Down syndrome or trisomy 21 (in British its called Down’s syndrome) is a genetic condition resulting from the presence of all or part of an extra 21st chromosome. Down syndrome is characterized by a combination of major and minor abnormalities of body structure and function. Among features present in nearly all cases are impairment of learning and physical growth, and a recognizable facial appearance usually identified at birth. It is named after John Langdon Down, the British doctor who first described it in 1866.
Individuals with Down syndrome have lower than average cognitive ability, normally ranging from mild to moderate retardation. Some individuals may have low intelligence overall, but will generally have some amount of developmental disability, such as a tendency toward concrete thinking or naiveté. There are also a small number of individuals with Down syndrome with severe to profound mental retardation. The incidence of Down syndrome is estimated at 1 per 800 to 1 per 1000 births.
The common physical features of Down’s syndrome also appear in people with a standard set of chromosomes. They include a simian crease (a single crease across one or both palms), almond shaped eyes, shorter limbs, speech impairment, and protruding tongue. Health concerns for individuals with Down syndrome include a higher risk for congenital heart defects, gastro-esophageal reflux disease, recurrent ear infections, obstructive sleep apnea, and thyroid dysfunctions.
Early childhood intervention, screening for common problems, medical treatment where indicated, a conductive family environment, and vocational training can improve the overall development of children with Down syndrome. While some of the genetic limitations of Down syndrome cannot be overcome, education and proper care, initiated at any time, can improve quality of life.
History
Down syndrome is firstly characterized by English physician John Langdon Down as a distinct from of mental retardation in 1862, and in a more widely published report in 1866 entitles “Observation on an ethnic classification of idiots”. Due to John Langdon’s perception that children with Down syndrome shared physical facial similarities with those of Blumenbach’s Mongolian race, Down used terms such as mongolism and Mongolian idiocy. Idiocy was a medical term used at that time to refer to a severe degree of intellectual impairment. Down wrote that mongolism represented “retrogression”, the appearance of Mongoloid traits in the children of allegedly more advanced Caucasian parents.
By the 20th century, Mongolian idiocy had become the most recognizable form of mental retardation. Most people with it were institutionalized. Few of the associated medical problems were treated, and most died in infancy or early adult life. With the rise of the eugenics movement, 22 of the 48 United States and a number of countries began programs of involuntary sterilization of individuals with Down syndrome and comparable degree of disability. The ultimate expression of this type of public policy was the German euthanasia program Aktion T-4 begun in 1940. Court challenges and public revulsion led to discontinuation or repeal of such programs during the decades after World War II.
Until the middle of the 20th century, the cause of Down syndrome remained unknown, although the presence in all races the association with older maternal
Age, and the rarity of recurrence had been noticed. Standard medical texts assumed it was due to combination of inheritable factors which had not been identified. Other theories focused on injuries sustained during birth.
With the discovery of Karyotype techniques in the 1950s it became possible to identify abnormalities of chromosomal number or shape. In 1959, Professor Jerome Lejeune discovered that Down syndrome result from an extra chromosome. The extra chromosome was subsequently labeled as the 21st, and the condition as trisomy 21.
In 1961, a group of nineteen geneticists wrote to the editor of The Lancet suggesting that Mongolian idiocy had misleading can-notations, had become as embarrassing term, and should changed. The lancet supported Down’s syndrome. The World Health Organization (WHO) officially dropped references to mongolism in 1965 after a request by the Mongolian delegate.
In 1975, the United States National Institute of Health convened a conference to standardize the nomenclature of malformations. They recommended eliminating the possessive form: “the possessive use of an eponym should be discontinued, since the author neither had nor owned the disorder. While both the possessive and non-possessive forms are used in the general population, Down syndrome is the accepted term among professionals in the USA, Canada and other countries, While Down syndrome continues to be used in the United Kingdom and other areas.
Characteristics of Down syndrome
Example with Down syndrome may have some or all of the following physical characteristics: oblige eye fissures with small skin folds on the inner corner of the eyes, muscle hypotonia, a flat nasal bridge, a single palmar fold (simian crease), a protruding tongue (due to small oral cavity, poor muscle tone, and an enlarged tongue near the tonsils), a short neck, white spots on the iris known as Brush-field spots, excessive flexibility in joints, congenital heart defects, excessive space between large and second toe, and a single flexion furrow of the fifth finger. Most individuals with Down syndrome have mental retardation n the mild (IQ 50-70) to moderate range (IQ 35-50), with scores for children with Mosaic Down syndrome (explained below) some 10-30 points higher. In addition, individuals with Down syndrome can have serious abnormalities affecting any body system.
