mosaic Down syndrome
(moh-ZAY-ik … SIN-drome)
A form of Down syndrome caused by having an extra chromosome 21 in some of the body’s cells. Cells with an extra chromosome 21 have three copies of it, while the other cells have two copies. Down syndrome is a genetic condition marked by certain physical features, delays (growth, development, and learning), and other health problems. People with mosaic Down syndrome can have the same physical features and health and learning problems as those who have other types of Down syndrome, but how mosaic Down syndrome presents can vary depending on how many cells have the extra chromosome.