Down syndrome
Genetic disorder / From Wikipedia, the free encyclopedia
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Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21.[3] It is usually associated with developmental delays, mild to moderate intellectual disability, and characteristic physical features.[1][12] There are three types of Down syndrome, all with the same features: Trisomy 21, the most common type; Mosaic Down syndrome, and Translocation Down syndrome.[13][14]
Down syndrome | |
---|---|
Other names | Down's syndrome, Down's, trisomy 21 |
An eight-year-old boy displaying characteristic facial features of Down syndrome | |
Specialty | Medical genetics, pediatrics |
Symptoms | Delayed development, characteristic physical features, mild to moderate intellectual disability[1] |
Usual onset | Mostly at conception, rarely after fertilization[2] |
Duration | Lifelong |
Causes | Third copy of chromosome 21[3] |
Risk factors | Older age of mother, prior affected child[4][5] |
Diagnostic method | Prenatal screening, genetic testing[6] |
Treatment | Physical therapy, Occupational therapy, Speech therapy, Educational support, Supported work environment[7][8] |
Prognosis | Life expectancy 50 to 60 years (developed world)[9][10] |
Frequency | 5.4 million (0.1%)[1][11] |
Named after | John Langdon Down |
The parents of the affected individual are usually genetically normal.[15] The probability increases from less than 0.1% in 20-year-old mothers to 3% in those of age 45.[4] The extra chromosome is provided at conception as the egg and sperm combine.[16] A very small percentage of 1-2% gets the additional chromosome in the embryo stage and it only impacts some of the cells in the body; this is known as Mosaic Down syndrome.[17][18] Usually, babies get 23 chromosomes from each parent for a total of 46, whereas in Down syndrome, a third 21st chromosome is attached.[18] It is believed to occur by chance, with no known behavioral activity or environmental factor that changes the probability.[2] Down syndrome can be identified during pregnancy by prenatal screening, followed by diagnostic testing, or after birth by direct observation and genetic testing.[6] Since the introduction of screening, Down syndrome pregnancies are often aborted (rates varying from 50 to 85% depending on maternal age, gestational age, and maternal race/ethnicity).[19][20][21]
There is no cure for Down syndrome.[22] Education and proper care have been shown to provide good quality of life.[7] Some children with Down syndrome are educated in typical school classes, while others require more specialized education.[8] Some individuals with Down syndrome graduate from high school, and a few attend post-secondary education.[23] In adulthood, about 20% in the United States do paid work in some capacity,[24] with many requiring a sheltered work environment.[8] Support in financial and legal matters is often needed.[10] Life expectancy is around 50 to 60 years in the developed world, with proper health care.[9][10] Regular screening for health issues common in Down syndrome is recommended throughout the person's life.[9]
Down syndrome is the most common chromosomal abnormality.[25] It occurs in about 1 in 1,000 babies born each year.[1] In the US this figure is given as one in 700 births.[13] In 2015, Down syndrome was present in 5.4 million individuals globally and resulted in 27,000 deaths, down from 43,000 deaths in 1990.[11][26][27] It is named after British physician John Langdon Down, who fully described the syndrome in 1866.[28] Some aspects of the condition were described earlier by French psychiatrist Jean-Étienne Dominique Esquirol in 1838 and French physician Édouard Séguin in 1844.[29] The genetic cause of Down syndrome was discovered in 1959.[28]