Cognitive development
Cognitive development in children with Down syndrome is quite variable. Many can be successful in school, while others struggle. Because of this variability in expression of Down syndrome, it is important to evaluate children individually. The cognitive problems that are found among children with Down syndrome can also be found among typical children. This means that parents can take advantage of general programs that are offered through the schools or other means. Children with Down syndrome have a wide range of abilities. It is not possible at birth to predict their capabilities. The identification of the best methods of teaching each particular child ideally begins soon after birth through early intervention programs.
Language skills show a difference between understanding speech and expressing speech. It is common for children with Down syndrome to need speech therapy to help with expressive language. Fine motor skills are delayed and often lag behind gross motor skills and can interfere with cognitive development. Occupational therapy can address these issues.
In education, mainstreaming of children with Down syndrome is controversial. Mainstreaming is when students of differing abilities are placed in classes with their chronological peers. Children with Down syndrome do not age emotionally/socially and intellectually at the same rates as children with out Down syndrome, so eventually the intellectual and emotional gap between children with as with out Down syndrome widens. Complex thinking as required in sciences but also in history, the arts, and the other subjects is often beyond their abilities, or achieved much later than in most children. Therefore, if they are to benefit from mainstreaming without feeling inferior most of the time, special adjustments must be made to the curriculum.
Some European countries such as Germany and Denmark advise two-teacher system, whereby the second teacher takes over a group of children with disabilities within the class. A popular alternative is cooperation between special education schools and mainstream schools. In cooperation, the core subjects are taught in separate a class, which neither slows down the typical students nor neglects the students with disabilities. Social activities, outgoings, and any sports and arts activities are performed together, as are all breaks and meals.
Health
The medical consequences of the extra material in DS are highly variable and may affect the function of any organ system or bodily process. The health aspects of Down syndrome encompass anticipating and preventing effects of the condition, recognizing complications of the disorder, managing individual symptoms, and assisting the individual and his/her family in coping and thriving with any retarded disability or illness
The most common manifestation of Down syndrome are the characteristics facial features, cognitive impairment, congenital heart disease, hearing deficits, short stature, thyroid disorders, and Alzheimer’s disease. Other less common serious illness includes leukemia, immune deficiencies, and epilepsy. Down syndrome can result from several different genetic mechanisms. This results in a wide variability in individual symptoms due to complex gene and environment interactions. Prior to birth, it is not possible to predict the symptoms that an individual with Down syndrome will develop. Some problems are present at birth, such as certain heart malformations. Others become apparent over time, such as epilepsy.
These factors contribute to a significantly shorter lifespan for people with Down syndrome. One study, carried out in United States, shows an average lifespan of 49 years.
Genetic research
Down syndrome disorders are based on having too many copes of the genes located on chromosome 21. in general, this leads to an over-expression of the genes. Understanding the genes involved may help to target the medical treatment to individuals with Down syndrome. It is estimated that chromosome 21 contains 200 to 250 genes. Recent search has identified a region of the chromosome that contains the main genes responsible for the pathogenesis of Down syndrome, located proximal to 21q22.3. The search for major genes involved in Down syndrome characteristics is normally in the region 21q21-21q22.3
Recent use of transgenic mice to study specific genes in the Down syndrome critical region is had yielded some result. APP (Mendelian Inheritance in Man (OOIM) 104760, located at 21q21) is an Amyloid beta A4 precursor protein.
It is suspected to have a major role in cognitive difficulties. Another gene, ETS2 (Mendelian Inheritance in Man (OMIM 164740, located at 21q22.3) is Avian
Erythroblastsis Virus E26 Oncogene Homolog 2. Researchers have “demonstrated that over-expression of ETS2 result in apoptosis. Transgenic mice over-expressing ETS2 developed a smaller thymus and lymphocyte abnormalities, similar to features observed in Down syndrome.
Sociological and Cultural aspects
Advocates for people with Down syndrome points to various factors, such as special education and parental supports groups which make life easier for parents.
There are also great strides being made in education, housing, and social setting to create “Down-friendly” environments. In most developed countries, since the early 20th century many people with Down syndrome were housed in institutions or colonies and excluded from society. However, in the 21st century there is a change among parents, educators and other professionals generally advocating a policy of inclusion, bringing people with any form of mental or physical disability into general society as much as possible. In many countries people with Down syndrome are educated in the normal school system and there are increasingly higher quality opportunities to mix special education with regular education settings.
Despite this change, reduced abilities of people with Down syndrome pose a challenge to their parents and families. While living with their parents is preferable to institutionalization for most people wit Down syndrome, they often encounter patronizing attitudes and discrimination in the wider community. In the past decade, many couples with Down syndrome have married and started homes of their own, overcoming many of the stereotypes associated with this condition.
The first World Down Syndrome Day was held on 21 March 2006. The day and month were chosen to correspond with 21 and trisomy respectively. It was proclaimed by Down syndrome International.
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