Historically, people with Down syndrome have been alluded to in writings and art, but it was John Langdon Down, an English physician, who accurately described the condition in a publication in 1866. He has since been known as the father of the syndrome.
In more recent history, advances in medicine and science have enabled researchers to investigate the characteristics of people with Down syndrome. In 1959, the French physician Jérôme Lejeune identified Down syndrome as a chromosomal condition. This accomplishment lead to further advancements in the study of Down Syndrome.
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Lejeune found that typically, humans are born with 46 chromosomes which generally occur in 23 pairs. A chromosome is made up of DNA and proteins organized into genes. These genes determine how our bodies form and function. In the case of Down Syndrome, the person has an extra chromosome, chromosome 21. An additional copy of a chromosome is referred to as trisomy.
Down syndrome is also referred to as Trisomy 21. The extra copy of chromosome 21 causes mental and physical changes in a developing person.
The majority of persons with Down syndrome (93-96%) have trisomy 21, a condition known as "nondisjunction," in which all body cells have three copies of the 21st chromosome instead of two. (illustrated above)
Three to four percent of the individuals with Down syndrome have translocation Down syndrome. This occurs when part of chromosome 21 becomes attached (translocated) to another chromosome. Affected people have the usual two copies of chromosome 21 plus extra material from chromosome 21 attached to another chromosome. They also result in having three copies of genetic material from chromosome 21 in all cells. https://www.massgeneral.org/children/down-syndrome/translocation-down-syndrome
1-2% of all persons with Down syndrome have trisomy 21 mosaicism, a condition in which only some of the body's cells have three copies of the 21st chromosome.
According to the Centers for Disease Control and Prevention and De Graaf et al (2024), about 5,000 babies with Down syndrome are born in the United States each year.
Developmental delays
Children with Down syndrome almost always have some degree of developmental delays, including language and memory deficits and other cognitive abnormalities.
There is a wide variation in the communicative and cognitive status of older children with Down syndrome. Some speak clearly and understandably, others have significant issues with grammar and articulation, and a small number depend on augmentative communication devices.
Many youngsters with Down syndrome attain functional levels for reading, writing, and math; others have been less successful in these areas. There is usually some degree of impairment in fine motor skills ( Ferreira-Vasques & Lamônica, 2015).
Some common physical features of Down syndrome include:
https://www.cdc.gov/ncbddd/birthdefects/downsyndrome.html
The incidence of Down Syndrome, the health risks with current treatment options, and a discussion about the increase in abortions when detected in utero will be detailed in additional sections of this course.
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Children with Down syndrome often have specific physical characteristics, including low muscle tone and distinct facial features.
References
De Graaf, G., Buckley, F., & Skotko, B. (2024). People living with Down syndrome in the USA: Births and Population. May 3.
Ferreira-Vasques, A. T., & Lamônica, D. A. (2015). Motor, linguistic, personal, and social aspects of children with Down syndrome. Journal of applied oral science: Revista FOB, 23(4), 424–430.
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