Down syndrome (also called Down's syndrome) encompasses a number of genetic disorders, of which trisomy 21 (a nondisjunction) is the most representative, causing highly variable degrees of learning difficulties and physical disabilities. It is named for John Langdon-Down, the British doctor who first described it.
Incidence of Down syndrome is estimated at 1 per 660 births, making it the most common chromosomal abnormality. Maternal age influences the risk of conceiving a baby with the syndrome. At age 20-24, it is only 1/1490, while at age 40 it is 1/106 and at age 49 it is 1/11. (Source: Hook EB. Rates of chromosomal abnormalities at different maternal ages. Obstet Gynecol 1981;58:282.) Genetic counseling and genetic testing such as amniocentesis are usually offered for families who may be at increased risk to have a child with Down syndrome.
The term was first used by the editor of The Lancet in 1961 . It was originally called mongolism or mongolian idiocy, after a perceived resemblance observed by Down between the faces of some of his patients with Down syndrome and the Mongoloid race. This usage is now viewed as both offensive and medically meaningless.
Children with Down syndrome are at an immediate disadvantage compared with children who do not have DS. The IQ of a child with Down syndrome is rarely measured above 60. Brains of children with Down syndrome are usually small and underweight. The cerebellum and brain stem are unusually small, as is the superior temporal gyrus. Educational progress may also be damaged by illness and disabilities, such as recurring infectious diseases, heart problems, poor eyesight, and hearing problems. Other physical characteristics associated with the disorder include presence of a simian crease.
Early educational intervention, screening for common problems such as thyroid functioning, medical treatment where indicated, a conducive family environment, vocational training, etc. can improve the overall development of children with Down syndrome. On the one hand, Down syndrome shows that we cannot jump over genetic limitations; on the other, it shows that education can produce excellent progress whatever the starting point. The commitment of parents, teachers and therapists to individual children has produced previously unexpected positive results.
Of the inborn disorders that affect intellectual capacity, Down syndrome is the most prevalent and best studied. Down syndrome is a term used to encompass a number of genetic disorders of which trisomy 21 is the most frequent (95% of cases). Trisomy 21 is the existence of the third copy of the chromosome 21 in cells throughout the body of the affected person. Other Down syndrome disorders are based on the duplication of the same subset of genes (e.g., various translocations of chromosome 21). Depending on the actual etiology, the learning disability may range from mild to severe.
Trisomy 21 results in over-expression of genes located on chromosome 21. One of these is the superoxide dismutase gene. Some (but not all) studies have shown that the activity of the superoxide dismutase enzyme (SOD) is elevated in Down syndrome. SOD converts oxygen radicals to hydrogen peroxide and water. Oxygen radicals produced in cells can be damaging to cellular structures, hence the important role of SOD. However, the hypothesis says that once SOD activity increases disproportionately to enzymes responsible for removal of hydrogen peroxide (e.g., glutathione peroxidase), the cells will suffer from a peroxide damage. Some scientists believe that the treatment of Down syndrome neurons with free radical scavengers can substantially prevent neuronal degeneration . Oxidative damage to neurons results in rapid brain aging similar to that of Alzheimer's disease.
Another chromosome 21 gene that might predispose Down syndrome individuals to develop Alzheimer's pathology is the gene that encodes the precursor of the amyloid protein. Neurofibrillary tangles and amyloid plaques are commonly found in both Down syndrome and Alzheimer's individuals. Layer II of the entorhinal cortex and the subiculum , both critical for memory consolidation, are among the first affected by the damage. A gradual decrease in the number of nerve cells throughout the cortex follows. A few years ago, Johns Hopkins scientists created a genetically engineered mouse called Ts65Dn (segmental trisomy 16 mouse) as an excellent model for studying the Down syndrome. Ts65Dn mouse has genes on chromosomes 16 that are very similar to the human chromosome 21 genes. With this animal model, the exact causes of Down syndrome neurological symptoms may soon be elucidated. Naturally, Ts65Dn research is also likely to highly benefit Alzheimer's research.
