|
|
![]() |
 |
Trisomy 21 By Roxanne Jackson
|
|
Abstract
Abstract
Down’s syndrome is a genetic disorder that includes a combination of birth defects including some degree of mental retardation, characteristic facial features, and often heart defects, along with visual and hearing impairments. The severity of all “Down’s syndrome” problems can vary.
|
 |
Keywords
Keywords
Downs Syndrome, Trisomy 21, Dr. Langdon Down, Nuchal Transluency,Sandal Gap,
|
Introduction
Introduction
Down’s syndrome occurs in about one out of 800 live births.4 So far the exact cause of Down’s syndrome has eluded discovery. Advanced maternal age is associated with a high incidence of Trisomy 21 but even women of typical child bearing age can have affected babies. The purpose of this paper will explain what Down’s syndrome is, the causes, what to look for to help in diagnosis, and what tests and treatments are used. Then conclusion will answer how Down’s syndrome affects babies and what to look for during ultrasound for early detection.
|
 |
Body
Body
The name Down’s syndrome comes from the physician, Dr. Langdon Down. In 1866, he was the first to describe the physical features and medical problems in regards to the disorder. It would not be until 1959, that the cause of Down’s syndrome would be linked to the presence of an extra chromosome. People with Down’s syndrome have three copies of chromosome number 21. Down’s syndrome is also referred to as Trisomy 21. The term Trisomy is used to describe the presence of three chromosomes rather than the normal pair of chromosomes.
Down’s syndrome, a chromosomal disorder is the most frequent cause of mild to moderate mental retardation in the U.S.3 The extra chromosome comes from the mother’s egg about 90% of the time. It has been known for some time that the risk factor related to the likelihood of a Down’s baby increase with the advancing age of the mother.
The cause can come from either mother or father. There is no way of predicting whether a person is more or less likely to make an egg or sperm with 24 chromosomes. Therefore, an error occurs when the 46 chromosomes are being divided in half during cell division called non-disjunction. An egg or sperm cell keeps both copies of the chromosome number 21 instead of just one copy. If this egg or sperm is fertilized, the baby ends up with three copies of the number 21 chromosome. However, two other types of chromosomal abnormalities, mosaicism and translocation, are also implicated in Down’s syndrome although to a lesser extent. Regardless of the type of Down’s which a person may have, all people with Down’s have an extra, critical portion of the number 21 chromosome present in all or some of their cells. This additional genetic material alters the development and causes the characteristics associated with the syndrome.
Down’s syndrome is usually suspected after birth as a result of the baby’s appearance. There are many physical characteristics which form the basis for suspecting an infant has Down’s syndrome. Many of these characteristics are found to some extent in the general population of individuals who do not have Down syndrome. Hence, if Down’s syndrome is suspected, careful evaluation is required to confirm the diagnosis. Some infants with Down’s syndrome have only a few of these traits, while others have many.
|
 |
The name Down’s syndrome comes from the physician, Dr. Langdon Down. In 1866, he was the first to describe the physical features and medical problems in regards to the disorder. It would not be until 1959, that the cause of Down’s syndrome would be linked to the presence of an extra chromosome. People with Down’s syndrome have three copies of chromosome number 21. Down’s syndrome is also referred to as Trisomy 21. The term Trisomy is used to describe the presence of three chromosomes rather than the normal pair of chromosomes.
Down’s syndrome, a chromosomal disorder is the most frequent cause of mild to moderate mental retardation in the U.S.3 The extra chromosome comes from the mother’s egg about 90% of the time. It has been known for some time that the risk factor related to the likelihood of a Down’s baby increase with the advancing age of the mother.
The cause can come from either mother or father. There is no way of predicting whether a person is more or less likely to make an egg or sperm with 24 chromosomes. Therefore, an error occurs when the 46 chromosomes are being divided in half during cell division called non-disjunction. An egg or sperm cell keeps both copies of the chromosome number 21 instead of just one copy. If this egg or sperm is fertilized, the baby ends up with three copies of the number 21 chromosome. However, two other types of chromosomal abnormalities, mosaicism and translocation, are also implicated in Down’s syndrome although to a lesser extent. Regardless of the type of Down’s which a person may have, all people with Down’s have an extra, critical portion of the number 21 chromosome present in all or some of their cells. This additional genetic material alters the development and causes the characteristics associated with the syndrome.
