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Why should we be concerned about Down syndrome?
Chromosomal abnormalities are a widespread medical problem, with Down syndrome being the most common genetic condition. One in every 800 to 1,000 children is born with Down syndrome.
More than 50 percent of miscarriages are caused by a chromosomal abnormality. As many as 25 percent of all miscarriages are caused by a "trisomy", which is the presence of three copies of a particular chromosome, rather than the normal two. The most common form of Down syndrome is also known as Trisomy 21, because it involves an extra copy of the 21st chromosome. About 25 percent of children conceived with Down syndrome survive past birth. Individuals with Down syndrome possess varying degrees of mental retardation, from very mild to severe. Back to Table of Contents What impact does Down syndrome have on society?
Individuals with Down syndrome are becoming increasingly integrated into society and community organizations, such as school, health care systems, work forces, and social and recreational activities. Due to advances in medical technology, individuals with Down syndrome are living longer than ever before. In 1910, children with Down syndrome were expected to survive to age 9. With the discovery of antibiotics, the average survival age increased to 19 or 20. Now, with recent advancements in clinical treatment, as many as 80 percent of adults with Down syndrome reach age 55, and many live even longer.
In the United States, approximately 350,000 families are affected by Down syndrome. Approximately 5,000 children with Down syndrome are born each year. As the mortality rate associated with Down syndrome is decreasing, the prevalence of individuals with Down syndrome in our society will increase. Some experts project that the number of people with Down syndrome will double in the next 10 years. More and more Americans will interact with individuals with this genetic condition, increasing the need for widespread public education and acceptance. Back to Table of Contents Is Down syndrome hereditary?
The additional genetic material which causes Down syndrome can originate from either the father or the mother. Approximately 5 percent of the cases have been traced to the father. In general, the chance of having a second child with Down syndrome is about one in 100. The chance is greater if one parent carries a translocated cell, which can be determined through genetic testing. Down syndrome does not otherwise "run in families" and a sibling, aunt or uncle is at no greater risk of conceiving a child with Down syndrome. Back to Table of Contents Who is at risk of having a child with Down syndrome?
Down syndrome affects people of all races and economic levels. Women age 35 and older have a significantly increased risk of having a child with Down syndrome. A 35-year-old woman has a one in 350 chance of conceiving a child with Down syndrome, and this chance increases gradually to one in 100 by age 40. At age 45 the incidence becomes approximately one in 30. However, because younger women in general give birth more frequently, most babies with Down syndrome are born to younger mothers. Genetic counseling for parents is becoming increasingly important. Still, many physicians are not fully informed about advising their patients about the of incidence of Down syndrome, advancements in diagnosis, and the protocols for care and treatment of babies born with Down syndrome. Back to Table of Contents Why is it important to raise children with Down syndrome at home?
A greater understanding of Down syndrome and advancements in treatment of Down syndrome-related health problems have allowed people with Down syndrome to enjoy fuller and more active lives. Children raised at home and included in all aspects of community life can best reach their potential and function in society with a greater degree of independence. Parental love, nurturing, and support, as well as early intervention programs, educational opportunities, and community involvement, have a direct relationship to the degree that a person with Down syndrome is able to achieve his/her potential. Back to Table of Contents When was Down syndrome discovered?
For centuries, people with Down syndrome have been alluded to in art, literature and science. It wasn't until the late 19th century, however, that John Langdon Down, an English physician, published an accurate description of a person with Down syndrome. It was this scholarly work, published in 1866, which earned Down the recognition as the "father" of the syndrome. Although other people had previously recognized the characteristics of the syndrome, it was Down who described the condition as a distinct and separate entity.
Throughout the 20th century, advances in medicine and science enabled researchers to investigate the characteristics of people with Down syndrome. In 1959, the French physician, Jerome Lejeune, identified Down syndrome as a chromosomal anomaly. Instead of the usual 46 chromosomes present in each cell, Lejeune observed 47 in the cells of individuals with Down syndrome. It was later determined that an extra partial or complete 21st chromosome results in the characteristics associated with Down syndrome. Back to Table of Contents Why is Down syndrome referred to as a "genetic condition?"
The human body is made of cells; all cells contain a center, called a nucleus, in which genetic material is stored. This genetic material, known as genes, carries the codes responsible for all our inherited characteristics. Genes 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.
In Down syndrome, however, the cells usually contain not 46, but 47 chromosomes; with the extra chromosome being a number 21. This excess genetic material, in the form of additional genes along the 21st chromosome, results in Down syndrome. Because 95 percent of all cases of Down syndrome occur because there are three copies of the 21st chromosome, it is often referred to as "trisomy 21."
Chromosomes may be studied by examining blood or tissue cells. Individual chromosomes are identified, stained and numbered from largest to smallest. The visual display of the chromosomes is known as a karyotype. Back to Table of Contents What causes Down Syndrome?
Down syndrome is usually caused by an error in cell division called non-disjunction. However, two other types of chromosomal abnormalities, mosaicism and translocation, are also implicated in Down syndrome - although to a much lesser extent. Regardless of the type of Down syndrome which a person may have, all people with Down syndrome have an extra, critical portion of the number 21 chromosome present in all, or some, of their cells. This additional genetic material alters the course of development and causes the characteristics associated with the syndrome.
Nondisjunction is a faulty cell division which results in an embryo with three number 21 chromosomes instead of two. Prior to, or at, conception, a pair of number 21 chromosomes, in either the sperm or the egg, fail to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body. This faulty cell division is responsible for 95 percent of all cases of Down syndrome.
Why nondisjunction occurs is currently unknown, although it does seem to be related to advancing maternal age. Many people are surprised to find out that 80 percent of children born with Down syndrome are born to women under 35 years of age. This is because younger women have higher fertility rates. It does not contradict the fact that the incidence of births of children with Down syndrome increases with the age of the mother.
Although nondisjunction can be of paternal origin, this occurs less frequently. Because this error in cell division is often present in the egg prior to conception, and women are born with their complete store of eggs, it has been postulated that some environmental factors may be implicated in nondisjunction. However, despite years of research, the cause (or causes) of nondisjunction, is still unknown. There seems to be no connection between any type of Down syndrome and parents' activities, before or during pregnancy.
Mosaicism occurs when nondisjunction of the 21st chromosome takes place in one of the initial cell divisions after fertilization. When this occurs, there is a mixture of two types of cells, some containing 46 chromosomes and some containing 47. Those cells with 47 chromosomes contain an extra 21st chromosome. Because of the "mosaic" pattern of the cells, the term mosaicism is used. Mosaicism is rare, being responsible for only 1 to 2 percent of all cases of Down syndrome.
Some research has shown that individuals with mosaic Down syndrome are less affected than those with trisomy 21; however, broad generalizations are not possible due to the wide range of abilities that people with Down syndrome possess.
Translocation is a different type of chromosomal problem and occurs in only 3 to 4 percent of people with Down syndrome. Translocation occurs when part of the number 21 chromosome breaks off during cell division and attaches to another chromosome. While the total number of chromosomes in the cells remains 46, the presence of an extra part of the number 21 chromosome causes the features of Down syndrome. As with nondisjunction trisomy 21, translocation occurs either prior to or at conception.
Unlike nondisjunction, maternal age is not linked to the risk of translocation. Most cases are sporadic, chance events. However, in about one-third of cases, one parent is a carrier of a translocated chromosome. For this reason, the risk of recurrence for translocation is higher than that of nondisjunction. Genetic counseling can be sought to determine the origin of the translocation. Back to Table of Contents What is the chance of having a second child with Down syndrome?
In general, it is estimated that the risk of having a second child with trisomy 21 or mosaic Down syndrome is about 1 in 100. The risk is higher if one parent is a carrier of a translocated cell. Back to Table of Contents Are any prenatal tests available to detect Down syndrome?
Yes. There are two types of procedures available to pregnant women: screening tests and diagnostic tests. Screening tests estimate the risk of the fetus having Down syndrome; diagnostic tests tell whether or not the fetus actually has the condition.
The most commonly used screening tests are the Triple Screen and the Alpha-fetoprotein Plus. These tests measure quantities of various substances in the blood (alpha-fetoprotein, human chorionic gonadotropin and unconjugated estriol) and together with the woman's age, estimate her risk of having a child with Down syndrome. These screening tests are typically offered between fifteen and twenty weeks of gestation.
Screening tests are of limited value and are often performed in conjunction with a detailed sonogram. These tests are only able to accurately detect about sixty percent of fetuses with Down syndrome. Many women who undergo these tests will be given false-positive readings, and some women will be given false-negative readings.
