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Down syndrome

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. It is usually associated with developmental delays, mild to moderate intellectual disability, and characteristic physical features. The parents of the affected individual are usually genetically normal. The incidence of the syndrome increases with the age of the mother, from less than 0.1% for 20-year-old mothers to 3% for those of age 45. It is believed to occur by chance, with no known behavioral activity or environmental factor that changes the probability. Usually, babies get 23 chromosomes from each parent for a total of 46, whereas in Down syndrome, a third 21st chromosome is attached. The extra chromosome is provided at conception as the egg and sperm combine. In 1???2% of cases, the additional chromosome is added in the embryo stage and only impacts some of the cells...

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wikidata.org 0 views · 2024-12-26 22:34:07