Epstein, Charles J. Department of Pediatrics, University of California, San Francisco, California.
Last reviewed:April 2019
Show previous versions
- Nervous system abnormalities
- Maternal age
- Prenatal diagnosis
- Trisomy 21 and phenotype
- Gene dosage effects
- Mouse models
- Related Primary Literature
- Additional Reading
The set of physical, mental, and functional abnormalities that result from trisomy 21, the presence in the genome of three (rather than the normal two) chromosomes 21. Down syndrome is one of the most frequent genetic causes of intellectual disability (formerly known as mental retardation). The genetic aberration that causes Down syndrome is trisomy 21, in which an individual has a full or partial extra copy of chromosome 21 (Fig. 1). This additional genetic material modifies the normal progression of development and leads to the identifying characteristics of Down syndrome. The physical abnormalities that together give rise to the distinctive facial appearance associated with this condition include upslanting eyes with epicanthic folds (folds of skin over the inner corners), flatness of the bridge of the nose and of the middle portion of the face, and a tendency to protrude the tongue, especially when affected individuals are very young. Many other minor, functionally inconsequential abnormalities of the ears, hands, and feet may also be present in individuals having Down syndrome, and stature is generally reduced. See also: Chromosome; Chromosome aberration; Developmental genetics; Genetic mapping; Genetics; Human genetics; Intellectual disability
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 10,000 highly qualified scientists and 45 Nobel Prize winners.
MORE THAN 8700 articles covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 19,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information