Down syndrome is a genetic condition caused by the presence of an extra copy of chromosome 21 in a person's cells.

Down syndrome is caused by an error in cell division, resulting in an extra copy of chromosome 21. This can occur during the formation of the egg or sperm or during early fetal development.

Common physical characteristics include almond-shaped eyes, a flat facial profile, small ears, a protruding tongue, and a single deep crease across the palm.

Down syndrome can be diagnosed during pregnancy through prenatal screening tests such as non-invasive prenatal testing (NIPT) or diagnostic tests like amniocentesis or chorionic villus sampling (CVS).

The three main types are trisomy 21 (most common), translocation Down syndrome, and mosaic Down syndrome.

Therapies include speech and language therapy, occupational therapy, physical therapy, behavioral therapy, and educational interventions.