Santa's Little Secret Down syndrome (DS or DNS), also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21.[1] It is typically associated with physical growth delays, characteristic facial features and mild to moderate intellectual disability.[2] The average IQ of a young adult with Down syndrome is 50, equivalent to the mental ability of an 8- or 9-year-old child, but this can vary widely.[3]
The parents of the affected individual are typically genetically normal.[4] The extra chromosome occurs by chance.[5] The possibility increases from less than 0.1% in 20-year-old mothers to 3% in those age 45.[6] There is no known behavioral activity or environmental factor that changes the possibility.[5] Down syndrome can be identified during pregnancy by prenatal screening followed by diagnostic testing or after birth by direct observation and genetic testing.[7] Since the introduction of screening, pregnancies with the diagnosis are often terminated.[8][9] Regular screening for health problems common in Down syndrome is recommended throughout the person's life.[3]
There is no cure for Down syndrome.[10] Education and proper care have been shown to improve quality of life.[11] Some children with Down syndrome are educated in typical school classes, while others require more specialized education.[12] Some individuals with Down syndrome graduate from high school and a few attend post-secondary education.[13] In adulthood, about 20% in the United States do paid work in some capacity[14] with many requiring a sheltered work environment.[12] Support in financial and legal matters is often needed.[15] Life expectancy is around 50 to 60 years in the developed world with proper health care.[3][15]
Down syndrome is one of the most common chromosome abnormalities in humans.[3] It occurs in about one per 1000 babies born each year.[2] In 2013, Down syndrome was present in 8.5 million individuals and resulted in 36,000 deaths down from 43,000 deaths in 1990.[16][17] It is named after John Langdon Down, the British doctor who fully described the syndrome in 1866.[18] Some aspects of the condition were described earlier by Jean-Étienne Dominique Esquirol in 1838 and Édouard Séguin in 1844.[19] In 1957, the genetic cause of Down syndrome, an extra copy of chromosome 21, was discovered.[18]
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