what is mosaic down syndrome

Mosaic Down Syndrome, also known as mosaicism, is a type of Down Syndrome that is diagnosed when there is a mixture of two types of cells in the body. Some cells have the usual 46 chromosomes, while others have 47 chromosomes, with the extra chromosome being chromosome 21. Mosaicism is usually described as a percentage, and a baby would be said to have mosaic Down Syndrome if 5 of the 20 cells analyzed in a chromosome study have the typical number of 46 chromosomes, while the other 15 have a total of 47 chromosomes due to an extra chromosome 21. Babies born with mosaic Down Syndrome can have the same features and health problems as babies born with trisomy 21 or translocation Down Syndrome, where the extra chromosome material is present in all the cells. However, it is possible that these babies may have fewer characteristics of the syndrome than those with other types of Down Syndrome. Studies have shown that the percentage of mosaicism doesn’t accurately predict outcome, and mosaic Down Syndrome cases can vary greatly, ranging from having very mild features to having most of the features of non-mosaic Down Syndrome.