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Down syndrome or Down's syndrome, [12] 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.
The average IQ of a young adult with Down syndrome is 50, equivalent to the mental age of an 8- or 9-year-old child, but this number varies widely. [3] At the same time, they enjoy a rich social and emotional awareness. [4] Down syndrome is the most common chromosome abnormality in humans, [3] occurring in about one per 1000 babies born each ...
In the 21st century, those terms are no longer used as medical terminology, deemed an unacceptable, offensive and misleading description of those with Down syndrome. [1] The terminology change was brought about both by scientific and medical experts, [ 2 ] as well as people of Asian ancestry, [ 2 ] including those from Mongolia.
Karyotype for trisomy Down syndrome. Notice the three copies of chromosome 21. Trisomy 21 (47,XY,+21) is caused by a meiotic nondisjunction event. [3] A typical gamete (either egg or sperm) has one copy of each chromosome (23 total). When it is combined with a gamete from the other parent during conception, the child has 46 chromosomes.
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Research has found that there is a correlation between advanced paternal age and risk of birth defects such as limb anomalies, syndromes involving multiple systems, and Down syndrome. [74] [35] [93] Recent studies have concluded that 5-9% of Down syndrome cases are due to paternal effects, but these findings are controversial. [74] [75] [35] [94]
The exact characteristics of Down syndrome were not observed, so more genes involved for Down syndrome phenotypes have to be located elsewhere. Reeves et al., using 250 clones of chromosome-21 and specific gene markers, were able to map the gene in mutated bacteria. The testing had 99.7% coverage of the gene with 99.9995% accuracy due to ...
Down Syndrome is a genetic disorder that was first described in 1866 by British doctor John L. Down. [2] It was discovered to be caused by an extra chromosome by French pediatrician Jérôme Lejeune in July 1958, less than two years before Tricia was born. [3] Medical advice in 1960 was typically to institutionalize children with Down Syndrome.