While there are a number of commercially promoted dietary supplements on the market, especially in the USA, mainly involving various combinations of vitamins and minerals, none of these have been medically approved for use in the UK for the mass treatment of people with Down syndrome and none appear to lead to any proven lasting benefits, and all remain highly controversial.
Advocates for people with Down Syndrome stress that they have the same human rights and emotions as any other human being. The abuse and forcible institutionalization of people with Down syndrome was closely linked to early twentieth-century racial and eugenic theory, culminating in the murder of many people with Down syndrome and other disabilities by the Nazi government in Germany in the 1930s-1945, and the creation of compulsory sterilization programs around the world which targeted the mentally disabled.
Today, Down Syndrome is considered a ground for abortion in an increasing number of countries. The number of children born with Down Syndrome is decreasing due to a large number of abortions after an early diagnosis of Down Syndrome during pregnancy. In a hearing before the German Parliament, doctors stated that 90% of all children prenatally diagnosed with Down Syndrome are aborted. This number is consistent with the official statistics, wherein 1500 children with Down Syndrome should, statistically, have been born per year (at a prevalence rate of 1:600), but only 63 p.a. were listed in the 1995 birth register.
Providing what advocates call outdated and biased information on the personality of a child with Down Syndrome, doctors often encourage mothers to have abortions. Changes in sociological theories and long standing knowledge from special pedagogics have not had a noticeable impact on medical professionals' views on raising a developmentally disabled child. Teachers trained in special education or Down Syndrome parenting groups can provide thoroughly researched information and organize encounters with disabled children, giving future mothers first hand information on life with a disabled child.
It has been widely recognized in democratic countries that the housing of people with Down syndrome in psychiatric institutions and their exclusion from society is inapt and ignores their abilities as well as their human rights. Under the influence of social role validation and inclusion, people with Down syndrome are increasingly being offered better chances for realising their potential for personal and social development. Despite this welcome change, the reduced abilities of people with Down syndrome pose a practical and ethical problem to their parents and families. While living with their parents is preferable to institutionalization for most adults with Down syndrome, they are often treated as children (and not as mentally disabled adults) for all their lives. A different and even more serious problem emerges when the parents die and leave the adult with Down syndrome behind. If there are no siblings willing or able to take the disabled person in, some institution will have to provide an apt and comfortable environment for the person with Down syndrome, as they are usually unable to run their own household, apply for a regular job, get a driver's licence and take care of insurances etc. One increasingly popular model in Europe lets four to six people with Down Syndrome share an apartment in a normal residential area, taking care of the daily household duties themselves and receiving support from a skilled caregiver in organizing their routines and in dealing with institutions or potential employers.
Many children in the UK are now educated in mainstream schools, learn to read and write, and are likely to live productive and valued lives as part of their families and communities. However, full-time mainstreaming proves difficult after the first few years of schooling, because the intellectual gap between children with and without Down syndrome widens at this age. Many children with Down syndrome do have difficulties reading and understanding more than a rather basic vocabulary. Complex thinking as required in sciences but also in history, the arts and other subjects is usually beyond their abilities. Therefore, if they are to benefit from being mainstreamed without feeling inferior most of the time, special adjustments must be made to the curriculum. Some European countries such as Germany and Denmark advise a two-teacher system where the second teacher takes over a group of disabled children within the class. A popular alternative is cooperation between special education schools and mainstream schools. In cooperation, the core subjects are taught in separate classes in order to neither slow down the non-disabled students nor neglect the disabled ones. Social activites, outings, and many sports and arts activities are performed together, as are all breaks and meals.
Individuals with Down Syndrome share many of the characteristics of their parents, with an average life expectancy of 49 years in the USA versus 77 years for the whole population () thanks mainly to improved diet, housing, health and social care. Many children and adults with Down's syndrome enjoy a satisfactory quality of life, and the extra chromosome may confer some health benefits, for example, reduced incidence of certain cancers caused by double immunity: lung cancer, for instance, is virtually unknown in people with Down syndrome.
Notable people with Down syndrome include: