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Down syndrome: overview, causes, features, diagnosis, and support

Down syndrome is a common chromosomal condition caused by extra genetic material from chromosome 21. It affects physical development, learning, and health; outcomes vary widely and lifelong support improves quality of life.

Author: Leandro Alegsa Creation date: November 13, 2022 Last updated: May 25, 2026

simple.wikipedia.org · CC BY-SA 3.0

Overview

Down syndrome is a genetic condition that arises when there is extra genetic material related to chromosome 21. It is sometimes called trisomy 21 and is one of the most common chromosomal differences present from birth. The amount of extra material and the pattern of cells affected influence the characteristics of each person: most have a full extra copy in every cell, while a smaller number have a translocation or a mosaic form. Individuals with Down syndrome show a wide range of abilities and require differing levels of support across their lives.

Genetic basis and forms

The typical cause is an extra full chromosome 21 in the cells of the body (trisomy 21). Alternative genetic mechanisms include Robertsonian translocation, where extra chromosome material is attached to another chromosome, and mosaicism, in which only some cells carry the extra chromosome. For more general information on the condition as a genetic disorder, see genetic condition. Understanding the specific genetic mechanism can be important for family planning and recurrence risk discussions.

Common physical and developmental features

People with Down syndrome often share certain physical traits and developmental patterns, although no two individuals are identical. Typical features can include a flatter facial profile, an upward slant to the eyes, a single deep crease across the palm, and reduced muscle tone in infancy. Some of these features relate to what was historically described by early physicians; see the account by John Langdon Down and biographical context for the physician who first characterized the syndrome. Descriptive terms once used in the past, such as the historical label noted in early literature, are now recognized as inaccurate and offensive; a historical reference is available at historical terminology.

Health considerations and common coexisting conditions

People with Down syndrome are at higher risk for certain medical conditions, and medical surveillance throughout life is important. Commonly monitored issues include:

Congenital heart defects (some require surgery in infancy or childhood)
Hearing and vision problems, including differences in eye shape such as an epicanthic fold (typical eye features)
Thyroid dysfunction and other endocrine issues
Increased susceptibility to respiratory infections and sleep-related breathing disorders
A slightly higher risk of certain blood disorders and, in adulthood, early-onset Alzheimer's changes more often than in the general population

Regular pediatric and adult medical follow-up, early intervention therapies, and preventive care support better outcomes.

Diagnosis and prenatal testing

Down syndrome can be diagnosed before birth, at birth, or later in life. Prenatal screening options include maternal blood tests and ultrasound markers, and noninvasive prenatal testing (NIPT) that analyzes cell-free fetal DNA. Diagnostic tests that give a definitive result include chorionic villus sampling and amniocentesis; for information on the latter procedure see amniocentesis. Families who receive a prenatal diagnosis are offered counseling about possible outcomes and available options. In many regions, prenatal diagnosis leads to complex and highly personal decisions about pregnancy management; resources describing options, including termination, are available at pregnancy decision resources.

Education, supports, and quality of life

With early intervention, inclusive education, medical care, and social supports, many people with Down syndrome attend school, form friendships, hold jobs, and lead fulfilling lives. Educational placement and therapies are tailored to individual strengths and needs, and community supports such as speech therapy, occupational therapy, and social services play a major role. Public attitudes and policies vary by country and have changed substantially over time, promoting greater inclusion and rights for people with intellectual disabilities.

Language matters: modern usage emphasizes respectful, person-first or identity-first language chosen by individuals and families. Outdated and derogatory terms that appeared in historical descriptions are no longer acceptable. Advocacy groups, medical organizations, and communities of people with Down syndrome encourage dignity, full participation, and accurate information. For further reading and support networks, see general resource links and local organizations represented through trusted health services (genetic condition, physician history).

Portrait of Chris Burke, who has a mild form of trisomy 21, at age 42.

Designation

The name Down syndrome refers to the British physician and pharmacist John Langdon Down, who first described this syndrome comprehensively in 1866. The name originally chosen by Down was English Mongolian idiocy (from which the term Mongolism is derived), because he suspected that the syndrome was a regression to a Mongolian tribe, because of the facial features characteristic of Down syndrome and the shape of the eyes, reminiscent of members of an Asian ethnic group of "Mongols". In 1965, Mongolia submitted a request to the World Health Organization (WHO) to stop using the term Mongolian Idiocy and its derivatives because of the negative as well as racist connotations. The WHO unanimously accepted this request. Already in 1961, the renowned British scientific journal The Lancet, at the request of an international group of nineteen recognized geneticists, had changed the term to Down's Syndrome. Use of the term mongolism gradually declined and disappeared in the early 1980s; since then it has been used only in articles on the history of the syndrome. The term Down syndrome is the most widely used. Trisomy 21 is preferred when referring to the disorder in conjunction with other chromosomal abnormalities.

History

Early history

Due to the mechanisms of origin of trisomy 21, it is assumed that there have always been people with Down syndrome. The earliest evidence to date comes from the megalithic tomb of Poulnabrone in Ireland. In a genetic study, trisomy 21 was detected in the approximately 5500-year-old skeleton of a boy.

The Tübingen human biologists Alfred Czarnetzki, Nikolaus Blin and Carsten M. Pusch also demonstrated the typical symptoms on the skeleton of a woman who died near Tauberbischofsheim around 2550 years ago at the age of 18 to 20.

Research

Down syndrome was first mentioned as a clinical picture in 1838 by the psychiatrist Jean Étienne Esquirol and described in more detail in 1846 and 1866 by the physician and pedagogue Édouard Séguin.

In 1866, the English neurologist and pharmacist John Langdon Down described Down's syndrome, named after him, for the first time scientifically as an independent syndrome that could be distinguished from other diseases and disabilities. It was not until 1959, 63 years after Langdon Down's death, that Marthe Gautier, Raymond Turpin and Jérôme Lejeune identified the genetic cause of the syndrome: they discovered that each cell of the affected person had 47 chromosomes instead of the usual 46, i.e. that there had to be a triplication (trisomy) instead of a duplication in one chromosome. They could not yet determine which chromosome was tripled. Only later was it proven that the 21st chromosome was affected (trisomy 21).

Two chimpanzees - whose chromosome 22 corresponds to chromosome 21 in humans - were found to develop symptoms similar to those of humans with trisomy 21 due to trisomy 22.

Nazi period

Under the National Socialist dictatorship, people with Down syndrome were deliberately murdered through the systematic killings of the sick during the National Socialist era as part of National Socialist "racial hygiene":

Euthanasia of children, murder of children in hospitals in "children's specialist wards
Action T4, adult "euthanasia", murder of psychiatric patients and disabled persons in 1940/1941 in killing institutions
Action 14f13, murder of concentration camp inmates in the killing centres of Action T4
Aktion Brandt, murder of psychiatric patients and disabled persons in hospitals from 1943 onwards

Child with Down syndrome (with his father)

Survivor of the murders of the sick during the National Socialist era with Down syndrome: Walter Kistler

Questions and Answers

Q: What is Down Syndrome?

A: Down Syndrome (or trisomy 21; old name mongoloid idiocy) is a genetic disorder in which most people have an extra copy of chromosome 21, or part of it. This causes a mental handicap that can range from mild to severe.

Q: Who first described Down Syndrome?

A: John Langdon Down, a British doctor, was the first to describe it in 1866. He called it mongoloid idiocy because he thought children with Down syndrome had faces like that of Blumenbach's Mongolian race.

Q: How common is Down Syndrome?

A: Of every 800 to 1000 babies that are born, one is diagnosed with Down syndrome. Older women have a higher chance of having a baby with the condition.

Q: What kind of problems do people with Downs Syndrome face?

A: People who have this condition take more time to learn new things and may experience discrimination in education and society in general. Some people may have average intelligence but other developmental issues instead while others may have severe learning difficulties.

Q: How can pregnant mothers find out if their foetus has Downs Syndrome?

A: Pregnant mothers can be told whether their foetus has Downs syndrome through procedures such as amniocentesis or sound scans.

Q: What percentage of pregnancies resulting in diagnosis for Downs Syndrome are aborted?

A: In the United Kingdom and Europe 92% of such cases are aborted

Author

AlegsaOnline.com - Down syndrome - Leandro Alegsa

Creation date: November 13, 2022
Last updated: May 25, 2026

URL: https://en.alegsaonline.com/art/28771