Downs Syndrome, It Is One Of The Most Frequently Occurring Chromosomal
Down’s Syndrome, it is one of the most frequently occurring chromosomal abnormalities found in humans effecting people of all ages, races and economic levels. It is a chromosomal anomaly in cell development that results in a person being born with forty-seven chromosomes instead of the normal forty-six chromosomes. People with Down syndrome may have mild to severe learning disabilities and physical symptoms, which include a small skull, extra folds of skin under the eyes, and a protruding tongue.
Roughly one out of every one thousand children born making it the most common genetic disorder. Down syndrome affects over 350,000 people, in the United States alone.
Down syndrome has plagued the human race since the beginning of time. For centuries, people with Down syndrome have been depicted in art, literature and science as outcasts and rejects of society. 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 publication 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.
Down syndrome, being a genetic disorder, begins to develop at the cellular level after conception. The human body is made of cells. All of these cells contain a center, called a nucleus, in which genetic code of each human being is stored. This genetic material, known as genes, carries the codes responsible for all our inherited characteristics from the mother and the father.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. 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.
Down syndrome is usually caused by an error in cell division called non-disjunction. However, two other minor types of chromosomal abnormalities, mosaicism and translocation, are also causes of Down syndrome. Regardless of the type of Down syndrome that a person may have, all people with Down syndrome have an extra, critical portion of the number 21chromosome 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.
Non-disjunction is a faulty cell division that 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. What is ironic is 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. What is even more amazing is that it does not contradict the fact that the chance of having a child with Down syndrome increases with the age of the mother. Although nondisjunction can be from the father, this occurs less frequently the case. Because this error in cell division is often present in the egg prior to conception, and women are born with their life supply of eggs, it has been determined that some environmental factors may be the cause of nondisjunction. However, despite years of research, the cause 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, another less significant cause of Down syndrome, 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.
The diagnosis of Down syndrome is usually suspected after birth as a result of the baby’s appearance. There are many physical characteristics that form the basis for suspecting an infant has Down syndrome. Many of these characteristics are found in normal, healthy children who do not have Down syndrome. If the slightest traces of Down syndrome are suspected, a karyotype will be performed to obtain the diagnosis. Some infants with Down syndrome have only a few of these traits, while others have many. Doctors’ look for traits like low muscle tone, flat facial profile, a somewhat depressed nasal bridge, a small nose, an upward slant to the eyes, an abnormal shape of the ear, a single deep crease across the center of the palm, an excessive ability to extend the joints, small skin folds on the inner corner of the eyes, excessive space between large and second toe, and an enlargement of tongue in relationship to size of mouth.
Once a child is diagnosed with Down syndrome he or she is extremely exposed to many health related 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 made it possible for most of these health problems treatable. In 1910, children with Down syndrome were expected to survive to age 9. With the discovery of antibiotics that number increased to 20. Down syndrome patients today have a life expectancy of approximately fifty-five years. Adults with Down syndrome are at increased risk for Alzheimer’s disease. Whereas approximately 6% of the general population will develop the disease, the figure is about 25% for 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.
For a person who has Down syndrome life is extremely different than an average person. One of the biggest misconceptions of a person diagnosed with Down syndrome is that they are severely retarded. Although most people with Down syndrome suffer from some form of mental retardation most people with Down syndrome have IQs that fall in the mild to moderate range of retardation and is not an indicator 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 is 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. This is tremendous progress, since before Down syndrome was understood most children with Down syndrome were institutionalized and excluded from society. 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. This may even include 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.
The future of Down syndrome patients keeps looking brighter and brighter as time goes along because of the developments in science, technology and the increased public awareness of Down syndrome as it has done in the past. 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 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. Research on Down syndrome is making great strides in identifying the genes on chromosome 21 that cause the characteristics of Down syndrome. Scientists now feel strongly that it will be possible to improve, correct, or prevent many of the problems associated with Down syndrome in the future.
