division. If the resulting sperm or ovum receives a chromosome 14 (or another chromosome), with a piece of chromosome 21 attached and retains the chromosome 21 that lost a section due to translocation, then the reproductive cells contain the normal or balanced amount of chromosome 21. While there will be no Down syndrome associated characteristics exhibited, the individual who develops from this fertilized egg will be a carrier of Down syndrome. Genetic counseling can be sought to find the origin of the translocation.
However, it is important to realize that not all parents of individuals with translocation trisomy 21 are themselves balanced carriers. In such situations, there is no increased risk for Down syndrome in future pregnancies.
Researchers have extensively studied the defects in chromosome 21 that cause Down syndrome. In 88% of cases, the extra copy of chromosome 21 is derived from the mother. In 8% of the cases, the father provided the extra copy of chromosome 21. In the remaining 2% of the cases, Down syndrome is due to mitotic errors, an error in cell division which occurs after fertilization when the sperm and ovum are joined.
Researchers have established that the likelihood that a reproductive cell will contain an extra copy of chromosome 21 increases dramatically as a woman ages. Therefore, an older mother is more likely than a younger mother to have a baby with Down syndrome. However, of the total population, older mothers have fewer babies; about 75% of babies with Down syndrome are born to younger women because more younger women than older women have babies. Only about nine percent of total pregnancies occur in women 35 years or older each year, but about 25% of babies with Down syndrome are born to women in this age group.
The incidence of Down syndrome rises with increasing maternal age. Many specialists recommend that women who become pregnant at age 35 or older undergo prenatal testing for Down syndrome. The likelihood that a woman under 30 who becomes pregnant will have a baby with Down syndrome is less than 1 in 1,000, but the chance of having a baby with Down syndrome increases to 1 in 400 for women who become pregnant at age 35. The likelihood of Down syndrome continues to increase as a woman ages, so that by age 42, the chance is 1 in 60 that a pregnant woman will have a baby with Down syndrome, and by age 49, the chance is 1 in 12. But using maternal age alone will not detect over 75% of pregnancies that will result in Down syndrome.
The age of the mother is an important consideration in assessing Down syndrome risk. As a woman gets older, her eggs are more likely to divide abnormally. At age 25, the risk for Down syndrome is 1 in 1,250 births. This risk increases to 1 in 385 at age 35 and jumps to 1 in 30 at age 45. However, 80% of babies with Down syndrome are born to mothers who are younger than age 35. The reason for this is that women under the age of 35 have a higher rate of giving birth.
Women who have a child with Down syndrome are more likely to have another baby affected with the condition. Also, mothers who have Down syndrome themselves are 50% more likely to give birth to a child with Down syndrome.
Parents can pass down a chromosomal abnormality called balanced translocation, which contributes to Translocation Down syndrome. In this instance, the parent does not have signs of Down syndrome, but has genetic material "balanced" between chromosome 21 and another chromosome, posing an increased risk for the child if that material attaches to the other chromosome when the cell divides. Not all cases of Translocation Down syndrome occur this way, however.
A Down syndrome diagnosis can be made during prenatal testing. A diagnosis can also be made shortly after birth. In this case, the doctor may suspect that a baby has Down syndrome based on the presence of possible characteristics of the condition. A Down syndrome diagnosis is confirmed with a special blood test.
Prenatal screening for Down syndrome is available. This blood test goes by several names, including:
Multiple marker screening test.
- Maternal blood screening test.
- Triple screen.
- Quad screen.
Tests used to make a Down syndrome diagnosis include:
- Chorionic villus sampling (CVS).
- Percutaneous umbilical blood sampling (PUBS).
In amniocentesis, a sample of the fluid surrounding the fetus is withdrawn. Fetal cells in the fluid are then examined for chromosomal abnormalities.
- CVS is similar to amniocentesis, except that the procedure is done in the first trimester, and the fetal cells needed for examination are taken from the placenta. Neither procedure is used routinely, except when there is a family history of genetic defects, the pregnant woman is older than 35, or other medical indications are present.
- Percutaneous umbilical blood sampling is the most accurate method used to confirm the results of CVS or amniocentesis. In PUBS, the tissue is tested for the presence of extra material from chromosome 21. PUBS cannot be done until a woman is 18 to 22 weeks pregnant.
To confirm the Down syndrome diagnosis, the doctor may request a blood test called a chromosomal karyotype, which looks at a person's chromosomes. The karyotype of a person with Down syndrome will have an extra chromosome 21.
Initial treatment: It is normal to experience a wide range of emotions when your baby is born with Down syndrome. Even if you learned about your baby's condition while you were pregnant, the first few weeks after birth often are very difficult as you learn to cope with the diagnosis.
A confirmed diagnosis of Down syndrome requires a karyotype test. This test usually is done on a sample of your baby's blood if it is done after birth. It may take 2 to 3 weeks to get the complete results of this test. This waiting period can be extremely difficult, especially if earlier test results were uncertain and your baby has only subtle characteristics of Down syndrome.
Your newborn with Down syndrome will have regular checkups and various tests during the first month. These tests are used to monitor his or her condition and to help health professionals look for early signs of common diseases associated with Down syndrome and other health conditions. These checkups also are a good time to begin discussing issues of concern about your newborn.
Ongoing treatment: Making sure that your child has regular medical checkups, helping to manage his or her adjustments to social and physical changes, and promoting independence are important parts of ongoing treatment for Down syndrome.
Physical exams allow your health professional to watch your child for early signs of common diseases associated with Down syndrome and other health conditions. Health professionals look for specific problems at various ages, such as cataracts and other eye conditions during a baby's first year.
Treatment to teach independence and self-sufficiency is influenced by your child's intelligence level and physical abilities. Although it may take extra time for your child to learn and master skills, you may be surprised at how much he or she will be able to do.
Often different types of therapy, such as speech therapy, can help children with Down syndrome learn necessary skills. These therapies are used throughout life, even during adulthood. The specifics change as your child grows and develops.
When helping your child with Down syndrome achieve independence, it is also important to be aware of his or her vulnerabilities and potential social problems. Although your child can overcome many challenges, he or she will always need support and guidance.
Treatment if the condition gets worse: Children with Down syndrome often are born with or have an increased risk for developing:
Diseases, such as heart disease.
- Health conditions, such as frequent respiratory infections.
Treatment is specific to the type of disease or health condition that develops. For example, medicines may be used to treat symptoms related to heart disease. Surgery sometimes may be needed to correct problems such as cataracts or bowel obstruction.
As a parent of a child with Down syndrome, you play an important role in helping your child reach his or her full potential. Most families choose to raise their child, while some consider foster care or adoption. Support groups and organizations can assist you in making the best decision for your family.
Having a child with Down syndrome is full of challenges and accomplishments. Common frustrations and frequent highs and lows can all lead to exhaustion. Take good care of yourself so you have the energy to enjoy your child and attend to his or her needs.
Medicine and medications:
Medicines are not used to treat Down syndrome. But medicines are used to treat other diseases associated with Down syndrome and other health conditions that may develop, such as antibiotics for ear infections and thyroid hormones for an underactive thyroid gland.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.