The procedures available for prenatal diagnosis of Down syndrome are chorionic villus sampling (CVS), amniocentesis and percutaneous umbilical blood sampling (PUBS). Each one of these procedures carries a small risk of miscarriage as tissue is extracted from the placenta or the umbilical cord to examine the fetus's chromosomes. The procedures are about 98 to 99 percent accurate in the detection of Down syndrome. Amniocentesis is usually performed between 12 and 20 weeks of gestation, CVS between 8 and 12 weeks and PUBS after 20 weeks. Back to Table of Contents How is Down syndrome diagnosed in the newborn?
The diagnosis of Down syndrome is usually suspected after birth as a result of the baby's appearance. It is a particularly difficult time, coupled with the natural stresses of childbirth. Although there is no easy way to be informed, most families agree that having the baby present, being together, and being told as soon as possible is the best way to proceed.
There are many physical characteristics which form the basis for suspecting an infant has Down 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 syndrome is suspected, a karyotype will be performed to ascertain the diagnosis. Some infants with Down syndrome have only a few of these traits, while others have many. Among the most common traits are:
- Muscle hypotonia, low muscle tone
- Flat facial profile, a somewhat depressed nasal bridge and a small nose
- Oblique palpebral fissures, an upward slant to the eyes
- Dysplastic ear, an abnormal shape of the ear
- Simian crease, a single deep crease across the center of the palm
- Hyperflexibility, an excessive ability to extend the joints
- Dysplastic middle phalanx of the fifth finger, fifth finger has one flexion furrow instead of two
- Epicanthal folds, small skin folds on the inner corner of the eyes
- Excessive space between large and second toe
- Enlargement of tongue in relationship to size of mouth
Back to Table of Contents Do babies with Down syndrome have medical problems?
Children with Down syndrome are at increased risk for certain health problems. Congenital heart defects, increased susceptibility to infection, respiratory problems, obstructed digestive tracts and childhood leukemia occur with greater frequency among children who have Down syndrome. However, advances in medicine have rendered most of these health problems treatable, and the majority of people born with Down syndrome today have a life expectancy of approximately fifty-five years.
Adults with Down syndrome are at increased risk for Alzheimer's disease. Whereas approximately 60f the general population will develop the disease, the figure is about 25 0.000000or people with Down syndrome. Many individuals with Down syndrome have the changes in the brain associated with Alzheimer's, but do not necessarily develop the clinical disorder. Back to Table of Contents How does Down syndrome affect a person's development?
All people with Down syndrome have some level of mental retardation; however, the level usually falls into the mild to moderate range and is not indicative of the many strengths and talents that each individual possesses. Children with Down syndrome learn to sit, walk, talk, play, toilet train and do most other activities - only somewhat later than their peers without Down syndrome. Because speech is often delayed, careful attention should be paid to the child's hearing, as retention of fluid in the inner ear is a very common cause of hearing and speech difficulties.
Early intervention services, which begin shortly after birth, help children with Down syndrome develop to their full potential. Quality educational programs, along with a stimulating home environment and good medical care enable people with Down syndrome to become contributing members of their families and communities.
People with Down syndrome are highly responsive to their physical and social environment. Those who receive good medical care and are included in the activities of the community can be expected to adapt successfully - to attend school, make friends, find work, participate in decisions which affect them and make a positive contribution to society.
The person with Down syndrome has the same emotions and needs as any other person and deserves the same opportunities. Back to Table of Contents What does the future hold for people with Down syndrome?
People with Down syndrome are people first. They may have some of the characteristics generally associated with this condition, but they are overwhelmingly unique and must be treated as individuals. Over the past few decades, beginning with Section 504 of The Rehabilitation Act of 1973, continuing with The Education for All Handicapped Children Act of 1975, and culminating with the passage of the Americans with Disabilities Act in 1991, people with Down syndrome have been granted equal protections under federal law.
Ensuring equal treatment and access to services is a struggle that every family of a child with Down syndrome faces. Daily, these individuals strive to accomplish the same goals as everyone else: self-fulfillment, pride in one's achievements, inclusion in the activities of the community and the challenge of reaching one's full potential.
Daily, people with Down syndrome venture out into the community: to schools, jobs and leisure activities. Some live with family, some with friends and some independently. They form ongoing interpersonal relationships and some may marry. Women with Down syndrome are fertile and can have children.
The opportunities available to people with Down syndrome today have never been greater. However, it is only through the collective efforts of parents, professionals and concerned citizens that acceptance is becoming widespread. It is the goal 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 community life. | (c) Copyright 1997, National Down Syndrome Society. All rights reserved. Back to NDSS Welcome Page Back to Top
Last updated October 14, 1997
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