Down’s syndrome is usually suspected after birth as a result of the baby’s appearance. There are many physical characteristics which form the basis for suspecting an infant has Down’s syndrome. Many of these characteristics are found to some extent in the general population of individuals who do not have Down syndrome. Hence, if Down’s syndrome is suspected, careful evaluation is required to confirm the diagnosis. Some infants with Down’s syndrome have only a few of these traits, while others have many.
|
 |
There is no medical treatment for Down’s syndrome. However, specialized care and assistance is helpful in assisting the individual.
A child with Down’s syndrome may have eyes that slant upward and/or small ears that fold over at the top a little. Their mouth may be small making their tongues appear big. The nose might also be small, with a flattened nasal bridge. Some babies with Down’s syndrome have short necks and small hands with short fingers. Children with Down’s generally have one single crease that goes straight across the palm and a second that curves down the thumb, rather than having three creases in the palm of the hand. A child or adult with Downs’s syndrome is often short and has unusual looseness of the joints. These are not all absolute with every case of Down’s syndrome; however, most will have some of these traits. All of these problems peril in comparison to the problems that affect a Down’s child internally.
|
 |
Babies can be born with signs and symptoms of congestive heart failure such as a fast respiratory rate, labored breathing, difficulty completing feedings, sweating with feedings and poor weight gain. Children with partial AV canals can be asymptomatic because the extra blood flow to the lungs is not enough to cause symptoms of congestive heart failure. In addition to the heart defects associated with Down’s syndrome, isolated elevated blood pressure in the lungs is seen with higher frequency in patients with Down’s syndrome. This high pressure may be related to malformation of the lung tissue, although the exact cause is not known. The higher pressures may limit the amount of blood flow to the lungs and therefore decrease the likelihood of symptoms of congestive heart failure seen in babies with complete AV canals or large ventricular septal defects. Other complex congenital heart diseases including Tetralogy of Fallot, atrial septal defects, patent ductus arteriosus and hypoplastic left heart syndrome comprise the rest of the heart disease in Trisomy 21.
|
 |
Conclusion
Conclusion
A baby with Down’s syndrome will grow and develop like other babies. He or she will be able to do all of the things that the normal child can do, only at a somewhat slower pace. Compared with typical children, an individual with Down’s syndrome is smaller and their development is somewhat slower. For example, they may experience a delay in their speech and language development. A few children with Down’s syndrome will not be mentally retarded but border line, in the average intellectual range. Most typically, mental retardation function is mild to moderate.
Down’s syndrome can affect any women regardless of age, family history, or health1 Down’s syndrome is usually caused by an error in cell division called nondisjunction. It is not known why this occurs. However, it is known that the error occurs at conception and is not related to anything the mother did during pregnancy. It has been known for some time that the incidence of Down’s syndrome increases with advancing age.
It is undeniable that certain physical features of fetuses with Down’s syndrome can be identified sonographically. A few of these features represent actual structural abnormalities that have clinical consequences regardless of karyotype.3
The diagnosis must be confirmed by a chromosome study (karyotype). A karyotype provides a visual display of the chromosomes grouped by their size, number and shape. Chromosome may be studied by examining blood or tissue cells.
|
Bibliography
1. Cioffi-Ragan, Darleen: Comparison of Conventional Transabdominal and Transvaginal Ultrasound and 3D Transvaginal Ultrasound in the Evaluation of First-Trimester Nuchal Translucency. JDMS 2002; 18:189-192.
2. Bromley, Bryann MD, Lieberman, Ellice MD,DrPH, Shipp, Thomas MD, Benacerraf, Beryl MD: Fetal Nose Boone Length. J Ultrasound Med 2002; 21: 1387-1394.
3. Bromley, Bryann MD, Lieberman, Ellice MD,DrPH, Shipp, Thomas MD, Benacerraf, Beryl MD: The Gentic Sonogram. J Ultrasound Med 2002; 21: 1087-1096.
4. Nelson, David, Gibbs, Richard: The critical region in trisomy 21. Sciencemag.org 2004; vol. 306: Oct 22, 2004.
5. Hagan- Ansert, Sandra; Textbook of Diagnostic Ultrasonography, Fifth edidition: 2001, vol.2 Trisomy 21.
|
|
|
Copyright CVTC 2003. All Rights Reserved.