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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.
It is estimated that chromosome 21 contains 200 to 250 genes. [3] Recent research has identified a region of the chromosome that contains the main genes responsible for the pathogenesis of Down syndrome, [4] located proximal to 21q22.3. The search for major genes involved in Down syndrome characteristics is normally in the region 21q21–21q22.3.
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.
Mattel debuted its first Barbie with Down syndrome, the latest in the toymaker's efforts to create more diverse and inclusive versions of its iconic doll.
Chromosome 21 is both the smallest human autosome and chromosome, [4] with 46.7 million base pairs (the building material of DNA) representing about 1.5 percent of the total DNA in cells. Most people have two copies of chromosome 21, while those with three copies of chromosome 21 (trisomy 21) have Down syndrome.
It is the second-most common condition due to a third chromosome at birth, after Down syndrome for a third chromosome 21. [4] Trisomy 18 occurs in around 1 in 5,000 live births. [3] Many of those affected die before birth. [3] Some studies suggest that more babies that survive to birth are female. [2] Survival beyond a year of life is around 5 ...
This is a list of people with Down syndrome, a condition also known as Down's syndrome or trisomy 21. Down syndrome 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 developmental delays, characteristic physical features, and mild to moderate intellectual disability ...
The most common aneuploidy that infants can survive with is trisomy 21, which is found in Down syndrome, affecting 1 in 800 births. Trisomy 18 (Edwards syndrome) affects 1 in 6,000 births, and trisomy 13 (Patau syndrome) affects 1 in 10,000 births. 10% of infants with trisomy 18 or 13 reach 1 year of age.